If you are looking for a very high power system with excellent polars, MTM rules. but they must be wide horizontally and narrow vertically, which is what one usually wants. Two 15's and a "widish" horn and you have an excellent setup. A little big for me and I would question the audibility of the significantly higher cost design. Good value? I don't know.
Whazzat?
Naive, I'd say
lol lets see your TL design.....how about youstate what it is that you disagree with, so we can debate it like gentleman, instead of making snide comments =)
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I'm not saying I wouldn't invest in another 18" to make this happen if I so chose...but, I have a pair of 18"s and 15"s.....I was thinking MTM but with a 3 way crossover. I have a feeling the 15" will sound better at the cross-over than the 18"....but if it were 2 18"s, in a 2way MTM they wouldn't have to work so hard....also, the polar between the 15" and 18" is pretty good crossed below 90hz, looking at about 65hz. The one thing I have neglected is the polar between the horn and woofer, a thing, that the MTM doesn't struggle with.
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It looks like a resistive vent, i.e. an a periodic enclosure. Probably better than a TL
We've talked about this option before and I think I was concerned about height after moving horn to ear level (~48") but maybe that will be my sacrifice for the greater good.
I've been trying to imagine how a mtm with mismatch woofers would perform and it reminded me of ported/TL and how HornResp figures performance of the summed sources. For example.... if group delay of the port is 18ms and the woofer was 6ms is the resulting group delay. I'm just wondering about phase/polar. I guess in the MTM configuration I could also just use really low order crossovers...that might be a good option to explore.
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It looks like a resistive vent, i.e. an a periodic enclosure. Probably better than a TL
I'm having a hard time connecting you calling me naive and your last post.... If you think I could do better, differently, speak up, thats why am I here, to be criticized. I know what an aperiodic vent is and TL can be tuned to be aperiodic, but this is called Tapered TL.
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It is hard to predict what the mismatch in woofers would do but it is unlikely to be beneficial. The idea is for them to be matched and MTM's only really work with a limited range of crossover types otherwise you get some very odd lobing patterns. There are many 3 way speakers that place a mid above the tweeter with woofers below but I can't say I have seen one of the size yours would be. 3 way with the mid above the horn will increase centre to centre difference which may or may not be a problem for integration depending on the crossover frequency. You would probably get a better result from running the horn and 15 as a speaker together and using the 18's as separate subwoofers elsewhere in the room where they will work better.
If you have dropped the 2 way as a design limit then there is no reason why you can't go into the more well trodden route of separate subs
Hi Fluid, thanks for responding. The last main idea was to have the horn and 15 be the two way and the 18" subwoofer. I personally want my subs right there with the rest of the system. I know of the practice of using multiple subs, I envision 2 more "subs" sitting behind me, symmetrically aligned with the subs in the front. WE have this brought up all the time; whats a 2way plus stereo subs....a 3 way or a 2.2 system.
OK you addressed the polars. A (W/M)TM would cause concern of the polar... at 60hz (potential xover) theres not much change, the polar is a little less narrow but the whole idea (of the mtm) is a thin polar on the vertical axis is it not? On axis everything is fine. So I don't know what to think of that.
The TMW is the fallback configuration for sure. After I feel like I'm creating a good setup I like to push that to the side and say, "what about this" so please forgive if I try your patients. In the TMW, I'm still thinking shallow xovers except on the horn itself. The 48db high pass is killing me on group delay of the 15...the low pass on the 18", I can make 48db work, group delay isn't such an issue for some reason.
I was just reminde of the issue I've neglected this whole time, the polar from woofer to horn....12" from center horn to bottom of horn box, approximately....another ~8" from top of enclosure to the middle of a 15"..... maybe I should get another pair of 15's MTM and then the 18's are my dedicated satellite sub.
OK you addressed the polars. A (W/M)TM would cause concern of the polar... at 60hz (potential xover) theres not much change, the polar is a little less narrow but the whole idea (of the mtm) is a thin polar on the vertical axis is it not? On axis everything is fine. So I don't know what to think of that.
The TMW is the fallback configuration for sure. After I feel like I'm creating a good setup I like to push that to the side and say, "what about this" so please forgive if I try your patients. In the TMW, I'm still thinking shallow xovers except on the horn itself. The 48db high pass is killing me on group delay of the 15...the low pass on the 18", I can make 48db work, group delay isn't such an issue for some reason.
I was just reminde of the issue I've neglected this whole time, the polar from woofer to horn....12" from center horn to bottom of horn box, approximately....another ~8" from top of enclosure to the middle of a 15"..... maybe I should get another pair of 15's MTM and then the 18's are my dedicated satellite sub.
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Great post! You made my day!!
Docali you are my superman. We'll make DonK, the Incredible Hulk....or maybe Iron man.
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So they crossed a radian thats rated to 500hz at 300hz....in horn thats rated to 800hz.............................................................but the Axi, rated to 300hz....people are very critical in their speculation of even being able to do what it claims....specualtors
Have a look at the ctc......so much for the polar at crossover and why not bring the drivers as close together as possible?
Best Room Under $50,000 at LAAS
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I will find this Clayton Shaw lol.
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Do you know why you want the subs sitting right there? A double bass array is an excellent setup for active mode cancelling, rarely is the best place for the subs right next to the speakers in any of the configurations for multiple subwoofers. The only real reason to have a sub next to the satellite is because you want stereo bass or there's nowhere else they fit. The three way vs 2.2 is semantics, calling it a different name doesn't change what it does, seems like an argument for the sake it so I won't add fuel to the fire
At 60Hz distance is not really an issue no. An MTM is either for increased power handling, a tighter vertical polar or both. The vertical polar comes with off axis lobing so there is no free lunch there. A 15" pro woofer indoors would likely blow your head off if run at full power so I can't see the need for two especially if there is going to be a driver crossed below it. There was a design posted earlier with two 15's either side of at XT1464, I quite like it but it seems overkill.
What do you consider to be shallow? Complementary linear phase is the way to go if you want steep, no group delay. Acoustic LR4 is also a good target to aim for, yes it has group delay but it really is not audible. If you plan to push the horn as low as possible then steep may be needed. Just because the driver can get to 200Hz on the horn doesn't mean it can do it loud without excessive distortion, a steep crossover could help with that.
It has probably been avoided because you seem to have wanted a horn that beams as a trade off for going very low. It's somewhat at odds with then wanting to follow conventional wisdom and match the polars at the crossover
At 200Hz it is debatable if it really matters that much anyway as you are at the mercy of the room at that point.
If it was me I would pick the horn that I want, build it and measure it with the driver I chose and measure the 15 in the box that it will be in. That way you can see what the best match will be between them. The sub can be separate and put wherever you want.
As I said before it is important to consider the system together. Think about the horn, the woofer and the cabinet they will go in, separate horns with big rollbacks can work but most of the best results come from integrating the horn and woofer into a cabinet to minimize diffraction. Maybe if you ask Don nicely he will model you a horn with a separate woofer box and one where it is integrated so you see the difference.
You have said many a thing lol.
I do want stereo bass
I bring up MTM because 1...it puts the polar dead center of the HF. I like that. 2...with the 15's its the only way they can reach 30hz at the goal spl (115db) (AETD15m). Maybe I'm being Crazy (Docali says I'm crazy all the time lol!~)...the TMW would only pull the center of the polar down to the middle of the horn and woofer....I hope I'm right by putting phase lag at 0 in xdir.
You nailed it on the crossover stuff. I will be using minimum phase because I won't tolerate the excess latency of FIR processing. If I was shown otherwise I would consider it later I guess. My amps have build in dsp that is minimum phase.
"Just because the driver can get to 200Hz on the horn doesn't mean it can do it loud without excessive distortion" Oh for sure, I was thinking the same thing. Steep filter. "At 200Hz it is debatable if it really matters that much anyway as you are at the mercy of the room at that point." - I know! I've buried all the crossovers into the room, its great.
":Think about the horn, the woofer and the cabinet they will go in, separate horns with big rollbacks can work but most of the best results come from integrating the horn and woofer into a cabinet to minimize diffraction" - wise comment. Don is already on it with the horn roll back. The best I know to do for the box is to put the angle or round over on the edges.
Good points....I guess as long as I get all the drivers time aligned, I won't have much phase lag and the polar will be center of horn and mid, at the center of xover. Thats not exactly the end of the world....When it comes to crossing over the 15" to the 18", this is where I thought shallow xovers would be choice. Slightly wider polar than if it was a TMM...and then up top, a shallow low pass on the mid, and steep HP on the Horn...
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A particular MTM with the XT1464 has been my model and the box to try to beat for several years.
It's been the Peter Morris PM60 (with XT1464) and PM90 (with HF950) horns using two horn loaded 12"s ....
They simply rock, and image as well.
Below are a set of measurements made from one, recently put up on the Square Wave thread.... good square waves are even harder to get than flat mag and phase traces...
I've also made modular MTM's, MMT transmission's, and simple MT's, all with the same drivers.
All measured nearly identical in the far field where imaging becomes optimal (>3x longest speaker dimension ),
but the MTM's "virtual vertical center" gave it a bit of an imaging edge.
Out of the various builds I've tried, I think a synergy may be the only one that has better potential imaging.
Anyway, I'd go MTM with 12"s or even down to 8"s, depending on desired SPL, with separate subs. A flippin 3-way
Stack em on the subs for 1/4 WL goodness and stereo bass, ..use more subs ala Geddes if you want...
Better tie in with 12"s and under, than 15"s, to whatever horn other than a really big horn,imo.
Maybe copy the new Meyer X-40 with a killer mabat horn design...(uses 8"s) or alter the PM designs if you're after being creative.
And you'll have speakers that can be moved if that matters.
(Because a pure aside....if you ever want to hear how much we routinely leave on the table SQ-wise, ....despite all our meticulous driver selection, simulations, careful construction design, tuning, tweaks, etc, etc........take a powerful, clean, well tuned, portable rig like we currently talking, outside, and be prepared to both laugh and cry. Laugh for joy at how good it sounds. Cry realizing the necessary SQ deflation, having to go back indoors. )
Anyway, my 2 cent recommendation
It's been the Peter Morris PM60 (with XT1464) and PM90 (with HF950) horns using two horn loaded 12"s ....
They simply rock, and image as well.
Below are a set of measurements made from one, recently put up on the Square Wave thread.... good square waves are even harder to get than flat mag and phase traces...
I've also made modular MTM's, MMT transmission's, and simple MT's, all with the same drivers.
All measured nearly identical in the far field where imaging becomes optimal (>3x longest speaker dimension ),
but the MTM's "virtual vertical center" gave it a bit of an imaging edge.
Out of the various builds I've tried, I think a synergy may be the only one that has better potential imaging.
Anyway, I'd go MTM with 12"s or even down to 8"s, depending on desired SPL, with separate subs. A flippin 3-way
Stack em on the subs for 1/4 WL goodness and stereo bass, ..use more subs ala Geddes if you want...
Better tie in with 12"s and under, than 15"s, to whatever horn other than a really big horn,imo.
Maybe copy the new Meyer X-40 with a killer mabat horn design...(uses 8"s) or alter the PM designs if you're after being creative.
And you'll have speakers that can be moved if that matters.
(Because a pure aside....if you ever want to hear how much we routinely leave on the table SQ-wise, ....despite all our meticulous driver selection, simulations, careful construction design, tuning, tweaks, etc, etc........take a powerful, clean, well tuned, portable rig like we currently talking, outside, and be prepared to both laugh and cry. Laugh for joy at how good it sounds. Cry realizing the necessary SQ deflation, having to go back indoors.
)Anyway, my 2 cent recommendation
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True, if you want me to stop just let me know
Fair enough, ask yourself why though.
If the physical height of the speaker is an issue then polar position makes more sense, if you can move it up and down then I don't think that represents a real problem, more of a choice, make sure to look at some sims of the lobes you will generate to make sure that is trade a off you are happy with.
I have attached two screenshots from rephase showing an LR96 linear phase crossover. With no optimization 16384 taps is needed to get an exact match to the textbook slope. You can see that the red and blue lines are virtually on top of each other. Blue is ideal red is actual. That gives 185ms latency, so less than 2/10 ths of a second after pressing play before sound starts.
If that is too much with a little optimization, you can get the same exact match with a 4096 tap filter and 46ms delay. You could take it further if 46ms of your time is too precious to waste after pressing play to hear sound
The flat line through the middle of the graphs is the phase response.
That being said minimum phase LR4 acoustic is still a good target.
If you want to go MTM then I think you should seriously consider putting the waveguide in the box with the woofers for the reduction in diffraction or if nothing else just to make it easier to build. Diyuser's speaker above is a very good model to start from.
You would say that
No offence was meant by it, your's is the build I was referencing and I think it is very well thought out. I came very close to buying 4 15PR400's after seeing it as I have the same horns sitting around, who knows maybe I still will 
