small room acoustic

[genelec79]

Hi everybody. I know that this kind a question are repeating always,but i please you to help me with my question.
I have a small room where i make arrangments and i have really big problem of chosing the right sounds in bass region, cause of bad acoustic. The room is 4.40m long,2.30m wide and 2.45m height. I have made some traps (but i think that it was wrong building)! I made also some rockwol apsorbers 10cm deep and put them in the corners of celing. So yesterday i have found calculator for room modes (axial,tangential and oblique) and i get the results. My question is,how can i locate where to put some apsorbers for example for a axial,tangential and oblique mode of the room? i know that they are different in the movement,but still dont get it how to find proper place for treatment. Thanks for advice!

[jwl]

Understanding which modes are at work in your room can be useful for an engineer.... for instance, if you know you have a 10dB peak at, say, 65Hz, you'll know to be very careful with that frequency.

However, at the end of the day the answer is always the same for small rooms: you need to add more broadband bass traps, which will flatten your frequency response across all frequencies. It's all about coverage area, the more traps you add to the more room corners (as a starting point), the flatter your room will get.

If you want to run a test to see which parts of your room should get bass traps first, then this simple test is very useful: RealTraps - Filtered Noise

[genelec79]

Thanks jwl for the answer. I decide to made a superchunk bass traps(to remove old ones and build a new ones-sorry for my bad English ). The Rockwoll Sonorock panels are 100cm x 62,5 cm. What will be the best option for cutting them-(is it deeper traps equal lower freq and more apsorbtion)?? Thanks again!!

[ciro]

In a room that size, you should covered the biggest possible region "around" the monitors - behind,above, beside, below,corners,etc- (SBIR) with 4" (at least + gap) mineral wool traps.
It should includes a thick (maybe thicker than 4") on ceiling (IME).
Plus, obviously, all the corners you can treat (chunks are a great way,like you said) and thick traps at rear wall.

For the room modes (axial) analysis and the two similar dimensions, seems you have high energy (issues) in the 70/80 hz and upper harmonics.

Ciro

[Weasel9992]

Originally Posted by genelec79

Thanks jwl for the answer. I decide to made a superchunk bass traps(to remove old ones and build a new ones-sorry for my bad English ). The Rockwoll Sonorock panels are 100cm x 62,5 cm. What will be the best option for cutting them-(is it deeper traps equal lower freq and more apsorbtion)?? Thanks again!!

If you're doing superchunks, just make sure the triangles are 17" per angled side by 24" at the base...I'd give it to you in metric, but I'm an ignorant American. Sorry. You can make them larger of course, but this is a very typical size.

Frank

[genelec79]

Guys,thanks for the answers. Cause the rockwool plates are 39,37" (100cm) and 24,2" (62,5 cm) (i`m not an ignorant American ee),the easiest way to cut them is to make 4 of 1 and it will be (31,1 " at the base and at the sides 24,6"). I hope that will work! Thanks one more time.

[Weasel9992]

Originally Posted by genelec79

Guys,thanks for the answers. Cause the rockwool plates are 39,37" (100cm) and 24,2" (62,5 cm) (i`m not an ignorant American ee),the easiest way to cut them is to make 4 of 1 and it will be (31,1 " at the base and at the sides 24,6"). I hope that will work! Thanks one more time.

That'll work just fine.

Frank

[foxfyr]

Originally Posted by jwl

However, at the end of the day the answer is always the same for small rooms: you need to add more broadband bass traps, which will flatten your frequency response across all frequencies. It's all about coverage area, the more traps you add to the more room corners (as a starting point), the flatter your room will get.

Yes and no!

Sure, you will potentially address the modal peaks below 300Hz, but you will also over damp the response of the room above 300Hz, where the soundfield is dominated by specular reflections - resulting in a grossly overdamped room!

The judicious application of bass traps an certainly help. But as far as simply using them indiscriminately and simply covering maximum surface area, one would be better off using a more selective bass trap - albeit more complex- such as a skinned bass trap that will reflect the higher frequencies (shorter wavelengths) in order to preserve the semi-diffuse soundfield necessary for the sense of space in the room - unless you simply like anechoic chambers!

There are quite a few variants of these traps, ranging from high Q Helmholtz resonators tuned to the offending frequencies, to bass traps using perforated or resonant face panels to more advanced designs such as embodied in the RPG BAD product line (Take a look and read up on their design goal and the method to the madness behind them)

Unfortunately, room modes do need to be addressed - but NOT at the expense of the preponderance of the room response where imaging and the sense of space predominates!

And at that point you will want to be looking at time domain response measurements such as the envelop time curve - ETC. ...Not the frequency response curve.

[jwl]

Well said, Foxfyr.

I should have clarified that when I say to put as many bass traps into the room as you can, I mean a)for small rooms, and b)using bass traps that don't absorb flat into the highs.

For corner bass trapping, you are better off using limp mass reflective membrane bass traps, which give increase low frequency absorption (where most small rooms need the most help), and are semi-reflective at higher frequencies to avoid overdamping the room.

There are commercial traps like this (all of our bass traps, for instance), and you can DIY them using something like rigid fiberglass with FRK.

I generally only recommend full-bandwidth absorption at reflection points to start off with, use the above bass traps judiciously, and then spot-treat any remaining areas. Of course diffusion can also be used at various places if there is budget for it.