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I have a huge hump at 30Hz

I am happy with my system and I'm down to working with the room. I have about a 10dB hump in response at 30Hz. At 40 and 25 Hz it is pretty flat compare to the rest of the bass range so I have a pretty narrow range to deal with. The long dimension of my room is about 17 feet which would predict this response. It is not a huge problem since most music doesn't hit that frequency, but I would like to get rid of it. Is there an inexpensive way to deal with this?

I know that Rives makes a parametric bass EQ but I have to think there is a solution for less than $2800. I've read about helmholtz resonators but have yet to find any detailed instructions for building one. I've looked into tube traps but they don't have the high Q I need to get rid of the hump.

I'm thinking that an active EQ may be the only solution for such a narrow band of frequencies. Any ideas?
herman
sidssp
1,077 posts
 
I would suggest putting a pair of 16” or 20” tube traps at the corners if you can afford them. After that, if you are using sub and are feeding the sub with line level signal from preamp, you can tamp the bass peaks with a low cost equalizer like the Behringer Ultra Curve Pro DSP 8024 or the newer ULTRACURVE PRO DEQ2496. But I would not put them in the signal path to equalize the main speakers.
sean
6,231 posts
 
Herman: Are you using any type of room treatments now ? How are you measuring your in-room response ? Sean
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rlapporte
62 posts
 
If you want to avoid electronic intervention, you are probably limited to playing with speaker and listening position and/or helmholtz resonators. I have 5 helmholtz resonators in my room, custom designed for two different low frequency absorption areas. Rives may also be able to help guide you toward these or other passive solutions. I would certainly first try playing with listener and then speaker positioning if it is possible in your setting. Just mark your present locations, as you may create more problems than you solve. I have found changing distance from speakers by a matter of inches can alter the amplitude of a bass frequency tremendously. The same can be said for speaker positioning. These methods would obviously not change the total bass energy in your room, but would alter it at your listening position. In my room (almost 20x30) I have found that placing woffers closer to the wall, and closer together, increases bass in the 16-50hz range while reducing nodes in the 60hz area. I have found this same effect with many speaker systems, including dipoles. For better or worse, all of my systems have included separate subs and allowed for great experimentation. Best of luck.
herman OP
2,238 posts
 
Thanks so far. I am measuring with my modified (Sean instructions) Radio Shack SPL meter and confirmed by a local dealer with a nice RTA.

My room is treated with some damping but it is my understanding that 30 Hz is too low to be damped by any practical means. I have poked around on the ASC web site and it looks to me like their tube traps work across a wide range but still don't affect 30 Hz much.

The problem as I see it is the narrow range. A huge hump at 30 and almost flat at 25 and 40. Can a Helmholtz resonator be constructed to tame such a narrow peak? Rlapporte, when you say custom designed do you mean by yourself or someone else? Can you share this design?

I'll continue to play around with sub placement. That may be the key as suggested.
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