New DIY MTM Towers designed by Dennis Murphy and Paul Kittinger

R

roadrune

Audioholic
Thanks to Swerd for emailing me plans!

I have some questions though, sorry if some of them have been answered, but i cant remember seeing it (i have read the entire thread).

1. Would it affect the sound if i built them in solid 26mm (aprox 1") oak? I would naturally keep the internal dimensions the same.
2. Would it make sense to use 4 binding posts for each speaker for bi-amping, connecting tweeter and woofers seperate?
3. The plans say unflared port, would it be better with a flared, if so flared in one or both ends?
 
Swerd

Swerd

Audioholic Warlord
1. Would it affect the sound if i built them in solid 26mm (aprox 1") oak? I would naturally keep the internal dimensions the same.
As long as the internal dimensions are the same as in the plans, it does not matter how thick the materials are. In the USA ¾" (19mm) thick medium density fiberboard (MDF) is commonly available. Two layers are used where the drivers are mounted on the front, but ¾" thick MDF for the rest of the cabinet is good enough. You will find that these cabinets are very heavy, and using thicker MDF will be much heavier. Internal cross braces are more effective at minimizing cabinet resonance, than using thicker layers of wood.

Solid oak or other hardwood should not be used for two different reasons. Hardwoods when stimulated by speakers have frequencies at which they naturally resonate. These vibrations color the sound. This may be desired in a musical instrument, but not in loudspeakers. MDF or good quality plywood, such as Baltic Birch, are much less resonant. The other reason is that hardwoods all absorb water vapor. They will shrink in the dry winter and expand in the more humid summer weather. A well constructed speaker cabinet, with 6 sides, cannot adapt to these changes in dimensions. As the hardwood expands and shrinks, the wood will crack and eventually split open. MDF or plywood do not change dimensions as the weather changes.

If you want an oak finish, I suggest you use oak veneer. MDF is flat and smooth and provides a good surface for veneer, and it doesn't expand and shrink as the weather changes. In the USA, good quality plywood with an oak outer layer is also available. I don't know what is available in Norway.
2. Would it make sense to use 4 binding posts for each speaker for bi-amping, connecting tweeter and woofers seperate?
Yes, you could use 4 binding posts. You would wire the woofer and tweeter networks separately to each pair of posts. Although this is commonly advocated in audio, there is no real advantage for this. However, if you build these speakers, you are free to build it as you like.

These speakers do not require powerful amplifiers – any amp that delivers an honest 50 watts will easily drive these speakers. And there are many home theater receivers available with about 100 watts per channel. The ER18 MTM speakers can easily handle much greater power, but they do not require it. I personally don't think bi-amping would provide any audible benefit.
3. The plans say unflared port, would it be better with a flared, if so flared in one or both ends?
Yes, you can use a flared port. The plans do describe that somewhere. According to the predicted bass response, it should not make an audible difference, but if you wish to use a flared port it will not cost much more.
  • Ports tubes are 3" (76mm) diameter
  • If not flared, the tube is 2¾" (70mm) long.
  • If flared on one end, the tube is 3¼" (83mm) long.
  • If flared on both ends, the tube is 3¾" (92mm) long.
 
R

roadrune

Audioholic
Thanks.

Then i'll stand clear of oak and go for veneer.

I'm thinking bi-amp since my plan is to build a 7-channel amp, and a cheap and great diy amp is the 2x50w 3116, so i thought i could use 7 of those were i use the same input for 2 and 2 channels, making it 7-channels in but 14 outputs divided in 7 channels (hope this is possible to understand)
 
Swerd

Swerd

Audioholic Warlord
I'm thinking bi-amp since my plan is to build a 7-channel amp, and a cheap and great diy amp is the 2x50w 3116, so i thought i could use 7 of those were i use the same input for 2 and 2 channels, making it 7-channels in but 14 outputs divided in 7 channels (hope this is possible to understand)
That sounds interesting. I wish I knew more about building electronic components, but I'm afraid I don't. I only know about building speakers :). I know this project will be difficult at times, but I also hope it's fun and rewarding for you.

Please come by here now and then to let us know about your progress and your problems.
 
R

roadrune

Audioholic
That sounds interesting. I wish I knew more about building electronic components, but I'm afraid I don't. I only know about building speakers :). I know this project will be difficult at times, but I also hope it's fun and rewarding for you.

Please come by here now and then to let us know about your progress and your problems.
I don't know anything about building electronics either, but we also have good forums in Norway, and i can build "anything" from a good drawing :)

I'm really looking forward to getting started, and once i have i will post some pics here :)

By the way; were you saying that there are no audible difference between flared and non-flared ports?
 
Swerd

Swerd

Audioholic Warlord
By the way; were you saying that there are no audible difference between flared and non-flared ports?
The cabinet was originally designed and modeled with a non-flared port. The modeling data predicted that with a high voltage signal, the air velocity in the port would be a little more than 3% of the speed of sound. In ported loudspeakers people can usually hear noise from the port if the air velocity is more than 5% of the speed of sound. With this design producing an air speed of 3% of the speed of sound, and with the port on the back of the cabinet, it is reasonable to predict it will not be heard.

However, I would still use a flared port in the ER18 MTM. It can do no harm, it will cost very little extra, and I think flared ports do look better. After doing all the other work it takes to build these, why not? It is like choosing to use nice looking gold plated brass binding posts instead of cheap plastic posts. They both work equally well, but one looks nicer than the other.

See post #2 of this thread:
"At this same elevated input, the port’s air velocity should be just over 3% the speed of sound, and the system should generate about 103 dB. With a rear mounted port, there should be no audible port noise:"

 
R

Researcher

Enthusiast
Researcher-
Will you be building the ER15 center channel to with these ? I'm considering that even though the ER15 uses a ribbon tweeter while I built the dome tweeter version of the ER18s. Seems like they should blend though, maybe even compliment each other.
Hi David, I swear if I had more room space at home I probably wouldn't had finished these in a month + days like I did, finding the proper work space for building the ER18s was difficult here, I only were able to work on one enclosure each time; so it took more time while the glue dries, varnish dries, etc, etc etc in one cabinet to repeat the same process in the other; I'm pretty sure if I had a big garage or basement these would be still in bare mdf like this :D:D:D:D:

IMG_0194.jpg


So after some weeks having these boxes occupying almost an entire room I felt the urge to finish quickly to free up the space.

About the center channel, I don't know why Meniscus only sells the ribbon version, or if it's the only version available of this design; I don't think it would make such a big difference after all we're talking about the same designer Dennis M. (dunno if Paul K had any input), almost same drivers (only smaller). If I count by the pictures I've seen around the web of the center channel I'd probably say that it has been built at most by...2 people in the world :p.

Also, I've been further testing the multichannel system, and found that a pair of Overnight Sensations are more of my liking as surrounds, the Speedsters are brighter than the ER18s it doesn't matter that much for movies and series, but for multichannel music it gets distracting...even more distracting than multichannel music itself:p...yeah stereo for music some may say...
 
D

David LR

Junior Audioholic
Hi Researcher -

Looks like you have exercise equipment mixed in with your speaker project ! Had to give up the weights while building your speakers ?? Not a bad trade.

Regarding your multi-channel testing, are you using subs with the ER18s ? Curious, because the bass
is really quite good out of the ER18s alone. I watched Master & Commander last night, one of my favorite movies. If you're familiar with the movie you know there is some impressive cannon fire during the ship to ship fight scenes. The ER's did very well in that regard, not so sure how much a sub would help. If you are using subs, how does that change the character of the sound vs ERs alone. One of the arguments for a sub is that it relieves the mid-range driver of low frequency duties, making for a cleaner mid-range. Any thoughts ??

I have a "baby" surround system, that is, only front "presence" speakers (Yamaha 7.1 Receiver) & a center channel, cobbled together using small two-ways that I've built over the years. No surrounds, no subs, not an ideal center channel however it's enough to experiment. I plan to install in-ceiling speakers for the
side & rear surround speakers. Anyway, your multi-channel test results & observations would be welcome.
 
R

Researcher

Enthusiast
Hi Researcher -
Looks like you have exercise equipment mixed in with your speaker project ! Had to give up the weights while building your speakers ?? Not a bad trade.
I really do give up everything while building speakers! :p

Since I got the tube amp I wanted to build the ERs mostly for 2 channel music listening, it was and still my primary goal to have a decent stereo setup; I have an eight year old Marantz SR5001 for everything else but do not watch so many movies so I haven't properly tested them with more demanding material like the film you mention.

My impression is the ERs were not voiced to output a lot of bass all the time, only when the source material really requires it, think I read somewhere they can go as low as 38-37 hz, Swerd knows a lot more about this surely. That's plenty of bass IMO for music at least; of course it depends on many other factors as device configuration, room size, room treatment (or lack of) etc etc, but I don't think a sub it's really needed with the ERs. One possible issue here is: almost any 5.1/7.1 soundtrack have a dedicated LFE channel, I wonder how much we'll loose but not outputting anything from it.

I have a sub in a weird setup it's a passive sub connected to other receiver (I'm planning to work on this later), it's crossed below 40hz and honestly I hear very little difference when it's on or off, perhaps a tad more bass but the ERs do most of the job.
 
D

David LR

Junior Audioholic
My impression is the ERs were not voiced to output a lot of bass all the time, only when the source material really requires it, think I read somewhere they can go as low as 38-37 hz,
Right- very purposely & meticulously designed that way. No muddy sound ! From the
very first page of this thread it says that the "F3 is 35HZ with useful sound to 31HZ", so, lots of bass when called for. I'm sort of a pipe organ buff so if I want to hear (feel) the 16hz produced by a 32' pipe gotta get a sub woofer, but that's probably pretty rare anyway.

Thanks for your feedback.
 
R

roadrune

Audioholic
What is the internal diameter of a 3" port in mm? It should theoreticly be 76,2mm, but the ports in Norway differ from 68-70mm.
 
Swerd

Swerd

Audioholic Warlord
In the USA, a company called Precision Sound Products makes flared port kits for speaker cabinets. Their 3" flared port kit would be just right for the ER18 MTMs. Can you find them in Norway? http://www.psp-inc.com/index.html

In the USA, they are sold by Parts Express and Madisound.

If you can't find them, any PVC or CPVC plastic drain pipe with an inner diameter as close as possible to 76mm would be alright.

A cardboard mailing tube can also work.
 
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R

roadrune

Audioholic
Nope, i can only find them in the US, same as the crossover parts, and the shipping is stupid high, like $100...
I'll search a little more around and see what i can find..

Is there any tolerances on the crossover components, or do they haveto be the exact specified values?
 
Swerd

Swerd

Audioholic Warlord
Is there any tolerances on the crossover components, or do they haveto be the exact specified values?
For all crossover components, a tolerance of ±10% is alright. If the diagram calls for a capacitor of 10 µF, anything from 9 to 11 µF would work.
 
R

roadrune

Audioholic
Finally got started with cutting of plates, today i cut all the plates and drilled all the holes in the braces, one little tip her when you have problem with clogging, drill to it starts clogging, then turn the plate and drill the rest from the opposite side, this way you will get next to no problems with clogging. To clean the teeth of the holesaw i used a steelbrush, taking care not going towards the teeth.

Also i only marked the first plate, and then always kept the next plate underneath it so that i got a copy every time. Not something i would recommend for anything that needs to be superprecice, but plenty accurate for the braces.

I used the holesaws i had laying around, so in my braces there will be 5 holes.
IMG_0766.JPG
IMG_0767 [71418].JPG


Also i have one question: is it possible to measure the 0.1 inductor that should be unwounded to .06 without a lcr-meter? E.g. using a standard multimeter?
 
ARES24

ARES24

Full Audioholic
About the center channel, I don't know why Meniscus only sells the ribbon version, or if it's the only version available of this design; I don't think it would make such a big difference after all we're talking about the same designer Dennis M. (dunno if Paul K had any input), almost same drivers (only smaller). If I count by the pictures I've seen around the web of the center channel I'd probably say that it has been built at most by...2 people in the world :p.
I'm a people!!!

The center channel came about because I asked Dennis what his thoughts were on a center channel to go with my ER18 ribbons. It is possible that he might have a dome version rattling around somewhere.
 
D

David LR

Junior Audioholic
I'm a people!!!

The center channel came about because I asked Dennis what his thoughts were on a center channel to go with my ER18 ribbons. It is possible that he might have a dome version rattling around somewhere,,a
...and thank you for doing that ! I don't think Dennis does have a dome version, I called Meniscus and asked them the same thing, the answer was negative. so, as the only, uh, "people" in the whole world to have built the dome tweeter version, I will just use your design. After running the Yamaha YPAO adjustments i should blend fairly well I think.
 
R

roadrune

Audioholic
Got a router table in the mail:)





IMG_0769.JPG


So i finished the braces, a bit thin edges but i think it should be ok.

IMG_0777.JPG


IMG_0779.JPG
 
R

roadrune

Audioholic
Got to do a little work today...

Routing holes and inserts(?) for the ports:
IMG_0783.JPG
IMG_0786.JPG

IMG_0787.JPG


Test Assembly, missing dados for the second baffle plate:
IMG_0788.JPG
 
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