[papomaster]

Hey all!

I'm trying to set my newly bought subwoofer, but I think there might be some resonances around 30-35 Hz in my room since it seems to overboost one frequency with every kind of bass note being played. I have made a test tones cd with 1 Hz jumps, so I will be able to note if there is indeed a standing wave in my room or if the sub is just boomy (it's a B&W sub, so I really doubt that).

My question is : if it is the room, how do I fix it? Can I just put some objects (like chairs) to make the room asymmetrical and remove the standing wave? Or move the sub in order to reduce the problem?

 

[883dave]

Quote:

Originally Posted by papomaster /img/forum/go_quote.gif Hey all! I'm trying to set my newly bought subwoofer, but I think there might be some resonances around 30-35 Hz in my room since it seems to overboost one frequency with every kind of bass note being played. I have made a test tones cd with 1 Hz jumps, so I will be able to note if there is indeed a standing wave in my room or if the sub is just boomy (it's a B&W sub, so I really doubt that). My question is : if it is the room, how do I fix it? Can I just put some objects (like chairs) to make the room asymmetrical and remove the standing wave? Or move the sub in order to reduce the problem?

Start your research at sites like ASC (acoustic science corporation), Rives Audio...

 

[gregorio]

Quote:

Originally Posted by papomaster /img/forum/go_quote.gif Hey all! I'm trying to set my newly bought subwoofer, but I think there might be some resonances around 30-35 Hz in my room since it seems to overboost one frequency with every kind of bass note being played. I have made a test tones cd with 1 Hz jumps, so I will be able to note if there is indeed a standing wave in my room or if the sub is just boomy (it's a B&W sub, so I really doubt that). My question is : if it is the room, how do I fix it? Can I just put some objects (like chairs) to make the room asymmetrical and remove the standing wave? Or move the sub in order to reduce the problem?

If you are getting a standing wave at a particular frequency you could make a helmholtz resonator which is tuned to the problem frequency. Chances are that your problem is not just a single standing wave, in which case you could do with some decent bass trapping. A simple solution would be some rolls of loft insulation in the corners of your room. A chair is not going to fix the problem.

Although making your room asymetrical will help with the standing waves, you will almost certainly need some bass trapping as well. There are many quite expensive commercial solutions to bass frequency problems, as a general rule, DIY solutions work just as well at a fraction of the cost.

Here's a good article to start you off: Acoustic Treatment and Design for Recording Studios and Listening Rooms

G

 

[NightOwl]

Here's another link to some inexpensive diy acoustic treatments.

Jon_Risch's Web Site, Cable Main Page

 

[twylight]

Bass traps, do first reflections while you are making the traps - a great upgrade than possible electronic thing for a theater or listening room - DIY if you can buy stuff and use a hot glue gun...and a stapler.

 

[papomaster]

If I use some fiberglass, there seems to be two ways of doing corner bass traps:

- A layer of heavy fiberglass put at 45 degrees to cover the whole corner.

- a large (1 foot diameter) cylinder of fiberglass just standing close from the corner.

Am I wrong?

 

[Bmac]

The only thing I don't like about DIY room treatment is it usually doesn't look as good as something you would buy, and depending on how much you consider your time worth it may be cheaper to just buy a treatment.

My suggestion is to buy some cheap corner bass traps from Ebay. You can get 8 lineal feet with a claimed NRC of 1.35 for around $50. It's probably just as cheap as DIY and you save all the time and hassle and end up with IMO better looking results.

If you're looking for broadband sound absorption I would recommend looking at something like Sonex acoustical foam. I think it looks better than rigid fibreglass panels (DIY or not), and offers comparable NRC. At $37 per 2' x 4' panel if you buy 8, it's not that much more expensive than the cost of DIY. Here's a link:

Sonex™ Classic Colortec is the only architectural foam product offered by Sonex™ that is Class 1 Fire Rated yet charcoal or light grey color throughout.

 

[linuxworks]

standing waves?

I think you're using your waterbed incorrectly!

 

[mulveling]

The treatment suggestions have been mentioned, and rightly so. They're necessary, to at least some degree, for achieving maximum sound quality in the overwhelming vast majority of rooms. However, they are a difficult/expensive route.

One thing that is cheap and easy (assuming you have full control over decor & layout), with equally great effect, is to vigorously experiment with positioning of your seating, the main speakers, and the subwoofer. Avoid stuff like sitting in the middle along any room dimensions (bass peaks/nulls), and try to avoid stuff like having yourself or the speakers very close to any hard boundary (though I realize that can be tricky). Try weird stuff like firing down the diagonal of the room, perhaps even in a slightly asymmetrical manner.

 

[papomaster]

I have already tried a lot of different positions for the speakers, and they all give huge dips with huge peaks, and sometimes moving an inch sideways can reverse everything : a dip becomes a peak and a peak becomes a dip. That's why I will try asap to do bass traps at least to help with those HUGE peaks somewhere in the 35 Hz region.

I've found these designs, and they seem interesting since they only involve a cardboard tube, two pieces of plywood and sand, and they seem quite easy to raise very high (those tubes can be bought up to 8', do only one can cover floor to ceiling).

Build an awesome bass trap

Would these work just as right?

 

[Bmac]

Whoever wrote that has no idea what they are doing. That will not absorb sound. For good sound absorption you need acoustic foam or rigid fibreglass. Even carpets hung on walls can work, but a cardboard sonotube will not absorb sound. It may look like a real bass trap but real bass traps are full of rigid fibreglass, not cardboard.

 

[gregorio]

Quote:

Originally Posted by Bmac /img/forum/go_quote.gif Whoever wrote that has no idea what they are doing. That will not absorb sound. For good sound absorption you need acoustic foam or rigid fibreglass. Even carpets hung on walls can work, but a cardboard sonotube will not absorb sound. It may look like a real bass trap but real bass traps are full of rigid fibreglass, not cardboard.

Not true unfortunately. Carpets on walls will absorb mid/high frequencies but will have no effect on low frequencies. Ideally, place dense rockwool triangles in the corners. If you want to make it pretty, just build a stud frame for them and then cover, still relatively cheap. If your problem is specifically at 35Hz and nowhere else, have a look at a helmholtz resonator.

You could easily make acoustic panels yourself, make a rectangle out of 1x4 wood, put thin plywood on the back, fill with rockwool, cover with material and hang on the wall. Bare in mind though that treating the corners is particularly important when treating a room for bass freq problems. Unfortunately, low freq problems are the most difficult to solve.

G

 

[linuxworks]

standing waves?

sounds like you are not using your waterbed properly.


(sorry)

 

[Bmac]

Quote:

Originally Posted by gregorio /img/forum/go_quote.gif Not true unfortunately. Carpets on walls will absorb mid/high frequencies but will have no effect on low frequencies. G

I wasn't implying that carpets will absorb bass, just that they will absorb sound as opposed to dense cardboard, which will absorb very little.

 

[gregorio]

Quote:

Originally Posted by Bmac /img/forum/go_quote.gif I wasn't implying that carpets will absorb bass, just that they will absorb sound as opposed to dense cardboard, which will absorb very little.

I haven't tested dense cardboard but I imagine it would be quite absorptive in the higher frequencies, it may even be effective at lower freqs but without knowing the absorption co-efficient I can't be sure. Bare in mind that even solid wood absorbs high frequencies.

G