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MultiWay Conventional loudspeakers with crossovers 

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22nd August 2004, 06:43 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, 07:03 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, 09:51 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, 02:20 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, 02:28 AM  #5  
diyAudio Moderator

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23rd August 2004, 04:16 AM  #6 
diyAudio Member
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, 10:58 AM  #7  
diyAudio Moderator

Quote:
__________________
Remember: life is ten per cent what happens to you, ten per cent how you respond to it, and eighty per cent how good your reflexes are when the Tall Ones come at your throat with their pincers. 

23rd August 2004, 12:48 PM  #8  
Banned
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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