Mantis Recording Control Room Tested!!

[abraxxus]

Allright, So the results are in. We went in today with a reference measurement mic, my mackie 824's and a laptop. We setup the monitors where they will go, setup the omni ref mic at mix position and ran some tests, including, pink noise, and full sweeps. The signal was split to the program on the laptop (called smart something??) and to the monitors. Here is what we found.

Everything from 160Hz and up looked pretty good.

85Hz we had about -27db
150Hz we had about +15db.

Now to correct this! we had some items we were stuffing in corners etc.. We took some regular old 4" rigid insulation, cut into 2'x4' chunks and placed them in diffrent locations. First was behind the monitors in the corners. This worked pretty good on the 85Hz range, we gained about 10db with those.. Then we took bags of insulation and stuffed them behind the monitors, that got us another 7db at 85Hz, and pretty much fixed my 15Hz!!

So, behind the corners, we decided that Im going to stuff them with as much insulation as I can get in the space..

We still have a problem with the 85Hz range...... Our thought ( And why Im posting this here today) is to build some tuned Helmholtz resonators at 85Hz. We dont know how big they need to be to up the db to where we want it.. We have read some about this pre drilled pegboard stuff. Its supposed to be tuned to about 150-170Hz as is ( if its sealed, with some rigid behind it) So thats a thought as well..

And WOW! Room sounds great so far, I cant wait to fix these problems

Thoughts??
Thanks in advance!!!

-Abe

[Sword9]

Who did the testing?

Do you have the graphs that smaart outputs? I assume it was perhaps Smaart. I always liked seeing how rooms differed in different places in the room.

[abraxxus]

Here are some pix - Hope these help.

Pix from testing
http://www.mantisrecording.com/gallery/ ... refgraph01
http://www.mantisrecording.com/gallery/ ... r00?full=1

General CR pic.
http://www.mantisrecording.com/gallery/ ... t00?full=1

Im not done uploading all my pix, but here is the root of the albums:
http://www.mantisrecording.com/gallery

[Shaz]

Hello,

I am interested in doing the same thing for my control room. Could you let me know exactly what program you used? or is there a freeware available on-line to do something like this?

Also, Is omni mic absolutely necessary to do this kind of testing or can I use a directional condenser?

Thanks

Shaz

[Ethan Winer]

Shaz,

> is there a freeware available on-line to do something like this? <

You can use the demo version of ETF, available here:

www.acoustisoft.com

Or you can download a series of test tones from my company's site:

www.realtraps.com/test-cd.htm

> Is omni mic absolutely necessary <

I don't know about "absolutely necessary" since you're measuring the relative response at different frequencies. But an omni mike is recommended.

--Ethan

[Shaz]

Thanks for your reply Ethan. I will check out the programs you mentioned tonight.

I was looking at the Behringer Measurement Mic ECM8000, it's reasonably priced. Would it be a good choice for these measurements?

http://www.music123.com/Behringer-Measu ... ic?match=1

Shaz

[Ethan Winer]

Shaz,

> I was looking at the Behringer Measurement Mic ECM8000 <

I don't have one of those, but I've heard only good things.

--Ethan

[AVare]

> Is omni mic absolutely necessary <

I don't know about "absolutely necessary" since you're measuring the relative response at different frequencies. But an omni mike is recommended.

--Ethan

A directional mike has low fequency proximity boost. An omnidirectional microphone IS NECESSARY for testing.

Andre

[Ethan Winer]

Andre,

As I said: "you're measuring the relative response at different frequencies." Emphasis added this time.

--Ethan

[knightfly]

I have to agree with Ethan on this one, with the same reservations he stated - this is a board with a wide range of budget/experience in its membership, from people wanting to "get away with" blankets as a "vocal booth" up to pro studios and name recognition. I've been in both situations, and it's sometimes frustrating when the funds simply aren't there to still try to get the best results you can with what you have; even $50 or so for a Behringer ECM8000 may be stretching the budget for some of us.

Therefore, as long as people remember that they are NOT doing "NIST-quality" work and only want/can afford COMPARISONS, I feel that using what you have available can give some insight. The main thing under those circumstances is that you follow the Scientific Method as far as possible (never change more than ONE variable for a "comparison") and that you fully understand the limitations in the accuracy of your results, IOW all you will be able to claim is that one is "better", period.

Shaz, that being said my own recommendation to you would be this - if you don't already have one of the Radio Shack SLM's, I would buy that BEFORE buying the Behringer mic - reason being, is that the RS meter has an RCA output that can be run directly into your sound card so will work as an OMNI mic -(it is relatively flat up to about 8 kHz IIRC, and ETF ships with a CAL FILE that helps make it flatter responding for all but the last octave or two at the top of the audio range) -

it also can (and should) be used on the console to maintain a constant SPL during mixes, so you're not trying to fight the Equal Loudness contours by allowing the mix to "creep up" from various changes. Your ears can NOT give you an ABSOLUTE level, so it's possible for you to listen to too-loud stuff without even realizing it. Bad for ears, bad for transportability of mixes.

Gotta run, hope this helps... Steve

[abraxxus]

Hey guys - thanks for all your input on this! Here is an update on what I have been doing.

I did my research (mostly reading on this site) and setup my monitors where They should go (I think . I dont really have enough room to soffit mount my 824's Really wish I did, and if anyone can think of a way to do it, I would appreciate the info.
I went out on a mission to find some insulation (OC703 or Rockwool), What I found was that the 703 was an unholy price, It had to be shipped by the truckload - *Truckload!* - to the dealer, who was SPI in this case. They still wanted $1.79 a sqft. WOW! Then I found Roxul AFB that was half the driving distance for $0.40 a sqft. So. I went down and got 5 bags of that stuff.

So now Im loaded with absorbative material, and I spent all weekend placing stuff in diffrent locations, corners, walls, floor, sides etc... I made a 2'x4' resonator with 1/8" preforated pegboard. We did the calculations and it should be tuned somewhere around 135 or so. It actually worked on 40-50hz range.

Placing all the Roxul in the room got my -27db 85Hz problem to about a -14db. Is this "good enough" ? I still see that big dip in my response chart in everything I listen too. Ive come to hate it! =) Anyway, After about 12 hours or working on this Saturday, I started moving the mic around to diffrent areas in the room, I found that If I moved the mic up 2' and forward a foot, The room looked really really good! Played some well mixed music, stuffed my head in there and man it sounds great! but... that kinda blew all the science out the door. Why place my monitors at ear level, and at an equalateral triangle then? I just moved mix position and it sounds better, and the response chart says so too... Whats up with that?

So I went back and looked at modes again, I dident think I could calculate this correctly because of the non-paralell shape of the room. So I did the calculation off the *outside* structure. Check this link:

http://www.mantisrecording.com/crmode.html

Here is my conclusion after the weekend:
I should build out the room with corner and slat absorbers just like John says to do, re-test room.....

OR

Attempt to build some tuned resonators targeting my 85hz problems into the corner traps, or build some small preforated Helmholtz boxes. We may even experiment with tuned tube traps made from the concrete form stuff....

What do you guys think?

Thanks alot guys!!
-Abe