Home Theater Forum and Systems banner

1 - 15 of 15 Posts

·
Registered
Joined
·
35 Posts
Discussion Starter #1 (Edited)
Hi,

I've finally achieved a satisfactory FR (thread here and here) with my mains + subwoofer; however, with concrete walls and wooden floors there is a lot of reverb and I'm thinking this is why the sound isn't *that* good at all...

My first RT-60 is shown below, and I'm wondering, is this horrible? I've read that it should ideally be within 300-500 ms...



Topt = Green
T30 = Purple

I'm looking into room treatment now in order to lower the reverb, but I'd like your thoughts on the initial results with no treatment :)

Room dimensions are:
Depth: 12.96 ft
Length: 25.85 ft
Height: 8.23 ft

See layout below :)
 

·
HTS Senior Moderator
Joined
·
5,288 Posts
What are the room dimensions? Decay time curve is dependent on the volume of the space.

Also, RT60 really isn't valid in small room acoustics. It's more for larger venues. You certainly wouldn't want things to be 30-50ms. Think, more like 300ms.
 

·
Registered
Joined
·
35 Posts
Discussion Starter #3
bpape,

Hi, thanks for the reply. Here are my room dimensions:



I forgot at zero on each interval, so yes, I mean within 300 - 500 ms.

On the right side of the living room there are large windows, but they are covered with a curtain, so hopefully they've taken the worst reflections...

Best regards,

Peter
 

·
HTS Senior Moderator
Joined
·
5,288 Posts
Curtains are high frequency absorbing only. It would be better if there was something thicker at the side wall reflection zones to better address any SBIR and not unbalance the absorption curve. For this application and that size of room, I would be looking to be no more than 400ms in the bottom and probably around 250 in the upper end.
 

·
Registered
Joined
·
35 Posts
Discussion Starter #5
Wow, 400 ms and 250 ms is a far cry from where my measurements put me at the moment :)

Would my first are of interest be the tridhedral corner or the point of first reflection?


Reference

I've heard that bass traps are the best way to start out seeing as they also do broadband absorption. Would you agree?
 

·
HTS Senior Moderator
Joined
·
5,288 Posts
Bass control is the first thing I would tackle as it covers the broadest range of frequencies. Bringing down the bass decay time also helps 'unmask' low level information like imaging cues, micro-dynamics, and low level harmonics.

Tri corners are certainly nice to do though I would not concentrate all my efforts there. Certainly not at the expense of dealing with non-modal bass issues, SBIR, and early reflections.

IMO the best course of action is a moderate amount of bass control, reflections, and any modal/non-modal bass issues. Then you can look at the other things like limited range bass control and diffusion to help with flutter echo - usually up higher in the room.

Whatever you do, don't get sucked into the trap of foam. Can't tell you how many rooms I redo weekly when people have spent a lot of money on foam and realize it just doesn't work very well.
 

·
HTS Senior Moderator
Joined
·
5,288 Posts
.5 at 100Hz is not what I call a good bass trap - sorry. I would highly recommend staying away from any foam based product. Fiberglass or mineral wool cores yield MUCH better performance.
 

·
Registered
Joined
·
35 Posts
Discussion Starter #9
Ok thanks! I guess that sounds a lot like a DIY project.

Unless you're willing to spend some big $$$ (which I'm not really at the moment...)

I'll supply some new readings once I've added some acoustic treatment to the corners :)
 

·
Registered
Joined
·
35 Posts
Discussion Starter #10
Hi,

I've treated my ceiling around the 1st reflection point with absorbing "tiles" 3x3 and put an acoustic picture on my rear wall now :)

The RT60 (T30) has improve around 0.1 ms, but the audible improvement is surprising!

Since my listening room is rather small I've been told not to use RT60, but rather look at ETC. However, I've tried to search the web on how to read it to no avail... Can someone help? I've included measurements (L,C,R) before and after my room treatment (here).

ETC (center position no treatment)


ETC (center position with sound treatment)


I'd love some opinions :)
 

·
Registered
Joined
·
1,295 Posts
Here is a good goal.

no reflections higher than -15db for the first 5ms... from 5ms-10ms you want no higher than -18 and from 10-20 you want no higher than -20 and 20-40ms you want to be around -24db.

anything beyond 40ms adds ambience/space but you should be down to -30db around 80ms. This has been my learning in recent studies and practice. I've spent some time chasing reflections and it makes a difference.

If your couch is all the way up against the wall like that you need some 2 or 4" absorption panels. You have a ton of reflections in the first 5ms and this means behind your head... and floor... and that side wall.

Something that would really help is some simple 2" 2x4 panels from GIK that would be placed to the far left at intervals around every 4' or so would really help bring down some later reflections but your critical spots are very close. meaning they are first and close second wave from teh back right corner. absorption isn't the end all fix but your setup could benefit from it.
 

·
Registered
Joined
·
1,295 Posts
Here is your left channel... the red line would be your goal. Your MOST critical area is 0-5ms. Really you want this closer to 20 but I feel you can get away with it around -15db.

You can see the absorb vs. no treatment it did improve slightly but the acoustic tiles doesn't seem to have helped much. You need some 2" thick panels to improve this.
 

Attachments

·
Registered
Joined
·
35 Posts
Discussion Starter #13
Hi Tally,

Thanks a ton for taking a look at my .mdat file and providing the graphs above :) It certainly makes more sense now. The left side is not improved that much, but looking at the right side it's much better when looking at the before/after ETC. However, it's not near the ranges you recommend (unfortunately!).

Two questions:

1) If the direct sound is 0 ms, what are negative ms then?

2) How did you overlay my before and after ETC :)?
 

·
Registered
Joined
·
1,295 Posts
Hi Tally,

Thanks a ton for taking a look at my .mdat file and providing the graphs above :) It certainly makes more sense now. The left side is not improved that much, but looking at the right side it's much better when looking at the before/after ETC. However, it's not near the ranges you recommend (unfortunately!).

Two questions:

1) If the direct sound is 0 ms, what are negative ms then?

2) How did you overlay my before and after ETC :)?
1.
The portion of the response before the initial peak at time=0 is actually due to the system's distortion - looking closely, there are scaled down, horizontally compressed copies of the main impulse response there - each of those copies is due to a distortion harmonic, first the 2nd harmonic, then the third, then the fourth etc. as time gets more negative. The initial peak and its subsequent decay after time=0 is the system's response without the distortion
2. Top buttons... says overlay then click impulse and then select the tests you want to use.
 

·
Registered
Joined
·
59 Posts
Hello

The measurement clearly shows the reflections from the right wall and the back wall.

I would recommend
1. A smaller listening triangle (make it also equilateral)
2. moving more into the room with the triangle. Especially move away from the back wall.

That will help you to delay the arrival time ofthe reflections by more than 5 ms.
The additional distance also reduces the level of the reflections. You can get another -3 dB at least - for free.

Just make an experiment and set up a small listening triangle on the middle of the room. The length of each side not more than 2-2,5 meters (about 6,5 to 8 feet).

Listen to the difference. ;-)

Cheers
 
1 - 15 of 15 Posts
Top