New room with problems

Mmaxed

Active Member
After finally moving the business out of the house I now have a room to dedicate to a listening room. Problem is it sounds like crap.

It is a basement room about 11' x 20' with very low 6' 8" ceiling. There are heating ducts running along the ceiling full length of the room on one side. Floor is rubber backed carpet on concrete. Walls are 1/4 inch paneling on the studs, nothing behind it. Ceiling is the old rigid ceiling tiles. No furniture at this point and there may never be much.

The biggest problem with the sound is that the mids are harsh. The vocals on California Dreamin' will shred my ears. It's a nail on the chalk board type thing. At first it sounded like a transistor radio at the end of a tunnel, but with some playing with speaker placement that has improved somewhat.

I believe I need some absorption, but how much?

My goal is a rich, smooooooth sound. My ringing old ears can't tolerate bright or harsh. I have been heading that way with my equipment and was getting pretty close in the living room. Set up wasn't ideal for sound stage and imaging but was getting pretty good there too.

Thanks for any help.

Mark
 
After finally moving the business out of the house I now have a room to dedicate to a listening room.
:banana:
Problem is it sounds like crap.
If definitely does not have to. If you have freedom to change wall, ceiling, and floor surfaces, you can have this room sounding awesome.

I believe I need some absorption, but how much?
I filled out a spreadsheet for you from this post I made to answer this very topic. Since you have such unusual surfaces, it's tough to find absorption values, so these results are going to be pretty rough, but at least it's a starting place. The forum won't let me attach a spreadsheet to the post, but I can e-mail it to you if you'd like to see what I did (just send me a PM).

I did find some data for a wood paneling wall, but I don't know how well that compares to yours. With material that thin, the way it's mounted to the studs and the stud spacing does matter. You may actually have some pretty good absorption in the low frequencies due to the panels flexing between studs.

I could not find any data for non-acoustic ceiling tiles. It's not surprising, since a manufacturer would have no reason to do an acoustic test on a non-acoustic product. I'm guessing these are just rigid, plastic tiles, so I used the values for vinyl floor tiles.

Here's the way it looks based on just the basic surfaces and your room dimensions (assuming 1 person and one recliner in the room).

63 - 0.56
125 - 0.30
250 - 0.44
500 - 0.46
1k - 0.43
2k - 0.48
4k - 0.51
8k - 0.56

You do look like you might have a little peak somewhere in the 500 Hz band, which could make the mids jump out at you a bit. You also seem to have high values in the 2 kHz band and up, which would definitely make it seem harsh. Generally you want the values in the higher octaves to be a little lower than the values in the low octaves.

Keep in mind that low frequency values, especially in the 63 Hz band, are pretty dubious for small rooms like this. Room modes are more important than statistical values for absorption, so you'll want to look at the room modes for your room shape too when evaluating low frequencies.

But the high frequency stuff, in your problem areas, is easy to fix. This is especially true since it'd be so easy for you to just swap in acoustical ceiling tiles. I added in the following treatments to the calculation:

-Replaced a little more than half of your existing ceiling tiles with NRC 0.8 acoustic ceiling tiles (these should be located more in the center of the room and on the end near your speakers).
-Added a 60 s.f. rug over the floor (should be placed between you and the speakers)
-Added 16 s.f. 2" absorbers on each side wall (should be placed in the first reflection location)
-Added 24 s.f. of 3" absorbers on the wall behind your speakers.
-Added a 16 s.f. 3" absorber on the wall behind the listening position.

With those changes the Sabine formula spits out these numbers:

63 - 0.42
125 - 0.24
250 - 0.26
500 - 0.23
1k - 0.20
2k - 0.20
4k - 0.21
8k - 0.22

Very smooth from the 1k band on up, with much less harshness. In addition to just general statistical reverb, it's possible you have some harsh reflections from the ceiling or walls. Swapping out ceiling tiles and placing side absorbers in the reflection points should help with that considerably.

For low frequency the Sabine formula predicts boominess, and your room does have several modes that fall in the 63 Hz octave band, so it's likely that after you treat your surfaces the low end will jump out at you as boomy or muddy. You can battle against that with bass traps in a couple of corners. I would just build or buy some tube shaped traps and stand them up in 2 of your corners, moving them from corner to corner to find the best sound.
 
Thanks Rev! You definitely put some effort into this. Great help.

Your chart makes it look slightly tamer than the room reverb report I did at ATS. In talking to ATS they said to treat the older hard ceiling tiles as drywall, so I think you were on track with what you used.

I was about ready to order up a bunch of acoustic insulation from ATS if I can't track some down locally. Your research confirmed what I would need as I had been making a WAG about how much to order based on some reading I have been doing. My guess was actually very close to what you came up with.

I do have one question. On the ATS site they list the preferred reverb time for a listening room as 0.40 to 0.60 seconds at 1000Hz. Your target numbers after treatment are much lower than this. Are you using the same scale? If so why the difference? I have read where you can get a room too "dead". I think I'm quite a ways from that, but curious.
 
Same scale. Slightly different objective.

I usually aim for less than 0.5 seconds for a room like this, which you already seem to be at. But your complaint is that mid and high frequencies are harsh, so we want to smooth those out and bring them down to a level that matches the low frequencies better. So my final numbers are more about a smooth response and a lack of harshness.

When predicting or measuring RT in a small room, we always have to remember that the formulas don't work quite as well as they do for medium or large rooms. So we don't want to focus on the absolute values as much as the relative values. We can still get a sense of the acoustic signature of the room, even if our absolute values are off by a tenth of a second. That's not to say that we should not consider absolute values, only that we should take them with a grain of salt.

The great news about your room is it will be extremely easy to tune. If it's too dead, start putting back rigid ceiling tiles until you like how it sounds. If it's still too live, start putting in more acoustic tiles. You can easily switch out absorption 4 square feet at a time, so you can tune your room until it's just right. Just make sure you mount your wall panels in good locations to take care of those first reflections.

Since your room is already fairly dead, you can also substitute diffusion for absorption on the side walls. Diffusive elements break up reflections by scattering the sound back into the room instead of absorbing them, so you still get a little reverberation. You can also use diffusers to help break up standing waves if you have any that are bothersome. You can test this by putting a bookshelf or CD rack or something with an irregular surface shape at the spot of a first reflection off one of your side walls and see if it helps with harshness or imaging.

If you want to combine diffusion and absorption, put the absorption on the side of the room with your speakers and put the diffusion behind you.
 
More info put in a way that I can easily understand. Brings up more questions.

Since the old ceiling tiles have the tongue and groove thing going on it is a pain to replace part of them. I assume it will be OK to just put panels up over the existing tiles?

I hadn't considered putting more absorption on the floor. Just figured the existing carpet, poor as it is would be enough........ I was going to ask how important that is but thinking about it while my typing finger was trying to get through this post I decided it could be quite important. Worn berber carpet, while better than the concrete under it, is still going to be reflective in what is an important location.

Last question for now. If a room is too dead, does imaging and sound stage suffer?
 
Be very careful of using formula's only, they can only describe so much in a room before speakers are placed there.

An ideal thing to do is collaborate formula's with actual measurements. Not many formula's take into consideration the dispersion pattern of the speakers, or their bass performance where the speaker actually sits in the room. This can only be verified by actual measurements of the speaker in the room.

When I do installs of high end hometheater and two channel systems, I always do pre-analysis first using calculations. But I always follow up with actual measurements of the speakers in the room because what is done in the lab does not always pan out in the field.
 
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Last question for now. If a room is too dead, does imaging and sound stage suffer?

It highly depends on the performance of the speaker in this kind of room. What will suffer for sure is the sense of spaciousness in the room. Speakers are sometimes measured and voiced with some room interaction in mind, and a dead room will often change that voicing. Unless that room is dead at all frequencies(20hz to 20khz equally), it is likely you will have sound that is bottom heavy and dry. The problem is that a dead room usually effects the midrange and highs, and leaves whatever problems occurring in the bass frequencies intact unless they are deaden as well.

One thing we know for sure, most speakers do not sound very good in anechoic chambers. They may measure well, but they don't sound good with actual program material. What you want is an ideal combination of a good frequency response, decent reverberation time, along with a decent sense of spaciousness.
 
Thanks Sir T. What you say makes sense and make me feel better about the path I am on. I will get material to build up some panels and will be able to add, remove, or change placement to get the balance I need.

Don't know if I will get into measurement at this point. While I can see the value, it seems like a big step for those of us who are somewhat computer challenged.
 
Since the old ceiling tiles have the tongue and groove thing going on it is a pain to replace part of them. I assume it will be OK to just put panels up over the existing tiles?
Oh... THAT kind of ceiling tiles. I was thinking you had drop-in tiles, not the kind that are stuck to the ceiling. That does change things. Do you know what they're made of? Are they the perforated kind? If you could take a picture that would help.

Taking a measurement would be helpful, if you have a good enough microphone and a computer that you can put in your room. Do you have any good quality microphones, like you might use for recording, or a sound level meter? (A lot of sound level meters have a pass-through for the audio signal, so you can use them as a mic pre-amp that can be plugged into the line-in on your computer.) If so, you could take some measurements of your room using REW, which is free.
 
Asbestos.

:scratch2:Could be? Judging by the paneling and the rest of the basement I'm guessing they were installed in the '70s. They are a brown fibrous material with the white on the outside. We replaced some in the laundry area about 10-15 years ago with some that are almost the same.

Rev, they are not perforated.
 
Oh yeah, I think those are asbestos. I'm a little too young to recognize it immediately but, man, that stuff was everywhere.

Are they like this?

3773917892_9369c134ec_m.jpg


I'm personally not bothered by asbestos if it's in a quiescent state, but I know it makes a lot of people nervous. You might want to have someone check on those tiles to see if they are. I'll bet there are several asbestos removal companies in your area that would check them for free.

I'll bet there's absorption data for asbestos tiles out there somewhere.
 
They would be paper and asbestos which wasn't banned from products until 1978. I would cover them with a layer of fresh paint and then another layer of acoustic tiles. If you remove them, wet them down till they are dripping wet and wear a respirator. Use dish soap to help lower the surface tension of the water to aid in saturation. (or have it professionally removed as suggested by Revman.)
 
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