New DIY MTM Towers designed by Dennis Murphy and Paul Kittinger

[Swerd]

In Roadrune's nice pictures of his setup , the offset tweeters are to the outside. Correct me if I'm wrong, but I always thought the tweeters went to the inside of the setup (imaging ?). That's how mine are set up. Probably one of those things that make a theoretical difference but maybe not audible. Which way is the theoretically correct way ??

Here is a better answer to your question:

High frequency sound coming from tweeters will interact with cabinet edges, causing small peaks and valleys in the frequency range of about 4 to 8 kHz. The exact frequencies are determined by the distance from the tweeter to the cabinet edge. This is called diffraction, and in effect, it creates new points of origin for sound in addition to the tweeter.

If the tweeter is centered in a tall narrow cabinet such as in many MTMs, there will be two identical tweeter-to-edge distances, with identical diffraction peaks and valleys that add up. If the tweeter is slightly off center there will be two slightly different tweeter-to-edge distances. They may generate more peaks and valleys than with a centered tweeter, but because they are at differing frequencies and won't add up, they will each be smaller in amplitude.

Dennis Murphy always prefers off-set tweeters in his designs because he can easily see the difference in his measurements. He is not certain that this makes an easily audible difference, but off-set tweeters are easy to make at no extra cost during construction, so why not do it.

The exceptions are speakers like the Philharmonic 3 or the Salk HT1 & HT3 where the tweeters are centered, but the cabinets are not rectangular, and the front baffles don't have parallel edges.

So, off set tweeters can make a measurable difference in a single speaker in mono. What happens in stereo? Are off-set tweeters better toward the outside or the inside? People wonder and argue which is better. I doubt if it makes any difference. Take your pick.

This explanation is, of course, an oversimplification. A longer discussion of cabinet edge diffraction can be read here http://www.salksound.com/blog.php

 

[David LR]

Here is a better answer to your question:

High frequency sound coming from tweeters will interact with cabinet edges, causing small peaks and valleys in the frequency range of about 4 to 8 kHz. The exact frequencies are determined by the distance from the tweeter to the cabinet edge. This is called diffraction, and in effect, it creates new points of origin for sound in addition to the tweeter.

If the tweeter is centered in a tall narrow cabinet such as in many MTMs, there will be two identical tweeter-to-edge distances, with identical diffraction peaks and valleys that add up. If the tweeter is slightly off center there will be two slightly different tweeter-to-edge distances. They may generate more peaks and valleys than with a centered tweeter, but because they are at differing frequencies and won't add up, they will each be smaller in amplitude.

Dennis Murphy always prefers off-set tweeters in his designs because he can easily see the difference in his measurements. He is not certain that this makes an easily audible difference, but off-set tweeters are easy to make at no extra cost during construction, so why not do it.

The exceptions are speakers like the Philharmonic 3 or the Salk HT1 & HT3 where the tweeters are centered, but the cabinets are not rectangular, and the front baffles don't have parallel edges.

So, off set tweeters can make a measurable difference in a single speaker in mono. What happens in stereo? Are off-set tweeters better toward the outside or the inside? People wonder and argue which is better. I doubt if it makes any difference. Take your pick.

This explanation is, of course, an oversimplification. A longer discussion of cabinet edge diffraction can be read here http://www.salksound.com/blog.php

 

[David LR]

Thanks again Swerd for another great answer. Always good to learn. I read the linked article by Jeff Bagby, twice, I'll need to read it again slowly & carefully to fully understand and then I'll probably only retain 10 %.
Sure is nice to have guys like Jeff Bagby & Dennis Murphy contributing to DIY audio to the benefit of us all.

I get most of my audio education from this website & also from the Parts Express forum where Jeff Bagby is a regular contributor. From what I've read, Jeff Bagby & Dennis Murphy seem to be the two designers at the very top so I'm glad to have a Murphy design in the house. Can't stop until I've got a Bagby design though !

Until reading the article, I forgot that a baffle roundover also smooths out diffraction effects, along with the offset tweeter. If these were bookshelf speakers I might experiment with in vs out placement of the tweeters but they're just to big for that. I know mine are placed too close to the wall though, not much I can do about that, WAF factor being what it is !

 

[Researcher]

Just ordered the ER15 & another Overnight Sensations kit from meniscus, those will surely keep me busy during the rest of the year.

About the ER15, the OP there mentioned something about bracing not being in the right dimensions, I tried to get more info about this possible issue but he never replied...once I get the plans from meniscus I'll probably have a better idea about it. Anyway, after building a pair of ER18s this single box should be a piece of cake!!

I've been using a pair of Overnight Sensations as surrounds in a 5.1 setup, the regular TM, not the bipole surround design, and must say they do the work very well together with the ERs, tried other speakers but sound too "bright" or harsh compared to the ERs specially with music. Of course there might be hundreds of better options in the market, but the OS are inexpensive, and very easy to build. I was tempted by the bipoles but don't have enough wall space to accommodate a couple of those.

...now this is the mighty & powerful speaker I'm using currently as center channel:

 

[David LR]

Just ordered the ER15 & another Overnight Sensations kit from meniscus, those will surely keep me busy during the rest of the year.



View attachment 18291

Sounds great, looking forward to your review & impressions. Are you using a sub with the ER18s' and if so
what changes did notice ??

Good luck on your "little build" !

 

[Researcher]

Are you using a sub with the ER18s' and if so what changes did notice ??

David, I use sub only when the material has a LFE channel, and the pair it's connected to the AVR but I watch a movie every 2 years!...most of the time they are hooked to the tube amp for listening 2 channel music, without a sub, bass output it's impressively clean and articulate but depends on the recording.

Since day one, my opinion was these speakers are very revealing and unforgiving and still is. Honestly, I've been dissapointed to listen to some CDs from my collection, which for many years thought they had better sonics. My "problem" was, I grew up listening to many treble/bass busted speakers, which masked many of the limitations and flaws of poorly recorded or mastered albums. These ER towers are very neutral, not like any other speaker I owned in the past, but I'm still getting used to them, it has been quite a learning curve!.

P.D: I was impressed by their performance when playing the soundtracks of House Of Cards, very deeeeeep deeeep low frequencies on those, no sub needed at all.

 

[David LR]

David, I use sub only when the material has a LFE channel, and the pair it's connected to the AVR but I watch a movie every 2 years!...most of the time they are hooked to the tube amp for listening 2 channel music, without a sub, bass output it's impressively clean and articulate but depends on the recording.

Since day one, my opinion was these speakers are very revealing and unforgiving and still is. Honestly, I've been dissapointed to listen to some CDs from my collection, which for many years thought they had better sonics. My "problem" was, I grew up listening to many treble/bass busted speakers, which masked many of the limitations and flaws of poorly recorded or mastered albums. These ER towers are very neutral, not like any other speaker I owned in the past, but I'm still getting used to them, it has been quite a learning curve!.

P.D: I was impressed by their performance when playing the soundtracks of House Of Cards, very deeeeeep deeeep low frequencies on those, no sub needed at all.

Researcher
Interesting. Ever done an A-B comparison of your tube amp with your AVR (in 2 channel mode) ? Must be a significant difference or else you wouldn't be using a tube amp. Planning to use your ER15 center for music listening ? If so, I wonder if the tube amp will be able to handle the extra load, or, how do you plan to do that anyway ? (I'm sure you've "researched" it )


Thanks.

 

[FingerlessHackWoodworker]

Just a hint, before gluing up all 4 sides of the cabinet, install the polyfill stuffing, the crossover board(s) and wiring (keep the wires long enough to extend out the driver holes, and trim them later). A dry-test assembly of the cabinet should let you figure out whether to leave the front baffle or one of the cabinet sides for last. Not everyone does it this way, but I find it easier than trying to get everything through a woofer hole once the cabinet is all glued up.

Thanks for the tip Swerd. I had been considering same thought, couple of weeks ago, but for a very different reason. I thought it would be easier doing the glue up in stages. Generally, standard wood glue tends to set within 20 minutes (manufacturer suggestion). So it is expected that all clamps are at pressure and aligned as need be within 20 minutes. Clamps can be removed about after 2 hours and no loading of glue joints for about 24 hours. I like to use a square, to assure adjoining faces are square, during glue ups and this really eats into that 20 minute window of time, considerably. Your tip has confirmed that I too will take your suggested approach for both reasons.

 

[FingerlessHackWoodworker]

Thanks again Swerd for another great answer. Always good to learn. I read the linked article by Jeff Bagby, twice, I'll need to read it again slowly & carefully to fully understand and then I'll probably only retain 10 %.

I had to laugh. Good to know I am not the only one whom suffers at only retaining maybe 5% of what I too have read in this regard. Just kills me, once someone else points something like this out, my memory kicks into gear and does the oh yea now I remember; but until that moment, its dead in my head. Swerd, thanks for activating some my dormant neurons. I must say 'some', because speaking quite frankly, some are beyond resuscitating. And in this case, for once I don't mind the kid in the front of the class with his bloody hand raised up all the time because he has the answer. It's like I get to cheat from your test-sheet and never get caught.

 

[FingerlessHackWoodworker]

Work and life in general has really gotten in the way of progress and the dilemma of how to buy the driver bundle. I have decided to buy driver bundle piecemeal as the extra cash gets earned. Just purchased two mid/woofers and one ribbon tweeter.

Here are some photos of the braces rounded over and tips.

I saved these brace cut outs to be used as supports for when I did the router 3/8" rounding:

The two smaller cut-outs were stacked up such that the router is being supported (by the jig and cut-outs) while the opposite cut-out is being rounded over:

The same thing is done but using the larger cut-outs stacked on top of each other to round over the opposite opening:

Here are the braces rounded over:

Notice the braces are indeed holy. They incorporate the flying buttress (developed in the Gothic Period of architecture) used in many holy cathedrals.

 

[FingerlessHackWoodworker]

Ended up using some cheap chinese "wood" as veneer, not looking to bad when the price was $16 shipped
View attachment 18282 View attachment 18283

roadrune, thanks for sharing; nice job!

I noticed you do not have a wide base mounted to the bottom of your speaker boxes. When I dry clamped my boxes and stood them up, I confirmed the boxes are very pron to falling over. That is in my opinion. Did you add any weight (sand, lead, etc.) at the bottom of the boxes?

 

[FingerlessHackWoodworker]

Here is a better answer to your question:

High frequency sound coming from tweeters will interact with cabinet edges, causing small peaks and valleys in the frequency range of about 4 to 8 kHz. The exact frequencies are determined by the distance from the tweeter to the cabinet edge. This is called diffraction, and in effect, it creates new points of origin for sound in addition to the tweeter.

Swerd, thanks for this info. I recall the importance of rounding baffle edges from "Introduction to Loudspeaker Design" by John L. Murphy. He mentions, "Other authors report further reduction in the ripples with careful driver placement and edge rounding." I have every intention of implementing these findings. I seem to recall Roadrune mentioned he rounded/beveled the driver holes on the inside of his cabinet boxes. Of the two books I have read on speaker building, I don't recall bumping into such a suggestion. I take that back. I recall mentions of rounding off internal edges, but for some reason my brain assumed the driver edge was exempt. If driver edge is not exempt I can only guess this to be the reason. I assume, this edge can measure out to be an unfavorable high-freq-wavelength (or maybe not necessarily hi-freq) distance away from a driver's center point. That is if the driver's sound source is considered to be a point referenced from the driver's center. Or, if various unfavorable high-freq-wavelength distances are made up of the many concentric circles. The concentric circles I am referring to are all the circles that when summed up equate to the speakers surface area.

In a long winded way, I am asking, should the internal driver holes be rounded off?

I have been considering keeping the cross-over on the outside of the box. The thought was maybe to place cross-over in a base. Meaning, I would build a base platform to mount the boxes onto which could house the cross-over and also make the boxes less top heavy. Any thoughts?

 

[roadrune]

I find the speakers sturdy enough as-is. Even with spikes 1" in from the edge.

You need to chamfer the driverholes.

 

[FingerlessHackWoodworker]

You need to chamfer the driverholes.

Thanks Roadrune.

 

[SpeakerBuilder101]

I completed a set of ER18 speakers am getting a bit of ear fatigue when listening to them, even at short amounts of time. If I ignore the fatigue (though hard to do) these are fantastic sounding speakers. All equipment was from Meniscus's kit.

Ribbon tweeter versions, enclosures are pretty close to the designs with some of the faults listed below, and currently in a pretty poor location.

Known faults in my implementation:
- Interior supports do not have rounded edges
- Front baffle which the drivers are mounted to is not rounded, but a 45 degree
- Rear port is not yet glued in, though if this was the cause I would expect either poor base response or mechanical noise from it moving
- Working on correcting soon
- When I routed the hole for flush mounting the tweeters I made it ~1/4" too large, so about 1/8" all around of a gap

I am hopeful to get some hints and direction on how to narrow down what could be causing/contributing to the fatigue and eventually (hopefully) what could be done to remedy. it occurs at every reasonable listening level, even fairly quiet it is exposed. The only thing different in my setup are the speakers, standard equipment is NHT classic 3 powered by an Arcam AVR 300. Room is a vaulted ceiling living room with no walls within 6 feet to left or right. They will be moved to another location eventually, but will be a bit till I can get that room ready.

My first thought is to disconnect the speakers one at a time and see if it is impacting both or just one of them. Going to ask around work to see if someone has a mic and measurement application to get some readings off of it, though this is a bit of a long shot.

Any other ideas would be appreciated.

 

[FingerlessHackWoodworker]

- When I routed the hole for flush mounting the tweeters I made it ~1/4" too large, so about 1/8" all around of a gap

SpeakerBuilder101, real sorry to hear. I am not saying this is a smoking gun; however, was the 1/8" gap-edge rounded off? Maybe knowing this added piece of info might be helpful input for someone with more knowledge than me, which is not much.

 

[ARES24]

Just ordered the ER15 & another Overnight Sensations kit from meniscus, those will surely keep me busy during the rest of the year.

About the ER15, the OP there mentioned something about bracing not being in the right dimensions, I tried to get more info about this possible issue but he never replied...once I get the plans from meniscus I'll probably have a better idea about it. Anyway, after building a pair of ER18s this single box should be a piece of cake!!

I've been using a pair of Overnight Sensations as surrounds in a 5.1 setup, the regular TM, not the bipole surround design, and must say they do the work very well together with the ERs, tried other speakers but sound too "bright" or harsh compared to the ERs specially with music. Of course there might be hundreds of better options in the market, but the OS are inexpensive, and very easy to build. I was tempted by the bipoles but don't have enough wall space to accommodate a couple of those.

...now this is the mighty & powerful speaker I'm using currently as center channel:

View attachment 18291

I don't know what comes in the Meniscus kit for the ER15 but you might get some answers here.

 

[roadrune]

Can anyone recomend a cheap but good enough inductance meter from ebay?

 

[FingerlessHackWoodworker]

Originally I had intended to cutup some veneers out of Leopardwood but had to much trouble locating some, other than a 4 hour drive and a price through the roof. So I settled on this beast:

2.5" x 11" x 89" Curly Maple. Picture does not do the wood justice. The grain is very impressive. It will be a challenge to cut this down into most of the required 1/4" thick panels. That is if I am able to cut with enough control to walk away with 6 veneer sheets. Will need to visit the wood store again for the tops and bottoms-- or more if I screw up.

 

[David LR]

Originally I had intended to cutup some veneers out of Leopardwood but had to much trouble locating some, other than a 4 hour drive and a price through the roof. So I settled on this beast:View attachment 18379

2.5" x 11" x 89" Curly Maple. Picture does not do the wood justice. The grain is very impressive. It will be a challenge to cut this down into most of the required 1/4" thick panels. That is if I am able to cut with enough control to walk away with 6 veneer sheets. Will need to visit the wood store again for the tops and bottoms-- or more if I screw up.

Nice looking hunk of wood, looks like your dog would like to give it a chew ! So, do you use a large
band saw to slice off the 1/4" pieces (isn't this what they call resawing ? )? Do you feed the whole chunk through or cut it into more manageable lengths first. Good luck with the process, looks like beautiful wood.

Dave