DTQWT-12

[richidoo]

Here you go Face:
http://www.audionervosa.com/index.php?topic=3070.msg37684#msg37684

I got mine from Bradco Supply a subsidiary of ABC Supply. There are a lot of warehouses around the country. My local warehouse in Raleigh did not have it in stock, but they transferred a roll up from Charlotte warehouse for free.  Total was about $80. I learned about it from the speaker designer Troels Gravesen published an email from a guy who used it with good results.
http://www.troelsgravesen.dk/tips.htm   scroll down to "Mail from Michael."

[richidoo]

I have all the bitumen sheets cut to size and ready to  glue them in. The low odor contact cement does not work well at all. Apparently the sticky window in the drying time is very narrow, or is just sucks. Back to the store for the full odor good stuff.   Also discovered that the contact cement doesn't stick to the heat activated adhesive on the back of the bitumen. My heat gun was hot enough to melt the tar substrate but not hot enough to activate the heat glue layer.  It is just a thin layer of polyethylene-like plastic, so I'm not surprised glue won't stick to it, it is meant for torch heating and a huge roller.  Worst case I'll stick it on with 3M Super77 but I would prefer more control over where the glue goes because I still have wood parts to glue on and don't want to contaminate those spots.   

A little frustrating right now! But nothing we can't figure out. My son graduated from elementary school yesterday so he is home helping me out.

[richidoo]

Henry and I figured out a system to streamline the bitumen install, and it works good. I completed bitumen on the first speaker tonight. My fingers are covered with 77 glue, mixed with tar and garage floor soot, and it doesn't wash off. We had finger food for dinner tonight and my girl was grossed out when I licked the olive oil off my blackened fingers. 

Super77 works good. Spray it on heavy and place it on the wood immediately. The carrier solvents will evaporate into the wood quickly to tack it on. Within 10 minutes it is permanent. Next time I buy the Rubberoid I will get it without the heat "glue" on the back. On some of the pieces the glue layer was loose from the tar and had to be peeled off before I could use 77.

The bitumen does help to take down the higher freqs of the wood resonance. Even on a knock test of a 12 x 12" MDF board the improvement was obvious. The lower freqs still remain though, which is why bracing is so important.

I installed all the braces into the cabinet after the bottom half of bitumen was installed.  Then I used a couple pieces of wood blocks to jig the braces to the center height. Then I did the bitumen on the top half.

Tomorrow I do the bitumen and braces on the other speaker, then felt and acoustistuff and I can close it up.

Pics coming.

[richidoo]

Some pics:


Braces, not glued, before damping, from bottom of speaker


Braces, from top


GAF Ruberoid rubber modified bitumen roofing membrane. See previous post for product details. Get the plain unglued version for hot tar application. not the heat and stick version.


10 x 1 meter x 0.1" thick, cut in half, flattening in the sun. Like my roses?   


Damping bitumen installed. What a bitch of a job. But it works!


Detail of damping and braces, rear bass horn, looking from top. The bass drivers are separated by the narrow brace closest. No damping is needed near the woofers due to their frames' rigidity.


Braces are damped both sides. Bottom of front horn is not damped, due to no room to install it, and front baffle is already two layers of dissimilar wood, ply and MDF, laminated together with glue.


Brace and damping detail, looking from top.


This is the side (aka lid) with the damping. The internal baffle edges and braces will glue to the undamped strips and holes.  And yes, it fits! After a bit of trimming. On the second speaker I was able to mark the location of internal baffles on the lid better than the first speaker, so the damping of the second lid will be easier, because the lines are accurate.

[djdube525]

I see you got booted out of the kitchen once you started working with the GAF Ruberoid material. 

I'm amazed at how quick the progress is coming along. Looking really good!

Dave

[richidoo]

Thanks Dave!

I moved outside mostly because of the fumes of the glue, but you're right the raw material is clean but the installation process is dirty. I'll be using the same glue again for the felt, then I'll start the wood finishing which will also require ventilation. But I'll be back inside asap!

[rollo]

Richidoo looking good there. Does the Bitumem have an odor ?



charles

[richidoo]

Yes, but it is very slight. I must hold it up to my nose to smell anything, and even then it is slight. It is a cross of petroleum and rubber. Old school "bitumen" was canvas dipped in asphalt. This is FG cloth with a layers of rubberized tar on each side. The rubber seems to lock in the odor of the tar. A couple weeks ago before I ordered it I visited Home Depot to smell the roofing products.     The other brands had a very strong asphalt odor, but all the GAF products with rubberized asphalt had hardly any smell.

After I cut the bitumen pieces to size, I kept them inside for a couple days, warehoused in the dining room, of course. Nobody smelled anything. I have a bionic sense of smell, and I couldn't smell it at all. So it should be OK. I was worried about it until I smelled the GAF products at home depot. Then I ordered it with small chance of stinking. Lucked out.

I think I would use GAF Ruberoid SBS Dual Smooth next time, without the heat weld film, which just peels off and prevents good adhesion to the speaker, but it is not quite as heavy. Good adhesion is more important for vibration treatment.  This stuff will work good inside component metal cases, as layers inside TT plinths, etc.

http://www.gaf.com/Roofing/Commercial/Products/Modified-Bitumen-Roofing/Ruberoid-Modified-Bitumen-SBS-Membranes/Ruberoid-SBS-Dual-Smooth.aspx

[Face]

I left a roll of Storm Guard in my car few a few hours on a sunny day, big mistake.  The car stunk for a whole day, and the roll itself had a strong odor for a few days.  I couldn't walk by it without making a disgusted face.   

[djdube525]

AHAHAHAHAHA...

Rich... I just noticed the caption under your Avatar - "Like a G-6"...

I never have paid attention to the lyrics in that song... except for that phrase. I was wondering why someone would write a song about a Pontiac.     

[richidoo]

I left a roll of Storm Guard in my car few a few hours on a sunny day, big mistake.  The car stunk for a whole day, and the roll itself had a strong odor for a few days.  I couldn't walk by it without making a disgusted face.   

That's funny Face!  A bottle of girl's hair conditioner leaked in my car back in college. Talk about stink! I don't know why I was with a girl that deliberately tried to smell like that. Oh, yeah, now I remember. 

Pontiac G6      "Like a G6" by Far East Movement. One of my favorite songs of all time!! 

[richidoo]

All the bitumen damping is installed. My knees are black and my back is killing me.

I also cut out all the felt pieces that will be glued inside for acoustic damping. I am using this felt
http://www.rugpadcorner.com/superior-felt-jute-rug-pads.aspx
It is thick, dense and luxurious, it would even make a nice carpet pad! This will be all glued in by today.

I picked up a bunch of Acoustistuff from Shane last night, thank you sir!  That will go in the closed ends of each horn for damping of the higher frequency peaks generated in the horn. Theoretically we only want the lowest resonance generated in the horn, but the upper harmonics also escape. Acoustic damping helps reduce the upper harmonics which would interfere with the midrange driver's contribution. That's one of the tradeoffs of horns / TL.


Green is the felt, yellow is the acoustistuff.  This pic is the smaller DTWT, not the  DTQWT-12.

Rich

[richidoo]

All bracing, damping and felt is installed. Interior wire holes and exterior binding post holes are drilled.


Felt at top of speaker


Rear horn with felt


Closeup bitumen and felt layers


Lid ready to glue to speaker


Midrange hole


Gluing cross braces with 90 degree angles and weights


Weights on shelfs. The cross braces were aligned with a T-bar perpendicular to the bottom. They lined up perfectly to the lid.


Next up:
Build the crossovers and install them with wiring and binding posts, but no drivers
Stuff the horns with acoustistuff
Glue on the lids
Trim the lid edges flush to the box with router and flush trim bit
Route the woofer holes (carefully!)
Sand, stain and varnish with General Finishes products.
Install drivers
Tip a cold one while the tubes warm up... 

It is nice to be able to see the light at the end of the tunnel.... or is that a train?

[ebag4]

Looking good Rich  !  Even though it is a speaker with large panels it appears you are doing everything possible to keep the cabinets from resonating, well done.   I am curious why you haven't already routed the woofer holes, was there a specific reason that made it best to wait?

Best,
Ed

[richidoo]

Hi Ed,
The woofer's OD is 12.5", and the through hole is 11-1/2". The rear panel width is only 11-5/8". The mounting flange recess will cut into the side panels' edge. To flush mount the drivers I need to cut the mounting flange recess before I cut the through hole in order to use the same centering pin location so the recess and through hole are concentric. Recess must be cut before through hole, so the sides must be glued on before cutting the recess. A little trickier but no biggie.
Rich