m
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Posts: 16
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Post by m on Dec 9, 2005 13:08:14 GMT -7
Hi all. Just joined the forum but have been reading about IB setups for the past week or so. I'm hoping to get under the house next week and begin on the construction of my own IB setup and have been pondering it's eventual output. Currently I have a single 15" subwoofer in a ported enclosure (tuned around 25Hz if it really matters) being driven off of a smallish 200W amplifier. It works well but the large enclosure is a serious eyesore and I like the idea of having the sub under the house. My question is this. I realize that there are a lot of variables to determine how loud a system will be so I'm not asking what SPL do you think I'll hit. Just going by numbers if I take another 15 like my enclosed one, mount them (two total) IB under the house and feed them each 200W (they are rated for 1200RMS) should I be close in output to the single but with much better extension? I am planning the manifold to hold up to 6 15's but won't have them 'till about April next year. I'm just wondering if I'll at least be close to my enclosure system or should I just wait until I can do it right the first time. I understand the increases expected from doubling up enclosures and power figures but I don't think those rules apply quite the same way for IB. Thanks in advance for any responses.
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Post by ThomasW on Dec 9, 2005 15:48:02 GMT -7
2 in an IB certainly won't have the same output as 2 in 25Hz ported boxes, but they'll play lower.
Here are a couple of options
1) Instead of a 6 driver manifold (really big opening) I'd go with a cube using 4 higher excursion units. Make cut outs for 4 drivers, and cap 2 openings off. Run with your pair until the budget allows the purchase of better higher excursion drivers.
By next spring we should be drowning in new drivers from both Ascendant and Adire.
2) Make a temporary manifold for your pair. Then see what's available in the spring. It could be that the $200ea 18"s coming from Asceendant are what your want. Start with 2 add more if needed
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m
New Member
Posts: 16
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Post by m on Dec 9, 2005 21:28:25 GMT -7
It's only 1 15 in a ported enclosure with 200W on it. For the IB I'd be adding a second 15 and another 200W to it. It would be 2 IB 15's with 400W compared to a single ported 15 (same driver) with 200W.
Thanks for your reply.
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Post by ThomasW on Dec 10, 2005 0:33:11 GMT -7
Yes I realized that, and that was the basis for the opening sentence in my first post.
Any sub alignment one gets +3dB from acoustic coupling with the addition of a second driver, and an additional +3dB from a doubling of output power.
If you need to see a computer sim grab Unibox 4.0 or WinISD Pro. Set the box size to the largest value it will accept.
The overall output will be limited by the excursion of the drivers (not voice coil heating) and the amount if room gain.
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m
New Member
Posts: 16
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Post by m on Dec 10, 2005 7:41:12 GMT -7
2 in an IB certainly won't have the same output as 2 in 25Hz ported boxes, but they'll play lower. Sorry, when you said that I thought you had missread my post and was thinking I was running a pair of enclosed 15's. I have WinISD and have used it extensively with normal enclosures and seeing the response curves gives me a good idea of what to expect from the finnished product. All the reading I've done about IB setups has said that the sound is totaly different from enclosed subs...I just didn't want to rely on the curves that ISD gave me when I've never heard an IB setup before. Thanks for your quick replies.
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Post by ThomasW on Dec 10, 2005 9:10:44 GMT -7
The sims don't tell you about room gain, nor do they explain the sound quality differences between an IB and a "box" sub. They do provide info about what power levels do with regard to excursion, frequency, and guesstimated output levels. in anechoic space
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m
New Member
Posts: 16
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Post by m on Dec 10, 2005 9:33:44 GMT -7
Well that's what I meant. I can fairly accurately predict how a sub will sound using ISD now that I've done a few dozen enclosures with it. I'm at a loss with the iB setup though LOL. I'll likely try to get the manifold (If I can fit an array I will do that instead) under the house tomorrow or the next day. I figure it won't hurt to have it ready. If two subs won't do it for me I'll just use the enclosure 'till I can get the new subs in there...at least it'll be ready for when I have more subs. Thanks again for all your help. I'll post pics when it get's done and share the results.
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m
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Posts: 16
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Post by m on Dec 12, 2005 15:38:53 GMT -7
Well I got the IB in yesterday and as expected it has prodigious amounts of clean subsonic bass. Next will be hunting down all the little things tht are vibrating and making noise. Since the manifold is in the crawlspace near the furnace (was the only place to put it) I get a lot of vibration through the heating ducts. I'm gonna have to figure out a way, short of wrapping them in sound deadening, to quieten them up. Overall I'm very pleased with the outcome and may even hold off on going with 4 15's as I haven't been able to get these ones to full output yet (watched WOTW yesterday in DTS at reference and they didn't break a sweat and they still shake everything in the house. I'll hopefully get some pics of it soon and post them up.
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Post by ThomasW on Dec 12, 2005 15:50:22 GMT -7
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m
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Posts: 16
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Post by m on Dec 12, 2005 16:01:04 GMT -7
Is the PE stuff the same as using Dynamat or brown bread that we use in car audio? If so i can get quite a bit of that cheaply. Wasn't planning on covering up the ductwork in it (not sure if it interferes with any codes or not) but it may be a thing to try as a last resort. thanks for the link.
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joest
Junior Member
Posts: 51
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Post by joest on Dec 12, 2005 16:06:12 GMT -7
You could stop by any of you're local home centers & pick up some duct wrap for you're ducts. It's a simple roll of foil faced fiberglass insulation. It may or may not work quite as well as what Thomas mentioned but would cost less money & is simple to use. Or if you wonted you could also replace the offending ducts with a flexible insulated duct. I had replaced my original metal ducts with this for the same problem as you & problem solved. Plus the added benefit of better hot & cold air from the register
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m
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Posts: 16
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Post by m on Dec 12, 2005 16:42:46 GMT -7
Well the problem for me isn't so much for the smaller diameter ducts but more for the main duct that feeds them. I could try to wrap it though...just not sure how well the wrap would work on a larger square pipe. I'll have to give it a shot though. Thanks for the suggestion.
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joest
Junior Member
Posts: 51
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Post by joest on Dec 12, 2005 16:49:14 GMT -7
The insulation I'm talking about can be used for either or, cold air return or regular heat ducts. I know it will stop a decent amount of noise / vibration, but compared to the sheet products you can buy I dont know how it would compare. I can say that it is accecpted by building codes where as I'm not sure on the other.
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Post by ThomasW on Dec 12, 2005 17:23:39 GMT -7
For a larger flat surface the PE stuff works well. Also you don't need to cover the entire exposed surface. It's easy to apply just peel off the blue backing and stick it on...
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m
New Member
Posts: 16
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Post by m on Dec 13, 2005 8:45:58 GMT -7
Yeah sounds good. It'll be just like doing the 1/4 panels of a car or the doorskins. Hopefully I can get around to it in a week or so. So far so good though. The room is pretty small so the 2 15's can really energize it easily. The more I listen to it the less I think I may need to run 4 of them. I'm sure that once I get use to it though...I'll want more ;D.
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Post by davepete on Dec 28, 2005 9:29:04 GMT -7
According to Vance Dickason's Loudspeaker Design Cookbook, compared to one driver you gain 3db from two drivers connected in parallel, you lose 3db from two drivers connected in series, but you gain 3db from doubling the cone area (I'm assuming this is "acoustic coupling"). The power doubling should give another 3db as you note, so in total, if he connects his drivers in parallel he will have +9 db over a single driver. If he connects in series he will have +3db.
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Post by ThomasW on Dec 28, 2005 10:36:11 GMT -7
davepete,
'm' is adding a second amp, he's not wiring the drivers together.
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Post by davepete on Jan 2, 2006 0:29:21 GMT -7
davepete, 'm' is adding a second amp, he's not wiring the drivers together. Of course. The alzheimers is kicking in, it seems. Dave
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