DIY Subwoofer Risers

[Big Daddy]

Originally Posted by kareface

At the db levels most people watch movies at and the frequency range that subs produce, that style of foam will usually do little if anything to reduce vertical node energy. Even the pressure equalization bass traps that come in the subtraps mentioned in the first post, which are much more LF effective then foam for their size are only rated down to 70hz for an 8' ceiling (which is the US average according to bd). My subs aren't even crossed over till 60 & my ceilings are shorter then that even. I'm looking to build a pair of risers that come up about 18 inches. The problem I've run into is how to best dampen the excess node energy. Especially for LF, density matters for mass dampening. It just doesn't seem like something that would be as effective. I have used high density foams for STC dampening before, but the wall mart stuff looks to have a much lower pcf then that. Correct me if I'm wrong here.

I agree with you. The cheaper foam and the carpet are for aesthetics and for dampening. Several people used the thicker and denser bass trap type foam and I discussed using sand with a couple of people. Unfortunately, sand makes the riser box impossible to move unless you put it on a dolly. The bass trap type foam is too expensive and has to be ordered online. That defeats the reason for making a DIY riser as it becomes more expensive than the risers available from outside vendors.

Although the foam from Wal-Mart is not ideal, they are very cheap and available everywhere. Several layers of such foam and a thick carpet on top of it will make the riser more attractive and can serve as a dampening medium for higher frequency noises that may come out of poorly designed ports or elswhere. There are a few craft and fabric shops that sell thicker and denser foam. There is no doubt that heavier and denser foam or sand are more effective, but we shouldn't put a subwoofer on top of a tall riser or a hollow box without filling the bottom.

[kareface]

Originally Posted by jlafrenz

High density foam can have isolation and absorption properties it is also inexpensive and easy to find. The goal is to minimizing the amount of energy transferring into the floor and then other objects in the room.

Most foam products that aren't too rigid will have some absorption qualities. However isolation is a different matter. Resins, epoxies and rubbers have better isolation properties. Do you have a source for that information? It's the first time I've heard of it. Also, even if that was the case it would only offer isolation if it was resting on the foam and not on the legs of the riser. Putting rubber on the feet of the riser would be a great idea tho, as BD suggests in the guide.

Originally Posted by Big Daddy

I agree with you. The cheaper foam and the carpet are for aesthetics and for dampening. Several people used the thicker and denser bass trap type foam and I discussed using sand with a couple of people. Unfortunately, sand makes the riser box impossible to move unless you put it on a dolly. The bass trap type foam is too expensive and has to be ordered online. That defeats the reason for making a DIY riser as it becomes more expensive than the risers available from outside vendors.

Although the foam from Wal-Mart is not ideal, they are very cheap and available everywhere. Several layers of such foam and a thick carpet on top of it will make the riser more attractive and can serve as a dampening medium for higher frequency noises that may come out of poorly designed ports or elswhere. There are a few craft and fabric shops that sell thicker and denser foam. There is no doubt that heavier and denser foam or sand are more effective, but we shouldn't put a subwoofer on top of a tall riser or a hollow box without filling the bottom.

Thanks BD, that makes sense. That is exactly what I wanted to know. I agree that sand would be a good idea to prevent the mass-air resonance if the enclosure was sealed, but if the sides are open you're better off going with some type of dampening. I think I'll just have to go with a high pcf insulation, I just wish there was a more effective option.

Edit. A poster over on HTG had the following suggestion:

Terry Montlick (PhD in acoustics) over at AVS is one of the few people I know who has done any measuring/modeling at low frequencies. He says fluffed up fiberglass works better at LF. It's not really about mass, it's about getting good penetration and getting the fibers to move, creating heat to absorb energy. It sorta shows up with the 70* measurements with thin material but Terry says it's more obvious with thicker material (like a foot or two) and lower freqs. Makes sense to me but no guarantees as it's very hard to measure down low.

I think I'll be going this route, I'll test the effectiveness of both the higher and lower pcf solutions. It'll be interesting to see which of the 2 solutions is more effective.

[Big Daddy]

kareface,

Check these sources.

http://www.aapusa.com/index.html

http://www.800nonoise.com/foam.htm

http://www.thefoamfactory.com/acoust...usticfoam.html

[kareface]

Originally Posted by Big Daddy

kareface,

Check these sources.

http://www.aapusa.com/index.html

http://www.800nonoise.com/foam.htm

http://www.thefoamfactory.com/acoust...usticfoam.html

Cool, thanks. Man, some of the foams on the 800 noise site are terrible, a 10% reduction at 125hz with 1.5 inches of material. Gotta love the foam factory tho, great site.

[erict]

Originally Posted by kareface

Cool, thanks. Man, some of the foams on the 800 noise site are terrible, a 10% reduction at 125hz with 1.5 inches of material. Gotta love the foam factory tho, great site.

And only 20min from me I walked in there and you wouldn't believe all the remnants and scraps And cheap in cost to boot. The place is huge.

[jlafrenz]

I think the way I typed that and how it reads may sound odd. Foam can be used to isolate (separate) the platform the ground.

[kareface]

Originally Posted by erict

And only 20min from me I walked in there and you wouldn't believe all the remnants and scraps And cheap in cost to boot. The place is huge.

You bastid! I actually have a foam place not to far from me. I've never gone there tho, I generally only use foam for speaker building and adding extra sound/thermal insulation above subfloors. Nice setup btw, got a good laugh from one of your pictures.

Originally Posted by jlafrenz

I think the way I typed that and how it reads may sound odd. Foam can be used to isolate (separate) the platform the ground.

Are you talking about acoustic isolation? If you are just resting the riser on the foam there may be some degrees of this, but you'd be better off using legs on the riser and placing some rubber feet below them. This reduces the physical transmission area (imagine isolation spikes) and the rubber has much better isolation properties then foam. The same principle is applied to isolation clips for sound proofing rooms, you reduce the area of transmission to the clips with a rubber joint.

[erict]

[QUOTE=kareface;2917907]You bastid! I actually have a foam place not to far from me. I've never gone there tho, I generally only use foam for speaker building and adding extra sound/thermal insulation above subfloors. Nice setup btw, got a good laugh from one of your pictures. QUOTE]

He has that look like here we go again

[jlafrenz]

With the foam I am talking about keeping the platform separate from the ground and the sub. There may be some acoustical isolation, but that I am not sure of. One of the designs that was suggested to me was to use 2 layers of high density foam with concrete or granite in-between. It was suggested that I use 2" think foam. The foam would have some acoustical absorption, but the concrete or granite would handle most of the work. I actually ended up going with rubber feet (hockey pucks) with my granite slab and no foam.

[GAWD]

me again with my stupid questions. I did some math on the materials I'd need to make a 2ft riser. Comes out to about 60$.(The way I want to make it anyway)

Now an Auralex Gramma would cost me 65$. Anyone have any experience going from the Gramma to the sub being raised 8+ inches?

I did a "little not accurate" test last night by placing my sub on paint cans (8" tall and only thing I had handy) and did not really notice a difference.

BUT I have noticed a difference going from the standard feet to placing the sub on Auralex MoPads (speaker de-couplers)

Anyone try Gramma or SubDude and DIY risers?

Stay the course and get my hands dirty (also leaves me on Big Daddy's good side) or use an xacto knife and open a box

[kareface]

To be honest, the best 'before & after' FR graphs I've seen comparing risers was a little disappointing. They had little if any impact below 80hz. I suspect it's extremely situational tho. A smaller riser doesn't do anything for the vertical decoupling, it would only be used to isolate the sub from secondary resonance (which is very room dependent). It's likely one of those things that is hot or cold, it'll help for some, but if your subs crossed over pretty low and you are already using isolation spikes I wonder how much benefit you'd actually see from them. I think after looking at the over all impact I might put the sub riser on the back burner for a little bit and work with other room treatments first. I'll see if I can find a few more objective tests of them, I'm curious to see how they fair.

[jlafrenz]

I have not read through this entire thread so I may have missed something. It seems as though many people are trying to get their subs quite high off the ground. I can't say that I totally understand this. I realize that it helps avoid passing energy into the floor and decouples it, but why not just use a material that is better suited for this purpose and does not require such height?

[progers13]

Originally Posted by jlafrenz

I have not read through this entire thread so I may have missed something. It seems as though many people are trying to get their subs quite high off the ground. I can't say that I totally understand this. I realize that it helps avoid passing energy into the floor and decouples it, but why not just use a material that is better suited for this purpose and does not require such height?

That is an understandable question. Please read post # 2 HERE for the answer to that and other questions.

[jlafrenz]

Originally Posted by progers13

That is an understandable question. Please read post # 2 HERE for the answer to that and other questions.

Thanks for that link. I now see it is more about the way the sub interacts with the room itself as opposed to the trying to decouple it from the floor and reduce vibrations.

[duder1234]

Quick question for ya guys, (its about speaker stands, but along the same lines of vibration/sound isolation)

What happens if you have multiple "polls" holding up the stand as opposed to a single "tube" or rectangle? Does the greater number of polls create more problems (i.e. vibration and or make the speakers sound different than a single poll design)?

Like such:

http://www.studioacoustics.com.au/product_pics/SS26.jpg

THANKS!

[kareface]

Originally Posted by duder1234

Quick question for ya guys, (its about speaker stands, but along the same lines of vibration/sound isolation)

What happens if you have multiple "polls" holding up the stand as opposed to a single "tube" or rectangle? Does the greater number of polls create more problems (i.e. vibration and or make the speakers sound different than a single poll design)?

Like such:

http://www.studioacoustics.com.au/product_pics/SS26.jpg

THANKS!

Even if it did, it wouldn't be to a degree that you'd be able to noticed any difference between the two. What would matter much more is how the stand rests on the ground. Rubber feet or spikes would be much more influential for isolation then the number of poles that lead to the top platform.

[duder1234]

Thanks kareface, thats what I wanted to hear!

[GregBe]

Originally Posted by kareface

To be honest, the best 'before & after' FR graphs I've seen comparing risers was a little disappointing. They had little if any impact below 80hz. I suspect it's extremely situational tho. A smaller riser doesn't do anything for the vertical decoupling, it would only be used to isolate the sub from secondary resonance (which is very room dependent). It's likely one of those things that is hot or cold, it'll help for some, but if your subs crossed over pretty low and you are already using isolation spikes I wonder how much benefit you'd actually see from them. I think after looking at the over all impact I might put the sub riser on the back burner for a little bit and work with other room treatments first. I'll see if I can find a few more objective tests of them, I'm curious to see how they fair.

I think you are right in that it is situational. For me, putting my sub on a Gramma, really helped isolating the sub from the floor, but when I tried to raise the sub up 1' and then 2', my frequency response got worse. I would guess the concept is similar to any sub placement...one size does not fit all. In some rooms, the best place is in the corner, in some rooms, it sounds better to pull it out some. I am sure the same goes for vertically raising the sub off the floor.

[Fors*]

Originally Posted by GregBe

I think you are right in that it is situational. For me, putting my sub on a Gramma, really helped isolating the sub from the floor, but when I tried to raise the sub up 1' and then 2', my frequency response got worse. I would guess the concept is similar to any sub placement...one size does not fit all. In some rooms, the best place is in the corner, in some rooms, it sounds better to pull it out some. I am sure the same goes for vertically raising the sub off the floor.

I agree, when moving the sub to different locations, you are dealing with the horizontal modes, and the same thing applies when raising the sub, except you are dealing with vertical modes. And every room is different, since those darn bass waves love to interact with anything/everything in a room.

[manu4panjab]

i use old tea table(which is now useles in house these days)and place three pillow under it and man its awesome difference now no more muddier bass and bass is now less localizable here are pics