Pro Coaxial Compression Drivers


2008-02-23 10:28 pm
I am curious if anyone has played around with some of the coaxial compression driver setups from the likes of BMS, B&C or 18Sound to name a few. Are there inherent issues to be taken into account?

Links to some that I am considering:

B&C 8CXT -
BMS 8CN552 -
18Sound 8CX400F -

I was thinking these 8" coax's would work well as surrounds in ported enclosures and some sort of TMW for LCRs. All pointers and opinions welcome.
I haven't tried any of the 3 drivers you list. A couple of comments though:

The B&C
I like the look of the specs for the B&C 8CXT the most. The Fs is high at 76 Hz though. The woofer appears to have the smoothest curve but the compression driver response is pretty ragged.

The BMS:
The BMS 8CN552 has a high Fs of 87.6 Hz and the frequency response curve provided (driver in a 10 L box) suggests that the usable lower limit is more like 110 Hz. The high frequency response curve provided has a broad peak from about 1500 Hz to 6KHz -- this will take some heavy duty crossover work to "fix".

The 18 Sound
The rising response of the 18 Sound woofer can be tamed in the crossover. However no matter what you do the response will be pretty ragged in the critical midrange. It has the lowest Fs of the group but its still relatively high at 64 Hz.

Based on the specs I'd get the B&C (prices being equal). Note that I don't know of any coaxial that will generate as smooth a frequency response than two seperate drivers of equivalent cost. But this may not be a critical a problem for you. I'm biased though -- I'm the very satisfied owner of Hawthorne Silver Iris 15" coaxials mounted in a large OB.

Hopefully ScottG and other more knowledgeable DIYers than me will comment.
Yes - the Silver Iris does have a ragged high frequency response. I read someplace that this a function of the woofer cone shape providing poor loading for the compression driver. Despite this it has a very smooth easy-going sound to it - that why I disclosed that I was biased towards coaxial drivers.


2006-02-16 10:49 am
I have yet to find a coaxial driver without a ragged response, and I've been looking at them for years. And yes, it's mainly due to the horn loading of the compression driver by the woofer's cone. The only graph you'll find without such a response are those from Radian, which is either only because they're ridiculously smoothed, or because their crossovers have smoothed it out (as they were supposedly measured with their corresponding passive crossovers), but I highly doubt that. However, the Radian coaxes are supposedly very good sounding. I've seen every bit of scarce info on the net regarding these units, and I remember coming across more than one person saying that they closely resembled that of the older Tannoy dual concentrics. I actually purchased one of the 12" in-ceiling models (yeah, crappy stamped steel frame) to try on an open baffle, with the intention of mating them with Alpha 15A's on OB if all went well. However, I still haven't gotten around to it, due to finances and staying busy lately. And I need to figure out the crossover too.


2006-02-16 10:49 am
John L said:
I have seen the graph specs on the Silver Irises, and I did not see anything ragged in it. Does anyone have the link to the chart?

I have some response graphs of all the Hawthorne woofers (including the SSI), which might have been taken by Eminence, although I'm not exactly sure. As far as graphs of the high frequency unit, these two seem to be all I have..


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