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:

Clarion CD360 pre-amp 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:

Ported MDF woofer cabinet.

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:

Simulation of a 3rd order crossover network

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.

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