Tom, thanks for the encouragement. Infinite baffle, is that doable with 8x8 wall. As I have a farm and can do outside measurements, been looking for some scaffolding. How high?
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The larger the baffle the lower the frequency of the baffle step where the wavelength drops off the edge of the baffle. You can calculate where the 8x8 glitch will occur. Circle is cleaner than square. Put the driver in the middle of the baffle. Now, there's the floor (ground) bounce to copy with; so, if possible, tilt the baffle parallel to the ground, firing the driver upward with the mic 1 or 2 meters away (whichever protocol you use.) Firing up does lots of stuff right if you can manage the particulars. We also used an infinite baffle or ground plane. Hole in the ground with known-sized insulated box in the ground. Compare and subtract low frequency enclosure back pressure against open air performance. That ground-plane "sandbox" provides zero baffle step response, which is what you want to know. Correct the curve for box pressure rolloff and you have the true infinite baffle measurement. I will repeat that measurement series after 10 feet of snow melts from my neighbor's flat field. Or we can rent the Bell Labs anechoic chamber in New Jersey for perhaps $1K / half day (guessing). |
@Beetlemania, Let me say that off the top of my head I can't think of any amp manufacturer that's complete line is ideal for all Thiel's. Yes, it's somewhat complicated, but most of the difficult leg work has been done and the results are often readily available. With such information it's not too difficult to get a fairly good idea of what's going on with such interactions. As for the impressions of others? Well, I'm cautious about that. I have no idea what some of these strangers experience might be. We've had posters repeatedly state that particular amplifiers were "high current" when they weren't. At least not by my definition of that. Subjective impressions are important. After all in the end, one should like what they're buying. But, I sometimes wonder why they do. I have occasionally offered my own subjective opinions, with the caveat that others might disagree. But, I do try to offer some objective perspective too. I prefer to make decisions based on what I know, not on what I don't. Let's look at some of the examples that you cited: https://www.stereophile.com/content/thiel-cs16-loudspeaker-measurements Notice that impedance stays below the rated 4 Ohm load of the amplifier referenced most of the time, and with a phase angle that might be stressful. https://www.stereophile.com/content/ayre-ax-7-integrated-amplifier-measurements re: distortion: …."However, it more than doubled each time the impedance was halved, implying that low-impedance speakers are best avoided."... ..."Considering the fact that Ayre's Charlie Hansen eschews negative feedback, the AX-7 still provides excellent linearity and basically good measured performance, provided the amplifier isn't asked to drive speakers with an impedance that drops below 4 Ohms."... *To be fair we might want to take the above measurements with a grain of salt, as the reviewer as some point replaced the fuse with a different from recommended value. ______________________________________________________ https://www.stereophile.com/content/thiel-cs24-loudspeaker-measurements ".....it's impedance plot (fig.1) indicates that the CS 2.4 demands a lot of current from amplifiers. Not only does its impedance drop to 2.7 Ohms at 600Hz, but it stays significantly below 4 Ohms between 100 Hz and 50kHz, and there is a difficult combination of 4.5 ohms magnitude and -45degrees electrical phase angle at 80 Hz.".... https://www.stereophile.com/content/ayre-acoustics-ax-5-integrated-amplifier-measurements …." into 2 Ohms the (not shown), the Ayre clipped at 220 Watts with one channel driven, with a higher level of distortion at lower powers." Quite a bit less than the 500 Watts per channel of an amp capable of doubling down an down again from it's 125 Watts at 8 Ohm rating. I don't think it takes a genius to figure out why this stereo amp was only tested into 1 channel at 2 Ohms. ______________________________________________________ https://www.stereophile.com/content/thiel-cs72-loudspeaker-measurements "Like most Jim Thiel designs, the CS7.2 features quite a low impedance over most of the audio band (fig.1), with a magnitude dropping below 2.7 Ohms above 8 kHz and ranging between 2.9 Ohms and 4.2 Ohms between 60 Hz and 8 kHz." https://www.stereophile.com/content/ayre-v-1-power-amplifier-measurements …"While the amplifier easily meets specified power into 8 Ohms, it didn't do so into 4 Ohms, though the line voltage was slightly lower than normal."...…."In order to test the amplifier using continuous test signals into 2 Ohms, we had to replace - at Ayre's recommendation - the V-1's internal 10 amp resistor-fuses 15 amp versions". I'm willing to make concessions due to the line voltage issue. Note that this stereo amps 2 Ohm output was again only measured into 1 channel and put out 555.5 Watts into that one channel, rather than outputting the 800 Watts of a similarly rated 8 Ohm power amp that can double down and double down again. I Couldn't find anything on the Ayre V-5. _____________________________________________________ https://www.stereophile.com/content/thiel-cs37-loudspeaker-measurements ….".....the 3.7's impedance remains between 2 and 3 Ohms over much of the audio band (fig.1), and that there is a demanding combination of 3.8 Ohms and -40degrees capacitive phase angle at 60Hz. Thiel specifies the impedance nominally at 4 Ohms, with a minimum of 2.8 Ohms. I actually found the impedance to 2.4 Ohms at 125Hz. The difference being academic, either mandating the use of an amplifier that has no problems delivering high currents." 35 Watt Fischer. Really? "It didn't acquit itself too badly." I'd rather hear that my blind date had a nice personality. _______________________________________________________ https://www.stereophile.com/content/thiel-cs5-loudspeaker-measurements Yada, yada, yada. See above, I'm sure your get the point. _____________________________________________________ I'm confident that you are aware of most of the following, but for the sake of those that might not. Remember sensitivity predictably decreases as impedance decreases. That power requirements for increased volume levels is exponential. What might appear to outrageous amounts of Watts into lower impedances, really isn't. Furthermore, the inability to increase power as such, causes more distortion from the amp (if not down right self destruction), and at higher volume levels can effect frequency response deviations from the loudspeakers, and perhaps even timber perception for the listener. It's not all about volume levels, but more about amplifier linearity and minimizing distortions. And even actually protecting the loudspeakers from damage. It behooves one to at least listen to an amplifier truly capable of handling the actual load of a loudspeaker to get a baseline, before deciding to accept otherwise preferred distortion artifacts. Otherwise one might find themselves as though they were haphazardly running through a maze blindfolded. Some Thiel's are somewhat unique and require more discriminating amplifier choices. Good listening my audiophile friends. |
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