[bpape]

Again, we're not testing what the trap will do per se in a given space to fix all of the problems.  This is purely an experiment to show differences in different designs, and to show what difference, if any, there is between a tube with and without sealed end caps. 

Bryan

[Ethan Winer]

"what range are we testing for?"

All that matters are frequencies below 300 or maybe 400 Hz. Above that it's not bass trapping anymore, and it certainly won't be a tuned trap as some claim for hollow capped tubes.

--Ethan

[bpape]

I guess the question of "what range are we testing for?" arises.

If we are testing bass traps, what level should we start with. I had thought I would just be putting the sealed servo sub in the room. But if we want the 500 hz range or something, I need to get a real set of speakers in there, so its going to involve more setup...

-Tony

20-300 is usually what I personally look at.  The sub can be run without a crossover in place to allow it to run higher.  The fact that it may not be flat really shouldn't matter as again, we're looking at relative changes between treatments.  If there's a hump or dip in response in the sub, it's there and the same for all of the players.

Bryan

[bdiament]

Hi Ethan,

Right, and that's how the lowest mode is determined. Only half of a wave needs to fit to support resonance...

I know.  Thanks.

Best regards,
Barry
www.soundkeeperrecordings.com
www.barrydiamentaudio.com

[bdiament]

Hi Tony,

I guess the question of "what range are we testing for?" arises.

If we are testing bass traps, what level should we start with. I had thought I would just be putting the sealed servo sub in the room. But if we want the 500 hz range or something, I need to get a real set of speakers in there, so its going to involve more setup...

-Tony

Is this purely a measurement test?
If so, just to be safe and complete, I'd want to go up past the range where room modes will be an issue, so I'd test to at least 300 or 400 Hz (though the larger issues will occur lower down).

I would suggest however, since you're going through the trouble, incorporating listening too and that would mean full range music.  The persistence of a room mode will effect how you hear (or don't hear) low level detail up into the midrange.  I'd want to hear the effects on well recorded familiar music, not just see a numeric representation.

I think the most informative test will be the one that most closely emulates how (and, as I've suggested, where) you'll be using the devices in the long run.

I don't know if listening will be possible in the tests you have in mind.
Just my perspective.

Best regards,
Barry
www.soundkeeperrecordings.com
www.barrydiamentaudio.com

[TRADERXFAN]

So I am not too familiar with fiberglass products. When I go to home depot to get the insulation to stuff in the tubes, what should I get, and should I really be firmly packing it in, to be properly made?

Any tips on how to do that part? or get it back out?

-Tony

[BobM]

"Firmly" packing the tubes is probably not something that will be easily done, since the tubes themselves are not solid. They are actually 2 halves and have seams. Packing them tight is bound to open the seams (it did for me). I would just push in whatever anmount you can get away with and still hold the 2 halves together without opening up.

BTW - glue alone does not hold the 2 halves together very well. I had to use a strip of packing tape.

[bdiament]

For the closed tube design, it is critical to *seal* the tube, along the seam that runs its length and at the ends (I used plywood circles).

Liquid Nails helps make a good, airtight seal.

Best regards,
Barry
www.soundkeeperrecordings.com
www.barrydiamentaudio.com

[Ethan Winer]

Liquid Nails helps make a good, airtight seal.

Of course, Tony should be sure to do the unsealed test first.

--Ethan

[Ethan Winer]

When I go to home depot to get the insulation to stuff in the tubes, what should I get, and should I really be firmly packing it in, to be properly made?

You want plain old fluffy fiberglass, the kind used for attic insulation etc. You can pack it a little, but probably not more than 2:1 or 3:1 at the very most. Packed 3:1 makes fluffy fiberglass have about the same density as 703 rigid fiberglass.

--Ethan

[TRADERXFAN]

ASC makes what they call a MATT (music articulation test tone) that you can find on Stereophile test CD #2.  This is an excellent signal for checking the effects of room issues (and treatments).  Listening to the MATT via headphones, then via your speakers (with and without treatments or with treatment A, then treatment B) will be an education in itself.  The headphones of course, will give you the tone without room effects.  After hearing this, you'll find it a lot easier to hear what the room/treatments do in between the pulses of the tone.

There was a link to this test tone to download, and some other tutorials on how it should be used. 

I don't think its something that I could really measure. I will use the signals available on the room eq wizard software, periodic pink noise, sinewave plots, and waterfall.

-Tony
http://www.acousticsciences.com/matt.htm

[bdiament]

There was a link to this test tone to download, and some other tutorials on how it should be used. 

I don't think its something that I could really measure. I will use the signals available on the room eq wizard software, periodic pink noise, sinewave plots, and waterfall.

-Tony
http://www.acousticsciences.com/matt.htm

You can record it and look at the waveforms to see how much decline there is in the signal between the pulses.

I would think it most important to measure those effects you seek to quantify.  The thing is room issues are time based, not amplitude based (though some of the symptoms will show up in amplitude measurements).  You need time-based tests to get a good picture of what is going on.  Perhaps the waterfall plots will be useful.

Best regards,
Barry
www.soundkeeperrecordings.com
www.barrydiamentaudio.com

[TRADERXFAN]

I don't think I can record a picture of the waveform with REW. However, the waterfall plot, showing the time decay, should point out resonance.

On a different note, I always seem to underestimate these things I get myself into...  I picked up the pipe insulation this afternoon.  And just got back from the store this evening with 2 bales of unfaced r-13(116 sq feet each). Althought I think its packed a lot tighter than its going to be in the tube

The more I think it through, the more it seems like its going to be a royal pain messing with this stuff...

-Tony

[Ethan Winer]

just got back from the store this evening with 2 bales of unfaced r-13(116 sq feet each). Althought I think its packed a lot tighter than its going to be in the tube

If you haven't already opened the plastic bags, please test those first. Leave them as they are, sealed in the bags, and stand them up leaning into the corners.

--Ethan

[TRADERXFAN]

If you haven't already opened the plastic bags, please test those first. Leave them as they are, sealed in the bags, and stand them up leaning into the corners.

--Ethan

Ok, I can do that.

Last night I setup the mic and measurement equipment and practiced with the waterfall plot. I tried various combinations of 1-3 panels and placement of the 6in mineral wool.  And I found out this sub doesn't have a crossover defeat on the amplifier. I also have an SVS that does, so I might swap it for that.

The wife is under strict orders to not disturb the microphone. (Let's see how long before I knock into it myself  )

Any benefit to looking at lower than 20 hz?

I definitely have a long resonance at 55hz, and a huge null at 170hz (guessing its mic height on that one)
I'll gather some pictures and some of these initial plots, before I settle in on the final testing placement.  The room is bare except for a small set of plastic drawers, which I will move out.  Also there is a closet door, metal, with extra sheets and blankets and such in there. If I measure drywall to drywall its a beautiful dimensioned 13x13x8 room  .  Should I take off the closet doors?  There is probably some kind of resonance there and there blankets behind probably are having some effect.  I realize we are just doing comparison and overall success of treatment is not the goal. However, if it can be more controlled, then perhaps the effects will be more helpfull in informing others who read this about them?

Now that there is some progress, this is starting to get interesting.

-Tony

[bpape]

Test the room the way you're going to use it.  If the doors will be on, leave them on.

As Barry said, time based measurements will be far more telling of performance than pure frequency based ones - especially with a minimal amount of samples available.

No need to look below 20Hz.  Usually, if you look from 20-300Hz, that will give you a pretty good idea of what's happening.

Bryan

[Ethan Winer]

Should I take off the closet doors?

No, but definitely shut all the doors to the room when you run the tests. An open door is like a bass trap. So that will make the difference between trap types smaller than having the doors shut. And ideally you'll do all the tests the same day, one after the other.

--Ethan

[TRADERXFAN]

Some initial waterfall plots here...

http://www.audiocircle.com/index.php?action=gallery;area=browse;album=2362


Doesn't seem to do much at these sub bass frequencies...

-Tony

[Ethan Winer]

Yeah, this is why you really need to test about eight panels to see a clear trend. If you change the displays to show up to 300 Hz you'll see more affect.

What's the difference in trap placement between Image 4 and Image 5?

--Ethan

[TRADERXFAN]

Yeah, this is why you really need to test about eight panels to see a clear trend. If you change the displays to show up to 300 Hz you'll see more affect.

What's the difference in trap placement between Image 4 and Image 5?

--Ethan

Good catch. That was a duplicate. I deleted one.

Not sure why the waterfall cut off early. The frequency plot went to 500hz. I will have to try and figure it out.

-Tony