Otica h-frame MTM questions for Danny and Ebag4 plus other stuff

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lacro

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Seam hiding MDF is a challenge for sure. Epoxy can help hide the seams, but I find the flexible (relatively) epoxies are a better choice. The seasonal temperature/humidity changes that cause the MDF seam print through can be helped with epoxy. Which epoxy you choose can also make a difference. Wests system epoxy is a great product, but it is one of the hardest epoxies, almost brittle. An old wood strip canoe/kayak builders trick was to use System Three epoxy (slightly softer) for initial coats, and use Wests epoxy (very hard) for the final coat. In theory the underlying coats allow for some movement without cracking, and the hard final coat adds abrasion resistance. Speaker cabinets don't flex like a boat, so this is probably not an issue. However, I prefer non blushing flexible epoxies with slow hardeners (longer pot life) for all applications.

On my last speaker build a X-CS Encore center channel, I used thickened epoxy for gluing the panels instead of yellow carpenters glue. Then I coated the cabinet with Raka Epoxy (slow hardener) thinned 5-10% with Lacquer thinner. I waited a day, and scraped off any runs/thick spots with a utility knife blade, and lightly sanded the surface. Then I applied 2 more not thinned coats of epoxy, sanding between coats.

Thinning epoxy is normally not a good idea as it can weaken the epoxy, but for speaker building, it's not a problem. The penetrating ability of the thinned epoxy, especially on edges really stiffens the MDF. The subsequent coats of not thickened  epoxy make for a nice dent resistant hard surface that helps prevent seam print through.

If your going to paint the cabinets, It's best to use some type of transition primer over the epoxy as some coatings have solvents that might attack the epoxy. I just use Zinsser Seal coat (shellac). Also, I wait 5-7 days for epoxy to fully cure before applying anything.

Epoxy has an extremely long shelf life. I have used 15 year old epoxy with no problem. The pumps do make life easier but I don't use them for accurate measuring, just for transferring to mixing cup. I prefer to use a digital gram scale to weight the epoxy/hardener. I can mix very tiny amounts using the scale. Most epoxy suppliers list their mixing ratios by volume and also by weight.

mlundy57

Larry,

Which of the Raka resins and hardeners do you prefer?

Mike

tosob

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Can you veneer over the top of the resin? Would you use wood glue or veneer over the resin and wet it out like you would glass?

ebag4

I'm still trying to figure out that bottom portion of the MTM you did by hand with multiple angles.
Mike (Flavo), this is something that I posted for Mike (MLundy) yesterday, I thought it might help to clarify:



It's not completely accurate because the cutout for the MTM base actually has a back portion, but it covers the basic concept.

Best,
Ed

flavo

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Ed, I've been following your post quite closely so I saw this when you posted over there. It's very helpful and I'm very appreciative.  :thumb:

There has turned out to be a wealth of knowledge being posted in here. I'm 100% positive that all of it is going to be quite helpful to me and likely many others.

Thanks everyone  :D

With the servo kits:
Wiring from the amp to the speaker. I'm assuming I'll need hook up wire and a connector. Danny offers the Neutrik so I'm assuming that's the best option? When I get that from him, does it come with male and female ends and the female end will get inserted into the H-frame?

The servo subs will be used for both my 2 channel rig and my HT amp. Is there some sort of switcher that is recommended for this process so I don't have to keep switching the plugs out?

The same goes for the MTM with serving double duty. Can I use a switcher of some sort without degrading the signal?


Captainhemo

Yeah,   the wire and connectors Danny sells are great. You  do get a male  / female combo.  People do it different ways.  Some put the   female connector inthe cabinet, some put it in the amp box and leave a pig tail  out the back of the sub with  the male conector.  Some even  put a female connector in both the  sub cabinet and the amp box then make a  cable  with  a male connector at each end.
In any event, it's very important to be sure not to cross anything, sometimes   the sub will still  play when wired incorrectly but it won't function properly.  Sometime , depending on  how you mistakenly cross wires,  you'll end up with a   a very loud buzz, and not the kind you want  either   :lol:
I did up some wiring diagrams  and posted in a  wiring  specific thread that may be of use

http://www.audiocircle.com/index.php?topic=149708.msg1600884#msg1600884

If you  are  planning to watch  movies  with long drawn out bass/explosion type scenes, you'd  be better of with a sealed  12"  servo sub for the HT duty.  This really wasn't what the Ob subs were designed  for
As for the switching,  can't help  you  there but I'm sure  some others will  jump in.  Personally, I don't like to add  to  the signal path if I don't have to....  IIRC,  Mike has used both sets of  inputs on the A370, one for 2-ch  system input, one for HT system input , that may work  for you  at least for the subs ?



jay

lacro

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Larry,

Which of the Raka resins and hardeners do you prefer?

Mike

Mike,
There are lots of good epoxies, and everyone has their favorite. I just settled on Raka after having consistent good results building boats. It has all the attributes I wanted.  I like 127/350 mixed 100 to 44 ratio by weight, 2 to 1 by volume.

Here's the description of the 350 hardener from Raka site. I feel it's a pretty accurate description:


DESCRIPTION OF SPECIAL HARDENER 350 NON BLUSHING

We feel this hardener is second to none in its ability to resist blushing, white clouding and water spotting.   Blushing is the greasy surface film on cured epoxy caused by humidity in the air as the epoxy cures. 

We tried many non blushing type hardeners before we settled on the 350 formulation.  Regardless of the most extreme humidity or cool dropping temperatures our tests show this hardener gives an excellent high gloss and clear, blemish free coatings.  This formulation also has the best resistance to cratering and trapped air bubbles in the cured epoxy coating.

Raka 350 like our other hardeners has good strength properties, excellent water resistance and the best general chemical resistance of our hardeners.  Cured epoxy using the 350 formulation will also give better flexibility to resist impact and wood deformation.   The 350
is mixed by volume one part hardener to two parts of our 127 or 900 H.P. Resins. This system has a good pot life approximately thirty minutes at room temperature yet is relatively quick curing compared to other hardeners and can be used in temperatures down to 60 F  .   The wide temperature use ability of this system will simplify the needs of many customers who do not want to have to carry a combination of fast and slow hardeners.   350 reaches a tack free stage quickly and can be sanded in less than twelve hours at room temperature.   350 is more expensive than our other hardeners but when combined with our economical Resins the average price per gallon is the best competitive value around.

Early B.

The servo subs will be used for both my 2 channel rig and my HT amp.

Nah, don't do that. Get a separate sub for HT.

Danny Richie

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Nah, don't do that. Get a separate sub for HT.

The servo subs will work great in both applications.

flavo

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My understanding is that the h-frames aren't made for HT but more for musicality. My plan was to build the h-frames and I talked myself into building a sand box or similar sub for the rear of the room. Well once I talked myself into that I figured the Otica MTM portion was only another $600 over the sandbox sub. Funny how I can talk myself into this stuff. Not that I should be spending the money.
So while the plan was to get the low end dialed in and then do the MTM when I had the cash to do it. Now I'm guessing the sandbox is on the back burner. BUT, it will be getting added to the system in the near future. Maybe I'll sell some stuff that's laying around.  :lol:

WC

How small of a room would the OB servo subs work in?

I have an L shaped room. The top of the L is 8' long x 9' wide. The bottom of the L is 8' long x 17' wide, but the usable space is more like 8' x 11' with the 11' wall having an opening to another room 30" tall x 10' wide up 30" from the floor. 8' tall ceilings. Could it work on the 9' wall at the top of the L or at the wider 11' space at the bottom of the L (with the wall opening)?

Captainhemo

You can pretty much place them right up against a side wall as there are nulls  to the side of each  sub. But, you need  to have the sub towers pulled out  at  least 3' from the  front wall so there is room behind them.
I think Mike is using a pair  in a prety small  space with good results,  12' by  12'  if memory serves me  right  ?

jay