Vented Sub: how much lining? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 15 Old 08-13-2019, 10:05 AM - Thread Starter
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Vented Sub: how much lining?

Hey all,

I'm in the process of building a very narrow variation of the VBSS and was curious what people's thoughts are on how much lining to use. Based on what I read at data-bass on their test (https://www.data-bass.com/data?page=content&id=79), it looks like the lining helps smooth out response issues with enclosure / port resonance. Granted, they were stuffing pillows in rather than lining. The trade-off was efficiency, where it looks like SPL and especially port contribution dropped quite a bit.

That said, this is a fairly atypical box. Akin to the stonehenge, but even more narrow at only 10" deep. Total dimensions are 31"x49"x10" and will be right up against the back of a couch.

Given all that, does this look like overkill lining, just right, or is lining not something worth the loss in SPL? This is lined with UltraTouch R6.7 (~1.8")

Thanks!
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post #2 of 15 Old 08-13-2019, 11:34 AM
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Looks like an amount I'd strive for.

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post #3 of 15 Old 08-13-2019, 11:43 AM
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None is required for ported boxes.
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post #4 of 15 Old 08-13-2019, 12:10 PM - Thread Starter
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Quote:
Originally Posted by Shadowed View Post
None is required for ported boxes.
I was curious if there would be a vote for none - in the VBSS thread and some others I've seen it recommended to line the walls. Have you not noticed any improvement by lining the walls? Interested to know more!

I'm also somewhat curious on the effect on efficiency / SPL when lining. The experience I linked was basically stuffing a vented sub with pillows which might have a more profound effect?
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post #5 of 15 Old 08-13-2019, 12:24 PM
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Quote:
Originally Posted by Mark Bevier View Post
I was curious if there would be a vote for none - in the VBSS thread and some others I've seen it recommended to line the walls. Have you not noticed any improvement by lining the walls? Interested to know more!

I'm also somewhat curious on the effect on efficiency / SPL when lining. The experience I linked was basically stuffing a vented sub with pillows which might have a more profound effect?
There was one member who used a couple of pillows in the center of a very long box to help alleviate standing waves.

Higher frequency boxes ie: non-subs can benefit from lining is my understanding. Box fill is beneficial for sealed cabs.

.

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post #6 of 15 Old 08-13-2019, 01:49 PM
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Fill isn’t even required for sealed. Lining to help with standing waves if there are any. I have two MBM’s with no lining and there isn’t an issue.


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post #7 of 15 Old 08-13-2019, 01:51 PM
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Ported here, with no lining. If there are any problems, I can't hear them. 3dB variance from tune frequency up to 100hz. Sounds good to me!
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post #8 of 15 Old 08-13-2019, 02:00 PM - Thread Starter
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I've read that if any interior dimension of the box is 1/4 of a wavelength in pass band, it can cause a standing wave (citation needed). Since this thing is pretty long in two dimensions, the height would put it around 1/4 wavelength of 100hz and the width around 70hz. Could be an interesting problem that the lining might help address (or pillows as mentioned earlier).

Given the long dimensions of this box, lining may be appropriate where it might otherwise not be? If so, then the next question would be - how much does it take to kill 70-100hz standing waves?

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post #9 of 15 Old 08-13-2019, 02:31 PM
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But you already have it lined I have two ported boxes 48x32x24 and no lining

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post #10 of 15 Old 08-13-2019, 02:37 PM - Thread Starter
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Quote:
Originally Posted by johnson636 View Post
But you already have it lined I have two ported boxes 48x32x24 and no lining

Ha, yeah - I'm about to attach the baffle and wanted to get some thoughts on it before changes become difficult. Easy enough to take out some lining right now, later it will be more annoying. I'm most wary of over lining it for no benefit and losing spl as a result. If there's no real detriment to this lining, then I'll just leave it and continue on till I stump myself with another design decision
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post #11 of 15 Old 08-13-2019, 02:45 PM
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post #12 of 15 Old 08-13-2019, 02:52 PM
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This topic has always confounded me. Go on Facebook and check out pages of respected builders like JTR and PSA and you’ll see them lining their vented subs. I changed an amp on one of my Hsu subs and it was lined. And guys on here like Bill Fitzmaurice says do line them. On the other hand, other guys who definitely know a thing or two about subs say don’t bother. Check out the GSG site. Those guys are pros and they say not to line them.

On my four mini marty’s I lined two and didn’t line the other two. By ear and by REW I can’t detect a lick of difference. On the VBSS’s I just built I lined them (pretty much like yours). Why? Because it’s Matt’s design and the instructions say to line them.

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post #13 of 15 Old 08-13-2019, 03:36 PM - Thread Starter
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I'm also fuzzy on the length a dimension needs to be to cause issues. If it's the full wavelength, then it's way up in the 280hz range and well beyond the pass band of a subwoofer. At 1/2 wavelength it's 140hz, conceivable some up here, but with 80-100hz crossover likely not much? I recall 1/4 wavelength being about the shortest to cause issues, which the 48" would definitely bring into play.

Based on what I've been reading today, the best case scenario would have been to not have a dimension at or greater than 1/4 wavelength of anything in the pass band - but I'm space constrained and this was purpose built to a location, couldn't be avoided. Good to know as a general guideline though.

Now it's a matter of whether trying to address that issue is worth it or not. I'd imagine the most effective area to try and control the standing wave along the 48" width would be on the left and right sides of the box and maybe even on the left and right sides of the braces around the driver.

Or maybe I just close it up and measure later, haha. Stuff a pillow in if it bothers me

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post #14 of 15 Old 08-14-2019, 04:50 AM
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Leave the lining as is, seal it up and let's get rocking. No need to over think it...
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post #15 of 15 Old 08-15-2019, 10:59 PM
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Quote:
Originally Posted by Mark Bevier View Post
Ha, yeah - I'm about to attach the baffle and wanted to get some thoughts on it before changes become difficult. Easy enough to take out some lining right now, later it will be more annoying. I'm most wary of over lining it for no benefit and losing spl as a result. If there's no real detriment to this lining, then I'll just leave it and continue on till I stump myself with another design decision
Stuffing causes the heat exchange when the air is compressed to change from adiabatic to isothermal (or maybe vice versa, I always forget). This can make the box appear effectively larger, in theory like 40%. Nice for sealed boxes!

For ported, trickier. You don't want to block airflow around the ports, and if the box appears larger it will throw off the tuning unless you compensate. Stuffing by itself cannot cause loss of SPL, however a lowered tuning will lose some SPL at higher bass and gain some lower down.

Lining can be viewed as a layer of stuffing, but more to absorb high frequencies inside the box so they don't transmit out through the box walls or cones or ports. What you have looks good, according to science, the gods of acoustics, and the tea leaves I'm looking at
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