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Old 1st December 2012, 08:14 AM   #1
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Default Latest opinion on using pink insulation for 2x15s?

Hi everyone

I have posted asking for advice on a 2x15 ported box of about 600 watts and about 36x24x18 external size covering about 50-150Hz range. I was wondering what the consensus was on using regular ole Home Depot pink insulation in something like this please?

How much (if any) should I use please? A few inches of thickness tacked to the walls? A loose fill of 9-inch thick batts maybe? What should I do about the keeping the port area unobstructed? Enquiring minds need to know!

This is probably a less serious question, but I was also thinking about standing waves. I would imagine they can be a real problem when the power cranks up, but I suppose the pressures inside the box are what makes air come out of the ports. Physics and acoustics were never my strong suit. But it ocurred to me that one way to break up standing waves would be to fasten randomly angled surfaces inside. That would bounce the air around the box no doubt; it could also make things sound dreadful. I don't know if JBL and EAW fix randomly angled surfaces inside their 2000-watt boxes. I suspect not. But what if they ain't as smart as me?

Thanks very much
Phil
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Old 1st December 2012, 09:32 AM   #2
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Looking at the constructions ( assemblies ) of various boxes I see many reinforcing panels
with holes that keep the walls of the box from vibrating; I think that those panels inside
( something also called matrix, from B&W) keep from standing waves also.
They are used mostly in tower style enclosures, that's why I say this.
Usually the boxes for frequencies under 100 Hz, subwoofer range, don't need any filling/stuffing because they aren't seen by the waves, the box itself is so little respect to the lenght of the waves involved. Going upper in frequency....150 Hz is already mid-bass...well,just keep the panels firm !
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Old 1st December 2012, 10:53 PM   #3
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Hi
Thanks for your reply.
It would seem from your reply that I would not have a problem if this were a sub box of, say, under 100Hz, but are you suggesting the frequencies from 100 to 150Hz could be problematic requiring some Pink treatment please?

I am crossing over into a pair of Celestion-loaded EV 3-ways on poles, and I didn't really see the point of asking them to bang harder at a lower crossover point than around 150 if they are going to be 6 feet off the floor.

I was going to give the 2x15 more bracing, but you think I should still use some Pink for the area betweeen 100 - 150Hz please?
Thanks
Phil
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Old 4th December 2012, 09:48 PM   #4
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I'm building a pair of portable PA subs right now, I will not be stuffing them as I want maximum output from the port. If there is a HF resonance I will notch EQ it out.
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Old 5th December 2012, 04:47 PM   #5
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Default mid-bass resonance

Quote:
Originally Posted by turbodawg View Post
I'm building a pair of portable PA subs right now, I will not be stuffing them as I want maximum output from the port. If there is a HF resonance I will notch EQ it out.
Hi
I am assuming your "subs" to be in the region 30-sub-100Hz? I use the term "bass boxes" for mine as I want them to cover no lower than 50Hz and because of the nature of the setup with the mids and my application, I don't really see that I gain anything by not crossing over until into the mid-bass at around 250.
What you said about resonance and eq interests me because I'd thought that "resonance" was a property of poorly braced walls while the Pink was to do with absorbing standing waves. Of course, everything has a natural resonant frequency, but I was wondering a couple of things:

What do you hear when resonant frequencies are present? It probably isn't hard to notch them out given the limited number of sliders that cover the bandwidth once you identify you have a problem.

As I will be using these well above subs frequencies, should I put in any Pink? I don't want to obstruct the ports, so I guess I would be limited to tacking a few inches to the back and sides only. But I don't want to do what I don't have to do, of course.
Thanks for your interest
Phil
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Old 5th December 2012, 06:02 PM   #6
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Quote:
Originally Posted by phmosele View Post
Hi
I am assuming your "subs" to be in the region 30-sub-100Hz? I use the term "bass boxes" for mine as I want them to cover no lower than 50Hz and because of the nature of the setup with the mids and my application, I don't really see that I gain anything by not crossing over until into the mid-bass at around 250.
What you said about resonance and eq interests me because I'd thought that "resonance" was a property of poorly braced walls while the Pink was to do with absorbing standing waves. Of course, everything has a natural resonant frequency, but I was wondering a couple of things:

What do you hear when resonant frequencies are present? It probably isn't hard to notch them out given the limited number of sliders that cover the bandwidth once you identify you have a problem.

As I will be using these well above subs frequencies, should I put in any Pink? I don't want to obstruct the ports, so I guess I would be limited to tacking a few inches to the back and sides only. But I don't want to do what I don't have to do, of course.
Thanks for your interest
Phil
I'm using the term correctly in refering to the air resonating in the cab producing a response peak.

My "bass bins" will be crossed over with an f3 around 120-150 hz with a corresponding cut in the mains. Since I am not stuffing I might have a response peak(s) in the midbass which I will EQ out.

The design is well braced and will be internally coated with damping material, and should have minimal panel resonances.

Sure, there will be some higher frequency sound coming from the port, delayed and out of phase, but I feel that the tradeoff with more low frequency port output is preferable. I may try just a small amount of stuffing though.

My tops will be doing very little bass and will get lots of stuffing.
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Old 5th December 2012, 06:10 PM   #7
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I've heard of people using black roofing mastic for internal damping coating, although I've seen specially designed sheets of stuff for acoustic damping.
Any mileage in picking up some roof tar for the job please?
Thanks
Phil
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Old 5th December 2012, 06:14 PM   #8
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I'd probably start with a lining of it on the interior walls of the cabinet,and see how that works. It should help tame some internal reflections in the box,etc.

Then if ya like,try it with the box lightly stuffed. It's not hard to remove if you don't like it. (Assuming you can still remove the driver to gain access inside)
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Old 5th December 2012, 06:57 PM   #9
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Quote:
Originally Posted by DigitalJunkie View Post
I'd probably start with a lining of it on the interior walls of the cabinet,and see how that works. It should help tame some internal reflections in the box,etc.

Then if ya like,try it with the box lightly stuffed. It's not hard to remove if you don't like it. (Assuming you can still remove the driver to gain access inside)
Yes, I'll still have access inside
Thanks
Phil
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Old 5th December 2012, 07:36 PM   #10
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Quote:
Originally Posted by phmosele View Post
I've heard of people using black roofing mastic for internal damping coating, although I've seen specially designed sheets of stuff for acoustic damping.
Any mileage in picking up some roof tar for the job please?
Thanks
Phil
I used roofing mastic on a birch ply sub box a while back, worked well. Took a while to dry and stop smelling.
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