The car is equipped with a nice Harmon Kardon 7.1 speaker system comprising a front center channel, a component pair in the front doors, a two-way 6.5″ speaker in each of the rear doors and a single subwoofer mounted in the parcel shelf of the car.

Notice the dual wirings...

After some further research on the topic, I stumbled on some pictures of the installed factory subwoofer. If you zoom in on the picture, the print on the back of the voice coil seems to say the following.

So that gives us the data we need to look for an upgraded subwoofer for my car. It also tells us that the factory setup is not a sealed ‘free air’ install or infinite baffle install but rather a large vented setup using the entire 12.4 cubic feet of trunk space as a subwoofer box venting through about 6 2″ wide vents. Interesting.

Vented trunk space is clear in this picture

Now looking at the install pictures, I further wondered: Would it be easier to install a higher quality shallow mount subwoofer in the factory mounting location ? Or do I stand to gain some good bass by mounting a regular subwoofer to the same location on the opposite side of the parcel shelf protruding into the trunk ? To perform this comparison, I didn’t have any data about the factory subwoofer, however I thorough search on Amazon and came up with two possible candidates. Each of these candidates is an 8″ subwoofer. Both are electrically equivalent with an equivalent resistance of 2 ohms. Both are from the same manufacturer, which should make this a fair comparison of the design appropriation of each of these subwoofers for our application.

Product	Kicker 08CVT82	Kicker 07CVR84
Style	Shallow Mount	Typical Subwoofer
Size	8 inch subwoofer	8 inch subwoofer
Voice coil	Single 2 ohms	Dual 4 ohms
Power Handling	200W RMS / 400W Peak	200W RMS / 400W Peak
Frequency Response	25 to 350 Hz	30 to 500 Hz
Sensitivity	84.8 dB	83.1 dB
Displacement	30.4 Cubic Inches	41.1 Cubic Inches
Max Excursion (ExMax)	0.226″	0.408″
Qms	10.641	9.36
Qes	0.597	0.912
Qts	0.565	0.831
Vas	0.364 cu. ft.	0.495 cu. ft.
Mounting Depth	3.38″	4.31″
Resonant Frequency (Fs)	49.2 Hz	44.3 Hz

Somethings jump at me right off the bat here. The regular subwoofer has about 1″ more depth to it (or 25% deeper) but it has almost double the max excursion. Also if you look at the resonance figures (Qms, Qes, Qts) we see that overall the shallow mount is less resonant and more damped. This makes sense since this subwoofer has limited space to work with so it can’t be allowed to have a great excursion , and we expect to see it installed in tiny boxes which require more damping. The last thing to note here is a slightly higher resonant frequency (Fs) for the shallow mount which means I’d expect slightly deeper bass from the regular basket woofer.

Now this is all expectation and I wanted to go one step further and analyze my expectations against simulation results… To perform the simulation, I needed two figures from my enclosure to enter into the simulator:

My enclosure volume:
Is my trunk volume which is a massive 12.4 cubic feet as I looked it up online.

My enclosure tuned frequency:
I estimated this around 40 hz. If you listen to the sound system on my car, it plays songs like 50 Cent – Hustler’s ambition with authority. But the system struggles to play deeper bass notes stereotypical of some of the more experimental techno music I listen to. It also struggles to play some of the higher bass frequencies into the mid-bass region. So my guesstimate of 40hz is just that a guess, but it is probably true and serves well for illustrative purposes here.

Plugging all the numbers above into the simulator you can see here the response of the shallow mount on the bottom curve, with the response of the deep basket subwoofer on top.

There is no comparison here as the regular subwoofer holds at least a +3dB gain over the shallow mount almost for the entire frequency range. Amazing.

What this means is that I stand to DOUBLE my bass loudness by simply swapping the top mounted shallow mount for a regular subwoofer trunk mounted, using the same amplifer, and the same ‘enclosure’! That is awesome for a low buck upgrade to my factory sound system without the complication of a full subwoofer box, amps, wiring …etc

Then I thought, what do I stand to gain if I sealed the bass ports and turned this into a free air install with a sealed trunk acting as my box…

As you can see from the picture above, sealing the bass ports on the factory trunk would give me a reasonable gain in the subsonic frequencies which would be fun for some genres of trance music, but I will loose all that nice authoritive bass when listening to hip hop and other genres of music (a 15dB drop will kill the bass). So unless I was going to upgrade to a higher powered amplifier, going to a sealed solution was probably the wrong way to go in this application.

Then I thought, I wonder how differently the two subwoofers in question here would perform in their own optimized enclosures… The optimum enclosure for the shallow mount is a tiny 1.1 cubic foot box tuned for a frequency of 35 Hz, while the optimum enclosure for our regular subwoofer is a much larger 5.4 cubic foot box tuned for a much lower frequency of 21 hz.

Looking at the plot above, you can see that shallow mount, when used properly can give a very good frequency response playing as deep as 30hz (where the gain rolls off to -3dB). However, the regular subwoofer, with it’s lower resonant frequency, slightly less damped cone, and greater excursion is able to add another 10hz of subsonic playing as low as 20hz (where the gain rolls off to -3dB)…. So let’s recap what we just found out:

1- In a hap hazard enclosure, the regular subwoofer will play louder and deeper than the shallow mount.

2- As we already knew, sealed enclosures play deeper into the subsonic but there may be a loss compared to a tuned vented box depending on port tuning. For factory systems with limited power from the factory amplifier, vented enclosures are probable the best bang for the watt.

3- Shallow mounts can perform really well if used in the right sized enclosure and are a great option when space limitations are an issue.

Very interesting results and I’m really considering now purchasing myself a single Kicker 07CVR84 and installing it in my trunk using an 8″ spacer ring (at least 0.4″ thick to allow it to reach max excursion without touching the bottom of the parcel shelf).

Note: Click here to purchase Kicker 08CVT82 Shallow Mount Subwoofers and make the most out of your limited space enclosure! Or click here to purchase the more powerful Kicker 07CVR84 subwoofer for your car.

Technorati Tags: 2 ohm, 4 ohm, DVC, Shallow Mount Subwoofers, SVC

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1. Choosing a stable amplifier for your car sub woofer

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:

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

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1. Subwoofer Tube Enclosures – Explained

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

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2. 15 inch SPL competition subwoofers

Big woofer , big bass!

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