problem at 100hz

[Telemaster]

I have a home studio that is about 12 x 35ft with a 25ft. cieling. The walls are wood and dry wall. 100hz is all but disappearing at my mix position. Any quick fixes?????

Thanks,
Telemaster

[DigitalDon]

What's your mix position? Are your speakers facing the short wall (12') or the long wall (35')?

DD

[Telemaster]

the speakers are centered against the 12ft wall, perpendicular to the 35ft wall.

Telemaster

[laptoppop]

Your room has two double modes at right around 100 Hz. This means that your room tends to resonate/ring at that frequency. It also means that sound coming from the monitor is being cancelled out by the sound from the walls/ceiling.

It may seem counter-inuitive, but I believe you need to absorb some bass around that frequency to make it sound louder at the mix position.

I would recommend Helmholtz absorbers tuned to 100 Hz. You can get a lot more information on that on John Sayer's site (the SAE reference - Recording Manual, or the "Wall Units" link). You could also go with Panel traps as in Ethan Winer's stuff, but I prefer the absorbers myself, and you can tune them more easily to the problem range for your room, while still absorbing across a wider range.

-lee-

[Ethan Winer]

Tele,

> 100hz is all but disappearing at my mix position. <

Lee is correct about having double modes near 100 Hz. But that doesn't explain your reduction at that frequency. I believe what's really happening is acoustic interference caused by reflections off the walls, floor, and ceiling are creating the dip. I'm pretty sure you have problems at other frequencies too. In fact, for any given location in the room you should be able to find a frequency that is reduced and another that is increased. And vice versa - for any given frequency you'll find places where that frequency is too loud and others where it's too soft.

The best solution is bass trapping that absorbs the entire range of low frequencies. As opposed to building or buying a trap that's custom tuned to 100 Hz. Yes, trapping that one frequency will help that one frequency, but it will not help all the other frequencies.

Since your room is so large and has such a high ceiling, I'm hesitant to recommend doing anything further until you try this simple test: Play a variety of low frequency sine waves one at a time, and walk around the room listening for places where it gets louder and softer. Play 80 Hz and walk around, then 100 Hz, and so forth up to maybe 150 Hz. If my suspicions are correct, you will find places in the room where every frequency has a skewed response.

Let us know what happens.

--Ethan

[Telemaster]

Thanks for your help guys!! I've tested 80 thru 150 hz and walked around the room. You were right. All of those frequences change in volume as I move around the room.

Thanks,
Telemaster

[Ethan Winer]

Tele,

> All of those frequences change in volume as I move around the room. <

I assumed that would be the case, but I've never actually tested that in a huge room like yours. In that case the solution is the same as for a more typical sized room - simply install bass traps that treat the entire low end.

--Ethan

[Telemaster]

Thanks Ethan...

Would you suggest corner bass traps or the panel traps discussed on your web site?? Also... how far does the plywood extend from the wall in your panel trap?? Should the panels also be skewed from square???

Thanks again,
Chris Lindsey (telemaster)

[Ethan Winer]

Chris,

> Would you suggest corner bass traps or the panel traps discussed on your web site?? <

Possibly a mix of both. In normal sized rooms you can usually get good results by putting bass traps in the corners only. And for corners, fiberglass or my company's MiniTraps do a great job. But for your room, which is very large, you probably need additional trapping on the walls. Depending on your budget you can do that with wood panel traps, very thick fiberglass and a large air gap, or MiniTraps.

> how far does the plywood extend from the wall in your panel trap?? <

The two types of wood panel traps in my plans are two and four inches deep. This is one big advantage wood panel traps have over fiberglass-based traps - they absorb very low frequencies without a lot of depth.

> Should the panels also be skewed from square??? <

I'm not sure what you're asking. If you build panel traps exactly as shown in my plans, they will do a great job. Just understand that for a room as large as yours you'll need a lot of them to truly solve the low frequency problems. It's really a matter of covering a sufficient percentage of the room surfaces. That is, covering 30 percent of the surfaces does much more than covering only 5 percent.

--Ethan

[ebeam]

Ethan-

I'm going to be building some bass traps and other absorbers for my room(s). Anyhow, you mention on your web site that the bass traps should be caulked to the wall to provide a good seal. I'm more interested in a design where I can hang them from a couple hooks and move them around to different rooms and positions when tracking and back to the control room for mixing. So, instead of sealing the traps to the wall, can you put a piece of plywood on the back and seal that? Or is the coupling with the wall the important part? Thanks.

[Ethan Winer]

Beam,

> can you put a piece of plywood on the back and seal that? <

Yes, but the back must be at least two or three times more rigid and massive than the front panel.

--Ethan

[ebeam]

OK, that makes sense.

The dimensions of your traps are 2'x8' but I'd like to make mine 2'x4'. With a normal fiberglass absorber (like your mid/high absorber) the lowest frequency it is effective at is determined by the thickness of the fiberglass and the distance from the wall. With the bass traps, I assume you are utilizing the resonance of the plywood to determine that frequency. So, if I build mine half as long, am I going to raise that frequency? If so, can I compensate by making them deeper?

[Ethan Winer]

EB,

> With the bass traps, I assume you are utilizing the resonance of the plywood <

A wood panel bass trap works just like a shock absorber. The mass is the front panel and the spring is the air trapped inside the sealed box. So making the trap shorter does not affect the center frequency, and four feet tall is fine. But understand that for all the effort it takes to build each box, you are covering only half as much surface area. So you'll need to build twice as many to get the same improvement.

--Ethan