Edgar

DeciBels (dB) are a measure of power ratio. The equation is as follows: dB = 10*log10(power out / power in) You are using 12 dB of attenuation, or "-12 dB". Let us assume that "power in" equals 16 Watts: -12 = 10*log10(power out / 16) -1.2 = log10(power out / 16) 10^(-1.2) = power out / 16 16 * 10^(-1.2) = power out 1 = power out

There's nothing wrong with that. I have my system set up so that when the volume control is set at 100% the amps will just barely start to clip with the source at maximum level. That way I cannot possibly overdrive my system. That is as it should be. Basically, you want as little amplification as possible after the noisiest stage in your signal chain. In your case that is the miniDSP. Otherwise you are also amplifying the noise. It's fine if what you want to do is heat the room. You paid good money for those Watts, so why not turn them into sound instead of heat? Think about it: with 12 dB attenuation, if you send 16 Watts to the driver, only 1 Watt actually gets there.

It would be tough to be so "sloppy" with DSP implementation that it caused excessive noise. Distortion, perhaps; clipping, limit cycles (idle tones), etc., but generally not broadband noise. I suspect that the analog stages are at fault. I looked over the miniDSP site and found no evidence of digital I/O capability -- that would be the easiest way to determine if it is, indeed, a problem in the analog stages. A pity that the folks at miniDSP don't make a SDK (software developer kit). It looks like they're using some flavor of the Motorola/Freescale DSP56K -- I've done enough DSP56K work in the past that I could just about code in my sleep.

Thanks, Don. I was actually referring to Geddes' JAES articles, but that paper summarizes the point very well. Greg

Working entirely out of memory here (draw your own conclusions about that), but I believe that the first time I saw a distinction between the two was in something that Earl Geddes wrote. He makes a strong distinction between horns designed for acoustic loading, and waveguides designed to avoid higher-order modes (internal reflections) -- and the geometry associated with that also leads to constant-directivity. Greg

I suspect that this is the case. PWK at times would expound about the benefits of horn-loading, at other times about the benefits of corner-loading. Without context it's difficult to know to which he referred here. It may be that "perfectly matched horn" that makes all the difference in the world. Evidently it's just not as simple as compression ratio, throat area, or mouth area; it's a combination of them all. For any given driver there is an optimum throat size (optimum from the standpoint of maximum SPL output), but then everything just goes downhill from there if the horn isn't the proper shape, size, or length. Indeed, but the concept of the perfect impedance match is compromised by the large bandwidth that we expect from these devices. If one thinks of antenna design as a similar impedance matching task, then the resulting antenna efficiency can be MUCH higher than our acoustic impedance-matching devices because the antenna's bandwidth can be so much smaller. Yes, and we actually have two strikes against us in that respect. At high frequencies not only is the space in the far-field, but the dimensions of the transducer are a significant fraction of the wavelength so the impedance mismatch is not so bad. At low frequencies the space becomes part of the horn, and the dimensions of the transducer are so small relative to the wavelength that the impedance mismatch is very bad. That's an interesting observation, and a viewpoint that I had not considered previously. I'm just not sure how to translate it into a woofer design strategy! Greg

I have, from the T/S parameters, the K31 with an Sd of 530 cm² or 82 in² each; from my Hornresp model the throats are a combined 580 cm² or 90 in². So the CR = 2*530/580 = 1.83! It works out to 2*82*1.83 = 300 excurson equivalent for the Jubilee. Greg Edit: And the KHorn works out to about 450 excurson equivalent.

Cult of the Infinitely Baffled

My apologies. A limitation of the written word is the inability to convey intonation, like the difference between "confrontational" and "curious". I misconstrued your intent. My experience with TQWP woofers has been casual; I have never really listened critically to multiple examples under controlled conditions. But I have always been impressed by what I heard. So I have no specific recommendations, sorry.

Do I have to build them in order to appreciate them? Why the challenging tone? I said that they sound really good.

In the most general terms, an acoustical horn is an impedance transformer and an acoustical waveguide controls directivity. In the early days of little or no amplification, horns were designed to make minute signals as loud as possible, and things like beamwidth and directivity were secondary. Later, as cheap amplification became available, it became worthwhile to trade some sensitivity for pattern control. So horns and waveguides, though very similar in configuration, are designed for different purposes.

While I agree with your subjective assessment of tapped horns, my pedantic side forces me to point out that a tapped horn is not so much a horn as a variant on the tapered quarter-wave pipe (TQWP) concept. In fact, tapped horn, TQWP, "transmission line", "acoustic labyrinth", "Transflex", and "Air Coupler" are all variations on the same theme. And, properly executed, they sound really good, too.

That is a very significant observation. But it raises more questions. The fact is that, given enough cone area, the modulation distortion from a direct radiator will be as small as that from a horn -- PWK himself said that modulation distortion is "closely proportional" to excursion. Under such circumstances the sonic difference is not a result of modulation distortion. So ... what is the cause? One can hear differences in the "character" of the bass from the same woofer in different enclosures (particularly closed vs vented), even though distortion is comparable in all cases. What is the cause? These questions are rhetorical. My point is that not all of the sonic character of a horn can be attributed to reduced modulation distortion. And I like horn bass, too. But, as we all know, it is a real challenge to get that last octave with a horn.

Yes, I am aware of all the issues of pressure vs velocity, impedance mismatch, etc. However, the statements above are only assertions. It is a fact that increasing cone area decreases cone excursion, and some point is reached at which the direct radiator cone excursion equals the horn driver cone excursion. Even PWK says that distortion is closely proportional to cone excursion (Part III of the articles that you cited; Conclusion). The only questions are: At what point are direct radiator cone excursion and horn cone excursion equal (for the same output)? Is it when cone area equals horn mouth area? Win exactly the comparison that PWK was trying to make by stating that the KHorn was equivalent to a 36" woofer. It's not. In Part I of the articles that you cite, PWK said on page 145: "Among means to reduce distortion, one of the most obvious would appear to be to increase the diaphragm area. [...] Increasing the number of direct-radiator loudspeakers has also been used. This also improves efficiency, although not to the extent realizable with well-designed horns; however, the bulk and cost equal or exceed that of horns, and difficulties with polar response arise." Apart from the polar response issue and the cost issue, which I addressed in an earlier post, it would appear that PWK agrees with me. Again, the only question is, how big does a direct radiator system have to be in order to have performance comparable to a horn with respect to everything that we have identified: transient response, dynamics, sensitivity, and distortion? I suspect that it's when cone area equals mouth area, or something pretty close to it, but I cannot say for sure because I just haven't studied the math in depth.

I'm not so sure about that, but I can't cite the math off the top of my head to say one way or the other. I suspect that two systems with the same radiating area and the same sensitivity will have the same modulation distortion properties. I suspect that PWK was embellishing a bit. A 36" woofer would have an Sd of around 900-950 square inches. A KHorn has a mouth area of around 475 square inches. All other things being equal, the 36" woofer will win. Can you cite a reference for that? I'm not challenging you; I just want to study the math for myself. Greg

To be fair, my question to Keele cited a "living room" context, where directivity, at least at bass frequencies, is really not an issue. Almost everything is in ½Pi or Pi space. Again, it was I who posed the question in transient response terms, not he. But pursuing the modulation distortion topic; if the direct radiator cone area equals horn mouth area, then cone excursion for the direct radiators should be comparable to cone excursion for the horn driver, so that modulation distortion should also be comparable. That was the reason that I specified cone area = mouth area, to try to put things on an apples-to-apples basis. For example, the KHorn mouth area is just under 500 square inches. To equal that, one would need 4 GPA 515-LF drivers. Those four drivers, at ~100 dB sensitivity each, would yield ~106 dB sensitivity. That's comparable to the KHorn. But that would be a very large and expensive loudspeaker system.

I asked a similar question to D.B. (Don) Keele a while back. My question was posed from the standpoint of what horns do best (in my opinion); dynamics and transient response. I asked Keele whether a direct-radiator bass loudspeaker could match the dynamics and transient response of a bass horn, assuming that the combined total cone area of the direct radiator drivers was the same as the mouth area of the horn. His answer was that, since the direct radiator loudspeaker would have greater bandwidth capability than the horn (the direct radiator could go both lower in frequency and higher in frequency than the horn), the direct radiator would actually have better transient response than the horn. I think that this needs to be qualified, however. Even under the conditions described above, the horn is likely to have greater sensitivity than the direct radiator (play louder for the same power input). This is not anything intrinsic to horns or direct radiators, but is a result of the reduction in sensitivity that occurs when drivers are designed for greater excursion, as most are today. And, as a result, the horn will be subjectively capable of greater dynamics than the direct radiator, simply because of its greater sensitivity. Now, if one were to use some extremely high sensitivity direct radiators (with limited excursion capability), like perhaps several GPA 515-LF @ ~100 dB/W, then the dynamic differences between horns and direct radiators might just be eliminated.

Adapt one of these mechanisms.

To be clear; the PEQ for the Danleys should only be applied to the channels that feed the Danleys. In other words, the Danley PEQ should come after the crossover, not before it. Otherwise you are applying the Danley PEQ to the main speakers -- not good.

I'd really like to see a "Space Program" style effort for US energy independence.

St. Louis No affiliation.

Maybe adapt it to a TQWP subwoofer, something like this.

I use each for what it does best -- solid state for bass, tubes for midrange and treble.

You make an inportant point, cfelliot; it may not be necessary to run a virtual machine at all, if the installer (and possibly the program) for AutoCAD can be run in compatibilty mode. Don, by all means try this first! There is a compatibility wizard in Windows 7 that will help you determine whether this will be possible. Greg

Daddy Dee, XP Mode is only available with Professional, Enterprise, and Ultimate. Don has Home Premium; that is the reason that I recommended VMware Player. In at least one way, VMware is a superior choice, because it fully utilizes multicore CPUs. Microsoft's Virtual PC can be used with multicore CPUs, but only utilizes one core. Greg