Quick Slot Absorber Questions?

[seamus]

Thanks for the reply.
Yeah, I don't think that the 62Hz issue is due to room modes, actually.
If I take a measurement from a foot or so closer to the back wall, it moves up to around 70Hz.
To me, that would suggest that it's a reflection from the back wall, I guess.

Sorry for the confusion.
I meant that once I took out those front corner soffits, the RT60 increased noticeably.

It occurs to me that it might be proper to include a link to another forum that I have been getting help from, as well.
http://www.gearslutz.com/board/studio-b ... ion-3.html

Seamus

[Soundman2020]

Seamus, I noticed from the other thread that you have not yet sealed your walls, that the have gaps around the edges and holes in them. It occurs to me that this might well have something to to do with your problems. Not quite sure what it might be doing, but it wouldn't surprise me at all that it is doing something to mess up your room acoustics. Maybe it would be a good idea to finish that first, before continuing with your testing?

- Stuart -

[seamus]

Thanks, Stuart.
I'm going to go and seal it up tonight.

I think that you are right.
I wonder if it would act as a Helmoltz to some extent.

Thanks, again.
Seamus

[seamus]

You know, maybe that 62Hz null is modal in nature.

I do have that 1,0,1 at 59.4Hz that you mentioned, Stuart.

When I moved the mic back, maybe the null wasn't moving in the frequency range, but it was moving in amplitude. In other words, maybe I just moved out of it, and there was a different problem rearing it's head in the new spot that is unrelated.

What's the margin of error on this when taking into account things like structure and/or materials?

Could it be +/- 2.5Hz?
It seems like it could very well be.

[Soundman2020]

When I moved the mic back, maybe the null wasn't moving in the frequency range, but it was moving in amplitude. In other words, maybe I just moved out of it, and there was a different problem rearing it's head in the new spot that is unrelated.

That would actually make sense, since room modes / standing waves are, by nature, "fixed" in the room. As you move about the room, you'll go from peak to null of the same mode. So you might well be right: as you moved the mic to a different spot, you were looking at a different mode, or indeed an entirely different problem.

I think I'd be more concerned about what is happening at your mix position, than what is happening elsewhere in the room. If you have a major null at peak at the rear wall or side window or anywhere else isn't an issue: for example, you will ALWAYS have major problems in the exact middle of the room anyway, no matter what, which is why it's a really bad idea to put your mix position there. So I reckon I'd concentrate on what is happening at the mix position.

It's hard to say what the margin of error might be: that depends on may things, not least of which is the accuracy of your physical measurements (room dimensions) and the accuracy of your test measurements (mic, pre-amp, meter, test tones, etc.). Also, there is the issue of the logarithmic nature of the musical scale: a difference of 2.5 Hz at the bottom end of the scale is nearly two entire notes, but at the top end it isn't even a tiny fraction of one note: It is totally irrelevant. At the frequency of your problem, the difference between 59.4 and 62 Hz is nearly an entire note: it's the difference between an A# and a B, so it IS a big issue in that octave. If it were the a couple of octaves higher, the difference between 259.4 and 262, it would be irrelevant, but that low in the scale, I'd say it matters, and precision is important. So if you think it might be a "margin of error" thing, then perhaps you should re-measure your room with great accuracy, and also use very accurate single-frequency tones (1 Hz. accuracy), rather than sweeps or pink noise, to scope it out in better detail.

But either way, it seems like you might need to be thinking about a tuned trap to deal with that issue.

IMHO!


- Stuart -

[seamus]

Yeah, it occurs to me that the room may be shorter than I think it is.
You can't hire good help these days.

After repositioning the speakers, I got that 62Hz up to -12dB.
I also have a 115Hz and a 155Hz (approximations) null at -12dB.
Good extension down to 30Hz, though.

Here is a copy/paste from that (ahem) other forum that I posted:

"I spent a few hours moving speakers around last night.
I got the response to +/- 12dB from 30Hz to 300Hz.

-10dB at 30Hz
-12dB at 60Hz ish
-12dB at 115Hz ish
-12dB at 150Hz ish

An interesting position was that at the farthest possible place from the front wall and the side walls (while still having them a couple of feet apart) yielded a FLAT response down to 80Hz... and then it dropped like a rock. So much so that at 60Hz it was already -30dB.. and it kept on falling.

The 1/4 wavelength of 60Hz is about 4'8", which is about how far they were from the side walls during that particular test."

Well, I am intending to build superchunks in all the corners that I can.
If that doesn't touch the 60Hz thing, I will build a tuned trap of some sort.
I assume that the superchunks will help the 100Hz-200Hz area pretty well.
I would actually rather build a slot type, but if a panel trap would work better for the 62Hz, that's what I'll do.

You totally right about the 2.5Hz on the musical scale.
My brain doesn't link acoustics with music as much as it should.

Thanks a lot, Stuart.
Seamus