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post #31 of 239 Old 05-01-2014, 06:40 AM
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There was actually another builder who did the same trial and error approach and was basically pleased with the results with the vents open, Can't remember the exact thread. Maybe somebody does. Just another factoid, Edison used the trial and error method extensively and that is how he developed the light bulb.
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post #32 of 239 Old 05-01-2014, 08:24 AM
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Originally Posted by BIGmouthinDC View Post

There was actually another builder who did the same trial and error approach and was basically pleased with the results with the vents open, Can't remember the exact thread. Maybe somebody does. Just another factoid, Edison used the trial and error method extensively and that is how he developed the light bulb.

My thought would be to start taking readings once I have all of the hard surfaces in place and prior to stuffing my columns making them bass traps and putting in my corner traps. I'll try to see what the optimum is at that point, then begin to add elements (column bass traps, then corner bass traps) and see if it changes things. I suspect it should not change the optimum, but might simply affect the amplitude of the response curve.
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post #33 of 239 Old 05-01-2014, 09:45 AM
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I used a similar technique to Big for the construction of my riser. I remember reading the thread he referenced as well, and the forum member posted measurements of the room with the vents closed off and opened up, the difference significantly favored the vents being open. He didn't do any fancy calculations, he punched as many vents in as he could fit without endandering the structural integrity of the decking. If you have enough holes/vents at the periphery of your riser, it will act in a relatively broad-band fashion just like corner trapping. Until you have everything situated in a completed room, I think it would be hard to ideally tune a riser anyway if you were aiming for more narrow band control. I think it makes more sense to get as many holes in the riser as you can, complete the room, and move subs around to attenuate any nasty nulls.
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post #34 of 239 Old 05-01-2014, 10:06 AM
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In a PM I asked Stew if he still had Home Theater Builder magazine July 2003 and September 2003 article's, unfortunately no.
https://www.avsforum.com/t/453984/home-theater-builder-magazine-article-on-risers#post_4452058
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post #35 of 239 Old 05-01-2014, 10:10 AM
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Originally Posted by uscmatt99 View Post

I used a similar technique to Big for the construction of my riser. I remember reading the thread he referenced as well, and the forum member posted measurements of the room with the vents closed off and opened up, the difference significantly favored the vents being open. He didn't do any fancy calculations, he punched as many vents in as he could fit without endandering the structural integrity of the decking. If you have enough holes/vents at the periphery of your riser, it will act in a relatively broad-band fashion just like corner trapping. Until you have everything situated in a completed room, I think it would be hard to ideally tune a riser anyway if you were aiming for more narrow band control. I think it makes more sense to get as many holes in the riser as you can, complete the room, and move subs around to attenuate any nasty nulls.

Good points. I'm interested in understanding the size of the vents given my size of riser and how I can impact the room response. My vents are not ones that open or close. I'm talking about screwing a couple layers of plywood over the holes, partially & fully to see if I can affect the room response and if so, how does it move the response. My vents are sized already. 4'x36" in the back and 4"x30" on each side. If I see that it is better for the sides to be 24" for some reason, I can either block them from underneath or invest in new vents and block it up. If I see a trend as I move the sides from 16 to 20 to 24 to 30 and the room keeps getting better, I may cut open to 36" and buy a new vent if I get what I want. It is likely my mistake for buying the vents up front even before I was done the riser, but I'll eat the cost on them if it is worth it to me.

I'll know better as I take measurements and overlay the graphs.

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post #36 of 239 Old 05-01-2014, 10:14 AM
 
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Quote:
Originally Posted by mtbdudex View Post

In a PM I asked Stew if he still had Home Theater Builder magazine July 2003 and September 2003 article's, unfortunately no.
https://www.avsforum.com/t/453984/home-theater-builder-magazine-article-on-risers#post_4452058







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post #37 of 239 Old 05-01-2014, 10:17 AM
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Originally Posted by Jeff in Canada View Post


I'll know better as I take measurements and overlay the graphs.

 

Hi Jeff,

 

Any thoughts on when you'll do this work?  Are you thinking over the next 3-4 weeks, 3-4 months, or 3-4 years :-) 

 

I am still at least (being optimistic) a month away from needing to work on a Riser, but I am somewhat limited in my bass trap placement, so, this could be a fantastic option for me.  I don't have the knowledge, skills, or equipment to do any of the testing you have outlined.  I appreciate you taking it on!

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post #38 of 239 Old 05-01-2014, 10:27 AM
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Originally Posted by Jeff in Canada View Post

Good points. I'm interested in understanding the size of the vents given my size of riser and how I can impact the room response. My vents are not ones that open or close. I'm talking about screwing a couple layers of plywood over the holes, partially & fully to see if I can affect the room response and if so, how does it move the response. My vents are sized already. 4'x36" in the back and 4"x30" on each side. If I see that it is better for the sides to be 24" for some reason, I can either block them from underneath or invest in new vents and block it up. If I see a trend as I move the sides from 16 to 20 to 24 to 30 and the room keeps getting better, I may cut open to 36" and buy a new vent if I get what I want. It is likely my mistake for buying the vents up front even before I was done the riser, but I'll eat the cost on them if it is worth it to me.

I'll know better as I take measurements and overlay the graphs.

I look forward to your findings. It will be interesting to see if the behavior of the riser trap becomes more broad band as you open up the vents more and more. I can see how it would conceivably be more narrow band with only some vents open, especially if you favored one area of the riser. I peeked through your build thread, and you've got a really nice room coming along, great work!
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post #39 of 239 Old 05-01-2014, 10:31 AM
 
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I'm planning to experiment, and I am the type that's not afraid to tackle the unknown or undo or redo a mistake- but my project has not even begun. I've got twins due any day now, and we won't break ground until the end of the summer at this point, and I'll be doing a remodel of the home at the same time which has a priority (certain areas) over the theater so I'm about a year away at least- and probable more like 2 years away. I am really interested in his results though and wish to follow and bookmark it- I can't afford a professional plan to get one but I'd like it. I'd also like to understand it even just a little, because I am like that. I imagine plugging a hole isn't too hard to do either if it's not a good effect. Experimenting before the carpet is installed on the riser makes it super easy to conceal too.
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post #40 of 239 Old 05-01-2014, 10:45 AM
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Thx Mfusick for posting that, was it you by chance who bought those issues from Stu?

Ahh, kids and priorities.....been there and still there.....

Here's 5 years ago me tearing up my riser to add vents....and my then very young kids playing while I was working....used to get them to bed and work in the HT till 1am, or go to bed and get up at 3am before leaving to work just to get 2-3 hours work in a day...
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post #41 of 239 Old 05-01-2014, 10:50 AM
 
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No I was a subscriber but I think I lost all my magazines from back in the day. I might have them in storage. But to answer your question I got those from another AVS member via email. It seemed appropriate I posted them up for you. biggrin.gif
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post #42 of 239 Old 05-01-2014, 12:03 PM
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Quote:
Originally Posted by kmhvball View Post

Hi Jeff,

Any thoughts on when you'll do this work?  Are you thinking over the next 3-4 weeks, 3-4 months, or 3-4 years :-) 

I am still at least (being optimistic) a month away from needing to work on a Riser, but I am somewhat limited in my bass trap placement, so, this could be a fantastic option for me.  I don't have the knowledge, skills, or equipment to do any of the testing you have outlined.  I appreciate you taking it on!

I have an Omnimic. My trimmer just texted me and told me he will be at my house Monday to start fitting for panels. So, I'd think 3-4 weeks I'll have measurements.

I'll be ordering an INuke 6000DSP from Parts Express as soon as they are in stock for subs 3-4. It should all be a go before 4 weeks though.
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post #43 of 239 Old 05-01-2014, 04:53 PM
 
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post #44 of 239 Old 05-01-2014, 07:52 PM
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interesting, but the openings aren't along the room boundaries.
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post #45 of 239 Old 05-01-2014, 08:16 PM
 
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interesting, but the openings aren't along the room boundaries.

I had considered this myself; I was under the impression that the opening are best close the walls and corners because that is where the trouble is, and where what you want to absorb begins or is strongest.
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post #46 of 239 Old 05-01-2014, 08:37 PM
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I had considered this myself; I was under the impression that the opening are best close the walls and corners because that is where the trouble is, and where what you want to absorb begins or is strongest.

On the back wall (centered) I have a 36" vent @ 3-7" off off the wall. The two on the side are 30" long @ 3-7" from the wall and are at the 16 - 46" from the back wall.

If I need to get those right up to the corner I can always cut 12 more inches out and by 42" long grills.

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post #47 of 239 Old 05-01-2014, 09:03 PM
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IF the riser is going to function as a resonant absorber (which is what the premise here is, though other efforts have been made) the opening should be at the high pressure zone of the offending standing wave. Most often, the strongest resonances (and therefore most offending) are the axial modes. The lowest will generally be the first axial length mode, so that mode and its multiples will have high-pressure zones at both the front and rear walls of the room. To affect improvement in those modal resonances, the vents should be all the way at the rear wall. If the axial width mode is a problem (which it could easily be as well) - the first axial width mode will usually be below 80Hz, and at that modal frequency response will vary wildly across a single row of seats (assuming one subwoofer, or subwoofers not distributed left to right across the room) - in that case vents along the left and right walls are optimally positioned to absorb.

(Sorry for the poorly constructed response, I hope it's decipherable)
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post #48 of 239 Old 05-01-2014, 09:18 PM
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IF the riser is going to function as a resonant absorber (which is what the premise here is, though other efforts have been made) the opening should be at the high pressure zone of the offending standing wave. Most often, the strongest resonances (and therefore most offending) are the axial modes. The lowest will generally be the first axial length mode, so that mode and its multiples will have high-pressure zones at both the front and rear walls of the room. To affect improvement in those modal resonances, the vents should be all the way at the rear wall. If the axial width mode is a problem (which it could easily be as well) - the first axial width mode will usually be below 80Hz, and at that modal frequency response will vary wildly across a single row of seats (assuming one subwoofer, or subwoofers not distributed left to right across the room) - in that case vents along the left and right walls are optimally positioned to absorb.

(Sorry for the poorly constructed response, I hope it's decipherable)

I am going to have 4 subs and two will be placed in the back corner. I didn't want the sub to sit straddling a vent....so I moved it to what will be the edge of the sub. I am debating about putting two 14" long vents along the back wall in the corners. That would leave about 8-10 inches between vent openings. On the carpet about 6-8" between grills. (meeting at 90 degrees)

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post #49 of 239 Old 05-02-2014, 11:55 AM
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I'm planning to experiment, and I am the type that's not afraid to tackle the unknown or undo or redo a mistake- but my project has not even begun. I've got twins due any day now, and we won't break ground until the end of the summer at this point, and I'll be doing a remodel of the home at the same time which has a priority (certain areas) over the theater so I'm about a year away at least- and probable more like 2 years away. I am really interested in his results though and wish to follow and bookmark it- I can't afford a professional plan to get one but I'd like it. I'd also like to understand it even just a little, because I am like that. I imagine plugging a hole isn't too hard to do either if it's not a good effect. Experimenting before the carpet is installed on the riser makes it super easy to conceal too.

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https://www.avsforum.com/t/1527883/mocha-theater-construction/0_100#post_24672041

Interesting design here ^ for a bass trap riser.

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I had considered this myself; I was under the impression that the opening are best close the walls and corners because that is where the trouble is, and where what you want to absorb begins or is strongest.
Based on your room design the riser will not be against the back wall unless you changed your mind and are going with bar outside the theater now. we can discuss it in your thread
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post #50 of 239 Old 05-02-2014, 12:05 PM
 
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I had imagined this, and I had not planned to do a bass trap riser if this is the case. I'll be better off doing something more effective in the walls and corners I think. The option I had was put the entire back area on a small riser, including the bar. That was the only way I was going to try it. Seems like too much wood though.
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post #51 of 239 Old 05-03-2014, 09:47 AM
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would the riser designed like this be used in conjunction with corner traps - would both corner traps and a vented riser be needed - asking for my soon to start build but thought it would be a good questions here rather than start a new thread - i had thought that doing corners would be the way to go but this gives me something else to consider -
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post #52 of 239 Old 05-03-2014, 10:22 AM
 
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would the riser designed like this be used in conjunction with corner traps - would both corner traps and a vented riser be needed - asking for my soon to start build but thought it would be a good questions here rather than start a new thread - i had thought that doing corners would be the way to go but this gives me something else to consider -

You could use corner traps sure. They are different so no reason you need to do only one or the other.

I think a lot of people use the corner traps in the front corners, it lends itself well to a nice screen wall look with the angles on the sides of the screen which looks attractive. I'd look for an alternate treatment plan in the back myself probably, but that might be more of my design layout. I plan to do a mini corner trap in one corner on the floor and place the sub up above that elevated - placement of subs has a lot to do with what corner traps seek to achieve. Place your subs properly and you won't need them much. Multiple locations is a great option for smooth bass response in the listening position. Most tend to place all theirs subs in the front hidden behind the screen because it's easy and it's aesthetically pleasing. Packing in tons of high powered subs in one location can provide lots of bass, but not smooth bass. Take those same 4 subwoofers and spread them out around the room and you'll get a better result I think. Of coarse all this happens to be dependent on the room itself, the subs themselves, the frequency we are talking about etc.. etc.. but in general you'll benefit from good placement which is often multiple locations.

Ideally if you had 4 subs you would want only 2 of them behind the screen or on the front wall (or corners) and one of them you should elevate up near the ceiling and the other on the floor. The other two subs you'd put in the back of the room, opposite, one on the floor and one on the ceiling. That's going to sound best in the center of the room (listening positions) Not so easy to do for some people.

Without measuring your room and calibrating for it - then it's hard to tell you from a design stage specifics about what exactly you should do without a degree in sound and physics. Most just take the simple broad approach with fingers crossed, and then once the room is done you can calibrate the room and further treat it or modify for optimal results. It's kind of like a 2 stage effort if you really want the best results. You can't just plan the room and treat it from a theoretical perspective and then never got back and measure or calibrate afterwards and get the best results, and at the same time you can't do nothing and treat nothing all through the design and construction phase and then only post project completion attempt to calibrate either. You really need both for a good result. You can do some things with EQ and crossovers, and you can do some things with placement of speakers (pull them off the wall etc) to some degree but it's not a fix all effect.

I think 80hz requires the speakers be about 3 feet from the wall to prevent major issues, so crossing over LCR at 80hz to subs and putting them behind a 3 foot false screen wall is not exactly a bad idea. There is some solid science behind that. Building a baffle wall for them (or even baffle plates) can also provide some benefits. But for bass- it's hard to treat and it's very room dependent. Adding in extra large furniture or changing the dimensions of the room (floor, ceiling, walls) even just a little bit in reality from theory can vary the results. There is only so much theory you can apply- at some point you'll need to look at the reality of the room and measure it to really get an accurate picture and perfect result.

For a noob that doesn't have a science degree (like me) and can't afford professional plans I think the best solutions is to do as much research as you can, and plan as much treatment and beneficial design elements into your design from the begining focusing on those treatments and design elements that provide the most bang for you buck - and are a broad solution to common issues and not so pinpointed that they might not apply. There is some common issues that most rooms face, focus on treating those and trying to get 80% of the way there and you can always learn to calibrate and measure your room after the fact and really narrow in on the last remaining treatments.

Punching some holes in the corners of your riser seems pretty easy to me, and they could be closed up if the result is not good pretty easy too. Corner traps are another area that seems pretty easy to do if you plan from it from the beginning. There is a lot of other bass treatments available to handle the waves too- so you might want to check out some of those in the big thread. A lot of the best solutions incorporate multiple different solutions that all work in synergy with each other. Good luck.
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post #53 of 239 Old 05-03-2014, 10:52 AM
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thanks for the great response - to me i would like to do what i can without going overboard and I should be able to do traps in the front upper corners but will have my av gear on one side and movies on the other in the lower half - i was planning on traps in the back and may just add vents in the riser as well and see what happens - i am ok with crossing my fingers :-)
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post #54 of 239 Old 05-03-2014, 03:11 PM
 
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post #55 of 239 Old 05-04-2014, 07:44 AM
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So how do you tune or figure out where to tune, a riser? I plan to build a riser in my 17ft by 14ft room, and will definitely include vents in the two rear corners, in addition to where the top of the riser meets the rear wall, and where each side meets the rear and side walls. Is that a good plan?
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post #56 of 239 Old 05-04-2014, 08:29 AM
 
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So how do you tune or figure out where to tune, a riser? I plan to build a riser in my 17ft by 14ft room, and will definitely include vents in the two rear corners, in addition to where the top of the riser meets the rear wall, and where each side meets the rear and side walls. Is that a good plan?

This is the million dollar question.

You could consider a broadband bass trap design that uses a grate along the edges/room boundaries. Might be more consistent and predictable this way, if you try to tune the riser and port opening to handle a certain specific frequency you really need to know the specific problem frequency you are treating and tune the design to that. That's easier said than done I think.
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post #57 of 239 Old 05-04-2014, 08:36 AM
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I'm building a HT in a 64'x15'x9' basement great room, it will occupy 26' of one end. The riser will be 12'x9'x10" placed in the center with 2 33-35" walkways each side. Can I ask my question here or start a separate thread for riser build??

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Originally Posted by udtsealeod View Post

I'm building a HT in a 64'x15'x9' basement great room, it will occupy 26' of one end. The riser will be 12'x9'x10" placed in the center with 2 33-35" walkways each side. Can I ask my question here or start a separate thread for riser build??

You already posted ^ so might as well just asked your question in the first post wink.gif
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post #59 of 239 Old 05-04-2014, 02:10 PM
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Diagram of HT location within great room and riser within HT. Would like recommendation on my riser build 12'x9'x10". A 3-chair curved seating arrangement (6' length) will seat in front of a 36" high 2' counter with four chairs (5' length) with a 1' step = 12'.
What should be placed under the riser to dampen sound?
Any special insulation between stringer?
Any damping between 2-3/4" plywood?
Carpet covering riser with lighting and outlets. Is a pad required?

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post #60 of 239 Old 05-04-2014, 02:53 PM
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Quote:
Originally Posted by udtsealeod View Post



Diagram of HT location within great room and riser within HT. Would like recommendation on my riser build 12'x9'x10". A 3-chair curved seating arrangement (6' length) will seat in front of a 36" high 2' counter with four chairs (5' length) with a 1' step = 12'.
What should be placed under the riser to dampen sound?
Any special insulation between stringer?
Any damping between 2-3/4" plywood?
Carpet covering riser with lighting and outlets. Is a pad required?


Just an observation: a seating distance of 16ft is 4 ft longer than I ever recommend. Move everything closer. screen looks a tad high with the bottom 36 inches from the floor. You really don't need a riser for the first row. For that matter you can do a row of seating and back sit at bar with no riser at all.


On dampening sound, what sounds are you planning to make on the riser? You could consider Uboats for isolation if you need to isolate the riser. Just one source with some nice pictures: http://www.truesoundcontrol.com/products/UBT50.html
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30lb roofing felt or Green Glue
pad is a good idea on the horizontal surfaces.

You do need to calculate the throw ratio, I see a note but no answer, 23 ft may be too far depending on screen size.
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