advise for mtm concept - Home Theater Forum and Systems -

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post #1 of 12 Old 09-12-09, 08:26 PM Thread Starter
Join Date: Aug 2009
Location: fremantle west aussie
Posts: 47
advise for mtm concept

Hello all
I have been working on this project for some time now, and just getting towards the end of the tunnel
I designed the boxes to maximize a 1200mm sheet of mdf with little wastage in cutting etc I think that the term used in cd process is nesting
At present I have contracted a woodworking company to cut out the panels using a cnc machine, the first boxes will be proto out of 18mm sheets that they use to protect the veneered stuff, my cabinet maker suggested this as it is basically free comes with the good panels! When all the tweaking has been finalized we will use 25 mm veneered mdf for the final product.
I requested that the driver reliefís be rounded on the rear of the baffle to add in air movement from exhaust of the cone, hope that this is the correct practice
I have included a hand drafted design for your perusal; the top section is in its own enclosure I havenít drawn in any bracing but intend to rout out another dividing panel mid way in both upper and lower chambers, these will get the useaual relieving so not the take up to much volume
The mtm section was placed off centre in an attempt to cancel diffractional sound it may give an unappealing appearance but I hope that it is functional
Driver centre line placement is 145 mm this is the wave length for my desired crossover frequency which will be 2380 Hz
The mains are a bit of a worry for me at present as the cone excursion seems excessive for the load, peerless indicate that they will handle 150 watts which is the criteria that I used in bass box also the crossover is another area of concern, I used third order two way for the mtm and have tried to use separate second order for the bass driver, this is going to present some problems with impedance
If any of you have any advise in this area I would be more than grateful
The snap shoot of the bass xo is an overlay of the mtm section I was hoping that this May workout but am unsure at present
I will provide enough terminals on the rear of the cabinet to bi wire and or bi amp, I know that bi amping will ease the cross over worries but would like to keep the equipment list down
I hope that I get some sound advice (no pun intended)
Cheers speedie
Attached Thumbnails
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advise for mtm concept-mtmxo-custom-.jpg  

advise for mtm concept-mymtm-custom-.jpg  

advise for mtm concept-mymains-custom-.jpg  

advise for mtm concept-mainsxo-custom-2-.jpg  

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post #2 of 12 Old 09-12-09, 11:09 PM
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Re: advise for mtm concept

I think you should not have the mids and tweeter offset so much. Put a roundover on the edges of the baffle, and it should work out ok with 1/2 or less of the offset. Or offset the tweeter more than the mids. I just don't think it looks right to me that far off center.

And the graphs would be more helpful if my old eyes could read them.

Also, the Peerless 830869's are out of stock everywhere I checked. If you have them already, no worries, but you might want to comfirm availability.

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Last edited by seattle_ice; 09-12-09 at 11:43 PM.
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post #3 of 12 Old 09-13-09, 07:28 AM
Join Date: May 2007
Posts: 20
Re: advise for mtm concept

first of all: really nice. well thought through as well.

I suppose you put the drivers off center to get a smoother frequency response from the tweeter? Although technically this is very good - it does look a bit odd because the bass driver is not off center als well... but that's just taste... If it doesn't bother you - why not?

Have you thought aboutt maybe crossing over the bass a bit lower? Your mid section has pretty good extension and should be able to handle a 150Hz cross over point without problems. 240 seems to be quite high, considering the 12db filter, the bass will play very high up into the mid section, which wouldn't be really necessary.

The crossover is quite complicated, especially when the bass will be added. Of course three way systems are always like that. Usually I would suggest going half-active (is that the proper term? It's what we call it round here ... ) Considering the cost of the parts needed, it's often cheaper to get a plate amp with high level inputs which does the filtering for you. You're then able to adjust the level of bass as needed, add boosts or subsonics etc. Depending on the module of course.

I remember a project where the parts for the cross over needed would have been just as expensive as a full blown active setup (which we used then). Maybe this is an option for you?
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post #4 of 12 Old 09-14-09, 02:16 AM Thread Starter
Join Date: Aug 2009
Location: fremantle west aussie
Posts: 47
Re: advise for mtm concept

To date I have had some well appreciated input from those that are prepared to either read my post then digest what is being expressed
It seems that we as individuals either lack the fortitude or just sit back and weight (really heavy) for someone else to do the hard work
Surely out of all the individuals out there, there must be someone who has undertaken a similar concept or knows of someone who else has
I donít want someone too build these towers for me, only need some serious input as toward my direction
Cheers to the world speedie
Ps luv Jeff Beck stuff
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post #5 of 12 Old 11-18-09, 07:23 AM Thread Starter
Join Date: Aug 2009
Location: fremantle west aussie
Posts: 47
Re: advise for mtm concept

Well I still havenít gotten my boxes from the cnc dude seems like time flyís by
Would anyone like to comment on the offset idea that I propose I have used this to help with diffractional loses but as far as aesthetics go it does look well not symmetrical
Would it be a reasonable idea to say leave the tweeter where it is and then bring the two mids back onto the centre axis?
This would maybe defeat the geometry of the mtm concept
Any comments greatly appreciated
Cheers speedie
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post #6 of 12 Old 11-18-09, 10:51 AM
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Re: advise for mtm concept

Hey, seems some designs I saw have the tweeter offset and the mids centered on the baffle, no? I think many monitors roundover the front baffle edges as well as flush mounting the drivers. Wish I had more input, sorry. Designing speakers is tricky, so many do not wander down this road, but rather use proven designs to build and finish on their own(the typical recommendation). I'm planning a 3way using active xovers for the woof-mid and passive mid-tweet to begin, then transitioning to full active. Good luck with your plan.
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post #7 of 12 Old 11-18-09, 04:25 PM
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Re: advise for mtm concept

I actually think the design looks ok the way it is. On the other hand, I have seen many designs where the mid-woofers were centered in the cabinet and only the tweeter was offset.
Check out the designs in this link. They use the offset tweeter and centered mids. Maybe you'll like that look.
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post #8 of 12 Old 11-18-09, 04:55 PM
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Re: advise for mtm concept

Most of the designs I have built offset the tweeter by 3/4 inch...Your mileage may vary.
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post #9 of 12 Old 11-25-09, 10:24 PM Thread Starter
Join Date: Aug 2009
Location: fremantle west aussie
Posts: 47
Re: advise for mtm concept

well gents i finaly got my drawings to the cnc dude today and it shouldnt be to long before i get the cutouts back i have wound the inductors bought the caps and are ready for some assembly time
will post some snaps as they are being built
cheers speedie
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post #10 of 12 Old 11-27-10, 07:34 PM Thread Starter
Join Date: Aug 2009
Location: fremantle west aussie
Posts: 47
Re: advise for mtm concept

I canít believe that is one year since I posted on this project time flyís
I have finally got the cabinets cut out at a different machine shop
There has been some drama but they are in my workshop in flat pack at present
I really need to get my into gear and get on and finish them as I have placed an order with emotiva for a 2&5 channel amp,cd player and there processor
I will take some photos of build and post when finished
Cheers speedie
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