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Author Topic: Surround?  (Read 4042 times)

Sonovo

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Surround?
« on: November 06, 2007, 04:09:29 pm »

What, if any special requirements/treatments are neccessary when dealing with a surround room as opposed to a stereo room?

With several added sound sources, will room node excitement change (or be amplified)? I would expect that issues dealing with reflection would be the same, just for more speakers.

What about the sub? Are there special problems to deal with there?

Would a good stereo room be a good candidate for a suuround room, or are the requirements different?

Cheers,
Thor
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New Room

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Re: Surround?
« Reply #1 on: November 07, 2007, 02:29:44 am »

I would imagine that a good surround room would be a good candidate for a stereo room, but not vica versa.
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gullfo

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Re: Surround?
« Reply #2 on: November 07, 2007, 10:24:56 am »

room modes are room modes but the position of things in the room, and the differences between soffit mounted or free standing monitors will introduce design challenges. my take is a surround environment takes a bunch more "smaller" adjustments (details) to get things working right as opposed to a stereo room.

in an existing stereo room with free standing monitors, its probably "easier" to "extend" that into a surround room than if you have monitoring with soffits as the additional surround baffles will change the room reflections/absorption, bass response, etc.

subs are always a challenge to find the right placement. if you currently have a sub and its set for the room, then you are probably ok as its not likely to change much in a free standing monitoring situation, but will likely need to be changed if the room boundary configuration is updated.
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Ethan Winer

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Re: Surround?
« Reply #3 on: November 07, 2007, 04:00:45 pm »

Sonovo wrote on Tue, 06 November 2007 16:09

What, if any special requirements/treatments are neccessary when dealing with a surround room as opposed to a stereo room?

The main difference from my perspective is you have more first reflection points to deal with. There shouldn't be much difference in the low end, assuming the speakers are set up properly with bass management so the lowest frequencies come from a single subwoofer source. But higher bass frequencies can be an issue as explained below.

Quote:

What about the sub? Are there special problems to deal with there?

No problems that aren't present in a stereo room that uses a sub. But subs can be a problem because bass frequencies around the crossover point now come from four (or six) places instead of only two as with stereo. Bass is tough enough to get right in any room, without worrying about additional peaks and nulls caused by multiple disparate arrival times. (I can't believe I actually used "multiple disparate" in a sentence!)

Quote:

Would a good stereo room be a good candidate for a suuround room, or are the requirements different?

My living room setup is fabulous for both. Some people wrongly believe (IMO) that a stereo room should be liver sounding than a home theater surround room. But I disagree with that. Small room ambience is generally lousy ambience, and the best solution is to absorb (or diffuse) it.

--Ethan

Sonovo

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Re: Surround?
« Reply #4 on: November 07, 2007, 05:44:11 pm »

Gulfo, Ethan, thanks for the informative replies.

Let's see...

I don't have any subs at present. My current monitors are -3dB at around 37Hz, the room is well treated for both bass and primary reflections (actually sounds pretty good).

Existing monitors are free standing towers, dipoles (I know, those in the know want us all to use point sources, yet I'm using a line source). Let me at least try it first and see, ok? Razz

I expect due to the monitor type I'll have to be extra careful about dealing with the rear wave of each monitor, in adition to the issues already mentioned with additional reflections.

Room size is around 9m long by 5 or 6 m wide.

From what other mastering folks have recommended, I'm considering going with dual subs. There was a suggestion to try out opposite corner placement (which will need to be verified through listening and measurement).

Ethan, does that mean I need to tune the subs response to both the speakers and to the room/nodes? Through both placement as well as crossover and level adjustment? Phase as well this far down?

Would a surround room without subs (but with response say down to around 34Hz or so) be usable, or is 20-35Hz an important part of the equation (for music, I expect film requirements will be different).

Thor
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gullfo

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Re: Surround?
« Reply #5 on: November 07, 2007, 08:48:49 pm »

here's some interesting articles on surround, sub placement and adjustments

http://www.wsdg.com/data/edithtml/resources/technology/Image s//070321%20-%20dk%20-%20js%20-%20v5%20-%20Ov...doc

http://www.genelec-ht.com/documents/publications/Multichanne lControlRoomAcousticsandCalibration.pdf

http://www.genelec-ht.com/documents/publications/Placementan dRoomAcousticsInteraction.pdf

http://www.rbdg.com/newsroom/designSurroundPro/

http://www.linkwitzlab.com/frontiers.htm (since you mentioned dipoles - page 4-5)
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franman

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Re: Surround?
« Reply #6 on: November 07, 2007, 10:39:35 pm »

I have to agree with most of what's already been posted. I find the biggest issues in critical (mastering) surround rooms to be:
1. Control of first reflections from additional sources
2. introduction of some diffusion for the rear speakers (diffusion in the front half of the room out of any direct path of the L-C-R speakers).
3. Dealing with the typically whacky LF response of the center speaker.. (It's sitting on a modal axis and it's always going to excite the width modes more than the L-R)
4. placement of subs..

This is a big topic!! I don't know about the E-Trap concept but I do know if you want your room to sound natural down to the lowest octaves, you will need to have trapping to cope with frequencies down in that range. This can be distributed tuned traps with lots of broadband... VERY deep broadband trapping and lots of it... specific tuned traps for room anomolies (and lots of broadband trapping).. starting to see the common thread here??

In our best sounding rooms (LF wise) we have areas in the ceilings (large areas) with 3-4' deep broadband porous absorption! I know it sounds like a lot and it is.. It takes some serious real estate... that's why it's nice to have the ceiling height to put it up there!!

Sub placement is a real trial and error thing. Looking for a natural transition from full range L-C-R to subs (assuming no bass management) is a good starting point... Then move woofer (or woofers) around to get most even response. More woofers will generally make it easier to achieve a smoother response. I believe this is because you are exciting rooms modes and creating boundary interference from multiple locations instead of one... simple but true!

Please remember... use your ears!! It's all about what it sounds like at the end of the day!! I also would agree that a great surround room will generally work quite well for stereo.. the opposite is not necessarily true!
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Sonovo

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Re: Surround?
« Reply #7 on: November 08, 2007, 03:57:06 am »

Gulfo, thanks for the links!

Francis, thanks for the tips!

I think I will make new measurements after the last treatments, and concentrate on getting additional monitors in place sans subs first. When that works I'll get the subs (if needed) and spend some time finding the best positioning.

I have superchunks in each corner, over 1m from the corner and out (almost 2m along the hypotenuse) which help damp things on the bottom end. Might need more I suppose.

The weakest part of my room is that I don't have high ceilings, just standard height (about 2m50cm or so).

Anyway, I now have enough info to get to work, thanks again!

Thor
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Ethan Winer

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Re: Surround?
« Reply #8 on: November 08, 2007, 02:24:50 pm »

Sonovo wrote on Wed, 07 November 2007 17:44

Let me at least try it first and see, ok? Razz

LOL, the rear radiation, which is a byproduct of the design - not a design goal (IMO) - is its undoing.

Quote:

Ethan, does that mean I need to tune the subs response to both the speakers and to the room/nodes? Through both placement as well as crossover and level adjustment? Phase as well this far down?

Yes, it's a big mess and all placements are a compromise. Very Happy

Quote:

Would a surround room without subs (but with response say down to around 34Hz or so) be usable, or is 20-35Hz an important part of the equation (for music, I expect film requirements will be different).

If you're not doing film, and your speakers are -3 dB at 37 Hz, you should be all set.

--Ethan

StudioRhythm

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Re: Surround?
« Reply #9 on: November 10, 2007, 01:25:24 am »

franman wrote on Wed, 07 November 2007 19:39

In our best sounding rooms (LF wise) we have areas in the ceilings (large areas) with 3-4' deep broadband porous absorption! I know it sounds like a lot and it is.. It takes some serious real estate... that's why it's nice to have the ceiling height to put it up there!!



Sorry to hijack, but I just have to follow up on this! How do you approach this -- 4' of 703 (or equivalent), a certain thickness (8"-12"?) of 703 plus an airgap stuffed with regular fluffy insulation, or...? Thanks!!

Ethan Winer

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Re: Surround?
« Reply #10 on: November 10, 2007, 11:20:54 am »

StudioRhythm wrote on Sat, 10 November 2007 01:25

4' of 703 (or equivalent), a certain thickness (8"-12"?) of 703 plus an airgap stuffed with regular fluffy insulation, or...?

As fiberglass is made thicker / deeper, you can get away with lower density. So if you have four feet available you can get similar results for less money with the fluffy type.

But I'll be interested to hear what Fran has to say about what he uses when four feet is available.

--Ethan

franman

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Re: Surround?
« Reply #11 on: November 13, 2007, 07:54:12 pm »

Ethan Winer wrote on Sat, 10 November 2007 11:20

StudioRhythm wrote on Sat, 10 November 2007 01:25

4' of 703 (or equivalent), a certain thickness (8"-12"?) of 703 plus an airgap stuffed with regular fluffy insulation, or...?

As fiberglass is made thicker / deeper, you can get away with lower density. So if you have four feet available you can get similar results for less money with the fluffy type.

But I'll be interested to hear what Fran has to say about what he uses when four feet is available.

--Ethan


Ahhh... now everybody wants to know the 'good stuff'... we would typically do 4" of unfaced 703 in the framing (the boundary with the room, just behind the fabric)... with these deep traps, I agree with Ethan.. you can just 'hang' some unfaced Batt insulation (R11 or R19) in the deep cavities... Sometimes, we will hang 'baffles' of 2-4" thick 705 as well... those are the two most common installations for deeeeep porous trapping. ok.. now I've given away our biggest secret.. *LOL
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jfrigo

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Re: Surround?
« Reply #12 on: November 14, 2007, 01:03:24 am »

I've experimented with several variations on these traditional deep traps. How have your experiences been with variations? Have you experimented with "waveguides" in the traps? In other words, hanging baffles at angles rather than perpendicular? Also, how about making the hangers/waveguides from 703 or 705 attached to either side of something harder (masonite, pegboard, plywood etc) rather than simply insulation alone? And how deep do you like to make the soft, fluffly stuff at the back of the trap even though you use hangers in ther cavity? And do you ever use a graduated cavity, in other words, the front and back surfaces are not parallel?

So that you don't think I'm all ask and no tell, I tend to like a double thick layer of the soft stuff in back, and a single layer on the sides of these traps. I also like to use space outside the footprint of the room when possible to gain some depth. If you have a 8' tall soundlock or something similar, and a 12' tall room, you can trap the top 4' of the room extending into the space above that soundlock/booth/lounge/hallway or whatever. I don't suppose you'll spill the beans about how you decide on the spacing for the hangers...  sometimes I don't use even spacing accross the whole trap... I'll leave it at that.

Thanks.
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franman

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Re: Surround?
« Reply #13 on: November 14, 2007, 11:24:35 pm »

We often angle the front of these traps from the rear (surface).. this is typical.

We often attach the hanging baffles to 1/2" Sound Deadening Bd (2" of 703 or 705 on each side)

We often put 2" of 703 at the back surface of these traps and have typically 4" on the front framing (room side)

I'm gonna leave it that too. Cool
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jfrigo

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Re: Surround?
« Reply #14 on: November 15, 2007, 02:38:06 am »

Thanks for continuing the discussion. I thought it may be interesting for lurkers to see all the possibilities with these. I think many people never imagine all the variables.
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StudioRhythm

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Re: Surround?
« Reply #15 on: November 15, 2007, 11:21:49 am »

Thanks for all the info, Fran and Jay. Very helpful -- there certainly seem to be a lot of options out there!

Are there any papers/books/test results that might be good places to research these type of traps, or any way to quantify exactly what they're doing (and how?) Having never built or seen anything like this, I just don't have any sense for how a 4' deep trap of this type would compare to just filling the whole thing with insulation, and it'd be interesting to know more about how these hanging traps function.

Thanks again for sharing your time and knowledge, it's very much appreciated! (as is all "the good stuff"...!  Very Happy )

gullfo

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Re: Surround?
« Reply #16 on: November 15, 2007, 01:05:55 pm »

i believe that actual math used to reliably predict the performance of these type of hanging baffle traps is limited to some basic 1/4 wavelength definitions related to the hanging and baffle lengths, as well as the cavity properties (pressure and velocity). beyond that (and someone feel free to divulge it  Rolling Eyes ), its mostly "rule of thumb" type stuff, you would have to build it, measure it, and adjust it to get the desired response characteristics.
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franman

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Re: Surround?
« Reply #17 on: November 18, 2007, 11:08:12 am »

Trap bandwidh is basically limited by 1/4 wavelength depth (or width if you want to look at low angle of incidence action)... there is no 'magic' to the baffle spacing IMHO. I've seen people 'tweek' these and say that they are tuning the bass traps??? I tried on at least three projects to measure the response at the trap (and the room) as we moved the baffles closer to and further away from eachother.. I could tell no difference. These are just large areas of porous absorption that are free to move easily thus allowing the friction to be converted efficiently to heat... that's how I it. so we space them ____ inches apart... (there has to be some mystery left after this forum, right??) Cool  Cool
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gullfo

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Re: Surround?
« Reply #18 on: November 18, 2007, 01:19:16 pm »

there doesn't seem to be much info regarding "hangers" (ala Tom Hidley). here's the response from Jeff Cooper when I was asking about the broadband absorbers on p.49 of his book "Building a Recording Studio" http://www.amazon.com/Building-Recording-Studio-Jeff-Cooper/ dp/0916899004

Quote:

From our experience, broadband traps have an effective low frequency cutoff equal to 1/7th of the wavelength absorbed. To compute this, measure the total panel length (i.e. L+S where L is the panel size and S is the hanger size per the diagram in the book) and use the formula on p.5 for wavelength.

For example, a ceiling hung trap constructed of free-hanging fiberglass-covered panels, each measuring 24" long, on 6" hangers (total length = 30" or 2.5 feet) would be effective above 2.5' x 7 = 17.5' Effective cutoff wavelength 2.5 x 7 = 17.5 ft. (per formula on p.5) Frequency = V/l = 1130/17.5 = 64.5 Hz

As long as the entire cavity was lined with absorptive materials and the trap blankets were at least 12" on center, this trap would be effective at all frequencies above 64.5 Hz.  To decrease the cutoff frequency and make a basstrap effective down to 40 Hz, the panel length would need to  be approximately 4 ft. long (including hangers). Very often, this type of broadband trap is constructed with  varying sized panels, giving a more contoured absorption curve.  An exact formula, relating panel spacing, size, hanger depth, etc. is empirical and not readily available.

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Sonovo

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Re: Surround?
« Reply #19 on: November 18, 2007, 03:13:11 pm »

A few more questions about the setup and room.

I spoke with an acoustician and a designer, and one suggestion that I really liked involved expanding the size of the room. Before I do it, I'd like to hear any comments people here might have.

Basically there is a 'wall' of closets that divides the room in two parts, the main studio and a smaller kitchenette/office area.

The suggestion was to tear down the closets, and instead put up shelves/closets on what will be the new rear wall.

I'm thinking that this is going to change the room nodes as the room's proportions will be changed. However, it might be positive as it will place the rear wall much farther from the listening position (currently about 1.5m, after removing closet divider it will be about 4m).

I also think it will make placement of the rear speaker channels much easier than my current setup.

Current dimensions:

width: 5m 70cm
length: 7m 50cm (created by a wall of ceiling height closets)
height: 2m 50cm

Expanded dimensions:

width: 5m 70cm
length: 10m 20cm (closets removed)
height: 2m 50cm

It was also suggested to put tracks in the ceiling where the closets are now and hang acoustic panels that can be used as a kind of room divider (as well as absorbing much of the rear reflections) or opened up, depending on the work being done. I don't know if this would have any real effect, or if there are any products that would be appropriate and are finished on both sides. Also, due to the added length to the rear wall without the closets, I'm not sure I need any absorbtion for rear reflections at all.

Any thoughts? Good idea? Bad idea? I guess the acoustic treatment I had done in February will have to be redone, but perhaps not completely, maybe just augumented?

Cheers,
Thor
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gullfo

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Re: Surround?
« Reply #20 on: November 19, 2007, 12:35:48 pm »

if you can make the room larger, then i second that approach.
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Sonovo

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Re: Surround?
« Reply #21 on: November 19, 2007, 05:19:22 pm »

Cool,

I think I'll go that route. It will make everything nicer, more user friendly, customer  friendly and modern. A positive change all around.

So, if I want try hanging acoustical panels from ceiling tracks (rather like sliding doors, but not full length), where would I go to find something appropriate? Anyone making panels that look good from both sides?

Thor


gullfo wrote on Mon, 19 November 2007 15:35

if you can make the room larger, then i second that approach.

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