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[finetuner]

Dear board,

This is my first post and i would like some advice for my small mastering studio (18'  x 9'  x 8' ).

Currently the speaker-end half of the room is dressed with 7 pillars of tube traps: all 6' 8'' high (composed of 2 half lengths), 18" diameter at the corners and halfway the room, 9" in between.
I also have an undeep panel absorber hanging at the ceiling at both long ends of the room.

At the best compromise listening position (38% from rear wall) i still have some peaks @ 60, 180 Hz and dips @ 70 and 140Hz.

I probed the walls with an SPL meter and found the strongest resonances at 60Hz near the lower part of the front wall (behind the speakers) and some higher octaves beside the speakers.

So i wondered if i should better replace the lower tube traps at the speaker wall by a large bass/panel absorber, covering the entire with.
It might be a good idea to include two slanting parts, pointing to the middle (hope that makes sense).
This would also create more overall depth for the absorber.

Now comes the question;
Would a straight panel absorber, covering the whole lower half of the wall, be just as effective when i put one of the left-over tube traps in front at the middle. It would not create more depth to the existing construction but offers some diffusion and will be a bit easier to build.

For the absorber i can go as deep as 2' behind the speakers and some 2'6" pointing foreward in the middle.

Sorry for the long post.
Any thoughts/advice welcome.
Thanks,
Peter

[finetuner]

OK, a picture tells more than words...

[Steve Hudson]

Are these the only acoustic treatments to your room? What have you done to control first reflections and reverb time of the room?

[finetuner]

First reflections are pretty much tackled by the smaller tube trap pillars along the side walls. As said, they're 6'7'" which easily includes ear / tweeter height.

The entire roof is covered with open woodfibre panels (sorry i don't know the exact word in english, but they're also called Heraklith panels).

The floor has hard / dense carpet tiles.

Finally,  one of the absorber panels that i described earlier (the rear one - not drawn in the images) is actually hanging downwards and thus covering the upper-third of the rear wall approx.

Oh yeah, and some small HF absorbers along the side walls at the rear half (not drawn either since they're not relevant to the subject). 2 at each side.

Delay time (mid and high) and stereo image seem both ok/pleasant.
Maybe the lows are a tad slow, but that's probably related to the resonance i'm trying to adress now.

I should also mention that the room is a 'box in a box' construction. Below 60Hz, there don't seem to be a problem as the energy can escape.

Speakers (PSI 25/3) are 3-way but modest in size with 9" woofers and front port. Roll-off around 38Hz.

Peter

[Ethan Winer]

finetuner wrote on Tue, 25 September 2007 13:33

So i wondered if i should better replace the lower tube traps at the speaker wall by a large bass/panel absorber, covering the entire with.

Peter, generally speaking you cannot have enough bass trapping. Especially in a smallish room with approximately 2:1:1 dimensions. So the short answer is Yes.

--Ethan

[finetuner]

Thanks Ethan,

i thought it would, and adding the slanted / pointed section  will further improve it as the total volume of the trap will be increased right ?

regards,
Peter

[gullfo]

i would take a slightly different tack... instead of simple absorbing everything, i'd add some slat resonators tuned as needed to the front and sides. basically keeping the existing tube traps in place. i'm not sure if you have a cloud overhead or not, but i'd add a small one over the desk

[finetuner]

Hi Glenn,
Thank you for the drawing. I appreciate that !  A different approach, interesting.

I think i was reluctant towards building a tuned trap / resonator so i wouldn't have to worry about calculation errors and construction margins. Not being an expert you know..

The benefit of your idea would be to save construction material since a resonator should be more efficient is that right ? Or are there other issues?
I think those angled slats will look cool (well actually warm, when made of wood) and provide some diffusion.

I actually thought that a freq. like 60Hz would just need plain depth to absorb (deminish).
Or is the triangular space behind the front resonators, meant to be stuffed with rockwool anyway ?

regards,
Peter

[brett]

the experts have chimed in, and I am far from that...but looking at your design it makes me wonder about symetry in bass treatment. Why no rear corner treatments and why so far back and barely off center? 38% from the front wall would be best to avoid rear wall modes from getting into your ears. Seems like you are using mid feilds. Again, why so far back? Can some of you experts comment on listning position, speaker placement and the lack of symetry in treating the bass.

[finetuner]

Here's a real picture to get a better feel of the dimensions:



The monitors are not nearfield but more like larger midfields (fullrange) as described earlier.

So i didn't want to place them too close to the front wall and keep a reasonable distance like 8'. That's what commands my listening position in the rear half of the room.

Fortunately, the room modes/peaks are far more present at the front wall than the rear anyway. The door is in one of the rear corners, so i couldn't even place a trap there. But again, there's no problem in those corners.

Btw, 38% is a rule of thumb that provides a good compromise between peaks and dips of interfering standing waves (room modes), measured from either front or back wall.

Peter

[gullfo]

the resonators are broadband and should be efficient for the frequencies you're targetting. you'd calculate things for a design frequency of 60hz on the long axis (assuming thats where you're having problems) and about 170hz on the side units. since they span a range you have a margin of error in building them... the back doors are acting as traps by letting sound out...

the resonator spacing should fit in your space as-is.

you don't want to be too close so 8' is probably ok but you don't want to be @ 50% in any position if you can help it (obviously side-to-side can't easily be avoided...) as Brett pointed out about 38% from the front and about 42% from the floor-ceiling to avoid putting yourself or speakers in nulls.

[franman]

I'm getting in a little late on this one.. just a few comments..

Glenn, where do you find all the time to do all the sketchup drawings??

Peter, I would guess that some tuned resonators may be called for in your specific situation. If you play a sine wave at the offending frequency(s) out of one speaker, and move around with your ear or SPL meter, find peaks.... This may be what you've already done??

Panel absorbers work fine. They just take a lot of space to get in sufficient sabines... Helmholtz cavity traps might be better for the lower octave stuff. These are easy to build as well...

I would definitely spend some time messing around with the listening position is you are as close as you appear to be to the middle (of the depth) on the rooms... You want to be in the middle side-to-side for symmetry, but avoid being in the middle in height (and this applies to you woofers as well) and the front to rear...

Glenn.. you love the slat absorbers!! As do we!! We use them is almost every control room as a broad band treatment... No problem with that idea, I just think Peter may need some targeting tuned traps with this small room...

Also, please do be sure Peter, that you have sufficiently covered the first reflections!! These will really mess things up!!

[gullfo]

yea, the slats are just one idea that i'm comfortable with, but it may be Peter needs some panel traps to fine tune it or even just a set target frequency for the slats. the tuned cavity is a nice idea since it might be a nice fit in with the tube traps...

as far as drawing, having a newborn around keeps me going all hours    (plus i'm pretty efficient w/ CAD)

[finetuner]

Thanks for your advice guys, i really appreciate it!

Francis, i did probe the room with sinewaves (using files from Ethan Winer's site) and an SPL meter. However, i played both speakers simultaneously. I reckeoned, that would resemble the normal situation. So it's better to do it with one channel at a time?
Learned something again

I might come up with a plan using both panel an slat absorbers. Did some reading in the meantime and lost some fear of the latter haha. Like you said Glenn, with the slanted front and a some mufflin' against the back of the slats, they will have a broader Q and become more 'forgiving'.

The strongest and lowest peak (60Hz) is mainly at the front-floor corner.
So i may not need absorption covering the entire height.

At least at the rightside (it has a few narrow windows), i hope that i can keep some daylight coming in by utilising one of the side absorbers only half height. It seems that the offending resonances are present at lower regions anyway.

I realise that i should not forget first reflections this way. But if i keep those smaller tubes at the side in place, that should be covered. If not, then the side absorbers should have sufficient height and will be dressed with soft material or maybe a diffusor. I assume that you can cover slats with a soft surface as long as the slots remain unblocked.

As Glenn mentiond earlier, it's a good idea to look (measure) right above the listening position. I already know that some peaks exist there as well. Depending on the broadness (or not) of peaks, i'll determine what type of absorber will prove best.
No cloud yet, just a panel absorber above the speakers, almost against the front wall (plus one at the rear end).

As to the top-floor positioning, there's not much i can change about that. There's a comfortable working height, which dictates tweeter height and the ceiling is fixed obviously...

Since this is all very important and interesting stuff, i ordered a book called 'master handbook of acoustics'. I think all studio techs should have a basic understanding of this. At least i want to learn more.
Thanks again for your time.
(And Glenn, congratulations!)

Cheers,
Peter

[franman]

Yes Glenn... most harty congratulations!!! the little ones will keep you busy!!

Master Handbook of Acoustics!! Yes, required reading by everyone who's trying to do 'something right' in this acoustics thing!! Good going!