DIY TC Sounds LMS-5400 18" + 2x18" PR 200L

[robertcharles123]

Ilkka,

I have one of my boxes started and my actual measurements of the cubic feet is 9.26 cf per woofer. This includes all braces and the woofers and passives. That is very close to the ten feet you mentioned. What do you think?

Thanks,

Robert

[robertcharles123]

Ilkka,

How much power did you throw at the 5400's to get the results?

Did you come close to clipping the amp?

[Ilkka]

robertcharles123 wrote:

Ilkka,

I have one of my boxes started and my actual measurements of the cubic feet is 9.26 cf per woofer. This includes all braces and the woofers and passives. That is very close to the ten feet you mentioned. What do you think?

Thanks,

Robert

Sounds really good. You should get a slightly flatter frequency response (and more max output around tuning) than what I measured.

[Ilkka]

robertcharles123 wrote:

Ilkka,

How much power did you throw at the 5400's to get the results?

Did you come close to clipping the amp?

I used a single bridged Crown CE4000. The manufacturer spec says 3600W when using 230V line voltage, which I used. Unfortunately I don't know how close to clipping I was, since I don't measure the amp output/waveform. But I can say that if you throw 2-3 kW to that subwoofer (and you have multiples of them!), make sure your room and house are properly constructed.

[robertcharles123]

Any thoughts on dampening material for these boxes or subs in general. I'm not partial to fiber glass.

[Mike P.]

Egg crate foam is used by many with excellent results.

[WmAx]

Mike P. wrote:

Egg crate foam is used by many with excellent results.

For a point of reference, it should be noted that the average 2" egg crate foam sold as 'acoustic foam', has no appreciable absorption effect in under about 600-700Hz. A premium grade 2" foam, such as Auralex or EchoBuster, will not have an appreciable absorption effect under about 400Hz.

-Chris

[Mike P.]

WmAx wrote:

For a point of reference, it should be noted that the average 2" egg crate foam sold as 'acoustic foam', has no appreciable absorption effect in under about 600-700Hz. A premium grade 2" foam, such as Auralex or EchoBuster, will not have an appreciable absorption effect under about 400Hz.

-Chris

My point of reference would be my first two Shiva unlined sonotubes. They has a "boomy" sound and an obvious resonating problem. I lined them with 1.5 inch thick open cell egg crate foam and the problem was solved. I've since built 5 more subs with egg crate foam installed for lining and have no problems with resonating or "boomy" sound. My personal experience is that egg crate foam works.

[WmAx]

Mike P. wrote:

My point of reference would be my first two Shiva unlined sonotubes. They has a "boomy" sound and an obvious resonating problem. I lined them with 1.5 inch thick open cell egg crate foam and the problem was solved. I've since built 5 more subs with egg crate foam installed for lining and have no problems with resonating or "boomy" sound. My personal experience is that egg crate foam works.

That is against known physical action(foam of this type/thickness having any appreciable value at the bandwidth at subject here). I would propose that sub-conscious biasing may be one factor at play here.

-Chris

[Mike P.]

WmAx wrote:

That is against known physical action(foam of this type/thickness having any appreciable value at the bandwidth at subject here). I would propose that sub-conscious biasing may be one factor at play here.

-Chris

I agree it's easy to fool the ears. That has been well documented over the years. But in this instance it would also mean I would not have noticed any difference by placing my hand on the cabinet when it was unlined and then lined. Would you have a link to ""no appreciable absorption effect""? I'd like to read up on this.

[WmAx]

Mike P. wrote:

I agree it's easy to fool the ears. That has been well documented over the years. But in this instance it would also mean I would not have noticed any difference by placing my hand on the cabinet when it was unlined and then lined. Would you have a link to ""no appreciable absorption effect""? I'd like to read up on this.

"No appreciable absorption effect" is in reference to credible co-efficient testing of different materials - as can be found in many databases. You can research/look up this data, or you can refer to Ethan Winer's RealTraps web site, which has(or had) a database of lab test measurements of different materials, including two foam vendors(Auaralex and Foam By Mail). Rod Elliot's site(sound.westhost.com) also has some testing of various material as it relates to absorption in a small midbass application, which the general results match up with known general absorption properties established by other testing.

The only appreciable effect the foam can be expected to have in your subwoofer application, is that it can in some instances, reduce the port(or passive radiator) output due to physical air-coupling losses that can be induced in the system alignment. However, this seems unlikely based on the relatively thin foam you used based on the subwoofer cabinet size. For foam to be effective at say reducing the long dimension half-wave modal resonance at bass frequencies, or 1/4 wave null effect based on driver to nearest boundary point; you would have to use a high grade acoustic foam, such as Auralex, in 5-6" thickness. Alternatively, you can use 4" of 6-8lb/ft^3 mineral wool board for similar absorption properties. It must be clear, though, that this amount of material will certainly result in measurable loss in port efficiency/output.

-Chris

[robertcharles123]

What about polyfill or poly batting?


Thanks,

Robert

[avaserfi]

robertcharles123 wrote:

What about polyfill or poly batting?


Thanks,

Robert

These materials are even less effective than typical foams. At about 2" ployfill does not have an appreciable effect until frequencies above 1kHz. As shown in this article.

If you use OC705 or 8lb mineral board wrapped in a cloth fabric such that nothing is exposed you will have no issues with any fiber escaping into your room via the port while achieving effective dampening.

[noah katz]

"The only appreciable effect the foam can be expected to have in your subwoofer application, ..."

An important reason to use stuffing is to increase the box effective volume.

The decrease in Fb of my 12 cu ft dual Avalanche 18 subs indicates >20% volume increase.

I used 3 layers of 2 lb/cu ft on all sides.

"...is that it can in some instances, reduce the port(or passive radiator) output due to physical air-coupling losses that can be induced in the system alignment."

Not sure where you came up with "physical air-coupling losses", but the issue, which is much more likely with ports, is restricting the movement of air because of its high velocity and the distance it moves.

[Ilkka]

http://www.diysubwoofers.org/talksho...ages/41415.htm

Here's a good read on the subject.

I would say that when the size of the enclosure goes above ~5 ft^3, stuffing the enclosure with "dampening" material becomes less and less effective and also less important. With small enclosure one can gain substantial volume by using a lot of dampening material, but with larger enclosures it becomes harder because one would have to use A LOT of fiberfill etc. Especially with ported subwoofer it usually starts to restrict the airflow before becoming enough effective.

With well built enclosures, I haven't found any difference in "SQ" whether the enclosure has been stuffed or not. Usually I use some but not much stuffing in the subwoofers I build.

[Mike P.]

WmAx wrote:

"No appreciable absorption effect" is in reference to credible co-efficient testing of different materials - as can be found in many databases. You can research/look up this data, or you can refer to Ethan Winer's RealTraps web site, which has(or had) a database of lab test measurements of different materials, including two foam vendors(Auaralex and Foam By Mail). Rod Elliot's site(sound.westhost.com) also has some testing of various material as it relates to absorption in a small midbass application, which the general results match up with known general absorption properties established by other testing.

The only appreciable effect the foam can be expected to have in your subwoofer application, is that it can in some instances, reduce the port(or passive radiator) output due to physical air-coupling losses that can be induced in the system alignment. However, this seems unlikely based on the relatively thin foam you used based on the subwoofer cabinet size. For foam to be effective at say reducing the long dimension half-wave modal resonance at bass frequencies, or 1/4 wave null effect based on driver to nearest boundary point; you would have to use a high grade acoustic foam, such as Auralex, in 5-6" thickness. Alternatively, you can use 4" of 6-8lb/ft^3 mineral wool board for similar absorption properties. It must be clear, though, that this amount of material will certainly result in measurable loss in port efficiency/output.

-Chris

I was looking for a link showing ""no appreciable absorption effect"" when used in subwoofers since that is what is being discussed here. I've searched and can't find anything. Since I have 2 retired Shiva sonotubes on hand, I may pull the foam out of one and see if there is any difference. According to what is being stated here they should perform the same.

[noah katz]

There's a bit of a red herring here re absorption.

The original question I believe was about absorption at somewhat higher, audible freq, whereas most of the responses were about the low absorption coefficients at low freq.

In fact that's good, as absorbing it would just reduce the output we built the sub for.

"I would say that when the size of the enclosure goes above ~5 ft^3, stuffing the enclosure with "dampening" material becomes less and less effective and also less important."

Not what I found, see above.

Sure, you have to buy more, but you have to buy more of everything for a bigger sub.

[Ilkka]

noah katz wrote:

The decrease in Fb of my 12 cu ft dual Avalanche 18 subs indicates >20% volume increase.

I used 3 layers of 2 lb/cu ft on all sides.

So you measured the Fb before and after adding the fiberfill? Is that a ported subwoofer? How did you measure the Fb?

[noah katz]

Yes, I measured before and after, by freq of impedance peak across driver, w/a series resistor.

Though pricey, I use foam, not fiber, as I have found it to lower freq more, and easier to get it to stay in place.

[WmAx]

noah katz wrote:

An important reason to use stuffing is to increase the box effective volume.

Yes, but the subject I was discussing was not stuffing, but using a thin(1.5") layer of foam, which is not going to have a substantial effect such as if one used a moderate level of stuffing or lining with thick materials. Of course, in a ported/PR system, this is a double edged sword. Stuffing for effective volume increase is only feasible in sealed systems. Using enough material to increase volume by a substantial degree in a ported system will cause the port to lose appreciable output. Now, one could use this as a technique for a specific target tuning, as long as one realizes the inter-relationship of factors so that they can accurately target a desired response.

Not sure where you came up with "physical air-coupling losses", but the issue, which is much more likely with ports, is restricting the movement of air because of its high velocity and the distance it moves.

Here is an article on this subject:

http://www.geocities.com/kreskovs/Box-1.html

Another article on this subject

http://sound.westhost.com/articles/boxstuff.htm

-Chris

[ec114]

As TC/Audiopulse's PRs seem unobtainium now, and prolly $$$ anyway, the AE/CSS 18" PRs look like a decent replacement, especially given their extremely compliant suspensions. Any other large PR alternatives?

Right now, trying to keep a small box, and allowing for some FR drop from 50Hz down to 20Hz anechoic, 180l with 2x2500g PR, 15.3Hz, appears to be a decent overall design? Some output sacrificed for the size, probably, but should still be a lot better than sealed...

Oh, and this is actually for the 18" Ultra, which spec-wise looks really close to the 5400.

Never having dealt with PR or vented modeling before, any opinions welcome; thanks!

[bobgpsr]

ec114 wrote:

Never having dealt with PR or vented modeling before, any opinions welcome; thanks!

I like using UniBox for modeling passive radiator based subwoofer designs.

But it does require you to have Microsoft Excel.

[ec114]

bobgpsr wrote:

I like using UniBox for modeling passive radiator based subwoofer designs.

But it does require you to have Microsoft Excel.

Oops; yeah, my numbers were from UniBox. Didn't run the equations myself. But, if anyone's interested, I'd appreciate a sanity check, Unibox or otherwise.

[ec114]

Ok, here are the UniBox pix:

[vinculum]

This excusion chart looks very close to what the Acoupower 18" driver and these PRs model like. You really need to make sure there is a HPF inserted near the tuning frequency because things get out of hand very quickly with the PRs at and just under tune. (with maximum power anyhow)

Sounds crazy, but 4 PRs per driver would give so much more excursion headroom. Higher cost immediately comes to mind, but compare the costs of 2 TC Sounds VMP's @ $250 each and the cost of 4 AE PR's @ $129 each. $500+shipping vs. $516 plus shipping. Not much of a cost difference if you were able/willing to buy the TC PRs. Making a box would be more challenging. bottom firing active driver and a PR on each side of a square comes to mind. Just an idea i had floating around in my head...

Dr V

edit : After a little modeling, it appears the necessary HPF used to curb the active drivers excursion below tuning also takes care of the PRs no matter how many you have. Maybe 4 PRs would indeed be a waste of money?