"Stupid" question about room size and general call-out for help WRT family room HT. - AVS Forum
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post #1 of 19 Old 05-17-2013, 11:31 AM - Thread Starter
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Ok, this probably sounds dumb, but I'm curious how one determines "room size" in a situation where a room opens up to other areas as it pertains to things like room modes and the like. I know the real answer is "measure, measure, measure" with something like REW rather than just guess by sizes, etc...but...humor me.

Here is an image of our family room (it's old, and some of the equipment has been since changed, but...).



The image has been taken from the adjacent dinette/kitchen. You can also see the french doors in the room, which open to a living room.

The question comes in determining how "big" the family room really is. You can see in the image that there exists some boundary reinforcement due to the half-wall and arched entry, but there's also the very large opening between the two rooms. Further, I wouldn't say the french doors themselves add a whole lot of boundary reinforcement, though they do rattle "nicely" with the bass, ugh....

The family room itself measures 15' wide by a bit over 19' long (speakers fire down this direction) with 8' ceilings.

The kitchen/dinette area that it opens to is about the same size (a few feet longer) and opens itself to the foyer, dining room, etc.

So, when calculating room modes, because of the half-wall adding some boundary gain, would I use the 19' length, or, because of the really large opening, should I use the 40'+ length added by the adjacent kitchen area?

Further, would having those french doors (and the leakage they allow) add even more volume?

With regards to acoustical treatment, I suppose I should focus primarily on the family room area itself but would adding treatment to the adjacent rooms (if WAF will even entertain it) help at all?

Moreover, lacking a full rear wall, the couch position is sort of in the middle of the "room" as a whole (which I suppose is not ideal), but if you count that half wall as a rear wall, then we sit right against the rear of the room.... So...how's that all work out?

Overall, I guess this room is pretty normal, but just wondering what the half-wall and french doors do to us in terms of its overall acoustic behavior, if anything.

Also kind of curious what you all may recommend doing to optimize a room like this for a 5.1 configuration (with a heavy focus on 2ch. music). Currently, I have the speakers pulled out so their front baffle is around 3' from the rear walls and a little over 4' from the sides -- problem here is they are closer together than the listening distance which is about 17', so golden triangle ratio is way out of whack. Worse, I can't really pull them far enough apart, either they end up on the side walls (and the right one starts firing into the love seat) or I compromise. Plus, I'm not allowed to bring them further from the rear walls (to pull them close to the listener to assist with the triangle) because then they start to crowd the love seat (and I'd have to move the TV forward, too, and then waste a ton of the rear space of the room, which WAF doesn't like, lol). Moving the seating all forward is a non-option (wife wants the couch close to the half-wall)...so...what's the best compromise? I know it's all an experiment to position speakers, one which I'll start to undertake when I get new speakers, but before that experiment begins, I'd just like to have an idea where to start so I'm not just randomly moving 300 lbs of speakers around the room, lol.

Anyway...any suggestions, even "that room sucks, build a dedicated one and give up", I'll gladly take. I do have a full basement, so it's certainly not impossible to start over there...but, I'd certainly prefer to optimize this one since we're in it all the time.

edit: In case you're curious, here's an old shot from inside the room.



The furniture layout is unchanged, but that dinky little subwoofer is now a Seaton Submerssive HP and I'm hoping once I go 5.1 to figure out a better solution than the (mostly) unused equipment stand (which pretty much houses my wife's nick-knacks and my currently unused Parasound amplifier) and way undersized TV stand. But, I lack imagination, lol.... I'm not sure whether I want to have something custom built or what... I really want to audition the JTR Noesis stuff and, if I like it, get the 212 and 228 for center and add another SubM-HP...but...don't know where to put it all. Plus, then eventually I want to get rid of the DLP and wall-mount a nice sized (80+ inch) set...but, then I'll have to push all the speakers closer to the wall...or fabricate some false-wall thing.... I just don't know what to do frown.gif.
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post #2 of 19 Old 05-17-2013, 11:44 AM
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It can get complicated quickly. The opening will introduce a discontinuity related to its dimensions so the analysis would not be for a perfect rectangle. The only modes you typically care about are LF; modes above a certain fequency are broken up by other things and do not contribute as much (if at all).

Calculate frequencies where you might have issues using f = (1127 feet/second) / (dimension in feet) -- or (343 m/s) / (X m) -- and realize the 1/4-wave dimensions cause large peaks or dips. Or use one of the many on-line room mode calculators; some draw out the modes in a nice visual presentation.

I suggest a drawing to help in visualizing the room to help us help you.

My guess after skimming your post is that you may want some absorbers near the couch and to face the speakers straight ahead (no toe-in) to maximize stereo separation.

Places like Ethan's site at www.realtraps.com have a lot of info about room acoustics.

HTH - Don

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #3 of 19 Old 05-17-2013, 12:14 PM - Thread Starter
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Originally Posted by DonH50 View Post

It can get complicated quickly. The opening will introduce a discontinuity related to its dimensions so the analysis would not be for a perfect rectangle. The only modes you typically care about are LF; modes above a certain fequency are broken up by other things and do not contribute as much (if at all).

Calculate frequencies where you might have issues using f = (1127 feet/second) / (dimension in feet) -- or (343 m/s) / (X m) -- and realize the 1/4-wave dimensions cause large peaks or dips. Or use one of the many on-line room mode calculators; some draw out the modes in a nice visual presentation.

I suggest a drawing to help in visualizing the room to help us help you.

My guess after skimming your post is that you may want some absorbers near the couch and to face the speakers straight ahead (no toe-in) to maximize stereo separation.

Places like Ethan's site at www.realtraps.com have a lot of info about room acoustics.

HTH - Don
I realize the modes primarily effect bass, that's why I'm concerned about how much the "boundary" that would determine my modes should be considered... Is the boundary the half-wall, or the rear wall of the kitchen? I mean, even in normal "small" rooms, the bass may get "trapped" by the corners of the wall, but it easily passes through the drywall... But still, you use the drywall as the end of the room. So...how much is that tiny half-wall trapping the bass, and how much is escaping through the opening -- which is predominant, and therefore which length should be used in the room mode calculator.

I suppose, in all -- maybe with my limited placement options, maybe it doesn't even matter. This may be more academic than anything, because I guess at the end of the day, it comes down to "measure, measure, measure." But knowing what I may be dealing with before starting would help me.

As for a drawing, I'll see what I can do with better measurements...but I was hoping the pictures would give everyone a good idea.

edit: I guess what it really comes down to is I have this space and no imagination for how to best make an HT room out of it frown.gif. So, I'm looking for ideas, what I can do to make it work...maybe what others with similar layouts have done.
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post #4 of 19 Old 05-17-2013, 01:23 PM
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Calculating room modes is only for calculation and instantly fails when you introduce problems like this. You'll likely have resonances at both distances. In any irregular shaped room, you'd either need complex software or measurement to accurately pict the modes of the room. But really, you're interested in trapping any low frequency resonance, not just modes themselves. If measurement isn't possible, you can get a demo disc that plays through the low frequencies with a sine wave so figure out what bumps are the most prominent at listening position. Volume isn't really what you consider for low frequencies when there is objects in the way. Even if all boundaries (including the floor) were constructed the same, they'd all have different behavior at that half wall. So it isn't really of much use to "calculate" what to do there. And in either case, mode calculators are more meant for looking at things before construction, not actually telling you what the room response is. IOW you're trying to be analytical but doing it the wrong way really...if you want to analyze the room, the only accurate way to do that is through measurement. Either way...the entire longer distance is probably a frequency quite low, so that resonance probably wouldn't affect the overall room response as much as the smaller dimensions (height & width).

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post #5 of 19 Old 05-17-2013, 01:36 PM - Thread Starter
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Originally Posted by GIK Acoustics View Post

Calculating room modes is only for calculation and instantly fails when you introduce problems like this. You'll likely have resonances at both distances. In any irregular shaped room, you'd either need complex software or measurement to accurately pict the modes of the room. But really, you're interested in trapping any low frequency resonance, not just modes themselves. If measurement isn't possible, you can get a demo disc that plays through the low frequencies with a sine wave so figure out what bumps are the most prominent at listening position. Volume isn't really what you consider for low frequencies when there is objects in the way. Even if all boundaries (including the floor) were constructed the same, they'd all have different behavior at that half wall. So it isn't really of much use to "calculate" what to do there. And in either case, mode calculators are more meant for looking at things before construction, not actually telling you what the room response is. IOW you're trying to be analytical but doing it the wrong way really...if you want to analyze the room, the only accurate way to do that is through measurement. Either way...the entire longer distance is probably a frequency quite low, so that resonance probably wouldn't affect the overall room response as much as the smaller dimensions (height & width).
Understood...so, I suppose at this point, it really is "measure, measure, measure" lol. Honestly, I guess that's what I figured.

My biggest take away from your post is that the length of the room is behaving a little more like a "large room" than the 19' dimension, so at least one room mode should be pretty low. I suppose this is "good" for bass (while maybe not so great for echo/reverb...).

That said, since you were kind enough to post.... I have been looking through the Realtraps and GIK websites and I really would like to get some stuff in this room that is WAF friendly. Maybe you have some suggestions?

I was thinking trying to incorporate bass absorption behind the front speakers since I have some room, maybe angling a few larger panels floor to ceiling and installing them as more "permanent" fixtures to accent...then maybe putting some chair-rail around the room and affixing it to the traps so the room starts to look a little more like a hexagon at the front...? Then, a few more artistic looking panels at some reflection points.... I'm just thinking out-loud here...in the end, any room treatment I do has to blend in or the WAF kicks in and I get kicked out, lol. Right now, I'm pretty much "wasting" the entire rear 2' of the room anyway since I have the speakers pulled out.... So, I could, I suppose, build some sort of false-wall out of ply/drywall and acoustic material...but, I don't know how that will effect the main speakers. I don't want to build something like that and then have them sound like they are "pushed up" against a wall...does that make sense? What I'm trying to say is, we're "told" to pull speakers out into the room for a variety of reasons, if I go ahead and build some false wall and put acoustic stuff on it, then slam the speakers against it, do I lose the whole benefit of the space behind the speakers....? Ugh...I don't know if I'm communicating correctly....
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post #6 of 19 Old 05-21-2013, 11:35 AM
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Originally Posted by DreamWarrior View Post

Ok, ...I know the real answer is "measure, measure, measure" with something like REW rather than just guess by sizes, etc...but...humor me....
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...This may be more academic than anything, because I guess at the end of the day, it comes down to "measure, measure, measure." ...
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Understood...so, I suppose at this point, it really is "measure, measure, measure" lol. ....
You knew the answer all along...

Like Alexander says, calculations fail in real world living spaces. Their underlying assumptions are typically violated in residential spaces, but acoustic measurements don't care about assumptions. Now we may resort to calculations, based on measurements, as the calculations point the way to changing the measurement. It's itterative unless you have lots of experience.

The most important part is identifying a problem first, before thinking about solutions, so your mind is free to consider actual solutions, not just ways to repurpose what you'd been thinking of doing.

Have fun,
Frank
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post #7 of 19 Old 05-21-2013, 01:39 PM
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So, when calculating room modes, because of the half-wall adding some boundary gain, would I use the 19' length, or, because of the really large opening, should I use the 40'+ length added by the adjacent kitchen area?
IF your main seating area is the couch facing the TV, then I wouldn't worry about length modes since all seats will be at the same location in room length (whether that length is 19' or 40'). That means they'll exhibit the same length mode related problems. The room correction system in your receiver should be able to address these peaks and dips, since they will be similar from seat to seat.

What will be different across the width of the seating area are problems related to room width modes. Unlike room length, there is no question how wide your room is. A 15' wide room will have room modes at 38Hz, 75Hz, 113Hz, etc. By placing the sources of pressure (subs, speakers) at locations of least pressure (nulls) you can keep these modes from being excited.

If you have a single subwoofer, put it at the midpoint of room width to knock out the 38Hz mode. If you have 2 subs, place them ¼ of room width (45") in from the side walls to cancel the first three width modes. Of course, if you're crossing over at 80Hz or below, then the subs aren't going to help much at the third (113Hz) mode. In that case, you can use your large speakers at the ¼ points to take care of the second and third width modes (move your crossover down to, say, 60Hz). If you add a centre speaker, then you'll have three pressure sources above the crossover point, so you'll need to move the L/R speakers 10' apart.

All of this will do two things: minimize width based peaks and dips in the low frequencies using placement alone (haven't used bass traps or EQ yet), and improve consistency from seat to seat (makes it much easier for the room correction in your receiver to choose which problems to fix). Of course, measure measure measure to confirm results and fine tune placement.

Sanjay
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post #8 of 19 Old 05-21-2013, 01:42 PM - Thread Starter
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You knew the answer all along...

Like Alexander says, calculations fail in real world living spaces. Their underlying assumptions are typically violated in residential spaces, but acoustic measurements don't care about assumptions. Now we may resort to calculations, based on measurements, as the calculations point the way to changing the measurement. It's itterative unless you have lots of experience.

The most important part is identifying a problem first, before thinking about solutions, so your mind is free to consider actual solutions, not just ways to repurpose what you'd been thinking of doing.

Have fun,
Frank
Yeah...I guess at this point I'm just at a bit of a loss as to how optimal I can make a room like this. Basically, am I starting off trying to optimize something that can't be optimized with any semblance of WAF?

I think the HF is a little easier to tackle -- most of the HF absorbing stuff can be made "pretty" (GIK art panels and the like), so I can hang a few and they'll look like art and get away with it. But, the bulky/clunky LF absorption stuff is where I'm worried. It is harder to hide and disguise. So, I suppose I was hoping that if the room "acted" bigger, that I maybe could get away with less LF absorption and still get pretty good quality.

I suppose, what was attempting to figure out, before really diving into REW and investing, was if this room was worth investing in at all, or if I'm heading down a path which just won't ever yield satisfactory results.
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post #9 of 19 Old 05-22-2013, 12:57 AM
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As for WAF, typically if you involve them in the fabric selection process you can end up with panels that are both aesthetically and acoustically pleasing. Guilford of Maine makes a crazy large line of fabrics and you can actually order samples for free from their website (with quick shipping too!) so I would recommend starting that process soon.
TriTraps are usually a good option in the corner as they take up little floor space but give good results acoustically. Or you could look for more spaces that aren't as noticeable when treated, like soffit style traps in a ceiling corner.
As for trapping behind speakers, they do help give the same effect as spacing your speakers out from a wall. Really, the reason you see so much conflict about distance from walls is because the actual 'distance' referred to is misunderstood. If a speaker is a good 2 meters/yards from the front wall, then SBIR will be reduced to frequencies so low that it won't contribute much to the overall system. However, speakers 60cm/2 feet from the front wall can give some nasty nulls down at 60-80 Hz. Treating between the wall and the speaker effectively reduces SBIR a good bit and if the treatment is thick enough can effectively remove negative SBIR effects. You can read more about SBIR here: http://gikacoustics.com/speaker-boundary-interference-response-sbir/

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post #10 of 19 Old 05-22-2013, 01:35 AM
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IF your main seating area is the couch facing the TV, then I wouldn't worry about length modes since all seats will be at the same location in room length (whether that length is 19' or 40'). That means they'll exhibit the same length mode related problems. The room correction system in your receiver should be able to address these peaks and dips, since they will be similar from seat to seat.

What will be different across the width of the seating area are problems related to room width modes. Unlike room length, there is no question how wide your room is. A 15' wide room will have room modes at 38Hz, 75Hz, 113Hz, etc. By placing the sources of pressure (subs, speakers) at locations of least pressure (nulls) you can keep these modes from being excited.

If you have a single subwoofer, put it at the midpoint of room width to knock out the 38Hz mode. If you have 2 subs, place them ¼ of room width (45") in from the side walls to cancel the first three width modes. Of course, if you're crossing over at 80Hz or below, then the subs aren't going to help much at the third (113Hz) mode. In that case, you can use your large speakers at the ¼ points to take care of the second and third width modes (move your crossover down to, say, 60Hz). If you add a centre speaker, then you'll have three pressure sources above the crossover point, so you'll need to move the L/R speakers 10' apart.

All of this will do two things: minimize width based peaks and dips in the low frequencies using placement alone (haven't used bass traps or EQ yet), and improve consistency from seat to seat (makes it much easier for the room correction in your receiver to choose which problems to fix). Of course, measure measure measure to confirm results and fine tune placement.

So when you mention midpoint or 1/4 for two would this be on the front or rear wall and with two could you place them at opposite walls and 1/4 points? And how did you determine that 10 feet apart for L&R is appropriate distance? Just trying to understand how this would translate for me with a 4m wide room so interested in the math
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post #11 of 19 Old 05-22-2013, 07:55 AM
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I feel your pain, I have a similar "open concept" situation with a need to keep things wife-pleasing (both asethically and financially). It sounds like you have an advantage over me as you seem to understand the "measurement" side of life and I'm just starting to learn it. However, I'll share my experience and thoughts just in case it helps.

My favorite comment on this thread so far is from fbov: "The most important part is identifying a problem first."

I'm not sure you've done that, have you? wink.gif

Like me, you seem to ponder the complexities of "how to start" - when people like us should probably "just do it" and then adjust for specific problems.

I would consider your living room the main listening space and I would set it up as best as possible for your 5.1 sound according to guides like this one:
http://www.realtraps.com/art_room-setup.htm

Without measurements, you can contemplate wife-friendly acoustic wall panels at the "first reflection absorption" points. Guildford of Maine has already been mentioned, I've also seen full on art-panels for sale which might be another option.
http://www.atsacoustics.com/art-acoustic-panels.html

From there, I would see what problems you are left with, and tackle the problems based on your listening preferences.
Is bass too boomy?
Is there still "not enough" sound in the dining/kitchenette area?

I'm thinking that if you first treat your living room as your focal point, and plan for your "sweet spot" to be there on that living room couch - you can setup accordingly and then address other problems as they crop up.

Such is my novice advice!

I'm at the point where I've done the best set-up I can and am now assembling a tool kit (SPL Meter, Mic, REW) to help me fine-tune it with treatments and such. At this point, the sound carries through to the back of my kitchen/bar area adequately and I've not need to place speakers behind the listening-couch. I'm actually running 2.1 now too, but plan on making that same leap to 5.1 within the next year (if not by end of summer).

Good luck! I'll be curious to know how this all turns out for you and what you end up doing!
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post #12 of 19 Old 05-22-2013, 11:07 AM
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So when you mention midpoint or 1/4 for two would this be on the front or rear wall and with two could you place them at opposite walls and 1/4 points?
When I say ¼ of room width in from the side walls, that can be anywhere along the length of the room (front wall, back wall, behind your sofa, etc). In your case, with 4m wide room, the first three width modes will be at 43Hz, 86Hz, 127Hz.

If you played a 43Hz tone and walked across the width of your room, you would notice that it was loud at the side wall, was very quiet at the midpont of room width and got louder again at the other side wall. Placing your pressure generator (subwoofer) at the location of least pressure (null at midpoint of room width) would keep the 43Hz mode from becoming excited.

If you played a 86Hz tone and walked across the width of your room, you would notice that the sound would peak at the side wall, null at ¼ of room width, peak at the midpoint, null at the next ¼ point and peak again at the opposite wall. Placing two subs, each at the null locations, would knock out the first three width modes.

Problem is, you subwoofer(s) would likely be crossed over to your speakers below 86Hz and certainly below 127Hz. So you have to use the woofers in your speakers to address the 2nd and 3rd width modes, by placing them at ¼ points of room width (2m apart). This will work well for a 2.1 set-up; you can adjust soundstage width by moving your seating and/or speakers towards each other.
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And how did you determine that 10 feet apart for L&R is appropriate distance? Just trying to understand how this would translate for me with a 4m wide room so interested in the math
With 3 speakers across the front, you now have 3 pressure generators, so you're better off placing them at nulls of the 3rd width mode, which would mean the L/R speakers would be 2/3rds of room width apart. Sub and centre speaker stay at the midpoint of room width.

If you have Excel, there is a free room mode calculator that you can download from the Harman site, which will give you these locations:
http://www.harman.com/EN-US/OurCompany/Innovation/Pages/Calculators.aspx?CategoryID=Calculators

Sanjay
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post #13 of 19 Old 05-22-2013, 02:19 PM - Thread Starter
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Ugh -- I'm so stuck at analysis paralysis. Is REW the best option out there? I know it's "cheap" because I just need a laptop measurement MIC, etc. However, I do have (quite an expensive) SPL meter w/ 1/3 octave filters (Ono Sokki LA-5110) that will at least show me some spectrum analysis.... I have a feeling the microphone on that is many times more accurate than anything I can buy cheaply, it is lab calibrated, my dad got it from work for cheap when they firesold all their stuff before going out of business.

So, I guess how does using something like a spectrum analyzer compare to REW? And how accurate can REW be made given its roots in a PC? Is there any comparable test equipment that I can purchase to do this that doesn't need a PC/laptop and will be more accurate -- maybe on the used market? Just curious.... I know most guys use REW, just wondering if it's because it's cheap, or just really better than anything else.
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post #14 of 19 Old 05-22-2013, 02:57 PM
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It all depends if your Ono Sokki has an analog output that would feed an analysis PC, then you'd have to verify that there are no filters on that output. SPL meters have a unique job, to integrate a spectral range, with frequency weighting, and calculate the total sound pressure. They incorporate A- and C-weighting curves in their calculation, while you'd rather than no weighting filter applied. the calibration you reference most likely was to verify the proper weighting functions.

You won't beat a high end spectrum analyzer with a $50 mic and freeware. You can do most of the analysis, but a lot slower, a non issue for hobbyists, I hope! You do need a good sound card or outboard DAC, and the mic may need a mixer or other interface (popular mics require 48V phantom power). I use these bits, and it's PC-independent:
- Behringer EMC8000 (same as PE's EMM-6, $50)
- Behringer Xenyx 802 mixer $65 (or Blue Icicle USB mixer $60)
- Behringer UCA202 USB DAC $30

About $150 for the parts, with shipping, or you can get a measurement system like PE's Omni-mic for $300.

As to the relative value vs. high-end professional analyzers, it's up to you. Just keep in mind that you can measure things you can't hear, and you can hear things you can't measure.

HAve fun,
Frank
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post #15 of 19 Old 05-22-2013, 03:46 PM - Thread Starter
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It all depends if your Ono Sokki has an analog output that would feed an analysis PC, then you'd have to verify that there are no filters on that output. SPL meters have a unique job, to integrate a spectral range, with frequency weighting, and calculate the total sound pressure. They incorporate A- and C-weighting curves in their calculation, while you'd rather than no weighting filter applied. the calibration you reference most likely was to verify the proper weighting functions.

You won't beat a high end spectrum analyzer with a $50 mic and freeware. You can do most of the analysis, but a lot slower, a non issue for hobbyists, I hope! You do need a good sound card or outboard DAC, and the mic may need a mixer or other interface (popular mics require 48V phantom power). I use these bits, and it's PC-independent:
- Behringer EMC8000 (same as PE's EMM-6, $50)
- Behringer Xenyx 802 mixer $65 (or Blue Icicle USB mixer $60)
- Behringer UCA202 USB DAC $30

About $150 for the parts, with shipping, or you can get a measurement system like PE's Omni-mic for $300.

As to the relative value vs. high-end professional analyzers, it's up to you. Just keep in mind that you can measure things you can't hear, and you can hear things you can't measure.

HAve fun,
Frank
I guess I'm more questioning how a spectrum analyzer compares to REW with regard to its capabilities. I realize that REW incorporates a spectrum analyzer, but it also seems to do more, like generate the waterfall graphs. So, the meter I have is a spectrum analyzer, I can turn it on, play a pink noise signal from a test disc, and then see where all the peaks are at a given position, but that's all it'll do. So, the question is, how much more helpful to me is something like REW? Moreover, can I use the data collected by the spectrum analyzer I have to generate the same types of graphs REW does through some other piece of software?

I ask all this because, honestly, while I have the equipment (handed down by my dad) I really don't know how to use it to do anything real useful. I just know, "hurr da derp look, I see the pretty bar graph move up and down and, hey, 60hz stands out" but great, I move the meter a few feet to the left/right/front/back etc and, "durrrr ummm...yep, the spectral balance is shifting". But how to translate all that into "ok jerkface, you should probably move your speakers out a foot, bump the x-over down, push the sub to the middle of the room, etc" is what I'm completely lacking. And, while I enjoy this "hobby", I don't enjoy pushing around speakers for hours/days/months and/or moving around acoustic panels, buying more of them, etc. I suppose I am a bit more of a measure twice cut once guy, lol...if that's possible, it'd be more up my alley, lol.

Further, I have XT-32 in my receiver, so certainly it should "do something" good for me...but, of course, the general consensus (which makes complete sense) seems to be that XT-32 can only do so much, so one is better off disabling XT-32, getting things as right as possible, and THEN letting it clean up the stuff that's just not feasible with "better" methods.

Make sense? Call me lazy, call me crazy...but...I'd rather be listening to music than test tones and moving stuff around. I'd just like to spend a day, take some readings, and then plot a course of action -- is that possible? Is it possible with REW? Is it possible to do with the spectrum analyzer I have (call it something similar to this -- though mine is hand-held and lab-grade, read more accurate, but smaller screen, and it won't generate pink noise, but I have a test disc that has a pink-noise track on it)?

edit -- I've been reading through many of the REW threads like this guy right on the top of this (thanks to all the people in there)...so, I've been trying to educate myself. But -- I suppose I closer to wanting an algorithmic approach, not a tweak/test/tune sort of thing...I mean, this is science, there should be an algorithm that says, "take these measurements, average, view plots, do x, y, z" no? Also, like I said, I'm willing to make the investment in REW, but if I can do it with what I have (which I know to be tons more accurate than a $50 mic and laptop) than I might as well try. If it's not possible, then hey, REW or the Dayton Omni-Mic software it is....
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post #16 of 19 Old 05-23-2013, 07:02 AM
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A spectrum analyzer won't generally do time-domain analysis so you are missing one key piece of room analysis. In fact, a real good SA is overkill for room analysis -- you really don't need sub-Hz resolution and large dynamic range (I have used $100k+ SAs for audio work, and much more expensive RF units, but for tweaking your room I would suggest something somewhat less expensive and easier to use wink.gif ). However, especially for the bass region, 1/3-octave analysis is far too coarse. And I would not bet the farm on an older SA being more accurate than REW with a decent calibrated/corrected mic.

Many programs, and test instruments, are PC/Windows based so it is not the PC that is the issue.

REW takes advantage of calibrated mics and the ease-of-use compared to an older SA would make REW an easy win for me with just an inexpensive (~$50 - $200) calibrated or corrected mic. I am using RPlusD and an Earthworks measurement mic, maybe $2k worth of SW and gear plus preamp and notebook, but honestly I suspect I would get the same results using REW and one of the inexpensive mics with a cal curve.

As for the learning curve, plus time/money/effort to improve your room's acoustics, only you can decide if it is worth it. All the folk on this thread think so, as do many other audiophiles, all studios and theaters, etc. There is science mixed with art because rooms are too complicated for simple programs to analyze and suggest solutions. Flow dynamic simulators work well but cost tens of thousands of dollars and up, and have a steep learning curve to use effectively. Tweaking with a decent analyzer strikes me as a good blend of science theory and practice.

FWIWFM - Don

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #17 of 19 Old 05-23-2013, 09:52 AM - Thread Starter
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Very much appreciated Don -- I suppose I have to just bite the bullet and put in the time and/or hire someone to do it. Pity my time gets consumed so fast.

I suppose at this point I have to decide whether it is worth it to start analyzing now in preparation for when I buy new main speakers, or just put it off. I've been on a quest to replace my current speakers for a while and probably pick up another SubM HP to help balance out the bass and give me a little more kick...so, since my time is limited, I may just have to wait.

Further, I am considering going with horn loaded designs for the mains, so I may find that I need to focus more on positioning them than treatment for the highs because of their directionality, but the LF treatment will still be a primary concern and that'll be where, as I take it from your post, REW and its toolset will vastly outperform a SA.

So...thanks for setting me straight!

I still want to plan a little, I'm going to try and get a drawing together and stuff so maybe I can start planning coverage area for the horns and such...maybe it'll help me get closer to ideal in-room placement for them, anyway.... And, maybe toss a few ideas around for building the bass corner bass treatment into the room in an aesthetically pleasing way, maybe even getting some built-in shelving for my amps and such, too.... Was thinking about building some corner cabinets for gear and the wife's "pretty stuff" lol, then maybe flanking them with bass absorbers of a fabric that blends in nicely to the wall color and trimming the whole thing to make it look like it's part of the wall.....

On a side note; can anyone in the tri-state area (I'm in South Jersey) recommend a good, relatively local, acoustic guy that may be able to assist? I'm sure a little professional help can't hurt....
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So, for grins, I had a little time this morning that I decided to use to pull out the spectrum analyzer. Seems XT-32 didn't do a bad job at flattening the freq. response, but I ruin it all by cranking my sub levels and running the bass really hot, lol.

I also learned a bit about what my receiver does with different settings -- I suppose some of it should have come as no surprise, but it did. One thing was that I was hearing some really nasty noises from my floor-standers on some music which was really making me keep the volume levels down. I had tried in vein to fix them before, by messing with the x-over slopes and such, but it wasn't going away (so far as I could tell). Turns out, though, XT-32 must have bumped up some of the bands around 60hz and they were sounding unnatural. But, worse, the speakers were unable to reproduce them cleanly w/ XT-32 pushing the bands up, so while they weren't bottoming, they were certainly distorting (I can tell this because w/ XT-32 off it doesn't happen, the speakers sound fine, the room sounds overall a bit worse, though). Of course, the problem came when I'd try to get rid of the unnatural sound by changing the x-over -- it wasn't really fixing anything, just moving it into the sub (which was gained up already) and making it worse.

My first attempts, to diagnose was to "turn off" the sub by setting it to off in my channel levels receiver option (NOT in the speaker configuration). What I *thought* this would do was, since the speakers were set to small, to just turn off the sub output and keep the mains x-over setting set in speaker configuration to high-pass the speakers. So, I expected that when I moved the x-over point in speaker configuration that it'd actually, I don't know, do something, lol. But, it became quickly obvious that the receiver was ignoring the x-over point and just running the speakers full range. Which, looking back, makes sense -- I turned the sub channel off, so the receiver routes the bass to the mains...but...I turned the channel off under levels, not under configuration and when I did this, configuration still showed the sub configured so I thought it'd just high pass the mains and "protect" them from the bass they can't handle since they were set small and given an x-over point -- not so. So, I turned the sub on in the receiver channels setting and then just powered down the sub to hear the mains discretely. Then I could mess with the x-over point until they started sounding cleaner (i.e. when whatever band XT-32 boosted was out of the x-over point they were high-passed for so they weren't being driven by the booted band into distortion). Then, I turned back on the sub, and tweaked its gain a bit. But, overall, there's some bass non-linearity around the x-over point (settled on 80hz, would have preferred 60hz) that has been created and I'm not sure I like it.... Don't know how to get rid of it, though. My guess is I must have a null somewhere in the region and XT-32 is trying to fix it by gaining it up (which it probably shouldn't do, cuz you can't fix a null by gaining it up...but...).

Oh...and about that level meter...turns out, it has a midi output, but I'm not sure how useful that is for use with a laptop/PC though...anything I can connect the midi output to and use it with REW?

edit: haha, the programmer in me -- I typed null as NULL because I'm so used to do so while programming.
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MIDI can contain some useful info but often does not (just the key codes); I would not bother to figure out how to interface it even if if possible. You could look and see what codes it outputs, might be worthwhile. I do not know but seriously doubt REW would do anything with MIDI. < EOL > smile.gif

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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