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post #1 of 191 Old 04-13-2014, 04:47 PM - Thread Starter
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I am ready to begin building my riser! It will be 13’ wide (wall to wall) by 5’ deep. Height is 12” inches with 6” steps similar to this one done by Bass Addict:



I’ve seen a few different build approaches, so have a few questions going in:

1. I was initially thinking I’d use 2x12 boards, but now wonder about building with 2x6 for a “bottom half” and then adding a second 2x6 section on top of it and attaching the two with glue/brackets. I wonder if there is a preferred way to reduce noise, complexity, etc. Planning on using 3/4” plywood on top.

2. Should I attach the rear and side boards to the walls, or just fit it in there nice and snug?

3. This is a second level media room, so do I need to add underlayment since the riser is on top of the subfloor and not a concrete foundation? Also, I see some risers built on top of existing carpet, which I have but had assumed I needed to pull it up.

Thanks for your input.
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post #2 of 191 Old 04-13-2014, 05:25 PM
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If you want to keep it simple build a perimeter box of 2x12s hang 2x8s or 2x10 stringers then push it back into place. Add steps in front of the box instead of cutting notches and make them giant sized for a grand feeling. I dislike notch steps as I think they can be dangerous in the dark. You said 5 ft deep, I assume you will only have upright seating. Recliners won't fit.

With a subfloor you can skip the underlayment.

to keep it quiet use at least two layers of 3/4 decking and stuff with loose fill insulation, If you plan to have a lot of guests don't forget step lights.

Pictures from Rawlinsway in no particular order. You can see I built it in two parts, the first is a 12 ft wide piece, because that was how long the lumber was and then a filler for the rest of the width.










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post #3 of 191 Old 04-13-2014, 09:08 PM - Thread Starter
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Thanks for the reply and the pics. I wonder why you recommend hanging 2x10 stringer vs using 2x12. Cost? I would think 2x12 would give more stability.

My wife and I like the look of notched steps since we have limited space in the room. I was planning to have step lights and/or rope lighting underneath the decking overhang. Is that not sufficient from safety standpoint?

Final thing you said that worries me. I was planning on getting the Paliser Bullets. Their specs show they an overall depth of 41" plus another 4" clearance from the wall for reclining. I figure if the decking is 60" deep, then that was going to give me about 15" from the front of the seat to the edge of the riser. I guess 15" isn't a huge amount of space (true, the leg rests would hang over the edge when reclined), but I thought it would be sufficient. No?
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post #4 of 191 Old 04-13-2014, 10:17 PM
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Using less expensive wood for the stringers offers several advantages.

1) cost
2) Easy of construction, if the floor is uneven you just get the perimeter to sit reasonably flat and whatever undulations exist in the floor won't matter.
3) But the trump card is that it is based on Erskine group design principles of turning the riser into a bass trap. For that to work the entire riser needs to function as a connected volume with insulation, building the stringers shorter than the perimeter acheives that. Of course you need to pop in some vents at the riser wall intersections.

Stability, just add the supports as shown in my picture.

reclining seating requires 6 1/2 ft of riser depth. First the front row is pushed back tight to the front edge, and when they recline the seat comes back a bit. Second your legs and feet stick well past the end of the foot rest. Got to a store with a tape measure and check it out. I think I positioned the chair at 65 inches for this picture.

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post #5 of 191 Old 04-14-2014, 09:44 PM - Thread Starter
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Thanks for the helpful explanation as always. One clarification
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Originally Posted by BIGmouthinDC View Post

Of course you need to pop in some vents at the riser wall intersections.

You lost me there. Can you elaborate?

Perhaps related, why not attach the perimeter to the wall?
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post #6 of 191 Old 04-14-2014, 10:19 PM
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they are in the pictures. Standing base waves exert their maximum pressure at the boundaries of the room, the vents act to reduce the standing waves.

Stages are isolated, Risers can be attached. but I wouldn't use the wall as a way of holding up the riser.
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post #7 of 191 Old 04-15-2014, 09:40 AM
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So how do you know where to place the vents if you wanted your riser to function as a bass trap ?

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post #8 of 191 Old 04-15-2014, 10:14 AM
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Hire the Erskine group for a design.
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post #9 of 191 Old 04-15-2014, 10:50 AM
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Quote:
Originally Posted by BIGmouthinDC View Post

Hire the Erskine group for a design.

I should have asked the question more clearly; my fault. I meant to ask what is the alternative to hiring Erksine group ?

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post #10 of 191 Old 04-15-2014, 11:35 AM
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You look at some of his completed theater designs and then without knowing all the details of the actual science you copy it crossing your fingers that it just might actually work.
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post #11 of 191 Old 04-15-2014, 11:57 AM - Thread Starter
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Doing a little research and saw someone say that bass traps have to be tuned to the room or could make things worse. Yikes. Perhaps I should just be happy with a riser that has 2x8 stringers for their lower cost and ease of use, fill it with insulation, and not go down the path of bass traps for my modest media room...
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post #12 of 191 Old 04-15-2014, 12:03 PM
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I guess I'm asking how to figure it out?

Is it like calculating port tune on a vented sub ? Or different?

I originally abandoned the idea due to lack of understanding, I think I want to know more than I want a bass trap riser actually.

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post #13 of 191 Old 04-15-2014, 12:53 PM
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It's akin to port tuning a sub, but more complicated. You've seen reference to port length compensation, or how the port length from one calculator or another is wrong or what have you? There are various correction factors that must be determined for port area and length based on the grill and the proximity of nearby structures, like the wall. Then there are volume correction factors based on insulation and proportions because the theoretical models assume an empty sphere. These sorts of corrections are easy enough with subs, but when you quadruple the volume and don't get a second chance at tuning it, the corrections are more important.

Dennis says there are only two designers he is aware of who have worked out the details and verified the models enough to offer the service professionally. The details are intellectual property; trade secrets, if you will.
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post #14 of 191 Old 04-15-2014, 01:07 PM
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Would be an interesting community project to figure all that out. ^. More minds is better than one. Thanks for great response!
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post #15 of 191 Old 04-15-2014, 02:54 PM - Thread Starter
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back to basics... for those of us who don't want a highly tuned bass trap but just a nice riser, do we want to build a riser "functioning as a connected volume filled with insulation" if we aren't planning to tune it or make vents?
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post #16 of 191 Old 04-15-2014, 03:14 PM
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It is the easiest to build and wire.
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post #17 of 191 Old 04-16-2014, 01:33 PM - Thread Starter
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Thanks. I did some more research and came across another idea I wanted to ask the experts about...

I saw someone put their sub on the riser behind their back row. As they built their riser, they included a box filled with sand on which the sub could sit. From the pics, the box was presumably isolated from the rest of the riser.

I like the idea of placing my sub in this way. Do I need to build this sand box before I do? What are the problems if I don't? My alternative is just to sit it on the floor.
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post #18 of 191 Old 04-16-2014, 02:04 PM
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If you want to provide sand for your subs, do it the same way you would do sand in a stage for a sub: away from the walls and not on a second floor (without consulting an engineer). That's what I've done.



I was sure I had more and better pictures, but I don't. This is 6 0.5 cubic foot bags of sand in a cavity made by two 16" bays of my riser. I scabbed on some scrap OSB to keep the sand from pouring out under the joist, since the rim is 2x12, but the others are 2x8, then I lined with 6mil plastic - stapled in place, then started trucking sand. This cavity was 8' long (nominal) and needed about 16 or 17 cubic feet of sand (some 33 bags, IIRC)
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post #19 of 191 Old 04-16-2014, 08:41 PM - Thread Starter
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I think I follow. However, this is a second floor room, and I was thinking about something like this to keep the weight down.
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Originally Posted by Spaceman View Post







The sand box is isolated from the rest of the riser, then covered with separate decking piece, then carpet for the sub to be placed on top.

I have 13x13 feet room, so enough for one row of seats but not two. So I do like the idea of moving the row up a bit and placing the sub behind on the riser. My question is 1) is something like the above sufficient and 2) is it critical? Like I said my alternative is to put it on the floor or on the riser with no sand.
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post #20 of 191 Old 04-17-2014, 06:50 AM
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I can't verify it with math, but to me that much sand is insufficient. I'd skip it.
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post #21 of 191 Old 04-17-2014, 08:45 AM - Thread Starter
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Insufficient so not worth the trouble? If a sand box in the riser like above is better than the floor, then I'll do it.

If not, I still wonder what everyone's opinions are about putting the sub on the riser vs the floor?

Riser will be 2x12 with 2x8 joists, two layers of decking, and stuffed with insulation. Can't say the same about the floor.
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post #22 of 191 Old 04-17-2014, 09:34 AM
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Not worth it to me... Others will disagree. That's fine. I'm sure the benefits vary with mass of sand, but I'm not sure about the shape of the curve.

I don't see much difference between a sub on the floor of a second floor room versus a similarly constructed riser. I'd go with the location that lead to the smoothest/best response and ignore the impacts of floor construction.
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post #23 of 191 Old 04-17-2014, 10:55 AM - Thread Starter
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Thanks for your thoughts! I'd love to hear others' opinions/experiences on sub placed on floor vs riser with/without sand box before I begin cutting wood...
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post #24 of 191 Old 04-18-2014, 07:07 AM - Thread Starter
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Big, do you have an opinion?
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post #25 of 191 Old 04-18-2014, 09:59 AM
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Quote:
Originally Posted by HopefulFred View Post

It's akin to port tuning a sub, but more complicated. You've seen reference to port length compensation, or how the port length from one calculator or another is wrong or what have you? There are various correction factors that must be determined for port area and length based on the grill and the proximity of nearby structures, like the wall. Then there are volume correction factors based on insulation and proportions because the theoretical models assume an empty sphere. These sorts of corrections are easy enough with subs, but when you quadruple the volume and don't get a second chance at tuning it, the corrections are more important.

Dennis says there are only two designers he is aware of who have worked out the details and verified the models enough to offer the service professionally. The details are intellectual property; trade secrets, if you will.

Looking at implementations of risers built and shown on AVS (some Erskine designs and others not) makes it pretty clear to me how the physics work.....and no doubt clear to others. I understand that Erskine Group drawings are copyrighted but I do not believe they have a patent. Clients may be violating a non-disclosure agreement by posting information....I have no idea.

BigMouthinDC has in my opinion given you great advice so far and I thing you should take it. If you are looking for suggestions on vents, I'll give you mine. The vents have a lip over the carpet of 3/4" from the hole you cut in the plywood all around. I'd leave 1" between the vent and the base molding (so 1" + 3/4" + base thickness away from the wall where you cut the hole) Get a 4" wide vent. For your size of a riser, I suggest a 30" vent in the back centered along the wall, and for the sides I suggest a 20-24" vent on each side. I'd put the side vents just touching the 1/2 way point on the riser and extending the 20 or 24" toward the back wall. (20" is probably the better choice. You could also go 16" if you want.

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post #26 of 191 Old 04-30-2014, 10:34 AM
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I'd guess any DIY riser that had grates and 4x10 cut outs stuffed with pink fluffy would be somewhat effective at capturing bass and diminishing room problems, just make sure the openings are near the outer edges of the room like walls and corners. If you mess up the port a little on a DIY sub it still works fine, just the tuning is a little off from ideal but the port still works fine. I'd imagine this was much the same thing. Even less ideal would work better than none.

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post #27 of 191 Old 04-30-2014, 12:05 PM
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That's true to some extent. The concern that Dennis has expressed in the past is that the tune of the absorber may shift to a frequency that needs no absorption or is a null at the listening position - in this case you've made things worse. To some extent the insulation mitigates the negative outcomes by broadening the Q, but I don't know the extent.
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post #28 of 191 Old 04-30-2014, 09:05 PM
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Quote:
Originally Posted by HopefulFred View Post

That's true to some extent. The concern that Dennis has expressed in the past is that the tune of the absorber may shift to a frequency that needs no absorption or is a null at the listening position - in this case you've made things worse. To some extent the insulation mitigates the negative outcomes by broadening the Q, but I don't know the extent.

My plan is to take readings after the room is completed with the holes sealed in the riser. I'll then measure with them unsealed. I'll also likely take readings with different combinations of blocked, open, partially blocked etc, to better understand how it is affecting the room. I'll post my findings. I suspect that through empirical data I can create a function.

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post #29 of 191 Old 04-30-2014, 10:22 PM
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Quote:
Originally Posted by Jeff in Canada View Post

My plan is to take readings after the room is completed with the holes sealed in the riser. I'll then measure with them unsealed. I'll also likely take readings with different combinations of blocked, open, partially blocked etc, to better understand how it is affecting the room. I'll post my findings. I suspect that through empirical data I can create a function.

Excellent.
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post #30 of 191 Old 05-01-2014, 06:23 AM
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Quote:
Originally Posted by Jeff in Canada View Post

My plan is to take readings after the room is completed with the holes sealed in the riser. I'll then measure with them unsealed. I'll also likely take readings with different combinations of blocked, open, partially blocked etc, to better understand how it is affecting the room. I'll post my findings. I suspect that through empirical data I can create a function.

Trial and error approach... I love it. Don't let me miss the results when you do it; I am very interested.

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