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Line Array sub...
14 replies to this topic
Posted January 31 2003 - 02:04 AM
I've been toying with an idea for a sub. Do to a very strict WAF, I need to fit a subwoofer behind a couch that is pushed up close to a wall. It looks like about 9 inches of space between the couch and wall. I could build a box roughly 9 X 15 X 60... giving about 5 cu ft. One thought is to arrange 8 of the PE 6 1/2 drivers (PE 295-305) in a line array across the 9 X 60 top of the box. Tuned to around 35-40 Hz it doesn't look to bad, not great, but maybe enough for my customer. Looks like I could build this for around $150 w/o amp. The couch and the wall will prevent puting drivers on those sides of the box. The ends will be small (9 X 15). Comments? Thoughts, other suggestions?
Posted January 31 2003 - 08:30 AM
If you could get another inch or so out of the box, I would go with some 10" subs. 6 1/2" drivers are really for midbass and won't get you that rumle that subwoofers get you. Another option would be the Tangband 8" driver. It is said to be a great little sub and can provide the impact that you so desire.
Posted January 31 2003 - 11:17 PM
Cam- Yeah, I've tried to figure on some way to fit a larger driver into the area. Even the 9 inch dimension may be too large. I had given thought to laying down some sono tube, with drivers in each end, but that limited me to one or two small (8")drivers. The eight 6.5" give the equivalent area of two 12 inch drivers... though they do not sweep the same volume. The customer does not want extreme volumes, but would like to get more extension below what his current 5 1/4 two ways provide. The WAF does not allow for a cube or tube in sight. The couch can not be moved any further away from the wall. No way to add an IB to the room, finished areas above and below and no spare closet to steal. I have another acquaintance that lives in an apartment, and this line array concept would work for him too, if I could make it work. I'm sure that there is a real need for this kind of sub. I just need to find away to optimize it. Anyone with the proper software care to model this and give me some comparisons to some common budget subs, i.e. the Sony SW-40 or the PE DLS? Thanks for any help and guidance.
Posted February 01 2003 - 12:41 AM
Dan, Tricky problem statement... but I think you can make something workable with it. What's the couch made of? I would consider firing the woofers into the back of the couch. My platform sub fires up from underneath the couch and it works great. Alternatively, can you increase the height at all (couches are usually taller than 15")? One thought is to angle the top of the box to increase that 9" top dimension. Note that if you could do 45 degrees, that dimension becomes 12.72. Of course you then must watch the depth of the driver to ensure the magnet doesn't hit the back wall... If you really are stuck with 6-1/2" drivers, the tough part will be finding ones that go deep enough. The venerable Vifa P17WJ can probably get you into the 30s. If you're willing to add some complexity in the form of electronics, you can use a Linkwitz transform for a sealed sub and dial it to the response you want... or you can use a simple 2nd order active EQ circuit to extend a 4th order (vented) sub to 6th order with a half-octave or so lower cutoff. That same Vifa P17 is flat to 32Hz (1.2 cu ft) in this configuration. Good luck!
Posted February 01 2003 - 02:41 AM
There are a lot of 12s with a mounting depth of less than 9 inches. The height of your box is 15". Why not go with a single 12" like a Shiva or a PE DVC12". You could have a really long port in the box if it fired to the side (the port fires to the side and the driver into the back of the couch.
Posted February 01 2003 - 04:28 AM
Dan, Why not try the Dayton 8" woofers? They'll definitely go lower than the 6.5" woofers, and they would still fit the 9" width. Or use a Shiva or DVC 12 and build an end table.
RAD Home Theater
RAD Home Theater
Posted February 02 2003 - 07:17 AM
Hi all, thanks for responding. Firing into the back of the couch is un-acceptable. We tried puting a speaker against the back of the couch and it was very muffled. It is a heavy over-stuffed leather couch. The sound was similar to standing outside a "roller Boomer" car... i.e. only a "wump, wump, wump" sound. Not crisp, but muffled. The actual box shape would need to be a trapazoid. The top narrower then the bottom, as the back of the couch "leans" back toward the wall. I'm probably limited at the top. I do not think I can get the 9 inches, maybe 7.5. Dave, Thanks for suggesting the P17, I've used them before in 2-ways, they are an excellent driver. The PE 6.5 will get into the 30's for about 1/3 to 1/4 the price. If I have to use 8 drivers, price per driver is an issue. I may bag the idea, as I don't know how good or bad this line array would be.
Posted February 02 2003 - 01:39 PM
Why couldn't you put one or 2 10-12" drivers facing either forward or back on a seperate full length strut inside the box, so that there is free space in front of the driver, and then vent out the ends? If you isolate the front and back sections and vent each to the sides you should get away from the muffled thumpa/thumpa sounds and still get good low extension. Using a tempest or similar driver, you should be able to get down into the 20's without a problem. Most people would be happy with mid 30's for a while, especially with music, but would eventually complain about missing the lows with movie effects. It's not necessarily about total volume, but about the quality of that volume, especially if you lose the low bass. If I could figure out how to put a drawing up here I would show you the idea, but I could email you a rough draft of the idea later if you want. Bill
Posted February 03 2003 - 12:55 AM
I was going to suggest the same as Frank... could you squeeze a couple of 8's into the bottom of the box? Then port it up out the top or out the sides. I think that could work very well considering the limitations.
Posted February 03 2003 - 03:42 AM
Here's an idea. Mention in passing to your wife that the room is stuffy. Build an IB box install drivers where it's all ready to go, including the trim and grille. Make shure the grille resembles an air return vent. When the wife goes out slap the IB up real quick. If she notices when she returns tell her you installed another return vent to help air flow. You would actually get brownie points for working on the house without her asking, plus an excellent sub.
there's no way I'd actually try that.
there's no way I'd actually try that.
"Boy...You got a panty on your head!" -Raising Arizona
Posted February 03 2003 - 07:22 AM
"Firing into the back of the couch is un-acceptable. We tried puting a speaker against the back of the couch and it was very muffled. It is a heavy over-stuffed leather couch. The sound was similar to standing outside a "roller Boomer" car... i.e. only a "wump, wump, wump" sound. Not crisp, but muffled." I'm trying to understand this. Was this a full-range speaker playing a full-range signal? That would certainly sound muffled since high-frequency sound can't propogate through the couch. Was it a full-range speaker driven by an amplifier that was connected to your receiver's subwoofer output? That could sound pretty boomy too, especially if it wasn't calibrated. A good quality sub shouldn't have any problems behind a couch. The only thing that might get muffled a bit would be the midrange response. But your receiver's already using a low-pass filter - probably a 4th order - to reduce midrange as much as possible. So the extra filtering is more of a feature than a problem.
Posted February 03 2003 - 09:49 AM
I know these are car audio drivers but you could put 4 of these 8's in a sealed box of less than one cubic foot. Feed them 2000 watts, and with a 16.5mm One way DUMAX verified Xmax they they should be better than those 6.5's.
Posted February 03 2003 - 10:23 AM
Thanks for the input. A down firing system may be the best way to proceed. Maybe something along the lines of four 8 inch drivers, that would be about equivalent to two 12 inchers in area. I'll have to run it past my customer and take some better measurements of the available volume and see where I might push the envelope some.
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