2,5 way MTM, horisontal or vertical. any reason to not do it?

[FE3T]

I am currently looking into building some High effiency HT speakers with 8" woofers and a small horn with a compression driver.
To get them to play far enough down, i need to tune low and use a second
8" as a 0,5 woofer to get things linear again.

Are there any reason not to place the drivers as a typical MTM design?
and since i want to make the center channel identical, just use it horisontal.
Wouldnt the 2,5 way solution be less troublesome than a regular 2 way MTM?

[sreten]

Hi,


There is no reason to use the typical 2 way MTM layout for a 2.5
way, though it has been done, similar to an inverted MT layout.

Typical 2.5 ways are MMT, with issues similar to a MT.

You are correct that a 2.5 way MTM centre has less issues
than a 2 way MTM for the same c/o point, and they do exist.
(Only less issues I suppose with correct c/o design, its the
control of the lobing axis needs more thought for dual use.)

But there is no reason to go MTM for the other speakers.

rgds, sreten.

see : http://zaphaudio.com/Waveguidetmm.html

[ByronInLawrence]

There's no reason not to do it. But you will not get the benefit of an MTM design. The advantage of having a woofer/mid on either side of the tweeter is that, in the X-over region, lobbing caused by one mid and the tweeter will be cancelled by mirror-opposite lobbing between the other mid and the tweeter. With a 2.5-way system, the second mid-woofer will not have output in the mid-tweeter X-over region. So it won't cancel any lobbing. Still, I can't think of a reason why its a bad idea. If there's some other reason you like MTM designs, or if you may want to convert it to a conventional 2-way some day. I can't say whether or not a 2.5-way is "less troublesome" than a conventional MTM, but any time you've added a crossover, you've added complexity.

[FE3T]

Originally Posted by sreten

Hi,


There is no reason to use the typical 2 way MTM layout for a 2.5
way, though it has been done, similar to an inverted MT layout.

Typical 2.5 ways are MMT, with issues similar to a MT.

rgds, sreten.

see : Zaph|Audio

To be honest, the tread was made to find out if there was any important reasons to AVOID a 2,5 Way MTM setup, if there are none, i have good enough reasons to use the design.

Originally Posted by ByronInLawrence

There's no reason not to do it. But you will not get the benefit of an MTM design. The advantage of having a woofer/mid on either side of the tweeter is that, in the X-over region, lobbing caused by one mid and the tweeter will be cancelled by mirror-opposite lobbing between the other mid and the tweeter. With a 2.5-way system, the second mid-woofer will not have output in the mid-tweeter X-over region. So it won't cancel any lobbing. Still, I can't think of a reason why its a bad idea. If there's some other reason you like MTM designs, or if you may want to convert it to a conventional 2-way some day. I can't say whether or not a 2.5-way is "less troublesome" than a conventional MTM, but any time you've added a crossover, you've added complexity.

My main reason for thinking about building a 2,5way MTM, besides whats mentioned in my first post are that it would be easyer to build 5 identical speakers , and i must also admit that i find the MTM better looking than a MMT, espesially in a center channel.

I have also often seen comments about the 2 way MTM not being especially good as a horisontal center channel because of a narrow horisontal spreading of the sound, and belives that a 2,5 way version migth be better in this area

[sreten]

Hi,

Fair enough, the issues for the main speakers are the same as an inverted MT.
That is the listening axis, which for an inverted MT is usually the M, unless its
a very tall speaker and the axis is either the tweeter or the M/T midpoint.
Of course you can build a tall MTM 2.5 way with the top woofer 0.5 way.

The centre is always going to be a problem in terms of assymetry with a horn
tweeter and its arguable in this case whether 2.5 way is better than 2way.

IMO a different design for the centre may be a better option.

Take at look at : Zaph|Audio - ZDT3.5

Some of the issues are discussed, a centre isn't the same as the others.

rgds, sreten.

[FE3T]

Originally Posted by sreten

Some of the issues are discussed, a centre isn't the same as the others.

rgds, sreten.

Zaph`s site have a well deserved place in my favorites folder

And atleast, a MTM center will let me experiment betwin 2,5 way and 2 way.
since Zaph`points out that less baffle step are needed for a center speaker, i migth get away without using the second 8" as a 0,5 woofer and implement it as the second woofer in a 2 way MTM system instead.
The horn loaded compression driver are hard to get away from since the system migth end up with a sensitivity in the 96-97 db/1w area if i can avoid any additional BSC (The plan are to wall mount the front and surround speakers in respektive corners, and hope for a little help in the 70hz + area)

Components planned used are:
JBL 2118H (dual)
B&C DE250 @ 1,6khz
RCF H100 Horns
28L cabs tuned to 70hz
(JBL used the same 8", volume, and tuning in their Cabaret 4612, also a 2,5 way design)

[weltersys]

Originally Posted by FE3T

To be honest, the tread was made to find out if there was any important reasons to AVOID a 2,5 Way MTM setup, if there are none, i have good enough reasons to use the design.
My main reason for thinking about building a 2,5way MTM, besides whats mentioned in my first post are that it would be easyer to build 5 identical speakers , and i must also admit that i find the MTM better looking than a MMT, espesially in a center channel.

I have also often seen comments about the 2 way MTM not being especially good as a horisontal center channel because of a narrow horisontal spreading of the sound, and belives that a 2,5 way version migth be better in this area

Building five identical speakers is easier than "mix and match", but a 2.5 crossover is a lot harder to get right than a two way.

I'm using some 2.5 way Seas co-ax in my boat, they are great.

MTM work well vertically, properly done less output is directed at the floor and ceiling, while horizontal dispersion is whatever the drivers and horn is.

Placing an MTM sideways is generally not a good idea, as the dispersion is different on and off axis from left to right. Not a problem in the middle seat, just everywhere else.

A sideways 2.5 MTM will not be as objectionable from that standpoint, but still will not have symmetrical horizontal dispersion, which will be evident in the crossover region.

From a design standpoint, considering surround and center don't require extended LF, given the same amount of transducers, I would go with five matched 2 way cabinets and put the other 5 woofers (or dedicated woofer type speakers) in sub(s).

Have fun !

[FE3T]

Originally Posted by weltersys

From a design standpoint, considering surround and center don't require extended LF, given the same amount of transducers, I would go with five matched 2 way cabinets and put the other 5 woofers (or dedicated woofer type speakers) in sub(s).

Have fun !

Well i does feel that they should atleast be able to reproduce 70-80hz , and with the drivers i have, that would not be possible without having a 0,5 woofer boosting the 70-150hz area 3db. just a 2 way with these vould result in 125-130hz -3db and using them for sub duty wouldnt be a good idea, they are after all 8" PA midbass units with 97db/1w sensitivity

A regular 2 way MT system able to play 70 hz -3db would force me to use other drivers and to end up with a sensitivity atleast 6db lower.

[DJNUBZ]

Did you every complete this project? How did it turn out?