Home Theater design - 5.1 vs. 7.1 and Consumer vs. Pro - AVS Forum
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post #1 of 22 Old 07-31-2009, 10:44 AM - Thread Starter
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What a fantastic forum! I've been reading for several weeks, but now I could really use some help with my particular setup.

I am building a small home theater in my basement (see image below... the actual room is 26.5 x 14.5 x 7.5, but I'm planning to build a partition in the basement to bring the rear speakers (if I use 7.1) closer and the front. I will also be building a wall about 15 inches from the front wall to hide the speakers and flush-mount the TV. I will probably build decorative columns around the perimeter to hide the surrounds as well.

So far I have the Denon AVP-a1hdci processor, a PS3 along with a 60" Kuro Pro 141-FD Elite Plasma display. I am currently looking at purchasing up to 7 Genelec HT206 active speakers for the room.

I am having a difficult time selecting speakers. Due to the narrow shape of my room, the side surrounds will be placed in front of row-two in the theater. If I get 7.1, there will be speakers on the back wall as well. Since these are direct-fire speakers, I'm thinking 7.1 might help create an immersive audio experience for everyone (for an additional $3k). Speaking of which...

I have a film music background and have done a lot of critical listening, I'm considering getting (5) Genelec studio 8050A's which have a broader frequency response (down to 38hz) and 8 inch bass driver... it might be a better bang for the buck. Many studios use these actual monitors for their 5.1 reference rooms.

Which is a better choice for this application.... the consumer Home Theater speakers or Professional monitors (the same used by many studios when actually mixing the tracks)???

I'm trying to achieve a balanced and impressive theatrical experience. Any suggestions would be greatly appreciated!

P.S., The dimensions to the center recliner are for the planned speaker placement... the front of the speaker will sit about 15" from the wall.
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post #2 of 22 Old 07-31-2009, 12:47 PM
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Originally Posted by jlp1021 View Post

I'm trying to achieve a balanced and impressive theatrical experience. Any suggestions would be greatly appreciated!

With your both pairs of surrounds separated by only 30 degrees, you won't hear much (if any) side vs rear separation in the surround field. And with all four surrounds well behind the listening position, there won't be any stable imaging at the sides. I would move the side speakers more in line with the sweet spot, even if that means placing the left side speakers above or next to the door.

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post #3 of 22 Old 07-31-2009, 01:14 PM
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Originally Posted by sdurani View Post

With your both pairs of surrounds separated by only 30 degrees, you won't hear much (if any) side vs rear separation in the surround field. And with all four surrounds well behind the listening position, there won't be any stable imaging at the sides. I would move the side speakers more in line with the sweet spot, even if that means placing the left side speakers above or next to the door.

I agree with this suggestion by experience. Due to my own HT room limitations, I had to place my side surrounds slightly in front of the prime seating positions or sweet spot (elected not to mount high above the door) in order to achieve great 7.1 envelopment. When placed behind the first row and too close to the rear surrounds, I was disappointed.
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post #4 of 22 Old 07-31-2009, 06:23 PM
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I agree with Sanjay and snpanago.

My room is of similar size to yours, probably even shorter in length. I only have one row of chairs.

I moved my side surrounds up to be in line with the chair seatbacks (they were about a foot behind the chairs) which greatly improved the side imaging.

I also moved the back surrounds about a foot closer to each other on the back wall to increase the spacing between them and the side walls/side surrounds. I do not get great L/R imaging from the back surrounds, but side/back/side pans are outstanding. Helecoptors in the surround channels make me duck!

I would go with good consumer speakers. They are designed to sound good at all volume levels with proper frequency response and dispersion. Pro speakers are designed only to play LOUD!
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post #5 of 22 Old 08-01-2009, 07:19 AM
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Listener preference studies suggest that first reflections from approximately 60 degrees from midline (range 30-90) are the most important in contributing to auditory source width and image broadening. The relevance to multichannel content is that signals from these direction can help create the impression of a different acoustic environment than the actual room used for playback. Hence, the new Audyssey DSX suggests that 6th and 7th channels should be the wide front channels, rather than side surrounds.

Furthermore, International Telecommunication Union, Recommendation ITU-R BS.775-2 suggests a much broader range of angles for surround speaker placement where two or more sets of surrounds are used, with surrounds positioned as far forward as 60 degrees from midline. On the Audyssey website: "The second tradeoff is related to the ITU recommended placement of the two surround channels at ±110°. Surrounds at ±90° were found to produce the most envelopment compared to other angles, while surrounds at ±135° produce better rear phantom imaging capability. Thus ±110° was selected as the best tradeoff between envelopment and imaging [with 5.1]"

In his book "Sound Reproduction," Floyd Toole makes a composite recommendation for surround speaker placement, based on his extensive experience and psychoacoustic research. Suffice to say that the side speakers can be used much farther forward than Dolby suggests with very good results, as pointed out earlier in the thread. You should definitely consider moving the side speakers forward, even if it means putting them in front of the second row or even, potentially, just barely in front of the front row. You really should experiment and find your personal preference here.

In terms of the rear surrounds, you may wish to mount them on the side walls, rather than the back wall. Doing so would put them close to 135 degrees for the sweet spot. However, putting them on the back wall would allow you a little more flexibility in terms of speaker options and acoustic treatments. For example, they wouldn't have to be angled forward, which would create lots of issues with the nearest side wall.

You mentioned constructing partitions in the front and rear. Because you are doing so, and because you have a very small room where the speakers will have to be positioned very close to the walls, you should seriously consider speakers specifically designed for in- or on-wall applications, since the adjacent boundaries would result in seriously compromised performance for typical speakers, which would require significant equalization to turn down the bass but which would still leave a huge null centered around the frequency equal to 565/2xdistance (in feet) from the bass driver to the boundary, so around 300 Hz or so for the Genelec 8050A speakers you mentioned. Flushing mounting the speakers would avoid this cancellation but still require significant equalization for the Genelecs. The HT206 appears to be out of production, but looking at the technical specifications, these appear to be designed for free field applications, i.e. placed significantly away from room boundaries.

in theory, putting LOTS of absorption on the walls behind and near each speaker could be helpful but a little unpredictable. You should definitely consider allocating a significant portion of your budget to room treatments, specifically bass trapping and some amount of absorption and diffusion (lots of absorption on the front wall, the parts of the rear partition near the opening in the middle, and the back wall so that the center channel speaker doesn't just bounce back, also near the ceiling, floor, and corners; diffusion at ear level on the side walls and the sides of the back wall). Without any consideration of room treatment or appropriate use for the loudspeakers, buying the Genelecs for this room in the applications you describe would be a little like taking an expensive sports car and then crippling its performance by putting on bicycle tires and then driving around in subzero ice or offroad (!).

Lastly, you may wish to use multiple subwoofers (don't listen to anyone who mentions the Harman paper because your room doesn't fit the needed assumptions) to provide a similar and smoother bass experience for multiple listeners.
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post #6 of 22 Old 08-01-2009, 10:42 PM - Thread Starter
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Wow! Thank you all for the fantastic responses. Youngho.... quite impressive- thank you for such a detailed and tailored response. Based on the suggestions you have provided, I have made a few changes to my sketch. Please take a look and let me know what you think. Here are a few notes regarding the update:

1) The Left surrounds reflect Youngho's suggestions... placing the side surrounds just in front of the door puts the speaker at 60 degrees. The rear left surround is also placed on the side wall at 135 degrees.

2) The Right surrounds demonstrate bringing the side surround perpendicular to the sweet spot at 90 degrees (just next to the door on the other side). This would actually also be 60 degrees for the second row of seats. I have left the rear surround on the wall at 150 degrees.

3) I should have clarified that the speakers I'm looking at are the Genelec HT206B's which have replaced the HT206's. Nonetheless, these are probably not designed specifically for on-wall mounting... I'm not sure. I'm looking at the Genelec's because they are active speakers (amps and speakers engineered to provide the Genelec character without other influence).

4) Youngho made an excellent observation: I plan to use Audyssey to handle problems with the room. If I buy the Genelecs to get a neutral sound (as much as possible), I'd better put some acoustic treatment in the room to avoid EQ'ing as much as possible! I've got some additional research to do in this area. I do plan on placing a curtain on the back wall (and even a pair of doors that can close behind the curtain (if advisable).

5) I'm planning on placing a subwoofer in the front wall; off-center. The sub is suggested for a larger room up to 4,000 cu. feet (my room will only have about 2,000 cu. feet), but the next model down is only a few hundred dollars cheeper and apparently disappoints (sales talk I'm sure, but buying two of the smaller ones gets a little pricey... I have to check).

6) A note about partitions in the room. I'm planning these simply because I thought they might help. The front wall makes sense to me to hide the speakers and gear.... the back on the other hand, doesn't need to be there at all if you think it shouldn't. This would increase the room length by another 7 feet.

So.... what do you think? Am I on the right track?

Thanks again to those that have voiced their opinions... it's much appreciated!
LL
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post #7 of 22 Old 08-02-2009, 12:46 AM
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(1) The 60 degree surround in front of the door is a bit too far forward when the angle is (re)measured from the same side rear [nearside] seat (maybe 40 degrees?); it's too close an angle to the same side main. [And you might want to reserve the 60 degree position for a possible future "front wide" speaker...?]

(2) Rumor(?) says that DTS has a new post processor ["Advanced Neo"] coming 'soon' which supports up to 6 rear surround speakers. In your place, I'd wait to see what is announced at CEDIA in September. Then look where you might put the (say) 6 rear speakers in the future, but only install 4 of them now.

(3) I'm a big fan of a single Center Surround speaker under certain conditions, and of having the option for center-back co-located Left and Right Back speakers, so I'd probably move the rear door off center to preserve a central rear pillar.

(4) Wire now for Front Height speakers in the future.

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post #8 of 22 Old 08-02-2009, 01:17 AM
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Quote:
Originally Posted by jlp1021 View Post

Wow! Thank you all for the fantastic responses. Youngho.... quite impressive- thank you for such a detailed and tailored response. Based on the suggestions you have provided, I have made a few changes to my sketch. Please take a look and let me know what you think. Here are a few notes regarding the update:

1) The Left surrounds reflect Youngho's suggestions... placing the side surrounds just in front of the door puts the speaker at 60 degrees. The rear left surround is also placed on the side wall at 135 degrees.

2) The Right surrounds demonstrate bringing the side surround perpendicular to the sweet spot at 90 degrees (just next to the door on the other side). This would actually also be 60 degrees for the second row of seats. I have left the rear surround on the wall at 150 degrees.

3) I should have clarified that the speakers I'm looking at are the Genelec HT206B's which have replaced the HT206's. Nonetheless, these are probably not designed specifically for on-wall mounting... I'm not sure. I'm looking at the Genelec's because they are active speakers (amps and speakers engineered to provide the Genelec character without other influence).

4) Youngho made an excellent observation: I plan to use Audyssey to handle problems with the room. If I buy the Genelecs to get a neutral sound (as much as possible), I'd better put some acoustic treatment in the room to avoid EQ'ing as much as possible! I've got some additional research to do in this area. I do plan on placing a curtain on the back wall (and even a pair of doors that can close behind the curtain (if advisable).

5) I'm planning on placing a subwoofer in the front wall; off-center. The sub is suggested for a larger room up to 4,000 cu. feet (my room will only have about 2,000 cu. feet), but the next model down is only a few hundred dollars cheeper and apparently disappoints (sales talk I'm sure, but buying two of the smaller ones gets a little pricey... I have to check).

6) A note about partitions in the room. I'm planning these simply because I thought they might help. The front wall makes sense to me to hide the speakers and gear.... the back on the other hand, doesn't need to be there at all if you think it shouldn't. This would increase the room length by another 7 feet.

So.... what do you think? Am I on the right track?

Thanks again to those that have voiced their opinions... it's much appreciated!

I like it that you are incorporating new information in planning your room. I have a couple of things for you to consider. Ethan Winer has excellent guidelines for setting up rooms including the 38% rule here http://www.realtraps.com/art_room-setup.htm
This may give you more ideas as to where the prime seating/listening position(s) might be placed within your space. Also, your new speaker positions may indeed work out and sound excellent. However, based on asymmetrical placement of the 4 surrounds within your rectangular room, there may be some complex wave reflections that interact at both rows of seats (not sure of this). You may find that there are enough feet of separation between the front row of seats and the rear wall, that the side surrounds could be placed at a nice height on a line just to the rear of the first row of seats. And the rear surrounds can be placed likewise on a line on the rear wall or at the back of the side walls. I know you've used suggested angles and degrees of separation on your intial setup plans....however....you seem to have plenty of space between the front row of seats and the rear wall to experiment with placement, well before you make any permanent wiring and mounting moves. Same with the Subwoofer placement, especially if purchasing just one. Bass from subwoofers is very heavily influenced by room characteristics. You can find entire threads or internet articles regarding methods to find the best location for your sub to reduce room nulls and maximize its frequency response output.
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post #9 of 22 Old 08-02-2009, 06:59 AM
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Please take any and all of my suggestions with a handful of salt. I highly recommend buying "Sound Reproduction" by Floyd Toole.

Quote:
Originally Posted by jlp1021 View Post

1) The Left surrounds reflect Youngho's suggestions... placing the side surrounds just in front of the door puts the speaker at 60 degrees. The rear left surround is also placed on the side wall at 135 degrees.

I would highly recommend experimentation in situ here. I believe that the best all-around compromise would probably be 90 and 150 for the side and rear surrounds, but you should really consider trying it a few different ways, if you can.

[quote]
2) The Right surrounds demonstrate bringing the side surround perpendicular to the sweet spot at 90 degrees (just next to the door on the other side). This would actually also be 60 degrees for the second row of seats. I have left the rear surround on the wall at 150 degrees.
[quote]

I assume that this diagram is simply illustrating four different possibilities for surround placement (60, 90, 135, 150). I think the situation illustrated by the right surrounds will probably represent a better experience for all listeners compared to the left surrounds. Obviously, you would want a symmetric setup.

Quote:


3) I should have clarified that the speakers I'm looking at are the Genelec HT206B's which have replaced the HT206's. Nonetheless, these are probably not designed specifically for on-wall mounting... I'm not sure. I'm looking at the Genelec's because they are active speakers (amps and speakers engineered to provide the Genelec character without other influence).

Looking at the Genelec website, it does appear as though they do have a "bass roll-off" control that appears to dial down the bass below a hinge frequency of around 250 Hz, so maybe this would work out okay, assuming that you could do some basic measurements.

Quote:


4) Youngho made an excellent observation: I plan to use Audyssey to handle problems with the room. If I buy the Genelecs to get a neutral sound (as much as possible), I'd better put some acoustic treatment in the room to avoid EQ'ing as much as possible! I've got some additional research to do in this area. I do plan on placing a curtain on the back wall (and even a pair of doors that can close behind the curtain (if advisable).

Keep in mind that Audyssey will be of relatively little help with the cancellation that will occur at around the frequency calculated by 565 divided by twice the distance from the bass driver to the wall. Boosting a null like this will be frustrating for you and your amplifiers. Looking at the data on adjacent boundary effects in Toole's book, I surmise that wall mounting with at least 4 inches of fiberglass behind and around each speaker will probably help reduce this cancellation (you would need significant absorption below 500 Hz).

Really heavy, thick velour curtains draped at 50% of their flat width, with some air space (say, 4-6" behind them) will provide reasonably broad-band absorption, rolling off below 1 kHz. Having an opening in the back can have pluses and minuses. The opening will change the standing wave patterns and act as a partial "absorber," since not all of the reflections off the rear wall will make their way back into the room. Closing off the room may help make your standing waves a little more predictable and possibly contribute to low frequency gain (cabin gain), assuming that the room is relatively "tight" in terms of air movement.

Quote:


5) I'm planning on placing a subwoofer in the front wall; off-center. The sub is suggested for a larger room up to 4,000 cu. feet (my room will only have about 2,000 cu. feet), but the next model down is only a few hundred dollars cheeper and apparently disappoints (sales talk I'm sure, but buying two of the smaller ones gets a little pricey... I have to check).

Optimizing subwoofer performance can be complicated. You will definitely want to take measurements and experiment here. Just think about your priorities (deepest bass possible? smoothest bass for multiple listeners?) and future upgrade plans (later add more subwoofers and/or processing like parametric equalizer or JBL BassQ?)

Quote:


6) A note about partitions in the room. I'm planning these simply because I thought they might help. The front wall makes sense to me to hide the speakers and gear.... the back on the other hand, doesn't need to be there at all if you think it shouldn't. This would increase the room length by another 7 feet.

If you're looking to hide the front speakers gear, maybe you could build a partial partition in the center so that you can hang your television and flush-mount the center channel speaker. You might create large panels consisting of wooden frames with an acoustically translucent cloth like Guilford of Maine stretched across them. These could be placed to the sides to hide the left and right speakers, which would be placed directly behind them. Also, you could hide LOTS of absorption back here.

One thing to consider is that you can construct some of the partitions as large panel/diaphragmatic bass traps. I know that some experts like Terry Montlick argue against it, but Toole describes some of the bass trapping that drywall confers. Also, I believe Earl Geddes (www.gedlee.com) discusses methods of wall construction in his book on home theater, as well as at www.diyaudio.com (look for a very long thread about multiple subwoofers in the loudspeaker forum).

With regards to a center rear channel speaker, Toole and Holman argue against it, even though Audyssey seems to incorporate it.
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post #10 of 22 Old 08-02-2009, 07:19 AM - Thread Starter
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Originally Posted by snpanago View Post

based on asymmetrical placement of the 4 surrounds within your rectangular room

Sorry folks.... I should have clarified that I will probably keep things symmetrical. I just wanted to illustrate both options. Based on SoundChex point that the nearest seat will be at a much narrower angle than 60 degrees, I'm leaning towards the 90 degree side surround.... on both sides. I'm not sure about the rear's yet. Also, I'm reading about the 38 percent rule... I could bring the back partition in closer to the seats to help achieve this and place a regular sized door off-center in the back.... At this point, I've got a lot of options, the room is just studs and concrete now.

By the way, I should mention that the ceiling is only 7.5 feet high. I'm planning on doing a drop ceiling of about 2 inches to run the XLR cables (and maybe even fiber optic stars. To make things even tighter, I'll probably put in a riser for the second row of seats!
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post #11 of 22 Old 08-02-2009, 07:30 AM
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One thing to consider is that you can construct some of the partitions as large panel/diaphragmatic bass traps. I know that some experts like Terry Montlick argue against it, but Toole describes some of the bass trapping that drywall confers. Also, I believe Earl Geddes (www.gedlee.com) discusses methods of wall construction in his book on home theater, as well

I agree with Floyd on many points. This is one where we differ. Softwall construction (while remaining code compliant) provides very little low frequency bass absorption. What is presumed to be low frequency absorption is high transmission losses through the partition. Furthermore, such methods cannot be considered broadband, indeed can be rather narrow, difficult if not impossible to predict, and likely within spectra you want left alone.

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post #12 of 22 Old 08-02-2009, 07:59 AM
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Originally Posted by youngho View Post

One thing to consider is that you can construct some of the partitions as large panel/diaphragmatic bass traps. I know that some experts like Terry Montlick argue against it, but Toole describes some of the bass trapping that drywall confers. Also, I believe Earl Geddes (www.gedlee.com) discusses methods of wall construction in his book on home theater, as well as at www.diyaudio.com (look for a very long thread about multiple subwoofers in the loudspeaker forum).

Actually, I don't remember arguing this (though I might have said it in reference to some cases). I certainly recommend panel bass absorbers under the appropriate circumstances.

But one thing to be aware of is that a panel trap may provide undesirable resonance while still curing the resonance it was meant to treat. This can happen if the trap resonance doesn't match the problem resonance well enough.

This was brought home to me in a recent room design. We built a set of panel traps, but are scrapping them after they were discovered to do more harm than good. They had broad enough Qs to easily cover and eliminate the problem resonance. But their amplitudes were just too high (they were too good), so that the self-generated resonance at other frequencies became a new problem!

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post #13 of 22 Old 08-02-2009, 10:27 AM
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Actually, I don't remember arguing this (though I might have said it in reference to some cases). I certainly recommend panel bass absorbers under the appropriate circumstances.

I'm sorry, I didn't mean to misrepresent your opinion. The word "this" was meant to refer to the use of drywall for bass trapping, not diaphragmatic absorbers. "Pronoun problems," as Bugs Bunny might say.

I was hoping to hear what commercial panel absorbers you might recommend, like perhaps the RPG Modex Plate or Broadband? I was also hoping to hear what suggestions a professional like yourself might have for the original poster's room. I know that there can be a wide variety of opinions. I'm just curious to hear yours. I read about your role in the TWBAS room on UltraAudio.

Take, for example, the back wall. I've seen many professional installations use diffusers, instead of absorbers, in the middle, but Toole has more than once suggested using absorption in the middle and diffusion off to the sides of the rear wall. In TWBAS, which seemed to be designed for two channel playback, you used a diffuser above an absorber.

For the original poster, the 38% rule is just a rule of thumb that Ethan Winer freely acknowledges that "may not end up the best place to sit due to other factors - wall properties, speaker location, speaker type, furnishings in the room, and a host of other conditions that can affect frequency response." Interestingly, although Ethan doesn't mention it, most listeners will sit with their ears about 36" or so off the ground, so close to 38% in standard sized rooms. Unfortunately, if you do construct a riser, the second row will be much closer to midway between the floor and ceiling, so consequently, they may perceive a relative null at around 75 Hz or so if you set your crossover frequency too high and have the subwoofer on the floor. I don't know what your budget for the subwoofer is, but there is a slightly insane subwoofer from Danley called the TH Spud that can be used as a riser for the second row. I'm sure this would be massive overkill for your project.
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post #14 of 22 Old 08-11-2009, 03:55 PM - Thread Starter
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Thanks again for your help. I have ordered the book by Toole that you recommended and am currently in the process of trying to get some additional guidance from a few difference acoustical treatment companies. For absorption/reflection treatment of the walls, what do you think about panels like these from GIK Acoustics? http://www.gikacoustics.com/gik_242_elite.html

What is the best way to determine what kind of treatments I need for this room? I simply have studs, concrete floor and joists for the ceiling so I have a really blank slate to work with. The only isolation I need to really concern myself is the ceiling since it's a basement.

Thanks again!
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post #15 of 22 Old 08-11-2009, 06:05 PM
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Originally Posted by jlp1021 View Post

Thanks again for your help. I have ordered the book by Toole that you recommended and am currently in the process of trying to get some additional guidance from a few difference acoustical treatment companies. For absorption/reflection treatment of the walls, what do you think about panels like these from GIK Acoustics? http://www.gikacoustics.com/gik_242_elite.html

What is the best way to determine what kind of treatments I need for this room? I simply have studs, concrete floor and joists for the ceiling so I have a really blank slate to work with. The only isolation I need to really concern myself is the ceiling since it's a basement.

Toole discusses various forms of acoustic treatments in his book, as well as years ago in this white paper (http://www.harman.com/wp/pdf/Loudspe...ndRoomsPt2.pdf). From GIK Acoustics, you would probably want to start with 244 or Monster "bass traps" that are actually broadband absorbers (I did clarify this with the company). The problem with panels thinner than 4" is that they tend to absorb too much of the mids and highs relative to bass frequencies (from what I understand, RealTraps avoids this by adding a limp mass membrane that helps with bass absorption but makes it more reflective at higher frequencies). In terms of DIY panels, one might use FRK fiberglass panels, which have a metallised paper facing for a similar purpose.

There is no best way. Different people take different approaches when it comes to room acoustics, so please keep in mind that all of the following may be controversial.

1. Home theaters are generally designed to be "deader" than stereo listening rooms. If you plan to use the room only for this purpose, that would be fine. I'm going to focus on that usage.
2. Most folks would agree that absorption on the front wall is desirable. This should be located behind and between the front speakers. If using fiberglass, probably at least 4-6" thick with some air space behind it would be desirable. If you're making it yourself, you might even consider layering different densities of fiberglass (looser in front, thicker in back).
3. Absorption or a limited amount of diffusion on the rear wall behind the listening position is probably desirable, as discussed in the book and white paper. I have seen a number of professional installations with a diffuser in the middle of the back wall. Unfortunately, good diffusers tend to be thick and expensive. If I recall correctly, you will have French doors in the middle of the back, so you could mount 4-6" fiberglass on the insides of the doors themselves.
4. Floor reflections are almost never desirable, so a thick cut pile carpet with a very thick hair felt underlay is probably about as good as you can do. Because this is a very large surface, this may make some rooms seem a little "dead", but again, for home theaters, this may be fine.
5. Side walls start to get controversial in terms of appropriate treatments. The standard "first reflection" approach advocated by many professionals may not be as applicable in home theater because of the heavy usage of the center channel speaker, which may benefit from having its first reflections left intact. Doing so may help broaden the apparent source of sound (think of virtual images), which can be particularly helpful when looking at a large screen but listening to a point source. Certainly, eliminating flutter echoes will be helpful, but this can be done with diffusion, angled or curved reflectors, and/or absorption. If you're handy, you can do quite a lot of this yourself.
6. Bass trapping is always a good thing. However, you may wish to take some basic measurements in your room once you've constructed your partitions and put some stuff into the room in order to identify your problems and spend your money where it's needed most, since different products may have different absorption at different frequencies. You may be able to address some bass problems by using multiple subwoofers (placement and setting of level and phase or delay will be absolutely critical) and judicious use of parametric equalization. There are many ways to approach this, including the superchunk, panel straddling the corner, Helmholtz resonator, membrane or diaphragmatic absorbers, etc. Unfortunately, it's difficult to compare different methods and products.
7. In terms of the ceiling, absorption or lateral diffusion at the first reflection point from the main speakers would be helpful. You'll have to look into a floating ceiling and methods of "sealing" the room if you're worried about isolation.

Sorry I can't be more specific, I have only a casual amateur's interest. You should identify a budget and do some reading/learning (after which you should increase that budget for acoustic treatments because you'll realize how important the room itself can be).
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post #16 of 22 Old 08-11-2009, 06:29 PM
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I believe that the best all-around compromise would probably be 90 and 150 for the side and rear surrounds, but you should really consider trying it a few different ways, if you can.

Josh, the above is how I would place my surrounds, based upon your new diagram. The 60-degree rear spread should allow you to hear stereo separation behind you. If not, experiment with spreading the rear speakers slightly wider, until you can clearly separate sounds coming from over your left shoulder vs sounds coming from over your right shoulder. Place the speakers on temporary stands (step ladders, stacks of boxes, whatever) that you can move around. For a sound source, use the calibration noise from your pre-pro.

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post #17 of 22 Old 08-24-2009, 01:32 PM - Thread Starter
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Thank you once again for your detailed suggestions. They are quite helpful!

I have also been reading Toole and getting some suggestions from a expert at GIK. I have identified my reflection points and plan on finding the appropriate absorption material to place on the side walls. I am trying to be a little artistic which is making things more difficult. Please see the attached images. I have a foundation wall that comes up 22 inches high from the floor and 6 inches into the room. With this ledge, I have an opportunity to be a little creative.

In the one view, you can see the side wall straight-on and toward the right of the image, you can see where I've marked the reflection points (little blue squares) and where 2 inch absorption panels probably need to be. You will see the black rectangle around the door here as well (this is going to be a challenge). Each color in the graphic represents a 1 to 2 inch thick panel (stretched fabric over a frame). The back wall (dark blue) is painted drywall. The second graphic shows my version of the "column" from the side that will be used to hide the speaker. I have enough room to place 4 inches of absorption material on the sides, top and bottom of the speaker.

So, if the absorption panels are behind the cloth, the design shouldn't really matter.... correct?? And here is the big question.... which material would work best for this. Guilford of Main 2100 .... is this hard to work with? I will have to purchase everything online, so I can't really go see it in person to know how difficult this is going to be (or if it will even look good once it's done). I was even thinking of creating this design simply using drywall, and then placing the panels where they need to be, but built into the wall.

I am pretty handy and plan on doing this all myself except perhaps purchasing a few bass traps and tri-traps from GIK.

Since my walls are up to 6 inches thick on the sides, would there be any benefit to 6 inch panels (where the design allows.... bottom portion of panel and 2-4 inches thick at the top). Speaking of which... now I need to identify what kind of insulation I'll use (cotton, fiberglass, etc...)

Any suggestions or comments?

Thanks again!
LL
LL
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post #18 of 22 Old 08-25-2009, 04:46 AM
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Thank you once again for your detailed suggestions. They are quite helpful!

Great, I'm glad, but keep in mind that your personal preferences are paramount.

Quote:


I have also been reading Toole and getting some suggestions from a expert

Take a look at chapters 16, 21, and 22, in particular. This is where you will find the most relevant and highest value information for your project.

Quote:


attached images. I have a foundation wall that comes up 22 inches high from the floor and 6 inches into the room. With this ledge, I have an

This foundation wall runs along the bottom of the front, right, and most of the left walls?

Quote:


In the one view, you can see the side wall straight-on and toward the right of the image, you can see where I've marked the reflection points (little blue squares) and where 2 inch absorption panels probably need to be. You will see the black rectangle around the door here as well (this is going to be a challenge). Each color in the graphic represents a 1 to 2 inch thick panel (stretched fabric over a frame). The back wall (dark blue) is painted

Sounds like an awful lot of mid- and high frequency absorption to me, which may result in an imbalanced sound. I would consider diffusion or angled reflectors. If you prefer lots of absorption, an alternative to what you propose could be something more like the RPG Abflector, since the absorption from angles (say, 60) can be idiosyncratic compared to absorption from a normal incidence (90 degrees). It would be nice if they absorbed perfectly like black holes for sound, but they don't. Take a look at Chapter 21. Or here: http://www.avguide.com/blog/robert-h...iracle-upgrade

Take a look at this interview with Keith Yates for an alternative perspective regarding the use of absorption relative to diffusion and angled reflection: http://www.hometheaterdesignmag.com/...rs/1007listen/

Quote:


drywall. The second graphic shows my version of the "column" from the side that will be used to hide the speaker. I have enough room to place 4 inches of absorption material on the sides, top and bottom of the speaker.

Take a look at Chapter 12 to see why I made this suggestion, paying special attention to the graphs.

Quote:


So, if the absorption panels are behind the cloth, the design shouldn't really matter.... correct?? And here is the big question.... which material would work best for this. Guilford of Main 2100 .... is this hard to work with? I will have to purchase everything online, so I can't really go see it in person to know how difficult this is going to be (or if it will even look good once it's

The actual absorption material itself probably isn't critical, as long as it represents resistive absorption. You may find better results by layering less dense material towards the front and more dense material towards the back. I don't know if any cloth is "the best", but Guilford of Maine is a consistent and readily available commercial product, so I think of it like some of the "pro monitor" speakers that are used outside of the studio. Take a look at Chapter 21 to see how cloth covering can alter the absorption characteristics of fiberglass.

Quote:


done). I was even thinking of creating this design simply using drywall, and then placing the panels where they need to be, but built into the wall.

As long as you're comfortable with the possibility that the panels may not be exactly the dimensions that you allot for them, that could give you a somewhat "modular" approach. If you took this approach to both side walls more generally, you could trade out absorption panels for diffusion ones to adjust to personal preference, although the depth for the latter would be more than for the former.

Quote:


Since my walls are up to 6 inches thick on the sides, would there be any benefit to 6 inch panels (where the design allows.... bottom portion of panel and 2-4 inches thick at the top). Speaking of which... now I need to identify

Yes, either thicker absorption or an air gap behind the absorption would generally be beneficial.
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post #19 of 22 Old 08-25-2009, 08:06 AM - Thread Starter
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I've got some reading to do today.... thanks again for your input! Just a few quick things:

---This foundation wall runs along the bottom of the front, right, and most of the left walls?---
It runs along the front and left. I plan on building out the same ledge on both sides to make things symmetrical.

---Sounds like an awful lot of mid- and high frequency absorption to me, which may result in an imbalanced sound.---
I should clarify that the colored panels in the drawing are not completely filled with insulation. Only where the reflection points are (three panels on each side hidden behind the fabric). They would be hollow the rest of it, so the sound would reflect off of the drywall behind them. I've read that the GOM is also somewhat transparent "visually" so you would be able to see the framing behind it... if this is the case, my idea might not look so great when all is said and done.

I also plan on having two bass traps in the back center of the room, tri-traps in the front corners and absorption panels behind each of the 3 front speakers as well.
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[quote=jlp1021;17059599]
[/i]It runs along the front and left. I plan on building out the same ledge on both sides to make things symmetrical.
[/quote

Great, some overall symmetry of the acoustic environment is helpful.

Quote:


[/i]I should clarify that the colored panels in the drawing are not completely filled with insulation. Only where the reflection points are (three panels on each side hidden behind the fabric). They would be hollow the rest of it, so the sound would reflect off of the drywall behind them. I've read that the GOM is also somewhat transparent "visually" so you would be able to see the framing behind it... if this is the case, my idea might not look so great when all is said and done.

Oh, I see. If you decide to place absorption at the first reflection points towards the fronts of the side walls, you should consider thicker panels, like the GiK 244. I believe that the lighter GOM colors are more visually transparent than others, so consequently they can require a white scrim underlay (you can get a sense of that here: http://www.rpginc.com/residential/pdfs/FR701.pdf), but I would imagine that this would depend on the color of the wall or material behind the GOM, too. If you used a darker color of GOM fabric (probably desirable for home theater, anyway) painted everything behind the GOM a nonglossy black, including the framing, I suspect that this would be less visually obvious.

If you're a handy guy who can cut wood to specific widths and depths, you might look into constructing wide QRD diffusers like http://www.rpginc.com/products/qrd73...20Brochure.pdf for each side wall, which you could then cover with your GOM cloth. You can find information about doing this online, sorry, I don't know much about it. It wouldn't be as sleek as your design, unfortunately, but you could cover it with GOM fabric to hide it, like in this very nice example: http://www.hometheaterdesignmag.com/...s/107illusion/
. It looks like the left part of the front wall could accomodate at least 3' wide, the back part quite a bit wider. The nice thing about wider panels is that they can accomodate longer sequences and also allow for diffusion further down the frequency spectrum into the transition zone. Obviously, the door would be handled differently, so you could place an absorption panel on it and another one across from it on the opposite sidewall.

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post #21 of 22 Old 07-08-2010, 06:07 PM - Thread Starter
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Okay... so it has been quite some time since my last post. I've been working hard to get regular design elements figured out (lighting and structure in particular) before moving forward with the build. While trying to figure out how to make a decent presentation and include the elements I want (superb sound without fan noise from a projector, star ceiling, soffit's, decent way to hide the speakers, etc...) I've been struggling with a 7.5' ceiling height and 13'10" room width, I stumbled upon a build that provided quite a paradigm shift.

The Saga of the "Old Vic" build has truly inspired me.

I'm sure there will be significant differences in my build, but Moogie is doing very much what I would LOVE to do. So..... I just made my first call to a very reputable structural engineer in my area. I think I may very well start the dig under my house. The current basement can become a lobby/game room and I've got plenty of room under the rest of the house to really have FUN!

Staying within the existing footprint, I have a 20' x 40' space with possibly a 10' ceiling for the theater.

Now, I know this is much larger than I would want, and was curious if anyone had a few pointers on ideal room size.

I'll probably be upgrading the smaller speakers I purchased and going with a large curved screen, but by going this route, my constraints will only be financial (which can be a burden, but I plan to do a great deal of the work myself). Any thoughts?
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post #22 of 22 Old 07-09-2010, 06:36 AM
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I would just use the entire room. It will allow you to have ALL the listeners in a large sweet spot and away from room boundries.

Imagine you walked into a movie theatre with a 200-seat capacity, but all the seats had been removed except for about 40, clustered around the best location in that auditorium. There wouldn't be a bad seat in the house. No one too close to the left wall or right wall, no seat too far back or front.

Something similar can be done in a 20' x 40' room. The space around the seating can be filled in: up front you can do a nice stage, in the back maybe do a food prep area or bathroom or projection booth/room with equipment & media storage.

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