New DIY MTM Towers designed by Dennis Murphy and Paul Kittinger

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roadrune

Audioholic
All measurments are smoothed 1/24oct and taken in one run full range.

Measured 10 cm from tweeter centre:

10 cm.jpg


Measured 1meter from tweeter centre, the 2k dip dissapears which make me Guess it's not really there, but apears from the mic being Close to the tweeter and not the woofers?
The 140 dip must be a room null.
1m.jpg


Both measured at MLP, the bass is a little higher then the mid and highs, but not enough to make the mids sound weird IMO?
Begge LP.jpg


I did not have time to change the stuffing at this time.
 
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roadrune

Audioholic
When i get the time, i think i will make a set of outer baffles in 12mm mdf as per design, with rounded edges to see if the issue is caused by difraction.

I'll just attach them with the driver screws and using neoprene gasket so the original baffles stay untouched.
 
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shadyJ

Speaker of the House
Staff member
You might set the window to the range that you are actually measuring, it will help you see the measurements more clearly. Set the window from 20 Hz to 20 kHz. Right now you have it at 2 Hz to 30 kHz, so you are only using 2/3rds of that graph space.
 
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MrBoat

Audioholic Ninja
I started reading this thread thinking it was a new build. I had considered the ER18 kits at one point and thought I had searched this DIY forum thoroughly. All I can say is, it's a good thing I don't have room for large speakers. I'd probably be living with a pair of these or the Statements in my LR, along with my new Rottweiler puppy in which to guard them with.
 
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roadrune

Audioholic
IMG_1222.JPG


So i found time...

The difference is to my ears audible, more then i would have expected, but less then i hoped.

The measurements however are almost identical as previous, so the difference might be psycological...

But i am still wondering what is causing this, i have a couple of theories:

Crossover: i may have done something wrong here, but cant really imagine what, the issue is the same on two different pairs built at different times.
Can more expencive caps be THAT audible? I have standard caps now.

Stuffing: i have the excact amount polyfill specified, but have not tried to change the amount, can that have a big impact in the mids?

We have tried different placements in four different rooms, and with 6 different amps, and alot of sources, so i am confident that the issue lies in the speakers themselves.

Now in my HT i have built a couple of bassmodules to take care of the low end from the fronts (2x8" sbacoustics in a 70litre closed enclosure and Linkwitz transform on each main)
The crossover is at 200hz and managed by a Minidsp 2x4hd with Dirac Live.
This helps quite a lot, but not enough...

Any tips? Could it be that the speakers just are not as good as i have hoped in the mids? The bass and treble is really good though!
 
Swerd

Swerd

Audioholic Warlord
After living with these for a while, several audiophile buddies independently have pointed out severe lacks in the midrange in both of my pairs (being more of a basshead i cant hear the same, but again i am not good at pointing out what exactly is the problem with my ears).
You posted several frequency response measurements.

Measured 10 cm from tweeter centre:


First of all, ignore the large peaks and dips below 300 Hz. It’s not possible to tell what is due to the speaker and what is due to reflections from the ceiling & floor, and opposite walls. Yes, that dip at ~140 Hz (in both of your graphs) is caused by floor bounce. Sound from the woofers, reflected off the floor, arrives at the microphone out-of-phase with sound directly from the woofers.

At 10 cm, your microphone is too close to the speaker. If you were measuring the tweeter alone, or the woofers alone, it would be alright, but with both working, 10 cm is too close.

I believe the very large dip centered at 2 kHz shows the crossover working. It appears as a large dip because within 1 octave of the crossover frequency (1 to 4 kHz), the tweeter and woofers are both producing roughly equal amounts of sound, but the microphone is closer to the tweeter and further away from the woofers. As a result, the tweeter’s and woofers’ sound arrive at the microphone out of phase with each other, and they cancel each other out.

Measured 1 meter from tweeter centre:



It’s better when you move the microphone to 1 meter. The 2 kHz dip disappears completely. What happens if you move the microphone further away, to 2 or 3 meters?

I do not understand why there is such a large difference in response from about 300 Hz to about 4 kHz. Something is clearly wrong. I can’t tell if it’s the speakers or your measurement methods. It rises centered at 500 Hz, falls from 600 Hz to 1 kHz, rises again centered at 2 kHz, only to fall again above 3 kHz. The loudness varies from a low of about 83 dB between 800-900 Hz, to as high as 89 dB at 500 Hz – an overall change of 15-16 dB. That’s very large!

The predicted responses when Dennis Murphy designed this crossover were flat (±3 dB) within two octaves of the crossover frequency. This flatness across the crossover range often causes people to think his speaker designs sound too bright because they are used to speakers which have mid range dips. But I never heard his designs lack in mid range.
So i found time... The difference is to my ears audible, more then i would have expected, but less then i hoped.

The measurements however are almost identical as previous, so the difference might be psychological...
Was this to test if rounded-over front baffles caused the large variation in mid range response? Your measurements (with and without rounded over baffles) were almost identical. I’m not surprised by that. Rounded over front baffles could not make such a large difference as your measurements indicate.
But i am still wondering what is causing this, i have a couple of theories:

Crossover: i may have done something wrong here, but cant really imagine what, the issue is the same on two different pairs built at different times.

Can more expensive caps be THAT audible? I have standard caps now.
I’m only guessing after seeing a few frequency response graphs, but the first thing I would look for is an error in the crossovers. It could be in part selection or wiring.

Your photos show you have the ribbon tweeters. There are different crossovers for the ribbon tweeter version and the dome tweeter version. Are you certain you used the correct crossover version? The reason I ask is because of the crossover frequency apparently centered at 2 kHz. It has been some time, but I remember the dome tweeter version has a lower crossover frequency (perhaps at 2 kHz?) than the ribbon tweeter version. The Fountek Neo CD3 tweeter cannot go down to 2 kHz, but the dome tweeter can.

When you purchased crossover parts, did they differ from the original design? By how much? Variations of ±10% are alright, but larger than that can cause problems.

More expensive caps do not make that audible a difference, if any at all. It is much more important to have cap values (as well as inductor and resistor values) as close as possible to those of the original design.
Stuffing: i have the exact amount polyfill specified, but have not tried to change the amount, can that have a big impact in the mids?
That would mainly effect lower frequencies, not the mid range. I don't think it's the polyfill.
 
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panteragstk

panteragstk

Audioholic Warlord
I started reading this thread thinking it was a new build. I had considered the ER18 kits at one point and thought I had searched this DIY forum thoroughly. All I can say is, it's a good thing I don't have room for large speakers. I'd probably be living with a pair of these or the Statements in my LR, along with my new Rottweiler puppy in which to guard them with.
I'd like to have both just cause. I'll probably end up with the ER18 at some point. Have to cross the other projects off the list first.

I miss my Rottie. He was the best dog I'll ever have. :(
 
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roadrune

Audioholic
Hi Swerd, i was hoping you would chime in :)

Yes, i am shure that i have built the right crossovers, and that the parts vary by no more then 10%.


FullSizeRender.jpg
IMG_0790.JPG


I also built two pairs with the same issues at different times.

Starting to think about my measurments... all measurments is both speakers, so the close range might be affected by the other speaker, i will take new measurments when i have the time.

I measure with a umik using rew.
 
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roadrune

Audioholic
Ok, New measurements, now With only one speaker at a time, but graph for both speakers shown, again With 1/24oct smoothing:

LP:
Lp H7v.jpg


2M:
2m hv.jpg


And 1M:
1m hv.jpg


You can see it's much smoother the closer the measurement, since the room (which is partly treated but not enough obviously) plays more and more part the more i move away from the speakers.

Still at 1 meter i would GUESS that the room is affecting below atleast 200, and from there and up it's not to shabby, but still not good enough.

Also for the fun of it i measured both woofers at really Close range, like 1" (With the tweeter active) and there it is pretty smooth, except from the null at 800, and until it rolls of:
bass.jpg
 
Swerd

Swerd

Audioholic Warlord
I emailed Dennis Murphy this morning about your problem. I hope he has the time to respond.

Your crossover board photos look correct to me.

What software and microphone are you using to make your frequency response graphs?
 
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roadrune

Audioholic
Thanks for helping!

I use a Umik-1 from Minidsp and REW.

The issue can be heard easily on Dire Straights Telegraph Road at the last 5 mins.
 
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MrBoat

Audioholic Ninja
What is so different about your room than an average living space? I know there are rooms that are problematic overall with regard to MLP, but somewhere, those speakers themselves should sound good. Have you tried arranging them in a near field type arrangement? When I first built my speakers, I plugged them in one at a time and listened to it pretty much point blank. The speakers sounded good starting out, regardless of the room.

Have you had other speakers in that room that sounded good without much fuss? Do you have any you could borrow to try out to compare against those?

ETA: I just read back a bit and see where you have tried other things and 4 different rooms.
 
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roadrune

Audioholic
It is possible i just expect more from them that they are capable of, as said in the bass and treble they are really good, but in the mids they are far behind my B&W 683's which i imagined should have been nowhere near as good as the ER18's.

My room (Ht) is somewhat acousticly treated, but not as much as it should have been, also the shape of the room is bad for sound.
 
Swerd

Swerd

Audioholic Warlord
Your first frequency response curve, done with the microphone 10 cm distant (below), had a very large null centered at the 2 kHz crossover frequency. This is what happens if the tweeter was wired in the opposite polarity to the woofers. I know this null disappeared when you moved the microphone further away, but I'm trying to think of things that are easy for you to check.

In this design, the plus terminal on each driver should be wired to the plus (source) side of the crossover circuit. Check both woofers and the tweeter. I attached the schematic diagram below.

I know, first hand, how easy it is to get this wrong :rolleyes:.



ER 18 MTM Ribbon Schematic.png
 
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Swerd

Swerd

Audioholic Warlord
All the capacitors in your photos are Solen or Bennic. All are very good quality.

I cannot imagine they could be the source of your problem.
 
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roadrune

Audioholic
I am 110% shure the polarities are correct.

I'll check them tomorrow :D
 
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roadrune

Audioholic
All drivers are connected in phase, unless the red dot means negative in either the woofers or the tweeter...

I took out the drivers and verified with a meter, the positive obviously have connection to negative, but with a ohm or two in resistance, positive to positive the same, and negative to negative no resistance whatsoever.
 
rojo

rojo

Audioholic Samurai
What I'm wondering is, what is causing that hill from 300Hz down? And didn't you say you had your subwoofer crossed at 200Hz? Why is that necessary with transmission line towers?
 
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