Bass Traps - but first room analysis

[Bluzzi]

I am having a friend come over tonight to do some spectrum analysis of my room. I know I have issues (although mixes come out OK but I am guessing some things because I know there are problems) and I just want to "see" what measuring can show.

Other than measuring some white noise from the listening area are there any other useful measurements we can do to get a hint of whats going on? Its a small room of 11,5 by 16 feet and 7 feet high. The left wall has my window into the tracling room and its 4 by 6 feet so its quite big and its slightly slanted. The back wall is covered with cedar.

The board is about 1/4 into the room and I sit about 1/3 or more into the room. I'm using KRK v8 for now and although I'm getting good frequencies from them the image is almost non-existant. I've got some nodes for sure (although 1 in the low bass is actually pleasant and is where people are sitting. Almost like having a subwoofer, very "felt" bass without being woofy. SO maybe not accurate for mixing but its impressive).

So my main problem is imaging (which I guess could be caused by phase problems).

I'm kind of worried of loosing that bass if I use Bass traps and I'll need a subwoofer.

if I can get an image of the frequency response I'll post it here and maybe some of you can recognize the problems.

thanks

jim

[tINY]

Make sure you have at least 1/12 octave resolution and that you measure in several locations.



-tINY

[Trev@Circle]

I'm kind of worried of loosing that bass if I use Bass traps and I'll need a subwoofer.

This doesn't make any sense. If you get some decent treatment you will hear what is actually there rather than what your room modes are tricking you into thinking is there. This will have an instant impact on your mixes as you will find that they suddenly transfer better to other rooms and systems. So in answer to your question, it isn't just about imaging, you can't even begin to address that properly until you sort out the bottom end. Corners first then mirror points is the way forward.

[beyond]

bass traps don't make you lose bass, they show you the bass man! Listen to a sweep from 20hz to 250 hz....it should sound pretty even....if you hear very large peaks or dips: that's your problem...

[Bluzzi]

Originally Posted by tINY

Make sure you have at least 1/12 octave resolution and that you measure in several locations.



-tINY

Thanks, we went down to 1/24th but that was ridiculous. At 1/12 and lower it pretty well showed what I was hearing at mix and back of the room positions. The room is actually quite good and the tech was very surprised. The low end has mostly very narrow dips and rises but by a few dbs. The mid has 1 high peak the rest are negligible. The high end is quite smooth and rolls off quite gently and its the way I like it. The bars did not look as drastic as some of the examples I've seen here form other control rooms so I consider myself really lucky.

Theres a bump in the 128hz center and one at about 1.2khz. The 128hz one is wider and the only one I will bother with. I'll be putting some bass traps in the front corners to start and then we'll re-measure and compare.

The other thing I did was to calibrate the monitors. My right one was a few dbs lower.
The HF was set to flat and it measured high so I switched to cut (I think it was 1db) and it became flatter.
I also put them upright with tweeter on top rather than sideways with tweeter on outside and it improved the imaging quite noticably (we used a reference CD for that). Reflections off the mixing console is more noticeable than I believed.

The best thing that happened is that I am more confident of my ears now! My feeling is that I'm hearing mostly the effect of reflections off the console and ceiling.

I'll try and report my experience after I install corner traps and do a mix or 2.

Thanks again for all your suggestions. Remember to trust your ears in the end! Bass traps or no bass traps.

jim

[Sean Sullivan]

I should calibrate my monitors, I'd hate to think one is a few db louder/quiter...this is a noob question but that is HF? Could you explain how you calibrate them in more detail?

[TheArchitect]

What do you use for analysis? Probably the sound card on the PC but I cannot get ETF to function on my test PC.

[Bluzzi]

Originally Posted by upinflames

I should calibrate my monitors, I'd hate to think one is a few db louder/quiter...this is a noob question but that is HF? Could you explain how you calibrate them in more detail?

For that he used a hand held unit that is a mini analyzer. He fed pink noise from it to one speaker and measured average db. Saved the number and repeated for the other speaker. Nothing fancy. My speakers have a gain adjustment in the back that I would tweak while he measured to match the first speaker.

If one of your speakers is off by 1 or 2 db I wouldn't worry too much. I was just doing it because the instruments to do it were there. You can balance by ear quite well. Or if you have an oscillator and an omni mike feed some tones

jim

[Yiannis]

Originally Posted by upinflames

...this is a noob question but that is HF?

High Frequency

[Bluzzi]

Originally Posted by TheArchitect

What do you use for analysis? Probably the sound card on the PC but I cannot get ETF to function on my test PC.

It wasn't my equipment so I'll try and reach the tech today and ask him. He had a hand held unit with a microphone. It actually was also a mini analyzer but he didn't use it for the main measurements just to generate pink noise mostly.

He was using a PC laptop with XP but I didn't take note of the name of the software. He had an external interface. I think it was a simple Tascam one.

You need to feed both your source (pink noise etc.) and your room sound (omni microphone) into it. It then computes the difference in time between the 2 and compares between source and speaker output picked up by mike. There are many ways to look at the spectrum but the easiest for me was when we did 1/12, 1/6 etc octave vertical bars. It shows source and result superimposed. You can see right away where your dips and peaks are.

I think its an important process to go through before and after you add some traps etc. Then you can "see" what effect the traps had (the tech can save the before response and compare with the after one).

jim

[Ethan Winer]

Originally Posted by Bluzzi

Other than measuring some white noise from the listening area are there any other useful measurements we can do to get a hint of whats going on?

Jim, just as important as the raw response is modal ringing - an extended decay time for some, but not all, bass notes. This article explains how I use the ETF software:

RealTraps - Optimizing Acoustic Treatment using ETF

The advice is general enough to apply to other room measuring programs as well.

I'm kind of worried of loosing that bass if I use Bass traps and I'll need a subwoofer.

As others explained, this is not the way it works. Bass traps do three things:

* reduce peaks
* raise nulls
* reduce modal ringing

All of these are necessary in any room that's used to record or mix music. If you'd like to learn more about this fascinating subject, see my Acoustics FAQ.

There's a lot of additional non-sales technical information on my company's site - articles, videos, test tones and other downloads - linked under my name below.

--Ethan

[Bluzzi]

Ethan, thanks for yoru comments. your site is great and I read and looked at probably all your videos. They really helped me understand certain notions.

I just happen to love the boost in the back of the room which is for listeners not mixing. The mixing position is actually not bad at all. Its very workable. But I know it can be improved.

I will be adding treatment in the front corners by using 4inch rigid insulation cut into 2 foot triangles and stacked floor to ceiling. That will be step 1. Step 2 will be more 4inch thick pieces suspended 1 or 2 inches from front wall. I'll use 3 then 3 more later. Step 3 if required will be to hang more 4inch pieces from the ceiling bove the console. After that we'll see.

My back wall is beautiful cedar strips and if I need any bass trapping there I would try the ceiling corner first (from width to width). The door is on one side so I can't do the vertical corners in the back without impeding on the door.

I find I can compensate pretty well for most frequency problems in the room. What I find fatiiguing is compensating for the lack of imaging. I am not sure how much the room and the speakers have to do with it. Until I try another set of monitors here (I am trying to get the K&H 0300 for a demo) I won't know.

Putting the monitors upright had a very noticeable increase in image perception but its still not there for me. From what I've gathered here and there I'd say I'm getting some smearing from the console and the ceiling above it and thhat is why the monitors sounded better when I changed position. I also think the untreated back wall (about 1,5 feet from monitor's back) is exagerating the bass a bit and causing more smearing in the image perception.

I'm ordering the first batch of 4inch today for the first step.

Thanks again, your a truly great help to our community.

jim

[Ethan Winer]

Originally Posted by Bluzzi

What I find fatiiguing is compensating for the lack of imaging. I am not sure how much the room and the speakers have to do with it. Until I try another set of monitors here (I am trying to get the K&H 0300 for a demo) I won't know.

This is due much more to untamed early reflections than what loudspeakers you use. Do you have absorption at the first reflection points now? If not, take care of that before you look into different speakers. Note that early reflections can happen at five different places:

* left and right side walls
* ceiling
* floor
* the wall behind you if it's closer than 10 feet

--Ethan

[Bluzzi]

Thats what I thought and I will be doing some treatment up in the ceiling above the console/mix position. The sides are glass on left and drywall on right but for the console its drywall on both sides. The back is cedar wood. The back will have to wait for now until I do the front wall and ceiling. I can experiment with sides to see how much it matters.

I have to go through the process of hearing then mixing before I'm satisfied with results.

Thanks again.

jim