Thinking similiar to Statement/Khanspires but ...

[ani_101]

No worries, there are plenty of raw MDF speakers with glue runs down the side, mine included... So if you can get them to a meet, it is always good

[Kornbread]

After some research it seems everything from sheetrock mud to shellac has been used to seal, or prep mdf for primer. Made a trip to the local hardware store and returned with a quart of Zinsser BIN, $15. This stuff was pretty easy to work with. Both speakers were up on the saw horses. I'd paint the up side of one speaker, then proceed to the up side of the next speaker, by the time the second speaker was coated, the first speaker was dry enough to rotate to the next side. The stuff dries quick, feels thick, and the fumes weren't too bad. Did a light hand sanding after the first coat, then coated a second time. I would have gotten the orbital after them, but it's raining again, and I have no dust removal system in my small 'shed'. It looks like it'll need a couple more coats to fill the end grain, especially the bases where there are 4 stacked layers of 3/4".

Has anyone had any problems with body filler or auto body paint/primer when using BIN?

davidroberts, I had already left for the hardware store before reading your post, or I'd likely came home with shellac. ... about the glue/water mix, I always worry about water and mdf. I know it's been proven many times here, but I still worry, plus some said it was difficult to sand.

Now, how do I get rid of the seems? body filler?

ani_101, Looks like you're from Minnesota. Hopefully, one of these days, I'll be able to join jhollander, and his crew on a pilgrimage to a meet nearer you.

Guys, I appreciate the replies.

There's another 4 channel chip amp (tk2050), power supply, minidsp, and binding posts on the way.

[davidroberts]

Right now I'm trying to figure the best way to seal the mdf before priming. Looks like a lot of differing opinions. Suggestions???

That is one of those can of worms questions. If you ask ten people you will get 12 different answers. I suggest that you test several methods and find the one you like.

One popular way is to seal the ends by painting a 50/50 mixture of glue and water on them.

I have had great results painting the surface with boiled linseed oil. It has a bit of an odor until it is dry but two coats is all it took. Another method I have had good luck with is clear shellac lacquer. Again apply a couple of coats. Just like the oil the mdf soaks it up rather quickly.

The whole intent is to create a moisture barrier so that the mdf doesnt expand/contract with humidity changes which in turn will make the seams visible.

I used the boiled linseed oil method on some craftsman trim installed in three rooms in my house and so far it has been installed for a year and I have no cracks or blisters.

I believe there is actually a thread here by LunchMoney were he tested several different methods.

[Kornbread]

Amazing progress.... these should be some heavy hitters. Where are you located, and would these be coming to a DIY meet near you(me)?

Heavy is right. My back has met its limit.

South East, (swamp east) Missouri, a bit of interesting local information IIRC, regarding the largest swamp draining effort of its kind: http://www.semissourian.com/story/1900459.html

I would love to attend a meet, but work and school will more than likely rule that out. We'll see...

For me, finishing is the hard part, and if I can't get these looking good, I'd be too embarrassed to show them to anyone, no matter how good I thought they sounded.

Right now I'm trying to figure the best way to seal the mdf before priming. Looks like a lot of differing opinions. Suggestions???

Kool, now a line under everything typed, and it's red. I really dislike this forum software.......

[ani_101]

Amazing progress.... these should be some heavy hitters. Where are you located, and would these be coming to a DIY meet near you(me)?

[Kornbread]

These things are bloody huge! They'll be nearly as tall as the man fridge when the feet are on. Out of 3 sheets 3/4" and 1 sheet of 1/2" mdf, there is less than half a sheet of each remaining. My aching back can attest for their weight.


Easy part is done. Eh ... not going to mess with it, just turn your head. There are a few red spots on the left one, and a trail on the floor. It seems every project I take on requires a contribution in blood.



Plans are to finish these in a quality dark (cherry) red automotive paint. That's the plan, but not necessarily what's going to happen. What are my options in sealing the mdf in preparation for primer? There are a couple half gallons of fiberglass resin left over from a sub box build. It worked excellent as a weather proofing agent. Can I use it on the bare mdf, bondo later, then primer, paint? Or will the resin be hard to get nice and smooth?

Glue and water mix? But how does that withstand primer? Will it lift years later?

What are my options in prepping the mdf? Keep in mind, these may be sitting for a while before I get around to painting them. Finishing is always the hardest part.

I'll hit Menards for some feet and denim tomorrow, or possibly rockwool from a local retailer. There about the same price, but I'm thinking denim will be the better sounding option, especially for that lively mid enclosure.

I'll try and get some dimensional measurements, and hopefully some frequency response measurements, in a day or two.

[---k---]

Wow. You're fast.
Looking forward to seeing your progress.

[Kornbread]

Rain, rain, and more rain.

The boxes are glued and it's time to trim the edges. The rain just won't stop long enough to do it.

Used carpet padding on all walls, added a few squares of 1" open cell foam in some areas, and polyfil in others. This is just for starters. I'll give it a listen first, then start experimenting with some denim insulation. Didn't hear any resonances humming into the larger chambers, but the mid enclosure definitely has some nodes. It needs work. Out of supplies at the moment, will have to pick up more when everything opens up tomorrow.

I was afraid there might be issues with mounting, and accessing, a passive crossover behind the lower woofer, if a window brace was used. And that is a lot of area without bracing, so I glued an extra 1/2" panel to the inside of the long walls instead.

[Kornbread]

Getting as much work done as possible while off work and out of school.

Used 4" pvc sewer drain for the vent. Mounted a 4" straight coupler in the bottom of the cabinet, then cut a length of 4" pvc, and glued a scrap piece of mdf to the end. Hit both ends with a 5/8" roundover. As long as I don't glue the pvc coupler, and pipe together, I have almost 3 adjustable inches to play with on vent length. This gives me some room to tune.



Front baffles cut and relieved. i Messed up; didn't get my measurements right with rs150, which left the tweeter barely overlapping the mids. Grinder .. literally ... grinder.




Gluing the mid enclosure up.



The bases coming together. Went a little overboard with the glue.



The shop is cool, so it's taking the glue a while to set. Need more clamps.

And thanks, ___k___ I didn't realize the tweeters were the same diameter.

[---k---]

No, still not decided on the tweeter. The xt25's are laying here, unused, but wouldn't they be a step down from the rs28? I know the xt25 has a good rep at their price point, but are they really comparable to the rs28's, or better? Whichever way I go, I can only cut the baffle once, so have to settle on a tweeter before finishing up.

And I have found reports of the basic minidsp 2x4, having a detrimental effect on sound quality. At the level this speaker should perform at, this may be a concern.

...time to get back at sticking boards together.

I've read a lot of good things about the xt25. Depending on who you talk to, it might be a small step down or not. I thought they both needed the same 104mm cutout, that's why I thought you could try one and then swap the other in later if you wanted to. Screw holes might be different, but just rotate the tweeter and make holes for both. ... you could always do a removable baffle so you can try different tweeters out later. ... just random thgouhts...

I've also read reports of some MiniDSP being less than perfect. Jon Marsh at HTGuide has posted comments several times. I believe him to be fair, but his comments must be taken with perspective. He is approaching it in comparision to DSP many times more expensive with similarly priced amps and processors, and with $200+ tweeters, etc.
No offense, I think with your build the MiniDSP will be more than sufficiently clear.

[Kornbread]

Have you figured out your tweeter yet? I've always heard good things about the XT25 tweeters. Here the good thing about using a Minidsp is that you can easily swap it out later for another similar size tweeter without having to redo passive crossovers. Minidsps really come in handy for experimenting....

No, still not decided on the tweeter. The xt25's are laying here, unused, but wouldn't they be a step down from the rs28? I know the xt25 has a good rep at their price point, but are they really comparable to the rs28's, or better? Whichever way I go, I can only cut the baffle once, so have to settle on a tweeter before finishing up.

And I have found reports of the basic minidsp 2x4, having a detrimental effect on sound quality. At the level this speaker should perform at, this may be a concern.

...time to get back at sticking boards together.

[---k---]

Moving forward.... all paper on the mids and woofers is definitely going to make it something different.
Have you figured out your tweeter yet? I've always heard good things about the XT25 tweeters. Here the good thing about using a Minidsp is that you can easily swap it out later for another similar size tweeter without having to redo passive crossovers. Minidsps really come in handy for experimenting.

I think with paper cones, you're going to get appearance irregularities. It won't affect the sound. I wouldn't worry about it. If you are, you probably should get the metal version. But of course mine have some scratches and small dents from moving and screw drivers....

[Kornbread]

More parts have arrived, a quad of rs225p-8a, #295-577. Again, they "look" rather unimpressive. One woofer has some discoloration (darkening) near the phase plug that resembles wet paper and some small irregular raised spots on one side. It's not damp, cone feels solid. Quality issues with the cones?

A trip to Menard's has yielded 3 sheets of 3/4" and 1 sheet of 1/2" MDF, a couple new router bits, (going to ebay the large 3/4 round bit).

Harbor Freight just opened a "somewhat" local store. Man ... I could get carried away in that pace, but managed to leave with only a 72" level/straight edge and a pair of large corner clamps for ~$35.

Time to get cutting.

[davidroberts]

I listen to Spotify quite a bit. Am I correct in thinking the silk dome rs28f might be just a bit more forgiving of poor quality sources than the aluminum dome?

From my experience the midrange drivers are more responsible for being forgiving of poor quality sources than the tweeters are. I have worked with Dennis Murphy on the RS WWMT, WMTW and WMT speakers and built both CJD's RS150 MTM and Jon Marsh's Modula MTM. I can tell you that to my ears the metal cone RS drivers sound amazing with good material but they really seem to bring out the worst in poor recordings.

If you really want to put your spin on things and make it your own you might consider the BG Neo3 for the tweeter. I have a set of GR Research Neo3 speakers that use this driver and it is very smooth and non-fatiguing to listen to.

In Unibox a pair RS225P-8 will give you a max spl of 114 dB. 3' ported enclosure will give you a F3 of 38Hz, 1.25' sealed will give you a F3 of 70Hz.

You could always do 4 RS150P-8's in a series parallel configuration. In a 1.25' ported enclosure you will get a max spl of 116dB with a F3 of 60Hz. This would keep the baffle width down and give you a symmetrical look. Once I get my measurement rig up and running I plan to try something similar.

[jhollander]

I'd skip the mid in the tube as it adds a bit of complication and limits your positioning near walls.