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DJL
Self Banned
Thanks for the reply... so does the dead air space "spring" act as a coupler between the ply and 703 mass?Ethan Winer said:
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gordone
Well-known member
Re: Re: Re: Re: Re: While you're at it . . .
Amen to that! When I first moved into my last townhouse (from a little apartment), I had a nice big room in the basement. Just drywall and linoleum flooring. The thing sounded like Carlsbad Caverns!!! I had a Soundelux U97 and a Neumann KM184 going into a Great River. I recorded mainly acoustic guitars and vocals. What I ended up getting on disk was an extremely accurate recording of my crappy sounding room. I think I would have been better off using my Shure SM58 into my Mackie 1202. Once I got some Auralex (sorry Ethan!) up on the walls, it was much better to track in. The room was pretty dead so all you could hear was the instrument being recorded and not all the ringy slapback echo from the bare walls.
Amen to that! When I first moved into my last townhouse (from a little apartment), I had a nice big room in the basement. Just drywall and linoleum flooring. The thing sounded like Carlsbad Caverns!!! I had a Soundelux U97 and a Neumann KM184 going into a Great River. I recorded mainly acoustic guitars and vocals. What I ended up getting on disk was an extremely accurate recording of my crappy sounding room. I think I would have been better off using my Shure SM58 into my Mackie 1202. Once I got some Auralex (sorry Ethan!) up on the walls, it was much better to track in. The room was pretty dead so all you could hear was the instrument being recorded and not all the ringy slapback echo from the bare walls.
chessrock said:
Ethan Winer
Acoustics Expert
LD,
> I've got eight of them. They don't appear to be airtight <
MiniTraps are not air-tight. The wood panel traps we used to sell are.
--Ethan
> I've got eight of them. They don't appear to be airtight <
MiniTraps are not air-tight. The wood panel traps we used to sell are.
--Ethan
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DJL
Self Banned
And if not... why must the wood bass traps be air tight, just for the dead air trap to work correctly?DJL said:
Oh, and why did you stop selling the wood pannel traps? Thanks again.
Ethan Winer
Acoustics Expert
DJ,
Read my previous post again, where I said "The air inside serves as the spring, and the panel is the mass"
> why must the wood bass traps be air tight <
Because the air is a spring, and it must be trapped to compress. Otherwise it would just leak out and be like a limp baloon.
> why did you stop selling the wood pannel traps? <
Because MiniTraps are better and cheaper. MiniTraps absorb a wider range - lower too - and cost much less and can be shipped for much less. It just made no sense to keep selling the wood panel traps.
--Ethan
Read my previous post again, where I said "The air inside serves as the spring, and the panel is the mass"
> why must the wood bass traps be air tight <
Because the air is a spring, and it must be trapped to compress. Otherwise it would just leak out and be like a limp baloon.
> why did you stop selling the wood pannel traps? <
Because MiniTraps are better and cheaper. MiniTraps absorb a wider range - lower too - and cost much less and can be shipped for much less. It just made no sense to keep selling the wood panel traps.
--Ethan
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DJL
Self Banned
I guess what I'm having trouble understanding is... what you mean by "spring"? Does the "spring" couple the sound wave from the ply to the 703? Please help me understand the "spring". Thanks.
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larrye
New member
To absorb the energy of sound it must be converted to something else, usually heat. The sound hits the cover, the cover is pushed inward, the trapped air is compressed, this changes the sound energy to heat energy and is therefore absorbed. It's like air shocks, if they leak they won't work.
larrye
larrye
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chessrock
Banned
Damn. This is some interesting stuff. Thanks for the physics lesson. 
I never thought of it like that, LarryE, but it's starting to click.
I never thought of it like that, LarryE, but it's starting to click.
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DJL
Self Banned
So the dead air trap "spring" is a coupler that couples the sound waves hitting the plywood to the 703 then. If that is so... would two springs and two 703's (in this order.... plywood - 1st spring - 1st 703 - 2nd spring - 2nd 703) be better? Also, how do you tune the trap for certain frequencies?
Son of Mixerman
Mix Junior
DJL said:
Air actually decouples the load from the box so the box won't vibrate. Like shocks on your car keep the road from vibrating your teeth. There are an infinite number of layering schemes, usually cost prohibitive. I know where I can get 2" thk panels with 73db of attenuation, but it will cost you 10 times of what Ethans MiniTraps will cost, if not more.
You will usually require several traps to balance the frequency response of the room.
Tuning comes from changing the gap so that certain wavelengths get rejected, and some pass into the trap. The slot size is based upon 1/4 wavelength and distance from the wall.
SoMm
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mixsit
Well-known member
DJL said:
The wood face, the air inside, and the fiberglass all act to convert air motion to heat. The fiberglass would add efficiency for a given amount of space. But the combined system including it being a sealed system is the tuning. Think two same sized speaker cabs, ported vs infinite baffle.
That's my guess (and that’s all it is.
Wayne
nwsoundman
Vintage Gear Junkie
From what I understand:
is that the 703 changes the Q of the trap. Basicly makes the trap more broadband. It also helps dampen the front panel. You want the panel to be exited by the pressure outside of the trap verus allowing the air inside the trap to exite the front panel making it easier to vibrate the front panel. The depth of the trap combined with the mass of the front panel determines the center frequency of the trap. There are other factors too like width relative to height. If you build a trap with too little surface area it will not be effective also if you build one too big it will flop about and not be very effective.
When you start talking about gaps or distance between slats that is refering to Heimholtz (sp?) resonators. Those and Ethans traps are two different beasts.
is that the 703 changes the Q of the trap. Basicly makes the trap more broadband. It also helps dampen the front panel. You want the panel to be exited by the pressure outside of the trap verus allowing the air inside the trap to exite the front panel making it easier to vibrate the front panel. The depth of the trap combined with the mass of the front panel determines the center frequency of the trap. There are other factors too like width relative to height. If you build a trap with too little surface area it will not be effective also if you build one too big it will flop about and not be very effective.
When you start talking about gaps or distance between slats that is refering to Heimholtz (sp?) resonators. Those and Ethans traps are two different beasts.
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DJL
Self Banned
Hey thanks everyone for all the great input... I'd like to know the formula for tuning a trap freq and how to apply it... along with how to test it to see if I did it right?
nwsoundman
Vintage Gear Junkie
DJL,
That Ethan would have to answer. I know mine have different responses. I built about two dozen of the them. Half high bass and half low bass. I found they were all pretty close to each other by type. If I go and hit each low trap around the center point they sound like kick drums. When I hit the high bass ones they are more like toms without alot of power. The frequency they resonate at is the same frequencies they absorb. Every board used to make them have different sounds so each trap will be a bit different from the other. I guess that will make it hard to tune each one very specificly. If I play a 100hz tone each trap vibrates at a different intensity.
Kirk
That Ethan would have to answer. I know mine have different responses. I built about two dozen of the them. Half high bass and half low bass. I found they were all pretty close to each other by type. If I go and hit each low trap around the center point they sound like kick drums. When I hit the high bass ones they are more like toms without alot of power. The frequency they resonate at is the same frequencies they absorb. Every board used to make them have different sounds so each trap will be a bit different from the other. I guess that will make it hard to tune each one very specificly. If I play a 100hz tone each trap vibrates at a different intensity.
Kirk
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DJL
Self Banned
Thank you Soundman... hopefully Ethan with help shine some more light on this subject. 
Ethan Winer
Acoustics Expert
DJ,
The formula for calculating frequency based on panel density and the depth of the air gap is in Everest's book. But you can just extrapolate from an existing design. For example, the low-bass trap in my plans has a center frequency of about 100 Hz. So if you make it twice as deep, or make the front panel twice as thick, it will then be at about 50 Hz. And all other such combinations.
--Ethan
The formula for calculating frequency based on panel density and the depth of the air gap is in Everest's book. But you can just extrapolate from an existing design. For example, the low-bass trap in my plans has a center frequency of about 100 Hz. So if you make it twice as deep, or make the front panel twice as thick, it will then be at about 50 Hz. And all other such combinations.
--Ethan
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DJL
Self Banned
Thank you Ethan. 
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Rod Gervais
New member
dwillis45 said:
1st off - what exactly do you have in the way of bass traps, etc.
2nd - what are you using for monitors,
3rd - what is it exactly that seems to suffer in your mix.
I don't see the answers to these questions - and they are as important as the theory being discussed.
Ideally you want your monitors to give you absolutely no color at all - and you want to hear exactly what is really coming out of your monitors.
If you sit in a bass null (for example) you're going to tend to mix bass heavy. Just the opposite if you're in a peak.
If you have problems with reflections of the walls/celing that destroys your stereo imaging then you will need to create a reflection free zone for your seating area.
But eventhing begins with a detailed explanation of your room and what exactly your problem area is before anyone can offer you truly constructive help.
Personally i have never used the Auralex site.
By the way - HI Ethan - great seeing you here my friend.
Rod
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DJL
Self Banned
Ethan, are your MiniTraps basically a shock absorber too, and if so... what serves as the spring? I'm trying to get a better grip on treatment and etc... thanks for helping me understand better how traps work.
Ethan Winer
Acoustics Expert
DJ,
> are your MiniTraps basically a shock absorber too <
No, MiniTraps work on a completely different principle than panel traps. Well, a mostly different principle, anyway. Panels traps are resonant enclosures that vibrate sympathetically when struck by sound waves. Fiberglass and foam instead absorb by offering resistance to sound waves that pass through the material.
MiniTraps are a combination of very dense rigid fiberglass,which is much better than foam, and a membrane. So there is some "spring" action in the fiberglass as the membrane flexes.
--Ethan
> are your MiniTraps basically a shock absorber too <
No, MiniTraps work on a completely different principle than panel traps. Well, a mostly different principle, anyway. Panels traps are resonant enclosures that vibrate sympathetically when struck by sound waves. Fiberglass and foam instead absorb by offering resistance to sound waves that pass through the material.
MiniTraps are a combination of very dense rigid fiberglass,which is much better than foam, and a membrane. So there is some "spring" action in the fiberglass as the membrane flexes.
--Ethan