Originally Posted by davidbeinct
Hey all, I posted a question about subs for Acoustat Model 3 speakers. They are large electrostatic panels with bass down to <32 Hz, and flat to around 40. However, I do get what panel enthusiasts know as "panel slap" down to somewhere between 60 and 80 Hz. This is more on tones, but I think I have occasionally heard it on music.
Most of the respondents pointed me towards Rythmik, either E or F15HP. Sealed will integrate better with the panels, I believe. There is one user on my thread who is having good luck with an SVS PB-13 Ultra.
I am between one of the two sealed 15" Rythmiks and the SVS. My biggest concern with the Rythmik is the lack of flexibility of setup. I can only use it with the bass management of my Parasound P5, which is rather rudimentary compared to even a basic AVR. This is a two channel only system though, and I don't think I want to try to find an AVR that can drive the big 'stats.
With the SVS I can choose between using my P5's bass management or running dual stereo interconnects in and a second set out using the sub's onboard crossover. This setup also allows me to delay the mains, which I believe gives me more placement flexibility. The phase control on the Rythmik can only delay the bass arrival times, correct? So I can only engage that if the sub is closer to my listening position than the mains, right?
Delay time is not just to adjust the distance difference, it is also used to account for the phase difference at the crossover point between HPF and LPF. For instance, your usage model is different from a bookshelf sealed model which starts to roll-off at say 70hz. So even though the same 12db/oct filter is used on front speaker, your Acoustat is only 12db/oct roll-off, and a sealed model will have 24db/oct and yet a ported front speakers will have 36db/oct. This is because yours is flat down to 30hz. A bookshelf sealed and ported front speaker have 12db/oct and 24db/oct roll-off already without any additional HPF. With different type of front speakers, we already have different phase difference at the crossover point.
Your P5's bass managment should be sufficient. I assume the HPF is a 12db/oct. As for the LPF on the sub, I recommend to use the control on our sub. I do recommend to keep the signal path going to Acoustat as simple as possible.
With the Rythmik I have to use the P5's sub out. This can either be run full range or with low pass activated. If full range I would engage the high pass filter from the P5 to run the panels with a 12 dB/octave slope crossover, and use the low pass in the Rythmik. Another option, I believe, would be to run the low pass filter out to the sub, and I can add another 12 dB/octave filter at the sub side to give me a fourth order crossover to the sub, matched with a second order crossover to the mains. Am I right that this is possible?
No, if you set the LPF at 24/80hz position, or 24/50hz position, you already get 24db/oct roll-off on the sub. You don't need to add any additional filter on the sub side.
Initially I thought I would go for an 80 Hz crossover point, to completely eliminate panel slap, even on tones. However, I am concerned that point might be too high and give me integration problems. Is the onboard crossover on the Rythmik flexible enough that if I want to use it to give me a 60 Hz crossover point I can? I have to admit the biggest weakness with Rythmik is their guidelines, which are not clear. Maybe having the sub and actually playing around would make it more clear.
If you meant literally panel slap, then what you need is the filtering bass signal from the Acoustat because the excursion increases by 8x when the frequency goes down by 2x for panel speakers. In comparison, sealed speakers only go up by 4x. So your idea of crossing over at 80hz or 60hz (using P5's HPF) is a sound one.
I recommend place sub close the panels to get more continous imaging result.