B&C DCX464 Coaxial Ring Radiator |
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fatfreddiescat
Young Croc Joined: 15 October 2010 Location: N.E.Wales Status: Offline Points: 1081 |
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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
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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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
Old Croc Joined: 11 October 2004 Location: Lancaster Status: Offline Points: 2716 |
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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.
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James Secker facebook.com/soundgearuk
James@soundgear.co.uk www.soundgear.co.uk |
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toastyghost
The 10,000 Points Club Joined: 09 January 2007 Location: Manchester Status: Offline Points: 10920 |
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The HE versions are better for that but yeah the scream is noticeable on the normal BMS
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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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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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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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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