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Another home theater "plz help" thread
Old 3 weeks ago
  #1
Here for the gear
 

Another home theater "plz help" thread

Hello,

Last year I started building a home theater. Since my budget is very small I've had to do with more basic and DIY stuff along with budget speakers/recievers etc.
But now I'm coming to an end in my build and need some help in decypher REW plots.

Note: I've been on this forum lurking more than I should have when I started building my room. But I'm still very much confused and overwhelmed by REW etc.
I checked the initial pinned post about how to present the graphs, but I must be dumb as I do not really understand what to do. Or it is because I'm not a native english speaker.

I've attached a REW measurement to this post if someone is willing to look it over.

Background to the measurement:
3 Subwoofers (2 in front and 1 in back near corner)
I've followed a guide to take measurements and use MSO (multi sub optimizer).
The result is then throwed into a minidsp 2x4HD.

I have a thread in a swedish forum with a lot of pictures if anyone wants to see what I've done:
https://www.minhembio.com/Sintei/
Apologiez if this is not allowed, but for the purpose of this post, I think it is relative.

Do I have to do more bass control?
Is decay times to long?

Some input is appreciated, thanks!

Sincerely,
Nicklas
Attached Files
File Type: mdat GearslutzREW.mdat (112.1 KB, 15 views)
Old 3 weeks ago
  #2
Gear Guru
 
Glenn Kuras's Avatar
Not sure what is up but I can't open the file. It might be on my side. Can you post the waterfall graphs and frequency. Might be also helpful to post a layout of the room and how you have things set up.
Old 3 weeks ago
  #3
Here for the gear
 

Quote:
Originally Posted by Glenn Kuras View Post
Not sure what is up but I can't open the file. It might be on my side. Can you post the waterfall graphs and frequency. Might be also helpful to post a layout of the room and how you have things set up.
Thank you for replying!

I'm using REW V5.20 Beta 26. It seems there is some backwards incompability as I can open it fine there.
But in REW 5.19 it throws an error when I tried it.
I'll look into this when I get home.
And also post more info about the room and set up


Added some screenshots. But since they do not comply with the pinned posts on how to share screenshots, I doubt you'll see anything
Attached Thumbnails
Another home theater "plz help" thread-decayaftermso.jpg   Another home theater "plz help" thread-spectrogramaftermso.jpg   Another home theater "plz help" thread-waterfallaftermso.jpg   Another home theater "plz help" thread-base-after-mso.jpg  
Old 3 weeks ago
  #4
Lives for gear
 

Your frequency range only covers 15 Hz to 200 Hz? And you seem to be doing the tests with both speakers? Or maybe just one? You should do your tests across the full spectrum, and do separate measurements for left, right, and both. Here's a tutorial on how to set up REW properly: How to calibrate and use REW to test and tune your room acoustics

- Stuart -
Old 3 weeks ago
  #5
Here for the gear
 

Quote:
Originally Posted by Soundman2020 View Post
Your frequency range only covers 15 Hz to 200 Hz? And you seem to be doing the tests with both speakers? Or maybe just one? You should do your tests across the full spectrum, and do separate measurements for left, right, and both. Here's a tutorial on how to set up REW properly: How to calibrate and use REW to test and tune your room acoustics

- Stuart -
I will definitely do those settings/tests according to your guide and get back to you.
The above measurements are of subwoofers only.
I see that there are 2 lines in the SPL.. one (the above one) is before optimisation. And the lower one is after. Rest of screenshots are after optimisation.
I use 3 subs and each have their own PEQ. Cutoff in the minidsp is 90Hz for all three. And in the receiver the cutoff for all other speakers (7.3.4 system) is 80Hz according to reference standards.
I've focused on subs at the moment as from reading across the interwebs they are the hardest to tame.

Sincerely
Nicklas
Old 3 weeks ago
  #6
Here for the gear
 

Quote:
Originally Posted by Soundman2020 View Post
Here's a tutorial on how to set up REW properly: How to calibrate and use REW to test and tune your room acoustics

- Stuart -
I did your tutorial.
Don't know if I did the right thing with the subwoofer.
Please let me know in that case.


Attached is an mdat file that works with 5.19 (as it is the only one installed now to avoid problems)

The file was too big, 28Mb? I had to divide it into 2 pieces. 1rst4 and last3.
Sincerely,
Nicklas Starkel
Attached Files
File Type: mdat first4.mdat (15.89 MB, 7 views) File Type: mdat last3.mdat (11.93 MB, 8 views)

Last edited by sintei; 3 weeks ago at 06:15 PM.. Reason: file not attached
Old 3 weeks ago
  #7
Here for the gear
 

Quote:
Originally Posted by Glenn Kuras View Post
Might be also helpful to post a layout of the room and how you have things set up.
The room is 5.7m in lenght and 3.5m in witdh and 2.4m up to ceiling.
However I have a semi lowered ceiling. Where spotlights and projector are. Meaning there are open space covered with speaker fabric.
Behind the fabric there is broadband diy absorbers which cover about 70% of the ceiling.
The front is also built with angles as well as the back. So the lenght of the room is shorter in some places.
The back sofa is on a podium.
I have treated first reflection points with diy broadband absorbers. However, they are to small and will be replaced with larger ones.
In the back corners there is basetraps (large insulation stacked from bottom to the top) The back wall has also been treated with some insulation.
I have a 7.3.2 system (3 subwoofers 12", where 2 in front an 1 in back).
It will be a 7.3.4 system as the speakers are there, but not connected yet.

Attached some images on how it looks.
Attached Thumbnails
Another home theater "plz help" thread-front2.jpg   Another home theater "plz help" thread-back.jpg   Another home theater "plz help" thread-ceiling.jpg   Another home theater "plz help" thread-front.jpg  
Old 3 weeks ago
  #8
Lives for gear
 

Quote:
Originally Posted by sintei View Post
I did your tutorial.
Don't know if I did the right thing with the subwoofer.
Please let me know in that case.

Attached is an mdat file that works with 5.19 (as it is the only one installed now to avoid problems)
Yep! You did it right. The data is valid.

Just checking: You did this set of measurements with the optimization turned off, correct?

First thing I noticed in your REW data, is that you have some type of interference, or "buzz" or "hum" getting into your system. See the first image below. That's the waterfall plot for JUST your sub. Those spikes sticking up at the same level all the time, never dying away, are the buzz I'm talking about. Notice that the are in a repeating pattern, every 1 kHz, and continue way above the range where the sub could be producing sound. I marked one of the spikes, at 420 Hz. It's also not linked to just one speaker channel: it's in everything. The second image is your L and R speakers, without the subs, and you can see the exact same spikes in the identical locations. Conclusion: this is something being picked up by your mic, cable, pre-amp, interface ("soundcard"), etc. It's not actually there in your speakers, as you would probably have heard it. My guess would be a faulty mic or mic cable. What mic did you use for the tests?

Anyway, the thing to note here is that those spiky issues are NOT acoustic: they are not really in your room at all. However, in the low end of the spectrum, they likely will get in the way of seeing important details, so it woud be good if you could figure out what is causing that, and fix it.

The next thing I noticed, is that your room is quite well damped (maybe a bit too well for some frequencies), but there's still a couple of modal issues that could probably be tamed more. Specifically, 57 Hz and 101 Hz. Those are very likely your 2.0.0 axial mode, and your 0.2.0 axial mode, which should be at 59 Hz and 98 Hz in theory, but allowing for a margin for variation in measurements, materials, temperatures, etc., the difference is minor. 2.0.0 is the second harmonic of the lowest mode that runs between the front and back walls of the room. 0.2.0 is the second harmonic of the fundamental mode that runs across your room, between the left and right walls). You could treat both of those with very deep bass traps in the vertical corners of the room, or you might be able to reduce them a little with parametric EQ. The room is well treated enough that you could do that, as long as you know what you are doing. Those are the two red "hot spots" on the spectrogram image below (third image).

After that, your next biggest issue is the dips at around 34 Hz and 80 Hz. 34 Hz seems to be interference between the subs and the mains. Take a look at all the FR curves at once, in the fourth image. You can clearly see that th 34 Hz dip is not there when JUST the subs or JUST the mains are playing, but it appears when the subs AND one or more of the mains is playing. So it's definitely interference between the two. If you are able, I would try adjusting the phase of one or more subs, or the timing with reference to the mains, to see if you can fix that dip. It's not an acoustic issue with the room.

80 Hz is hard to pin down. It might just seem to be a bigger issue than it really is due to the modal stuff on each side, but I think it's more than that. It's probably not modal, as there's no suitable modes in that region (just a couple of tangential modes), so it might be ceiling bounce, or maybe side wall bounce.

Quote:
I have treated first reflection points with diy broadband absorbers. However, they are to small and will be replaced with larger ones.
You might find that that has a positive effect on 80 Hz. Make your new traps deep (at least 6", ideally 8"), and use low density insulation in them, or perhaps layered insulation: the front 4" can be light stuff, and the rear 4" can be higher density stuff.

Quote:
I have a 7.3.2 system (3 subwoofers 12", where 2 in front an 1 in back).
It will be a 7.3.4 system as the speakers are there, but not connected yet.
You might find it better to set up the subs with two at the front and two at the back, as plane wave bass array. You have the ideal situation for that. However, your bass management system probably can't do that on it's own, so you'd need an external speaker controller to achieve that. But it could solve several of the above issues, all at once. I would consider that.

A couple of other final points:

1. there's some strong reflections happening within the first 16ms. You can see that on the fifth image below (ETC). You might want to find the source of those, and put absorption at the appropriate locations in the room. They are not enormous, and might even be beneficial, as this is a home theater, not a control room, so just put up temporary panels when you find the offending spots, to see if you prefer the way it sounds with those, or without them.

2. There's too much absorption in the 200 Hz region. You can see that on the last graph, below (RT60). Decay times are mostly reasonable, at around 200 ms, but there's a dip to roughly half that between maybe 150 Hz and 6 kHz.

3. The overall frequency response looks a bit like the famous "smiley face"! Visible on the "all curves" image below. Notice the slight decline from about 300 Hz to 3k, then the slight rise back up again, to 20 k? That's not acoustic: that's an EQ preference applied somewhere in your signal chain. And that's fine, if that's how you want it to sound. It's not a control room, so it does not need to be flat: it needs to be the way you like it. However, if that was not intentional, and you think it sounds a bit too "bright", then you could check your EQ settings, and level it out a bit.

That's just a few quick general comments. Should put you on the right track.

- Stuart -
Attached Thumbnails
Another home theater "plz help" thread-sintei-rew-wf-80-5k-s.png   Another home theater "plz help" thread-sintei-rew-wf-80-5k-lr.png   Another home theater "plz help" thread-sintei-rew-sp-15.500.png   Another home theater "plz help" thread-sintei-rew-fr-12-22k-all-curves.png   Another home theater "plz help" thread-sintei-rew-etc-30ms.png  

Another home theater "plz help" thread-sintei-rew-rt60-42-10k.png  
Old 3 weeks ago
  #9
Here for the gear
 

Quote:
Originally Posted by Soundman2020 View Post
Just checking: You did this set of measurements with the optimization turned off, correct?
I just realized, the subwoofers were going via minidsp with PEQ on. On the receiver, I tried turning everything off, but i do not know if it's own optimization was off. I could not find it.

Quote:
Originally Posted by Soundman2020 View Post
you have some type of interference, or "buzz" or "hum" getting into your system. What mic did you use for the tests?
I use a UMIK-1 (usb). I'll try to check what can be the cause of it.


Quote:
Originally Posted by Soundman2020 View Post
You could treat both of those with very deep bass traps in the vertical corners of the room, or you might be able to reduce them a little with parametric EQ. The room is well treated enough that you could do that, as long as you know what you are doing.
I will try to add more insulation and see if that helps. I could use the podium as a helmholz resonator but will try to fix it using minidsp/PEQ first

Quote:
Originally Posted by Soundman2020 View Post
After that, your next biggest issue is the dips at around 34 Hz and 80 Hz. 34 Hz seems to be interference between the subs and the mains.
Could be the PEQ in my subwoofers. I'll get on it!


Quote:
Originally Posted by Soundman2020 View Post
Make your new traps deep (at least 6", ideally 8"), and use low density insulation in them, or perhaps layered insulation: the front 4" can be light stuff, and the rear 4" can be higher density stuff.
I was actually aiming for that thickness (8" ~20cm) in my next build, so nice that you suggested the same!

Quote:
Originally Posted by Soundman2020 View Post
You might find it better to set up the subs with two at the front and two at the back, as plane wave bass array. You have the ideal situation for that. However, your bass management system probably can't do that on it's own, so you'd need an external speaker controller to achieve that. But it could solve several of the above issues, all at once. I would consider that.
Really tempted to buy a 4th subwoofer now But I'm on a budget and that budget has been passed 4 scores and 7 years ago

Quote:
Originally Posted by Soundman2020 View Post
2. There's too much absorption in the 200 Hz region. You can see that on the last graph, below (RT60). Decay times are mostly reasonable, at around 200 ms, but there's a dip to roughly half that between maybe 150 Hz and 6 kHz.
It must be all the dampening material in the ceiling. Perhaps I could remove some and see if that works better.



Thank you so much for the input. I enjoyed this lesson very much and it increased my knowledge in how to interpret the REW information.
I'll continue with the hints/tips.

Cheers!
//Nicklas
Old 2 weeks ago
  #10
Lives for gear
 
kgveteran's Avatar
 

I’ve never tackled REW,i had too many failed attempts. Looks like perseverance pays off.
I always try to Follow the threads on home theater set up and tweaking. I came here a number of years ago to learn how to build my current home theater and the information was priceless. I hope there’s more reply’s from these guys
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