Hi, I have a big resonance at 22hz. I know there's not much music down there and that I'd need big helmotz resonator to tame it. I was thinking to use an external eq before hitting my head prism da. What can I use that doesn't alter anything but 22Hz?

You might want to run a high pass filter. That's an extremely low frequency. I don't know if you'd have the real estate available to make a bass trap dip that low. Maybe start a gentle 6db per octave filter around 40 hz.?

I agree, unless you have a very large room and the time, money and materials to go after this wavelength it is probably best just to roll it off to begin with

Either roll it off as people have said, or if you need to get down to 20 Hz because you're doing post-production or something like that then I'd use a parametric EQ centered at 22 Hz and with a Q matched to the Q of the resonance.

Which Eq can I consider? Analog, digital? I want to keep my signal as virgin as possible and my room is very well treated. 22hz is the first modal freq.

30hz is a good starting place to roll off bass on an average mix. Even bass heavy music. at 22hz there is so little worth keeping that that its best to roll it off. Don't worry about bass that low, as it will actually be more of a "rumble" that will take headroom and energy away from most productions. Especially if you need to use limiting and get it loud. Plus having bass go that low without rolling off, will risk you burning your amp out or blowing out your subwoofer, both inside and outside of the studio. Trust me, I know from experience! Start rolling off at 30hz if you ask me

I'm suprised you even noticed a problem at 22hz lol

With an EQ you can correct the amplitude of the resonnance but not the long decay.
Have you identified the part of the resonance to deal with?

I don't really need that frequency. In fact I'd be happy to notch it out. I need to find the least obtrusive way in order to preserve my signal chain.

I have + 5db at 25 Hz wtih a decay equal at 1 seconde with a big band width (one octave ). This impacts on the rest of the reproduction. For the moment, the better solution I have found is a low cut at 40 hz / 24 dbo.

Which Eq do you use?

An Equalizer Plug-In : Fab filter pro Q

ARC2 and REW results. Very interesting.

We use a klark teknik dn360. http://bhttp://vintageking.com/klark-teknik-dn360

I have never seen measurements showing the effect on the decay with a modal eq by an equalizer.

Thank you.

It seems that this little box could fit the bill.
Only a downside: there's no wordclock.

If you can find one, a Bag End E-Trap will help with 1 or 2 user-defined specific frequencies down to around 20Hz.

They aren't in production now and were pretty expensive but occasionally come up on the used market for a good price.

Also check this thread:

https://gearspace.com/board/product-...-absorber.html

Lol. U r cool

Thanks Jens, very interesting!!

Do note that I don´t recommend anyone to rely on this technique to work as well as it did in this example. EQ does NOT replace acoustic treatment in general (in fact; I say the total opposite is true: IF you have a well-treated room; you might be able to use EQ to do some corrections). However; if only low order modes are considered, you can sometimes reduce the decay of these by applying filters that matches the resonance gain and Q.

In the above example, we choose to ignore the first axial length mode when designing the treatment (since it was such a low frequency and would require a lot of area to treat effectively) and instead focusing on other, higher order modes that would be more problematic if left untreated (this is a basement with heavy, solid walls: major modal issues when untreated i o w). Since we have access to DSP in the signal chain; two filters where applied (20 & 27 Hz) to the sub (or subs … a total of 8 18” sealed in this case) and the result is quite good.

Jens,

What are the general dimensions of this room?

Just over 28 feet long? If I got that right do I get a cookie?

The room is 7,91 x 3,66 x 2,27 meters. This is how it looked before treatment:

No cookie for you

If you would have thought of the small shift (down) of resonant frequencies in a room full of treatment; you might have got it right.

As you can see; the first axial mode before treatment is around 21,5 Hz, which translates to 7,91 meters (if we choose 340m/s).