Zaph and the MTM buyout

[Spanky Ham]

I couldn't resist Zaph's latest blog where he mentions the PE buyout of the MTMs. I bought five of them with the belief that they will make a good present for someone. I hope John comes up with a nice inexpensive crossover for this project. Is anyone else going to buy these? Jed, you seem to be buying everything. Are you in?

[Gir]

Already sold out!

[Hdale85]

Hmm..would have been nice to pick some of these up...I have a few family members that would like a nice little HT setup

[jkrutke]

Damn, those are sold out already? They must not have had many.

I just built my enclosures for those yesterday. It was easy because I used 45 degree miter corners, lined everything up flat on a table and taped them together with shipping tape. I put a bead of glue in each corner and folded it up into a rectangle. Seems to work well with small enclosures.

After considering the T/S parameters, I went with about .22 cu ft per MTM. That will work with vented. Sealed seems to get almost the same response no matter what is done with them, given the high Qts and low Vas. With 3/4" MDF on the sides and back, (no front) the outside dimensions were 6-5/16" W x 13-5/16" H x 7-1/2" deep. Internally that was 4-13/16" x 11-13/16" x 6-3/4". Make it that size and the baffle drops in perfectly.

I'll probably find some time to work up a crossover this weekend. I'll post it here.

[Ray Collins]

John,
The technique you are using works well on almost any size box; it is an old cabinet makers system. I also use a Merle clamp from MCLS to assure 90* corners...I don't always cut my miters spot on.

Ray

[jkrutke]

Here's the boxes so far. I did some chamfered edges for looks. I'm not sure if I'll just paint them, or take an even easier route with some stick-on vinyl fake veneer.

Enclosure drawing [PDF]

[peter_m]

Weird, I called them a fews days ago just to know if they were going to be discontinued, the sales rep just said they had plenty in stock and didn't expect to run out for a long time.... Either he was misinformed or someone decided to buy the whole stock... For the price it looks like it was a good investment...

Nice corners Zaph, that's the same technique I used on my B3S enclosures they turned out almost perfect, just have to fill a 1mm gap I have in a few places... I just had a circular saw bolted to the underside of an old desk... improvised table saw. What would be the best tool for such precision cuts?

[Ray Collins]

Peter_m,
Try using a saw board with your circular saw. I used one for several speaker projects before buying a table saw.

Pretty slick John...

Ray

[Tooker]

I picked up 5 of these after John posted they had possibilities and am thrilled at the prospects of having an affordable system designed by the Maestro!
Thanks John for your help to the DIY community.

It would be interesting to know how many of these PE had and where they all went.

Gregg

[craigk]

Zaph I know you do not like off topic, but you might be intersested ??????????

in the process of buying a pair of Focal BE tweeters for a project. would you be interested in running them throught the electric "grinder" to see how they spec out. thanks

[Spanky Ham]

John,
Nice boxes! I know you have a decision on how to finish, but for me it will be painting all the way. I can't wait to see the results of your crossover.


Craigk,
I am usually ok with some off-topic posts as long as they have some relation to the original thread topic. In this case, yours does not. A PM would be better.

[jkrutke]

Here's some design info for this $13 MTM plate:

(Image) - Measured drivers in-box
(Image) - Tweeter harmonic distortion
(Image) - Woofer harmonic distortion

Starting out with some individual driver information, just to get an idea of some capabilities of the drivers. The in-box measurement is in the one detailed in a post above. Not too many problems with the drivers. Workable enough for something in this price range. Smooth, with no major issues in the non-linear distortion. I had to use a non-standard semi near field measurement technique for the HD sweeps, since I did not have an enclosure yet. The woofers are slightly insensitive but somewhat higher impedance. The impedance when paralleled shouldn't toast many cheap receivers, and the sensitivity in that case will be merely low instead of bad.

(Image) - Crossover with modeled frequency response and impedance (3kHz 3rd order)
(Image) - As above, actual measured with filter in place
(Image) - Measured horizontal off axis

This design is meant for a freestanding stand mount setup. In other words, the L and R but not the C. It's a relatively simple 3rd order at around 3kHz that offers controlled vertical dispersion. For those trying to figure out which components to buy, don't sweat the details. Just get close, and DCR is not important. R11 above is a real 1 ohm resistor, and the only sensitive value is the .08 inductor. (.10 will miss the notch center frequency a bit)

Getting some actual measurements correlates well with the model. Diffraction ripple smooths out a bit off the horizontal axis.

While there is only a few dB baffle step compensation in this design, when run full range in a freestanding setup they still sound a bit bass heavy and warm due to sub-100Hz distortion. These speakers really need a sub with a proper active crossover to handle everything below 100Hz. That effectively removes the mud and turns it into a pretty good sounding system.

(Image) - Crossover with modeled frequency response and impedance (2kHz 4th order)

This design is specifically for horizontal center channel use. It maintains a taller vertical listening window which becomes the horizontal window when laid sideways. There is very little BSC in this design as it will typically be placed on top of a TV, and a mild rise up to 2Khz should preserve dialog in typical installations.

If the speakers will be wall mounted, this is probably the crossover to use for that also. Be aware that all the standard wall mounting disclaimers apply - if it doesn't sound good, blame your crappy placement rather than the design. I'm less inclined to care for the rear channels, but for the front left and right you really should not mount these on the walls. Use the other crossover and a set of stands for that. Or if you want, build the design into a floor standing tower. Put a couple of actively crossed over subs in the bottom chamber.

This is about all I intend to do for this design. I won't be pouring detail into it like I typically do for my other posted designs. (doesn't seem worth it for a discontinued buyout) I can say that those of you who managed to get some of these before they sold out won't be disappointed with your $13 purchase.

Here's a quick comparison with the nearest cost level system I have in the house right now, the ZBM4: The ZBM4 performs better in the bass even though it's only one 4" woofer. There's a little less mud there and I have no problems listening full range at low levels. This MTM plate really needs a sub to shine. Not surprisingly, the $13 plate beats the ZBM4 in output capability however. Otherwise, they sound similar with the differences probably a result of the power responses of the MTM and TM designs.

Mine will be dismantled to be painted. I'll post a picture later when they are finished. Paint takes a long time to dry in this cool weather. (basement) I actually tried the stick-on vinyl and peeled it off because I didn't like the way it looked.

Edit: I also have the following:

(Image) - Measured T/S parameters for a single woofer
(Image) - Sealed and vented curves of 2 woofers in a 6 liter MTM cabinet

Note that I only built the sealed and I didn't try the vented. Vented would require a somewhat high tuning, leaving the woofer to unload anytime there's any content at all in the bottom octave. Still, vented may lower distortion in the 60-120 Hz range by nature of lowering excursion, so it may make running full range more tolerable. If anyone tries it, let me know how it works.

(PDF) - Enclosure design

Finally, just to summarize everything in a single post, there's the cabinet design. The plate drops into it and bolts into some gussets nicely.

[jkrutke]

Also, I'm not interested in testing any Focal drivers.

[benchtester]

5 buyout MTM plates available

I have 5 of these PartsExpress MTM plates; but I have had to pare down my project list. They are New-In-Box.

I will let them go as a single lot for cost and shipping from Calif.. Send me a PM if you are interested.


*** SOLD ***

[dawaro]

I have 5 of these PartsExpress MTM plates; but I have had to pare down my project list. They are New-In-Box.

I will let them go as a single lot for cost and shipping from Calif.. Send me a PM if you are interested.


*** SOLD ***

Damn that was fast. I have been trying to find some of these since they sold out...

[jkrutke]

David, you can have my pair for cost and shipping (from Wisconsin) if you want them. PM me here.

My enclosures turned out so good that I want to use them for another set of drivers.

Edit: Gone.

[dmalphur]

I wasn't able to purchase any of these, but this might interest those who did. These MTM plates look identical to the Cambridge Soundworks Newton Series MC300IW In-Wall Speaker here. Nice discount from the MSRP of $199 each.

David

[ocool_15]

dmalphur,

The name Cambridge Soundworks came up on another buyout at parts express(289-096) shortly before these came in. It looks likely that is the company.

Lorne

[Spanky Ham]

Damn, I cant believe it has been this long. My speakers are still sitting in the shipping box. Hopefully one of these days I will get settled and build these out.