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Chris, I did ask myself the same question: perhaps my given PTR9 is demagnetized. I called the last night to the owner of the tweeters and he said that he uses them for 7 years and they driver should be fine. He also expressed a lot of doubts if the drivers are 88dB and he said that it more likely like 93dB. Actually when he told me that I did not believe him because I thought that it would not be possible. I tried the last light only one driver, later on I will try another – it is highly unlikely that they both are damaged and I think that 91dB is what they in fact are.

Unfortunately Nelson Pass’ comment are irrelevant:

Nelson Pass wrote:

Figure 6 shows the same curve, but isolates the ribbon tweeter, which is driven by a current source and actively crossed over at 12 dB/octave at 10 KHz.  You will notice that it doesn’t actually go away until down around 6 KHz, a typical example of why you don’t want to take textbook crossover values too seriously with real world drivers.

So, since he uses an active crossover then he has dedicated power amps to drives the tweeters. It is unknown what gain those amps have and it is most likely that the amp has 8dB more then the 99dB sensitive Lowther DX4s. Not to mention that in his graph the PTR-9 hit in the pick over 100dB… obviously it was amplified….

cv wrote:

I think at the frequencies involved you would NOT get the summing of sensitivity you are after as the radiation patterns would not overlap too much.

Well, with 2 drivers is will be questionable as connected in series they would make 16R and will sink the amp’ output minimizing the summation (unless another transformer ratio was used). With 4 drivers it would be possible to maintain the same impedance and regardless the frequencies involved the summation will take place. However, I agree that the amplitude of the summation will not be as predicable as at lower frequencies. The acoustic pressure will rise but at the same time, since the driver are organized into it is a line-array they will act as a small low-pass filter rolling off the HF. On the other hands, the line-arrayed 4 driver will shape the valve up front and more focus… effectively creating more pressure at the listening position and narrowing the latitudinal spread of HF. Of course to predict if exactly would be kind of difficult. The line-arrays might be complex thing…. :-)

Screw the Canadian ribbons with 92dB sensitively. Chris, now I am very pissed on you. I am keep wondering in dark and after all I am learning that you already use the 8 Aurum Cantus G1s drivers. Are you hiding form me or what? Anyhow tell me more about them and please send the picture of your custom baffle. Are they really 102db? – after the TADs I’m getting into sensitively paranoia. The 8 Aurum Cantus with removed baffles of exactly what I am considering now if I find a good sores to buy them. With the current leading price of $340 it is unlikely but I hope to find a better deal. Since the Aurum Cantus G1 should have very narrow horizontal dissipation I was considering putting them into something like a horizontal ark array….

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