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B&C DCX464 Coaxial Ring Radiator

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fatfreddiescat View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 18 July 2019 at 4:46pm
Originally posted by snowflake snowflake wrote:

I would say the same about BMS drivers. reviews typically measure distortion at 2.83V. increase the power by 20dB and you will get a very different distortion plot and realise that at high powers it is throat geometry that dominates distortion, not how expensive your comression driver is.

BMS being one of the very few that do publish distortion plots, good on them, the thought of the amounts of distortion generated if powered to their published peak specs looks to be higher than the fundamental.
Earl Geddes has some interesting ideas on distortion suggesting that people can not easily distinguish low order distortion in comps until in the 20-30% region and that the cause of them sounding rough when driven at higher levels is more to do with the waveguide.
Weltersys also a regular on DIYAudio has done some tests on various comp drivers, quite an interesting finding of his is in post #60 


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snowflake View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 18 July 2019 at 9:17pm
p224 of Olson says a 300Hz exp horn can pass 1 acoustic watt per cm2 of throat  at 6kHz with 25% distortion - which equates to 5, 10 or 20 watts for a 1", 1.4" or 2" horn. some of these drivers with ratings of 100W or more and sensitivites implying 50% efficiency must be producing mostly distortion if higher frequency signal is played. they can probably manage max power up to about 5*Fc of the horn at sensible distortion levels but the possible power falls by a factor of 4 per octave frequency increase.
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Timebomb View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Timebomb Quote  Post ReplyReply Direct Link To This Post Posted: 19 July 2019 at 8:44am
25% distortion at 6KHz will not be that audible, its not ideal but its not as bad as it seems from the numbers.  Try listening to a 12KHz sinewave and a 12KHz square wave and see if you can even tell the difference.   

The 1.4" throat is not really the throat though, on the BMS coax the throat is very narrow for the HF diaphragm, the maximum point of compression is right close to the diaphragm, a much smaller arear than 1.4" diameter.  The expansion starts from there.   Ill look up what Olsen said but i think the distortion in these drivers is mainly due to diaphragm breakup and ringing.  If you push the BMS coax too far it screams at you, there is clearly some resonant behaviour in the diaphragm, but on lower power they are very articulate, so much so that they can be too fast and "thin" sounding imo.      
James Secker          facebook.com/soundgearuk
James@soundgear.co.uk               www.soundgear.co.uk
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 19 July 2019 at 10:42am
The HE versions are better for that but yeah the scream is noticeable on the normal BMS
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 19 July 2019 at 12:37pm
Originally posted by Timebomb Timebomb wrote:

The 1.4" throat is not really the throat though, on the BMS coax the throat is very narrow for the HF diaphragm, the maximum point of compression is right close to the diaphragm, a much smaller arear than 1.4" diameter.  The expansion starts from there.

we can assume that the flare rate of this initial section is much higher though so that it only loads the HF diaphragm to the bottom of it's operating range.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 19 July 2019 at 12:40pm
Originally posted by Timebomb Timebomb wrote:

25% distortion at 6KHz will not be that audible, its not ideal but its not as bad as it seems from the numbers.  Try listening to a 12KHz sinewave and a 12KHz square wave and see if you can even tell the difference.     


at 6kHz perhaps not, but an octave lower than that is very much in the vocal range and distortion will be noticeable. @12kHz I guess we can't tell the difference because higher harmonics are beyond the audible range.
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