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Old 24th August 2006, 06:39 AM   #1
sqlkev is offline sqlkev  United States
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Default An old argument: TM vs. MTM

Going from a similar MTM to a more simpler TM, I enjoy listening to the TM a bit more. I know I'll lose some output (my main concern), but is there anything else that you can convince me to stay with another MTM ?

The more I think about it, the more I see that the Orion design is where I'm headed. I'd like to experiment with a full 4 way active system. But, don't have the amps and the processing power just yet.

What do you think?
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Old 24th August 2006, 11:03 AM   #2
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I am a few steps ahead on a similar journey. I started with MTMs, first with 6" drivers then 7". Went looking for quality sound in a space saving design, so built some 6" MTs. Still looking for something...

I am a bit of a dynamics nut, so the loss of maximum output level was a big deal to me. Note that I said dynamics, not loud average listening

Another factor that seems to affect the sound character is cancellation of some floor bounce modes in the MTM that are present in the MT. I was able to alleviate some of this with a big flokati rug with 2" of open cell foam under it between me and the speakers.

Even though the drivers and resulting system are more accurate than my older ones, there is something missing on peaks. I'm heading back to MTM land or possibly an open baffle Orion inspired design.

If you are ready to start on the "processing power" side and don't want to go digital, I bought extra filter boards for the group buy. If you plan to build the Orion, not a clone, buy SL's kit and boards. The group buy boards have all the features that SL says are necessary for a proper active system. See the group buys section, WIKI or my www button for info.
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Old 24th August 2006, 06:17 PM   #3
sqlkev is offline sqlkev  United States
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Thanks Bob,
What drivers are you using if you don't mind me asking? Dynamics is something that I'm sought after too and I'm sure with a simple 6" or 7" mid, it just won't cut it for me.

I have yet to analyze why I like the MT more or why it sounds better, but, like you, I've already found its weakness. (output + dynamics)

Currently, I'm comparing the dayton rs160/seas 27 MT vs. dayton rs180/seas 27 MTM. The MT is a boxed design and the MTM is a dipole. The processors are the Behringer deq and the dcx.

I've considered the active boards since the groupbuy started, but now that the DCX are back in stock again, it's really hard for me not to consider another dcx and chain both.

Would high efficiency drivers help me out? Or is there anything that I can do to improve on my MTM dipole?
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Old 24th August 2006, 06:51 PM   #4
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My current setup uses Focal 6W4254 midbass units and either a Focal TC120TDX or Fountek JP3 tweeter. I built otherwise identical boxes. The old MTMs used Focal coated paper drivers and the kevlar T120 tweeter. I also use a pair of RS150/27TDFC MTs in my bedroom. The bedroom speakers sound a little different than the mains, but are quite good. Hard to choose a favorite. Amazing since the bedroom total driver cost was 1/4 of what I spent on the Focals...

I'm either going to a Dayton RS225/RS150/27TBFC/G MTMWW or if I like the open baffle and waveguide experiments I'll probably end up with an RS225/27TDFC(waveguide) MTM on top of a pair of RSS315s per side. Daytons are excellent performers, and freight to Pennsylvania is cheap and fast.

I have all the drivers save the 315s on hand. Until I get the 315s my subs can handle up to 150 Hz fairly easily.

My guess is that you might be trying to get too much bottom end out of your MTMs. The RS180s are really large flange 6" drivers. Asking them to go as low as 200 Hz open baffle is probably asking too much (unless the baffle is huge).

I go back and forth on the high efficiency issue. On one hand the dynamics of my college roommate's A7-500s was wonderful, but they had a distinct ringing horn honk. Currently I lean towards drivers optimized for low distortion and using multiples to get the surface area needed for dynamics/extension. I have plenty of amplifier power available.
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Old 24th August 2006, 11:16 PM   #5
Salas is offline Salas  Greece
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It has been stated by gurus that ultimate room mating is dipole bass and cardioid midhigh. Did you ever try that Bob?
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Old 25th August 2006, 12:06 AM   #6
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Not yet Salas.

My room is on the small side - proper dipole spacing from the back wall will mean I have to put a speaker in such a way that the cables interfere with coming in the door. I guess it will have to be on casters so I can easily pull them out to a proper position and stow them when not in use.
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Old 25th August 2006, 03:19 PM   #7
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Quote:
Originally posted by salas
It has been stated by gurus that ultimate room mating is dipole bass and cardioid midhigh. Did you ever try that Bob?

Quote:
Originally posted by BobEllis
Not yet Salas.

My room is on the small side - proper dipole spacing from the back wall will mean I have to put a speaker in such a way that the cables interfere with coming in the door. I guess it will have to be on casters so I can easily pull them out to a proper position and stow them when not in use.
Hi Bob, and Salas;

I happened upon a very nice AES article by Juha Backman which seems to pretty much agree with my assessment of different woofer systems. I have favored cardioid woofers over dipoles for some time. Backman finds that in the modal region cardioid woofers are least sensitive to room placement where as dipoles are the most sensitive. Below the first mode, dipole SPL drops off because of the inability to pressurize the room, however, below the first mode he finds no advantage to cardioids over monopoles since both are capable of room pressurization. But monopoles are, of course, more efficient in that range. I have some excerpts from Backmans's paper over at my site in the discussion of the Mini design. http://www.musicanddesign.com/NaOMinidiscus.html


It has been my feeling for a long time now that the major apparent benefit of dipole woofers is really their weakness, the inability to excite the room below the fundamental. As a result, dipole woofers donít over load a room when the woofer's cut off frequency is below the room fundamental the way cardioid and monopole woofer do. The result is that the real devil here is that monopole and cardiod woofers aren't often tuned correctly to the room. There is a lot of, "the lower the F3 the better" attitude with regard to woofers, particularly for HT use, and that is a recipe for problems. But with a dipole with 20 Hz cut off in a room that can only support 35 Hz, the dipole just fades under 35 Hz. As a result the dipole wonít sound blotted or boomy when mismatched to the room. For a monopole or cardiod the first thing that has to be done is to optimize the F3 and Q (assuming a sealed box woofer) to match the room.

I know it's not the popular view as there is a great deal of favorable subjective evaluation of dipole woofers. But my own experimental, analytical and subjective evaluations seem a bit contrary to this and it was nice to see another effort which seems to agree. As I said, I believe the major reason for the positive subjective evaluation is the room pressurization factor.
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Old 25th August 2006, 03:57 PM   #8
Salas is offline Salas  Greece
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Martin Logan uses 'Force Forward' a.k.a cardioid and offcourse dipole mid-high by definition.

In Line Array professional systems circles though, after having made some systems with cardioid bass so to steer as much of the whole array output better, there was some consensus that in the end monopole was better. But there we talk humongus halls and open air.
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Old 26th August 2006, 08:00 PM   #9
sqlkev is offline sqlkev  United States
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Can you explain to me what exactly is a cardioid set up?
I also went over to John K's webpage and see that you chose the U frame for your Nao speakers. And here I'm getting the impression that you prefer monopole and cardioid over dipole?

While we're on the topic of dipole woofers, I have the bottom portion of the Phoenix dipole (by LR) with the original woofers that Linkwitz used. What can I do to get more output out from them? I have equalization power, but I'd prefer to make another box to get the best out of them.

Click the image to open in full size.
http://www.linkwitzlab.com/woofer.htm
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Old 26th August 2006, 10:27 PM   #10
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John K,

I for one am in agreement with you about a preference for cardoid or at a minimum cardoidish for the bass region on down. To me what makes is worth the extra effort over monopole is that we still have the highly directional sound (greatly reduced room effects similar to dipole) without the loss of extension.

I've read your description before about the lack of room pressurization being the limitation for dipole bass. In my mind though, for a dipole operating below the room fundamental, the baffle size ceases to be of importance and the room dimension itself causes the higher degree of cancellation between the 2 waves. ie On axis the front and rear waves must net to much less below the room fundamental with dipole.
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