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Post by jarery on Apr 7, 2016 20:38:34 GMT
I posted this also on Home theater forums so hope the cross posting is ok. As I learn more about REW and sound in general I have been experimenting with the Subwoofer placement and trying to find the best positions. I have been relying on Audyssey but now wish to make sure my placement is as best as possible, then add room treatments, then run Audyssey, then add any additional EQ with MiniDSP. Multi use home theatre Room is 22.5' deep by 14.5'wide x 9'high. Screen along the 14.5 wall. Open on the right side to another slightly shorter room which is again open on right to a shorter room. About 6k ft^3 I think. I have 4 subs, 2 are built into my front speakers so are basically fixed in position to the front corners. (GE Triton One's). Pulled out about 40" from front wall and 22" from sides. The other two are external Klipsch 15" subs and can be placed as follows: 1) Green sweep - Both on the front wall at 1/4 and 3/4 wall length positions, between the main powered speakers, ending up about 12 ft in front of MLP. 2) Blue sweep - Both behind the MLP, ending up about 5 feet in front of the back wall, spread about 5 feet apart on centers. 3) Red Sweep - One on the front wall and one behind the MLP Here are the 3 options I have available with Audyssey off. (Audyssey XT32 used to set distances between the sub pairs then turned off) dl.dropboxusercontent.com/u/...%20Tritons.jpg The red has a huge cutout at 27hz where the blue has one at 82, blue has much more gain from the near-field placement I suppose. Am I looking for which is the flattest (red) or the smoothest (blue) ? I cant decide which is the preferred positioning, any help appreciated as this indecision is driving me crazy lol. Green looks to be the worst (all on front wall) Without room treatments, and using Audyssey XT32 correction, I get the following  dl.dropboxusercontent.com/u/...20Audyssey.jpgHere the blue looks best but the green which was worst has the most extension down low? Red looks like something really bad is going on around 50-60 aaarrrgggggg I don't know which is best. Where do I place the subs so that some bass traps in the corners have the best hope of making a difference? |
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Post by Hexspa on Apr 7, 2016 21:42:54 GMT
Dear jarery, How are you? My name is Michael and I hope I can help. Is your listening position oriented along the short throw of the room? You should be oriented length-wise. You should not be using corrective room EQ (re: second image). Also, your graphs are only below 200Hz. It looks like your reference level is about, or higher than, 85dB. This brings two points: 1. For a room of your size, doing sweeps that loud isn't necessary. I calculate your room's volume to be about 2935.25 ft3 which, according to the chart at the bottom of this page, you want to calibrate your volume to 76dB and 2. It looks like your bass is 30dB higher than what logic would indicate the rest of your spectral response is. That tells me that your subwoofers are way too loud. It might be helpful if you post a non-smoothed graph of your entire spectrum. Additionally, as I have been told elsewhere, your response below 32Hz is not as significant as higher frequencies for reasons including speaker performance, room size and relative audibility. If you have a null, peak or ringing at 27Hz I wouldn't be as concerned as if it was at 50Hz and upwards. Lastly, the "cutout" (null) at 27Hz isn't "huge". While it is beyond the target of +/-10dB from what I imagine your reference level to be, it is so only by about 2-3dB which could be due to even the performance of your microphone. However, the null in your second picture could definitely be described as huge. Gaping even lol. Thanks, -m |
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Post by jarery on Apr 8, 2016 1:21:58 GMT
Hi, Thanks for the reply.
The layout of the room is as I mentioned above, the screen is on the short 14.5 wall, speakers are 40" out from the front wall. The room is 22.5 ft deep with my mlp 12-13 ft back from the speakers, or about 7' from back wall.
Don't use room correction? Do you mean just for figuring out sub placement or ever? I know some people have poor results with Audyssey or other room correction, but in my case it appears to me to be doing what its supposed to, so i'm confused by your statement? If I could achieve great results without it, I'm all for not using it though !
Room volume is 6k+ cubic feet, as I mentioned its open on the right, to a another 14' or so wide room just 2' shorter, then thats open again to another 12 x 12 os so room. In the sweeps i'm posting I'm not trying to set levels and reference volume. Thats done later. I move the subs to a position I want to test, adjust gains so they are all equal at about 75 db each. Then adjust delays till I get best integration, then record a sweep at whatever the combined SP level is. After that I set levels and distances again with audyssey. I'm not sure how lowering the sub volume levels would change the sweeps and room interaction other than to make them appear lower on the graph? But i can redo them this weekend if necessary. Much of what I read recommended running sweeps at as high a volume as one can.
These sweeps were just the sub lfe channel only, channel 4 in rew, 20-200 hz, they don't include the rest of the spectrum. They were also only the 4 subs not the mains or centre.
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Post by Ethan Winer on Apr 8, 2016 18:02:28 GMT
EQ can reduce low frequency peaks (below 100-150 Hz) that are present around the room, but it's not good to use EQ to raise nulls, or to lower peaks that are highly positional. Here's something to try that will give you a feel for what EQ can do, and when it might hurt: Turn off all EQ etc so you're just using the speakers and room. Then measure using REW as you did at the main listening position, and do it again two feet away. You'll probably see something similar to what I measured here: A common-sense explanation of audiophile beliefs--Ethan |
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Post by jarery on Apr 8, 2016 21:13:22 GMT
I only sent included the EQ responses to show what I was ending up with, but these sweeps after eq show it used a LOT of filtering. If I can achieve a decent end product without using EQ then i wont be using it.
As I posted, I'm having a difficult time on which of the three placement options should be my best starting point regardless of whether EQ is used or not. All of my three placement options have issues and I'm not experienced enough to know which of the three has correctable issues and which should be avoided.
On the first chart where no eq is used:
Green has a 30 db difference between 25-40 hz, highest peaks and lowest nulls therefor will take the most eq to flatten, or traps to minimize.
Blue is smoothest but is sloped and a large dip at 83hz
Red is flattest except for the dip at 27hz.
I don't wish to rely on eq. I wish to use multiple subs (4) positioning, and then room treatments to get as best as possible. Unfortunately I cant seem to find a good starting point.
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Post by Rock on Apr 8, 2016 22:02:17 GMT
Start with bass trapping the corners (12 in a rectangular room). It's something that you won't need to change if you cover all the corners. Reflection points may vary with speaker positioning but if you start with the 38% rule, you'll get first reflection absorbers in the ballpark.
At this point, you can experiment with placement and finally you can EQ out some of the worst low end peaks.
Cheers,
Rock
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Post by jarery on Apr 8, 2016 23:48:03 GMT
Rock
Thanks for the reply. Yes i plan on bass traps in the 2 front corners, and the front half of ceiling also. back corners I cannot use. I wish I could do all 12, but not possible.
I also plan on a panel on the first reflection on the one side wall, there is no wall on the other side. Lower priority would be 2 panels at first reflection on front wall.
Experimenting with placement was the purpose of this thread. I guess i asked too many questions though as it keeps going sideways lol. It will take me several weeks to either order in or make bass traps so i'm trying to lock that down first, figuring the trapping will happen in the same spots regardless of my sub positioning.
I really only have 3 variations on where I can place the 4 subs, as shown in red, green, blue sweeps in the graphs. I keep second guessing my placement though as none of them seem to be a clear front runner for me. So I came here to ask for advice on which of the 3 positions was the best based upon rew sweeps.
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Post by Rock on Apr 8, 2016 23:58:32 GMT
Jarery,
The traps will help tame the peaks and nulls. After you get them in you will have a better chance at figuring out the placements of your subs by trial and error. In other words, I think trying to locate your subs first is going at it backwards. Sorry, I don't have any other advice on locating the subs, just my 2 cents.
Cheers,
Rock
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Post by Hexspa on Apr 9, 2016 0:58:09 GMT
Correct me if I'm wrong but wouldn't running sweeps at higher than necessary volume just increase the room's effect - ringing, modes and decay? I suspect that sweeping your room at 120dB would yield different results than at 75dB which is the level to which you'll likely be calibrating. Then again emphasizing the room in this case could be valuable as when one uses a microscope to magnify the appearance of small things.
I already told you my reasoning for which position I'd choose but I didn't give my choice; go with red/no EQ - for now.
Two things I'll add are: you can still add treatment to other corners and walls if the rear isn't available and, when setting the levels for your subs, it'd probably be correct to do so at the listening position, as Rock mentioned, and at a specific frequency - but that should be obvious.
Your room will still generally have the same characteristics before and after treatment with the latter scenario flattening, shortening and focusing your sound's behavior - especially at the listening position given you care most for that spot specifically. So while Rock mentioned treating first I'd advise that, while finding the best spot now is valid, Ethan's link proves that small differences in placement can have considerable effects. Therefore you can pencil in your position now but expect to fine tune after treatment assuming you move the subs.
Also, jarery, you're right - I forgot about the low-end-only feature of REW.
Ethan, thank you for clarifying the appropriate use for corrective room EQ.
-m
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Post by jarery on Apr 9, 2016 16:41:55 GMT
My understanding of why calibration is done at 75db is because people and neighbours don't like calibrating at reference of 105 where it should be done, so the AVR manufacturers got together and agreed to do their auto calibration at -30db which is where the 75 came from. The higher above the noise floor the better so 85 is better than 75. In either case, I'm not calibrating, i'm comparing FR at different positions. As long as they are done at a relatively same level then comparisons and evaluations can be made.
Yes its obvious to do the testing at the listening position, i didn't think that was in question.
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Post by Ethan Winer on Apr 10, 2016 17:03:07 GMT
wouldn't running sweeps at higher than necessary volume just increase the room's effect - ringing, modes and decay? No. Acoustics is linear, so whatever happens at low volumes happens exactly the same at higher volumes. When I run REW sweeps or play high frequency sine waves, I never let it get too loud to avoid damaging tweeters. The HF content in normal music comes and goes constantly. But sustained sine waves can quickly overheat a voice coil and damage a speaker driver. --Ethan |
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Post by Hexspa on Apr 10, 2016 20:47:53 GMT
wouldn't running sweeps at higher than necessary volume just increase the room's effect - ringing, modes and decay? No. Acoustics is linear, so whatever happens at low volumes happens exactly the same at higher volumes. When I run REW sweeps or play high frequency sine waves, I never let it get too loud to avoid damaging tweeters. The HF content in normal music comes and goes constantly. But sustained sine waves can quickly overheat a voice coil and damage a speaker driver. --Ethan Got it, thanks! |
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