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post #31 of 59 Old 08-28-2017, 09:36 AM - Thread Starter
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Bumping for input on a couple questions. I was looking at adding a MiniDSP in between the sub outs on the MRX-720 and the Crown Amps that are driving the subs. I contacted Anthem Tech support to find out what the Vrms on the sub-outs are so I'd know which MiniDSP to get. Here is the reply from Anthem:

Quote:
AUG 28, 2017 | 12:13PM EDT
Brandon replied:
Hi David,
The subwoofer channel output is 5.2 Vrms, so you should be fine to add the EQ if you’d like.

Brandon B. | Technical Advisor | Paradigm/Anthem Support Team
Based on this, I'm assuming that if I wanted to add a parametric EQ into the signal chain, and I went with a MiniDSP, I'd have to go with the MiniDSP 2 x 4 HD? Would there be any negative effects going from the 5.2v out on the Anthem to the 2v out of the MiniDSP HD?

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post #32 of 59 Old 08-31-2017, 06:19 AM - Thread Starter
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More updates

So, some more build pics. Marked and routed the dados for the slot vent, test fitting, and checking for square.
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Next, dry fit test and rough trimming the waste from the proud ends of the side panels.
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Then, seal & varnish the internal surfaces of the slot vents and position the binding posts.
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After that, it was time to rough out the vent opening through the double-thick front baffle, and test fit the internal bracing.
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After test fitting all the pieces, the glue up begins. Gluing up the vent to the top / rear panels.
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I'll have a few more pictures this evening.
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post #33 of 59 Old 08-31-2017, 04:23 PM - Thread Starter
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Glued & Screwed

Rough portion of the build is complete.
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Next steps will be to wrap the curved sides with two layers of 1/8 barrel-bend ply to provide a nice even substrate for whatever veneer I end up going with. The top will get a 1/2 MDF vanity panel that will be radiused with 1/4" roundover bit. Bottom will get some type of footing in order to recess the spikes without breaking the bottom panel of the actual enclosure. Haven't decided how i'm going to do that just yet.
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post #34 of 59 Old 09-01-2017, 06:15 AM
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Damn Void, rocking the skills with the hand tools...

RESPECT
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post #35 of 59 Old 09-01-2017, 06:33 AM - Thread Starter
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Thanks @Shreds . I've got a large assortment of hand tools. Various hand planes, rabbit planes, saws, chisels, spokeshaves, cabinet scrapers, roundover tools...stuff I used to get started. The hand plane in the picture is a 1902 Stanley Bailey #7 Jointer plane. The hand saw in that picture is from Bad Axe Tool Works. They make some excellent hand saws, but they are not cheap. So, it's the only one I own at present.

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post #36 of 59 Old 09-01-2017, 07:02 AM
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Awesome project, Void. You've definitely got the skills on display with this build! I love the locking miter joints, and I understand your fear... I'm too scared to attempt them myself. Your implementation looks pretty flawless.

Regarding the MiniDSP, I THINK I remember reading that the actual output voltage varies by frequency and volume setting, so the manufacturer's spec is a ballpark figure at best. There are a few guides around with steps showing how to measure the actual output, at least in terms of use with a MiniDSP. Having said that, I'm sure you would be well served with a 2x4 balanced, which seems to be the best all-around tool for the job (I am working on getting mine set up now). The unbalanced uses RCA connections, and the balanced does require some cable butchery to connect it... but it does have a higher output voltage than the balanced model.
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post #37 of 59 Old 09-01-2017, 07:16 AM - Thread Starter
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Quote:
Originally Posted by OJ Bartley View Post
Awesome project, Void. You've definitely got the skills on display with this build! I love the locking miter joints, and I understand your fear... I'm too scared to attempt them myself. Your implementation looks pretty flawless.

Regarding the MiniDSP, I THINK I remember reading that the actual output voltage varies by frequency and volume setting, so the manufacturer's spec is a ballpark figure at best. There are a few guides around with steps showing how to measure the actual output, at least in terms of use with a MiniDSP. Having said that, I'm sure you would be well served with a 2x4 balanced, which seems to be the best all-around tool for the job (I am working on getting mine set up now). The unbalanced uses RCA connections, and the balanced does require some cable butchery to connect it... but it does have a higher output voltage than the balanced model.
Thanks @OJ Bartley .

I think you're right about the MiniDSP and the Anthem specs. I do think I remember seeing a guide on how to measure the actual output voltage using a multi-meter, so I may dig that up and give that a go. The sad part is, the Anthem will do just about everything via ARC except EQ. So, I'd really only be using the MiniDSP to add the bump that @LTD02 mentions in post 5.

I may not even need it, so I put off ordering it until after I have the new sub in position, and have run ARC and done some post-ARC room measurements with REW / umik. I'm sure I will have a TON of questions around that process.

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post #38 of 59 Old 09-01-2017, 07:31 AM - Thread Starter
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While I'm at it, I have another, more immediate question I need answered. So, when I knock on the cab, on all sides, it responds with a satisfying, high-pitch rap. That suggests to me that I have the enclosure well braced, and have sufficiently subdivided all the panels so that I should have 0 flex. However, when I knock on the cab (sides, top, bracing) while I have my ear right up to the baffle opening, I can hear a distinct ringing / echo inside the box / port.

So, I loaded the sub into the enclosure and hooked it up. The good news is, I have no air leaks and even with ****ty room placement, it sounds pretty damn good. At 20Hz, there is a slight audible chuffing when I am 6 inches from the port. Nothing audible from 4 feet away, and definitely nothing audible at MLP. But that's also at like -19 on the receiver and a sustained 20Hz tone with 1100 watts.

Here's my problem. While playing music (at volumes louder than I would consider comfortable), I can hear some echo / ringing coming from the port with the sub crossed over at 110Hz (which is what the Anthem set it to). I can't hear it from 2 feet away, so I doubt I'd hear it at MLP. But, I also listen to a lot of acoustic music, so I'm concerned that might be an area where that ringing might be audible. Given what I heard when doing my "knock test", I'm wondering if I should spray the inside of the cab with some undercoating treatment? Would that rubberized coating eliminate that echo / ringing effect I'm hearing? And if so, would the non-smooth surface of the coating effect the performance of the air movement inside the cab? Keep in mind, I would not be spraying this inside the port area. Mainly, this would coat the top, bottom, sides, and braces.

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post #39 of 59 Old 09-01-2017, 07:57 AM
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Have you put any kind of absorption material on the inner walls? That might help to soak up some of the internal sounds. Maybe fiberglass or denim?
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post #40 of 59 Old 09-01-2017, 08:31 AM - Thread Starter
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Quote:
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Have you put any kind of absorption material on the inner walls? That might help to soak up some of the internal sounds. Maybe fiberglass or denim?
No. The last group of pics show the internal surfaces. They are nekkid. I couldn't really add any material before assembly because I couldn't guarantee that the curved sides would align exactly with the braces and it was more important to have solid glue joints.

I thought about finding someone who could spray the interior with some fiberglass, but that would add a ton of weight, and I'm not sure it would actually damp those internal sounds any better than the undercoating spray.

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post #41 of 59 Old 09-01-2017, 09:46 AM
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I started some threads on the topic of science in enclosure design and dealt with the issue of ideal subwoofer enclosure properties vs that of full range speakers.

With full range you want the lowest resonant frequency, very high damping, and very high density. With subwoofers density and damping are completely unimportant. The only thing that matters is stiffness, as long as you operate the speaker below the enclosure wall resonance. That means you want the resonance as high as possible in a sub enclosure, opposite of what you want in a full range enclosure.

Good news for you is that plywood is stiffer than mdf, curved walls are stiffer than straight walls, and bracing adds stiffness without adding a lot of mass. All of that pushes up the resonant frequency. My only critique is that you added a lot of ribbing but not a lot of cross-bracing. At sub frequency the enclosure primarily operates as a pressure vessel and so cross bracing is much more effective at reducing flexure of the walls. If possible I would add more cross-bracing. Try to also make sure that if you do anything to add mass to the walls, it also adds stiffness. Otherwise you drop the resonant frequency and risk it getting close to the operating range.

As for the ringing you hear, add damping material such as fiberglass insulation, cotton insulation, wool batting, etc to the inside of the enclosure. My preference is to line the walls with something that has sheet structure to it. Something like a medium density insulation such as the blue jeans insulation. In the middle add something with lower density and high breath ability like reticulate foam or wool batting. It should be roughly 25%-50% filled, but evenly spaced. Some tell you to leave an opening to the port. I personally disagree. If the material is low density and breathable then it should block the direct path to the port. That way it helps absorb more of the energy from ringing and higher pitched sounds the driver is making. It prevents them from escaping through the port.

You can also damp the port with reticulated foam. However when I experimented with this myself I found that if I filled the entire port then I needed to increase port area and shorten to the port to get the same tuning. It also reduces port output some. The advantage is less higher frequency noise and less distortion.


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post #42 of 59 Old 09-01-2017, 10:12 AM - Thread Starter
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My only critique is that you added a lot of ribbing but not a lot of cross-bracing. At sub frequency the enclosure primarily operates as a pressure vessel and so cross bracing is much more effective at reducing flexure of the walls. If possible I would add more cross-bracing.
Thanks for chiming in @mpoes !

So, the bracing I added is a pretty rigid structure, Each of the vertical braces, while being "0" braces, are 2 3/8" thick frames that are cojoined to the horizontal braces which themselves are cross-braced towards the rear. It creates an interlocking waffle pattern where the verticals are contacting all four sides of the enclosure while simultaneously joined to the horizontal braces that themselves contact all 4 sides of the enclosure.

The only additional cross-bracing I could add at this point would be an additional horizontal cross brace towards the front baffle attached to the existing top and bottom horizontal braces. It would have to be set back a little so as not to interfere with the magnet of the sub, which means it would only be contacting the left & right sides of the horizontal braces and not contacting the verticals at all. I could also add a cross brace on the vertical axis by attaching a beam dead center on the rear horizontal cross-brace.

I guess my question there would be, would it be necessary? Since this is a ported cab, I would assume internal pressure is greatly reduced vs. that of a sealed cab, because internal air forces are moved externally to the cab through the vent. How much would it truly benefit enclosure rigidity by adding a couple additional cross braces here? (I am genuinely asking.)

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post #43 of 59 Old 09-01-2017, 10:38 AM
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Quote:
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I thought about finding someone who could spray the interior with some fiberglass, but that would add a ton of weight, and I'm not sure it would actually damp those internal sounds any better than the undercoating spray.
What you want is something like the pink fluffy wall insulation between the ribs... Or denim insulation, cotton/wool, or even open cell foam mattress topper. That would help to absorb higher frequency sounds that originated inside the enclosure, and keep them from getting into the port.



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post #44 of 59 Old 09-01-2017, 10:47 AM - Thread Starter
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What you want is something like the pink fluffy wall insulation between the ribs... Or denim insulation, cotton/wool, or even open cell foam mattress topper. That would help to absorb higher frequency sounds that originated inside the enclosure, and keep them from getting into the port.
Yeah, I was thinking about some cheap, open cell foam, like mattress egg-crate on the walls / bottom between the ribbing. I'd be concerned about changes to the internal airspace that the sub driver would "see" though. That's why I was curious about the undercoating paint. A couple thin layers of that stuff wouldn't change the internal airspace volume too much, but would definitely deaden those reflective surfaces.

I'd like @LTD02 to chime in, if he's around. The link he provided about adding internal damping to ported enclosures was pretty enlightening. I guess I'm just questioning whether my concern is unfounded.

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post #45 of 59 Old 09-01-2017, 10:54 AM
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Thanks for chiming in Since this is a ported cab, I would assume internal pressure is greatly reduced vs. that of a sealed cab, because internal air forces are moved externally to the cab through the vent.
This is the biggest misconception of ported enclosures!

Around and above the port tuning internal pressure is higher then an identically sized sealed enclosure. At and above tuning the air pressure from the port and that from the driver's cone are in phase, both working together creating positive external pressure (negative internal pressure) or negative external pressure (positive internal pressure). This is what allows ported enclosures to generate greater SPL then sealed enclosures.

Only below tuning does the air flow from the port transition to out of phase with that of the driver and you see a cancelation in their outputs (driver moves in while air flows out of port and vice versa) leading to little pressure or SPL.
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post #46 of 59 Old 09-01-2017, 10:58 AM - Thread Starter
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This is the biggest misconception of ported enclosures!

Around and above the port tuning internal pressure is higher then an identically sized sealed enclosure. At and above tuning the air pressure from the port and that from the driver's cone are in phase, both working together creating positive external pressure (negative internal pressure) or negative external pressure (positive internal pressure). This is what allows ported enclosures to generate greater SPL then sealed enclosures.

Only below tuning does the air flow from the port transition to out of phase with that of the driver and you see a cancelation in their outputs (driver moves in while air flows out of port and vice versa) leading to little pressure or SPL.
Thanks @mtg90 ! I learn something new every day. And the way you've explained it actually makes a lot of sense. So given that, would you also advise additional cross bracing given the current structure I have in place?

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Thanks for chiming in @mpoes !

So, the bracing I added is a pretty rigid structure, Each of the vertical braces, while being "0" braces, are 2 3/8" thick frames that are cojoined to the horizontal braces which themselves are cross-braced towards the rear. It creates an interlocking waffle pattern where the verticals are contacting all four sides of the enclosure while simultaneously joined to the horizontal braces that themselves contact all 4 sides of the enclosure.

The only additional cross-bracing I could add at this point would be an additional horizontal cross brace towards the front baffle attached to the existing top and bottom horizontal braces. It would have to be set back a little so as not to interfere with the magnet of the sub, which means it would only be contacting the left & right sides of the horizontal braces and not contacting the verticals at all. I could also add a cross brace on the vertical axis by attaching a beam dead center on the rear horizontal cross-brace.

I guess my question there would be, would it be necessary? Since this is a ported cab, I would assume internal pressure is greatly reduced vs. that of a sealed cab, because internal air forces are moved externally to the cab through the vent. How much would it truly benefit enclosure rigidity by adding a couple additional cross braces here? (I am genuinely asking.)


A port isn't a pressure relief valve. There is still high pressure in a ported box. The port actually has a high pressure impedance at certain operating frequencies.

Adding bracing is always nice but I honestly think your box is fine. I highly doubt you will hear a difference. I doubt what you are hearing is actual wall ringing. I think it's a port resonance or high frequency noise escaping through the port. That will be fixed by adding damping material to the enclosure such as insulation.



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post #48 of 59 Old 09-01-2017, 11:07 AM - Thread Starter
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A port isn't a pressure relief valve. There is still high pressure in a ported box. The port actually has a high pressure impedance at certain operating frequencies.

Adding bracing is always nice but I honestly think your box is fine. I highly doubt you will hear a difference. I doubt what you are hearing is actual wall ringing. I think it's a port resonance or high frequency noise escaping through the port. That will be fixed by adding damping material to the enclosure such as insulation.
Thanks @mpoes . I think you may be right. It's kind of hard to tell where the actual high pitch ring is coming from with the echoing in the box...but I kind of feel like it's more audible in and around the port. So I know adding something like loose polyfill won't change the airspace requirements much, but what about something like the cheap egg-crate stuff? Like you mentioned, I think I would prefer some type of sheet form factor. I am not familiar with "blue jeans insulation". Is that literal blue-jean denim?

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post #49 of 59 Old 09-01-2017, 11:25 AM
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https://www.menards.com/main/buildin...4425678726.htm


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post #50 of 59 Old 09-01-2017, 11:45 AM - Thread Starter
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I see they make that in various ratings. Is it required to be R19? There's some smaller quantities in R6.7, but I'm assuming you linked to the R19 for a reason.

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post #51 of 59 Old 09-01-2017, 12:07 PM
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It can be whatever you want. The R rating is just the difference in thickness. As I mentioned earlier it is good to have much of the box filled. The walls can have the full density of that material in sheet form but the area between the driver and port needs to be less dense. You can shred a sheet of insulation to fill the volume of cabinet area between driver and port.

I picked R19 because it's what showed up when I googled cotton insulation and menards. It is a good size for what it's worth.


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post #52 of 59 Old 09-01-2017, 12:13 PM - Thread Starter
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Thanks @Mpoes12

I still have 2 lbs of Acousti-stuff fill that I could use behind the driver. As for the interior surface walls, I'm assuming with this insulation that the driver may see an airspace change? Since I cannot lengthen or shorten the port at this point, assuming I went with the R6.7 (which is only 2" thick) to line the side walls, top & bottom, how might this affect the tune of the port? Like, this cab, according to WinISD, is tuned to 23Hz. Would would be the + / - effect of adding this insulation, if any?

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post #53 of 59 Old 09-01-2017, 12:21 PM
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There have been studies of this topic and I've done my own experiments. It will slightly dampen and reduce efficiency of the port. That means less output, maybe a db or two. However I consider it a good thing. It also can slightly change the roll off below tuning. In general I wouldn't worry about it. People exaggerate he effect when they say it makes the box bigger. You won't see a drastic change in tuning and in fact there is no magic frequency for port tuning that is best. If it shifts up or down a few hz it won't be a problem. Inaccuracies in your port dimension estimates will cause a bigger shift than will acousti-stuff or denim insulation.


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post #54 of 59 Old 09-01-2017, 12:24 PM
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http://data-bass.com/data?page=content&id=79 this shows one decent study. The only thing missing is the impact in damping the port. I've studied that and it's similar but graveyard in impact.


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post #55 of 59 Old 09-01-2017, 12:25 PM - Thread Starter
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Originally Posted by Mpoes12 View Post
There have been studies of this topic and I've done my own experiments. It will slightly dampen and reduce efficiency of the port. That means less output, maybe a db or two. However I consider it a good thing. It also can slightly change the roll off below tuning. In general I wouldn't worry about it. People exaggerate he effect when they say it makes the box bigger. You won't see a drastic change in tuning and in fact there is no magic frequency for port tuning that is best. If it shifts up or down a few hz it won't be a problem. Inaccuracies in your port dimension estimates will cause a bigger shift than will acousti-stuff or denim insulation.


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Cool! Thanks @Mpoes12 . Also thanks to @mtg90 and @OJ Bartley !

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post #56 of 59 Old 09-01-2017, 12:44 PM
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Originally Posted by mtg90 View Post
This is the biggest misconception of ported enclosures!



Around and above the port tuning internal pressure is higher then an identically sized sealed enclosure. At and above tuning the air pressure from the port and that from the driver's cone are in phase, both working together creating positive external pressure (negative internal pressure) or negative external pressure (positive internal pressure). This is what allows ported enclosures to generate greater SPL then sealed enclosures.



Only below tuning does the air flow from the port transition to out of phase with that of the driver and you see a cancelation in their outputs (driver moves in while air flows out of port and vice versa) leading to little pressure or SPL.


I missed Matts post. This is right on the money and he is right, people often think a port makes the enclosure have a sort of pressure relief valve. It works because there is a slug of air with a mass that dictates its tuning frequency. That slug of air thus increases pressure at and around the tuning frequency. It's not a pressure valve. It's a tuned port. At tuning there is a point where the driver is at minimum motion. That would not happen if the air did not have mass in the port. In simplifying the process and was reluctant to post the technical detail Matt did, but his understanding fully matches mine.


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post #57 of 59 Old 09-11-2017, 04:33 PM - Thread Starter
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@Mpoes12,

Quick question. With regards to the denim insulation. Is it enough to lay it on all sides in between the ribs? I've noticed a change in the "ringing" sound I was hearing earlier (for the better), but I'm wondering if I should be laying a continuous layer on all four sides covering the ribs / cross braces. Here's a picture of what I have thus far. -- Also, I'm assuming a spray adhesive is sufficient to attach it in place?

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post #58 of 59 Old 09-13-2017, 01:07 PM
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That should be completely fine. As long as there's enough in there to suck up most of the echo and any high freq noise generated, I think you're all set. The glue is *probably* OK, although I don't know how it holds up over time. If you can give it a tug and it stays in place, there's probably nothing to worry about. I stapled it in on my HTM-12s, but then there's always the chance of a staple working its way loose and rattling, so either way.
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post #59 of 59 Old Yesterday, 06:47 PM - Thread Starter
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That should be completely fine. As long as there's enough in there to suck up most of the echo and any high freq noise generated, I think you're all set. The glue is *probably* OK, although I don't know how it holds up over time. If you can give it a tug and it stays in place, there's probably nothing to worry about. I stapled it in on my HTM-12s, but then there's always the chance of a staple working its way loose and rattling, so either way.
Thanks @OJ Bartley . I ended up going with it. The glue worked very well, and after mounting the sub, the sound was noticeably improved, even before room correction was applied. No ringing, no echoes.

Looks like it's gonna be a month or so before I can veneer the sub, though. Heavy figured quarter-sawn Eucalyptus or Curly Maple runs around $116 for a 2ft x 8ft sheet of veneer or $156 - $200 for a 4ft x 8ft sheet of veneer.

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