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Home » Sponsored » Pi Speakers » 4pi Commercial Dinner Theater Build
| Re: 4pi Commercial Dinner Theater Build [message #69127 is a reply to message #69126] |
Mon, 22 August 2011 15:36   |
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Wayne Parham
Messages: 18786
Registered: January 2001
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Illuminati (33rd Degree) |
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| dutchswan0311 wrote on Mon, 22 August 2011 14:48 | I am trying to figure out exactly what I want to do for our stage sound. I am thinking about stacking a 4pi built with an extra layer of ply on each side to make it the same width as the F20 (60"H,20"W,30"D), and then just stack it on the F20. Would it be okay to (1) flip the F20 over with the horn on top and then (2) stack a 4pi on top of the F20 flush to the front? The reasoning behind this would be to then build 1 cloth mesh grill to cover all of the drivers of the sub and 4pi (well, the drivers of the 4pi and the horn of the sub).
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I think they will work well that way, just be sure to delay the mains to match the path length of the subs. Orient the subs with the mouth near the floor. If the F20s sound good in the ~120Hz range, I'd low-pass them with a shallow filter slope, like ~90Hz second-order or ~120Hz third-order. This will make the F20s act as flanking subs, which smooth room modes in the upper modal region.
Run the mains full range or if you're really pushing the power, high-pass them at 60Hz. Having some overlap between mains and flanking subs will smooth the modes in the 70Hz to 140Hz range, usually vertical modes and self-interference off the back wall. More distant subs should be crossed over lower, with multiple sound sources to smooth the lower modes from 30Hz to 70Hz, usually horizontal modes between opposing walls.
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| Re: 4pi Commercial Dinner Theater Build [message #69284 is a reply to message #69280] |
Thu, 01 September 2011 21:36 |
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Wayne Parham
Messages: 18786
Registered: January 2001
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Illuminati (33rd Degree) |
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Flanking subs and distant subs are two different things, and serve two different purposes. Both provide extension, and beyond that, the main purpose of the flanking subs is to smooth the upper midbass and lower midrange and the main purpose of the distant subs is to smooth the lower bass. Flanking subs are close to the mains and are low-passed sometimes as high as 200Hz but more often between 80Hz and 120Hz, depending on the slope. Distant subs are put further away, and are low-passed below 60Hz.
Flanking subs are in near proximity to the mains, a meter or two away from the mains in all three dimensions. The mains are on stands and the subs are on the floor, the mains are forward of the wall behind them and the subs are pressed back to the wall. They are also both inside or outside the mains, whichever is most convenient. As I said earlier, these smooth the upper midbass and lower midrange modes. There is almost always a strong notch around 120Hz to 140Hz from axial modes between ceiling and floor, and also from self-interference from the wall behind the speakers and floor bounce. The flanking subs main purpose is to smooth these notches.
Distant subs are usually placed somewhere in the opposite side of the room. It almost doesn't matter where the distant subs are placed, as long as they aren't in the same place as the mains or flanking subs. We want diversity of positions for the sound sources in the modal range.
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| Re: 4pi Commercial Dinner Theater Build [message #69293 is a reply to message #69292] |
Fri, 02 September 2011 09:43 |
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Wayne Parham
Messages: 18786
Registered: January 2001
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Illuminati (33rd Degree) |
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Answers by numbers:
1. If I understood your picture properly, the west wall is on the left, where the mains are. So that would be where you would put flanking subs. Distant subs would be put somewhere else, more distant from the mains. The low-pass frequency is set empirically - if you can't tell they're on, then the crossover frequency and SPL is right. It should provide deep bass foundation but still be subtle, you definitely should not be able to tell where the rumble is coming from. So set the distant sub(s) crossover frequencies empirically. You can even use measurements to find what settings give smoothest response, if you have that capability.
2. Indoors subs should be in a different position in all three coordinates that the mains. It is different than outdoors, where we want to have them acoustically close, acting as a single source. Indoors, we want to spread things around. Wall reflections create multiple virtual sound sources, so we cannot create a point source anyway. It creates course interference, because the number of sources is fairly small, so the spacing between peaks and nulls is wide, and pretty obvious. The goal of the multisub configuration is to actually make even more interference, and by making the interference pattern more dense, it more closely resembles an averaged reverberent field.
3. All drivers should be pointed at the audience. It actually doesn't matter much what direction low frequency sound sources are facing, so if it is more convenient to point subs in another direction, you can do so.
As for lead time, I keep stock of all crossover parts, and many drivers. But I go through a lot of 2226 woofers and DE250 compression drivers. So it seems like every other month, I get backlogged on one or both of those drivers for anywhere from a week to a month. The TD12S often takes several months to fill. Everything else is usually either in stock, or if not, less than a week until the replenishments arrive.
We build the crossovers at time of order. Sometimes I'll have a couple on the shelf, but there are lots of versions and options. For example, a four π crossover for the PSD2002 is different than one for the DE250. Then there are the coil, cap and resistor options. So in most cases, we have to build the crossover at time of order.
All that to say you should expect at least a couple weeks lead time for a three π or four π kit. Right now, we're running about a week for one π, two π, two π tower and three π subwoofer kits. All other kits are taking two to four weeks. If you order all of them at once, it will take a little longer to get them all ready for you, but we can ship as we make ready rather than all at once, if that will help.
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| Re: 4pi Commercial Dinner Theater Build [message #69298 is a reply to message #69295] |
Fri, 02 September 2011 12:40 |
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Wayne Parham
Messages: 18786
Registered: January 2001
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Illuminati (33rd Degree) |
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It would probably still be best to order all at once, that way I'll know what I need to bring in. I keep stock of a lot of stuff, but if I need something, it would be best to know as soon as possible. The shipping would be the same either way, because the kits are packed the same way even at moderate quantity levels as they are in singles or pairs. The larger kits fit one per 20x20x16 box, smaller kits can fit two per box.
When we send out a large quantity, we palletize drivers and ship them separately, but that usually only happens with the 12π hornsubs. Those are usually sold in quantities that makes LTL shipment of palletized packages most effective. But your order is not so large that palletizing makes sense.
As for the distant subs, yes, I see what you mean now. That's a pretty good idea - the flanking subs for the mains on the north wall could be used as distant subs for the mains on the west wall, and vice versa. Just remember that flanking subs (closer to the mains) get low-passed around 80Hz - 120Hz and distant subs (further from the mains) get low-passed around 50Hz - 60Hz.
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