Introduction – Class D amplifiers :

Class D Subwoofer amplifiers, effectionately known as “Mono Block D’s” are very power efficient amplifiers.

Class D Amplifiers have an efficiency of around 70%, which means that a 2000 watt rated Class D will typically deliver 1400 watts to the subwoofer while wasting about 600 watts in heat. Still, this Class amplifier is the highest efficiency amplifier design available on the market.

The way these amplifiers achieve such a high efficiency is by first creating a high power full voltage square wave around the frequency of our input signal. A square wave is really easy to generate and control because it only requires a synchronous switching of the amplifier’s power transistors on and off to create that wave.

That high power square wave is then filtered by the low powered audio input signal (using low pass filtering, and feed back control loops) to shape the high power wave going to the subwoofers to match the input audio signal now both in its primary frequency (which was done when we generated the square wave), and in harmonics (which is taken care of by the filtering).

This is very similar to the performance of subtractive synthesizer that generates an square wave at your desired frequency , and then you subtract out the higher harmonics to create the sound shape that you want to play.

Which brings me to my main next point …

Amplifier stability :

Amplifier stability is the study of how hard you can push your amplifier and still have it work properly as a power amplifier (with high gain, low distortion, and a wide frequency range response).

In class D amplifiers, there are two things that affect amplifier stability:

1. Because the amplifier uses a feedback loop to filter the high power full voltage output signal, then there is always possibility for this feedback loop to get inverted and become a positive (rather than a negative) feedback loop.What this means is that rather than filtering higher harmonics, the amplifier may start to internally add its own noise to the system, and this will happen at some frequency that the amplifier internally resonates at.These types of phenomenon usually happen on power transitions, when the amplifier is switched on, when the power is interrupted momentarily or surged …etc As the amplifier charges its internal capacitors and electronics and approaches it’s stable steady operating state it goes through a transient period where it may become unstable.Of course internal compensation of these phenomenon using damping capacitors and control circuits is important, but sometimes external factors such as the load impedance of the subwoofer also comes into play into the modeling of the amplifier.
2. Thermal stability.As we said about 25 to 30% of the amp rated power is wasted in heat…. heat builds up inside the amplifier, the temperature of the internal components increases, the internal resistance of the amplifier blocks increases with temperature, the overall gain of the internal amplifier block drops as it’s resistances rise, which drives more heat, more resistance, less gain … until either the amplifier burns out, or the thermal overlaod protection circuits inside the power transistors and the amplifier power supply shut off and you are ‘embarrassed’ in front of your peers because your amp has just cut out.

Stability rating :

So what we typically see is an amplifier rating … “2 ohm stable” or “0.5 ohm stable”.

This means that the minimum subwoofer impedance connected to the amplifier should not be lower than 1 ohm (for example) for a 1 ohm stable amplifier.
This also the impedance that allows us to extract the most power out of our amplifier.

As I’ve explained before in our previous article on subwoofer capacitor ratings, the maximum RMS power you can extract from a certain amplifier will be as follows:

Power = V * V / R

Where V = the system’s rated voltage (typically 14 volts)
and R is the resistive impedance of the load or the subwoofer (typically 4 ohms for a single voice coil car subwoofer).

This makes the typical RMS power extracted from a single channel 14 volt amplifier into a 4 ohm load 49 Watts.

At the same time connecting another subwoofer in parallel with our original 4 ohm subwoofer will give us a total load resistance of 2 ohms.

With this new load value we can now deliver 98 Watts from the same 14 volt power source, so long as the amplifier is at least 2 ohms stable!

So how do we apply this knowledge practically ?

You can see from the example before that having an amplifier with the lowest possible stability rating gives you the ability and flexibility to add more subwoofers to your car’s audio system and extract more power from the same amplifier and the same power supply.

One great example of such an amplifier is the Kicker SX1250.1 which is a great and flexible amplifier. The Kicker SX1250.1 delivers up to 312 watts RMS to a 4 ohm load.
Working our same power equation backwards we find that it takes 35 volts to be able to deliver 312 watts RMS to a 4 ohm load. This tells us that our Kicker amplifier has a built in DC to DC step up voltage converter that will convert the incoming 14 volt power supply into a 35 volt internal power supply that the amplifier can then deliver to the subwoofers.

Furthermore. the Kicker is stable down to 1 ohm as follows:

	Maximum RMS Power	Speaker network impedance	Heat Dissipation (30%)	Supply Current / Fuse rating (amps)	Wire Gauge @ 14v (amplifier supply)	Wire Gauge @ 35v (speaker)	Capacitor
Stage 1	312 watts	4 ohms	94 watts	21 / 35	#6 AWG	#10 AWG	0.6 Farad
Stage 2	625 watts	2 ohms	188 watts	44 / 75	#3 AWG	#7 AWG	1.2 Farad
Stage 2	1250 watts	1 ohms	375 watts	89 / 150 (supplied)	#0 AWG	#4 AWG	2.5 Farad

So here’s the typical scenario in which such an amplifier showcases it’s flexibility.

Stage 1:

Let’s say you start with a basic install, coupling this amplifier with a 4 ohm single voice coil Mobile Authority MA120QS. The MA120QS is a 12″ subwoofer from Mobile Authority that can handle 300 watts RMS and 700 watts at peak and is a perfect match for our amplifier as a basic install.

This setup requires something like a 0.5 Farad capacitor, we draw a steady 21 amps of power (probably requiring a 35A fuse), and need 6 gauge wiring between the battery and the amplifier and 10 gauge wiring between the amp and the speakers.

The reason we need different gauge wiring here is that the amp is supplied with 300 watts @ 14 volts which is 21 amps. However, the amp delivers power at 35 volts to the speaker so the 300 watts get delivered using only 8.5 amps on the speaker side (due to the higher voltage) and so thinner wiring is allowable.

Stage 2:

After a while of bumping your 625 watt (peak) system around town and in competition, you may decide that you want to upgrade your system for more power.
A quick look around shows the Infinity 1262W car sub woofer. This subwoofer has two 4 ohm voice coils that can be wired in parallel for a total impedance of 2 ohms, at the same time the subwoofer has a power handling of 1500 watts peak (600 RMS) and is capable of taking everything that the amplifier can throw at it at a 2 ohm rating.

Typically to do this kind of upgrade (to double your power) you’d need a whole new system (subwoofers, amplifier, enclosure, wiring, capacitor …etc). However, since your amplifier is in fact 1 ohm stable (which means it is also stable at 2 ohms) you can retain the same amplifier, same enclosure and just upgrade your subwoofer, capacitor and wiring (if it isn’t already rated enough to deliver 1500watts).

Stage 3:

After a few months, you get more bass envy. You want more upgrades, you want a louder system and maybe want to go for an award at an SPL competition.

Your amplifier is 1 ohm stable and capable of delivering 1250 watts RMS or 2500 watts at peak. But you’re only using 1250 of those 2500 watts. A quick look around the shops comes up with the massive Pioneer TS W5102SPL car sub woofer.

This pioneer subwoofer is also a 12″ subwoofer, and if you had a deep enough enclosure to start with (or enough space on top of the enclosure to install it outside of the box playing inwards) would fit right in place of the MA and Infiniti subwoofers you had before.

What’s special about the pioneer is that it comes with two 2 ohm voice coils that when wired in parallel give a total impedance of 1 ohm and are capable of both extracting 2500 watts from our amplifier and withstanding the full force of that punch has the sub is rated for up to 6000 watts at peak!

Other considerations :

As I’ve explained, the amplifier will waste about 30% of it’s power on heating itself up. The kicker 1250.1 deals with this by having a fairly large amplifier area to help better diffuse the heat, as well as having a cooling fan on board, and a digital temperature display to monitor the stable operation of the amplifier.

Make sure you install the amplifier OUTSIDE of the subwoofer enclosure in an area where it sees plenty of fresh air and is able to evacuate its heat.

Make sure you have the right wiring / fusing / capacitor for your installation based on the current power level that you are running (rather than based on marketing figures, peak power numbers or out of the box ratings).

If you think that you’re possibly going to be upgrading your setup as discussed in this article, then it’s a good idea to err on the larger side for enclosure design, so that the enclosure can still be able to physically and audibly handle a larger subwoofer, requiring more space, and pushing more power.

Other cool features :

The kicker 1250.1 has other great features that make it a very flexible and professional amplifier that I want to touch on here….

Most amplifiers you’ll see come with a low pass filter to separate the bass signal from the rest of the music.
Some amplifiers may even have an adjustable low pass filter (crossover frequency) so that you can tune your subs to pick up where your midrange and midbass speakers drop off.
The kicker goes beyond that, it not only gives you an adjustable filter frequency, but it also gives you an adjustable crossover slope between a soft roll off of 6 dB/octave to a sharp wall drop of 48! db/octave)

As if that’s not enough, the Kicker also comes with an adjustable ‘rumble filter’. A rumble filter is a HIGH PASS filter that prevents imperfectly designed sub boxes from resonating and vibrating at subsonic frequencies. Sometimes (especially with a poorly designed vented enclosure) subsonic frequencies sound horrible from your bass port. A high pass filter can filter these frequencies out preventing your subwoofer from playing them and keeping your system clean.

The kicker 1250.1 has a variable frequency AND variable slope high pass rumble filter that allows you to get the most bass out of your system even in an imperfect enclosure.

That’s not all. If you’ve ready my article on DIY subwoofer equalization, then you know how important it is to EQ your bass frequencies to get linear performance out of your subwoofer system both for best sound pressure as well as for perfect sound quality. The Kicker 1250.1 comes with an adjustable bass cut/boost of -/+18 dB at a user selectable frequency. Want more punch at 40hz, then set up your frequency at 40hz and boost it up. Want more kick from the system ? move the frequency to 200 hz and boost it up there.

This amplifier is rediculous.

I’m not done yet, there’s one more ridiculous feature on here….

Do you like to listen to live recorded music ? Like bands playing live and special edition CDs and Live DJ mixes ?
Does it bug you that sometimes during live recording that the leveling for the show isn’t exactly perfect ? Sometimes the bass varies in loudness from track to track ? Sometimes the EQ of the live concert recording isn’t perfect ?

The Kicker 1250.1 comes with a built in signal process comprised of a comrpressor/expander network (also known as a compander). What this circuitry does is that it pre-processes the bass signal before amplifying it so that it is neither too loud and clipping, nor too quiet and weak. This compresses the signal when it’s too powerful, and expands it when it’s too soft giving you an always perfect and always full and rich bass sound !!!!!!!!

Note: Click here to get the feature packed bass master Kicker 1250.1, improve your sound performance, tune your system and save $600 off of MSRP!

Technorati Tags: 1 ohm, 2 ohm, 4 ohm, Car Subs, Crossover, dB, DVC, SVC, Vented

Tube enclosures are very efficient enclosures for bass creation and subwoofer applications. If you think about it, tribes used to use hollow logs and tube shapes to create their ancient drums. To this day, with advanced technology, acoustic modeling, and ‘if you can dream it , we can build it’ machining, we still have circular drums. Think about it, have you ever seen a square bass drum before ?

Now there are two reasons that a tube is very efficient at creating and amplifying bass frequencies:

1. A tube matched to the size of the drum surface (the drum skin) or in our case to the size of the subwoofer has it’s entire surface area in contact with the subwoofer surface.

So, any motion in the subwoofer, moves the entire air column in the tube, this is unlike a square shaped enclosure that allows for stagnant air to be trapped or turbulent in the corners of the subwoofer enclosure, a phenomenon that can create enclosure noise and bass distortion.

2. In a tube shaped enclosure, no two surfaces are parallel to each other except for the tube end plates (one of which has the subwoofer mounted to it). This prevents any standing waves of any frequency to exist inside the enclosure and is the primary reason a tube system requires less power (is more efficient) to create more base.If the enclosure were to resonate internally due to the parallel faces creating standing waves, then the subwoofer would have to overcome the pressure of these standing waves to create it’s own pressure waves in accordance with the music. This energy is wasted by the subwoofer and requires a higher power amplifier to create the same level of loudness.

If you’ve seen certain subwoofer boxes that are fairly deep (deep enough to create audible internal standing waves) you’ll find the front panel of the subwoofer box is mounted at an angle which prevents the same internal resonance phenomenon from occurring in a typical box enclosure.

Now here’s a product that takes advantage of this design:

The bazooka BTA8100 stands for Bass Tube with Amplifier 100watts. The BTA8100 uses a dual voice coil 8″ subwoofer powered by a  ’small’ two channel 100 watt RMS amplifier (also verified by the 7 amp fuse on a 14 volt system), that can peak at 200 watts momentarily to create a significant amount of bass from a very small enclosure.

The way the Bazooka bass tube creates such a big boom from a small enclosure is that it:

1. Uses a bass tube which is very power efficient
2. Focuses all of the energy on a very narrow frequency range of 35 to 85hz leaving out midbass and subsonic frequencies and focusing all the power on where most music ‘booms’ which is a pretty efficient way to add bass that most people will appreciate.
3. Uses a ported enclosure to further amplify the system response around the bass port tuned resonant frequency by 3+ db as per a typical ported system.
4. Brings the bass port all the way to the front to exit in the same plane as the subwoofer, usually a bassport tuned for a 1/4 wavelength and exiting in the same plane as the original speaker driver helps improve the subwoofer’s response in a vented or ported system to bring it closer to the response of a sealed system, while having the 3db gain advantage of the ported design.

Now we know the bass tube is 18.5″ long and so the length of the enclosure is double that (as the wave travels from the subwoofer surface, to the rear faceplate and backfowards to the port exit) of 37″. In free air, with no internal padding, at 30*C this 37″ corresponds to 1/4 of a 148″ wavelength which corresponds to a tuned frequency of 93hz which is very close to the highest cross over frequency of the 85hz low pass filter.

So the result of all of this efficiency, design and bass reflex tube tuning is an impressive 102dB sensitivity at 1W @ 1 meter.

Being a 100W RMS system, this system is best used in an open cabin such as in a hatchback or behind the rear seats of a Jeep. This allows the bass to travel easier into the compartment than it would if the system was installed in a sealed trunk in a sedan.

One thing Bazooka recommends to improve further improve how hard the system hits is to ‘corner load’ the subwoofer by installing the subwoofer (and the bass port) in a way where it is playing into the corner of the rear hatch or trunk area about 3″ to 5″ from the walls. Typically a subwoofer is rated (to 102dB in our example) by placing it in an open space and measuring it’s sound pressure, using 1 watt of power, with the microphone or pressure meter 1 meter away. This arrangement allows the subwoofer to play bass in all directions in 360 degrees of space.

By corner loading a subwoofer (and placing it in the corner), half of the audio is played out into space while the other half is reflected off of the wall (the corner) and played into the SAME space. What this does is that it allows both halves of the sound (the primary wave and the reflected wave) to stack up on top of each other giving between 6 and 12dB of additional bass gain using corner loading and room gain.

So what is the best application for this bass tube?

Because of how well the Bazooka tube is designed you will typically find TWO types of reviews on the internet for it:

1. WE HATE IT!

   The reason some people hate the bazooka tube is that it does not perform like a larger 15″ subwoofer in a 3 cubic foot enclosure. The bazooka tube does not play subsonic bass (typical of some genres of music) nor does it play good midbass in the 125 to 500hz region. So people that buy the Bazooka tube with the expectation that it is the same as having a full custom subwoofer box in their trunk, that they will be able to rattle the doors off of their car, or that they will be able to rumble the guy next to them at the stop light with 16 hz subsonic frequencies will be dissapointed.

2. WE LOVE IT!

   The people that love the Bazooka tube love that it is portable and easy to install and remove. Think of a Jeep Wrangler owner that loves to take his car apart, take the top off, remove the doors, take it in the mud, have a bass tube in the back that you can install and uninstall in no time. Have a plastic bass tube that isn’t carpeted that you can get wet or muddied (Bazooka even sells marine bass tubes that you really don’t have to worry about with water , rain and the elements).

   Or maybe you have a sound system that is completely flat on the low end and has no bass what so ever ? You want a quick , cheap, and very effective solution at adding some boom to your ride. Enough boom to be noticeable, to dramatically increase your enjoyment and your listening experience and something that your passangers will defiantely notice. At the same time you’re not looking to shatter glass, break any SPL competition records, or have your bass heard anywhere OUTSIDE of your cabin.If you’re this kind of person, you will love the bass tube, as it compliments your factory speaker arrangement (which typically does well for midbass, midrange and treble if you already have high quality speakers in there), and it will fill out the missing POWER in your music.

Here’s a great video of a larger application of a tube subwoofer

It’s really important to understand how a product works, and what it’s designed for, to get the most out of it and to know what to expect with it …

Note: Click here to get your Bazooka Subwoofer Tube and get $70.00 off!

Technorati Tags: 4ohm, Car Subs, dB, DVC, Vented

One of my first subwoofer boxes was a simple dual 8″ setup in a 12″x 22″ x 10″ box. That small 1.6 Cu.ft box was more than enough to fill up and rock out my 1991 Celica GT. The subs in the box were facing upwards and reflected beautifully off the glass hatchback door and into the cabin.

The thing is, a lot of first time diy’ers build their first DIY Subwoofer box using a single undivided enclosure with dual subwoofers and a 2 channel amplifier. Compared to having no bass at all, then a single enclosure with dual subs will sound like the greatest addition to the car’s sound system since sliced bread. I know I for sure loved mine, just as much as my friend Julian loved his dual 10s in his CRX hatch, and as much as my friend Dan love his dual 12s in the trunk of his Oldsmobile.

If you think about a typical single sealed box subwoofer install, then the amount of air trapped inside the enclosed and sealed box is fixed. The volume of the box is not fixed though because one of the box walls has a variable excursion part to it which we call a subwoofer. As the subwoofer moves in and out with reference to the box wall when the music moves the speaker cone, the volume of the box increases (when the sub moves out) and decreases (when the sub moves in).

As we know from physics density = mass / volume. So a fixed mass of air is manipulated inside a variable volume box and what this does is create a variable density area behind the speaker cone inside the box. As the sub moves outwards, the desnity and pressure of air inside the box drops. This low pressure behind the speaker (with regular pressure outside of the box) creates a suction on the speaker which tries to dampen it and return it back to its resting position. The opposite is true when the speaker dips into the boxes volume, as the pressure increases inside the box trying to push it back out.

This ‘overdamped’ nature of sealed boxes is what helps them create TIGHT bass with minimal distortion even when the speaker is slightly overpowered as the physics of the box dampen the possible distortions of the speaker motion and accelerate its return to its resting position to prepare it for the next bass hit, even when faced with a series of fast paced rolling bass lines.

Now although sealed boxes are great for clean tight bass, they don’t always hit as hard or as low as we’d like them to, especially when compared to a tuned vented box or a band pass system. One solution to helping a sealed box reach max excursion and create more bass is to neutralize the high and low pressure waves existing inside the sealed box. This gets even worse on a typical ‘newbie’ DIY box with TWO subwoofers in a single enclosure. As both speakers move inwards and outwards in phase, the pressure waves inside the box are exaggerated and neither speaker is allowed to go to maximum excursion.

Isobaric literally means of equal (iso) pressure (baric). And the way we achieve this ‘isobaric’ region is to operate two identically matched subwoofers within a tight enclosure. The two cones of the speakers are arranged so that they can move OPPOSITE each other in a way that the total volume of the box is fixed. Since the amount of air trapped in the box is fixed, and the total volume of the box stays fixed, then the pressure inside the box stays fixed (iso-baric) and the pressure inside the box is always equal to the pressure outside of the box. This way both subwoofers are surrounded on both faces by equal pressure and are no longer over damped by the box physics but rather damped by their own physical damping (electrically by the voice coil and mechanically by the design of the basket and surround material).

There are many different subwoofer arrangements that will allow you to reach an isobaric condition in your sub enclosures, but the simplest are by altering:

1- The direction of subwoofer mounting (flush into the box, or protruding with the basket ouside of the box)
2- The polarity of the wiring of one of the two subwoofers so that it moves in opposite direction to the other subwoofer

So what is the advantage of using an isobaric (or push pull as some may call it) subwoofer network ?

Well one advantage is that as stated before the subwoofer is no longer overly damped, which means more excursion and louder bass.
The second advantage is that now that the subwoofer is neutrally damped, it can actually increase the sound quality of the bass in your system so long as the subwoofer is not overdriven or overpowered.
The third and most interesting advantage of an isboaric arrangement is that you are now driving more power into the same box which combines the effects of both subwoofers resulting in a ’super sub’. This means that if you have a tight box space, that you can build a smaller box to give you the same operating characteristic as you need for a single box.

For example you purchase a 15″ subwoofer that requires a minimum 3.5 cubic feet of enclosure space. However, in the spare tire well in your car you measure out an available 2.0 cubic feet of space which is not enough for this sub. Setting up an isobaric setup with two identical 15″ woofers lower your space requirements by a factor of 2 down to only 1.75 cubic feet. What this also means is that any extra space you get over that 1.75 cubic feet will show up as bass extension as your isobaric subwoofer network will be able to hit harder and reach a LOWER corner frequency, as low as half an octave lower if you use an isobaric network in a 3.5 cubic foot box as recommended.

Here is an example of isobaric loading using two 15 inch subwoofers in a tuned vented box in the trunk of a Golf GTI. This box has been tested and proven to hit as low as 16hz!

So how do we use this information ?

1- If you (like i did) have a regular box equipped with two undivided subwoofers sharing the same space, then reversing the polarity of one of those subs will result in a stronger bass hit, and a lower overall frequency response. Have a box loaded with two 15 inch subwoofers ? Simply reverse the polarity on one of them and gain more power around the 16hz region simulating a big 18″. Have two 8 inch subs but want more of a 12″ sound ? Again do the same.

2- Sometimes you are limited for space, such as on a work truck. Work trucks need pretty much every last inch of space to haul tools and carry people around. So some people resort to installing midbass drivers (such as 6.5 inch “subs”) in their door panels. Mid bass drivers are great for 250 to 600hz mid-bass but they don’t really reach that far down into the bass frequencies on the frequency spectrum, especially if they are NOT installed in a ported enclosure with the right resonant frequency. One smart way to increase the frequency dynamic range of your truck would be to use a 6.5″ spacer ring to isobarically load your door mounted midbass drivers with two identical drivers mounted in plain sight. This will not only double your usage of your tiny in-door enclosure (as explained earlier about cutting your space requirements in half), but it will also allow you to gain more true bass from your midbass drivers and increase the overall feel that you get from such a small and minimally invasive install. (To pull this off correctly the speakers have to be wired out of phase (opposite polarity) so that they move in the same direction with the distance between them constant to maintain the isobaric region between them).

Note: Click here to start building your own isobaric network using undivided isobaric sub enclosures for two 12″ drivers and save $20 off retail.

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Technorati Tags: Car Subs, sub enclosures, Subwoofer design

Intro:

The following article talks about the theory and application of installing the right subwoofer capacitor to improve the performance of your bass system. It discusses some of the concepts and calculations of subwoofer capacitors and gives my recommendations on how to choose the right size capacitor for your audio system.

Article:

Here’s a little secret about audio and power ratings that most people don’t know….
The maximum RMS power you can deliver to a resistive load is equal to V*V / R

Where V = your power supply regulated voltage (of 12 to 14 volts in a car audio system)
and R is the resistive load of your subwoofer which ranges from 1 ohm to 8 ohms for different car subs and configurations.

Subwoofer Resistance	RMS Power (12V)	RMS Power (14V)
1 ohm	144 watts	196 watts
2 ohms	72 watts	98 watts
4 ohms	36 watts	49 watts
8 ohms	18 watts	24.5 watts

And thus there are 2 ways to get more peak power out of your subwoofer setup…

1- Get an amplifier that has a built in power supply with a step up DC to DC converter, for example boosting the internal supply voltage of the amplifier from 12-14volts to 24-28volts using a capacitor ladder or voltage doubler circuit.

2- Speakers are not entirely resistive load they are more of an inductive load (combined of a resistive part and an inductor coil). At the same time the amplifier is not a pure power source and has its own internal resistance and a capacitive nature as it stores and delivers power to the subwoofers. By studying and exploiting these characteristics of subwoofers and amplifiers it becomes possible to momentarily deliver a voltage spike between the amplifier and subwoofer giving it a higher momentary peak power. This is where the term PMPO (peak momentary power output) comes from and in the more educational circles is referred to as an ILS rating “If Lightning Strikes the amplifier, it may deliver 3000 watts to a 2 ohm load for a very short duration of time effectively consuming all of the energy inside the amplifier to overdrive the subwoofer for that short duration of time”

Anyhow, both the methods mentioned above of delivering more power to an unchanged load rely on the concept of power storage and momentary power delivery…. If we can charge an ignition coil using 14 volts for 1 minute, and then use that same amount of charge to deliver 24,000 volts to the spark plug for 10 milli seconds to ignite the mixture inside the engine, then similarly, we can charge our amplifier circuitry using 14 volt power and then deliver a momentary 200 to 300 volts (inductive load spikes on 14 volt fuel injectors with tiny solenoid coils can be as high as 60 volts and so on a larger coil such as a subwoofer voice coil higher voltage spikes are not out of the ordinary), then we can over extend our subwoofer’s performance and power delivery.

This is where a good audio capacitor comes into the question… An audio capacitor keeps a good amount of power stored near the amplifier, this doesn’t really affect RMS audio performance that much so long as the alternator charging system is capable of delivering a steady 14 volts to the amplifier at the back of the car. However, when it comes the time to reach deep into the amplifier to deliver our peak momentary power output of 3000 watts into a single channel (or however much your amplifier is rated for per channel) then having a capacitor bank charged and ready to delivery such power is critical. What’s even more important, and what makes a capacitor shine over having a second battery installed in the trunk of the car, is that a high quality capacitor, has a really low series resistance built into it. This extremely low E.S.R (equivalent series resistance) that is characteristic of a good audio capacitor allows the capacitor to deliver it’s stored power to the amplifier (and thus to the subwoofers) almost instantaneously. This is even more important when you think about a 125hz audio signal that need power to be charged and delivered in the amplifier 125 times per second.

Here’s a great example of a power audio subwoofer capacitor. The boss audio Cap10 capacitor here has an 10 Farad rating, a digital control circuit, and a voltage indicator, with an ultra low E.S.R. of less than 0.002 ohms.

A 10 Farad capacitor running at 14 volts can store up to 140 Coulombs of charge or 980 Joules.
When we look at the fastest possible ‘bass’ frequency of 250hz then we have a wavelength with a duration of 4ms.
If we deliver half of our charge energy of 980 Joules to our subwoofer in 4ms, and keep the capacitor running at 50% (i.e. it is charging and discharging at the equal rate of 4ms which is the most we can take without draining it) then the maximum power we can deliver with such a capacitor without draining it (for the next coming bass hit) will be:

Peak power (Watts = Joules / Second) = (980/2) / (0.004) = 122,000 Watts !

Hrm, so why do we need such a large capacitor for a 1000 to 4000 watt system ?

The reason we need such a large capacitor, is that although capacitors can discharge power very rapidly, they take a long time to charge up. For example our 10 Farad Boss Audio Cap 10 , connected to the battery power through a low resistance 2 ohm power cable, will draw 7 amps of power for 100 seconds just to reach full charge… if we use higher resistance lower quality power wires, this charge time will grow even more.

So we have to use a larger capacitor bank because we have to find a balance between the capacitor charge and discharge characteristic as follows.

Say we have a 3000 Watt sound system wired up to the Cap 10. That 3000 Watt system for a slow 250hz bass hit will consume 12 Joules of energy in those 4 milli seconds.
E=0.5CVV and so V= sqrt ( 2E/C)
We started with 980 Joules of eneregy at a fully charged 14 volts.
We delivered 12 of those 980 Joules to our 3000 watt system in 4 milli seconds.
Our new Energy level is 968 Joules and our new voltage is 13.9 volts.

Let’s redo this calculation with a 1 Farad capacitor and a 3000 watt system
1 Farad gives us an energy of 98 Joules at 14 volts.
To reach that level of charge it takes the capacitor 10 seconds of total charge time (which makes sense since it’s 1/10th the capacitance, it takes 1/10th the charge time).
But look at what happens when we deliver 12 joules to our 3000 watt system in 4 milli seconds?
Our new energy level is 86 Joules and our new voltage is 13.1 volts

Now you see from this comparison that the 10 Farad cap is still fully charged after the first 3000 watt bass hit, on the other hand our 1 Farad cap has lost 1 volt which it has to replenish.
How long does it take the 1 Farad to re-charge again ? The answer is about 5 seconds. So, a couple of consecutive 3000 watt bass hits and your 1 Farad cap becomes a drain on your system rather than a power source, whereas the larger 10 Farad still has a stable 13.x volt power supply to your amplifier.

Let’s go one step further and try to scientifically answer the question: How big a cap do I need for my system ?

The following is calculated as a minimum subwoofer capacitor required to maintain a voltage of 13.8 to 14.0 volts for the power level indicated….

Now this is the first time I crunch these numbers but it’s very interesting to look at things this way.

Another great feature of the Boss Cap10 is that it has built in digital circuitry to do 2 things:

1- Monitor your running voltage level and warn you if your voltage dips below a safe level.
2- To monitor the charging and discharging of the capacitor. A charged directional electronlytic capacitor can be dangerous without proper monitoring circuitry.

Reverse the polarity of the wiring on a bare electrolytic capacitor, charge it for 3 seconds and watch it explode (I’ve seen this mistake first hand in my EE250 laboratory back when I was in college). Reverse the polarity on a 10F capacitor and you’re asking for trouble.

Then again, fully charge a 10F capacitor and then accidentally short it, and watch the flames. As we stated before these caps have an ultra low ESR (equivalent series resistance) and so if you short a 14 volt capacitor that has an internal resistance of 0.002 ohms then the peak current it can deliver is 7000 amps. You really don’t want to be the fire starter.

So to be able to deliver to you a powerful, effective, and SAFE product Boss Audio has included an charging and discharging circuit monitor to shutdown against reverse polarity wiring and protect against short circuits and thermal overload protection. Totally awesome.

Note: Read more about the Boss Cap 10 Subwoofer Capacitor, deliver more peak power to your system, and save 150 dollars off of MSRP.

Technorati Tags: 10 F

A common thing to do on 2+2 seater sports cars such as the mitsubishi 3000GT VR4 is to get rid of the two rear seats for a sound system install or a carputer setup. The reason the tiny rear seats exist in those cars in the first place is to keep them in a lower insurance bracket as four seater family cars rather than 2 seater race cars. Realistically though, the largest person to be able to fit comfortably in such a seat is probably a 10 year old child.

Here’s one great example of a rear seat delete. This is a fiberglass enclosure where the rear seats used to be and the whole arrangement with a single center mounted subwoofer is pretty ominous. The center subwoofer is a single Rockford Fosgate T2 15 inch subwoofer.

The central placement of the subwoofer and the implicit lettering on the aluminum cone “POWER” amplifies it’s presence. On each side of the woofer is a large 5″ bass port aimed directly towards the back of the driver and passenger seats for a maximized effect.

Below the subwoofer, the owner has mounted a digital volt meter to monitor the car’s voltage with every single hit of the RF-1000 , 1000 Watt amplifier. I personally would rather use a purely analog gauge or a needle based gauge to reduce the amount of ‘averaging’ in the voltage reading… By doing so, you’ll be better able to see how low the voltage dips (if it does) during a bass hit and you can fix that problem, if it exists, with a capacitor for power storage and larger gauge wiring for faster current delivery.

What’s really cool about this subwoofer is that Rockford Fosgate has engineered it as a low hitting subwoofer optimal for a vented enclosure. RF does not recommend using this subwoofer in a free air installation or in a sealed box. But rather, placing this subwoofer correctly in a properly designed (fairly small sized box) can hit frequencies as low as 36 hz with authority from a tiny 2.25 Cuft box. This is exactly the power and uniqueness of 15 inch subwoofers as smaller subwoofers will not be able to generate that much sound (and thus, that much feel) at such a low frequency. To hit this tuned frequency (Fb) of 36hz, RF recommends a long (17″) and wide (6″) bass port to help the box breathe and resonate.

This dual voice coil sub is no lightweight, with a total weight 50lbs and a driver weighing in at 304 oz with a dual voice coil triple stacked driver, the sub is rated for 1000 watts RMS and 2000 watts at peak.

Note: Find out more about how you can feel the power of 15 inch subwoofers, and save over $500 off retail.
Note: Click here to get your own 7 color voltage display gauge and save $46 dollars off retail.

Technorati Tags: 4 ohm, Aluminum, DVC, Vented

The first time I attempted to build a subwoofer cabinet was back in 1999. Back then I was big into the music and DJing scene and wanted to add something to compliment our communal practice session setup. The setup had a great set of technics MK12 turntables, a Numark mixer with great feeling sliders and a nice LED matrix that can help you visualize the mix. We had the whole system running through an off the shelf 50 watt speaker setup that was very subpar so I decided that speakers and an amp would be my addition to the mix.

The objective:

One big downside to traditional PA speaker systems is that they relied on two drivers: A subwoofer, and a horn driver to cover the entire aural spectrum. The problem with this setup is its loss of fidelity for midrange frequencies which are very essencial to genres such as psychadelic trance, vocal trance and jazzy house. So the plan was to build a capable cabinet system that combined enough thump to fill up a house party littered with DJ’s and local talent, all the while being able to give a more rich audible experience than the typical 2 driver PA speaker (which is obviously designed more for filling a bigger room than filling it beautifully with perfect music).

The speaker design was simple and effective based on cheap (I was a college student at the time) but effective components:

Components:

A pair of crunch audio 15 inch subwoofers (one per cabinet), rated at 300Watts.
Four Midrange 5.25 inch speakers. Each of these would be able to handle 150Watts and so 2 were wired up per cabinet matching the 300Watt sub with a 300 Watts of midrange.
Two 3″ titanium bullet tweeter horn drivers, capable of an insane 300 watts each with a frequency response down to 3000 hz. Again one per cabinet to match the 300Watt mids and Lows.

At the time I couldn’t find a single 300 Watt midrange speaker so I used two 150 watt speakers instead of a single 300watt midrange driver.

The crossover:

Using my knowledge from electrical engineering classes I was taking at the time, I designed a simple 3 way crossover with a slope of 12db/Octave based on the impedances of the components that I had already acquired. I threw up the design into PSpice and simulated the crossover’s performance and optimized it, when that was done, I went shopping and picked up the closest inductors and capacitors I could find to the design values to build my Xover. Nothing in the real world is as perfect as it is when it’s designed on the computer. But the result was close enough to be awesome.

One of the other constraints of building this crossover is the fact that we’re crossing over the amplified signal. This means that all the components in our crossover need to have the current handling to be able to withstand 900 Watts of power without overheating and melting. As a solution to this design requirement, you’ll find that some home power audio manufacturers try to cross over the un-amplified audio signal between the signal source and the amplifier rack using a cheaper crossover network. This approach also opens up the opportunity to using different amplifiers for different goals within the system, such as using a power efficient class D MOSFET amplifier for the bass, while using a minimal distortion Class A or Class AB JFET amplifier for the mids and the highs.

Since my system was designed to be a versatile system to be used at home and on the road for events and parties, I chose to use an amplified crossover inside the cabinet housing to simplify using the speakers with any amplifier setup.

The cabinets:

The whole concept of this cabinet was the combination of high SPL with High Quality audio. With a typical 15″ subwoofer you find the setup always lacking some response, with a bigger bass sound but less definition on the faster bass hits. To avoid this stereotypical view of 15″ subwoofers I decided to make a fortified sealed box enclosure to place the subwoofers in rather than a louder vented enclosure. The box was built of 1/4″ MDF (medium density fiberboard), lined with fiberglass sound deadening to reduce enclosure noise, and sealed entirely with silicone caulking to prevent air leakage. If I recall correctly, the design parameter for minimum enclosure space was around 2.5 cuft, so I went with a larger ~3 cuft enclosure.

In order to prevent interference and distortion between the drivers for the bass, midrange and highs, the internals of the enclosure were baffled to section off each portion of the cabinet with 1/4″ MDF and also sealed with silicon caulking after running the wiring between the different internal chambers.

Testing:

Once the cabinets were finally completed, there was a nice amount of ‘theoretical’ debate between myself, my electrical engineering colleagues, and my DJ friends as to weather the final result was in fact a 300 Watt or a 900 Watt system.

After a lot of debate and back and forth conversation I reluctantly agreed to put my product to the test … If you’re familiar with ‘type testing’ procedures, all regulated industries usually ‘type test’ their products to determine maximum tolerances, maximum power handling, limits of destruction and tolerance…etc. I feared that this outing to my friend’s house would end up as a ‘type test’ for my cabinet and that my two weeks of hard work cutting / drilling and assembling MDF would end up with a blown cabinet just to prove the theoretical limits of this cabinet.

At my friend Joe B’s house we hooked up one of my ‘300′ watt speakers to his 1000Watt per channel Mackie amplifier. This amplifier was the corner stone of his own home style DJing and practice station, one that he also took to smaller style events to drive the PA system. We hooked up my speaker to the Mackie, and JoeB put one of his favorite records records on the Tech-12s and started to play… slowly and hesitantly JoeB turned up the gain on his amplifier looking for where and when the speaker would start to complain or distort…

As the knob turned farther to the right, I became more and more anxious , but the midrange and titanium tweeter drives came more and more to life and the system was just insane. The goal of having a high power and clean sounding system with liquid midrange , hard hitting bass, and crisp highs was obviously over acheived and I had apparently over engineered my subwoofer for the target. The knob kept turning right and my fears of blowing my speakers turned to elation and euphoria … Eventually Joe accelerated the rate at which he turned up the volume and cranked the system to MAX gain !!!!! 1000 Watts of Mackie power were now pumping through my ‘home made’ and ‘first ever’ made cabinet and the EQ had to be adjusted with negative corrections past 2000hz to make up for how vivid the mids and highs were… and all in all, the speakers did not complain, distort, or skip a beat.

Despite being a heavy MDF cabinet, on a hard wood floor, the sheer amount of power driving through the speakers made it start to walk across the room floor .

I later took my speaker home and realized that our little test on JoeB’s amp had finally broken in this cabinet and the system had never sounded so good.

Takeaways:

The only thing I didn’t know at the time about speakers and subwoofers was the true meaning of sensitivity in db. In order to achieve my goal of matching my subs to my mids to my highs in order to build a cabinet that could in all of its components take the abuse of 900 watts, I ended up buying the highest powered midrange speakers I could find at the time (10 years ago) with a rating of 150Watts each. These speakers although had good power rating, had significantly lower sensitivity than my subwoofer and my tweeters.

The result of this mismatch is that when using the cabinet at a lower power level (such as when we had friends over for a DVD night) that the midrange on the speakers – which is where the dialog is in the music spectrum – had a little less gain than the rest of the system. The bass, effects and rumble of the subwoofers were great, the highs were clear and crisp, but unless you were driving the system hard at a house party, at lower power levels the mids were a bit flat.

If you are working with a low power source such as a stock head unit or are going to be using your system at lower power levels often, try to choose speakers and subwoofers with a higher senstivity rating. Speakers with a higher sensitivty rating are able to produce higher sound pressure levels (measured in dB at a standardized distance of 1 meter away from a speaker driven by 1 watt of power) from the same amount of power. That is a speaker with 92db senstivity is about 11 times louder than an 88db speaker running at the same power level.

So if you’re going to power your speakers from a low power source, use higher sensitivity speakers. And if you’re building a balanced cabinet or a balanced system, choose speakers with close or the same sensitivity so that you don’t have to re-equalize your system every time you crank the volume knob.

Note: Interested in a pre-amp crossover for your system, check out this clarion MCD-360 two way / three way crossover, save 127 dollars off of retail and build a subwoofer system to enjoy clean undistorted bass.

Technorati Tags: 4ohm, Crossover, dB, SVC

Diy subwoofer equalization is unknown to most enthusiasts. Even more obscure is that not all subwoofers are created equal. Subwoofers depending on size, placement, and packaging have different characteristics unique to that setup. For example larger subwoofers such as 15 inch or 18 inch subwoofers require larger enclosures for the subwoofer to operate properly. This is partly due to the fact that the larger mass of a bigger sub needs more air inside the box to help the subwoofer move and oscilliate and dampen its oscillations correctly.

The rear wall of the subwoofer box acts as a reflection panel that the subwoofer uses to reflect and compound bass waves to help the subwoofer itself reach a higher peak response (or a harder hit). At the same time the air inside the subwoofer enclosure acts as an air cushion to help dampen the subwoofers return after it excursion and control its oscillation so that it does not distort the sound and is able to track the audio wave accurately; similar to the suspension on your car preventing never ending oscillations and controlling body shake so that the suspension can track the road’s surface.

A side effect of using a larger subwoofer is that a larger moving body in a larger enclosure is more naturally tuned with a lower resonant frequency. This is similar in nature to beating a larger bass drum vs playing the a smaller set of bongos. And so a different sized subwoofer, in a different sized enclosure, with a different set of ports or vents will have a different response to different audio.

These variations can be best understood and visualized through a spectrum analyzer that you can see used in SQ (sound quality) competition…

As you can see in the graph below, the loudness of the subwoofer , measured in dB, varies at different frequencies ranging from 15hz (the lowest possible human audible frequency) up to 200hz. These frequencies from 15 to 200hz are generally considered bass, where mid-bass drivers cover the lower midrange from 250hz up to 2000hz and midrange speakers shine in the range from 2000 to 8000hz where most human voice occurs, after that come the tweeters that take us from 8000 up to 16000hz or more.

Anyway, within that range of ‘bass’ frequencies a single vented subwoofer has the response curve shown above with a peak response at around 40 to 50hz. This response is great for music like Rap or hip hop or even psychedelic trance and hard techno with deep and even subsonic bass being a characteristic of these genres of music. However if you were to play things like classic rock and some pop songs on this same system, you will find your bass lacking because those tracks more commonly use bass sounds that are in the higher bass range closer to mid bass or around the 125 to 200hz mark. As you can see from the graph above, an out of the box subwoofer (even if designed by a great company) may not hit all the frequencies you want it to hit properly depending on your style of music.

Once solution to this problem is to get a subwoofer system such as the infiniti basslink system which has an internal sound processor designed for live signal processing to improve the performance of the subwoofer in its enclosure no matter what type of music you throw at it.

However, for the diy enthusiast or for someone who already has a set of subwoofers in possibly a home made enclosure, then a parametric equalizer such as the Clarion EQS746 7-band equalizer is the way to go. The EQS 746 has 3 of its 7 bands in the bass and midbass audio range 50 Hz, 125 Hz, 345 Hz. This is something you have to make sure you check for when shopping for an Equalizer that can tune your bass frequencies because some Equalizers only have 1 slider for anything below 500 for example and those won’t work for tuning the details of your bass subwoofer.

A quick way to know if you need such a product installed on your car is to think about this… “Do I constantly find myself playing with the gain knobs and bass boost on my system depending on what song or what genre of music I am listening to?”

If the answer to that question is Yes, then installing and tuning a parametric equalizer can give you a similar bass boost depending on the frequency range where you need the boost the most. This way when you listen to a song that has a different frequency bassline, that frequency will already be boosted and you won’t have to mess with the settings on your audio system from song to song. This way you can spend much more time enjoying your music and less time fiddling with the settings.

Two important frequencies to work with here are the 50hz and 125hz frequency. If you look at our original spectrum image you can see that at 40 to 50hz we have a peak response of 83dB whereas at 125hz the response rolls off to around 66dB. What this means is that your bass at 50hz (when listening to a Rap track with deep bass) is about 17 times louder than your bass at 125hz (when you are listening to rock or classical music). This large difference in loudness is exactly why you find yourself having to fiddle with your gain knobs and exactly what we are trying to solve here.

With the EQS746, (or any similar multi-band EQ) you can lower the gain for the 50hz frequency, and increase the gain for 125hz and 345hz respectively. With some trial and error, and while using music tracks that are known to be good ‘test tracks’ for testing the complete audio range of your sound system, you can find a setting that gives you the most ‘linear’ response across the entire bass range. You resultant spectrum analysis should look something like this:

Once you’ve found this flat response, you can adjust the overall gain of your system to increase the whole bass range up with reference to the rest of the audio to make up for taking some gain out of our 50hz range and reducing the overall power of our bass hit. Once you’ve made that adjustment, you are done and you now have ’set it and forget it’ awesome sounding system that can process anything that you throw at it.

Note: Click here to read more about the Clarion EQS-746, improve your bass with diy subwoofer equalization and save 100 dollars off of retail.

12 inch subwoofers are the entry level sized subwoofer into big bass. It’s true that you can get an 8″ or 10″ subwoofer to give you nice clean and responsive bass line, however if you really want to feel the music, without resorting to drugs, meditation, or the ‘high’ of playing live on stage; then your only resort is going to be a hard hitting sound system that brings the music alive, and part of a hard hitting sound system, besides ultra crisp highs and liquid midrange is a punch, responsive and very present bass line. I think it comes as no surprise for me to tell you that 12 inch subwoofers are the 5th highest sold car audio product online due to their impressive performance.

If you think about it simplistically, how hard 12 inch subwoofers (or any size subwoofer for that matter) hit is related to two things really:

1- The size of the subwoofer, that is to say , when the subwoofer moves forwards it pushes air creating a pressure wave and making sound. The amount of air the subwoofer moves per stroke is proportional to the surface area of the moving subwoofer. In this sense, a single 12″ Subwoofer has more than 2.5 times the area of a single 8″ subwoofer and that makes it move at least 2.5 times more air per stroke. Therefore a pair of 8″ subs will never hit as hard as a similarly designed 12 inch subwoofer, all other factors being equal.

2- On the other hand, we have to consider the volume of air being moved in total for the complete woofer cone stroke. This volume of air, especially if we’re talking about a sealed enclosure design, is going to be equal to the area of the subwoofer face multiplied by the length of its stroke.

The length of the subwoofer stroke is how far forwards or backwards the subwoofer moves with the bass signal. The maximum displacement (typically called xMax) is a measurement of the maximum distance the sub can move from its original position to move air and create sound waves. The key here is that the larger the subwoofer is in its diameter, the easier it is for it to have a larger displacement without really stretching or stressing the body and surround material of the subwoofer.

SVS 12 inch subwoofers

Think about it in terms of triganometery for a minute. For a 6″ subwoofer to move 2″ in forwards displacement means that the shape of the subwoofer body would have to be seriously distorted and and become an almost cone shaped triangle with a 42 degree inner angle. If we were to allow the subwoofer body to be flexible enough to distort like this then it won’t be able to transfer enough energy into the air because the subwoofer’s body would rather warp (being soft to allow for a higher displacement) than it would push the air forwards to create sound.

On a larger 12″ subwoofer though, a 2″ displacement is a very small angular motion for the subwoofer, a displacement angle of only 19 degrees compared to a massive 42 degrees for a 6″ subwoofer.

This means that larger subwoofers, for example 12 inch subwoofers, are not only able to move more air for a similar stroke, but typically we’ll find that they’ll also have a much longer stroke or max displacement enabling them to hit even harder than a PAIR of smaller subwoofers.

In order to take advantage of this phenomenon, we’ve seen in the last few years manufacturers make subwoofers that have a stiff center section (capable of effeciently transferring the subwoofer’s kinetic energy from the subwoofer’s body and into the air), with a thicker flexible surround section sometimes 1″ or even 2″ thick. This thicker surround portion allows the subwoofer to have a greater max displacement to produce louder bass. However, to get the best quality and best response out of this kind of system requires a higher power rating amplifier.

Here is a great video showing the excursion stroke of a pair of 12 inch subwoofers in a vented box. You can also see the amount of air these babies can move. This is truly the entry level into BIG BASS!