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Old 24th October 2007, 04:19 PM   #1
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Default bracing and damping help

ok I just bought my first to sets of speakers one is the infinity RSa's the other is the SM-120.
I notice when I rap on the cabinet with my knuckles the RSa's just give a quick tap noise and then it's dead silent the SM's sound like they have a little echo in there and sounds like the whole cab is vibrating fairly good.
I've also noticed when playing sounds through the SM's is they have this weird peak in the voice range that gives it some weird sound. I'm assuming either bracing or damping and maybe both would go a long way with helping these speakers out with sounding better.
My problem though comes with I'm not sure how much or what type of material to use to damp it or even where to start with bracing the box. I don't mind taking the drivers out that much it's more of taking the whole box apart to fix the problem I would rather stay away from.

any help here guys?
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Old 24th October 2007, 06:25 PM   #2
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It is difficult to do effective bracing with pre-built cabinets without a removable baffle or rear panel...

Having said that you should start by removing the drivers from the cabinets, then the stuffing, to see what you're dealing with.

There are two things I can think of:

1) Rib bracing - lengths of wood applied across the widths of the
interior panels.

2) Panels of mdf applied to the interior walls - effectively making
them thicker and thus more dead. The size of these will be
limited by what you can fit through the woofer cutout. This will
be less tedious than ribs.

Both of these will affect interior volume and thus bass response, but you might find that an improvement if the bass and midbass end up beeing less boomy. As for the midrange anomoly that may be an artifact of the driver design itself.

While you're in there you might as well add self-adhesive damping pads (PartsExpress, etc.) and foam & polyfill to absorb rear waves from the drivers, but again it depends on what is already there.

Of course traditional shelf bracing is best, but you'd have to be willing to remove the rear panel of the speaker - if you have a reciprocating saw you might not find it as difficult as you think - as long as no screws or nails were used to build the cabinets!
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Old 24th October 2007, 07:49 PM   #3
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from my understanding these are undamped unbraced bare cabs with drivers put into them. I can try cutting them apart but I don't want to end off worse then I started as I'm sure you can understand and I'm not the greatest with a saw as far as cutting straight lines.

as far as it goes I'm assuming rib bracing would be best since it would keep the internal volume about the same roughly while adding quite a bit as far as the bracing goes?

as far as the foam/polyfill how does one figure out how much needs to go in there?

also will this damping effect the sensitivity of the speakers much or will that stay the same?
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Old 24th October 2007, 08:22 PM   #4
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If you don't have the tools to make precise cuts it's not going to work too well - but remember if you can come up with the sizes/dimensions you want you can have the pieces cut for you at the lumber shop - just ads to the cost though.

Rib bracing would take up less volume than panels - again the trade-off is the time and work involved - placing the ribs inside through the woofer cutout takes some time and you don't want to drip glue on the outside of the cabinets during this process. BTW - I use Titebond III - bonds very quickly and is strong.

How much stuffing - I'm not the expert on this, but I'd use at least a half inch of the foam, more if you can afford it. As for polyfill - be generous on the sides, top & bottom and around the tweeter, but leave some open space behind the woofer - still use the poly there but let the driver breathe.

Remember you can experiment with the amount of polyfill but if you don't hear any differences then it doesn't matter. As for driver sensitivity I don't think it will be affected significantly - anyway you're always better off damping those rear waves so they don't vibrate the cabinets and/or come back out the drivers - whatever you lose in sensitivity you'll gain in tighter, cleaner sound.

P.S. - you can always turn your amp up a bit!
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Old 24th October 2007, 08:48 PM   #5
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To damp the panels I would use relatively thick "U" or "T" shaped steel bares glued on the larger panels. Then glue some 1-2mm lead sheets. Then apply 5mm thick bitumen.
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Old 24th October 2007, 09:01 PM   #6
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Effective for sure, but he may be looking for something a little easier to pull off, especially if he's not going to crack open the cabinets.
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Old 24th October 2007, 09:19 PM   #7
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No need to crack open the cabinets, he only has to cut the bares at the dimension of the woofer opening, their high stiffness allowing to get more efficiency than wood i.e.
Lead sheets can be rolled up a bit before being glued.
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Old 24th October 2007, 09:22 PM   #8
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What sort of adhesive do you recommend for attaching metals to wood?
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Old 24th October 2007, 09:50 PM   #9
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http://www.diracdelta.co.uk/science/...ue/source.html
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Old 25th October 2007, 02:14 AM   #10
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honestly as far as the sensitivity goes I wouldn't mind losing a bit. if I remember right these speakers are rated at something like 98-100. the RSa's I'm going to use as the surround speakers are by far much lower then that. so if I did lose a little I'm assuming it would help balance them out.


with the glue would gorrilla glue work as well for this situation? I have lots of that stuff that I could use if it would work. if not I can get other stuff as well.

the bars might not be a bad idea since they should be a little stronger per volume then wood would be. though lead might be a problem. I'm trying to be somewhat cheap with this as I don't have a lot of money to spare right now. though as a weird idea and fairly cheap as I can get them easily would the asphalt roofing shingles work for this?

with the foam and polystuff I'm assuming I could just tack that in place with a little glue a well to prevent it from moving around?

sorry about the very basic questions but I'm VERY much a noob at this.

time and effort I'm not too worried about it's just I would like to keep the cost fairly reasonable thouh if I can spread the cost out over a little time it won't be so bad. for one thing I still need to get an amp and a center channel plus I'm still debating on what to do for a sub at the moment. That and I don't want to mess someting up beyond repair with this cab.
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