Diagnosis, treatment & prognosis please.

[rayc]

I record in a downstairs room. It's 3.6m x 3.4m & 2.45m high.

Two sides are external walls (gyprock then 1 thickness brick) the other two are internal gyprock walls - one against a small corridor and the other has a sitting room on the other side. Directly upstairs is a bedroom.

Along one of the external walls is a window almost the entire horizantal length and about 1/2 the vertical height.

Apart from a wall length book case full of a wide variety of sizes of books on the wall opposite the window, very heavy drapes at the windows and almost all surfaces covered/cluttered with "stuff" there's no treatment in the room.

When I play/playback loudly I note that after a couple of minutes a slowly thrumming bass sound develops. When all music is stopped the thrumming continues for several minutes and sometimes even longer.

I did a freq test (downloaded from real traps) that gives some interesting info about the room's problems but doesn't indicate the thrumming (the test doesn't present longish periods of a wide range of freqs all at once).

I know I need bass traps & I a cloud for standing waves to assist in the monitoring position. However, I'm perplexed by the bass hanging around. I can sometimes come downstairs 5 minutes laters & it's still there albeit somewhat reduced and fading.

Any ideas?

 

[RAMI]

Not being an expert myself, but that doesn't sound like a "room" problem. That sounds to me like a piece of metal (from a heater, appliance, etc...) that vibrates with sound. II'd walk around the room and try to locate it. Put your ears up against the walls, eliminate one thing at a time. Sounds like one of those mysteries that, once solved, will have you saying "Of course, how did I miss that"?

 

[Supercreep]

Sounds like a structural transmission problem.

Bass traps won't help with that, really. You have to find the structure that is vibrating sympathetically with the bass (or drums or whatever) and decouple it. My first guess would be HVAC and then plumbing. The fix could be as simple as a rubber standoff, but could require something more drastic.

Good luck and happy hunting.

 

[chronicle]

after a couple of minutes a slowly thrumming bass sound develops. When all music is stopped the thrumming continues for several minutes and sometimes even longer.

I can sometimes come downstairs 5 minutes laters & it's still there albeit somewhat reduced and fading.

Any ideas?

Really? Several to 5 minutes? Are there any HVAC ducts common to the studio/other rooms. Can you hear it upstairs or in other rooms? How bout outside? I can't imagine a resonance of any kind lasting that long..by ANYTHING. The only thing that I can think of is perhaps a heater fan is running, and maybe when a certain frequency "couples" with the inherent fan resonance within a plenum or duct, it might continue to resonate louder for a while due to a duct length/resonance or something to that effect. But 5 minutes???

Are there any external noise rumbles, like passing trucks/buss's etc. Maybe it's only coincidence. Does this happen EVERY time you playback a certain frequency range? or Song? Are your speakers sitting on anything that can structurally transmit to the walls? Like a large box, or is there a large empty adjacent room? How bout ghosts? Heard any voices too? Seriously though..that's a weird one. Other than what I mentioned..I don't have a clue. But it does suggest an external noise producing element..that coincidentally happens. LF rumble is inherent in homes when in close proximity to freeways or heavily traveled roads close to a building. I used to live 3 miles from the closest freeway, but the rumble was so loud at night, I had a hard time going to sleep sometimes. Of course, this was the main Intercontinental freeway on the Pacific side of the US...Hiway 5, with EIGHT lanes...each way..incredible amount of truck traffic. I could feel it on the concrete driveway too. Can you feel it on your floor, or walls? If you do indeed discover it is freeway rumble or something like that, there isn't much you can do about it other than build a massive/decoupled room within a room to stop it.

The one thing I'm curious about though, is when you monitor during recording. Do you hear it then? Or during mix down? Even if you can't distinguish it DURING such activities, it may be occurring while you engineer,which will affect your engineering judgements as it may mask other anomaly's inherent in the CR/live room acoustics, which may cause bad translation to other systems/rooms. That's why it's important to find the source, and if possible, cure it.

Well, enough of my blabla. Good luck discovering the source.
fitZ

 

[Supercreep]

Yay fitZ!!!!!!

 

[rayc]

No ducting of any kind. Few homes in australia have ducting. No central heating - it's a very uncommon feature, ducted AC is rare but becoming more common, vacuum ducting is very rare indeed.
I did have an old piano in the room & removed that is case it was sympathetic undamped strings - no change unfortunately.
I'm near a road but not a busy one and am 20+m up a hill from it so the transmission of those vibes would be altered. I'm near a railway but not close enough to rattle the glasses. Noticeble traffic on either conduit doesn't often coincide with the sound.
I thought, for a short while, that it might be the new rainwater tanks installed just outside the room BUT they're completely full now & the sound hasn't altered in freq. as I'd have expected as they filled.
Could be water pipes.
The sound isn't a real interference when I'm in the mixing position and seems louder in the part of the room furthest from the mixing position.
I'm going to the visiting Picasso exhibition in Sydney on Saturday so I stick my ear to the wall on Sunday.
I laughed at the Fitz reference super. It's been a while since I had to endure reading a Fitzism.

 

[chuckduffy]

Several minutes? The mind boggles. Know someone who had a problem with an oil drum for the heating system, but never heard of anything on the order of minutes, and I've faced some downright bizzare environmental problems home recording over the past couple decades. Wow..

So enough of my mumbling - here's what I would do. Set up a track of impulses, spaced about 30 seconds apart. Gunshots, bomb going off, whatever. Loop the playback at high volume. Walk around and see what you find. If the police show up with tactical weapons, and you survive it's easily explained.

 

[aaronaycox]

I am with everyone else here; a sustained hum or rumble has to be driven by something. There is nothing I can think of that would have enough sustain to make noise for five minutes. Nothing within the hearing range of humans anyway.

You have a structural issue somewhere that is resonating. Once a particular frequency is hit it puts something else into motion and causes a chain reaction. The best example I can think of is the feedback of an acoustic guitar on a loud stage. I have set my bass down before while leaving everything on. All it takes is a single frequency to make a string vibrate. Once that happens you have an ongoing note that gets louder, and louder, and louder, and............. You get the point.

 

[chronicle]

It's been a while since I had to endure reading a Fitzism.

Ok, I'll start adding my signature at the BEGINNING...that should prevent any further discomfort on your part.

Although I should add..sometimes a cure can be short term pain vs long term death.