[SML] 125Hz room resonance

[Mike Katz]

Thank you, Stephen, for an informative and interesting reply!
Mike


Michael Katz
narishkup at gmail.com
C: 857.383.0020


On Thu, Mar 26, 2026 at 1:23 AM Stephen Lee via Stagecraft <
stagecraft at theatrical.net> wrote:

> A couple of thoughts:
>
> - I'm not sure how a resonance in your room (especially at such a low
> frequency) would give you Tinnitus at 8kHz. Are you sure the 8k isn't being
> generated by a CRT TV, electronic device, or switch-mode power supply
> (which are in just about everything these days)? You can use your RTA (or
> even a free RTA app on your phone) to listen close to devices and find the
> source of errant noise.
>
> - There are acoustical room mode calculators online that can give you the
> frequency peaks for a room of any size. Just enter the dimensions and it
> will calculate the resonances. Studio designers use these all the time to
> play with different room sizes before the walls go up.
>
> - I'm not surprised that a blanket had little effect on the low-frequency
> issues in the room. Low frequencies have long wavelengths and tend to be
> unaffected by materials that are thin.
>
> A good rule of thumb to use when designing wall treatment and absorber
> panels is the 1/4 wavelength principle. The material will start to lose
> effectiveness at wavelengths which are longer than the thickness of the
> material x 4. As an example, a 1kHz frequency has a wavelength of around a
> foot. If you cover a wall with fiberglass, you'd want it to be at least 3
> inches thick to fully absorb frequencies from 1kHz and above.
>
> A 100Hz frequency has a wavelength of about 10 feet, so things start to
> get challenging. There are a couple of things you can do to cheat the
> system, though. One is that the most effective slice of absorber material
> is the section right at the face, so if you need 2.5 feet of thickness, you
> can get most of the same results by getting a panel that's just a few
> inches thick and spacing it away from the wall by 2.5 feet. Another cheat
> is that small rooms (relative to the size of the wavelength) can often get
> away with far less material if strategically placed. The corners of a room
> are a good way to get distance away from a wall with less sacrifice of the
> room's useable space. Try hanging the same blanket across the corner of
> your room and see if that makes any difference.
>
> Stephen Lee
>
>
>
> On 2026-03-25 1:54 pm, Tim Catlett via Stagecraft wrote:
>
> Hey all,
>
> I've just encountered a problem that I think this group is well equipped
> to assist me with. While not directly stagecraft-related, stagecraft (and
> audio) knowledge is applicable. I deeply appreciate any advice in advance.
>
> My bedroom seems to have developed a 125Hz resonance (along with one more
> significant one at about 33Hz), which seems to have prompted my brain to
> give me "observational(?)" tinnitus, which is consistent tone with a
> perceived value of about 8KHz. It's very annoying.
>
> I tracked the tone around the room with an RTA and was able to identify a
> "hotspot", but it seems that even hanging a heavy soft-surface (woven wool
> blanket) has not dampened the problem. I'll also try putting foam behind
> the television when I get home today.
>
> Any advice?
>
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