DIY Subwoofer Risers

[PoorSignal]

I have a couple of computer desks in my room and I believe the bass is going into under the desks and bouncing around. One is a corner type desk

would installing pyramid foam under the desk improve the sound? I was planning some under the horizontal surface of the desktop as well as some on the stringer running along the back of the desk

[Big Daddy]

Originally Posted by PoorSignal

I have a couple of computer desks in my room and I believe the bass is going into under the desks and bouncing around. One is a corner type desk

would installing pyramid foam under the desk improve the sound? I was planning some under the horizontal surface of the desktop as well as some on the stringer running along the back of the desk

Bass frequencies interact with the room boundaries and bounce around in many different direction. However, the wavelegnths of the bass frequencies are too long to create standing waves under the desks.

I suggest that you buy some corner traps and some wall treatment from The Foam Factory and treat your room. If you want to put foam under the desks, it doesn't hurt, but I doubt it very much that it will help your bass frequencies.

[GregBe]

Originally Posted by Big Daddy

Bass frequencies interact with the room boundaries and bounce around in many different direction. However, the wavelegnths of the bass frequencies are too long to create standing waves under the desks.

I suggest that you buy some corner traps and some wall treatment from The Foam Factory and treat your room. If you want to put foam under the desks, it doesn't hurt, but I doubt it very much that it will help your bass frequencies.

Thanks for the link. Many of the more "professional" room treatments, seem far more expensive. How do these do? I have no desire to overpay if I don't need to.

[Big Daddy]

Originally Posted by GregBe

Thanks for the link. Many of the more "professional" room treatments, seem far more expensive. How do these do? I have no desire to overpay if I don't need to.

You can't get better deals than The Foam Factory. You can try Parts Express, but I don't believe they will be cheaper.

[crazyBLUE]

Originally Posted by Big Daddy

You can't get better deals than The Foam Factory. You can try Parts Express, but I don't believe they will be cheaper.

I will second that ! Big Daddy is right on the foam factory . This is where I got my bass traps & acoustic wall treatments !

& I'm A wall treatment Nut !!!!!!!!

[rkolinski]

Originally Posted by Big Daddy

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.

I hope you won't think I'm DUMB (feel bad that I can't logically figure this out) but does this formula hold true for the placement of 2 similar subwoofers? Also, I've been debating - I love my home theater equipment but also enjoy listening to older formats (e.g., LP's). So do I need an LFE (.1 channel) or should I use my 2 subs as Left and Right channel subs? My 2 right and left channel towers certainly have good base but they do not go as low as my 2 powered subs. Any suggestions will be appreciated and forgive me in advance for not being able to figure this out??

Rich

[GregBe]

Originally Posted by crazyBLUE

I'm A wall treatment Nut !!!!!!!!

Yes you are
I like it. I might need to pick up some of that.

[Big Daddy]

Originally Posted by rkolinski

I hope you won't think I'm DUMB (feel bad that I can't logically figure this out) but does this formula hold true for the placement of 2 similar subwoofers? Also, I've been debating - I love my home theater equipment but also enjoy listening to older formats (e.g., LP's). So do I need an LFE (.1 channel) or should I use my 2 subs as Left and Right channel subs? My 2 right and left channel towers certainly have good base but they do not go as low as my 2 powered subs. Any suggestions will be appreciated and forgive me in advance for not being able to figure this out??

Rich

Remember that there are no dumb questions. There are only dumb answers.

Here is my dumb answer.

Set your front speakers to SMALL and let the subs handle the low frequency bass.

Extensive studies at the National Research Council of Canada and at Harmon International have indicated that the best options for two identical subwoofers are as follows:

1. Put one in the middle of the right wall and one in the middle of the left wall.
2. Put one in the middle of the front wall and one in the middle of the rear wall.
3. Put one sub in the front right corner and the other sub in the front left corner.
4. Put one in the front corner and the other in the corner in the the rear of the room.
5. If you have two different subs, put the larger sub with better lower frequency extension in the front corner and put the smaller sub close to your listening area. The sub up front will provide you with deeper and lower frequency bass and sub near you will provide you with upper frequency bass sound.

After placement, make sure that each sub is adjusted separately so that the level of bass from each one in your main listening area is approximately the same. You do not want one sub to completely over power the other one. Even though the subs are identical, they interact differently with the room boudaries, depending on their position.

[rkolinski]

Originally Posted by Big Daddy

Remember that there are no dumb questions. There are only dumb answers.

Here is my dumb answer.

Set your front speakers to SMALL and let the subs handle the low frequency bass.

Extensive studies at the National Research Council of Canada and at Harmon International have indicated that the best options for two identical subwoofers are as follows:

1. Put one in the middle of the right wall and one in the middle of the left wall.
2. Put one in the middle of the front wall and one in the middle of the rear wall.
3. Put one sub in the front right corner and the other sub in the front left corner.
4. Put one in the front corner and the other in the corner in the the rear of the room.
5. If you have two different subs, put the larger sub with better lower frequency extension in the front corner and put the smaller sub close to your listening area. The sub up front will provide you with deeper and lower frequency bass and sub near you will provide you with upper frequency bass sound.

After placement, make sure that each sub is adjusted separately so that the level of bass from each one in your main listening area is approximately the same. You do not want one sub to completely over power the other one. Even though the subs are identical, they interact differently with the room boudaries, depending on their position.

THANK YOU Big Daddy!! I appreciate your response! I did send you a personal message but which gave you more info on my room dimensions/the kind of home I live in but forgot to mention this post. And you didn't answer my question about whether or not I should have stereo subs or use Y connectors and have 2 subs for one LFE channel? Any advice would be appreciated and feel free to either post your answer here or to respond to my personal message to YOU! BTW - Like I said, I LOVE, LOVE, LOVE the way YOUR home theater looks!!

Rich

[crazyBLUE]

Originally Posted by GregBe

Yes you are
I like it. I might need to pick up some of that.

Thanks GregBe !!

Originally Posted by Big Daddy

Remember that there are no dumb questions. There are only dumb answers.

Here is my dumb answer.

Extensive studies at the National Research Council of Canada and at Harmon International have indicated that the best options for two identical subwoofers are as follows:

1. Put one in the middle of the right wall and one in the middle of the left wall.
2. Put one in the middle of the front wall and one in the middle of the rear wall.
3. Put one sub in the front right corner and the other sub in the front left corner.
4. Put one in the front corner and the other in the corner in the the rear of the room.
5. If you have two different subs, put the larger sub with better lower frequency extension in the front corner and put the smaller sub close to your listening area. The sub up front will provide you with deeper and lower frequency bass and sub near you will provide you with upper frequency bass sound.

After placement, make sure that each sub is adjusted separately so that the level of bass from each one in your main listening area is approximately the same. You do not want one sub to completely over power the other one. Even though the subs are identical, they interact differently with the room boudaries, depending on their position.

Man I have totally been bad & put them in the wrong place Big Daddy .

[erict]

Originally Posted by crazyBLUE

I will second that ! Big Daddy is right on the foam factory . This is where I got my bass traps & acoustic wall treatments !

& I'm A wall treatment Nut !!!!!!!!

Since I live near them the place is just amazing when you walk inside. The place is huge with foam form the floor to ceiling. They have tons of remnants and very cheap prices. It's a foam paradise.

[Big Daddy]

Originally Posted by rkolinski

THANK YOU Big Daddy!! I appreciate your response! I did send you a personal message but which gave you more info on my room dimensions/the kind of home I live in but forgot to mention this post. And you didn't answer my question about whether or not I should have stereo subs or use Y connectors and have 2 subs for one LFE channel? Any advice would be appreciated and feel free to either post your answer here or to respond to my personal message to YOU! BTW - Like I said, I LOVE, LOVE, LOVE the way YOUR home theater looks!!

Rich

Thanks for the compliment. I wish the power company would give me a break on the monthly electricity bill.

Use a Y adapter and connect both subs to the LFE out (sub out) of your receiver. Stereo subs became popular in the 1980's and early 1990's That was mainly because subwoofers and amplifiers had fixed crossovers around 150Hz to 250Hz. We know that bass sound becomes directional when the crossover is set so high.

Also, it may be helpful to read A Guide to Bass Management.

[Big Daddy]

Originally Posted by crazyBLUE

Thanks GregBe !!
Man I have totally been bad & put them in the wrong place Big Daddy .

Those rules do not apply to Crazy people.

[crazyBLUE]

Originally Posted by Big Daddy

Those rules do not apply to Crazy people.

Thank you for accepting the fact that I am Crazy .

[erict]

I set up my second sub today and decided to make another isolation/riser for it. I thought outside the box and did something I haven’t seen before. It's two 1/2 MDF with 3" foam sandwiched in between. And those are not the legs, it's just sitting on a table

DSCF0825 (Medium).JPG

[duneaholic]

And it can serve as a TV tray when not in use!

[crazyBLUE]

Originally Posted by erict

I set up my second sub today and decided to make another isolation/riser for it. I thought outside the box and did something I haven’t seen before. It's two 1/2 MDF with 3" foam sandwiched in between. And those are not the legs, it's just sitting on a table

Attachment 7337

Nice job erict ~ Unique & original !!

I hope it is sturdy enough to hold the sub , is it ?

[erict]

Originally Posted by crazyBLUE

Nice job erict ~ Unique & original !!

I hope it is sturdy enough to hold the sub , is it ?

Why yes it sure is This sub only weighs 30lb and doesn't even compress it at all. It's amazing how stiff it became with six pieces of foam then putting the 1/2 MDF on top. It really helps distribute the weight well. I got an immediate 2db increase and a tighter bass response from it. I put it in the opposite corner behind my over sized chair and really works out well. Both of my subs are out of sight in my room. Just wanted to try something different

[crazyBLUE]

Originally Posted by erict

Why yes it sure is This sub only weighs 30lb and doesn't even compress it at all. It's amazing how stiff it became with six pieces of foam then putting the 1/2 MDF on top. It really helps distribute the weight well. I got an immediate 2db increase and a tighter bass response from it. I put it in the opposite corner behind my over sized chair and really works out well. Both of my subs are out of sight in my room. Just wanted to try something different

way totally cool on the outcome !

[erict]

Originally Posted by crazyBLUE

way totally cool on the outcome !

Yea I'm pretty satisfied on the outcome. The two different subs blend together well now.