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Poo compression driver
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Dr Burnz View Drop Down
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    Posted: 06 November 2007 at 1:16pm
Does anyone else find the P.Audio BM-D450 compression driver a bit poo? I get quite a bit of power compression when I use mine, crossed over @ around 1.8k. I've just swapped them over with BMS 4552ND drivers, and I can already hear a difference in clarity. I've not yet tested them at a continuous high output yet, but I'm guessing they will not compress as much as the BM-D450's. Am I expecting too much of a 1" driver? Should I have gone for a 1.4" or 2"? Just wanted to see if other people have experienced the same thing.
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ArthurG View Drop Down
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Points: 988 		Post Options Post Options   Thanks (0) Thanks(0)   Quote ArthurG Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2007 at 4:29pm
Well D450 is entry level pro stuff. Maybe you expect too much from this model. Try to higher the xover point around 2,5kHz  and/or higher the xover slope to get better sound at high volume from this  P.Audio.

On the other side, BMS 4552Nd is a better performer even if some guys (including me) don't like the high THD of BMS HF drivers. Compared to the P.Audio, You should be able to get 2-3 more dB of "clean" output.

Now depending on your application and requested xover point and SPL, you should go for the real stuff, a 3" VC HF driver from a top company like Beyma. You will immediately benefit from the change. 100% sure about the result. But (big but)  it costs bollox...


Edited by ArthurG - 06 November 2007 at 4:31pm
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ceharden View Drop Down
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Points: 11851 		Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2007 at 1:53am
What are they being used with?

1.8kHz is quite low for a 1" running at high levels.  Saying that in one of my cabs I cross some DE250's over at 1.6kHz but they're so efficient the midrange runs out long before the HF gets too hot!
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Dr Burnz View Drop Down
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I run them with the p.audio SN 15MB. I've just built 2 X15s but I'm not too happy with the sound n size. I think I'm gonna build a smaller cab with better drivers. In an attempt to improve the sound and performance of my x15s I got the BMS drivers.

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Dr Burnz View Drop Down
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What compression driver and horn combo would you recommend for a compact cab with a 12" cone driver?

I heard 18 sound horns are nice, and the DDS horns are also good. Beyma and B&C make good drivers. But which combination will give the most depth and natural sound in your opinion?
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Mark James View Drop Down
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Points: 5306 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark James Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2007 at 2:17pm
you are pushing that 450 a bit too low ours used to sound great 2.5<16khz, well it rolls off somewhere just before 18k anyway but you get the idea.
should have got a 1.4 in there realy!!!
insert silly sentence here
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tb_mike View Drop Down
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Points: 2744 		Post Options Post Options   Thanks (0) Thanks(0)   Quote tb_mike Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2007 at 7:39pm
Dont forget the horn - if its too short/small it will not load effectively low in frequency.You dont want to use a horn near its cutoff,john sheerin did some measurements and saw lots of delayed energy)bad( near cutoff.Which backs up the 'xover an octave higher'golden rule.

http://ldsg.snippets.org/HORNS/index.php

Quote B&C DE25 on a 500Hz tractrix horn
500Hz
1.5kHz
10kHz

What is interesting here is that near the low frequency cut off of the horn, energy storage goes way up. This was true of three different compression drivers on this same horn. Performance at 1kHz is much better with some drivers but it is not until 1.5kHz that performance really gets close to what you would expect from a driver operating within its intended passband without problems. Performance basically then remains similar to this until the top end of the response which of course varies from driver to driver.
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Mark James View Drop Down
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Points: 5306 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark James Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2007 at 8:01pm
yes also you may have it on horn not big enough/long/big enough mouth for this particular frequency range.
but seriusly i was impressed with the bmd450 from 2.5k up for its price, anything below here is a bit too much though........
insert silly sentence here
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ceharden View Drop Down
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Points: 11851 		Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2007 at 8:43pm
I use B&C DE25 and DE250 (one is updated version of the other) on the 18Sound aluminium flare.  Sounds absolutely stunning.

Incidentally one cab is an SN15MB with the DE250 crossed at 1.6kHz, sounds great!  You can get better 15" drivers tho.
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Mark James View Drop Down
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Points: 5306 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Mark James Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2007 at 11:47am
and i bet the de25/250 cost at least +50% of the price of the bmd.
but the b&c is a vastly better driver i bet. we are comparing two pieces of kit in a different price+performance bracket...... good point though ceharden.... do b+c do any 1" that play up to 20khz? or do they do bullets????? the only critisicm i can find within me, [the bmd doesnt play as heigh either]
insert silly sentence here
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Dr Burnz View Drop Down
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What 15 would be ideal to meat the B&C? I'm also not too impressed with the 15MB. Fair enough, its a very lightweight driver, but I wouldn't mind having a beefier 15" to cope in demanding situations, but still have the definition and clarity. I'd have to redesign the cab, but its the drivers that's the important bits.
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ceharden View Drop Down
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Points: 11851 		Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2007 at 2:14pm
Markk:  The B&C 1" drivers (eg DE250) play high enough that either your hearing runs out first or you really don't notice anything missing.  The DE250/XT1086 combo is FLAT to 14-16kHz.  Can't measure accurately above that due to sampling rate limitations etc.

Dr Burnz: What you are finding is the inherent problem of using a 15" driver and a 1" compression driver.  Heavyweight 15" drivers won't play high enough and the few which have light enough cones to hit 2kHz cleanly are exactly that, light, efficient but lacking in low end.  The SN15MB is a reasonable compromise.

My advice is use a 1" driver with 12" and 1.4" with a 15".  You don't need a really nails 1.4" driver.  18Sound do the 1424BT and B&C do the DE610 which are 2.5" diaphragm versions.  Both reasonably priced but just go low enough to meet a 15" nicely at 1-1.5kHz.

If you're planning to use the cabs for a drum monitor etc then you can get away with a heavier 15" and a 1" ignoring the midrange issues.  Otherwise you might have to rethink how you want the cabs to work in order to make significant improvements.
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