Determining Which Frequencies to Control

[Drummer4Life05]

So, I think I know how to control certain frequencies that may need controlling.
But, how do I find out which one's need to be controlled?!
Maybe I'm missing something obvious here, but I'm really unsure.

Any tips would be appreiciated!!

-Justin

 

[Michael Jones]

Ethan Winer has a room mode calculator, so does John Sayers, available on-line.
You input the dimensions of your room, and it will calculate the problematic frequencies for those room dimensions.

That's the simple version.
To really fine tune it, you'll need to run some sine waves, and listen for problems.

But the room mode calculators will get you in the ball park.

 

[Drummer4Life05]

Awesome.
Thanks a lot Michael!!

Now, about these sine waves. Can you explain how they work, and how they tell me which frequencies are the problematic ones? And don't I need some sort of meter or something too?

Thanks again!
-Justin

 

[c7sus]

When you run Ethan's mode calc, the problem frequencies will show up as overlapping, that is they'll be ringing in two or even three of your room dimensions.

After that you can run test tones to see where in the room you're having the most problem.

Here's a free test-tone generator you can run on your pc.

http://www.nt-instruments.com/default.asp?pLngCateId=217&pIntLevel=4&pLngPageId=276

 

[Drummer4Life05]

Cool. Thanks c7!

 

[Ethan Winer]

Justin,

> how do I find out which one's need to be controlled?! <

All of the answers you got about room modes are correct. BUT...

You need to absorb all low frequencies, not just those that correspond to your room's dimensions. For an in-depth explanation of the principles, have a look at my recent article from Electronic Musician magazine. It's now online at the Articles page of my company's web site:

www.realtraps.com/articles.htm

--Ethan

 

[Michael Jones]

Awesome.
Thanks a lot Michael!!

Now, about these sine waves. Can you explain how they work, and how they tell me which frequencies are the problematic ones? And don't I need some sort of meter or something too?

Thanks again!
-Justin

OK, I'm sure someone will jump in here and correct me if I don't get this exactly right, but here goes:

A sine wave is a pure tone, kind of like a tuning fork, that is, its tone is absent any harmonics. This is valuable because you know exactly what frequency your hearing, or more accurately, what frequency you're generating.

If the room mode calculator depicts a problem at... let's just say 1000 Hz, then you can generate a 1000 Hz tone in your room. (I have a yamaha O1V mixer that will generate a few selected tones, but there are some tone generators available on-line.)

So you play that tone in the room. Then you move around in the room, listening critically, and if you hear a difference in the tone, (most likely this will be a sort of... wah wah wah as the frequency tone is being either cancelled out or added to by the wave bouncing off the wall or ceiling) then you know at that point in the room, at that frequency, you have a problem.

So then, you choose an appropriate acoustical treatment, that will tame that problem frequency, or more appropriately, RANGE of frequencies for that area.

Now, there are people here on this board that are a lot smarter than me on this topic. They can simply look at a drawing of your room, calculate the modes, and knowing the wave length of those problem frequencies, suggest a treatment.

For instance:
Let's use the 1000 Hz example.
We know thats a problem frequency for our hypothetical situation.
I think the 1/2 wave length of that frequency is about 1.25'; it's 1/4 wave length would then be about 8".
8" from the wall is where the ideal place for a treatment to attenuate that frequency would be.
But 1000 Hz isn't going to be your ONLY problem frequency.
So they would design something that would attenuate a range of frequencies.
This is usually done by angleing a specific treatment across a wall or corner so that its depth from the wall varies; thereby varying the range of frequencies that it will attenuate.

 

[Altruist]

OK, I'm sure someone will jump in here and correct me if I don't get this exactly right, but here goes:

A sine wave is a pure tone, kind of like a tuning fork, that is, its tone is absent any harmonics. This is valuable because you know exactly what frequency your hearing, or more accurately, what frequency you're generating.

If the room mode calculator depicts a problem at... let's just say 1000 Hz, then you can generate a 1000 Hz tone in your room. (I have a yamaha O1V mixer that will generate a few selected tones, but there are some tone generators available on-line.)

So you play that tone in the room. Then you move around in the room, listening critically, and if you hear a difference in the tone, (most likely this will be a sort of... wah wah wah as the frequency tone is being either cancelled out or added to by the wave bouncing off the wall or ceiling) then you know at that point in the room, at that frequency, you have a problem.

So then, you choose an appropriate acoustical treatment, that will tame that problem frequency, or more appropriately, RANGE of frequencies for that area.

Now, there are people here on this board that are a lot smarter than me on this topic. They can simply look at a drawing of your room, calculate the modes, and knowing the wave length of those problem frequencies, suggest a treatment.

For instance:
Let's use the 1000 Hz example.
We know thats a problem frequency for our hypothetical situation.
I think the 1/2 wave length of that frequency is about 1.25'; it's 1/4 wave length would then be about 8".
8" from the wall is where the ideal place for a treatment to attenuate that frequency would be.
But 1000 Hz isn't going to be your ONLY problem frequency.
So they would design something that would attenuate a range of frequencies.
This is usually done by angleing a specific treatment across a wall or corner so that its depth from the wall varies; thereby varying the range of frequencies that it will attenuate.

I have been banging my head into the wall trying to wrap it around this mode calc stuff and sine waves and problem frequencies etc etc. Thanks to you I now have a bit of a base. Thanks a lot. That was very informative.

Geoff

 

[TexRoadkill]

You can do all the fancy calculations and in the end it seems that every room has problems around 200hz-800hz.

I would tune the high end by ear since that determines how live the room sounds and is a bit more subjective.

 

[Drummer4Life05]

Whew...you guys and fantastic!
I actually an idea of how this stuff works.

Ethan - I actually have that issue of EM, and I have read the article. Although knowing what I know now, I'm sure it will be a much better read! Thanks for reminding me!

MJ - Great information for me! That really gives me a strong starting point as to where to start. I used one of those online ones, but I didn't really know how that would tell you which one's are the problem ones. Thanks for the explanation!