New DIY MTM Towers designed by Dennis Murphy and Paul Kittinger

[AuralFission]

Fin.

 

[AuralFission]

I'm very impressed by the sound of everything. It comes across as clear without being piercing. One of the reasons why I wanted to try a ribbon tweeter. It sounds very smooth. To me, it sounds good with all kinds of music. As others have said, it doesn't need a subwoofer for playing music since it hits deep enough. With movies, it's fantastic. I can crank it really loud and there's no distortion. Everything still sounds clear. I built a center channel and a subwoofer since I wanted to use it for home theater. The sub is a sealed 12" Rhythmik and the center is the matching kit from Meniscus Audio. I'll post those builds later.

This is really my first foray into making something like this. Without a doubt, the hardest part was finishing. It's easy to screw something up when painting the baffles and getting a smooth finish is haaard. I'll admit, the finish isn't perfectly smooth, but I'm pretty happy with it. Thank you all for your previous posts since they helped me build confidence that I could build it myself before I even bought anything. I hope my posts do the same for anyone considering the same build or similar builds. If I ever have kids, I hope to give these to them so they can play their favorite music for their neighbors.

 

[Swerd]

@AuralFission

Wow, I loved your build photos, they're excellent. Thanks so very much.

You did the builds all with the Meniscus Audio kits, right? They look very good. I especially like their little terminal strips that are so useful for building crossover boards.

This was "your first foray into something like this"? You mean building speakers, right? From your photos, it doesn't look like your first time with wood working. Your workmanship shows. I loved your home made clamps with the built in cauls.

 

[TLS Guy]

Great work and build photos, which show that DIY is all about better speakers and NOT cheap speakers.

 

[KenM10759]

I also appreciate all the photos of the build! So I'm clear, you used plywood rather than MDF? Was that birch plywood and was it cheaper than MDF? I though MDF had the better damping qualities.

The photos of the veneer process were what interest me the most, in terms of cabinet build. I've been thinking about making some speakers like those, but would be taking a lot longer due to having to work over at my son's shop and build two pairs (one for him, one for me.)

If possible, I would like to build one pair with that same kit of components and one perhaps with "upgrade" LF drivers such as Revelators. If there would be a sonic benefit, I'd want the best crossover components for the job too. That would allow me to buy a little at a time until I had the full kit ready to build. Is there an "upgrade" list of components available?

 

[BoredSysAdmin]

@Steve81 Please sticky this thread

 

[Swerd]

Anyone who is interested in a copy of the ER18 MTM design with full info and diagrams and a part list with prices as of March 2017, please see the PDF files attached to the first post in this thread.

 

[roadrune]

And for anyone considering theese i have a completed pair, including center speaker, all with ribbons for sale.

They are in Norway but i can ship anywhere, whith or without cabinets.

 

[BoredSysAdmin]

Thank the god to instill a bit of wisdom back to photobucket and stop breaking half of the internet - ie: the Photos are back !!

 

[moves]

I'm a little late but excellent paint job!

Now here's where the fun begins. I had a gallon of high gloss, oil based polyurethane laying around and thought I'd experiment. I originally wanted to spray it on using the HVLP gun but after I shot a test piece, there's no way I'd want to do that again. It got on EVERYTHING and surface wasn't that smooth. The paint was a little messy and somethings got overspray on them. With poly, everything gets nasty. My arm hair was forever frozen in the overspray of polyurethane.

So out with the HVLP gun and in with the cheap, foam brushes. I did the test on the top surface of my speaker stands that have the same paint. I applied probably 6 coats at 2 coats a day. Of course applying poly with brushes leaves pretty extreme brush marks but because I built it up so much, I could wet sand it smooth pretty easily without sanding through the poly. By the way, it's advised to let the final coat of poly cure for at least a week.

Here are some pictures of my progress.


Here, I've done some wet sanding to smooth out the brush strokes with 600 grit.

1000 grit.

2000 grit.

After sanding, I used some Maguiars Cutting Compound followed by a random non abrasive polish I had laying around. I have to stress that these products applied the way I applied them is not ideal, it's simply what I had laying around.

Here's what 10 minutes of work looks like.

And here's what about 20 minutes of work looks like. Again, if I had better products, I probably would not have needed to spend so much time on them.

Here's a picture of a somewhat finished surface showing a reflection of my
TV. The result is an almost mirror like finish that feels like glass. I really like the end result. It's a lot of work but it's very rewarding. When I return from Utah, I will start on the enclosures!

 

[roadrune]

Thanks for the frequency response traces. I am waiting for Dennis Murphy's response. I hope he can make sense out of them.

I take it Dennis never came back?

Did you ever hear back from Dennis, @Swerd ?

 

[Swerd]

Did you ever hear back from Dennis?

No I never did. Lately he's been very sick, was in the hospital for 2 months. I'll try getting back to him after he convalesces.

 

[roadrune]

Oh, hope he will be well.

Anyway its not important, i just remembered this issue now for some reason and went through the thread again when i found the quote.

 

[roadrune]

Ok, so after a year or so of Storage i decided to pull them back out to see what i think now, so i connected them to my stereo amp in the living room With no dsp, filters or other stuff, just pure analogue sound.

I still think they sound somewhat dark and "enclosured" (does that make sense in English?) but definitive not bad, so i took a New set of measurements of one speaker only With the Umik1 placed at tweeter height one meter (3') in front of the speaker, measured Three times With the exact same graph, so here it is:

4m/s gating, 1/24 smoothing:

6m/s gating, 1/24 smoothing:

8m/s gating, 1/24 smoothing:

No gating, 1/24 smoothing:

And last, no gating and 1/6 smoothing:

To my brief experience a 1/6 smoothing tells me more about what i am hearing as it shows the bigger Picture.

As you can see, all but 4m/s gating have a dip in the 400hz region, which i believe is what make them sound dark combined With the high levels in bass, although it is not much more then recommended in housecurves from Dirac and others.

Since it is present in the 6m/s gating and up, but NOT in the 4m/s i suspect this dipis not room related, but actually gating related on the 4m/s. And therefore a real issue With the speakers.

Any ideas of what i can do to fix this? I dont believe they are designed like this...

Btw: the crossovers are working fine, With tweeters in opposite phase they have a significant dip centered at 2000hz.

 

[TLS Guy]

Ok, so after a year or so of Storage i decided to pull them back out to see what i think now, so i connected them to my stereo amp in the living room With no dsp, filters or other stuff, just pure analogue sound.

I still think they sound somewhat dark and "enclosured" (does that make sense in English?) but definitive not bad, so i took a New set of measurements of one speaker only With the Umik1 placed at tweeter height one meter (3') in front of the speaker, measured Three times With the exact same graph, so here it is:

4m/s gating, 1/24 smoothing:
View attachment 29853

6m/s gating, 1/24 smoothing:
View attachment 29854

8m/s gating, 1/24 smoothing:
View attachment 29855

No gating, 1/24 smoothing:
View attachment 29857

And last, no gating and 1/6 smoothing:
View attachment 29856

To my brief experience a 1/6 smoothing tells me more about what i am hearing as it shows the bigger Picture.

As you can see, all but 4m/s gating have a dip in the 400hz region, which i believe is what make them sound dark combined With the high levels in bass, although it is not much more then recommended in housecurves from Dirac and others.

Since it is present in the 6m/s gating and up, but NOT in the 4m/s i suspect this dipis not room related, but actually gating related on the 4m/s. And therefore a real issue With the speakers.

Any ideas of what i can do to fix this? I dont believe they are designed like this...

Btw: the crossovers are working fine, With tweeters in opposite phase they have a significant dip centered at 2000hz.

First question is, where were the speakers placed in the room? I would like to see you repeat those measurements with the speaker far from any room boundaries.

Also you need off axis measurements. It is impossible to get any sense of the power response into the room.

There certainly is the suggestion that the BSC is excessive for the location of the speakers. That is a common curse of speakers. BSC is so room/position dependent. That is why I have developed a system that can carefully adjust the right amount of BSC according to location at the touch of a knob. I can just look at my computer screen and set it just right in seconds.

Prior to that system which can be set by the touch of a knob, I used to voice my crossovers to room and position. For my recording location monitors I had switches on the back that would generally give me three levels of BSC to allow for different rooms in which I was working.

 

[roadrune]

Stupid question; what is BSC?

The speaker was about 1' from the front wall, no side bounderies.

 

[TLS Guy]

Stupid question; what is BSC?

The speaker was about 1' from the front wall, no side bounderies.

BSC is baffle step compensation. It is the frequency at which a speaker transitions from being a half space monopole to an omnipole radiator. The narrower the front baffle the higher the transition frequency. Basically it requires a 6 db increase in output below the transition frequency.
The problem is that it is highly boundary dependent also.

Generally designers set BSC for a speaker to be at least 14" from any room boundary. At 1' you are too close to the wall boundary. So that may be part or all of your issue. Also as I alluded to this previously there is the issue of off axis response and room interaction. An on axis response only, does not give you an impression of the room response. In general a wide dispersion with the off axis response being a mirror of the axis response is favored.
That is why I asked about off axis measurements. If the off axis response droops at too high a frequency then that can contribute to the speaker sounding as you say dark. This is especially important in the midrange. In general a driver will have excellent polar characteristics in its rigid pistonic range. At breakup the response generally narrows significantly unless the breakup is very carefully controlled. Very few drivers have this characteristic. Good "bend' drivers are far and few between.

In general (no hard and and fast rule here) I tend to steer clear of paper coned drivers, even treated ones. I favor metal and plastic cones, especially metal. This often makes them hard to design for, as although they remain pistonic well up the range as a rule, break up is then violent with dramatic peaks and troughs in the FR. This is just one of many issues that makes speaker design difficult.

 

[roadrune]

I will see if i can get some of axis out on the floor one of theese days.

 

[D Murphy]

From the looks of the 4ms plot vs the 6ms, the environment is too reflective to allow good results from a normal gating. You're getting all kinds of reflections with 6ms, and you should be able get cleaner plots with that signal window. The 400 Hz dip is almost certainly a room effect. Most woofers, including the pair you're using, are quite flat in that region. I don't know what would cause a woofer to have an inherent dip at that frequency. It certainly has nothing to do with the crossover, since it's 2000 Hz below the crossover point. I also don't know why a 400 Hz dip would cast a dark sound to the speaker. It would just be a little thin in the lower midrange.

 

[Sailor Mike]

This is a very old thread, I've just found it, and would like to add comments, you will see why.

In about 2007 I built a similar ER18RNX MTM speaker to this, for hifi; very similar dimensions but SEAS 27TDFC tweeter.
WAF factor was essential! This size was the limit.
It was inspired by an MTM by Zaph with different 6.5inch drivers, but I chose the ER18 for a good reason.

I wanted a fairly efficient speaker for my SET amp. ER18 is higher than average efficiency, but equally important it is very well behaved with breakup fairly high and not too bad. It tends to be the case that high efficiency drivers (e.g. with special materials like kevlar) suffer breakup somewhat worse than average; I think the combination of highish efficiency, good behaviour and high sound quality of the ER18 is almost unique.
(If anyone knows of a higher efficiency driver of this size that sounds equally good, please tell me!).

Anyway, the results of this MTM speaker with my 3.5 watt SET amp (45 triode, parallel single ended) are superb.
Tonality, instrument resolution and character, utterly superb natural sounding vocals, good tight bass.
A highly critical friend, into Naim dynamics, says that I've got some dynamics, and fast clean leading edges; it's not at all a slow and lazy sound that some SET systems have.
Another person commented, after hearing LP of Mozart clarinet quintet; he said his daughter was learning clarient so she played it around the house, so he knew what clarinet sounded like. He said on my system it was the first time on any hifi that clarinet really sounded right.

I see in this thread a comment that these speakers are not good with valve amps; I don't want to cause trouble here but, for the benefit of anyone considering them for a valve amp, I feel I can offer advice to the contrary.
Though I can see that high power is useful for home theatre, a valve amp works superbly for hifi. The volume is fine in my 18ft x 14ft room, and bass is tuneful and controlled. Excellent results!

A bit about matching.
A push pull valve amp should work fine with the speakers as designed; Zout of perhaps 2 ohms will have an effect, the Xover may not be quite right but it'll be close. Zout will change the electrical damping slightly. My guesswork is that normal voicing should fix any issues; try adjusting BSC by varying slightly the series inductor on the woofers, and slight adjustment to the dropper resistor on the tweeter. Both are things I recommend trying anyway.

For best results with a SET amp, more work on the Xover would be best. Assume 4 ohm Zout of the amp, work out how electrical Q and hence total Q changes, and remodel the xover. I did that for the 27TDFC with xover at about 1800 Hz (IIRC), a simple 2nd order; no zobel, it's not needed if the xover is done properly. I tried it, not good.
Final voicing was done by measurement and by ear, after the speakers had run in (most important!).

If anyone wants to try the above I suggest you contact Dennis who I'm sure would like to help with a design for a SET friendly xover..
If anyone wants to know my xover for 27TDFC I'll gladly look it up, send me a message.

These speakers are used in a very high end system; Teres turntable, Moerch DP8 arm, Zyx 4D, valve phono stage, way better than the LP12 I had; CD player is modified Marantz with TDA1541A dac, NOS, caps upgrades, lampizated (the best CD player I have ever heard, no joke); nice valve pre; the 45 PSET amp is better than my 300B amps. The speakers definitely belong in this system.

Regards to all.
Mike in the UK