Vader
Supporting Actor
- Joined
- Mar 19, 1999
- Messages
- 811
- Real Name
- Derek
Hi Ed,
As I learn more about acoustics, my complete ignorance is beginning to wane somewhat (now I understand the axiom "Ignorance is Bliss"). There are two main areas of confusion (currently), and I am really hoping that you can point out where I am all wet:
First, is the THD of my twin 20-39 PC+ cylinders. I have been unable to find THD data on the 12.3 drivers for these, so I am improvising using either the THD obtained by AVTalk for a single 20-39 PC+ using the 12.1 drivers (apples and oranges?), or the PB12 Plus/2 reviews posted by Ilkka on the shack. The AVTalk review is only of a single cylinder, so I am assuming that, since co-located duals give a 6dB headroom boost, a good approximation would be to use the curve 5dB below that of a single (i.e. the THD given by my duals at 95dB should be close to that from the single at 100dB). But, then I am still comparing the 12.1 to my 12.3, so I am probably way off here. OTOH, I am thinking that the PB12 Plus/2 is a better approx, since it is two 12.3 drivers (and the PB12 Plus is basically the box brother of one of my cylinders). That seems to match of resonably well, except below 25 Hz, where the cylinder's distortion seems to be considerably higher. To my reasoning, dual cylinders should outgun a single PB12 Plus/2 (same tune) slightly in both SPL and THD; due to increased port space and internal volume, even close to the tuning frequency (no EQ required due to greater volume?). Here's my confusion: When comparing the 12.3 to the 12.1 chart, it looks like the 12.3 actually has higher THD (most notably the 110 and 115 dB curves) than the 12.1. Everything I have read says that the 12.3 drivers are nipping at the heels of the (current) Ultra, but the tests of the Ultra cylinder at AVTalk show a significant discrepancy relative to the 12.3 drivers (from Ilkka's reviews). I thought I read somewhere that the 20-39 had < 10% THD down to the tuning frequency, but I couldn't swear to it. I am also interpreting from AVTalk that re-tuning to a lower TF (probaby 16Hz) might help. Where am I missing the boat here?
Second, the review of the single 20-39 cylinder at AVTalk shows that the FR starts a rapid drop-off at around 25Hz - about the same place where the THD shoots up (upwards of 28-30% at 100dB, if I'm reading this right...?); I would have thought it would not drop off that fast until the tuning frequency. The curves at SVSound show just this (even though they appear to be the 20-39 CS, using the 12.1 drivers). And Tom stated (I don't recall the forum or the post) that "even if you have a strong 20Hz response, if you drop off strongly a full octave above, that will seriously compromise your 20Hz capability" (I'm paraphrasing here). Yet the PB12 Plus/2 drops off at the tuning frequency of 20Hz. Is the 20-39 really closer to a 25 Hz tune than a 20Hz (native) one?
Prior to getting the SVS cylinders, I *was* blissfully ignorant about this stuff (thanks a lot, guys…..), but since I am somewhat compulsive/obsessive to begin with (so I am ), now am trying to learn all I can about it (and improve mytold… soundfield where I can). Don't get me wrong: I have absolutely no complaints about the Plus cylinders (except having to put padding under my jaw when I use them – hard floor, you know). But I don't want to turn left on the learning curve where I should have gone straight, if you get my meaning. Thanx for your expertise, and a fantastic review (one of many)!
As I learn more about acoustics, my complete ignorance is beginning to wane somewhat (now I understand the axiom "Ignorance is Bliss"). There are two main areas of confusion (currently), and I am really hoping that you can point out where I am all wet:
First, is the THD of my twin 20-39 PC+ cylinders. I have been unable to find THD data on the 12.3 drivers for these, so I am improvising using either the THD obtained by AVTalk for a single 20-39 PC+ using the 12.1 drivers (apples and oranges?), or the PB12 Plus/2 reviews posted by Ilkka on the shack. The AVTalk review is only of a single cylinder, so I am assuming that, since co-located duals give a 6dB headroom boost, a good approximation would be to use the curve 5dB below that of a single (i.e. the THD given by my duals at 95dB should be close to that from the single at 100dB). But, then I am still comparing the 12.1 to my 12.3, so I am probably way off here. OTOH, I am thinking that the PB12 Plus/2 is a better approx, since it is two 12.3 drivers (and the PB12 Plus is basically the box brother of one of my cylinders). That seems to match of resonably well, except below 25 Hz, where the cylinder's distortion seems to be considerably higher. To my reasoning, dual cylinders should outgun a single PB12 Plus/2 (same tune) slightly in both SPL and THD; due to increased port space and internal volume, even close to the tuning frequency (no EQ required due to greater volume?). Here's my confusion: When comparing the 12.3 to the 12.1 chart, it looks like the 12.3 actually has higher THD (most notably the 110 and 115 dB curves) than the 12.1. Everything I have read says that the 12.3 drivers are nipping at the heels of the (current) Ultra, but the tests of the Ultra cylinder at AVTalk show a significant discrepancy relative to the 12.3 drivers (from Ilkka's reviews). I thought I read somewhere that the 20-39 had < 10% THD down to the tuning frequency, but I couldn't swear to it. I am also interpreting from AVTalk that re-tuning to a lower TF (probaby 16Hz) might help. Where am I missing the boat here?
Second, the review of the single 20-39 cylinder at AVTalk shows that the FR starts a rapid drop-off at around 25Hz - about the same place where the THD shoots up (upwards of 28-30% at 100dB, if I'm reading this right...?); I would have thought it would not drop off that fast until the tuning frequency. The curves at SVSound show just this (even though they appear to be the 20-39 CS, using the 12.1 drivers). And Tom stated (I don't recall the forum or the post) that "even if you have a strong 20Hz response, if you drop off strongly a full octave above, that will seriously compromise your 20Hz capability" (I'm paraphrasing here). Yet the PB12 Plus/2 drops off at the tuning frequency of 20Hz. Is the 20-39 really closer to a 25 Hz tune than a 20Hz (native) one?
Prior to getting the SVS cylinders, I *was* blissfully ignorant about this stuff (thanks a lot, guys…..), but since I am somewhat compulsive/obsessive to begin with (so I am ), now am trying to learn all I can about it (and improve mytold… soundfield where I can). Don't get me wrong: I have absolutely no complaints about the Plus cylinders (except having to put padding under my jaw when I use them – hard floor, you know). But I don't want to turn left on the learning curve where I should have gone straight, if you get my meaning. Thanx for your expertise, and a fantastic review (one of many)!
Tom tested and measured the new 12.3 Plus woofer very intensely before approving the final design, and he has stated that the new 12.3 Plus woofer is superior in every way to the 12.2 woofer for watching movies or listening to music. So I'm sure that's the case. 
