Audible Physics +? build

Kornbread

Have a couple days before work resumes and I just cannot sit around the house doing much more than nothing.  A cold front just came through so fishing is going to be slow for a while, not to mention the drop in temperature and how much colder it is sitting in a boat out on the water.  Have some roofing to do but materiel will not be here till Friday.  Since the Sadies are pretty much buttoned up, what better to do than start another build. 

Time to use up some stock of the Audible Physics 6.5" woofer, better known as the MCM buyout part# 55-5615 or the 635-cp2.  Both @isaeagle4031 ; and @jr@mac have used this woofer with good results.  Wanted this as a large bookshelf but realized at the size I wanted to build I would also need to build new speaker stands to have the tweeter at the right height.  Nah.  So it becomes a floor-stander.   

The drawing is out in the shed so I'll post dimensions later.  It will be 1ft³ ported with tuning from 39 to 42hz with an F³ of 34-36hz.  With a 2.5" port, noise might be an issue so the port will probably be on the back, or if there is enough 3" pvc laying around, the port may find its way onto the front baffle.  The front baffle is two layers of .75" mdf. 

One reason for ported is that I did not want it to be a direct copy of Chucks MLTL design (not sure what JR did with the Mortimor design). 

Have not decided on the tweeter yet.  Others seem to like it but Ben seems to somewhat dislike the sb19st-coo-r and that is the one originally slated for this project.  Other than the sb19st, there are a pair of rst28a&f (still have to do the Ben mod) and several Peerless xt19td00-04 laying around here.  PE has the 2" mid on special again so I will probably be placing an order soon and adding another tweeter to the order is a nobrainer.  You know, I do seem to have an affinity to the xt25tg30 and they have this xt25bg30 that looks very tempting ... 

Finally got boy to put down the controller and help on a build.  Out of a full sheet of .75" mdf, we had about 10" left over.  The baffles are drying as we speak. 

Somebody mentioned, was it sand or salt, to help keep the wood from sliding while clamping?                       

     

 

kenrhodes

Salt is the traditional no slip for woodworkers.

Wolf

By all means- don't take my word for it. I dislike drivers that many have loved.
Did you get bad RST28F drivers too?

Kornbread

Still have not made up my mind on tweeter selection.   

jr@mac

I went sealed due to size constraints.

Nice woofer, you will enjoy it. 

Kornbread

Manu specs say Linear excusion P-P Xm 10mm and Max excusion P-P 25mm.  Looking at the thing there is no way it can move 25mm.  Does not look to be enough surround to move 10mm. 

What about the xt19td?

   

ani_101

Would suggest a slightly bigger tweeter crossing at or below 2500, closer to 2k would be better. The sb19 is pretty good, but ideal for 5" or smaller. Any of the sb26 would be good fit

Kornbread

ani_101 said:

Would suggest a slightly bigger tweeter crossing at or below 2500, closer to 2k would be better. The sb19 is pretty good, but ideal for 5" or smaller. Any of the sb26 would be good fit

   rst28? 

ani_101

I have not tried the rst28, so after Ben's mid if it turns out good sure. I tried the sb19 in a 3 way with the rs100p and in a two way with the hivi l6-4r. Though the hivi has a smooth upper without to much breakup, I preferred the smaller mid, even though the woofer in the 3 was smaller and f3 higher - the 3 way mid was the rs150p.

I am currently using the rs150p as a mid with the old rs28f and 15" woofer.

PWRRYD

I used the RS150P-8 in my Jonquils project and I thought its mids were really nice.  JMHO but I think the RS150P was the only really good size in the RS "Paper" line up.  The regular RS aluminum cone line up had a few more winners.

Kornbread

I'll try an rst28 then.  One of them is far enough off that it will get the Ben mod.  May have to mod both to get a matched pair.         

ani_101

Kornbread said:

I'll try an rst28 then.  One of them is far enough off that it will get the Ben mod.  May have to mod both to get a matched pair.         

If you need an extra pair of the rst28 let me know. You can have my pair at no cost.... 

Kornbread

Thanks for the offer @ani_101 but I have a pair of a and f, if I cannot get the f more in line with the other f, then I'll just use the pair of a.  It will be interesting to see if both the a and f can use the same crossover and the difference in sound. 

Got the back/side/a brace/and port glued in.  Going to be slow for a while as metal for the porch roof came in today.  House work comes before play.      

Kornbread

Finished the porch roof just in time as heavy rain is forecast from Thursday thru Saturday.  Now it's time to get back to work on this design. 

Did something a little different to the mdf box; one window brace about 1/3 way from the bottom and then glued thick mdf strips in a sort of broken cross configuration onto the large sidewalls of the four sections so that no undamped area has quite the same size, including the opposing side.    Then unfaced denim insulation, meant to fit between 2x4 studs, was pulled in half thickness and stapled to the interior.  The idea is to have varying thicknesses of insulation throughout the interior without getting too thick. 

Don't know if any of this stuff makes a bit of difference, but doing it made me feel better. 

                

rjj45

It's like Zen, man. We keep trying variations.

Kornbread

It was fine with a light rain and no wind but the rain picked up and the wind began blowing.  My little back porch workshop doesn't have a dry spot left.  These are the panel braces with uneven denim insulation stapled on.   

 

And this is as far as it got before the wind began:

Woolly worms or felt? 

After the baffles are glued on and trimmed,  I'll try to put a 3/4 roundover around the perimeter.  Fingers crossed none of the slots catch and tear.  The slots can be packed with different materials, even multiple materials with different densities.  Felt and chunky yarn here.

Comments???        

 

jhollander

Holy cat shit batman, that is cool.  I'm sure not everyone's taste but I admire the ingenuity. Might test without any felt to see if the grooves break up the diffraction signature.  Well done.

Wolf

It could work like some sound-panels do, and just lay felt over/atop the grooves.

Kornbread

Probably be doing a lot of experimenting with this pair.

Might call them the unibrow.  

6thplanet

Neat idea! I think you should have gone all the way around the tweeter to block the woofers surround effects. Just a thought.... What about different heights of felt on each concentric ring? Kinda "felt wave guide"

Kornbread

Had several ideas for the slot design but experimenting with some left over mdf pieces, before doing the actual baffle, ended badly when the slots were much closer together or when the slot ends were open leaving no support for the lands.  They would always get caught and rip a large chuck or the entire slot land off the board.  Before doing the slots I'd considered a waffle pattern and cutting the slots at different depths, but after the scrap experiments, nope, pretty sure the mdf would tear apart and didn't want to chance it.    

Different heights and materials for sure.  Should have lots of experimenting material from foam, felt, cotton batting, chunky yarn, dowel pins, dowel pins cut into different shapes, mix-n-match of materials, etc. 

Have one box far enough to test. Only went even with the center of the woofer with the 3/4" round then moved the bit back into the router from there up.  Going all the way around at full cut would have for sure torn the slot lands. 

Ideas for more materials to test???      

squamishdroc

Cool idea!

hifiside

Looks good. Wool felt is fun to experiment with.

Kornbread

Will a control baffle need sides or a top for accurate on and off axis measurements of the tweeter? 

jhollander

Yes for off axis, but you can use cardboard

Kornbread

What about Zinsser bin and affordably priced automotive paint?  So far, lacquer paint on lacquer primer sprayed over Zinser bin has staid put on the big towers but lacquer is hard to find around here and the colors are very limited.  Affordable options?  Really don't want to go rattle can.      

4thtry

Cool.  I think the lighter gray felt (left side) looks better in your picture.      

jhollander

I've not a seen a cheap auto paint. The General finishes water based paint sprays well.  The weather might be a bit of an issue.

Kornbread

Think it reached 50 today, took the boxes outside and sprayed bin.  It dried enough after a few minutes to move them back into the shed.  How much alcohol are you guys thinning bin with for hvlp spraying?  Both guns are Harbor Freight.  No matter what I do, the spray is too coarse and I'm thinking the bin is too viscous.

House paint?  Does that need a clear coat to get a nice deep shine on?   

jhollander

I'll cut up to 50% when I spray bin, I use a 1.8 or 2.0 mm tip and bump the pressure up. I usually only spray bin as a filler coat then after blocking prep with sealcoat, 3m pad before a color coat.

House paint is bad. If you can't get General finishes then a high quality trim paint like Ben Moore Advance, but again that's water based.

Pretty good luck thinning and rolling rustoleum, but you have the fumes and long dry times to deal with.

Kornbread

Thanks John.  Pulled the boxes out of the shop long enough to finish priming them, 42* outside, and the bin went on nice and smooth.  Much better than the rough previous attempt.