DIY Subwoofer Risers

[jerix]

Crazyblue, Big Daddy - THANKS...Ill do your suggestions. I have already several 1" cuts of foam materials to put below the sub but i am still thinking if i can attach a thin plywood platform between the legs and the wheels to where i can place the foam materials. This way, i can move the sub easily with the foam.

The only issue i can see with this design is the vacant space just below the platform.

[rmcdermid]

Waiting on an A2-300 and I built a riser to help the time pass.

[Big Daddy]

Originally Posted by rmcdermid

Waiting on an A2-300 and I built a riser to help the time pass.

Looks good. What kind of wood did you use?

[rmcdermid]

To be honest it was scrap plywood I had laying around. Should I have used something in particular? Even my crappy sonny that is fixing to go bye bye sounds a bit better now.

Thanks,
Ryan

[Big Daddy]

Originally Posted by rmcdermid

To be honest it was scrap plywood I had laying around. Should I have used something in particular? Even my crappy sonny that is fixing to go bye bye sounds a bit better now.

Thanks,
Ryan

No, plywood works ok. Put some foam under the riser. You can spray paint it black or cover it with carpet.

[rmcdermid]

I was debating some kind of acoustic paneling. I have tried to give it a sleek look and it seems some of that foam acoustic paneling would look good and serve the purpose. Thoughts?

[Big Daddy]

Originally Posted by rmcdermid

I was debating some kind of acoustic paneling. I have tried to give it a sleek look and it seems some of that foam acoustic paneling would look good and serve the purpose. Thoughts?

Any type of foam or acoustic panel that appeals to you is fine.

[PoorSignal]

Hi.. BD and others..
I couldn't finish reading this post but
I just built a platform using a couple 2x4s (3.75" high) supporting 1.5" thick counter top material, similar to one of the GRAMPA design on the first page. I don't plan to carpet it. Is that going to be OK at about 5" high..? and no fancy carpet wrap?

I know higher is better but.. don't want to block the TV

[Big Daddy]

Originally Posted by PoorSignal

Hi.. BD and others..
I couldn't finish reading this post but
I just built a platform using a couple 2x4s (3.75" high) supporting 1.5" thick counter top material, similar to one of the GRAMPA design on the first page. I don't plan to carpet it. Is that going to be OK at about 5" high..? and no fancy carpet wrap?

I know higher is better but.. don't want to block the TV

It should work without a carpet. Carpet will make the sub more stable and can act as a dampening material. It may also absorb air noises coming out of the port.

[PoorSignal]

I finished the stand for my front firing A3-300

a picture before the stand, the sub is heavy and pretty much sunk into the carpet even with its little legs on the bottom. The woofer is close to the ground also. When the bass hits, I can feel alot of vibration in the carpet right in front of the woofer.




I used some left over slab of wood counter top and redwood 2x4 for legs, it raises the sub about 5" off the ground. I am going to find some foam and insert it in the void between the legs. I feel less vibration in the carpet now, so that should mean more clean bass. The bass vibration is could now be felt in the stand. Hopefully it doesn't generate too much bad harmonics. It should be better than firing real close to the carpet.

I didn't get a db gain but actually had to turn up about half a db, but minor enough. Also it should safe guard against for someone's foot from the woofer.

Oh, I also built the tilted stand for my center channel

[Big Daddy]

Originally Posted by PoorSignal

I finished the stand for my front firing A3-300

a picture before the stand, the sub is heavy and pretty much sunk into the carpet even with its little legs on the bottom. The woofer is close to the ground also. When the bass hits, I can feel alot of vibration in the carpet right in front of the woofer.


I used some left over slab of wood counter top and redwood 2x4 for legs, it raises the sub about 5" off the ground. I am going to find some foam and insert it in the void between the legs. I feel less vibration in the carpet now, so that should mean more clean bass. The bass vibration is could now be felt in the stand. Hopefully it doesn't generate too much bad harmonics. It should be better than firing real close to the carpet.

I didn't get a db gain but actually had to turn up about half a db, but minor enough. Also it should safe guard against for someone's foot from the woofer.

Congratulations. It is a beautiful riser. I love the wood. It looks like butcher block high-end cutting board. Maybe, you can invite us over and cut some filet mignon on it.

[PoorSignal]

Originally Posted by Big Daddy

Congratulations. It is a beautiful riser. I love the wood. It looks like butcher block high-end cutting board. Maybe, you can invite us over and cut some filet mignon on it.

.. and we could grill the filets on the AVR grills

Yes that is what it is, very heavy board. I imagine maybe we will need to steal it from the sub during thanksgiving

[crazyBLUE]

Originally Posted by PoorSignal

.. and we could grill the filets on the AVR grills

Yes that is what it is, very heavy board. I imagine maybe we will need to steal it from the sub during thanksgiving

NO CARVING ON THE RISER ALLOWED !! I will make you A cutting board If I have to !!

[Fors*]

Very nice poorsignal. I used a round cutting board as well for my one sub, and the stuff is very solid.

[GregBe]

This is very intriguing to me. I have my sub on a Gramma already, my basement floor is wood over a crawlspace, so the decoupling really helps with the floor vibrations. I never thought about raising it up to help with the vertical room problems.

Here is my question...when you normally place a sub in a room, there are general rules of thumb, but it really takes experimentation. Is this the same when raising it up vertically. I saw Big Daddy's rule of 25%. My ceilings are 7.5 inches so I could easily figure out how high to go, but will this automatically be a good thing?

In my room, I get problems at 63 hz and 28 hz. It seems no matter where I put the sub or the seating, I have those two issues. I am wondering if fixing a vertical problem is the solution?

[Fors*]

Originally Posted by GregBe

This is very intriguing to me. I have my sub on a Gramma already, my basement floor is wood over a crawlspace, so the decoupling really helps with the floor vibrations. I never thought about raising it up to help with the vertical room problems.

Here is my question...when you normally place a sub in a room, there are general rules of thumb, but it really takes experimentation. Is this the same when raising it up vertically. I saw Big Daddy's rule of 25%. My ceilings are 7.5 inches so I could easily figure out how high to go, but will this automatically be a good thing?

In my room, I get problems at 63 hz and 28 hz. It seems no matter where I put the sub or the seating, I have those two issues. I am wondering if fixing a vertical problem is the solution?

Here is a quick question GregBe, but perhaps where you sit is the problem due to standing wave modes? Do you have the same issue at 63Hz and 28Hz when you are sitting in another location within the room? Have you measured any peaks in other locations within the room too? Do you sit with your couch against the wall? I ask these questions because if your sub is actually located within a null, I don't think the height of your sub will substantially change your problem, as a null is a null. But changing where you sit may provide you with better bass response. The only other thing I think that may help would be adding a second sub to help with any standing wave issues.

[GregBe]

Originally Posted by forsberg21

Here is a quick question GregBe, but perhaps where you sit is the problem due to standing wave modes? Do you have the same issue at 63Hz and 28Hz when you are sitting in another location within the room? Have you measured any peaks in other locations within the room too? Do you sit with your couch against the wall? I ask these questions because if your sub is actually located within a null, I don't think the height of your sub will substantially change your problem, as a null is a null. But changing where you sit may provide you with better bass response. The only other thing I think that may help would be adding a second sub to help with any standing wave issues.

Hi forsberg...thanks for the help. It does happen in other seats, and when the sub is in different locations (it varies how bad it is), so I think it is room related. I am seriously considering a second PB10. I am able to equalize out the peaks, so the end result is good, but I always like to get as flat as I can before eq. I have found that the more I eq, the more headroom I lose.

[PoorSignal]

hi again.. I was wondering where is the white 2" foam pad located at Walmart?

[rmcdermid]

I believe it is usually near the crafts section. I found it with the pillow innards.

[Big Daddy]

Originally Posted by GregBe

This is very intriguing to me. I have my sub on a Gramma already, my basement floor is wood over a crawlspace, so the decoupling really helps with the floor vibrations. I never thought about raising it up to help with the vertical room problems.

Here is my question...when you normally place a sub in a room, there are general rules of thumb, but it really takes experimentation. Is this the same when raising it up vertically. I saw Big Daddy's rule of 25%. My ceilings are 7.5 inches so I could easily figure out how high to go, but will this automatically be a good thing?

In my room, I get problems at 63 hz and 28 hz. It seems no matter where I put the sub or the seating, I have those two issues. I am wondering if fixing a vertical problem is the solution?

Type of Room Modes
The sound waves interact with the room boundaries (walls, floor, and ceiling) and create standing waves or room modes. The standing waves are different between floor and ceiling, side walls, and end walls, unless any of these dimensions are the same (the worst kind of room is a perfect cube). There are three basic types of modes: axial, tangential, and oblique.

Axial Modes are the strongest and the most important, and the easiest to compute. Tangential Modes are about half as loud, and Oblique Modes are about a quarter as loud. They tend to be the least important, but if an oblique room mode occurs near another mode, that frequency may still be a problem. It is best to calculate all room modes to see where any overlap may be.

There are two types of axial modes: Horizontal (side walls & end walls) and Vertical (ceiling & floor).

Since a room can enforce a wave twice as long as it is, the first fundamental frequency can be calculated by using the formula: Standing Wave Frequency = Speed of Sound / 2*Distance Between Boundaries. If we multiply this frequency by 2, we will get the second harmonic frequency and so on. Usually it is necessary only to look at the first three or four modes because the crossover frequency for most home theater rooms are set around 80Hz-100Hz. Let us now calculate the axial modes for a 15ft W x 20ft L x 8ft H room. You can do similar calculations for your room to find the optimum position for your subwoofer.

Width
The first resonance frequency: 1130ftps / 2x15ft = 37.7Hz.
The second resonance frequency: 37.7 x 2 = 75.4HZ.
The third resonance frequency: 37.7 x 3 = 113.1HZ, ignore, because it is above the roll-off frequency of 85Hz.
The subwoofer has to be placed at least 25 percent away from the wall (15x0.25=3.75ft) because of the first harmonic, but that is the point of minimum of the second harmonic. Therefore, the subwoofer can be placed anywhere between 3.75ft (minimum of the first harmonic) and 7.5ft (minimum of the first harmonic) away from either wall.

Length
The first resonance frequency: 1130ftps / 2x20ft = 28.3Hz.
The second resonance frequency: 28.3 x 2 = 56.6HZ.
The third resonance frequency: 28.3 x 3 = 84.9HZ.
Since all three harmonics are below the roll-off frequency of 85Hz, we should place the subwoofer in a position that avoids the maximum and minimum of the three waves – at least 25% (20 x0.25=5ft) from either end walls.

Height
The first resonance frequency: 1130ftps / 2x8ft = 70.6Hz.
The second resonance frequency: 70.6 x 2 = 141.2HZ, ignore, because it is above the roll-off frequency of 85Hz.
The third resonance frequency: 70.6 x 3 = 211.8HZ, ignore, because it is above the roll-off frequency of 85Hz.
The vertical position for a subwoofer is anywhere in the middle half of the room, keeping it at least 25% (two) feet away from either the floor or ceiling.

So, a 15ft W x 20ft L x 8ft H room will have the smoothest bass if the subwoofer is located 2ft from the floor or 2ft from the ceiling (6ft from the floor), between 3.75ft and 7.5ft from the side walls, and 5 feet from the end walls. This is done to avoid the coupling of the subwoofer to room modes.