My Room resonates at 80Hz

[Vladi]

I have posted a while ago on my bass problem, but I am still not very clear on how to solve it. My problem is with 80Hz resonance of my room. Here is how I found out.

I have noticed that with bass heavy music, some bass notes sound louder, while others much quiter. This gave me a very disturbing feeleing and unpleasant listening. One example would be Sade - Lovers Rock. I got the bass test CD so that I can test the SPL at different frequencies. I set the volume of pink noise so it measures 80dB, here is what I took as readings.

1KHz 80dB

200Hz 80dB

165Hz 78dB

125Hz 78dB

100Hz 76dB

80Hz >90dB

63Hz 82dB

50Hz 78dB

45Hz 76dB

40Hz 82dB

30Hz 70dB

At 80Hz, the whole room starts sounding like "wooooooooooooo", and in corners it is even louder. My main speakers are currently cut at 125Hz because of this, but the 80Hz coming from the suboofer also causes the same effect. First thing I tried is speaker position. My main speakers and subwoffer are 17" away from the back wall. The "wooooo" goes away if I place them 36" away from the back wall, but that is not an option, since the whole width of the room is ~14', and I will have only 9' left for the table and the sofa.

What else can I do to fight this?

Bass trap?

Sub EQ like Art 351 Equalizer?

Please share any opinions and advise.

[easylistener]

If placement can not be an option, then an EQ can help. Most eq only adjust about three to six db though. I would like to see a picture or diagram of your room. What type of sub are you using? To a search on eq because some of the guys here have had good luck with one or two.

[j-malotky]

Man, that sucks.

Since its 80HZ makes me wonder, since that is the normal default sub kick in frequency. If so, can you adjust this on your processor? Maybe run a test with your sub off?

If this is trully room harmonics, sounds like you have a serious peak problem at 80 Hz. The best way to solve that problem is to put convex deflectors on your walls to keep the bass from reflecting in a streight line causing the doubling / tripling effect of the wave lenghts reflecting back on themselves in the same wave form.

Look at Artos khorn room in the Archetecture section. Arto may have some suggestions for you in this area.

Good luck with the problem.

JM

[m00n]

Where did you get the bass test cd? What is it?

Thanks

m00n

[luchenbach]

I read this article on the Behringer Feedback Destroyer digital parametric EQ, and was very impressed. The best part is that you can get them for less than $150. See the article at:

http://www.snapbug.ws/bfd.htm

The author graphed the frequency response of his room from 16hz to 160 hz, and was able to minimize the peaks, and boost the valleys, to get a much flatter response.

G-

[easylistener]

I am will moon on this one where did you get the test cd?

[dougdrake]

Bass test CD:

www.stryke.com

Look down the left of the screen to Test CD.

DD

[ben.]

If you can't resolve the problem acousticly, your best bet would be a quality parametric EQ. Digital or analog, a true parametric will allow you to vary the attenuation level, frequency, and bandwidth. This will allow to remove just the right amount of resonance w/o removing surrounding frequencies and minimizing phase distortion (a problem with graphic EQs in general)

[Vladi]

Well placement is an option, but not that far away from the wall. The speakers will be seating 4 feet in the room, and the room is only 14 wide.

I will draw a diagram (something I wanted to do for a long time . I will post it later on tonite, and am very open to suggestions on placement.

I got the test CD for a friend, I can place the files on my web site so anyone can download them and burn them on CD. When I do that later on tonite, I will post back.

I am not sure what is graphic and what is parametric EQ. Which one should I be looking for?

I have tested without subwoofer:

1) Mains set to small, crossover at 125Hz, the resonance at 80Hz is unnoticable.

2) Mains set to large, the resonance at 80Hz is killing me.

From my original post, do you also see the peak at 40Hz?

[ben.]

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On 5/2/2003 4:49:18 PM Vladi wrote:

I am not sure what is graphic and what is parametric EQ. Which one should I be looking for?

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A graphic EQ has a slider for each freq, usually with very steep filters (slope). Unless they are of very high quality, they introduce more phase shift than they are worth for this application. A parametric EQ will have knobs that allow you to tune to the problem freq. It will also allow you to adjust the bandwidth of the filter (the spread of surrounding freqs- ie centered at 80Hz you could cut 75Hz-85Hz (very steep, narrow bandwidth) or 40Hz-120Hz (gentle slope, wide BW) and also any BW in between). Parametrics are generally more suited to your situation.

Any ?s please feel free to email or PM me.

[ben.]

Actually, re the 40Hz bump, that may be what's causing your problem. Try cutting 40Hz, and your 80Hz resonance may go away. It's common that room resonances are harmonics of another.

[Vladi]

Anyone who needs test CDs can download from my web server here http://12.213.128.107/TestCDs/

I will be looking for parametric EQ, any brands recommendation up to $200?

Cutting the mains lower does not help, in fact any freq below 125 and I start getting the resonance.

[ben.]

http://www.sweetwater.com/store/detail/EQ3B/

I am not affiliated, etc....

Ask for Michael Eads if you like. He is my rep & is very good. Mention Hollis Recording & Ben Clarke. He may or may not remember me-it's been a while since I've needed anything from these guys. The studio is pretty well settled for now.

Anyway, Presonus gear that I've used has been well constructed and sounds very clean. I'm offline until Mon, but again, let me know if you have ?'s. Also, let us know how it works out.

[JohnA]

Vladi,

What are the dimensions of your room?

Do a search on Jon Risch to find his web page. He has published a DIY bass trap for promlems like yours. There are commercially made versions, too.

[formica]

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On 5/3/2003 9:27:35 AM bclarke421 wrote:

Actually, re the 40Hz bump, that may be what's causing your problem. Try cutting 40Hz, and your 80Hz resonance may go away.

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I second bclarke421 on that one... even though your 40Hz resonance seems less pronounced because of your speakers natural roll off, it is obviously still there. Your test didn't go all the way down to 20Hz but it may be there too.

If you'd like to optimise you room through placement, there are some software such as CARA which will analyse your situation and make furniture placement recommendations. You basically tell it the region within which it can reposition a piece and it will calculate it out for you.

Cara at http://www.rhintek.com./

a review of Cara at http://www.hometheaterhifi.com/volume_9_4/cara-software-10-2002.html

For a parametric subwoofer EQ, i'd go with the Behringer 1124P as already mentioned, it's inexpensive and VERY flexible.... and is all the talk in DIY forums. I would try to EQ the sub only, as i don't like passing high-frequencies through any one.

http://www.behringer.com/02_products/prodindex.cfm?id=DSP1124P〈=eng

Test Tones? I'd just make my own... and burn them onto a CD. WinISD speaker design program has a tone generator built in if you have that already... OR i used NCH to make individual 10sec tracks for 1/6 octave. You can download it free at:

http://www.nch.com.au/tonegen/

Hope it's of some help...

Rob

[redwood forest]

Tube bass traps can partially solve your problem. Tube traps are nonselective with the frequencies they block. A bass tube trap not only lowers 80Hz, but all other frequencies in that bass range as well. While the 80Hz will be lowered to the desired level, all other frequencies in the bass range will now be much lower then before. The contrast between the 80Hz peak and the surrounding frequencies will still be there.

An equalizer works well as long as the it can be selective enough to lower the problem frequency and leave the surrounding frequencies alone. Good luck! Equalizers also have a problem with introducing distortion. I used to have one, but I got rid of it for that reason.

I would recommend a digital room correction unit. Using a microphone, the unit picks up the level of the entire spectrum. Frequencies that are higher or lower than the average will be adjusted so the end result will be a flat frequency response. You only need to calibrate the unit once unless you want to make changes in your room. Check out tactaudio.com

[m00n]

What is room resonation?

[JohnA]

aka standing wave. It is a peak in response caused by a dimension or 2 that coincides with the wavelength of the resonance.

There's no reason a bass trap cannot be tuned to a specific frequency like a speaker cabinet. It may not be simple, but it would be easier than changing the room dimensions.

[Colin]

Your loudspeakers SHOULD be 3 to 4 away from the front and sidewalls, and now you know why. The room can be causing the resonating bumps at 40 and 80Hz.

Taking the bumps out with tube traps will be very difficult, as most commercial traps capture not the low frequencies, but the high ones. A trap to effectively capture those specific frequencies may be tricky and bulky to construct. Think folded Klipsch horn and you get an idea of the dimensions of the problem.

A low cost equalizer worked very well for me. It reduced obnoxious room reflections at 50 and 5-9kHz. The key was to use only half of the required amount. In other words, your 10-dB bounce at 80-Hz should be cut only about 5-dB, so that it does not noticeably and adversely affect the surrounding frequencies.

Breaking up the square of the room and the flatness of the walls also helps. Find the reflection points of the loudspeakers along the wall. You can find them by sliding a mirror along the wall while you are sitting in your listening spot. When you see the reflection of the loudspeaker, the mirror is at the reflection point of the sound. Cover or break up that point.

[m00n]

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On 5/3/2003 3:45:31 PM Vladi wrote:

Anyone who needs test CDs can download from my web server here

http://12.213.128.107/TestCDs/

I will be looking for parametric EQ, any brands recommendation up to $200?

Cutting the mains lower does not help, in fact any freq below 125 and I start getting the resonance.

----------------

Turn your web server back on.

Also, you mentioned you started to notice that some bass notes were louder than others. How can you tell. Were you closely listening for this, or was just very obvious? It amaizes me when you guys can hear these descrepencies. I think I have a good ear, but, I sure don't notice things like that...

I would just love it if some of you guys with that finely tuned ear could come to my theater and listen and tell me what if anything was bad.