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Re: [Phys-L] Acoustics: Does a speaker create a displacement antinode? (amplifier power)

Most speaker manufacturers will quote a speaker efficiency in terms of an acoustic sound power (actually intensity) level (measured in decibels, relative to 1 pW/m^2) at a distance of 1 meter directly in front of a speaker for a 1 watt electrical input at a certain frequency, depending on the type of speaker. Or they measure the frequency response curve for a 1 watt signal at 1 meter.

For example, if a speaker has an efficiency of 100 dB SPL at 500 Hz, then the actual intensity output of the speaker is 0.01 W/m^2 at 1 m in front with an electrical input of 1 W. If you assume that the sound power is distributed hemispherically (an enclosed speaker), the area would be 2/3 pi m^2 or 2.1 m^2, the speaker efficiency is 0.021/1 or 2%. That's pretty typical. Klipsch is much more efficient, ranging from 105 to 115 dB. Bose tends to be less efficient, as are most guitar amp speakers at around 90-98 dB.

And remember, if you want to add 10 dB, you have to multiply the power by 10. So if you want that 100 dB speaker to output 120 dB at 1 meter you have to have an amp that will output 100 W without melting down.

-----Original Message-----
From: Phys-l [mailto:phys-l-bounces@phys-l.org] On Behalf Of Bill Norwood
Sent: Wednesday, April 09, 2014 12:40 PM
To: Phys-L@phys-l.org
Subject: [Phys-L] Acoustics: Does a speaker create a displacement antinode?
(amplifier power)

Bernard,

I mean whatever comes out of he speaker that commonly gets measured in
terms of dB - say a mfr will claim that his speaker will "put out" 120 dB I guess
right at the front plane of the speaker enclosure.

So, I would need to know for this case what amplifier power would be
required to drive a speaker at 120 dB vs. at 110 or 100 dB.

Bottom line is that I am trying to add an environmentalism aspect to my claim
that extremely loud, outdoor, band music not only contributes to sound
pollution for a neighborhood, but it also wastes a lot more electrical energy
than one might expect.

Thanks, Bill



On Tue, Apr 8, 2014 at 4:46 PM, Bernard Cleyet <bernard@cleyet.org> wrote:


On 2014, Apr 08, , at 12:55, Bill Norwood <bnorwood111@gmail.com>
wrote:

Hi Jeff,
Long shot here, but since you are looking a bit into audio:
If one increases by 10 dB the sound level out of a speaker at a
specified distance, by what factor has the amplifier power requirement
increased?
Thanks, Bill Norwood, U of MD at College Park


You mean sound pressure level???? by sound level OR do you mean sound
intensity?

I measured in Watt/m^2
p " " Pa


I proportional ~ to p^2

http://en.wikipedia.org/wiki/Sound_intensity


Sound pressure level (SPL) or sound level is a logarithmic measure of
the effective sound pressure of a sound relative to a reference value.
It is measured in decibels (dB) above a standard reference level. The
standard reference sound pressure in air or other gases is 20 µPa,
which is usually considered the threshold of human hearing (at 1 kHz).

http://en.wikipedia.org/wiki/Sound_pressure


from these and knowing the log manipulation rules "you" can find "your"
answer.


bc lazy


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