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MultiWay Conventional loudspeakers with crossovers 

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22nd August 2004, 07:43 PM  #1 
diyAudio Member
Join Date: Mar 2004
Location: Connecticut, USA

Is this how to compare speaker sensitivities?
A speaker's sensitivity, or SPL, equals the decibel level of 1 watt measured at 1 meter. Right?
Now...from googling around, I've found (I think) that multiplying watts times about 1.29 should increase the volume by 1 decibel. That fits pretty well with the general rule I've read that doubling watts increases dB by 3, and that watts x 10 equals double the volume, and that "double the volume" is subjectively measured at between a 6 to 10 dB increase. So, that should mean that a speaker with a sensitivity of 92 dB, supplied with 100 watts, and a speaker with a sensitivity of 88 dB, supplied with 277 watts, should produce about the same perceived volume. The math I used: 92dB  88dB = 4 decibel difference Multiply 100w @ 88dB times 1.29, 4 times 100w x 1.29 x 1.29 x 1.29 x 1.29 = 276.9w Is that right? If not, please enlighten me. 
22nd August 2004, 08:03 PM  #2 
diyAudio Member
Join Date: Feb 2004
Location: Stockholm

It seems right to me, even though I get the factor 1.26. Also, the more general power gain formula is 10^(dB/10), so 1 dB is 10^(1/10)=1.26, 3 dB is 10^(3/10)=2.00. But you get the same result (if you use 1.26), so your method is OK too.

22nd August 2004, 10:51 PM  #3 
Banned
Join Date: May 2004
Location: New Hampshire

Watts up?
Keep in mind impedance also. 2.83 volts into 8 ohms is one watt, but so is 2.0 volts into 4 ohms, and 4.0 volts into 16 ohms. You cannot compare the relative SPLs of different drivers without taking impedance into consideration.

23rd August 2004, 03:20 AM  #4 
diyAudio Member
Join Date: Mar 2004
Location: Connecticut, USA

Yes, but almost all automotive drivers are 4 ohm, and I wasn't thinking about other impedances.
But, could you explain what you mean? Isn't a watt a watt regardless of the volts and impedance used to get it? In your example of 2.83 volts into 8 ohms vs. 2 volts into 4 ohms, if both drivers have the same sensitivity rating, won't they be equally loud? If not, why? 
23rd August 2004, 03:28 AM  #5  
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23rd August 2004, 05:16 AM  #6 
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Join Date: Jun 2004
Location: New Orleans, LA

Aren't speaker sensitivities quoted as dB/w/m? At least all the ones I've seen are.
If so, then 2.83V only applies to 8 ohm impedence speakers. 
23rd August 2004, 11:58 AM  #7  
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23rd August 2004, 01:48 PM  #8  
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Join Date: May 2004
Location: New Hampshire

Quote:
For an 8 ohm speaker and a 4 ohm speaker with the same wattage sensitivity and the same voltage input the 4 ohm speaker will be 3dB louder, because with the same voltage input the 4 ohm speaker will be receiving twice the wattage as the 8 ohm speaker. If the two speakers are rated for SPL/2.83 volts the 4 ohm speaker will be 3dB higher than the 8 ohm speaker even though the SPL/watt is the same. Therefore the 2.83 v sensitivity rating gives a more accurate representation of how loud different speakers may be with the same voltage input. 

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