Budget project studio acoustic analysis with REW measurement

[Hashberry]

Equipment used for REW analysis


Krk rokit 6 monitors
Behritone cube mono speaker
Behringer ECM 8000 omni directional microphone

Room dimensions

26 ft length
12 ft width
8 ft ceilings

Construction details


Two walls are concrete. The 24 ft section and the 5 ft section.

The flooring used is tiles. (Should I cover the tile floor eventually ?)

There are four doors in this space which makes things more difficult. Also due to the odd shape there are really seven floor wall corners. In the photos provided, I have constructed two superchunk traps, with mineral wool packed floor to ceiling. The attached REW files and graph image measurements were taken with the three traps in the room. I do not have any REW measurements of the toom without treatment. Perhaps that is a mistake ?



The Krk monitors are two feet away from the wall.

The desk is 2ft off the ground.

The monitors are spaced four feet apart.

The front superchunk trap was packed with owens corning thermafiber and ultratouch denim insulation. The thought here is that a variation in density of absorption material would theoretically absorb more of the overall frequency response, particularly the mids and highs.

Within the master handbook of acoustics chapter on absorption the text states , “materials that have a porous composition with interstices between there matters can operate as porous absorbers” p 191

“If a sound wave strikes a wad of cotton batting, the sound energy causes the cotton fibers to vibrate”

So in essence this is simply energy transference. In this case sound energy is transferred via friction into heat energy.

“Cotton and many open cell foams are excellent sound absorbers because of their open-cell porosity” p 191

“The better the airflow through a porous material, the better its ability to absorb sound” p 191 of master handbook of acoustics

So if all this is true, why is it that the majority of projects use dense less porous material if airflow is such a critical factor to absorption? Is it simply that the denser glass fiber is easier to work with than more porous alternatives ? Or is the issue money ? The denim insulation is 60 $ per bag which does add up fast.


In the construction of these absorbers, is it worth the individuals time, and effort to construct panels that contain a density variation in order to obtain superior absorption ?


I am very new to acoustic, and have gained a lot of knowledge through the comprehensive collection of acoustics study material available here. I truly wish to express my gratitude to the effort people made to make this material so readily available.

This “little” project has quickly turned into an obsession as I become more aware of just how important the acoustics of a room is. Sound is fascinationg. Ifd only we could dye soundwaves with different colors and see it traveling in real time.


As far as construction changes is there anything about this room construction that if changed would make a drastic difference. By construction I mean walls, doors, flooring, and ceiling alterations.

As far as the acoustics goes goes, based on my Rew measurements what is the best direction to go in ? MY thought was to post what I am working with now then based on feedback I can add treatment in increments with the REW file. Because I do not know what I'm doing I'm afraid of putting a lot of work into this, then find out after the fact I did something wrong.


Does placing diffusion in a room this size make sense ?


With the vast amount of different types of treatment; from simple absorption panels, to helmholtz resonators, to slat absorbers, to cylindrical absorbers it is hard to know what direction is best suited with this room. Also as I read more different people have conflicting opinions. My goal is to get the room as acoustically accurate as I can on a budget using DIY methods, while at the same time gaining a basic knowledge and understanding of sound.


Are there any books that are a must read ?

Thanks for checking out my thread !

[Hashberry]

Did I make a mistake in the frequency range ? Should I have gone to 20,000 hz ?

[Soundman2020]

Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things!

Here's the instructions for calibrating and using REW: http://www.johnlsayers.com/phpBB2/viewt ... =3&t=21122

Did I make a mistake in the frequency range ? Should I have gone to 20,000 hz ?

Yep! 22,000, actually...

The flooring used is tiles. (Should I cover the tile floor eventually ?)

Nope! Tile es excellent. You could use a couple of small throw rugs as final "tweaking" for your room, perhaps, but apart from that, leave the tile as-is.

The Krk monitors are two feet away from the wall.
The monitors are spaced four feet apart.

Not correct for that room. There's going to be a big SBIR dip in your frequency response. Unfortunately I don't have time right now to do the math and figure out the optimal geometry. Perhaps next week.

The desk is 2ft off the ground.

How do you manage to get your legs under that? You must be sitting practically on the floor! Normal desk height is typically 28" or so, give or take an inch or two... but 24" is REALLY low. Must be uncomfortable.

The front superchunk trap was packed with owens corning thermafiber and ultratouch denim insulation. The thought here is that a variation in density of absorption material would theoretically absorb more of the overall frequency response, particularly the mids and highs.

There's some truth to that: varying density can affect absorption ranges. But the purpose of a Superchunk is NOT to absorb "the mids and highs"! On the exact contrary, most bass traps are treated such that they do NOT absorb the mids and highs. If they did, then the roam would be way to dull, dark, and lifeless.

This thread might interest you: http://www.johnlsayers.com/phpBB2/viewt ... =2&t=21368

And maybe this one too:

http://www.johnlsayers.com/phpBB2/viewt ... =2&t=20471

So if all this is true, why is it that the majority of projects use dense less porous material if airflow is such a critical factor to absorption? Is it simply that the denser glass fiber is easier to work with than more porous alternatives ?

There's an optimum density for each application, and each type of porous absorber. If the density is too high, then it won't absorb low frequencies very well. If the density is too low, then it wont absorb anything very well. It's all about impedance, and impedance varies with frequency.

In the construction of these absorbers, is it worth the individuals time, and effort to construct panels that contain a density variation in order to obtain superior absorption ?

For a typical home studio: probably not. For a high-precision professional mastering studio, tuned to perfection: yes, it probably is worthwhile. But even for Studio Three (see link above) I did not vary the densities inside the bass traps: I simple chose the best density for each device, based on what I wanted it to do.

I am very new to acoustic, and have gained a lot of knowledge through the comprehensive collection of acoustics study material available here. I truly wish to express my gratitude to the effort people made to make this material so readily available.

That's what the forum is here for!

Ifd only we could dye soundwaves with different colors and see it traveling in real time.

Now THERE'S an idea I'd really love to see implemented! You can figure out a lot from REW graphs, but it would be a hell of a lot easier if you could just walk around the room and look at the waves directly, in vibrant shiny colors! I love it! Maybe some smart guy can figure out how to do that with virtual reality goggles....

Does placing diffusion in a room this size make sense ?

For a room 26' long, yes, it's a real option, and probably worthwhile. But it should still be done carefully, choosing the right device for the job, and tuning it suitably.

With the vast amount of different types of treatment; from simple absorption panels, to helmholtz resonators, to slat absorbers, to cylindrical absorbers it is hard to know what direction is best suited with this room. Also as I read more different people have conflicting opinions.

As they saying goes: "There's more than one way to skin a cat"! (I'm not sure why anybody would want to skin a cat anyway, but that's the saying...)

Often the reason for apparently conflicting opinions simply because there are several different ways to design a room, based on several different design "philosophies", or concepts. Most of them work, and they all have basically the same goal, but use different ways of getting there.

My goal is to get the room as acoustically accurate as I can on a budget using DIY methods, while at the same time gaining a basic knowledge and understanding of sound.

Cool! With a room like that, you should be able to get reasonably good results... although you might have to relax the "on a budget" part... The biggest challenge will be in dealing with the strange shape, and the nooks and crannies.

- Stuart -

[Hashberry]

Stuart,

I am very grateful for your in depth response ! I have recently done work on the space. When able I will reply in detail to your response. To figure out the optimal geometry for speaker placement is there a forumula I can follow ?

[Soundman2020]

To figure out the optimal geometry for speaker placement is there a forumula I can follow ?

Not really, unfortunately. There are a couple of general guidelines, but many other factors come into play when refining speaker placement.

I wrote the following for another forum member a few years ago: You might find it useful...

--------------------

The basic layout for a control room is fairly simple. First key is symmetry. Total symmetry. If you don't have that, you cannot get a good stereo image, your sound stage will be distorted, and your mixes won't translate. So position your desk on the center line of your room, facing in whichever direction gives you the best symmetry. Symmetry means that the left side of the room is a mirror image of the right side, so if you have a closet on the left side, then you also want one on the right side, or you close up the closet and/or put something in front of it, to present the same type of surface as the other side of the room. symmetry means that the walls are at the distance and same angles. If the left wall is angled at 15°, then the right wall must also be angled at 15°. Symmetry means that if there is a fireplace on the right wall, then you need an identical one on the left wall, or you need to close up the fireplace / put something in front of it. If you have a window on the left with curtains, but only blank wall on the right, then either take down the curtains on the left, or put up identical curtains over your blank wall on the right

If you cannot find a place where the entire room is symmetrical, then at least the front half must be symmetrical. The rear half isn't so critical, but the front half is.

Don't forget to look up: the ceiling has to be symmetrical too. It's no use at all if the ceiling slopes upwards across the room, but great if it slopes upwards from front to rear. You should also aim to have your speakers firing down the longest dimension of the room, not across the shortest dimension.

So you found you symmetry. Now measure the distance from the front wall to the back wall, and place your chair on the room center line at a point of 38% of the room depth. So if your room is 4.5 m long, your chair would be 1.7 m from the front wall. The idea is that your EARS end up at this 38% location, not your nose, or eyes, or any other part of your anatomy. Now set up the desk on front of you, in a comfortable position. Now set up your speakers on very heave, massive, decouple stands so that they are at a height of 1.2 m above the floor. That height refers to the acoustic axis of the speaker, no the top or bottom. of the speaker cabinet. Check your speaker manual to find out where that axis is. If the manual doesn't say, then you can use a point between the woofer and tweeter, but much closer to the tweeter than the woofer.

Important note!!! The 38% and 1.2m measurements are not carved in stone! They are just starting points. You might change them later, but this is the point you start from. The reason for 1.2m is because that's roughly the height of your ears when seated for most people. Measure yours, because if you are very tall or very short, or like a very high or very low chair, it might be different. Use your own ear height for that measurement.

So now you have your chair and console in the correct location, and your speakers on stands at the right height. Now move the stands so that they are symmetrically set up on each side of the room center-line, and the speakers are about 1.5 to 2.5 m apart, and the same distance from your ears. So if you have them 1.8 m apart, then they should both be 1.8 m from your ears. If they are 2m apart, they need to be 2m from your ears. Etc.

Depending on the size of your room, you either want the speakers at least 1.5m away from all the walls, or if that isn't possible then you want them set up very close to the front wall. The reason for this is comb filtering and other phasing problems on first reflections. If your speakers are between about 20cm and 1.5 m from the front wall, then sound coming from the speaker and bouncing off the front wall back into the room will interfere with itself differently at different frequencies, causing comb filtering and phasing troubles: you won't ever be able to get flat response and a clear image. When the speakers are very close to the wall, those problems are all in the very high end of the spectrum, or beyond, where there isn't much musical energy anyway. Beyond 1.5m the problems move to the low end of the spectrum, where the human ear isn't so sensitive, sound isn't so directional, and the room modes are probably giving more trouble than the phasing.

However: if your speakers are close to the front wall, they will also be getting a free bass boost form the walls, so you will have to roll of the bass response accordingly. Most studio monitors have controls on the rear for exactly this purpose.

The speakers should be spread apart so they are roughly half the distance between the room center line and the side walls. NEVER put them in the corners!

OK, so your speakers are now set up on stands at the right place in the room, equidistant from each other and from your head. Now angle the speakers inwards so they are aiming at YOUR EARS (get someone else to sit in the chair while you do this so you know where to aim, or set up some kind of simulation of your head: Maybe a wig stand, or even just a ball).

Since the speakers are aimed at your EARS, not your nose, this means that the acoustic axes of your speakers will NOT meet over the chair: they will meet at a point many cm behind your head, and an angle of 60°. That point depends on things such as the dimensions of the room, the place where you set up the speakers, the size of your head, etc. and isn't important. You often find incorrect instructions for setting up speakers, saying "The speakers and your head should be at the vertices of a triangle". Wrong. That would only work for people who hear with their nose or their eyes, but for those of us who hear with our ears, the vertex will be BEHIND the head, not AT the head. What is important is that the distances to the speakers are correct, and the angle is correct.

This takes a bit of fiddling around with a tape measure, but it's very important to get it right. The distances are critical. Even a few cm difference between the "left-ear-to-left-speaker" and the "right-ear-to-right-speaker" distance will totally blow your stereo image. Accuracy is important.

So what happens if you can't make that geometry work out, due the size/shape of your room? You cannot find a location where you get the speakers far enough apart, at a good distance from the front and side walls, out of the corners, equidistant from each other and from your ears (which are at 38% of the room depth), and also angled so their axes meet at 60°? That's a lot of conditions to be met, all at once! That's a common problem: just put them in the best compromise location, and change the angle. You can angle them inwards more, so that the axis intersect is as much as 90°, if you have to. That just means that your sweet spot will be squashed up sideways and elongated lengthways, but that's the price you have to pay.

OK, so now you have your speakers set up correctly. To test if they really are in the correct location, turn them on, play music excelelntely recorded commercial music, and close your eyes. You should clearly hear a third "phantom" speaker directly in front of you. Things that are centered in the mix will seem to come straight out of that non-existent center speaker, and things that are not centered in the mix will seem to be clearly spread out on the sound stage, between the left and right speaker. Where effects have been used to give greater than 90° phase angles to some sounds, they can even appear to come from points outside the sound stage: further left than the left speaker, and further right than the right speaker.

If you don't hear that, then you did something wrong: go back and start again.


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- Stuart -

[Hashberry]

Is this product okay to use for super chunk bass traps ?

Owens Corning Ultrabatt

https://www.thermafiber.com/wp-content/ ... -Sheet.pdf


https://www.thermafiber.com/products/co ... nsulation/

[Gregwor]

Is this product okay to use for super chunk bass traps ?

Owens Corning Ultrabatt

I was looking for the cheapest insulation to use for bass traps, so I called Owens Corning. They told me the heaviest fluffy pink insulation was their EcoTouch R24 and was between 20 and 23 kg per cubic meter. That tells me that you can only use pink fluffy for low frequencies, and the only stuff is the EcoTouch R24. I've since used it with great success.

Greg