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Help me design my home theater - planning stage

27K views 147 replies 19 participants last post by  DIYHomeTheater 
#1 ·
I am a novice at designing theaters, and am self-taught by gleaning information from the Web for doing this. I have developed a design for my basement home theater and welcome any insights based on design reviews by the excellent comments people have made on this forum. My design principles are as follows:
  • Get the largest acoustically transparent screen as possible for the space available. Recognize that projectors may be too expensive today for such a large screen, but prices will eventually fall. I can change projectors, but not screens and false walls easily.
  • Trade a perfect' expensive- for an 80% good' reasonably-priced solution
  • Use the lessons learned from others


Accordingly, my plan (see attached floor plan) in no particular order (although I paid the most importance to the screen and seating) is as follows:

Room
  • Finished dimensions 28'5 long, 17' 11 wide, 8' 7-3/4 high
  • Carpet on floor
  • No lights in the ceiling, but sconces on the walls
  • A 6 high stage in front of the screen

Room Acoustics
  • According to Auralex Acoustics Inc., a 29' 10 room length delivers the most ideal frequency response between the possible dimensions listed' based on a similar plan
  • Room sound isolation to be achieved through RC channels , two 5/8 drywall panels with Green Glue in between
  • Mineral fiber between floor joists in ceiling? Not sure about this. (update 1/26/11: Installed R-19 in ceiling and R-13 in walls on advice of the Soundproofing Company. Was not expensive: Material cost ~$300. Seems like an entirely worthwhile thing to do based on its property to absorb low frequency bass)
  • Auralex-recommended schedule consisting of S3PP ProPanels, S3CT corner traps and SpaceCouplers suspended from the ceiling as follows (from Auralex):

  • S3PP ProPanels should be spaced evenly throughout the available open wall space to reduce room ring and slap back. Panels should start between 2 and 3 feet up from the floor

  • Additional low frequency absorption can be gained by spacing the S3PP ProPanels off the walls 203 inches, creating an airgap behind the panels. This can be easily done using small wood blocks or something similar

  • S3CT Corner Traps should be mounted in the available upper corners to help smooth low frequency inconsistencies

  • SpaceCouplers could be suspended from the ceiling over the listening areas to break up first reflections and help widen the sweet spots
  • Consider lower-cost, generic DIY alternatives for the above, if available

Screen
  • 2.40 aspect ratio, flat, 187 diagonal, 172.8 wide, 72 high (update 1/21/11: Revising screen dimensions based on discussions with Chris Seymour of Seymour AV and others on this forum. Brand Screen Excellence acoustically transparent Craftsman screen, 1.0 gain, EN4K material with GripFix. I chose this over others for its DIY-friendliness and good performance/cost update 1/21/11 - this fabric is no longer available for DIY market. Now considering the Center Stage XD fabric
  • Develop a 4-way masking system using the methods described on this forum

Audio: Use my existing B&W speaker system - 803 Matrix and HTM center channel, and 800 ASW subwoofer. Will need to purchase new surrounds and perhaps additional subs.

Seating
  • Two rows of 4-each 18' and 25' away from screen. Distances established by using Carlton Bale's calculator for THX recommended distancesupdate 1/21/11: moved rows forward with smaller screen and gave more space at the rear
  • Modify riser to function as a bass trap

Projector
  • Will need 1100+ calibrated lumen projector eventually. May initially get the BenQ W6000 which is reasonably priced and has high output. May not use entire screen initially
  • Anamorphic lens - most likely the Isco IIIs
  • Maximize throw distance to reduce distortion, but aim for about 20 foot-lamberts on screen

Equipment rack in separate room

HVAC: This is one area that I am not sure how to handle sound isolation. HVAC registers will be above and behind the seats and returns will be on the left wall between the doors. I have a variable speed fan which is usually very quiet. Also, our basement tends to be a comfortable temperature and I don't forsee the heating/cooling being turned on. But, just to be safe, I did get the HVAC engineer to consider options for acoustics. He recommended a separate thermostat in the theater and a separate trunk line with automatic gates' for the theater. I am not sure how to prevent sound from the rest of the house/air handler from reaching the theater, and am not sure if this arrangement will provide sound isolation. He suggested a liner in the ducts that absorbs sound. The contractor's recommendation is, "Install two 12x6 high wall registers behind seating. Install a 16x16 low wall return air grille with a 10x8 return duct. The new supply air trunkline and return air riser duct are to be lined to reduce noise." update 1/21/11: Dennis Erskine gave great suggestions. Located supply and return registers up high. Supply at the front and return at the back near PJ. Pointed downwards, bar-type, 4"x48". Insulated flexible 8" ducts. Air flow = 340 CFM for 10 people+equipment. Capable of being zoned separately in the future. Air speed at registers kept below NC20 noise criteria 250 fps.


Any suggestions will be welcome. Thanks, all!

Edited 1-21-11

I walled off the curved space in the theater on the advice of Auralex. The curved space is especially difficult to treat acoustically. By walling it off, I can use it for my equipment rack

 
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1
#102 ·
1. My biggest concern is with the height speakers. I think their location has been determined mainly by your desire to place them behind the screen. The problem is that if they are placed there, they will not be functioning properly when used as Audyssey DSX Height speakers. One of the important concepts of the Wide and Height speakers is that they fill the gap between the front and surround speakers. In your diagram, you can see that the Wide speaker is nicely filling in part of that void between the surrounds and the fronts. The Height speakers, however, are also meant to fill in the gap between the Wides and Fronts. This is why the recommended angles are 30, 45 and 60 for Fronts, Heights and Wides. In your diagram however, the Heights are located, not between the Fronts and the Wides but between the 2 Fronts. The bottom-line is that I would much prefer to locate the Heights on the side walls, close to its top corner with the false front wall. I think that would be a better compromise.


2. If the surrounds will be at 90 degrees from the main listening position, they should ideally be dipoles.


Other than these 2 comments, I think the lay-out is fine and should sound great.


Mark
 
#103 ·

Quote:
Originally Posted by streetsmart88 /forum/post/20209047


1. My biggest concern is with the height speakers. I think their location has been determined mainly by your desire to place them behind the screen. The problem is that if they are placed there, they will not be functioning properly when used as Audyssey DSX Height speakers. One of the important concepts of the Wide and Height speakers is that they fill the gap between the front and surround speakers. In your diagram, you can see that the Wide speaker is nicely filling in part of that void between the surrounds and the fronts. The Height speakers, however, are also meant to fill in the gap between the Wides and Fronts. This is why the recommended angles are 30, 45 and 60 for Fronts, Heights and Wides. In your diagram however, the Heights are located, not between the Fronts and the Wides but between the 2 Fronts. The bottom-line is that I would much prefer to locate the Heights on the side walls, close to its top corner with the false front wall. I think that would be a better compromise.

Mark:

I had the same concerns as you about the location of the heights, and never having done this before, I had to rely on someone who is knowledgeable and has listened to height configurations. You will recall that my previous plan called for the Heights to be in the ceiling.


However, that would have meant placing them only 5' away from the listening position (My ceilings are only 8'-6" high). At that short a distance, there is a chance that the heights would be distinguishable from the fronts since the latter will be about 15' away. That runs counter to the notion of having an acoustically seamless front stage. I think that the 45 degree angle works best if the ceilings are higher and the heights can be a further distance away.


Steve F. has experience with only wall mounted heights in the testing they did with Dolby and Onkyo. I was hoping that they had ceiling mounted results as well so that a fair comparison could have been done. He thinks that wall mounted heights perform very well. I did ask him about my concerns about wall mounting vice ceiling mounting. I was erroneously under the impression that by mounting on the wall the heights will be indistinguishable from the fronts and hence not serve a useful purpose. Ceiling mounting would have 'fixed' that 'problem'. His response was, "Yes, they (Dolby and Onky) both used the front wall. The difference will be "distinguishable," because the front L/Rs will be handling a different signal than the Heights. When Dolby did their Heights on-off A-B demo for us, the entire soundstage seemed to 'rise' when the Heights were on, just like it should have. But you were not aware of the individual speakers playing, just like you're not supposed to be. In a good theater system, the soundfield is expansive, three-dimensional, and continuous. You should never be able to "distinguish" your 'front' speakers from your 'height' speakers from your 'side surround' speakers, etc. The sound should follow the video and simply be realistic and believable.


I can mount these height speakers on the ceiling with some improvisation (they are designed to be wall mounted), but would rather defer that until I've had a chance to first test them out in the wall configuration which would also give a cleaner look and hide the wires better.

Quote:
Originally Posted by streetsmart88 /forum/post/20209047


2. If the surrounds will be at 90 degrees from the main listening position, they should ideally be dipoles.


Other than these 2 comments, I think the lay-out is fine and should sound great.


Mark

My surrounds will be dipole. They also have a bipole setting, but I'll try dipole first. Heights and Rears will be in bipole mode (as suggested by Steve). I was going to go with monopoles for the heights, but these specialized heights speakers come in dipole/monople. They are also not very expensive ($450 MSRP/pair), so this will not cost me anything significantly more. I have B&W 805 HTMs that I can use as wides. Steve thinks that they'll be OK with the Atlantic line in so far as timbre matching is concerned.


I intend to put two additional subs in the rear corners of the room. These are not shown in the figure. Only the two front subs are.

Thank you.
 
#104 ·
With regard to the Height speakers, I can see your concern about having them ceiling-mounted. If they will be only 5' away, there is a danger that they will be localizable. I have also never heard ceiling-mounted height speakers. Chris Kriakakis, the CTO of Audyssey, has said that they would work but I still don't think they would be ideal unless you can actually tilt the drivers so that they point at the Main Listening Position.


The main problem with your plan now is that the Heights have an even smaller horizontal angle than your Fronts. They should be between the Fronts and Wides.


Mark
 
#105 ·

Quote:
Originally Posted by streetsmart88 /forum/post/20212472


The main problem with your plan now is that the Heights have an even smaller horizontal angle than your Fronts. They should be between the Fronts and Wides.


Mark

True. I can move them out another foot or so each. If I move them any further, they will be outside the screen. Thanks.


PS: I've ordered more cable from Monoprice to wire for the heights and the wides.
 
#106 ·

Quote:
Originally Posted by DIYHomeTheater /forum/post/20212667


True. I can move them out another foot or so each. If I move them any further, they will be outside the screen. Thanks.


PS: I've ordered more cable from Monoprice to wire for the heights and the wides.

Can you put the Heights on the walls just beside the subs? This would give you a much better angle and still keep the Heights hidden. I assume that the false wall will have acoustically transparent fabric.


By the way, Audyssey DSX speakers (Wides and Heights) are supposed to be monopole. I don't think it will be a good idea to make them bipole or dipole. I suspect they are also used for panning (which had an extraordinary improvement in my system after installing DSX), in which case they must be monopole. Perhaps the Dolby Height speakers can be bipole but that isn't the case with Audyssey DSX and in my view, DSX is much better than Dolby Height.


Mark
 
#107 ·

Quote:
Originally Posted by streetsmart88 /forum/post/20212782


Can you put the Heights on the walls just beside the subs? This would give you a much better angle and still keep the Heights hidden. I assume that the false wall will have acoustically transparent fabric.

I suppose that I could do that. I plan on putting in sufficient extra cable to let me experiment with locations. One limiting factor will be the framing in the screen wall. That will constrain my locations somewhat.

Quote:
Originally Posted by streetsmart88 /forum/post/20212782


By the way, Audyssey DSX speakers (Wides and Heights) are supposed to be monopole. I don't think it will be a good idea to make them bipole or dipole. I suspect they are also used for panning (which had an extraordinary improvement in my system after installing DSX), in which case they must be monopole. Perhaps the Dolby Height speakers can be bipole but that isn't the case with Audyssey DSX and in my view, DSX is much better than Dolby Height.


Mark

I thought that they were supposed to be monopole too, but the desired effect is supposed to be diffuse. Hence, Atlantic's specialized Heights speakers are bipole/dipole. Here is a product review that specifically mentions, 'The idea of height channels is to widen the sweetspot, give a more enveloping surround experience, and to make the front soundstage, well, taller. Dolby recommends highly diffuse speakers that will not be as localizable as direct radiators.' But then, this review was done with Dolby PLZII. I need to check with Audyssey DSX. This AVS user seems to be pleased with the use of the bipoles in heights with DSX. Thanks

[/i]
 
#108 ·

Quote:
Originally Posted by audyssey /forum/post/17580021


The Wides and Heights for Audyssey DSX should be direct radiators (not dipoles or... quadrapoles--don't know what that is).
Quote:
Originally Posted by DIYHomeTheater /forum/post/20212825


I thought that they were supposed to be monopole too, but the desired effect is supposed to be diffuse. Hence, Atlantic's specialized Heights speakers are bipole/dipole. Here is a product review that specifically mentions, 'The idea of height channels is to widen the sweetspot, give a more enveloping surround experience, and to make the front soundstage, well, taller. Dolby recommends highly diffuse speakers that will not be as localizable as direct radiators.' But then, this review was done with Dolby PLZII. I need to check with Audyssey DSX. This AVS user seems to be pleased with the use of the bipoles in heights with DSX. Thanks

[/i]

My guess is that even with Audyssey DSX Height speakers that are dipole or bipole, you will still have a positive experience, but Chris Kyriakakis, CTO of Audyssey (see quote above), has specifically stated that they should be direct radiators. It may be different for Dolby Heights.


Mark
 
#109 ·

Quote:
Originally Posted by streetsmart88 /forum/post/20213595


My guess is that even with Audyssey DSX Height speakers that are dipole or bipole, you will still have a positive experience, but Chris Kyriakakis, CTO of Audyssey (see quote above), has specifically stated that they should be direct radiators. It may be different for Dolby Heights.


Mark

Indeed Chris Kyriakakis recommends direct radiators. (I went through each of his posts on the subject of Heights in the Audyssey thread):
  1. ""As close to the ceiling as possible" is our recommendation."
  2. "I understand the limitations of typical home ceiling heights. If you do decide to put height speakers in, place them as high as possible. But, only do that after you have installed the wides. They provide a more valuable audible benefit than the heights."
  3. "Yes, they are derived but not in the same way as matrixed content. Both the wides and the heights will be required to produce max SPL that is on par to what the front L and R channels produce."
  4. "That's the ideal case (45 degree elevation). Obviously real world rooms will vary. The rule of thumb is "as high as possible above your front speakers""
  5. "As with any multichannel system, it's always better to have matched speakers. The wides and heights should be direct radiators like L, C, R.""
  6. "The Wides and Heights for Audyssey DSX should be direct radiators (not dipoles or... quadrapoles--don't know what that is)"
  7. "It's both: 45° horizontal angle and 45° vertical angle as shown in the diagram. If the ceiling is not high enough to support a 45° vertical angle then the recommendation is to put the Height speakers on the front wall (outside the front L and R) and as high up as possible. Also, try to point them down to the listener. MultEQ will take care of the distances."
  8. "The tolerances on the placement of Wides and Heights can be ±10°."
  9. "The ITU recommendation for front L and R is ±30° (with the C at 0° in the middle). That spread was found to give good front stereo while still keeping a good match between picture and sound.
  10. In our experiments with Wides and Heights we found that there can be a ±10° tolerance from the optimum angles of the Wides. The Heights should really be as high as possible on the front wall (or in the ceiling pointing down)."
  11. "That's because the chart on our website shows the ITU recommendation for direct radiating surrounds. If you have dipoles at 90° then the Wides will be somewhat close to them if you place them at 60°. That is not a problem as the Wides are not playing the same content as the surrounds...The Heights should be as high as possible on the front wall corners and tilted down to the seats."
  12. "Mount them as high and wide as possible near the corners of the front wall and the ceiling. Ideally, your in-wall Heights will have tweeters that can be pointed down to the listening area."
  13. "The rule-of-thumb for the Heights is "as high as possible". In most rooms the recommended 45° angle is not possible given the ceiling height. So, with in-room speakers you should try to place them on the front wall as high up as possible and near the upper corners. MultEQ will take care of response issues. Try mounting them so they can be pointed down to the listening area. Alternatively, some use in-ceiling speakers that should be placed in the ceiling near the front wall."


And specifically in response to my question about my theater and my layout with the ceiling height limitation of 8-6", this was his advice:
"The best place for the Heights is on the front wall and as high up as possible. You need to maximize the vertical distance between the front LCR and the Heights in order to take advantage of the DSX processing...The Heights (and Wides) are responsible for direct and ambient sound. They should be direct radiators and not dipoles or bipoles."


So now I am wondering why Steve Feinstein of AT recommended bipoles. Perhaps they implemented the Dolby system and maybe Dolby calls for a diffuse Heights field. I'm going to have to follow up with Steve on the choice of appropriate direct radiators.


And most direct radiators are designed to be floor standing. Not sure how I will mount one high up and pointing in the right direction


Thank you
 
#110 ·
Quote:
Originally Posted by DIYHomeTheater
So now I am wondering why Steve Feinstein of AT recommended bipoles. Perhaps they implemented the Dolby system and maybe Dolby calls for a diffuse Heights field. I'm going to have to follow up with Steve on the choice of appropriate direct radiators.


And most direct radiators are designed to be floor standing. Not sure how I will mount one high up and pointing in the right direction


Thank you
I agree that the recommendation of bipoles for the Heights probably considers a Dolby Height system, which is totally different from Audyssey DSX. Between the two systems, I would opt for DSX any time because I've listened to both and DSX has a much bigger positive impact.


A direct radiator is a normal speaker, as opposed to bipoles, dipoles, tripoles, etc. A direct radiator can be a floorstander or a bookshelf speaker. I have seen only two setups with floorstanders used as Heights, one of which was in the Audyssey lab and another was an incredible feat of engineering. Nearly everyone else uses an ordinary bookshelf speaker for the Heights - I do. Typically, you use the same bookshelf speaker for your Heights, Surrounds and Surround Backs.



Mark
 
#111 ·
Quote:
Originally Posted by streetsmart88
Typically, you use the same bookshelf speaker for your Heights, Surrounds and Surround Backs.



Mark
But, for the LR surrounds you need dipoles, and bipoles for the rears, right? I have asked Steve to recommend appropriate direct radiating speakers for the heights that will match the 8200e LCRs. I have a pair of existing B&W HTM Matrix speakers that Steve thinks can be used with the 8200s. Should I use these for the Heights and get beefier speakers for the Wides, or use them for the Wides instead? I think that the Wides are more critical.
 
#112 ·
Quote:
Originally Posted by DIYHomeTheater
But, for the LR surrounds you need dipoles, and bipoles for the rears, right? I have asked Steve to recommend appropriate direct radiating speakers for the heights that will match the 8200e LCRs. I have a pair of existing B&W HTM Matrix speakers that Steve thinks can be used with the 8200s. Should I use these for the Heights and get beefier speakers for the Wides, or use them for the Wides instead? I think that the Wides are more critical.
Sorry, yes, if your LR surrounds are at 90 degrees, they should be dipoles. For the rears, there are varying opinions but I would agree that they certainly can be bipole. In my own setup, all speakers are direct radiators but this is partly a result of my particular room lay-out.


Yes, I believe that the Wides are more critical. If you listen to them carefully, they have pretty high SPL and the sound is full-range. That's why my own Wides are floorstanders.


Mark
 
#113 ·

Quote:
Originally Posted by streetsmart88 /forum/post/20216896



Yes, I believe that the Wides are more critical. If you listen to them carefully, they have pretty high SPL and the sound is full-range. That's why my own Wides are floorstanders.


Mark

Steve F. of Atlantic Technology wrote, '4400 LR's are about as close a match as it gets to the 8200e LRs.'


I am thinking of using them for the Wides (Closest match to my LCRs which will be 8200es) and my B&W 805 HTMs for the Heights. Or, should I switch the arrangement? B&W for the Wides? Although the B&Ws are close to the ATs in timbre, they may not be identical.


What is your opinion of DSX? Do you use 9.x or 11.x?

Thanks
 
#114 ·

Quote:
Originally Posted by DIYHomeTheater /forum/post/20218849


Steve F. of Atlantic Technology wrote, '4400 LR's are about as close a match as it gets to the 8200e LRs.'


I am thinking of using them for the Wides (Closest match to my LCRs which will be 8200es) and my B&W 805 HTMs for the Heights. Or, should I switch the arrangement? B&W for the Wides? Although the B&Ws are close to the ATs in timbre, they may not be identical.


What is your opinion of DSX? Do you use 9.x or 11.x?

Thanks

Given that the Wides are more important than the Heights, if I had to use the B&W 805 HTMs, I would use them for the Heights and use the 4400 LR's for the Wides.


I think that DSX is an awesome piece of technology. It's magical. The main feature is that it greatly expands both the depth and width of the soundstage, way beyond the limits of your screen, and it wraps you in a seamless cocoon of sound. In addition, it greatly enhances panning (left to right, front to back, up to down and vice-versa). Once you start reading more about acoustics and psychoacoustics, particularly the topic of good and bad reflections, then you start to get a glimpse at the science behind the technology. In a word, Audyssey MultEQ minimizes the effects of unwanted reflections, while DSX injects the good reflections so as to enhance apparent source width and listener envelopment.


I have an 11.x system. The Wides clearly contribute more. However, when I changed my speakers so that all of them were from the same family, the impact of the Heights was improved. Then, when I installed the Heights at the proper elevation (I had previously forgotten to take into consideration ear height), the effect was improved even more.


My conclusion is that if I were you, I'd get 2 pairs of 4400 LR's and use them for Heights and Wides. Otherwise, you'll always be wondering how much improvement you will have if you change your B&W 805 HTM's.


Mark
 
#115 ·
BigMouthinDC showed me how to hang doors. So today, he hung a 1-3/4" solid core door with a 12-1/4" jamb in the theater door. It was a little tricky, but he hung it perfectly. I installed the other door, but with a lot of help from Big. Thank you, Big!
 
#117 ·
Folks, I have been remiss in keeping you all up to date. I spent most of the year finishing the rest of the basement (doors, painting, trim, cabinets, bathroom, shelves). I made an opportunistic purchase of a used ISCO IIIL with a motorized sled. Here is the sled's users manual . I have never programmed one of these sleds - it offers control through RS232 and a latch relay. How does one control via RS232? Do I need a computer to send the commands for 'Go to home', 'Go to show', 'Stop', etc.?
 
#118 ·
Inspired by the Bacon Race Theater , I built a nearly identical stage this weekend.


I am planning on building a short riser for the front row (about 3" high). Reason: I want to be able to use a butt kicker or equivalent for tactile feedback to the feet which would otherwise not be possible on a concrete slab. Question for all: Are there any light fixtures that might work on such a short riser?
 
#120 ·

Quote:
Originally Posted by DIYHomeTheater /forum/post/21716616


I am planning on building a short riser for the front row (about 3" high). Reason: I want to be able to use a butt kicker or equivalent for tactile feedback to the feet which would otherwise not be possible on a concrete slab. Question for all: Are there any light fixtures that might work on such a short riser?

Why not mount the Buttkickers to the chairs themselves? Many chairs already have a landing area / mounting spot for the Buttkicker to mount directly to the chair. And then there are other "Brackets" that slip under the feet of the chairs for low or no profile (height) applications. You don't need to build a small riser IMHO.
 
#121 ·

Quote:
Originally Posted by TMcG /forum/post/21719031


Why not mount the Buttkickers to the chairs themselves? Many chairs already have a landing area / mounting spot for the Buttkicker to mount directly to the chair. And then there are other "Brackets" that slip under the feet of the chairs for low or no profile (height) applications. You don't need to build a small riser IMHO.

Because, Craig John (a contributor to these forums) told me that if your feet are on a concrete slab you dont get the full tacticle response - your body is out of synch with your feet. A raised platform addresses this discrepancy.
 
#122 ·
I've never had a guest that didn't sit in their reclining theater seat with their seat at least partially reclined and their feet off the ground, so the floor is irrelevant. If you are planning non reclining seats without a footrest it would make some sense.
 
#123 ·
My thoughts exactly, Big. Mounting one LFE into each chair is optimal, but you could also use this Buttkicker kit without building the riser at a rate of one per individual piece of furniture. If you are looking to shake this 3" riser with one of these kits, then that is an understandable approach to go with a small profile platform to cover multiple seats. But either way I don't understand how things could be mis-synched.
 
#124 ·
My 2nd design for the rear seat riser. This time, incorporating a bass trap design. The riser will butt up against the rear and side walls. The idea is to create four cavities in the riser in the ratio of 1:2:4:8 volumes. Each cavity will be separated by a floor to deck joist with no air passage allowed between them. Within each cavity the deck joists will have an air gap from the floor. I will install 4x14 standard air registers along the walls to let the low frequency waves in to the bass trap. Will this work? (see attached picture)

 

Riser Design.pdf 175.4873046875k . file
 

Attachments

#125 ·

Quote:
Originally Posted by DIYHomeTheater /forum/post/21727064


My 2nd design for the rear seat riser. This time, incorporating a bass trap design. The riser will butt up against the rear and side walls. The idea is to create four cavities in the riser in the ratio of 1:2:4:8 volumes. Each cavity will be separated by a floor to deck joist with no air passage allowed between them. Within each cavity the deck joists will have an air gap from the floor. I will install 4x14 standard air registers along the walls to let the low frequency waves in to the bass trap. Will this work? (see attached picture)

DIY - here is the formula for calculating the resonant frequency of a Helmholtz Resonator where f is the resonant frequency (Hz), c is the speed of sound (1120ft/s), p =3.14, S is the area of the port (ft 2 ), L is the length of the port (ft), and V is the cavity volume (ft 3 ).


Your first mistake is looking only at square footage instead of cubic volume as well. Second, it is significantly easier to deal with a single, large common volume than it is to deal with a "pipe organ" of different frequencies by dividing the volumes up into four different zones.


Unless you REALLY understand fully what you are doing AND have the accompanying caliber of room (full professional acoustic analysis / treatments), then just build the riser, fill it from floor to decking with the pink fluffy stuff and call it a day.
 
#126 ·
Quote:
Originally Posted by TMcG
DIY - here is the formula for calculating the resonant frequency of a Helmholtz Resonator where f is the resonant frequency (Hz), c is the speed of sound (1120ft/s), p =3.14, S is the area of the port (ft 2 ), L is the length of the port (ft), and V is the cavity volume (ft 3 ).


Your first mistake is looking only at square footage instead of cubic volume as well. Second, it is significantly easier to deal with a single, large common volume than it is to deal with a "pipe organ" of different frequencies by dividing the volumes up into four different zones.


Unless you REALLY understand fully what you are doing AND have the accompanying caliber of room (full professional acoustic analysis / treatments), then just build the riser, fill it from floor to decking with the pink fluffy stuff and call it a day.
Point well taken. Even when I was in graduate school I was not particularly good at solving partial differential equations. Today, I don't stand a chance.


I have converted my design to a single large partition using bar-type long registers. See attached.


(While I knew that resonance is a function of volume, not surface area, I provided the latter because I figured that it is more easily understandable).


Thanks.


Now, I have to correct some past mistakes. I had not thought of a riser going all the way to the rear and side walls, but to be an effective bass trap, it must. I will remove the baseboards that I had installed - hopefully easy because the finish nails were driven into two layers of drywall.

 

Riser Design ver. 2.pdf 173.283203125k . file
 

Attachments

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