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speaker dave

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About speaker dave

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  • Birthday 03/23/1955

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    Vintage audio, psychoacoustics, bicycling, shortwave radio, photography, record collecting (mostly classical piano).

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  1. speaker dave

    Roy F. Allison: 1927–2016

    As a young speaker engineer I wrote to many companies looking for work. Roy was the only one who took the time to write back and offer some personal advice and a friendly note.. A true gentleman. Rest in Peace Roy
  2. speaker dave

    Inconsistencies in AR's 12" woofer curves

    Hi Steve, Well, its not as simple as you say. First off there is always a compromise between axial response and spherically averaged response. The best axial performance will come from an LR approach. This always comes with a mild power hole, so that is a compromise. Subjective tests show (I believe) that power response holes are benign but it doesn't sound as if you would accept that. If you want your networks to add in quadrature then you can have flat power through the crossover but then you will have a rising lobe in the up or down direction. I don't know of any way to get dead flat response in both measurements, and to some degree a compromise is required. As to "1m on axis and you're done". I don't think that characterizes any of the better designers I know. Most are aware that 1m is a bit close for a good approximation to the far field, and will be looking at 2m response as well (which is generally adequate for the development of the far field response). Most look at response at a number of angles, possibly emphasizing near angles around a likely listening window, but nonetheless getting a good look at off axis performance. You keep repeating the term "energy" but I don't think that is being correctly used. Energy is seldom measured in acoustics although intensity (Watts / meter squared) is sometimes measured. You probably mean power response, another misnomer, used to refer to the power or energy weighted (i.e. pressure squared) spherical average frequency response. Frequency response (pressure) is sampled at points around a sphere and each curve is squared and weighted by the area it represents. The end result is not power (at least not without the right weighting factor), so "power response" is not strictly correct. Reverb rooms can be used for this, as long as they are calibrated and the corrections are applied. At the same time gated response in close is just as good for calculating the power curve, and the errors of 1m measurement are actually inconsequential if a spherical average is needed. Most of these "nouveau" designers should be able to calculate the spherical average if they wanted to . This is frequently measured in pro products as it is needed for directivity index, but it is not used much in consumer because equalization of power response is known to be an unreliable approach. This crops up frequently these days as DSP is making room EQ so easy. Everyone seems to be practicing a steady state approach which gives a result that is midway between correcting the axial response and the power response. Right off the bat they find that they need some sort of room curve (flat power response is always too bright) and those that have much experience at it are confounded that the room curve that works changes from room to room and speaker to speaker. Again, this is because concentrating on power response sends you down an problematic alley. Did I mention that SMPTE is working on totally revising the X Curve equalization method because they find that it doesn't make any 2 theaters sound the same? Again, looking at the room curve brings in the power response and equalizing power response is not going to get you to consistent sound. I know everyone here loves the early AR products, but I seriously doubt that EV would want everyone to worship them to the point of denying that not everything was known and understood in the classic days, and that real progress hadn't been made since. Really. Regards, David
  3. speaker dave

    Inconsistencies in AR's 12" woofer curves

    If you can optimize both then you have covered all your bases, but, of course, sidestepped the issue of relative importance. That is the more interesting question: if one can be optimized to be ideal (direct field or reverberant field) and the other must be compromised, then which one should get more of the designer's attention? I always point people to Floyd Toole's original study of the 25 systems that listeners rank ordered and that he subsequently measured. From best to worst there is a clear correlation between the axial frequency response of the systems and their order of preference. Looking at the power response of the same systems I would defy you to find any rhyme or reason connecting their rank ordering and their power response. Now, neither Floyd, nor Lipshitz and Vanderkooy found that power response was inconsequential. Peaks in power response are audible if high enough, and there seems to be a range of downward power response contours that are safest, but there is no particular power response curve that is mandatory, in contrast to axial frequency response. This is not the fashion of the hip, but more the understanding that 50 years of research have revealed since Vilchur's day. David S.
  4. speaker dave

    Inconsistencies in AR's 12" woofer curves

    Really? You can hold a pillow in front of your face and not hear a difference in a distant speaker's sound? Far field or not, I have never been unaware of the direct field of the speaker. Are you really conducting this test or simply assuming an outcome based on your beliefs? A couple of my observations: If you go to the cinema and they play background music prior to the show, you can close your eyes and point to the sound sources hidden behind the screen (no need to close your eyes I guess). This is well beyond the critical distance and the direct field is still detected and given an importance beyond its simple level would suggest. As a second experiment, from when we were debating cabinet diffraction, I had my wife take a ruler on edge near a tweeter and slowly vary its distance to a tweeter (thus imparting a comb filter to pink noise). I could hear it at any distance in a lively listening room. In fact when I put the speaker in one corner and moved to the diagonally opposite corner (as far as I could get away in that room), I could still hear the effect. Study after study is showing the greater importance of the direct field rather than the reverberant field. David S.
  5. speaker dave

    What is the prime determinant of sound quality?

    I've already conceeded that Vilchur was the first to market an acoustic suspension system as we know it, the modern middle efficiency sealed bookshelf speaker. The question of invention though is really down to the patent office and the application dates. Even if Vilchur arrived at the notion independently to RCA (which happens frequently), RCA has the prior art and can claim the legitimate right of invention. It is also not like the case of Armstrong and DeForest, where DeForest stumbled across something and only Armstrong understood its worth. Olson and Preston talk of the benefit of very low driver responance, of letting the cabinet be the primary restoring force, and of the improved linearity of the resultant system. They understood acoustic suspension. The high compliance radio speaker that they based the patent on was also a production item, so they did take actions to put their theory into practice. As much as we applaud the many achievements of Vilchur, he lost the patent case with EV because there was clear prior art. David S.
  6. speaker dave

    What is the prime determinant of sound quality?

    On the other hand I enjoy the odd "stupid pointless arguement". Regarding the invention of dome loudspeakers here are a couple of patents you should look up: 2237298 and 2442791 http://www.google.co...%20dome&f=false http://www.google.co...2442791&f=false Baumzweiger shows a dome radiator from 1941. By the way he talks about it as a microphone but in the preamble says that all are reversible transducers and equally valid as "receiving apparatus or transmitting apparatus". Baumzweiger later changed his name to Ben Bauer. Wente shows a nice dome radiator with an accordian shaped suspension in 1948 (applied 1945). My point was that Vilchur was careful to patent his suspension and magnet structure invention. A dome diaphragm would have been disallowed by the patent office due to the prior art. Now, as to the "invention" of the turntable... Regards, David S.
  7. speaker dave

    What is the prime determinant of sound quality?

    Hi Carl, Thanks for the curves. Besides the diameter difference the HiVi unit has a short flare that will narrow its dispersion from what its size might suggest. (Although we should ponder why manufacturers would add flares that narrow directivity if wide dispersion is such a key parameter.) A better comparison might be the KEF T27. It is closer in diameter and has a flat mounting plate with no wave guide. (Not a perfect unit in other regards.) AR did have one advantage in that they tended (in the early days) to use domes with no surround and that would keep the effective diameter right to the VC diameter. David S.
  8. speaker dave

    What is the prime determinant of sound quality?

    Oddly your arguement confirms my case: Electro Voice countersued and won based on the obvious prior art of the Olson/Preston patent (you really should read it). I agree that it was wise of Vilcher not to further pursue it. As to the tweeter patent, I don't see any mention of being a dome as a unique claim. It is a patent on a unique magnet structure and suspension. Apparently Vilchur didn't believe he had invented the dome radiator. Theory (see Beranek and Olson) says that dispersion is primarily determined by drive unit diameter. You can dabble with breakup modes and try and get a different effective area, but I don't know of any designs that look smaller than they are over any significant range. To claim that AR achieved wider dispersion than anyone else is to fall for their marketing. They had wider dispersion than the horns and larger cones that preceeded them. Not wider than later designs with similar sized domes. Wide spread beliefs aren't always factual. David S
  9. speaker dave

    What is the prime determinant of sound quality?

    The AR 1 was certainly the first speaker in the modern mold. It was the first I know of that was designed, woofer and box together, to have flat response even at the expense of efficiency. In the end, adding mass until the response was flat, was the real invention. "Acoustic suspension" is more the marketing hook. Not sure about the first domes. University did some early dome tweeters. Bill Hecht claims to have invented the soft dome. Philips did mid domes in molded paper. There must have been plenty of designers that tried the back radiation of a compression driver with no phase plug. It is Hard to find anything in speakers with no precedence. David S.
  10. speaker dave

    What is the prime determinant of sound quality?

    Although Edgar Villchur comercialized and popularized the Acoustic Suspension speaker he didn't really invent it and was predated by Olson and Preston of RCA. The RCA patent makes interesting reading. They discuss high compliance woofers, allowing the cabinet to provide most of the restoring force, and increasing linearity by relying on cabinet stiffness. Their interests were primarily in mass market radios but the example is acoustic suspension. http://www.freepaten...com/2490466.pdf I'm not sure that the AR domes have wider dispersion than any other manufacturers domes of the same diameter. For the most part a 1" dome is a 1" dome (and a 3/4" a 3/4") as far as dispersion goes. If you have any curves that show otherwise I would like to see them. As to Toole and wide dispersion, he does seem to advocate a fair amount of room involvement but his tests don't show that wide top Octave dispersion is needed for a speaker to do well in his tests. Look at the data in his original AES paper and see that his top ranked speakers average a directivity index of about 9dB at 10kHz. (Hemispherical dispersion would be a d.i. of 3dB.) His tests, more than anything, show that on axis flatness and smoothnes, plus off axis smoothness (free from power response peaks that would indicate resonances) lead to high test rankings. Especially wide dispersion is not a positive factor in his test results. David S.
  11. We've debated this over on DIY audio quite a bit. Cabinet wall damping is, of course, a very different thing than internal damping of the air cavity. One deals with resonances of the cabinet panels and the other with the internal standing waves related to dimensions. For cabinet damping and the origins of the BBC approach I refer people to a great paper by Harwood: http://www.bbc.co.uk...rts/1977-03.pdf He looks into typical cabinet materials and measures their stiffness and Q but the more interesting info is when he looks at typical cabinet construction and how the cabinet radiates at each panel resonance. He is a big advocate of panel damping (bitumen pads being the British favorite) but shows that damping is most effective when the cabinet walls aren't overly stiff or massive. Pushing up stiffness or mass will increase mechanical impedance and it becomes more difficult to damp the resonances. His general recommendation is thinner walls but greater damping mass. This falls in line with what Architectural Acoustics professionals know: that wall transmission loss is improved with "limp mass". That is, a very heavy curtain can give good issolation. Turn it into a stiff wall of the same mass and the issolation will be good except at the inevitable resonance frequencies where the wall becomes essentially transparent. As to stuffing, I have never been impressed with any of the polyfil or BAF materials. My measurements of their absorption properties have shown they don't compare to fiberglass or rock wool. They may up the apparent volume of a cabinet a little but they don't absorb internal standing waves. Most open celled foams are so-so but there are some closed cell foams that are good. Any good material will have published data on alpha vs. frequency (absorption). If you can't find certified measurements then it probably isn't a real acoustic absorber. Regards, David S.
  12. speaker dave

    Need help for AR-12 refurbish

    That looks like a very clean and professional repair ot me. I wouldn't worry about having a half roll where the previous surround was flat. Considering the alternative (dead speakers) it seems like a good choice. Clearly AR knew that the excursion required was nil and so gave it a flat surround, but foam surounds are fairly light and I'd bet the response is little changed. David S.
  13. speaker dave

    Shipping/packing AR-3as

    As to the standard size, it is easy to cut down a carton, at least in length. I've cut boxes down in two dimensions, which is more work but doable. I'd add to the good comments above: fist bag the systems so that the packing has less chance to burnish the surface. Corner protection is the biggest issue and you can build up your own corner protection with multiple layers of corrugated and lots of tape. Styrofoam tends to fracture apart, but there is a polyfoam (?) that is a waxier material that is tougher and can be assembled with hot melt. I agree about not trusting a UPS store. Most of them think a big box and a layer of "peanuts" in the bottom is the answer. This may sound like a lot of work but that is what it takes. Charge accordingly if you need to. David S.
  14. speaker dave

    AR-4x competitive with today's best?

    So the AM-5 was the worst of the three and the best seller by far. This just shows the strong imbalance between marketing/advertising vs. product quality. (something to think about as we enter the Presidential Campaign). At Snell we tried to stay away from the loudest theater demos and play HT selections with more of a music focus. My favorites were Kundun, James Tailor Live at the Beacon, Black and White Nights (Roy Orbison), Sessions on West 54th St. and a few others. Regards, David S.
  15. speaker dave

    AR-4x competitive with today's best?

    It's the million dollar glass of lemonade concept. You only need to sell just one (or maybe one pair).
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