I'd like to hear people's opinions on these comments, originally posted here (http://www.audioasylum.com/forums/MUG/messages/14/142475.html):
However, the power rating does not tell you how well the amp will match a certain type of speaker. Speakers are transducers, that store energy in their moving parts and couple to energy stored in the room air. This stored energy comes back to the amp at a later time and can cause trouble in the form of distortion. This distortion cannot be measured with resistive loads on a test bench.

Magnepans are inefficient speakers with low impedance. Their large panel areas couple to room air vibrations very well, even if they have low mass. The quality of bass they deliver depends on how well the amp can absorb the generated current from the energy stored in the room air. Amps with similar power ratings may differ widely in this aspect.

Wow. um.... This should start an interesting thread. :rolleyes:

Although correctly stating that the speaker is a transducer, the OP goes on to describe the system as almost a sort of acoustic capacitor. Now in all fairness, I can actually see what he's getting at... to a point.
If we consider a short single transient burst, the speaker emits the burst, which travels through the air, bouncing off other surfaces, back to the speaker. As a speaker is essentially a microphone in reverse, the returning sound waves could affect some change in the state of the amplification system. Low frequency, continuous waves would have a more pronounced effect, as the wave could be returning out of phase, causing the amp to be working harder at certain parts of the wave, and not as hard in others. I would expect this to be more evident in a speaker system with a very large radiating area, such as a planar speaker system.
Now, without empirical evidence, I can't state whether this is true or not, but the OP's awkward way of describing what's going on aside, it does seem... plausible.

At least that's my $.02.
*readies asbestos undies*

Interesting, maybe I will run my two channel system with only one speaker driven and scope the other speaker to look at the amplitude of the induced voltage. (this will have to wait until next Tuesday but I suspect minimal results)

Wow. um.... This should start an interesting thread. :rolleyes:I didn't want to start anything. I'm truly ignorant of the electronics. I tend to be an objectivist in this hobby and this forum tends to vet topics like this better then the Maggie forum hence the question here and not there.

the part about a speakers being a transducer is correct...it can create sound by moving the voice coil in responce to a variable voltage from the amplifier and thus driving the speaker cone to produce sound. The same speaker can also produce voltage when the cone moves (reacts to sound in the room) the voicecoil and induces a current in the coil (in effect, it becomes a microphone). However, there is no way this electromechanical device can "store" energy. It reacts to energy, but does not store it.

the part about a speakers being a transducer is correct...it can create sound by moving the voice coil in responce to a variable voltage from the amplifier and thus driving the speaker cone to produce sound. The same speaker can also produce voltage when the cone moves (reacts to sound in the room) the voicecoil and induces a current in the coil (in effect, it becomes a microphone). However, there is no way this electromechanical device can "store" energy. It reacts to energy, but does not store it.

Sure it can store energy. The cone has a resting spot created by the position of least resistance of the surround. The in/out movement creates increasing resistance the further it moves. When it is in an in or out position it is momentarily storing energy released when it returns to the resting position.

I'd like to hear people's opinions on these comments, originally posted here (http://www.audioasylum.com/forums/MUG/messages/14/142475.html):

That seems to have been written by someone who doesn't know much about electronics, electroacoustics, or acoustics.

Ok, the applied kinetic energy will move the voice coil and the displaced surround will return it a resting position. If that is "storage" OK, but the original article posted is techno-babble bs.

OK, pure thermodynamics, you put a transducer in a room and excite it. You will be heating the air in the room, so one could argue you are storing energy in the room. Totally useless with respect to music reproduction, but by theory yes.
(Agree with Mr. Lee)

(Agree with Mr. Lee)

One would be wise to do so....

Also, I would like to add the fact that while I did not agree with the OP, I was just trying to come up with some sort of explanation as to why he might post such a statement.

I suppose I could have just called him a tool, but that would just be insulting Home Depot and Lowes stores everywhere. :D

If only more of the forum members would just reference the most excellent anthologies published by the AES.... We could at least quit arguing about speaker cables!

Bob, Vol. 4 ended in 91, come on guys, has there not been enough worthwhile papers in 18 years to come out with another loudspeakers volume? More on motor design, materials, modeling? Or are we really still where we were back in the mid 50's. We all know the physics, just can't build it. I get the impression Mr Rice and Mr Kellogg would not be overly impressed by our progress.

Specifically on the issue of stored energy:

The only energy "stored in the room air" is that of the reverberant sound field. At all but the lowest frequencies, the phase of these energy waves at any particular frequency is random and non-coherent. So I can think of no predictable way in which this could influence an amplifier.

For the lowest frequencies (under 100 Hz), there are discrete room modes, where the stored room energy is coherent. This would be the only possibility for the room energy to even theoretically influence the amplifier, I think.

As for practical matter of whether this theoretical influence at very low frequencies actually does have an effect on amplifier impedance, I must defer to the opinion of Bob Lee, who has far more amplifier experience than me. My guess is that it gets lost in the high radiation impedance of the subwoofer.

Regardless of any of this, the quote from the OP still appears to be gibberish. :D

- Terry

While the original post in bs from what i can tell. He may be vaguely referring to the sound interacting with the cone at certain frequencies. Most know this as the resonant frequency, the frequency when the cone is most mechanically excited. This can in fact induce a back current as the coil acts as a generator.
Though this is all dependent of the movement induced electrically... i don't think, in any human listening levels, that the pressure waves created into the air around us is enough to mechanically induce movement in the cone, well at least not enough to matter.

I'd like to hear people's opinions on these comments, originally posted here (http://www.audioasylum.com/forums/MUG/messages/14/142475.html):


However, the power rating does not tell you how well the amp will match a certain type of speaker.


In general most fiers have no problems driving most ers. Most amplifiers are well-matched to most speakers and most speakers are reasonable amplifier loads. In these days of extended warrantys and liability, a manufacturer who builds an amp that can't drive many speakers, or a speaker that isn't easily driven by most amplifiers will be shortly put out of business.



Speakers are transducers, that store energy in their moving parts


True to a certain extent, but this tendency to store and later on release energy is represented by the speaker's impedance curve.


and couple to energy stored in the room air.


Most speakers are so ineffcient (less than 1%) that the degree to which they couple the energy they receive to room air is minimal, and the degree to which they return energy to the amplifier from room air is equally minimal. Minimal to the point of vanishing.


This stored energy comes back to the amp at a later time and can cause trouble in the form of distortion.


Do the math. Less than one percent of the power the amplifier delivers to the speaker is transferred to the air in the room. Less than one percent of the one percent or less energy that is transferred to the room air is returned to the amp. IOW less than 1/10,000 of the power the amp puts out completes this route.

In order to drive a normal reactive load, an amp has to be able to handle upwards of 30% of its output be reflected back from the electrical parts of the speaker. Compared to that, the 0.01% of the power that actually
makes the round trip through the air in the room is properly ignored.


This distortion cannot be measured with resistive loads on a test bench.


True, but it can be measured on the test bench using reactive loads or loudspeaker simulators. I've done this kind of testing, and to the surprise of many, it turns out that speakers loads don't cause amplifiers to produce signficantly more distortion than resistive loads. In fact,resisitve loads are generally the more stressful kind of load.


Magnepans are inefficient speakers with low impedance.


Their actual efficiency is more like 0.3% than the 1% that I used in my calculations above. Thus the absence of signficiance of coupling of energy back to the amplifier is even less important. Note that it was totally unimportant for more efficient speakers, so it is less important than totally unimportant, if you catch my drift. ;-)


Their large panel areas couple to room air vibrations very well, even if they have low mass.


Low efficiency means that they couple to room air vibrations much more less than the usual loudspeaker. Their lack of efficiency comes about because their mass is relatively high compared to the mechanical force that is available to move that mass.

We've just see two false claims, which are key to the argument being presented. Therefore, the argument is false.


The quality of bass they deliver depends on how well the amp can absorb the generated current from the energy stored in the room air.


Actually, the most significant source of the limited bass response that most people experience with magnepans is due to the fact that they are bipolar radiators at low frequencies, and there is nothing that prevents the out-of-phase bass from the back of the panels from cancelling the bass being produced by the front of the panels. Most people who get good bass out of Magnepans either have euphonic standing waves in their listening room, or have positioned the Magnepans in such a way that the bass from the back of the speakers is partially blocked from coming around and cancelling the bass being produced by the front of the speakers.

This problem with bass from the back of the driver cancelling the bass from the front of the driver is the most signficant reason why we put speakers in boxes.


Amps with similar power ratings may differ widely in this aspect.


Since the purported aspect is riddled with false claims, the conclusion is also false.

Thanks everyone for your thoughtful and detailed responses. They played out as I expected. The gentlemen I quoted also believes (http://www.audioasylum.com/forums/MUG/messages/14/141541.html) speaker wire is directional and speaker wire and cables can be improved by lifting them off the floor.

Thanks everyone for your thoughtful and detailed responses. They played out as I expected. The gentlemen I quoted also believes (http://www.audioasylum.com/forums/MUG/messages/14/141541.html) speaker wire is directional and speaker wire and cables can be improved by lifting them off the floor.Don't listen to idiots