John Sayers' Recording Studio Design Forum

I've read in EQ mag (June 07) about Bruce Swedien's Quick Sound Field techniques (see http://www.asc-studio-acoustics.com/qsf.htm), and I think it would make the best sound most easily out of my fairly live, but not good-sounding basement. Problem is, I can't spend 3k on sound treatment. The QSF concept is placing around 8 hemispherical diffusors pointed towards the talent in a semi circle around the mic, reflecting high freq's while absorbing low freq's with the rigid fiberglass inside (the other side is non-diffusive and can be pointed toward the talent for a gobo effect). I am wondering if painted cardboard concrete footing molds (tubes - exactly the same shape and size of the QSF units) filled with spray foam insulation might have the same effect, without the option of an absorbent gobo side? I have the tubes already - so I will try them without insulation to see if they improve the room sound on drums... but if the experts here think the insulation would not absorb low frequencies because of the regidity of the tube, or whatever, I will not bother trying to find a spray foam installer and begging for scraps/leftover spray....

Thanks, and I've been lurking here for a few years now, getting ideas for when I finally have my own studio space, and the time has finally come! It's been a big help. Actually had a bit of trouble finding it this time... but finally did.

My space: roughly 20' by 30' by 7' open plan basement, laminate floor on concrete slab (yay), ceiling tile (ugh) and paneling (double ugh!!). There's couches in the corner, and a mattress against the wall, not for sound treatment... just cause I don't have anywhere else to store it!

...also handy when your clients go bananas...




HOOK

Sorry, no. If you want to DIY some panels, use rigid fiberglass at least two inches thick. Four inches is even better.

--Ethan

What about using both? The tubes in front for quick sound field diffusion, with rockwool behind for room absorption? (I say Rockwool bc I already have some 8pcf Roxul that was given to me as construction leftover. I assume there isn't much acoustic difference between that and 703 for this purpose). Also, I presume I would have to fill the tube with something to lower its resonating frequency, or strap the rockwool to the backside of it to dampen it. ...Speaking of resonating frequency, couldn't a tube function as a panel trap at its res. freq.? I envision something like a pipe organ at the back of the room, tubular bass traps of different lengths and sizes tuned to various frequencies. If it worked, the coolness factor and fact that it was modeled after a musical instrument would be amazing!

So, for clarity and summation:

1. Would using rockwool mini-gobo / tube combinations produce a quick sound field effect?

2. Could tubes be used as panel traps (or perhaps more accurately bass hemholtz resonators)?

It depends entirely on the thickness and rigidity of the cardboard tubes. If you want to DIY a tube trap, you should imitate the way ASC makes theirs. In that case you'd cut it in half to get two half-tubes, and stuff each half with absorption.

--Ethan

It takes 8 DIY StudioTraps to make one QSF acoustic space

QSF is an acoustic space that saturates the Haas reflection time period. It can be generated by a particular arrangement of StudioTraps that create numerous early reflections the treble range and all the while maintaining an RT60 of about 1/10 second. I have tried other ways to get this sound effect and always end up pretty much with the same setup.

Correction: It is not derived from a hemispherical reflection pattern; it is generated by an array of hemi-cylindrical specular reflectors.

StudioTraps normally list at about $360 each, including stand. The goal being discussed here is how to make a DIY StudioTrap. The next issue should be how to set them up so that they create the QSF effect.

If I were to try to make a DIY StudioTrap out of sonotube and rock wool, following Eathan's not unreasonable suggestion and others, I'd start with an 8" sonotube (not 12"), cut short into 4' lengths. Then I’d cut sonotube in half to make two half cylinders. When cut, sonotube expands, tending to flatten out. We don't want a flattened out half cylinder reflector. We want a real half cylinder.

Side note: The size of the reflecting half cylinder is important. Too big and too much lower treble is reflected, too small and only the high treble is reflected. The diameter of the cylinder is in effect an acoustic cross over, bass pass / treble reflective. The diameter is also related to how loud the reflection is, the larger the diameter, the flatter the reflection and the louder it is. QSF kicks in at about 500 Hz.

Get a piece of fiberglass string reinforced plastic window screen 16" by 60". Hot glue the middle 48" of one long edge onto the outside edge of the 4' cut edge of the sonotube, about 1 1/2" back from the cut edge. Now you have two end flaps and the middle 4' along one edge is glued down at one edge. Wait at least 10 minutes for the hot glue to harden.

Now compress the half tube back into its cylinder shape and pull the screen tight over the other edge. You may need an assistant or some sort of jig to hold things in place. It’s like alligator wrestling. Hold the screen in position, hot glue it about 1 1/2" in from the edge on the other side and hold it for at least 10 minutes, till the glue really hardens. A jig, made of plywood 12"x48" and a couple 4' 2x2s nailed with an 8" space between makes a nice clamp for this job. Glue lines would be set about 2" back instead of 1/2" but that's OK.

Fill the half cylinder, screen faced cavity with some "703" or rockwool or equivalent very absorptive material. Personally, I would go to an upolstery material distributor, or a matress factory and get expensive foam, very soft and dense. Use this material insted of fiberglass or rock wool and make an itch free product but it costs the same as good fiberglass. Pull the end flaps over and hot glue them down to seal the half cylinder.

In studio work, it is very, very important that the talent never gets fiberglass or rock wool fibers stuck in their throat. The slightest fiber can choke the talent and stop a session. We also do not want to see glassfibers floating in the air, landing on CDs, getting sucked into hard drives, tapes, switches or mic capsules. At ASC, we go to great pains to literally seal our products. They just can’t ever leak fibers into the air, no matter how loud the sound gets. By the way, make sure that whatever acoustic material you stuff into your cylinder has a neutral smell.

All TubeTraps products are devoiced; they have no resonance characteristics at all. Their length has nothing to do with their frequency of operation, only the diameter. If you do not use serious absorptive material in the back side of the hollowed out half cylinder, the unit will resonate and blow sonic colors into the mic. That’s not good.

You can make your tube look better by wrapping the screen around the front of the tube, so it gets ride of the spiral groove. Still, the screen does not fiber seal the unit. The window screen only holds the absorptive material in place. We also don’t want the absorptive material to settle, as this would leave a hollow sounding, hollowed out cylinder shape at the top. When glue is under tension, do not reheat it. It will release and things will fly apart.

Get some felt at the craft store and lightly spray glue it down over the entire half-cylinder, both the front and back, top and bottom. It is acoustically transparent enough. You can use different colors, have fun with the covering. The felt will fiber-seal the product you have built. Now it is safe to use in an enclosed room, a studio

We have gone over what it takes to imitate the acoustic properties of a StudioTrap. The cut off frequency and roll off slope are not exactly the same, but close enough for DIY. What we haven't talked about is how to hold the StudioTrap up. I'd start with 3 long and 1 short stick and make a 6' tall tripod with a cross bar at 30" off the floor.

The QSF is created by a horse shoe pattern of StudioTraps, on 18” centers. The center of the reflecting surface is set about at voice or instrument height. High enough off the floor to backscatter the treble back into the mic and separated apart enough to let the bass vent out of the space. There are lots of ways to hold these half cylinders up off the floor. But we do not want to create a giant domino effect, where with one bump, the whole setup tumbles down.

With reflectors rotated away from the talent, flat side in, you will recreate that old familiar Studio-Dead sound. With reflectors rotated toward the talent, flat side out, you get that oh so desirable Studio-Live sound. The better the room the farther apart the StudioTraps can be set. As you raise the mic you can acoustically mix the QSF direct with a little room ambience for sweetning.

Bruce works in the Hit Factory and sets his 14 Traps about 3 feet apart and randomized the reflection pattern. He has been recording in QSF for over 12 years.

A regular engineer in a regular studio likes 10 Studios and will use a tighter pattern. At home, 8 Studios are used and the Trap pattern tightens down to 4 feet in diameter, with the individual Traps about 18” apart and all reflective.

Pete Townshend endorsed the QSF sampling booth something like the one shown in F Alton Everest book back in 87. The QSF booth specifically pictured in his book was used to develop deep space voice recognition algorithms.

The QSF is acoustically sorta like taking a direct signal and splitting it into two tracks. One track stays direct. The other track gets processed; the bass is rolled off and the treble gets turned into a random set of low level, time delayed signals stretching out about 30 ms. These two tracks are mixed back together, acoustically, to get the sound of the QSF effect.

What is missing with the DIY Studio is good looks, cleanlyness, convenience and most important, durability. Working engineers are always handling their Studios and what this DIY is missing is toughness.

By the way, whenever you want to know about TubeTraps, or bass traps in general, just call me or email me. I haven’t forgotten that one of my earliest acoustic projects was a DIY TubeTrap. Come to think of it, I’m the one who invented the TubeTrap.

Arthur Noxon
Acoustic Engineer
www.TubeTrap.com

That's what I've been saying!

How ya gonna get anywhere if ya ain't got no large batch a half round things whats gonna put it back in yer face!

Thank you Mr. Noxon for the detailed post. Very interesting. I do have Everst book you are referring to and the measurement shows a very flat result.



Has your company ever had any concerns about formaldehyde binders in the fiberglass? If so, what was your solution or recommendations for DIY folks.


Regards

Hai Arthur, welcome to the forum. Great first post

Great to see you here Art!

--Ethan

RE: Formaldehyde Binders

1) We were talking about DIY QSF using sonotube. I recommended to skip the rock wool or fiberglass version of sound absorption to avoid the itchy consequences of working with that material in a non factory environment. I recommended using expensive, soft, heavy foam that you can get at your local mattress factory or upholstery supply house.

I did not recommend anything with formaldehyde binders in it, that I know of. But now that you mention it, maybe the sonotube is glued together with formaldehyde adhesive. Maybe the foam rubber is formaldehyde based. Maybe the hot glue has got formaldehyde in it. I think I am going to go crazy worrying about all the formaldehyde based construction materials that surround me, oozing poisonous gasses…. Screw it, I’m just going to take a deep breath, hold it and charge forward into the life and world I was born into.

2) New topic. As to formaldehyde binder in 703 or other fiberglass products. About half of all ductwork of all commercial air conditioning systems is made out of a 703 type material. And the rest of the ductwork is metal, and it has a form of building insulation in it, which is a light density version of 703. The point here is that the snorkel tubes used in most occupied buildings to supply and return air for the occupants is made out of this very same material that your are referring to, a formaldehyde based plastic glue.

Since this type of product is certified for use in air breathing ducts it probably is good to go for use in a non air breathing objects, things that just hang or stand around in a room. All church sound panels, most all studio absorption and office noise control panels are made out of this material. We’re already surrounded by it, we can’t escape it.

My understanding is that the only time formaldehyde becomes an issue is when the material gets soggy wet and stays soggy wet and the glue decomposes.

If you are worried about formaldehyde and other gas vapors poisoning your body, you can get a box of low cost monitoring badges. You wear them and they measure your exposure to formaldehyde and other VOL vapors. See

http://www.acsbadge.com/residential.shtml#formaldehyde

It explains that formaldehyde is used in many residential applications, such as building materials, chemicals and fabrics. In the home you find formaldehyde based products such as glue used in building materials such as pressed wood products (hardwood plywood wall paneling, particleboard, fiberboard) and furniture made with these pressed wood products. Urea-formaldehyde foam insulation (UFFI). Combustion sources and environmental tobacco smoke. Durable press drapes, other textiles, and glues.

As to TubeTraps, which you didn’t actually ask about, we do use real fiberglass fiber. Fiberglass building insulation is compressed to density of about 0.4 pounds per cubic foot. Our material is compressed over 10 times, to about 5 to 6 pound density and it takes some serious glue to hold that springy mass of glass fibers together.

3) We have made non plastic glue acoustics. Years ago the top vocal talent in Japan lived part time in Malibu and wanted a west coast vocal studio. We got the job. We ended up with a studio that sounded great and yet had zero glue, zero plastic, zero formaldehyde and even zero paint. She gave all the protytpe products a sniff test before we made anything. Still, I was scared to death that she would start sneezing or her eyes and nose would begin to run. When the studio was done, she loved it. We called it our “hypoallergenic studio”. You guessed it, it was structurally made out of 100% stainless steel screen and a very rare type of sound absorbing material that is made out of 100% pure condensed glass vapor, not fiber. It is sub micron in size 10 times finer than fiberglass) and 100% fiber free because of how it is made. It is normally used in the manufacturing of molecular filters.

This wonderful sound absorbing material is twice as good as normal fiberglass sound absorbing and we supply it. It is called “WallWool” and it is not itchy at all. I believe it is the sound absorbing material of the future, only time will tell. The downside so far is that it is a blanket type felted material, a glass version of the blue jean fiber sound blankets that you can find out there these days. Felted blanket materials, like heavy vinyl, are limp sheet goods, which by their very nature are very difficult to hold in place.

The only way a bass trap works is if the sound pressure pushes air in and out of the sound absorbing material. It doesn’t work if the sound pressure actually pushes the sound absorbing material around. The core material for TubeTraps is very strong and doesn’t deflect under sonic pressure. Limp materials have no strength and are easily pushed around by the powerful sonic pressures. It takes lots of extra $upport to hold limp materials still while they are being battered by bass sound pressure.

Amazing how a question just a couple words long can generate such a long winded answer. I hope I answered your question about formaldehyde, well enough for round one, and then some.

When do we get to talk about the QSF around here? I thought this was the QSF discussion group. Has anybody here even heard a QSF recording space? Ever stuck their head inside a QSF recording space? Anybody ever flipped the reflectors inward to get that Haas saturated sound effect or outward for that traditional studio dead sound? What tricks do you have to pass on about QSF successes? What limits have you run into using the QSF?

Thanks for having me.
Arthur Noxon
www.tubetrap.com

Ouch.

1) Ethan says: “It depends entirely on the thickness and rigidity of the cardboard tubes. If you want to DIY a tube trap, you should imitate the way ASC makes theirs. In that case you'd cut it in half to get two half-tubes, and stuff each half with absorption.”

I want to be gentle but truthful. This comment is very, awfully misleading. ASC does not and has not ever cut a sonotube in half and filled the inside with sound absorption material. This is not, definitely not, and nothing like how a StudioTrap is made.

It does seem doable and I did address doing it in another post. However, I was just contributing my experience towards building this widget. I never built one, I don’t know how it sounds. I don’t know if it sounds good or bad. And after all is said and done, it’s how it sounds that matters, first and foremost.

I want to assure anyone who is interested. For the record: The TubeTrap and the StudioTrap are built exactly the same and are not built anything like how Ethan says.

2) The idea of a sonotube hanging in front of a sound panel does not work. I’ve tried something like that. It does works in the treble but it fails to work in the bass. The real QSF system backscatters the treble and vents the bass. You can’t absorb (vent) bass with 2” sound panel. If you don’t vent the bass you end up with that tubby vocal booth sound.

Also there ends up being a chatter stored between the sides of two cylinders that is a smearing effect. It’s just not clean and sparkling.

3) I have an idea. Get 8” sonotube cut 7’ long. Glue foam on the back half, good thick dense and soft upholstery or mattress foam. Pug the ends of the tube up with more foam so the tube doesn’t honk. Figure out how to stand the tube up so it doesn’t fall over. That should work. Use QSF out in the open, not against walls.

That’s it. Now I really need to get back to work.

Arthur Noxon
www.tubetrap.com

Is the above apply to Poly's/cylindrical diffusers too? Or only to half cylinder tube? The size of a poly is chosen in relation of the size of the room? Reflecting below 500hz with a poly is not good?
Why the axes of symmetry of the poly's on different room surfaces should be perpendicular?
A room full of poly's of the same size it is a bad things? What size or sizes of poly work best for a medium size room with drums?

Of course, and my point was only that a totally enclosed cardboard tube is even farther away from how your fine products are built. Thanks for being here to clarify.

--Ethan

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