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OscarS
diyAudio Member

Join Date: Jan 2011
Quote:
 Originally Posted by NoDestiny Something I have heard over the years, but never tested... Double displacement (cone area): +3dB Double power: +3dB Both: +6dB But I believe there is a flaw there. Wouldn't it be that if you double your cone area AND power, you get +3dB? If you double your drivers and split the power to both (adjusting so they get 50/50 of the same amount of power prior and not letting the drop in resistance at the amplifier push more power than it was), wouldn't that cut the cone travel in roughly 1/2, giving no gain in displacement? Therefor, by doubling your woofers and doubling your power, you gain 3 dB? I have done research trying to find the correct answer and seems pretty debated. Seems simple enough to test scientifically. I could be wrong on this. I have seen it calculated both ways. Obviously, the frequency response is definitely going to be extended with more drivers.
you're right. Doubling drivers while keeping power constant does not yield +3dB. IF it did, we could just keep doubling drivers and doubling drivers, ad infinitum, and we could achieve any SPL we ever wanted. Without even touching power. Not gonna happen. Double the drivers AND give the 2nd one the same power as the 1st (which is doubling power) is what gives the +3dB, and only +3dB. Not +6 dB as some claim.

 10th October 2012, 12:10 AM #1752 Djim   diyAudio Member   Join Date: Dec 2009 Location: Les Pays-Bas
Xoc1
diyAudio Member

Join Date: Nov 2008
Location: Devon UK
Quote:
 Originally Posted by OscarS you're right. Doubling drivers while keeping power constant does not yield +3dB. IF it did, we could just keep doubling drivers and doubling drivers, ad infinitum, and we could achieve any SPL we ever wanted. Without even touching power. Not gonna happen. Double the drivers AND give the 2nd one the same power as the 1st (which is doubling power) is what gives the +3dB, and only +3dB. Not +6 dB as some claim.
Doubling speakers without increasing power does yield a 3db increase!
Of course this is exponential so for each 3db we need 2 - 4 - 8 - 16 etc drivers.
The other rule is the speakers must be within a quarter wavelength of each other. So as the speaker stack increases in size the maximum frequency that the 3db gain effect applies drops.
At 100 hz the wavelength is 3.44 metres so a quarter wavelength is 86cm
Put simply if you have a pair of bass bins and you place them together, instead of separating them like a stereo pair, you gain an extra 3db, which can be very useful in a small PA setup.
Once you get above 2 subs in a row you can run into other problems, including beaming.

weltersys
diyAudio Member

Join Date: Jan 2008
Location: Florida
Quote:
 Originally Posted by Xoc1 Doubling speakers without increasing power does yield a 3db increase! Of course this is exponential so for each 3db we need 2 - 4 - 8 - 16 etc drivers.
You are correct, (and Oscar S is wrong), I did a lot of testing to prove it for David McBean, as he had a few doubts in some of his Hornresp programming:

Multiple Cabinet Combined Response

Some of the tests were running multiple cabinets in series, each doubling of cabinets halved the power to each individual cabinet, the output remained the same.
In addition to the 6 dB increase by doubling the quantity of equally powered speakers coupled within 1/4 wave length, the added frontal area effectively creates another boundary, which increases forward gain even more.

Horn Extender/Wave-guide for TH

Art Welter

 10th October 2012, 04:23 PM #1755 NoDestiny diyAudio Member   Join Date: Dec 2011 Location: Idaho, US Just to make sure we are on the same page... by "keeping the same power but doubling cone area", we are talking about going from 1 watt to a single driver to 1/2 watt per each driver of two (meaning, same exact amount of power in total)? By doubling your drivers and giving them the same amount of wattage per as before, you are doubling both drivers and total wattage.
turbodawg
diyAudio Member

Join Date: Feb 2004
Quote:
 Originally Posted by Xoc1 Doubling speakers without increasing power does yield a 3db increase!
People are being pretty unclear about this. If you double speakers, while powering the added speaker at the same power, you will add 3 db. So while the power per speaker stays the same, the system is actually pushing double the power. I think.

Efficiency and sensitivity conversion - loudspeaker percent and dB per watt and meter loudspeaker efficiency versus sensitivity vs - sengpielaudio Sengpiel Berlin

NoDestiny
diyAudio Member

Join Date: Dec 2011
Location: Idaho, US
Quote:
 Originally Posted by turbodawg People are being pretty unclear about this. If you double speakers, while powering the added speaker at the same power, you will add 3 db. So while the power per speaker stays the same, the system is actually pushing double the power. I think. Efficiency and sensitivity conversion - loudspeaker percent and dB per watt and meter loudspeaker efficiency versus sensitivity vs - sengpielaudio Sengpiel Berlin
According to that calculator (bottom of the page), I could have 1 driver w/ 200 watts and 99db sensitivity and produce 102dB @ 10 meters. Then, throw in another drivers w/ another 200 watts (so 400 watts total, doubling both total wattage and total driver displacement), you get 105dB @ the same distance. Therefor, doubling your power AND doubling your drivers will result in a +3dB gain, not +6. If you double your power PER DRIVER and double up the drivers, you will have gained 6, but then that's really quadrupling your power. Finally, a single driver with 400 watts will produce the same two drivers at the same power (but 200w each).

So unless that calculator is wrong, it seems that the drivers themselves don't actually "add" to the equation when it comes to gaining decibels, but simply gives you more "headroom" for more power from the amplifiers to become louder.

 10th October 2012, 06:27 PM #1758 Djim   diyAudio Member   Join Date: Dec 2009 Location: Les Pays-Bas Hi guys, Drivers are not completely passive electrical circuits. You need to realise that "doubling the cone area" also means doubling the motors. Doubling the motors means doubling the magnet power, which is an energy source! In other words, a system of two drivers has twice the motor power and therefore becomes two times more efficient (is 3dB) with the same power. Last edited by Djim; 10th October 2012 at 06:29 PM.
turbodawg
diyAudio Member

Join Date: Feb 2004
Quote:
 Originally Posted by NoDestiny According to that calculator (bottom of the page), I could have 1 driver w/ 200 watts and 99db sensitivity and produce 102dB @ 10 meters. Then, throw in another drivers w/ another 200 watts (so 400 watts total, doubling both total wattage and total driver displacement), you get 105dB @ the same distance. Therefor, doubling your power AND doubling your drivers will result in a +3dB gain, not +6. If you double your power PER DRIVER and double up the drivers, you will have gained 6, but then that's really quadrupling your power. Finally, a single driver with 400 watts will produce the same two drivers at the same power (but 200w each). So unless that calculator is wrong, it seems that the drivers themselves don't actually "add" to the equation when it comes to gaining decibels, but simply gives you more "headroom" for more power from the amplifiers to become louder.
Yes, I agree with with what you said.

 10th October 2012, 06:40 PM #1760 Djim   diyAudio Member   Join Date: Dec 2009 Location: Les Pays-Bas

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