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Bantams MTM Underway...

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  • joe_bernardi43
    replied
    those look great! I wish i could make it to DIY Indiana.

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  • Millstonemike
    replied
    Looking good.

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  • tomzarbo
    replied
    These are pretty close to being ready for measurements.

    On the Bantams I used foam speaker gasket foam tape to mount the tweeters, but this time I gave the electrical tape another shot. I was able to get it mounted with either 3 or 4 wraps, can't quite remember -- cutting the seam on the 'ghosted bump' of the beginning of the first layer. I finished up with some flexible caulk speaker gasket stuff that PE sells. It sealed perfectly.



    I had to cut the gasket that came with the ND-91's to get rid of the 'ears' for the mounting holes.



    Then I used about 1/4 of the 1/8" gasket tape to create a very small area of foam for a gasket. Then I cut down on the thickness with a razor blade so I wouldn't have to stress the mounting tabs on the cabinet when I torqued it down. I had some cracking on the center ones the first time I tried it... (fixed it with super glue) so I wanted to create less 'pressure' to be exerted. I wish PE would start selling thinner gasket tape; it would really make life much easier for me.



    So this is what it ends up looking like:





    and the back with it's 12 mounting screws:



    I felt like I was torquing down the head of a 350 Chevy small block with the back. Again I used a very thin width of gasket tape and cut most of it away for a tight seal without over-doing the torquing down process.

    I have about 8-9 coats of wipe-on poly on them and I used Rustoleum painters touch on the back. Two quick coats at one shot.

    Just under 12" tall... just enough wiggle room to put a few thin felt bumpers on the bottom; and I do mean thin. I cut it close with the height.

    I'd really like to get all the crossover bits in the base compartment, but we'll see.

    I have a few leaks on where the back mounts because like an idiot I put the gasket tape on the outside of the screw attachment points instead of the inside... (duh) I'm too tired, making some mistakes so I'm stopping for the morning. Hopefully I can get this one buttoned down and ready to fire up my Omnimic later tonight or Monday.

    TomZ

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  • MLS
    replied
    Originally posted by tomzarbo View Post
    Scott,
    Is it possible that the two woofers in the MTM each had their own airspace and passive radiator, each tuned to a different frequency?

    TomZ
    No. They were all in the same airspace.

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  • tomzarbo
    replied
    Things are getting shiny...





    About 5 coats of rub-on poly so far, probably another 3-4 to go. I always ask my wife what she likes regarding veneer, finishes, and color, and she said no darker on the cabinets, I had planned on toning them down a bit. The baffles are darkening up on their own with just the poly.

    Assembly followed by measurements this weekend Lord willing. I'm really excited to hear these things start making noise. I'm hoping the extra bass over the Bantams is enough to allow these to mimic a decent 5-6" two-way. Yeah, I know that's pushing it... but I'm hopeful!

    TomZ

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  • Wolf
    replied
    That would do it.
    Wolf

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  • tomzarbo
    replied
    Scott,
    Is it possible that the two woofers in the MTM each had their own airspace and passive radiator, each tuned to a different frequency?

    TomZ

    Leave a comment:


  • Wolf
    replied
    Nope the tunings will join to one net tuning, even if they are different.

    Later,
    Wolf

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  • tomzarbo
    replied
    Originally posted by MLS View Post
    Looks great Tom. I had a thought about the PR tuning. Could you try tuning one PR to a lower point by adding weight? I had a pair of Polk Audio RTA 11T's that was a MTM floor stander with two PR's tuned differently. That may allow for some lower extension. Just thinking out loud.

    Scott
    I suppose that is possible, though adding weight to these pr's would mean adhesive as there is no threaded rod or disc. Plus I use bass box pro for my box modeling, and with that program both pr's have to be the same. These nd91's can only reach so low. Still, I suspect more extension than the original Bantams. Interesting idea, but without the ability to easily add weight, it's hard to test it out.
    TomZ

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  • MLS
    replied
    Looks great Tom. I had a thought about the PR tuning. Could you try tuning one PR to a lower point by adding weight? I had a pair of Polk Audio RTA 11T's that was a MTM floor stander with two PR's tuned differently. That may allow for some lower extension. Just thinking out loud.

    Scott

    Leave a comment:


  • tomzarbo
    replied
    Kerry,
    Your pic startled me a bit when I saw it, the first one with the words 'dead inside' written on it... I thought for a moment it was my pic and I KNOW I didn't write that on any of my scraps. I like your solution too. That's really going the extra mile; It really takes a BUNCH more work to get these little last touches finished up. I guess it's what separates the men from the men with a lot of free time. I'm not sure I could have made that method work in this instance, it is really tight in there. I had to do some surgery on the ND91's to get them in there.

    I used those little screws #2 x 1/4" stainless, two per corner to get these mounted. Seems to be sturdy enough. The walnut is hard enough to give decent bite with the little bit of thread seated in the wood. Never would work for MDF.




    Here's a comparison between the little screws I'm using to hold the ND91's compared to our standard #6 at 3/4" long... Tiny buggers, no?



    They're starting to look like speakers almost:



    Binding post ready to go:



    More interference issues. Mounting screws for the Peerless side facing Passive Radiators:



    The solution:



    It seemed like a better alternative than shortening the screws.

    Ready for poly:



    I have the first coat of poly on the cabinet and bases, just the veneer, not the hardwood bits. I wanted to get Eileen's input with the samples I did on how dark to go with the walnut bits. I did several samples with darker/lighter stain and straight poly.

    Turns out she likes the look of the poly the best, which makes it easier... I like that better too. Too dark and you loose the light-shifting effect of the quilted grain in that walnut, I'd like to keep that if possible.

    Next weekend I hope to have these together and ready for measurements.

    Tom tired, must sleep.

    TomZ

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  • Navy Guy
    replied
    Tom, this is what I did with my rear mounted ND105-4 in my AP3 build. The TC9 is what's shown in the second picture but the ND105 wored the same way. I just used wood screws to compress the plate to the baffle.with a little bit of gasket material.



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  • biff
    replied
    Thanks Tom for the kind words - those do use the 3" radius roundovers for the corners, the compound angle at the top was so much fun, lol. In this case those Davis drivers frames are like Focal flat side rounded corners, so the back part of the baffles were cut flush for all three drivers sides, drivers mounted to the front mahogany, then that piece screwed and glued to the cab. I have found the split baffle makes the working much easier, for me anyhow.

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  • Wolf
    replied
    Some people have had ingenious ways to mount a rear-speaker setup. Mark65 used a ring that came a bit proud of the inside wall, and used a clamped sort on the thicker baffle areas to secure the ring.
    I don't recall whom, but others have used a set of dowels/blocks on the mounting points in the same manner. Others have bolted through the baffles (Paul Carmody?) like in Jeff's Continuums. I think you used some kind of split washer at some point to keep a driver in the mount. There are many ways to do it.

    Later,
    Wolf

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  • tomzarbo
    replied
    Originally posted by biff View Post
    Tom those rear mounts are def the way to go, so elegant and effective. If you need to do that again on such thick stock you might consider splitting the 7/8 board on the bandsaw into like a 3/8ths thickness cut for the front of the baffle with the roundovers for the drivers, then you can cut the back 1/2" on a scroll or jigsaw for the back part of the baffle, glue them back together and they will look just like yours but be easier. I did that with these, mahogany cut for the face laminated to MDF that was cut out oversize for speaker frames using Davis 16s with the odd frames. But yours are gorgeous.
    Wow, those speakers are just amazing looking... super nice!

    Took me two reads to understand what you were saying but I get it now. I have a band saw, I guess I could have pulled that off! Plus I could have maybe included some sort of blind nut to mount the drivers with on the inner part of the baffle, or some kind of mounting system. It gets complicated the smaller you go.

    I think I remember you working on those speakers awhile back, you used the large radius roundover pieces from MDF from that online supplier, right? I've used them before as well, possibly at your recommendation? Brain is fuzzy these days. Anyway, beautiful speakers, they are works of art.

    TomZ

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