Rebuilding Monitor 10's as MTM's?

Treker-1701

Hi All,

I was just wondering if anyone here has ever rebuilt a set of Monitor 10's (in my case I have 10A's) in an MTM configuration? If so, what were the results?

I have thought about doing this in the hope of ending up with a set of taller, skinnier speakers but with the same great sound I have come to know and love all these years.

Thanks for your input.

Regards,

Treker

Face

Wouldn't work correctly. Take a look at the vintage RTA line.

Treker-1701

Face wrote: »

Wouldn't work correctly. Take a look at the vintage RTA line.

Thanks for the input! Maybe I'll have some luck finding some old RTA's on Craigslist.

Regards,

Treker

heiney9

RTA 11's and 8's are a true MTM D'appolito array. You'd be better off finding a pair of those than butchering a good pair of 10's.

H9

dorokusai

I concur with that dude.....

Just a bad idea overall when you can find vintage Polk loudspeakers in that style of array.

Boywonder

I have spent considerable time pondering this very question. I think it would be a worthwhile exercise, preserving your original cabinets for bailout of course. If speakers are your hobby, why not, you might learn a few things. My thoughts would be to maintain the exact cabinet volume of the original, and consider putting the PR at the top of the cabinet for reduced floor coupling. This may also allow more "even" acoustic coupling of the mids with the PR (as opposed to the PR lower on the side baffle) but this may or may not be that important.

The image was modeled (in about 2 minutes, so it's rough) using the same LxWxH of the orig cabinets. This allows the exact same baffle dims for the PR, minimizing unknowns for unwanted baffle frequency response anomalies.

Another advantage of this mod would be that you can have the PR's facing outboard (toward the side walls) or inboard (facing each other) for tailoring the bass response.

You could also entertain a slimmer baffle for the MTM but that would also change the PR baffle since the volume has to remain constant.

This is not the first time this question has been asked......I have 2 sets of monitor 10's so maybe if the mood strikes I'll give it a try. If you are handy with MDF, you could knock out a cabinet in a couple of hours and compare it to to original monitor 10. The other nice thing is that you don't have to get mired in xover design.

Ricardo

I think it would be a great experiment. I say go for it.

dorokusai

Oh he wants to build new cabinets? I still think it's a bad idea but with Polk drivers since it's been done. If the option was for a new DIY MTM array loudspeaker, rock on.

Boywonder

Do any of the vintage MTM RTA line have 10" PR's?

dorokusai

Yes, the RTA15TL.

Mike Kozak

excuse the question, but what does MTM stand for?

Mike Kozak

midwoofer, tweeter midwoofer, found it

heiney9

Mike Kozak wrote: »

midwoofer, tweeter midwoofer, found it

A "true" MTM was the brain child of Joseph D'Appolito.

D'Appolito
A loudspeaker configuration developed by and named for Joe D'Appolito, in which a high frequency driver, or tweeter, is positioned between two midrange or low frequency drivers that each cover the same frequency range. Depending on the exact implementation the speakers can be positioned with a vertical and/or horizontal orientation. In either case the two midrange drivers serve a couple of purposes: they combine to create a larger effective woofer or midrange driver size, and they also serve to control the dispersion of the tweeter. The tweeter's output is somewhat corralled or contained by the sound coming from the midrange drivers in a similar way to how two parallel surfaces control dispersion. There are some variations on the design where two same sized woofer/midrange drivers may cover slightly different frequency ranges, however those aren't considered true D'Appolito designs. (Input from an inSync Reader:) The D'Appolito design specifies a third order crossover network. �The tweeter is coordinated with the woofer so that at the selected crossover frequency, the drivers all have similar horizontal dispersion. �(This is not easily accomplished because many drivers behave badly at the extremes of their range.) The advantage of doing it all correctly is one of the most seamless blending of drivers possible. The result is an absence of any sudden change in directivity with frequency. This may not mean much for monitors where there is a limited listening area, but in a typical room where a large percentage of the sound is reflected by the room, the effect is dramatic.

H9

shadowofnight

I've already done it ( Slightly modified MTM with the tweeters offset ala LSi type of arrangement ... mirrored of course ) ...extensively braced...10" PR mounted in the rear coupled to the 6.5" drivers in a push/pull manner ala CRS+ design.

I built these from scratch ( Didnt destroy a set of 10's :eek: ) with drivers/PR's/Crossovers ( Upgraded Caps ) I had gotten from Polk many years ago in a HUGE order I made.

I basically went with the slightly modified tweeter location to mirror a CRS+ baffle arrangement when layed on their side because I also had spare CRS+ crossovers and wanted to try with that configuration ( CRS+ super sized when the SDA crossovers were installed )

Both setups sounded fantastic...I needed a smaller footprint so kept the Montor 10 crossovers installed and used vertically.

It worked out really really well...so if you want to go for it , I say you do

Mike Kozak

pretty cool

heiney9

shadowofnight wrote: »

I've already done it ( Slightly modified MTM with the tweeters offset ala LSi type of arrangement ... mirrored of course ) ...extensively braced...10" PR mounted in the rear coupled to the 6.5" drivers in a push/pull manner ala CRS+ design.

I built these from scratch ( Didnt destroy a set of 10's :eek: ) with drivers/PR's/Crossovers ( Upgraded Caps ) I had gotten from Polk many years ago in a HUGE order I made.

I basically went with the slightly modified tweeter location to mirror a CRS+ baffle arrangement when layed on their side because I also had spare CRS+ crossovers and wanted to try with that configuration ( CRS+ super sized when the SDA crossovers were installed )

Both setups sounded fantastic...I needed a smaller footprint so kept the Montor 10 crossovers installed and used vertically.

It worked out really really well...so if you want to go for it , I say you do

Nice speakers!!! Not really a true MTM design, neither is the the LSi 9 or 15. Certainly a worthy variation. To the OP scour e-bay for a while because people are always parting out speakers. You can get the x-overs and drivers to experiment with and still keep your 10's unmolested.

H9

dorokusai

That's great work Shadow.

Boywonder

As heiney mentioned above, D'appolito MTM designs are used with odd order crossovers (usually butterworth 3rd order 18 db/octave slope) to accomplish two things; eliminate vertical polar tilt in frequency response, and to dramatically minimize the vertical "lobing" effect of the FR pattern.

Polar tilt means best FR for some odd-ordered crossovers is tilted 15 degress toward the floor (for tweeter in normal polarity). That's why a number of small 2 way monitor speakers have sloped front baffles (to straighten out the tilt so it's parallel with the floor). Sloping the baffle also helps with time-alignment of the acoustic centers of the drivers.

This is explained in great detail in the "loudspeaker design cookbook" by Vance Dickason, a great read for the speaker builder.

Face

Boywonder wrote: »

This is explained in great detail in the "loudspeaker design cookbook" by Vance Dickason, a great read for the speaker builder.

IMO, it's a great read for anyone in this hobby.

tx_polkhead

shadowofnight
wow those homebrew polkies look sweet!

RuSsMaN

Agreed, great work shadow.

shadowofnight

Thanks guys....here are the surrounds I made to complement those...Vance made a lot of money off of me...I wore out every copy of the cookbook I have ever owned

Damn...even with the grills ON , the time aligned smaller cabinets got dusty with that angle...time to break out the canned air


P.S. I made custom non resonant routered MDF grills for the 2 larger set of speakers...thats the reason just those drivers are not flush mounted...with the custom grills on they are perfectly flush mounted.

Treker-1701

Great looking speakers Shadowofnight! That is very similar to what I had in mind.

Did you keep the interior volume of the speakers the same as the 10's? Also, did you make the cabinets yourself (if so, great job!) or did you have a cabinet shop or someone else make them?

Later,

Treker

ben62670

shadowofnight wrote: »

I've already done it ( Slightly modified MTM with the tweeters offset ala LSi type of arrangement ... mirrored of course ) ...extensively braced...10" PR mounted in the rear coupled to the 6.5" drivers in a push/pull manner ala CRS+ design.

I built these from scratch ( Didnt destroy a set of 10's :eek: ) with drivers/PR's/Crossovers ( Upgraded Caps ) I had gotten from Polk many years ago in a HUGE order I made.

I basically went with the slightly modified tweeter location to mirror a CRS+ baffle arrangement when layed on their side because I also had spare CRS+ crossovers and wanted to try with that configuration ( CRS+ super sized when the SDA crossovers were installed )

Both setups sounded fantastic...I needed a smaller footprint so kept the Montor 10 crossovers installed and used vertically.

It worked out really really well...so if you want to go for it , I say you do

Very nice. I was thinking of doing the same, but the PR (12's)side mounted, and the mids tight to the tweeter for phase reasons. I don't like the looks of your speakers though. I'm kinda one of those black primer sharp edge kinda guys(read I'm not good at getting them finished:o). Actually I am going to finish mine AFTER I get moved. I don't want to destroy the veneer moving 300# monsters. I would not hesitate to pull the drivers from some monitor 10's. Most likely the boxes aren't show room condition, and if you can build, and finish you would have a very nice set of speakers better than most offerings under a G. IMHO
Ben

shadowofnight

The larger 2 pair of cabinets I made...the time aligned smaller 2 pairs were part of a pair of kits I purchased from Audio Concepts inc ( ACI ) http://www.audioc.com/speakers1/speakers.htm ....Those came with the cabinets assembled already ...just had to solder the crossovers together and wire up and mount the drivers ( Both Vifa drivers in those I believe ) .

I made the Polks much deeper to keep the same internal volume...also had to factor in the space taken up by the bracing and what was added by the enclosure dampening material ( Both Acousta-Stuf polyfill and the Sonic barrier acoustic foam )


Ben...I only like real wood veneer on very thick MDF...but in my youth I only built them black ( But still hated sharp edges ) ...you can still router and then still go black and that is very easy if you dont want to go the harder roundover method.

I experimented with the offset tweeters and the distance to be able to try them as larger CRS+'s...turned out it sounded fantastic vertical with the monitor 10 crossovers as well ...so that was the reason behind that.

I am getting together some MONSTER subwoofers at the moment that are going to be pushing over 400 lbs....requiring friends over and for them to be put together RIGHT where they will be used

ben62670

Where are you located S.O.N. ?
I like the way you think. BTW my Big ones are going to be 1.5" MDF veneered with cherry, mahogany, or teak. I do like the stone spray paint on the faces though.

shadowofnight

ben62670 wrote: »

Where are you located S.O.N. ?
I like the way you think. BTW my Big ones are going to be 1.5" MDF veneered with cherry, mahogany, or teak. I do like the stone spray paint on the faces though.

Bout 4,000 miles away on the other coast :eek:

I have the cabinets cut already...1" MDF with a layered 3/4" MDF sandwiched on top of that to flush mount the drivers without having to router and lose mounting depth for the drivers.

I havent decided yet if I am going with veneer yet on these or a full Rhino truck bed finish ( In black of course ) ....if I choose the Rhino lining I will get the individual cabinet pieces done before assy in the room.