John Sayers' Recording Studio Design Forum Archive

Gregwor wrote:If you run another test today, is that 30 Hz issue still showing up? What I'm getting at is maybe a truck drove by or something that caused it during this measurement.

Greg

Thanks Greg, a very sensible suggestion!

I've run multiple REW seeps and on average, the more recent measurements (with extra fluffy fibre traps in place) show slightly longer decay at 30Hz than measurements taken without the extra fibre traps. I ran some further tests late last night - to avoid any traffic noise - and the patterns seems similar. Curious

As an aside, I'm now almost certain that the 50Hz ringing is partly caused by mains hum. There are similar peaks at 100Hz and 200Hz that support this theory. At least that's something I can fix.

That 30 Hz "hump" is probably not modal, and unlikely to be traffic either. It's below the lowest possible mode for your room, so it's more likely to be the volumetric pressure issue for the room. Sometimes called "breathing" or "pumping". It is related to the acoustic compliance of the room, which involves many factors, not just the air: the way the walls are built, for example. Not easy to calculate, and not easy to fix, either... The best you can do is to roll off a little of the very low end in your final tuning. Fortunately, there's not too many instruments that get down to 30 Hz, so it's unlikely to be a big issue anyway! Unless you are planning to mix a lot of cathedral pipe organ music, in the very lowest notes of the lowest registers...


- Stuart -

^ Dammit, so there goes my "Cathedral Pipe Organ Dubstep" project! And probably my "Sousaphone Soloist" ambitions too. Acoustics is truly a cruel mistress.

In all seriousness, thanks again Stuart. You're a mine of useful information

I'm planning on doing as you suggest: roll off the low end a little to reduce the hump.

so there goes my "Cathedral Pipe Organ Dubstep" project!

Darn! I'm sure you had a winner with that new genre! I can see the hoards of fans beating a path to your door, with fists full of cash, begging you to take it, so they can ecstatically experience your latest album!

Oh well... it would have been interesting...

More seriously, that's quite common in small rooms, and there's just not any simple solution that I'm aware of.

Did you try adding some reflective/diffusive surfaces to recover a bit of the decay time, and maybe smooth it out a bit too? That's about the only remaining issue in your room.

- Stuart -

Soundman2020 wrote:Did you try adding some reflective/diffusive surfaces to recover a bit of the decay time, and maybe smooth it out a bit too? That's about the only remaining issue in your room.

No no yet, but that's a good call... and on my "to do" list