# Riser advice



## ivseenbetter (May 4, 2008)

I'm dragging this one up from the past. I find myself in a position where I need to build a riser for my room. I really like the design of this one due to the multi-purpose approach: 

http://www.audioholics.com/tweaks/do-it-yourself-diy-topics/multifunction-theater-seat-riser 

I am getting a dual MFW-15 setup so I think the bass-trap functionality will be useful. However, I have some questions on the build that I am hoping somebody can answer. 

1. Do those holes go on the sides or do they go on the front or back? 

2. From the pictures I am guessing that the carpeting goes over the holes...so you don't ever really see them?

3. I don't understand the need for the U-boats. I intend to place this over the existing carpet and pad in the room so will the U-boats not really be effective? Maybe I am confused on where they are placed. Do they go inside the structure or are they under it, touching the floor?

I’m sure I will have a bunch more questions as I get closer to doing this project but I guess I need these answered so that I can start the planning phase.

I posted the same questions on the audioholics forum and am awaiting answers there too. Hopefully somebody at one of these two sites can teach me! LOL


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## salvasol (Oct 31, 2006)

Since you're waiting for responses on Audioholics .... there will be no answer here :whistling: :bigsmile: :rofl2: :surrender:

I'm joking okay ... so don't be mad :T



ivseenbetter said:


> 1. Do those holes go on the sides or do they go on the front or back?


They'll go in the front; and if the raiser will not be against the back wall I read that you can leave the whole back side open to absorb better :yes:



> 2. From the pictures I am guessing that the carpeting goes over the holes...so you don't ever really see them? ...


That's correct.



> 3. I don't understand the need for the U-boats. I intend to place this over the existing carpet and pad in the room so will the U-boats not really be effective? Maybe I am confused on where they are placed. Do they go inside the structure or are they under it, touching the floor?


That is to decouple the riser from the floor ... you don't need them.
They'll go under the structure touching the floor (specially if is used in a basement to avoid that the moisture damage the wood).



> I’m sure I will have a bunch more questions as I get closer to doing this project but I guess I need these answered so that I can start the planning phase....


Not a problem ... there's always somebody willing to help :bigsmile:


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## akakillroy (Jul 9, 2008)

I just built something similar: HERE

The U-boats are to isolate the riser from the floor. Where are you placing this, wood floor, carpet floor, concrete?


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## andru (Aug 19, 2008)

Hi All
I really like your design carls64, it looks much the same as the auralex jpg.
But have you Guys considered that with a slight modification you could tune these risers into helmhotz resonators? You probably have... but i'll explain a little....
If you lengthed the neck of the resonator (the 2' hole) you can tune this baby for different frequencies. 
How could you lengthen it? 
One simple way would be to get some 6"x6", 6"x4" or 2"x4",
cut it into pieces to fit inside of the existing2" hole.
cut another 2" hole thru the new wood, clamp and glue on the inside of the riser so the holes line up... you could vary the thickness of the new timber to vary the effective frequency of each of the resonators.
This could allow you fo focus on troublesome room modes.
Effectively each hole or port is acoustically a separate resonator, even if they are not divided inside, interesting yes?

There are many helmholtz resonator calculation programs on the web... just google it.
It could make your riser a really valuable low frequency control device.... especially if you are lucky enogh to have the openings on or near a troublesome room mode or node.

happy trails
Andru


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## andru (Aug 19, 2008)

Hi All
I really like your design carls64, it looks much the same as the auralex jpg.
But have you Guys considered that with a slight modification you could tune these risers into helmhotz resonators? You probably have... but i'll explain a little....
If you lengthed the neck of the resonator (the 2' hole) you can tune this baby for different frequencies. 
How could you lengthen it? 
One simple way would be to get some 6"x6", 6"x4" or 2"x4",
cut it into pieces to fit inside of the existing2" hole.
cut another 2" hole through the new wood, clamp and glue on the inside of the riser so the holes line up... you could vary the thickness of the new timber to vary the effective frequency of each of the resonators.
This could allow you fo focus on troublesome room modes.
Effectively each hole or port is acoustically a separate resonator, even if they are not divided inside, interesting yes?

There are many Helmholtz resonator calculation programs on the web... just Google it.
It could make your riser a really valuable low frequency control device.... especially if you are lucky enough to have the openings on or near a troublesome room mode or node.

happy trails
Andru


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## ivseenbetter (May 4, 2008)

salvasol said:


> Since you're waiting for responses on Audioholics .... there will be no answer here :whistling: :bigsmile: :rofl2: :surrender:
> 
> I'm joking okay ... so don't be mad :T
> 
> ...


No worries! I'm not one to get mad...I get even! LOL..j/k. I appreciate your info. Unfortunately I won't be putting it up against a wall. It will basically be in the middle (maybe slightly back from center) so I guess I have to close off the back end...or at least put 2" holes in it. I have another question though, how are the holes in the front effective if I have a row of chairs in front of it? 



carls64 said:


> I just built something similar: HERE
> 
> The U-boats are to isolate the riser from the floor. Where are you placing this, wood floor, carpet floor, concrete?


The riser will be on carpet. The room is on my second floor (I know that isn't the best thing but the only option). So I don't need U-boats?


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## bpape (Sep 14, 2006)

Unless you know in advance what specific one frequency you're having problems with, building a Helmholz is much less desirable than the more broadband approach initially shown. If you can swing it, you can do the larger holes both in the front and the side depending on whether or not the room needs it, how much other broadband bass absorption you have, etc.

Bryan


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## ivseenbetter (May 4, 2008)

bpape said:


> Unless you know in advance what specific one frequency you're having problems with, building a Helmholz is much less desirable than the more broadband approach initially shown. If you can swing it, you can do the larger holes both in the front and the side depending on whether or not the room needs it, how much other broadband bass absorption you have, etc.
> 
> Bryan


I have none right now. I was planning on purchasing some of the products you provide through your company (thanks in large part to all the good feedback you receive on this site and the others I frequent) once I had everything settled in, but I haven't done anything as of yet since I don't have all the equipment installed as of now.


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## bpape (Sep 14, 2006)

Exactly. You'd be purely guessing. Just use the large openings as originally shown and get some good broadband control out of it. It's wider in scope and more efficient per unit area.

Bryan


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## salvasol (Oct 31, 2006)

ivseenbetter said:


> ... It will basically be in the middle (maybe slightly back from center) so I guess *I have to close off the back end...or at least put 2" holes in it*. I have another question though, how are the holes in the front effective if I have a row of chairs in front of it? ...


Hopefully Bryan can clarify this for us ... :hide: :bigsmile:


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## bpape (Sep 14, 2006)

If the rear of the riser is exposed to the room, then sure, use holes in that side too. Might as well get max benefit from it. 

As for the seating, well, the bass (some of it anyway) will go right through the seating and the riser is still going to provide additional absorption. 

Bryan


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## ivseenbetter (May 4, 2008)

bpape said:


> If the rear of the riser is exposed to the room, then sure, use holes in that side too. Might as well get max benefit from it.
> 
> As for the seating, well, the bass (some of it anyway) will go right through the seating and the riser is still going to provide additional absorption.
> 
> Bryan


Ok. Well, that seems pretty straight forward than. I just need to set up the front of the riser to be slightly "U" shaped to fit back of my front row seats. I think that would be pretty straight forward though. I'm going to wrap the whole thing in regular carpet. I believe somebody mentioned using vents or accoustically transparent covering but that is going to be too complex and/or expensive for me to do at this point. Maybe an upgrade for later down the road. How much of a difference would it make if I did decide to use that type of covering later down the road?


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## bpape (Sep 14, 2006)

Carpet will work just fine. Bass will pass right through it and the carpet will have the same HF absorption as if it was on the floor.

Bryan


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## ivseenbetter (May 4, 2008)

Thanks for the info Bryan. I will be drawing up the design of my room soon and submitting it to GIK so I can get some treatments done. I'm looking forward to working with you on that in the future.


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## bpape (Sep 14, 2006)

No problem at all. Happy to help. When you're ready, drop me a note and I'll be happy to take a look.

Bryan


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