Kill the foundamental or the harmonics ?

If I wish to have a good mixing room, and quite good for mastering, and I have a bump at about 30Hz that I can see causing a comb filtering at higher harmonics, and suppose I'm going for tuned traps, what should I target? There are two options as I see it: 1. Ignoring the 30Hz and absorb the harmonics 2. some traps will target 30Hz, some will target the more usable bass range. How much improvement in the comb filter of the harmonics should one expect from killing the resonating foundamental? Is it worth the effort, or should I just go for the harmonics and ignore the foundamental? Neither of my speakers supposed to go as low as 30Hz, and I wish them to have their natural rolloff rather then a peaky response. Maybe if I add a sub later, I'll just EQ that frequency? What would you do? Thanks Adam

Adam, I've seen people theorize that using traps tuned to a low mode will also help the higher related modes, but that's just not true. Further, 30 Hz is pretty low unless you're mixing movie sound tracks. So I'd focus on the higher bass range, between 60-80 Hz and 300 Hz. --Ethan

My teacher told me that killing the foundamental definetly has effect on harmonics, but indeed told that usually it's better to kill the harmonics if the foundamental is below the reasonable mixing range. Thanks :-) Adam

AdamZuf wrote:

My teacher told me that killing the foundamental definetly has effect on harmonics

Please ask your teacher for a detailed explanation and report back here with the answer. :) All tuned "things" work the same, whether mass/spring mechanical devices or electrical circuits. There's a center frequency and a bandwidth, with the effect falling off on either side of center based on the Q or bandwidth. The only way I can imagine trapping one frequency could affect other, far away, frequencies is human perception. For example, if you absorb all the mids and highs in a room with thin absorbers, then you'll notice the bass boominess more. But that's only perception. --Ethan

You got a point. well he was my teacher, I finished S.E. school- I'll probably call him when I'll have a bunch of questions or findings, but I will surely tell you his answer :)

i agree with your teacher. it has an effect. but is it the effect you want? i also agree with Ethan. please report back soonest. :wink:

gullfo wrote:

i agree with your teacher. it has an effect. but is it the effect you want? i also agree with Ethan. please report back soonest. :wink:

Stop being cinical :D I just hate it when I'm being tought the wrong way or in a non exact manner- Happened all the time in my S.E. studies... And it claims to be a good school...What's happening to the world :? :D

It depends whether you speak about panel traps or porous absorption. Harmonics are wavelength related. Porous absorption is wavelength related. Panel traps listen to another mechanisme and are related to the dynamic stiffness of air and will be tuned to one single center frequency. To catch these harmonics (assuming you leave the hole thing narrow band), you could design paneltraps with more cavities, creating more resonant frequencies. The advantage when adding an additional cavity and panel, you lower the original resonance (depends on mass ratios of course) and create a higher one. But that's so complicated that the idea is not really practical. But I know applications where the idea is used to make membrane dampers more broadband.

Eric_Desart wrote:

The advantage when adding an additional cavity and panel, you lower the original resonance (depends on mass ratios of course) and create a higher one... But I know applications where the idea is used to make membrane dampers more broadband.

I didn't understand, sorry.

AdamZuf wrote:

Eric_Desart wrote:

The advantage when adding an additional cavity and panel, you lower the original resonance (depends on mass ratios of course) and create a higher one... But I know applications where the idea is used to make membrane dampers more broadband.

I didn't understand, sorry.

A simple panel trap has a back wall, a cavity and a front panel. That means 1 single cavity tuned to one single frequency. If I make a more extended panel trap, by adding a second trap , where the front panel of the first act as as back wall from the second trap on top, I then have 2 cavities, which will result in 2 frequencies where the lowest will be lower than the simple original one and the highest will become higher, while the original resonance frequency disappeared. Hence I made a panel trap with 3 panels and 2 cavities. The number of frequencies equals the number of cavities. Only when the center panel should be extremely heavy then adding lightweight panels on both sides will keep both resonances close together. In physics this is referred to as a mass spring system with 2 degrees of freedom, while a simple panel trap or a standard drywall is a mass spring system with 1 degree of freedom. If you hear people talk here about triple leaf systems they refer to a mass spring system with 2 degrees of freedom. Eric

does building a "triple leaf" trap (MSM w/ 2 DoF) work? does affixing a panel trap over a section of wall cause it to become triple leaf? if i have three panels separated by 1/2 inch each, is that a triple leaf system?

Glen, It does work, since used with transparent lightweight foils (absorption in front of windows), while both MSMs are recognizable to be identified. I'm rather sure I could design such good working traps broadening their range. However triple leaf systems with random incidence, stiffness of clamming and whatever other phenomenon are difficult predictable. You must know the thread here at JS where Brian measured one of Ethan like panel traps on the wall. I should need to know more of these, to draw conclusions. Which I also made clear in that thread. Which effects played a roll? Anyhow too superficial and fast conclusions where drawn by some in that thread. I was only lucky that Brian confirmed my related care and question marks. PS: It's written normally DOF not DoF. The question here is in how far can men preserve the mechanical limp 2DOF system with straight incidence? There isn't enough data or studies to draw exact conclusions. And your 2 times 1/2 inch goes close to the phenomenon that I described and referred to in the ASC threads. With very small cavities something happens (damping but visco thermal), which was studied on scale or small models, but I never saw applied in real live, unless it could explain something of certain triple leaf window measurements (and possibly an ASC effect without them being aware of it).

mucho gracias senor! this clears up a number of things and clouds other ;-) I'll have to check Brian's thread on the panel traps.