Dissertation on DIY Control Room Acoustics

[geoffreyvenus]

Hi Audiophiles,

I've just began my journey into the world of acoustics and I'm currently in my final year of an Acoustics degree level course. My reason for this post is to hopefully get some advice on my project from an outside of university perspective, any insight would be hugely appreciated.

So basically my project entails, building my own acoustic treatment from scratch;

1 x Skyline Diffuser (Placed central of the south wall, inline with the back of the listeners head)

2x Absorption Panels (Rockwool RW3, 75mm thick) ( used a mirror to position these panels at First Reflection point, on east and west walls)

2 x Superchunk Bass Traps (each corner where west wall meets front wall, and east wall meets front wall)


Room Dimensions: My room was L- shape so the west wall is broken into three dimensions, this makes more sense in the room dimension image

Front wall was 2.99m
east Wall was 4.56m
south wall was 2.17m
West wall was (2m, 0.82m, 2.56m)
Height was 2.26m

The room consists of a wooden floor, however when treating the room I decided to add rugs to make the room more dead. The listening position was dead central of the room, using a U87 mic, with an equilateral spaced stereo pair of M-Audio AV40 Monitors

The idea is to use Room Eq Wizard to test my bedroom totally empty, and then apply the DIY treatment and do the same test, so as to ascertain what variances these created, and whether building acoustic treatment on a budget has the potential to create a "decent" listening environment.

In terms of positioning of the treatment I went for a L.E.D.E approach, so 2/3's of the room was absorptive, and the back of the room was diffuse. My listening position was also central and 2/3's from the front wall.

The room measurements I gathered are all included, please feel free to dissect this data and offer your opinions, whether that be negative or positive, all feedback is welcome.

Like I said, I'm only beginning my journey into the world of acoustics, thus some of my techniques or decisions may seem crude or uneducated, I guess this is why I'm seeking some guidance from the experts on this forum. Thanks for your time, if any more information is required please feel free to ask.

[Soundman2020]

Hi Geoffrey, and welcome!

1 x Skyline Diffuser (Placed central of the south wall, inline with the back of the listeners head)

The room is way too small to be able to use numeric-based diffusion. Your only real option for a room that size is absorption.

2x Absorption Panels (Rockwool RW3, 75mm thick) ( used a mirror to position these panels at First Reflection point, on east and west walls)

That's a good start, but you forgot the other major first reflection point: on the ceiling above you, between the speakers and you listening position.

2 x Superchunk Bass Traps (each corner where west wall meets front wall, and east wall meets front wall)

That's a good start, but not enough bass trapping for such a small room. You will need more than that.

The room consists of a wooden floor,

What type of "wood floor"? Parquet? Laminate flooring? Wood planks over joists? something else? What us under that? Many types of wood floor are unsuitable for studios. For example, if you have a raised wood floor over an air gap with a concrete slab underneath, then your best bet would be to take out the wood and just use the concrete as your studio floor. Nothing better!

however when treating the room I decided to add rugs to make the room more dead

In general, carpet is a bad idea for small rooms: it does the exact opposite of what you need. Carpet absorbs highs very well, mids vaguely, and lows not at all. What you need for a small room, is lots of low frequency absorption, some mids, and nothing in the highs. I would forget the carpet for now, treat the room properly, then if you still find the highs are giving you troubles afterwards, then you could add a throw rug or two as the final touch. But not as part of the basic treatment.

In terms of positioning of the treatment I went for a L.E.D.E approach,

LEDE isn't used much these days. That's a pretty old method, dating back to the 70's, and was abandoned after it was found to not be a very nice environment to work in: too unnatural. Modern studios are mostly designed using extensions of the original LEDE concept that get rid of the many negative aspects, such as RFZ, NER, CID, and other similar philosophies.

and the back of the room was diffuse.

That's fine if the room is large enough, but yours isn't. Read up on D'Antonio and Cox, and their recommendations for the appropriate use of diffusers.

My listening position was also central and 2/3's from the front wall.

It should be 38% from the front wall, according to Lachot. Placing it so far back makes rear wall diffusion even less appropriate, since your head is then very very close to the diffuser.

The room measurements I gathered are all included,

I'd need the actual MDAT file to be able to make sense of that, so maybe you could post it some place where I can download it to analyze it properly. There are some rather strange things in your graph that don't make a lot of sense, such as the angled (= increasing delay) in the spectrogram, and the extremely high signal level prior to the impulse in the pink IR graph. The fact that you didn't calibrate REW correctly using a sound level meter is also very confusing: if you really did have a 100 Hz signal hitting 130 dB, then your windows would be shattered and you'd be bleeding from the ears!

You also seem to have either the worst sound card on the planet, or something got messed up with the loop-back calibration. The response from a sound card these days should be nearly flat, with maybe some rippled at the extremes. But your graph seems to show a 30 dB drop off in response below 1 khZ...

However, what is clearly visible IN YOUR GRAPHS is that there is a major need for massive bass trapping in that room. Your first priority should be to get those huge modal issues under control, and that is going to require deep, large bass traps. That's where I'd start out. You do show a picture of superchunks under construction, but clearly there's not enough of them, or they are not big enough. Photos of the actual room would be useful.

Also, are you sure you got the mic back to the exact same position between readings? The graphs seem way too different to have been taken in the same room at the precise same location, with just the treatment you mentioned in place. Also, are you sure you didn't touch the calibration controls at all between the "before" and "after" readings?


- Stuart -

[geoffreyvenus]

Hi Stuart,

First off I just wanted to say thank you so much for going into such great detail concerning my project, its so refreshing to see somebody take time out of their busy schedule to reply in such depth. Also all the information you've discussed seems valid and I've taken alot on board. Like you've suggested Ive disregarded the LEDE concept, however for the time being I don't have the funds to purchase as much Bass trapping as I'd wish, however that will be my next objective. I've taken a few more measurements since we last spoke, and if you have the time I would be really grateful if you could take a look.

http://www.gearslutz.com/board/studio-b ... st10016293

Any further advice would be most appreciated, All the best Stuart.

Geoff

[geoffreyvenus]

p.s these new results have been established in a room with no carpet/rugs and the listening position has taken into consideration the Lathot 38% theory.

[Soundman2020]

these new results have been established in a...

The new results are not valid. There is something wrong with the way you are taking the readings, or with your sound card, speakers, or mic.

What mic are you using, and how do you have it set up? A photo would help.

What speakers are you using, and how are they set up? Here too a photo would be good.

What sound card are you using?

There's something major wrong with the setup you are using, so that has to be fixed before you can move forward.


- Stuart -

[geoffreyvenus]

Hi Stuart,

I think I may have made some progress with my room measurements, I tested the room without trying to calibrate the soundcard and got the following results

http://www.gearslutz.com/board/studio-b ... st10039483

As always thanks for your patience

[Soundman2020]

The data looks a little more convincing, but it seems you still did not calibrate REW against a proper sound level meter: the levels are way too low. The data says you tested your room at a level of about 65 dB, and got decay levels down to -10 dB. That would make your room a bit better isolated than the very best anechoic test chamber on the planet, which is pretty hard to believe!

Break out your sound level meter, use the "SPL Meter" button in REW, and do the calibration. Adjust REW so that it matches the reading shown by your meter ("C" weighting, "slow" response). The repeat the tests.

Also, you didn't say which speaker you were using for the tests (left or right)?

Finally, based on that sketch, it seems that you have your room set up backwards, with the listening position at the geometric center of the room! The way you have it set up now, there is no symmetry at all, and symmetry is critical for a control room. The only way to get symmetry in that room, is with the speakers at the other end. I would strongly suggest turning it around so that the speakers are up front where they belong (where you have the diffuser right now), with the desk just in front of that, and the listening position located about 38% of the room length (distance from front wall to back wall). You also show the speakers set up with the acoustic axes intersecting in front of the listening position: that makes no sense. The axes should intersect a foot or two behind the head of the engineer. So you need to fix that too, by moving your speakers further apart, and setting up your triangle better.

There's no need to take tests at that "B" position, by the way: You only need to test at the listening position itself, and perhaps at other critical listening points in the room, if any.

Once again, photos of the room would help to understand it much better.


- Stuart -

[geoffreyvenus]

Hi Stuart,

I've followed your instructions and calibrated the measurements against an SPL meter, I have also rearranged the room to correspond with your recommendations, i.e speakers at the other end. I tested the room untreated and treated using stereo, and untreated with left speaker by itself and right speaker by itself.

http://www.gearslutz.com/board/studio-b ... st10040853

hopefully these results will offer some insight into the behavior of my room. Thanks for you time

Geoff

[Soundman2020]

That's looking better: the results are more believable now.

Please can you update the sketch to show how you have the room set up now, with accurate dimensions and positions. And also post some photos. Photos are very important for checking that you have things set up correctly. Without that, there might be issue with the room that you didn't notice but that we might notice.

Also, are you sure you have your speakers set up exactly symmetrically, accurate to within a quarter inch? There's an unusually large difference between the let and right speaker graphs.

Both speakers must be located the exact same distance from the front wall, and the same distances from the side walls, and must be set up such that the acoustic axis is exactly 1.2 meters above the floor (47 1/4"), and with the exact same toe-in angle, such that the point where the acoustic axes intersect is also on the room center-line, about 18 inches behind the location of the engineer's head.

The speaker controls must also be set identically.

Please mark on your sketch the distances that the speakers are away from the walls right now.

We also need separate readings for the left and right speakers with the treated room, not just for the untreated room...


- Stuart -

[geoffreyvenus]

Hi Stuart,

Ive rearranged the room so that it appears more symmetrical , the picture illustrates how the room looks as we speak. I will try and take some photos to help give a better indication of my set up. I will also carry out some more testing each individual speaker in the treated room.

Thanks

Geoff

http://www.gearslutz.com/board/studio-b ... st10041168

[Soundman2020]

You have the speakers 20 inches from the side walls (which is good), but also 20 inches from the front wall: that's not a good idea, as the SBIR artifacts in both directions will occur at the same frequencies. Also, since the room is too small to be able to have the speakers far away from the front wall, then they should be right up against the front wall, with just a panel of absorption between the speaker and the front wall.

- Stuart -

[geoffreyvenus]

Hi Stuart,

since we last spoke Ive created a CATT acoustics model of my room, I just need to rearrange it so that it corresponds with your suggestion of making the listening position more symmetrical.

http://www.gearslutz.com/board/studio-b ... stics.html

Thanks

Geoff

[Soundman2020]

I don't use CATT so the model isn't much use to me, but the layout looks a lot better.

- Stuart -