Risers 101 - Page 8 - AVS Forum | Home Theater Discussions And Reviews
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post #211 of 229 Old 10-04-2016, 04:20 AM
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Most of what I have seen, is you need 6'6" minimum for a reclining row. I think I did mine closer to 6'9" and feel it is fine, but at 6' would definitely be too shallow.

Also, most of what I have read is that for a riser to act as a bass trap, the main dynamic is that bass pressure is mostly on the outer walls, so, if your riser is in the middle of the room, not sure how effective that would be.... this is all just based on recollection of what I have read, not any direct experience with this. If the rear of your riser is against the rear wall, then the rear edge might be good... but then, I would guess you might need even deeper than 6'6" to give room for the openings for the bass trap and the recliners.
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post #212 of 229 Old 10-04-2016, 05:14 AM
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I can certainly manage stretching the riser depth to 6'6". The riser will be in the back corner of the room so that shouldn't be a problem. So you're saying that I would just have to put some floor vent registers along the back edge of the riser? I thought there was also supposed to be some openings in the front face of the riser to absorb the bass.
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post #213 of 229 Old 10-04-2016, 09:53 PM
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Quote:
Originally Posted by BlueWRXPride View Post
I'm going to be starting to build a riser for my theater. The riser will be roughly 8'x6'. I'm not going to be making this an acoustically perfect room, but if I'm making a riser, I figure I might as well see if I can have it serve an acoustic purpose. What are some rough guidelines for size and placement of openings to give me a decent shot of having it act as a bass trap?

Also, is 6' deep enough to have room for a reclining rear row?
I believe 6'6" is the minimum recommended for a reclining rear row - that's what I went with and its a little tight, but do-able.

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post #214 of 229 Old 10-07-2016, 07:42 AM
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7' should be fine too, I'll just do that to be safe. How about cutouts necessary to try to make it a bass absorber?
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post #215 of 229 Old 08-15-2017, 10:23 AM
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Are these vents good for risers?

http://www.homedepot.com/p/Master-Fl...6X4W/100078188

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post #216 of 229 Old 08-15-2017, 10:26 AM
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Originally Posted by mpjmeyer View Post
No. You should pick something with more openess otherwise it's just like closing most of the cutout off again.
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post #217 of 229 Old 08-15-2017, 11:14 AM
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My pick, they will make them in just about any size, I like 4x48.




http://www.hvacquick.com/products/re...Linear-Grilles
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post #218 of 229 Old 08-16-2017, 05:19 AM
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Would only putting one vent along the back side of the riser be a waste? That would keep me from having to notch all the stringers on the adjoining wall since the vent would run perpendicular to them.
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post #219 of 229 Old 08-16-2017, 05:52 AM
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If you used two layers to cover your deck. then just set the blade on your circular saw to the thickness of the top and do a plunge cut for the cuts that run perpendicular to the stringers. The vent will fit right over the stringers, no notching required. When building a riser I either use two layers of 3/4 material or three layers of 5/8.
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post #220 of 229 Old 08-16-2017, 08:06 AM
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Is it OK to put 3 vents in the riser but the two on the side NOT in the back corners? Each vent is 4" x 36". I've got a sump pump hatch in the rear right corner so no room for the vent.

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post #221 of 229 Old 08-16-2017, 08:24 AM
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The bigger your vent area, the better it will work. Your riser is almost 15' wide, but the vent at the back is only 3' wide. I'd try to fit in more vent area.

In order for the vents to be effective, there has to be free airflow between the vents and the volume of air inside the riser. Make sure that the joists don't block the path from the vents to the volume of air inside the riser.
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post #222 of 229 Old 08-16-2017, 08:27 AM
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Quote:
Originally Posted by mpjmeyer View Post
Also, if they are going on top of the risers, you want something that is strong enough to support your weight if you step on it.
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post #223 of 229 Old 08-16-2017, 08:27 AM
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Would 3 layers of 1/2" be ok? I plan on doing 1/2" OSB - Green Glue - 1/2" OSB - Roofing Felt - final layer of 1/2" OSB

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post #224 of 229 Old 08-16-2017, 08:37 AM
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Quote:
Originally Posted by DaveClement View Post
The bigger your vent area, the better it will work. Your riser is almost 15' wide, but the vent at the back is only 3' wide. I'd try to fit in more vent area.

In order for the vents to be effective, there has to be free airflow between the vents and the volume of air inside the riser. Make sure that the joists don't block the path from the vents to the volume of air inside the riser.
The interior joists are 2 x 10s and the riser is made out of 2 x12s so there is some space underneath for airflow although the whole thing is filled with the pink insulation. I do not have any more real estate for any additional vents due to the location of the sump pump, unfortunately. The room is about 14' wide with all the wall treatments.

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Would 3 layers of 1/2" be ok? I plan on doing 1/2" OSB - Green Glue - 1/2" OSB - Roofing Felt - final layer of 1/2" OSB
Yes. I think the recommendation is actually 3 layers of 3/4" but most people only do two layers of 3/4" - I don't see why it would matter if you were at 3 layers or 2 layers to get to 1.5".
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post #225 of 229 Old 08-16-2017, 08:38 AM
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Three layers of 1/2" should be fine. At 1-1/2" it is equivalent to two layers of 3/4". I doubt that it would perform any better than two layers of 3/4", which would be less expensive and faster to install.

If you are going to the trouble of installing 3 layers, make them 3 layers of 5/8" and you will get 1-7/8", which will outperform the two layers of 3/4".

This may be splitting hairs, but if I were doing 3 layers with Green Glue in between two of the layers and roofing felt between the other two, I'd but the roofing felt between the bottom two layers and the Green Glue between the top two layers. That will give you the maximum damping on the surface that is closest to the room.
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post #226 of 229 Old 08-16-2017, 08:43 AM
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2 layers of 3/4" would be faster, but I already have most the 1/2" OSB in the theater ready to go. I would rather carry 3 more sheets of OSB downstairs instead of hauling 8 back up, returning them to the store and carrying 11 back down.

Would this be an ideal roofing felt for a riser?

http://www.homedepot.com/p/Warrior-R...14-0/100086691

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Last edited by mpjmeyer; 08-16-2017 at 09:15 AM.
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post #227 of 229 Old 08-16-2017, 10:05 AM
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That makes sense. I don't know about "ideal", but certainly acceptable. Roofing felt is pretty much a commodity item and any #30 felt should be just fine.
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post #228 of 229 Old 08-16-2017, 11:18 AM
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Any benefit to using 5/8 OSB + 1/4 plywood + 5/8 OSB? I've read several different references regarding sound waves using 2 different materials is supposed to outperform using only 1 type.
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post #229 of 229 Old 08-16-2017, 11:58 AM
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Quote:
Originally Posted by brazensol View Post
Any benefit to using 5/8 OSB + 1/4 plywood + 5/8 OSB? I've read several different references regarding sound waves using 2 different materials is supposed to outperform using only 1 type.
If you are trying to block sound, then yes. Three layers would be better than two. Unless you cover the entire floor, the reduction of sound transmission through the riser be irrelevant, since the sound would go through the areas of the floor without the riser.

What you are trying to accomplish with multiple layers of material on top of the riser is to make a solid floor that will not resonate. Mass is the main factor. Having two layers with damping in between would add additional benefit. I doubt that three layers would provide a measurable difference from two layers, assuming that the mass was the equivalent.
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