[SML] 125Hz room resonance

Fri Mar 27 19:21:41 UTC 2026

I'm finding this thread interesting as well.  There is a low frequency in
my bedroom as well some mornings - I only hear it when my head is on the
pillow, or slightly above it. I can't hear it if I sit up, or leave the
room. I think it's maybe a neighbor's heat pump. It's not my heat pump, or
fridge, and I don't have a furnace.... I've stepped outside when I've been
hearing/feeling it, and I can hear the soft whoosh of the neighbor's heat
pump, but no low frequencies.  I've made sure the bed frame doesn't touch
the wall, but I still hear it.  A mystery.

 - Jon

On Fri, Mar 27, 2026 at 12:07 PM Don Taco via Stagecraft <
stagecraft at theatrical.net> wrote:

>
>   This got me intrigued, and I quickly found out that there are all sorts
> of youtubes of generated tones. I couldn't hear the 8 kHz tone at all at
> first, but after trying a few lower and higher tones, I found I could hear
> it if I cranked the speakers up high enough. And I can certainly see that
> it would be annoying and how motivated you'd be to discover the source.
> Happy hunting!
>
> ------------------------------
> *From: *"Tim Catlett via Stagecraft" <stagecraft at theatrical.net>
> *To: *"Stagecraft Mailing List" <stagecraft at theatrical.net>
> *Cc: *"Tim Catlett" <tmcatlett at gmail.com>
> *Sent: *Friday, March 27, 2026 11:40:37 AM
> *Subject: *Re: [SML] 125Hz room resonance
>
> Thank you Steven.
>
> I really appreciate the information and the ideas.
>
> Regarding the 8KHz sound, that is only the "perceived" tone, measured
> against a tone generator and subjectively identifying the correct, or close
> enough, tone that is being "heard."
> The tinnitus, and many other physiological effects, can indeed be caused
> by low frequency tones, which is what we experienced multiple times at
> protests in Minneapolis.
> This is the first time something like that has ever happened in my bedroom.
> I know that was the cause because the tinnitus would reduce when I walked
> away from the room and went outside. It would also disappear after a full
> day at work, only to reappear shortly after I returned home.
>
> I'm going to try some different strategies and see what happens.
> Again, thank you for the info and I'll try to report back with any further
> details.
>
> *Tim Catlett*
> *(414) 975-4424*
> tmcatlett at gmail.com
>
>
> On Thu, Mar 26, 2026 at 12:23 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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>
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