Bring Your Home Theater to New Heights ("The Riser Article", HTB, Erskine 2003) - AVS | Home Theater Discussions And Reviews
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post #1 of 51 Old 01-05-2014, 11:58 AM - Thread Starter
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Bring Your Home Theater to New Heights
Building Your Seating Platform (Your Secret Weapon Against the Evil Room Mode)

Solving acoustic issues in residential rooms can be a daunting challenge, particularly when it comes to solving bass response problems. The good news is that bass response problems can be solved, and one of your secret weapons against uneven bass response can be a seating platform. The basic construction of a seating platform is very similar to a stage, but there are some important considerations and decisions you'll have to make before you begin. Don't forget, the purpose of a seating platform is to raise the seating height of a second (or third or fourth) row of seats providing a clear line of sight to the screen. Remember, while providing enough height for seating, you also need to leave adequate headroom as well. If you are planning on installing tactile bass units, or would like the option to do so later, read the Special considerations for tactile equipped platforms sidebar.

SECTION 1

Before you can determine the correct height for your seating platform, you need to mount your screen for the best vertical viewing angle. The vertical viewing angle is defined as the angle from eye level of the front row's center seat to the top of the highest protected image, or the top of the screen. The SMPTE (Society of Motion Picture and Television Engineers) notes that most viewers will experience physical discomfort when this angle exceeds 35 degrees. Various studies have suggested the optimum angle to be in the area of 15 degrees, which corresponds to the human cone of vision. Ultimately, you want the center of the Screen to be slightly above eye level and the top of the screen to fall in the range of 10 to 20 degrees (when possible). At the same time, you don't want the screen too close to the ceiling, or you'll get a light reflection Following these general guidelines, you can size the vertical height of your screen and, for our platform, take the measurement from the floor to the bottom of the screen.

Since the entire purpose of the raised seating platform is to provide a clear view of the screen from a second row of seating, the first step is to determine what that height should be. The easiest way to determine the minimum height of the platform is with a state drawing. On your drawing you want to mark the location of the bottom of your screen and head height for the front row. Since we're all different heights, and seating height can vary, you might want to sit in your theater seat and measure the distance from the top of your head to the floor. If you don't have your chairs, you can use an avenge height of 42". Now draw a straight line from the bottom of the screen to the back of your room, passing just over your head height mark (front row). Measuring 39" to 40" down from this line will be the minimum height requirement for your seating platform. Ultimately, if you have the actual measurement for your seats, you will be able to plan more accurately.

Figure 1

SECTION 2

From the angle of the line, you can easily see that the farther back from the front row of seats, the higher your platform will have to be. In fact, if you end up putting your seats farther back than you planned ahead for, you'll have a line of sight problem.

Figure 2

SECTION 3

It is a good idea to know exactly what seats you will be buying for the theater before you decide on your seating platform dimensions. When laying out your seating positions, you need to make certain you plan clearance for foot rests to extend in front and recliners to tilt back comfortably.

Figure 3

If your seating platform height is more than about 8" or 9" high, you'll also want to consider steps. In some locations, local building codes will demand steps for certain heights. Check with your local building department for this information in your area. If you build steps, your tread (the part of the step you step on) depth should be between 10" and 11". When building steps, once again, your seats come into play. You'll need to leave enough room between the steps for your front row seats. You don't want to have to change the step width once the carpet is down!

It's also a good idea to provide some kind of low level lighting at the steps to prevent accidents in a dark room. If you want to install rope lighting under the step edge, building your steps so the treads overhang by at least 2"

Now that the critical dimensions are known, you can start building your platform. In an ideal world, the platform should extend all the way to the back of the room and fill the width of the room. While this will decrease the possibilities of a "trip accident," as you'll see later, it will also be your stealthy bass response fix-it.

Like the stage, the room should be completely sheetrocked before you build, with any gaps between the floor and the sheetrock completely filled with a 50 year flexible caulk. Unlike the stage, however, the platform can contact the walls. For this project, we'll assume we've determined that a platform height of 9-1/2" is suitable.

The first step is to frame the perimeter of the platform using pine boards. Depending on the height of your platform, you may find that you will use a different size. We used a 2x8, which is very common. In this example, your 2x8s will sit directly on the floor and, because you don't want any rattles, you should lay down a layer of 30 lb. roofing felt over the floor. First, install a 2x8 against the back wall, gluing and screwing the 2x8 through the sheetrock to the studs. Before you screw it in, be sure it is level from side to side. Next, attach the two side 2x8s to each side wall, checking for level. These side pieces should be 5-1/2" shorter than the planned depth of your seating platform. When installing the sides, you may need to shim between the floor and the bottom of the 2x8, or even trim some of the 2x8 back to maintain level from front to back. The sides should also be glued to the drywall and screwed through to the studs.

With the sides and back in place, you can install the 2x8 across the front of your platform. When you do, make certain the top of the front 2x8 is even with the tops of the two sides, then check for level and make any adjustments in the middle that are needed for a level platform. Again, you'll want to screw and glue the front to the two sides. You now have your basic box frame in place.

Next, run 2x8s from the front to the back (as shown) inside the box frame. These 2x8s should be 12" on center and should be screwed and glued to the front and back of the box frame. Important: The 2x8 joists must run from front to back as shown!.

Now would be a good time to think about a few "convenience" items. First, it is a good idea to plan for an electrical outlet in the face of your platform. You'll want to install a single gang box in the face of the front riser and run the electrical cable for the outlet. Second, a phone jack would be a rather convenient accessory also in the face of the platform. If you have any plans to surf the internet or play video games, you'll want to install a 3" diameter PVC pipe from your equipment rack to the face of the platform riser. The PVC should terminate at a double gang box in the face of the riser. Also, don't use any 90 degree corners if you install PVC. IF you do, pulling wire later could be a challenge.

We don't fill the platform with sand, but every space between every 2x8 must be completely filled with fiberglass insulation. For this you want to use the non-backed fiberglass batt. Whatever thickness you use, just make certain you've completely filled the space. Johns-Mansville has formaldehyde free fiberglass batts that are excellent for this application.

SECTION 4 : The guts of your seating platform

The platform must be very solid and must not add rattles to the room. For the first layer of decking, run a bead of construction adhesive down the top edge of the joists. Using 3/4" tongue and groove plywood, install your first layer of decking. The decking should be screwed down to the joists and should extend 2" beyond your framing to the front. With the first layer down, cover it completely with 30 lb. roofing felt. Next install your second layer of decking using 1/2" plywood and screwing to the plywood below. When you install the second layer of decking, overlap the seams from the first layer. Finally, lay down another layer of 30 lb. flooring felt and screw down the final layer of decking using 3/4" tongue and groove plywood. You'll have a solid, echo-free platform.

Figure 4

SECTION 5

Now let's solve a few bass response problems using all of that fiberglass you just stuffed in your platform.

One of the characteristics of axial modes is that the frequencies at which the modes occur will always be at their peak pressure at the boundaries of the room. For length modes, the high pressure will be at the front and back walls. For width modes, it will be at the side walls, and for floor/ceiling modes, it is at the floor or ceiling. If you have a real time analyzer, you can place your microphone at the back wall, and you'll be able to see all the frequencies causing length modes (whether or not the mode is a peak or null at the listening position). If you want to determine the frequencies for all axial modes, you would place the microphone at the corner near the floor. Now let's use that information to reduce or eliminate those modes.

In the locations shown in blue, cut holes completely through the decking of your platform. The holes should be centered between your joists and be 4" x 10" in size. Be absolutely certain you do this in the corners! Get several pieces of light weight black fabric and place the fabric in the holes, spread out flat, to hide the fiberglass from view. After your room is carpeted, insert standard (or decorative) HVAC registers over the holes. They have no HVAC function, but some of the high pressure of the modal frequencies will be reduces. You can add more registers later if you need to, but you won't now exactly what is needed until you finish your room, install your furniture, and then measure the room's response with a real time analyzer. If there are any pesky problems remaining, you can also build useful columns, as you learned from our last issue (HTB, July 2003, Going Vertical) to create a perforated resonator for specific frequencies.

Figure 5

TECH TALK : Special Considerations for Tactile Equipped Platforms

There are a few differences in building a platform for Tactile Sound Transducers. The goal is to make the riser tight like a drum skin, solid on its outer edge only. The technique will make the tactile sound transducer perform efficiently and will also allow for irregular floors and wood materials so it will lay down better. While the riser will be strong and as solid as regular wood floors, more than enough to support the seating and the viewers without making noise and feeling weak, it will also allow the Tactile Transducer to perform efficiently.

Sidebar

For starters, only the outer joists should touch the floor. Also, the inner joists should be 2 inches smaller than the outer joists (i.e., using 2x8s for your frame and 2x6s for your inner joists). The inner joists can be spaced 16 or 24 on center and will be 2" off the floor and level with the top of your frame. The raised inner joists help in rurning the needed wires under the structure and prevent them from pinching as well as allowing the riser to float as much as possible. Tie the two center most joists together with a bridge pieces (see illustration). The TST will be mounted to the bridge, not the plywood flooring. This cross member bridge will make the transmission of energy as efficient as possible by making two joists move instead of just one. For your deck, use only one layer of 3/4" plywood. All wood joists should be glued with liquid nails or an equivalent before being screwed together to prevent creaking.

For this application, it is very important that you don't attach your platform to a wall or another riser. That would detract from the efficiency of the tactile effect and transmit unwanted vibrations to the walls. Isolation feet or other materials are another great way of improving the tactile response even more by decoupling the riser from the floor. Keeping the platform floating and unattached from the walls will give you a very professional look with the high performance that will allow you to gt every ounce of your tactile transducer and maximize the tactile effect.

BIO

Dennis Erskine is a member of SMPTE, AES, ALA, and IEEE. He and his firm specialize in the design of home theaters, listening rooms, and other acoustic spaces. Dennis can be reached at de@designcinema.com or visit his website, Design Cinema Privee Inc, at www.designcinema.com
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post #2 of 51 Old 01-05-2014, 12:00 PM - Thread Starter
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Addendums

The riser should NOT be attached to the walls: http://www.avsforum.com/t/1193579/should-riser-be-up-against-back-wall/

Most Erskine risers now use Green Glue rather than felt.

Erskine has been known to okay the use of three layers of 5/8" OSB rather than 3/4" + 1/2" + 3/4":
Quote:
Originally Posted by BIGmouthinDC View Post

The original decking design was for three layers 3/4,1/2, 3/4 of OSB with Green Glue. One night standing at Lowe's we discovered that the only 3/4 they have was T&G which was going to be a hassle so ... [Dennis] said three layers of 5/8 was going to be OK
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post #3 of 51 Old 01-05-2014, 12:07 PM - Thread Starter
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Dennis Erskine wrote an article for Home Theater Builder magazine in Sept 2003 that talked about building risers and using them as bass traps. This is a seminal article on building risers that has been referenced countless times since. Alas, the magazine has since gone out of business and they never did post this article online (that I can find). This is too important an article to allow to disappear to the ages, so I'm posting it here.

There is a set of photos of the pages that are posted here: http://www.avsforum.com/t/1043747/the-dark-knight-theater/#post_14176394. I tried running those through OCR, but the resolution wasn't good enough to capture the text very reliably. So I just transcribed the text manually and extracted out the diagrams.

I added a section on Addendums, since there have been some advances to riser building since the article came out.

Since the original copyright holder of these would be Home Theater Builder magazine and they are defunct, I'm assuming that it's fine to post this info here. If that's not true, then let me know and I'll delete this.
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post #4 of 51 Old 01-10-2014, 10:57 PM - Thread Starter
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Here are some build threads that follow the Erskine design either exactly or approximately.

Fixing my Riser - Converting an existing riser to one modeled after the Erskine design. Very informative!

The Rawlinsway Theater - Details on where to buy the vents here

Big in Ohio - An official Erskine design

If anybody else has good links, feel free to post them. The article is excellent, but build threads often have notable modifications and discussions that add quite a bit to the knowledge base.

Last edited by granroth; 10-09-2014 at 02:56 PM.
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post #5 of 51 Old 01-11-2014, 08:26 AM
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post #6 of 51 Old 10-15-2014, 08:15 AM
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I never saw this but very well done!

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post #7 of 51 Old 10-15-2014, 04:52 PM - Thread Starter
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I never saw this but very well done!
Mfusick, you have the original issue, right? Do you have the capability of doing some reasonable quality scans of the images? The versions I have above were from a pretty low quality scan of the pages.
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post #8 of 51 Old 10-15-2014, 05:43 PM
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Copyright vio....ah who cares. Royals are going to the series. . FYI...there are a few points not quite right. .
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Actually, I do care! I transcribed this and posted it for a couple of reasons:

1. It is a very commonly referenced article which forms the basis of how most people design and build risers these days
2. It is from an out of print magazine

If the article was still available in any reasonable fashion, then I would never have posted it. I subscribe to the common sense copyright theory which states that if copying an item will cause financial harm to the copyright holder, then it is wrong. In this case, nobody can be harmed by posting this article when the entity that could profit from it no longer exists.

But as I said in an earlier post -- if it's not okay to post this, then I'll delete it. Put more specifically, if Dennis would rather this not be here, then all it takes is a quick note and it's gone!

I guess there is a third reason:

3. There have been advances in risers in the 11 years since this article was published

That's why I have the "addendum" after it in the hopes that some of the common changes could be captured.
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I'm messing with you! Lol. I don't have an issue, and I have no idea if the publisher, or if anyone bought the rights. No clue.

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Granroth...I am about to start on my riser which will be sort of in the middle of my room (the other end of my HT will be a bar area). Will these riser treatments still produce benefits considering the open space behind?

Please feel free to comment on any acoustic red flags you see in my room (page 2 has a couple of recent photos).

Thanks!

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I threw out all my old mags...

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Quote:
Originally Posted by granroth View Post
Depending on the height of your platform, you may find that you will use a different size. We used a 2x8, which is very common. In this example, your 2x8s will sit directly on the floor and, because you don't want any rattles, you should lay down a layer of 30 lb. roofing felt over the floor.
Their new riser designs don't use roofing felt. Without revealing trade secrets, they use a mat. They wanted over $5,000 for the mat itself. Dennis takes a healthy margin on top of that, plus there is an installation fee. I don't know what roofing felt goes for, but the mat was pushing 5 figures installed in my room.

I needed to get the construction price of my room down to $100k and it couldn't be done. Interesting to see roofing felt recommended in 2003, but not an option 10 years later even if needed to meet a client's budget.

 

 

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the use of serenity mat (rubber mat from Soundproofingcompany.com) is not really a trade secret and the use of that instead of roofing felt is for entirely different reasons. There is a lot that has changed in the 10 years since that article was written, Serenity mat and Plywood/OSB overlay is now specified because of it's ability to better isolate the theater from the rest of the house. I've built plenty of theaters without it, and also ones with it, If you want to save money, skip it and forgo that additional bit of isolation. Use Felt under the stage and riser to protect the wood from the moisture in the concrete and to help it sit a little better by smoothing out some of the irregularities in concrete. Then put a good mat under the carpet.

If you want to use a mat, Buy the mat direct from Soundproofingcompany.com. You and a friend can install serenity mat it is really easy.

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Quote:
Originally Posted by thestoneman View Post
Granroth...I am about to start on my riser which will be sort of in the middle of my room (the other end of my HT will be a bar area). Will these riser treatments still produce benefits considering the open space behind?

Please feel free to comment on any acoustic red flags you see in my room (page 2 has a couple of recent photos).
It is critical to note that I am not an expert in anything! Well, anything AV related anyway. My contribution to that article above, for instance, was just transcribing it off of a scanned image of the article. Dennis Erskine is the actual expert in this case (along with SierraMikeBravo, also posting in this thread).

What I can typically help out with is transfers of common knowledge. That is, IF you are doing something that is very similar to what other people have done before, then I'm good at regurgitating those details.

In your case, you have two unique cases. The first is your placement of a riser and your goal to use it as an absorber (in addition to just being an object to raise your seats) and the second is that bump-out in your room caused by the equipment closet and mechanical room. Dealing with both requires specialized knowledge, which is unlikely to be found in any amateur (like me).
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Erskine base traps function as a pressure relief feature. As I understand the mechanics the standing bass waves in the room exert the maximum pressure at the room boundaries like a floor/wall intersection. Erskine places his vents at those locations. therefore the riser needs to be against the walls for his approach to work. A free standing riser in the middle of the room won't qualify. He discussed this a bit in his interview with Scott on the Home Theater Geek podcast.
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post #17 of 51 Old 10-16-2014, 06:12 AM
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Quote:
Originally Posted by BIGmouthinDC View Post
Erskine base traps function as a pressure relief feature. As I understand the mechanics the standing bass waves in the room exert the maximum pressure at the room boundaries like a floor/wall intersection. Erskine places his vents at those locations. therefore the riser needs to be against the walls for his approach to work. A free standing riser in the middle of the room won't qualify. He discussed this a bit in his interview with Scott on the Home Theater Geek podcast.
Based on the knowledge that sounds waves reflect off surfaces, should I still cut vents and where would you place them?

This stuff, as granroth admitted, is way over my head. I just want to try to do things right the first time. I asked in another thread if you inspect rooms for a fee. I am in your neck of the woods if that is a service you provide.

Thanks!

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But a riser trap isn't only solution, you can do a back wall just the same with same result

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But a riser trap isn't only solution, you can do a back wall just the same with same result
Well, my back wall will be a bar. I'm not sure what the hell to do to help ensure the room sounds good.

My room is 14' x 34' with one half of the room a HT and the other half a bar. I am hoping to make some maneuvers now so Audyessy isn't like "are you effing kidding me"?

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post #20 of 51 Old 10-16-2014, 09:44 AM
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I just want to try to do things right the first time. I asked in another thread if you inspect rooms for a fee. I am in your neck of the woods if that is a service you provide.
I'm a theater builder and a plagiarist of designs of people who have studied the science of acoustics. If you want advice on how to build something I can help, if you want acoustical advice you need to seek out the experts.
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post #21 of 51 Old 10-16-2014, 10:05 AM
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Originally Posted by BIGmouthinDC View Post
Erskine base traps function as a pressure relief feature. As I understand the mechanics the standing bass waves in the room exert the maximum pressure at the room boundaries like a floor/wall intersection. Erskine places his vents at those locations. therefore the riser needs to be against the walls for his approach to work. A free standing riser in the middle of the room won't qualify. He discussed this a bit in his interview with Scott on the Home Theater Geek podcast.
Big's assessment is correct. However, if you know the frequency creating most of the problems, you could design a riser to be a hemholtz resonator but that becomes very complex...and risky. Now the other caviat is, is if you think a six inch riser will suffice, not gonna happen.
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post #22 of 51 Old 10-16-2014, 10:19 AM
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Well, my back wall will be a bar. I'm not sure what the hell to do to help ensure the room sounds good.

My room is 14' x 34' with one half of the room a HT and the other half a bar. I am hoping to make some maneuvers now so Audyessy isn't like "are you effing kidding me"?
You can still do it behind the bar... imagine a riser.. with grates...or openings at the boundaries but instead of on the floor on the back wall. Make it thick enough and large enough to be usable in the frequencies you want. Corner traps are options too, which can be covered and make look like wood working or whatever...

you'll lose some space sure... but it can work.

Learning to tune a riser is an entire science unto itself... best to hire a pro for that.

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post #23 of 51 Old 10-16-2014, 01:07 PM
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I will interject my definitely biased opinion. You should always hire a pro if you don't know what you're doing.
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post #24 of 51 Old 10-16-2014, 01:16 PM
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Big, have you done any risers that were directly connected to the wall studs as per the transcript in an isolated room? I assume this approach would only be done in non isolated rooms with a gap left between riser framing and drywall in all rooms with proper sound isolation. Just common sense I suppose.
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post #25 of 51 Old 10-16-2014, 01:18 PM
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Originally Posted by SierraMikeBravo View Post
I will interject my definitely biased opinion. You should always hire a pro if you don't know what you're doing.
Ignorance is bliss.

Proud owner of E Group plans lol
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post #26 of 51 Old 10-16-2014, 01:41 PM
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Thanks for the comments folks... Yes, ignorance is bliss...until AVS exposes your ignorance and delivers a hearty "I told you so..." Very much trying to avoid that.

I will seek a pro. Any recommendations for someone in the DC area?

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post #27 of 51 Old 10-16-2014, 01:52 PM
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SirraMikeBravo if/when he comes to town. You will discover that most designers can work their magic with, a good set of photos, accurate measurements, telephone and Email. IMHO on site hand-holding is highly overrated. I do my best work via Skype.

Heck of a lot cheaper without travel costs added in. Even locally I want something for my travel time.

Last edited by BIGmouthinDC; 10-16-2014 at 04:18 PM.
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post #28 of 51 Old 10-16-2014, 03:23 PM
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Quote:
Originally Posted by thestoneman View Post
Thanks for the comments folks... Yes, ignorance is bliss...until AVS exposes your ignorance and delivers a hearty "I told you so..." Very much trying to avoid that.

I will seek a pro. Any recommendations for someone in the DC area?
There are several, but none in the DC area. Closest would be New York, but unless you have a huge budget ahem.... Kansas is the lucky ones! (Poor humor). Here is a list. Each will have a broad range of budgets, expertise and deliverables. These are in no particular order:

Anthony Grimani
Dennis Erskine
Theo Kalomarikis
Nyal Mellor
Dennis Foley
Keith Yates
Bryan Pape

And me....I"m way down here...

Those are the well known designers known on this forum. Most are on the west coast with two in the Midwest. Only one that I know on the East Coast. Dennis used to be in Atlanta. Hope this helps!!

Shawn Byrne
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CEDIA Certified Professional EST II - HAA Level III Certified -THX Certified Professional
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post #29 of 51 Old 10-16-2014, 04:25 PM - Thread Starter
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Quote:
Originally Posted by SierraMikeBravo View Post
Anthony Grimani
Dennis Erskine
Theo Kalomarikis
Nyal Mellor
Dennis Foley
Keith Yates
Bryan Pape
Some random opinions on a few of these, coming from a guy that has never hired any of them (so massive grains of salt are necessary!). This would be my short list if I ever did hire it out, though:

Anthony Grimani did a two-part Acoustics series on Home Theater Geeks, here: http://twit.tv/show/home-theater-geeks/177 and http://twit.tv/show/home-theater-geeks/178. IMO, these are the best primers to acoustics that have ever been made. Fantastic stuff and very easy to understand.

Dennis Erskine is practically a legend in AVS circles. Not sure that he ever deals with the sub-$100k projects personally, though -- I have a feeling he bumps those off to Mike SHAWN.

Nyal Mellor is new to me, as I hadn't heard of him prior to the Savoy build. He's extremely responsive and helpful on the threads, though, and his articles on Acoustic Frontiers are very well done!

Bryan Pape used to be almost as ubiquitous as Erskine, back in the day. It seems like nearly every theater made in the 2008-2010 years had acoustic plans done by 'bpape'. Lots of happy customers.

I've heard of all the others but don't know enough to have any opinion at all.

Last edited by granroth; 10-16-2014 at 06:04 PM. Reason: It's Shawn, not Mike. I knew that and was testing you all!
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post #30 of 51 Old 10-16-2014, 04:54 PM
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You gotta watch out for that "Mike" guy. Shady character.

Dennis still works on sub six figure theaters. He gives the "Mike" guy the theaters with 16x10x7 dimensions and two rows. I'll let you know, having done both, the constraints of a budget DIY theater are MUCH more difficult to deal with than a room with a deeper pocket. Solutions are a bit harder with the stringent constraints, so please don't consider budget theaters to be easy by any means. They are quite often more difficult and nothing to sneeze at.
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