I have a huge hump at 30Hz

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.

Herman, you are right, the 30 Hz can not dealt with correctly with absorption devices, particularly high Q factors. Even if you were able to absorb it you would bring down other frequencies as well. Your situation requires diaphramatic methods Helmhotz or capacitive style bass traps. Helmhotz can work quite well, but keep in mind they are tricky to build. High Q Helmhotz resonators are inefficient, which means they have to big and very very rigid. The best ones are poured out of concrete. I realize that's not likely a realistic option. You can do well with wood--I just wanted you to be aware of the issues. Placement of the resonators are very important as well. You want them at the lowest pressure zones, unlike absorbers that you want at the highest pressure zones. The capacitive traps can help as well, but you can't get very high Q factors with them (still they are much much better than absorption methods). They work much better to smooth out the frequency response across the listening room. For either of these methods, we can design these for you and figure out placement, it would be done on an hourly basis.

The other item you've mentioned is placement. There are a few tricks with placement that can help alot. Place the sub in the 1/4 wavelength cancellation point for 30 Hz. That will help quite a bit. This might not be very practical if you only have one sub.

Herman,
I would follow Rives recommendations on this one. I did not design my resonators and bought them from someone who had them built for him. I could find out who he used but Rives would likely be a greater resource. Mine are wooden and quite large. Mine are actually placed in high pressure zones, which according to Rives, sounds incorrect, although they help a great deal. I may have to talk to Rives and learn more from him. I certainly agree with others that you will not obtain the desired effect from absorption units such as Tube Taps.

Rives, if you would comment on the placement issue, perhaps we could all learn something. Thanks in advance.

Sure 30 is a big hump but I am turning 46 this summer and thats over the hump and let me tell you everything Hz alot more at 45.

Thanks again to everyone.

I just built a passive 2 pole high pass filter to feed my sub. After playing around with different component values and the settings on the sub, I have gotten much closer to a flat response. I'm only up about 5 dB at 30Hz and the rest of the bass region is flatter than it was. Given that my measuring tools are probably not that accurate anyway, I feel pretty good about the response I'm getting. Besides, it sounds good.