TMM or MTM................

[davideckhoff]

Hello all...........

I would like to use (2) Peerless HDS164's (830875) and (1) XT25 in a set of L/R front channel speakers for my front room, 200 sf, and want them to be of the best detail and imaging. What would the best configuration be? MTM or TMM 2.5? What are the pros and cons of the two? Any thoughs would be greatly appreciated!!!

Cheers and thanks........

David

[dthomas]

Provided Link: http://www.io.com/~patman/s1.html#crossover


> Hello all...........

> I would like to use (2) Peerless HDS164's
> (830875) and (1) XT25 in a set of L/R front
> channel speakers for my front room, 200 sf,
> and want them to be of the best detail and
> imaging. What would the best configuration
> be? MTM or TMM 2.5? What are the pros and
> cons of the two? Any thoughs would be
> greatly appreciated!!!

> Cheers and thanks........

> David

Depends on your experience. MTM is more difficult to implement and limits you to a lower crossover frequency. The latter may not be an issue as many tweeters will cross easily at below 2khz. You are also limited to 3rd order networks with an MTM though some thought is leaning toward this may not be as necessary as initially thought. Even order networks can create some horizontal dispersion issues in an MTM.

Personally I would lean towards the MMT. And make it a 2.5way to improve bass response. You do not need two woofers as your tweeter is more sensitive. But you do need more bass response to compensate for Baffle Step. So my vote is a 2.5way.

Here is a link to a project that is similar using the Morel MDT 30 tweeter.

Dave

[curt_c]

Both topologies can be done successfully, and will likely have little difference in detail and imaging, all else being equal

There are some differences, however.

An MTM:…
Will be taller than the TMM to put the tweeter at seated ear height.
Will have a simpler crossover. (when using a 2 way)
Will have worse vertical off axis performance, or demands a very low crossover point.

Another option is to make the MTM a 2.5 way. This will alleviate the issue with the vertical off axis performance mentioned above.

I’ve not used the XT25, but I recall the general impression was that a shunt conjugate filter should be used to flatten the impedance hump when crossing below 2K for reduced distortion and better power handling.

C

[davideckhoff]

> Both topologies can be done successfully,
> and will likely have little difference in
> detail and imaging, all else being equal

> There are some differences, however.

> An MTM:…
> Will be taller than the TMM to put the
> tweeter at seated ear height.
> Will have a simpler crossover. (when using a
> 2 way)
> Will have worse vertical off axis
> performance, or demands a very low crossover
> point.

> Another option is to make the MTM a 2.5 way.
> This will alleviate the issue with the
> vertical off axis performance mentioned
> above.

> I’ve not used the XT25, but I recall the
> general impression was that a shunt
> conjugate filter should be used to flatten
> the impedance hump when crossing below 2K
> for reduced distortion and better power
> handling.

> C

So..............it is better to layout the baffle as M-T-M and wire as T-M-M 2.5 Way?

David

[dthomas]

> So..............it is better to layout the
> baffle as M-T-M and wire as T-M-M 2.5 Way?

> David

Personally I think the MMT would be easier to align to get good baffle diffraction, imaging etc... But it is more about what you are trying to accomplish here. It also will be more flexible as far as crossover topology. The MTM can acheive similar results but a bit more difficult to acheive. By this I mean the layout of the drivers on the baffles is a bit more critical. The MMT is more flexible in regards to xo frequency with the tweeter also.

Also personally I like the look of an MMT in a tower better than MTM, but that is of no importance.

Either done as a 2.5 way will allow improved bass response by letting the lower woofer combine in to accomplish baffle step. This will be the weakest area for a midwoofer main. Of course if you supplement with a sub then maybe that is not part of your design criteria. What is your primary use of these speakers, Music only, HT only or both.

IMO I would select the the configuration that appeals to you. At the end of the day the primary difference of an MTM or MMT 2.5 way done right is the look you get. Pick the one that looks best and then design for the best imaging, flattest frequency response etc...

Also encourage more input from Curt C. he is very knowledgeable and is a great resource to anyone on this board.

Dave

[davideckhoff]

I will be using (2) of the peerless HDS164's and a XT25 in an ported arrangement that will still need a sub in the room for the lowend. The system will need to handle the front two channels of everyday stereo and some occassional HT. The room is a smallish living room with about 200 sq feet. Is this overkill in such a room? In other words.........would it be just as quality to go with a standard 2-way in this case due to the included sub anyway?

I was planning on using the HDS134's or HDS106's with an XT25 in a standard, ported two way configuration for small rear HT channels in the future.

For the front channels I was thinking that paralleling the (2) HDS164's in a MTM would make things easier by bringing the 8ohms of the HDS164's down to match the 4ohms of the XT25. Am I missing a more important benefit of crossing them over seperately? I want these to have as much detail and quality imaging as possible.

Am I expecting too much?

[dthomas]

> I will be using (2) of the peerless HDS164's
> and a XT25 in an ported arrangement that
> will still need a sub in the room for the
> lowend. The system will need to handle the
> front two channels of everyday stereo and
> some occassional HT. The room is a smallish
> living room with about 200 sq feet. Is this
> overkill in such a room? In other
> words.........would it be just as quality to
> go with a standard 2-way in this case due to
> the included sub anyway?

> I was planning on using the HDS134's or
> HDS106's with an XT25 in a standard, ported
> two way configuration for small rear HT
> channels in the future.

> For the front channels I was thinking that
> paralleling the (2) HDS164's in a MTM would
> make things easier by bringing the 8ohms of
> the HDS164's down to match the 4ohms of the
> XT25. Am I missing a more important benefit
> of crossing them over seperately? I want
> these to have as much detail and quality
> imaging as possible.

> Am I expecting too much?

First of all good driver choices. Secondly if MTM appeals the most to you then that is the right direction to go. I have built several MTMs and was very pleased. IMO I would not be concerned with matching impedance of the tweeter and midwoofers.

Probably the next thing to think of is crossover topology. Personally I think you can acheive great results with a first order series network at the expense of some loss in power handling in the tweeter. So if you like your audio ear bleeding a higher order network will be needed. Check out Andy G.'s site a lot of very good data on 1st order series networks. They are very easy to design especially with high quality drivers such as the one you have chosen. They definitely offers some improvements in dynamics and transient response which will equate to imrovements in detail. If you go first order you might need to notch the slight rise at 4khz in the woofer. Though I would model it and see exactly what role it will play.

Check out Andy's site lots of good reading.
<A HREF="http://users.tpg.com.au/users/gradds/">http://users.tpg.com.au/users/gradds/</A>

Here is a good example of a design using these drivers with crossover etc... Maybe good for some inspiration it uses a 1st, 2nd and 3rd order netowrk. This topology would easily adapt to an MTM.
<A HREF="http://www.troelsgravesen.dk/HDS164.htm">http://www.troelsgravesen.dk/HDS164.htm</A>

Sounds like fun... getting me motivated to start some dipole surrounds I have in the shop using Vifa P13 and a pair of Dayton neo tweeters.

Dave

[davideckhoff]

Provided Link: http://www.aanvilaudio.u-net.com/ap_center_1.htm


This is what intruiged me originally.......

[davideckhoff]

.............or check out the Tempo from the same link.

:-)

[dthomas]

> .............or check out the Tempo from the
> same link.

> :-)

David,

Exactly the right approach finding something that appeals to you and building your interpretation of it. Usually something catches my eye and I head in that direction.

The tempo talks as if they used a 1st order crossover. Something these drivers are easily suited for.

I encourage to readup on Andy G.'s site there is a ton of useful information. I just built a 3 way using a first order network. Transient response is amazing.

There is a little bump of about 3db at 4 khz in the woofers response. This may not bother you at all. At 3db it may not be objectionable at all. This also keeps xover costs low. The series topology of the crossover presents an easy load to your amp so that dynamic range is easily acheived at varied listening levels.

Let us all know what you do and how it turns out.

Got tickets to the Cheif/Cowboys game so I gotta go. Also finished off a media cabinet this morning for my latest project. It should be dry and ready to go into service when I get home tonite.

Good Luck,
Dave

[davideckhoff]

Provided Link: http://www.troelsgravesen.dk/HDS164.htm


Is the crossover used in the link a series crossover and if so what would be the indicator? I don't see it.....................

How would I go about designing a series crossover for this 2.5 set up?

David

[curt_c]

> Also encourage more input from Curt C. he is
> very knowledgeable and is a great resource
> to anyone on this board.

As are you Dave. You've already covered this subject succinctly...

C

[curt_c]

> How would I go about designing a series
> crossover for this 2.5 set up?

I'll let Dave explain that one...

C

[Andy_G]

The XT25 requires more than a normal 1st order series x-o.

I'm at Uni at the moment, but if David wishes to email me, I have an MTM x-o at home using the 850467 + Vifa XT. Fr and Imp are smooth as!!

I can't comment on how suitable it would be for driver mentioned, because all my info is on my home puter. But I would think it might be pretty close !

[dthomas]

> Is the crossover used in the link a series
> crossover and if so what would be the
> indicator? I don't see
> it.....................

> How would I go about designing a series
> crossover for this 2.5 set up?

> David

It uses a 1st order on the lower woofer a second order on the other woofer and a third order on the XT-25. The link that you sent on the "Tempo" eludes to the fact that it may be using a first order. But it does not really say for sure.

I have never used the XT25 and Andy has chimed in that he has a series crossover that he already worked out. Take a look at his design it should get you in the right direction. There are drawbacks to using a first order network but there also benefits. Dynamics and detail are probably the most prominent benefits. One thing I have learned about xovers that like most anything there is not a sure fire winning topology they are all trades.

Biggest concern I would have with an MTM using a first order is that the low crossover point would likely stress the tweeter a bit. As I stated before an MTM would using a first order with these drivers would definitely reduce power handling. In my opinion not enough to preclude these drivers from this approach. Also using low dcr inductors will help. Andy likely accounted for this issue in the MTM design he eluded to.

Dave

[dthomas]

Provided Link: http://img.villagephotos.com/p/2005-...s.parallel.jpg


> Is the crossover used in the link a series
> crossover and if so what would be the
> indicator? I don't see
> it.....................

> How would I go about designing a series
> crossover for this 2.5 set up?

> David

Sorry I ignored the last question. You can use Andy's calculator on his site for determining compenent values. I am using xover sim to model the responses. It can be downloaded at the FRD site.

Here is an example from Andy's site of a 2.5 way. The lower woofer is a simple first order network. You can calculate the value using any 1st order network calculator such as PCD also available at the FRD site. You would want to bring in the lower woofer around the baffle step point. This can be calculated based on your baffle width. As an example if you use an 8" wide baffle, baffle step would occur at around 570Hz, I would make the low pass on the .5 woofer about 1/2 of that around 250 or 300Hz.

Dave

[dthomas]

> The XT25 requires more than a normal 1st
> order series x-o.

> I'm at Uni at the moment, but if David
> wishes to email me, I have an MTM x-o at
> home using the 850467 + Vifa XT. Fr and Imp
> are smooth as!!

> I can't comment on how suitable it would be
> for driver mentioned, because all my info is
> on my home puter. But I would think it might
> be pretty close !

Andy,

I would like to see the crossover. What is the issue with XT 25 I have never used it?

Dave

[davideckhoff]

I have mailed Andy for the x-over and will look forward to seeing it. I will have to come up with some kind of "Series Crossovers for Dummies" book like the article available at Rod Elliot's ESP site about parallel design. I just have a difficult time finding a good all encompassing guide to go by.

I think this is the hardest part for a newbie. I teach nautical science by day and know next to nothing about electronics by night but I have been bitten by this bug and can't seem to make sense of it all.

I am putting together all of the test equipment as well as SE v11.0 in order to be able to design crossovers and make changes to them and at the same time be able to see how those changes effect the response curves.

All this and I must learn a new operating environment on the PC.................I am a Mac guy.

[dthomas]

> I have mailed Andy for the x-over and will
> look forward to seeing it. I will have to
> come up with some kind of "Series
> Crossovers for Dummies" book like the
> article available at Rod Elliot's ESP site
> about parallel design. I just have a
> difficult time finding a good all
> encompassing guide to go by.

> I think this is the hardest part for a
> newbie. I teach nautical science by day and
> know next to nothing about electronics by
> night but I have been bitten by this bug and
> can't seem to make sense of it all.

> I am putting together all of the test
> equipment as well as SE v11.0 in order to be
> able to design crossovers and make changes
> to them and at the same time be able to see
> how those changes effect the response
> curves.

> All this and I must learn a new operating
> environment on the PC.................I am a
> Mac guy.

Andy's site has a ton of great links to read up on. Also he is a great guy and very willing to help out. Play with the tools you will be surprised what you will learn also this site is full of very knowledgeable folks that are always willing to help out and are never short of opinions. I know the issue with the bug, I have been doing this for this for the past 5 years and I have yet to bore with it. By day I do fiber optic networks for Power Utilities.

You are on the right track with the drivers you have chosen. The Peerless woofers are great, never used the xt25. I am quite fond of Vifa drivers personally I think they have the best midrange of any drivers I have heard.

I just built a 3 way using some 7" buyout woofers ($14 each), vifa PL13 midrange and the Dayton Silk dome. In completed cabinets they were about $125.00 per speaker and they are exceptional for the price. I used a series first order and the first thing that hit me was how the sound seems to come from nowhere in particular. And the detail is exceptional. Easily better than most of the mass marketed high end hifi.

Plus the satisfaction of doing it yourself.

Dave

[Andy_G]

The res point of the XT can be rather noisy. It must be very well damped, or well avoided.