loudspeaker equivalent circuit - representation of acoustic power

[Malcolm Irving]

... Certainly for many/most efficiency is 5% or less. But there are some - for instance Electrovoice speaker/cab combination designs like the 50 year old "Eliminator" folded horn and I'm sure others besides - that claim an efficiency around 25% and that's not insignificant.

Yes, that's a very interesting point, comparing the measure impedance curve of a speaker on a 25% efficient horn, with one in free air, would probably show a significant increase in the resistive part of the impedance.

[Malcolm Irving]

Thanks everyone for the interesting and thought-provoking comments.

[glebert]

Not easy to do in practice, but operating a speaker in a vacuum would be an interesting experiment because all the acoustic load would be eliminated.
Comparing the measured impedance curve in vacuum with that in air, we could see which resistive elements of the equivalent circuit model have been reduced.

Wonder if you used front-to-front isobaric speaker configuration you can essentially get "half acoustic load" or something like that, and then compare to a single speaker (full acoustic load) and use that to infer the value of the acoustic load. Of course you have to make assumptions about the two speakers being well matched, etc.

[Malcolm Irving]

Wonder if you used front-to-front isobaric speaker configuration you can essentially get "half acoustic load" or something like that.. .

Yes, I think Orange used isobaric speakers in some bass cabs. The speaker facing the audience has most of the air load at its back cancelled by another speaker carrying the same signal. The two speakers are identical, co-axial and as close together as possible. I believe the main effect was that the low resonance dropped in frequency by about an octave (compared to a single speaker in the same cab).

Within physical limitations, you could put an identical speaker in front of the speaker under test as well as another behind it. This would almost eliminate the air loading at wavelengths which are relatively long in comparison to the gap between speakers.

[Old Tele man]

This GOOGLE page about Acoustic Impedance Analog equivalence (electrical vs. mechanical) should be helpful:

https://en.wikipedia.org/wiki/Impedance_analogy

and, here is an older (1943) book for further reading:

http://www.tubebooks.org/Books/Atwoo...0Analogies.pdf

[SoulFetish]

Quote:
"Acoustical Impedance. - Acoustical impedance is the complex quotient of the pressure applied to the system by the resulting volume current. The unit is the acoustical ohm.

Acoustical Resistance. - Acoustical resistance is the real part of the acoustical impedance. This is the part responsible for the dissipation of energy. The unit is the acoustical ohm.

Acoustical Reactance. - Acoustical reactance is the imaginary part of the acoustical impedance. The unit is the acoustical ohm.

Inertance. - Inertance in an acoustical system is that coecient which, when multiplied by 271times the frequency, gives the positive imaginary part of the acoustical impedance. The unit is the gram per centimeter to the fourth power.

Acoustical Capacitance. - Acoustical capacitance in an acoustical sys*tem is that coecient which, when multiplied by 271times the frequency, is the reciprocal negative imaginary part of the acoustical impedance. The unit is the centimeter to the fifth power per dyne."
~ Dynamical Analogies. Harry F. Olson, E.E., PH.D. 1943

(good eye, Old Tele man)

[catalin gramada]

Yes, I think Orange used isobaric speakers in some bass cabs. The speaker facing the audience has most of the air load at its back cancelled by another speaker carrying the same signal. The two speakers are identical, co-axial and as close together as possible. I believe the main effect was that the low resonance dropped in frequency by about an octave (compared to a single speaker in the same cab).

Within physical limitations, you could put an identical speaker in front of the speaker under test as well as another behind it. This would almost eliminate the air loading at wavelengths which are relatively long in comparison to the gap between speakers.

What about an isobaric with two in antiphase supplied at different power, meant a sort of acoustical attenuator Due to partial cancelling ?