Inexpensive woofers from MCM Electronics

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I recently found a line of low cost woofers from MCM Electronics. MCM has a wide variety of woofers some of which are ideal for open baffle dipole applications.

If you are looking for a way to build an inexpensive subwoofer for your home theater these will work pretty well for that too but they are far from top performers in that application. The total damping factor, "Qts" is far too high for any box application. (The measured Qts on these drivers is much higher than the manufacturer specification.) Qts is so high in fact that there is no such thing as a correct size box. This doesn't mean you can't mount it in a box, it just means it's going to be a bit boomy due to the high value of Qts and it's going to be "good for the price" but that's it. If however you choose to think "outside the box" no pun intended, you can build an audiophile quality woofer system with these drivers.

The most expensive woofer is not always the best depending on the application. For small box woofer systems you generally need something with a heavy cone, stiff suspension, low Q, and very high power handling. These usually have large magnets, large voice coils, and are typically expensive. For open baffle however you don’t need these features. For this application a small magnet, high Q, loose suspension is more suitable thus making it possible for many lower cost woofers to perform well.

A properly built and equalized open baffle woofer system can produce superior more natural sounding bass than any conventional “box” woofer system. Because of the front/rear cancellation however this type system requires far more volume displacement capability so typically multiple large drivers are used. (For a box system the volume displacement requirement increases as an inverse square function meaning that to produce 20 Hz you need four times more displacement compared to 40 Hz. An open baffle system is an inverse cube function so you need eight times more displacement to produce 20 Hz compared with 40 Hz.)

The ability to use low cost drivers makes it possible to build a very high performance multiple driver woofer system for a reasonable price. A perfect example of this can be found in this 15” woofer for less than $20/ea when bought in quantity. (price as of 1/20/2015… subject to change) While it has a stiffer suspension than I would like, its overall performance is excellent for such a low cost driver. Distortion and noise are low, better than many more expensive drivers. A typical open baffle system using this driver might consist of two floor to ceiling columns using six or eight of the drivers in each column depending on ceiling height. To get eight within a 10’ ceiling you will need to stager them slightly. Ideally these will be placed along the side walls of the home theater or listening room.

DSP must be used to equalize the open baffle system to correct for the front rear cancelation and any waveguide effect created by the depth of the open H-frame. Also, a steep high pass filter (4th order) should be used to attenuate ultra low frequency to avoid bottoming out the drivers. In this application, either six or eight of these inexpensive 15" drivers per column can produce significant output to below 20 Hz. The high pass filter can be set around 16 Hz with a 4th order roll off and this should adequately protect the drivers. Given the low cost of these drivers and the availability of inexpensive DSP products from miniDSP you can build a woofer system to outperform the most expensive “box” type woofer systems on the market and do it for about $500 plus amplifiers.

The 12" version of this same driver will also work well. With a 10' ceiling it would be possible to use nine in each column which would also provide significant output. Likewise, The 10" version also works well. Overall the larger the better however, the 15" is the best but the 10" is still a very good performer.

This system utilizes the 10" verison in a simple H-frame along with a far more expensive Tang Band W8 1808 8" driver and a Dayton AMTPRO-4 Motion Transformer. The other drivers in this system are far more expensive than the MCM 10" drivers and yet the bass quality in the sytem leaves little to be desired. It's amazing that such inexpensive drivers can perform so well in such a high resolution system.

The 8" and 6.5" versions are really too small to be very useful for open baffle applications. They would work fine for an ultra low cost solution in a sealed box but due to the high value of Qts they will tend to be boomy. For the money however all the drivers in this line are definitely a good value.

Distortion data for a 1 watt and 5 watt inputs... (1 watt from 10 Hz to 3 KHz and 5 watts from 20 Hz to 1 KHz) Also, impedance and frequency response. Frequency response was measured with the drivers in open air, no baffle.

15" version.

12" version.

10" version.

8" version.

6.5" version.