Binaural Listening? I had a very compelling demo, have you?

[Soundminded]

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This shows why a moving coil cartridge with its higher mass is a dumb idea but what does this have to do with acoustic suspension loudspeakers/

BTW, this is not the whole equation, it's the high school physics version and without the rest of it it's useless.

Here's the whole thing;

F(t)=ma + bv + kx

where F(t) is the position of an object as a function of time, m= moving mass, a=acceleration, b=damping factor (velocity dependent frictional loss), v= velocity, k= spring costant, and x= displacement.

You can see immediately the advantage an acoustic suspension speaker has over a ported design. For an AS speaker, k is NOT frequency dependent. It dependes only on the compression and rarifiaction of air trapped inside. The ideal gas laws which applies virtually in tact (Boyle's and Charles' laws) include P1*V1=P2*V2 where P is pressure and V is volume. (F force = pressure* area.) As the volume of air increases or decreases the pressure inside changes inversely and proportionally. The restoring force is the pressure difference between the inside of the box and outside of the box times the area. What's more it is applied uniformly over the entire surface of the cone. This eliminates differences in restoring force from the center spider to the outer surround which would tend to shear the cone and difference along the inner and outer circumference that would tend to twist the cone. Speakers relying on mechanically restoring the cone to its neutral position work against a force applied by the spider and surround that is not uniform with frequency and a column of air that has little resistance to air flow at its resonant frequency and its exact multiples and very high resistance at points halfway inbetween. The FR of a ported system is therefore very irregular with high Q at resonance and a falloff below resonance of 24 db per octave. The woofer/enclosure resonance freuency is therefore the systems practical lower limit. AS designs can be equalized flat for up to 2 or more octaves below resonance. The stuffing inside an AS design forces the speaker to work to push and pull air between the spaces between the fibers. These fibers create an enormous surface area and control b by virtue of their aerodyamic drag which is how they create the damping factor. By controlling b vis a v k and m, the FR can be tuned to any F3 desired. This is invariably done by trial and error. As stuffing is increased to increase b, the volume of are displaced works to increase k as the same time so there is a tradeoff. The speaker generally has a characteristic of low F3 (wherever you want it), response to whatever Q you want, and does not have nearly the same tendency to cone breakup and resulting harmonic distortion as ported designs. The price that's paid is efficiency. In 1960 an amplifier that could produce 25 wpc rms or more at 30 hz was an expensive amplifier. Today 150 wpc rms can be a very inexpensive amplifier unless you listen to the advertising claptrap of high end amplifier designers. But if you want to plunk down money for a Krell or Bryston it's your money.

I could not quickly find a good presentation of this law explaining how tuning mbk affects frequency response for damped oscillation. At the bottom of this link there's an explanation with a graph showing that the resonant peak decreases with increasing b. BTW; v (velocity) is dx/dt and a (acceleration) is d2x/dt2. (these are the first and second time based derivitives of position versus time.) Most textbooks give an approximate solution indicating the center of the resonant frequency and q based on the values of mb and k. One problem is that as you add stuffing to the box to increase b, you are displacing air which increases k, the trapped air's springiness at the same time so it's a tradeoff for a given box size and cone mass.

http://www.calpoly.edu/~rbrown/Oscillations.pdf

It was interesting that Villchur didn't understand that this is why his invention works. He thought it had something to do with thermodynamnics. While the system of course does not violate any physical laws including those of thermodynamics, that law is not useful in explaining how this system operates. A small amount of energy is lost heating the fibers in the stuffing but this is insignificant compared to the energly lost to I2R heating of the voice coil.

 

[Soundminded]

During my last two years in college, I roomed with a physicist. I can tell you from lifelong experience that every physicist, at least every one I've ever met has a screw loose in their brain. Every site I visited to find the solution of Newton's second law of motion for forced damped oscillation used different symbols and cutsie shorthands making the thing even more difficult to understand than it already is. Here's the one closest to a comprehensible answer.

http://www2.mae.ufl.edu/haftka/enganal/2_4.pdf

All this guy did is change b to c. Many use the notation omega zero for undamped resonant frequency and omega prime for the damped resonant frequency. omega = frequency in hertz *1/2pi

So the solution is that the damped resonant frequency is 1/2pi[sq rt (4km-bsquared)]/2m using the symbols in the text I used in school, Resnick and Halliday. Now you can see why the tradeoff between more stuffing increasing b and k at the same time matters and why they work against each other.

Here's a better view of what happens to FR as b changes.

http://en.wikipedia.org/wiki/File:Resonance.PNG

When b=0 you have an oscillator. Critical damping which has no bump occurs when damping is at 0.707 (=sq rt 2/2)

Here's a comparison of different resonant systems, mechanical and electrical

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

Scroll down to the table that lists "equivalent systems." You'll see that the electrical and mechanical resonance models are exact analogs. They use the same second order ordinary differential equations when you manipulate them. Only the symbols mean different things but the math is the same. BTW these models do not include the damping factor for any of them. In the electrical model, it's the resistor that's the equivalent of the mechanical damping factor and it's been omitted. So for a loudspeaker, the model is the superposition of the electrical circuit and the mechanical response, you have to take into consideration both. But more fun comes from the joker in the deck, the kicker when you realize that they are not independent of each other. That's because the electrical model actually should include an element not shown even on many of the sophisocated models, a voltage source that's associated with part of the load, the reverse emf. This stored energy source that kicks back at the amplifier is related to the mechanical resonance frequency and kinetic energy of the mechanical system. Whatever frequency the system is excited at, the speaker wants to generate a reverse emf and current at the resonance frequency. The mass of the speaker and its velocity (stored kinetic energy) are related to to the reverse emf. So is the reconversion efficiency of the speaker as an electrical generator. How this energy is damped out depends on the impedance of the amplifier output circuit including the speaker wire. A high impedance output increases the time it takes for that resonant energy to dissipate and tends to exaggerate bass output at the resonant frequency. This is one reason why tube amplfiiers with their high output impedance and thin speaker wire can create a boomy sound. Not so simple even when the equations are understood, is it?

 

[Gregadd]

The AR turntable was part of the system I had with the AR speakers. All that matters is that it was right.

BTW, this is not the whole equation, it's the high school physics version and without the rest of it it's useless.

Yes I was just providing proof of doing my homework. There are plenty of detailed examples.

It's a perfect application of Newton's second law of motion applied to forced oscillation. It's a classical problem in every college level text on physics and mechanics dynamics. Study that and we can discuss it. It 's a topic I know a little something about.

A friend had the AR 3a and the best he could do was a 60 watt amp.

It dependes only on the compression and rarifiaction of air trapped inside.

Intuitively that would appear to be a bad thing. The air inside the cabinet pushes back against the driver and propels the driver. So if I take two cymbals and crash them together. The trapped air tends to torque them out of my hand. Large woofers can have significant back extension.You are thus compressing a substantial amount of air.

 

[Soundminded]

The AR turntable was part of the system I had with the AR speakers. All that matters is that it was right.
Yes I was just providing proof of doing my homework. There are plenty of detailed examples.


A friend had the AR 3a and the best he could do was a 60 watt amp.

Intuitively that would appear to be a bad thing. The air inside the cabinet pushes back against the driver and propels the driver. So if I take two cymbals and crash them together. The trapped air tends to torque them out of my hand. Large woofers can have significant back extension.You are thus compressing a substantial amount of air.

"Intuitively that would appear to be a bad thing. The air inside the cabinet pushes back against the driver and propels the driver."

No actually it's a good thing. It's what the design relies on. The reason it's good is that the restoring force does not depend on frequency. It is also applied uniformly over the entire surface of the cone simultaneously. In that era, other speakers used accordian pleated surrounds that were tight and their force varied with frequency. Even with monster enclosures, it was very difficult to get them to produce very low frequencies. One reviewer wrote that AR1 was the least efficient speaker at 100 hz and the most efficient at 30 hz. When 2 separated by several feet were required for stereo, unless you had an enormous room, even if you liked the large speakers, there was a limit to their practicality.

Efficiency is not nearly as good in AS designs as ported designs can be. Horn designs are supposedly the most efficient, as high as 50%. AS designs can be as low as 1% or 2% AR3 is also a tough load because its impedance goes below one ohm at some frequencies. We blew up a 60WPC solid state Scott receiver that way. When I was recapping and refoaming my AR9s 4 years ago, I tried connecting them to a 100 wpc Sherwood receiver without the woofers connected to check for phasing and to be sure all drivers were operating. It didn't matter that the woofers weren't connected, the receiver shut itself down to protect itself after a few seconds every time. HT grade amplifier stages are not a usable choice for this type of system. Good quality solid state amplifiers IMO usually work very well.

I think it unfortunate that AR changed from a cloth surround woofer to a foam surround. My AR9s were very late versions. The woofers were manufactured OEM by Fostex/Tonegen for AR. Their surrounds weren't foam but they did deteriorate and had to be replaced. To my ears there is a difference in the sound of the cloth surround and foam surround woofer, at least as I remember the cloth surround versions. Actually I liked them better even though the foam surround versions work very well.

No speaker is purely only an AS or mechanically restored system, all of them have both elements, it's a matter of degree. An AS system needs some mechanical restoring force and must have a very slight air leak or it will become a manometer. That means changes to barometric pressure in the ambient air would alter the neutral point where the cone stays when no voltage is applied.

The AR turntable struck me as a knockoff of the Thorens split platter design at half the price with the addition of its innovative suspension to isolate it from shocks and acoustic feedback. At the show where it was introduced, a guy sat next to it with a steel hammer and occasional took a good whack at it on its top plate with no effect. The major criticism of it was its tonearm. Many people replaced it with SME and other arms. At about $79 for the entire turntable it was a very fine value. AR always stood behind its products with an excellent warranty policy. Others, Empire among them stole the best ideas from that turntable and incorporated them in their subsequent products. Immitation is the sincerest form of flattery.

 

[Kal Rubinson]

The AR turntable struck me as a knockoff of the Thorens split platter design at half the price with the addition of its innovative suspension to isolate it from shocks and acoustic feedback. At the show where it was introduced, a guy sat next to it with a steel hammer and occasional took a good whack at it on its top plate with no effect. The major criticism of it was its tonearm. Many people replaced it with SME and other arms. At about $79 for the entire turntable it was a very fine value. AR always stood behind its products with an excellent warranty policy. Others, Empire among them stole the best ideas from that turntable and incorporated them in their subsequent products. Immitation is the sincerest form of flattery.

I seem to recall that the original release was at $54(!) but I will have to check my files tomorrow.

 

[Gregadd]

I recall paying $57 for the store demo with Shure cart. Another salesman sold it before I could pick it up. The store made up for with a new one at the original price. A long time later I upgraded to SOTA. It also had a floating arm and platter.

 

[Gregadd]

We also know that for every action there is an equal and opposite reaction. So the sound being pushed into the room is also being pushed back into the speaker. WE can't absorb it all and it ha an effect on the sosund.

 

[Soundminded]

We also know that for every action there is an equal and opposite reaction. So the sound being pushed into the room is also being pushed back into the speaker. WE can't absorb it all and it ha an effect on the sosund.

While compressing air in a box of one to four cubic feet can create substantial air pressure inside the box and force on a speaker cone, I think compressing air in a room of several thousand cubic feet even with the doors and windows tightly shut and no large archways into adjoining rooms will have a relatively negligable effect on the cone from the pressure of the reflected sound waves even when it is loud. Theoretically it's true that it will but you have to consider the order of magnitude of the effect. One manufacturer, I think it was Linn said it didn't want its speakers demonstrated in the same room with the presence of other speakers for a reason something like this. Was that the real reason or were they just afraid of a direct side by side comparison?

 

[hvbias]

I enjoy binaural quite a bit with my Stax O2s. Unfortunately there just aren't many recordings. I would rather listen to a non-binaural recording of a reference classical performance than a binaural one of an average one.

If there are some romantic era (or earlier) composer classical binaural discs with great performances please recommend them, I am all ears

 

[Gregadd]

While compressing air in a box of one to four cubic feet can create substantial air pressure inside the box and force on a speaker cone, I think compressing air in a room of several thousand cubic feet even with the doors and windows tightly shut and no large archways into adjoining rooms will have a relatively negligable effect on the cone from the pressure of the reflected sound waves even when it is loud. Theoretically it's true that it will but you have to consider the order of magnitude of the effect. One manufacturer, I think it was Linn said it didn't want its speakers demonstrated in the same room with the presence of other speakers for a reason something like this. Was that the real reason or were they just afraid of a direct side by side comparison?

I suppose other speakers can act us passive radiators and "sing" along with the music.

 

[Soundminded]

I suppose other speakers can act us passive radiators and "sing" along with the music.

At what loudness level? At a level well below the sound produced by my heating and air conditioning system. I understand why some manufacturers don't want anyone elses speakers in the same room with theirs. They're not really afraid of how they might affect the sound coming out of their own products when they are not operating. They're afraid of how they might affect a prospective customer's decision of what to buy when they are. People who manufacture in this industry would have a much harder time "educating" their market if more of it demanded explanations of their theories that included at least an order of magnitude for what they claim than merely qualitative statements that do not give perspective of what that claim is actually worth in real terms. There's a lot more in most listening rooms to vibrate and create sound than another speaker cone. For example in mine there are the walls, ceiling, floor windows, and every loose object. (I only came accidentally close to shattering all 28 panes of glass in my listening room once. It was at the opening of a CD of Copland's organ symphony.) Funny how whenever I hear a buzz or rattle and wonder if something bad happened to my speakers I always manage to trace the source to something else buzzing. Maybe it's time to cut the bass a little

 

[Gregadd]

At what loudness level? At a level well below the sound produced by my heating and air conditioning system. I understand why some manufacturers don't want anyone elses speakers in the same room with theirs. They're not really afraid of how they might affect the sound coming out of their own products when they are not operating. They're afraid of how they might affect a prospective customer's decision of what to buy when they are

Not everyone has forced air heating (radiators for example). A/C can be turned off for example. Many manufacturers welcome direct comparisons. Magnepan is one example.