M8a MTM Build - Help always appreciated!

[seattle_ice]

I built a pair of MTM towers about 3 years back with the M8a/Vifa XT25 drivers which subsequently were sold to someone. I still have a set of these drivers hanging around and thought I might as well put them to use.

I am a craftsman with wood but with crossovers and speaker design - not so much.

First I would like to make sure the info I have is accurate;

1. Cabinet ~130L
2. 4" x 12" flared port (exit at bottom towards floor)
3. Baffle - critical dimensions:
Baffle

4. Crossover - When I made the first set of these, someone else assembled the crossovers for me. I will need some help with the BOM and How-Tos of laying them out.

I believe this is the correct crossover;

Zobel
Low Pass
High Pass

All suggestions are appreciated.

Darryn

[ThomasW]

Several people have built these both ported and sealed.

Pictures of the crossovers and most everything else is in the thread below.

http://www.htguide.com/forum/showthread.php4?t=3606

http://home.comcast.net/~audio-worx/page113Tibor-MTM.html

[seattle_ice]

Well, maybe I am just electronically challenged, because I have read through both of those threads, and every other one on this board that even makes a mention of the M8a, and I still don't have a good grasp on what parts to buy to put those crossovers together.

I can rewire a musclecar in my sleep, I have been building houses since I was 14 and I love building speakers, but unfortunately just don't have the knowledge about the electronic stuff that I wish I did.

Darryn

[ThomasW]

Example.....



L1011 is a .9mH inductor
L1031 is a .45mH inductor
C1041 is a .3mfd cap
C1031 is a 8.75 mfd cap
C1021 is a 72 mfd cap
C1061 is a 100 mfd cap
R1061 is a 5 ohm non-inductive power resistor
And so on.....



If you take the time to read questions and the answers starting with post #20 you'll find all the info about the parts needed.

Note that Madisound no longer has the $.90GE caps used to make the clusters. This means other caps must be used to create the high values used in this speaker and those are going to be very $pendy given the high values used.

Finally Pete Mazz has built this design twice for family members. You might send him a PM or email to see if he has any pictures of his crossovers and possibly a BOM.

[seattle_ice]

Thank you. That gives me a good starting point.

[seattle_ice]

Note that Madisound no longer has the $.90GE caps used to make the clusters. This means other caps must be used to create the high values used in this speaker and those are going to be very $pendy given the high values used.

I looked on their web site and it appears they have 5.0 and .68 GE caps. Would take a whole load of those for the biggest caps in the X-over. Are these the same caps? Caps

And what about these - Caps

[---k---]

Note that Madisound no longer has the $.90GE caps used to make the clusters. This means other caps must be used to create the high values used in this speaker and those are going to be very $pendy given the high values used.

No more spendy than the big caps all of us are using for the big 3-ways. I know my Khans have a 180 mdf value in the woofer section! Ouch!.

[ThomasW]

I looked on their web site and it appears they have 5.0 and .68 GE caps. Would take a whole load of those for the biggest caps in the X-over. Are these the same caps?

Yes those are what's left of 16,000 GE caps Madisound bought on close out

What values were the ones they offered before?

A lot more than I can remember.

And what about these - Caps

Don't have a clue about those. We decided on the GE caps after testing them in comparison to caps from Solen or PE.

Looking at the pictures of Tibor's caps. They're actually made from the 5mfd GE caps not the 10 mfd caps. When purchased in lots of 100pcs it cost Tibor $10 to make a 100mfd cap.

[seattle_ice]

The difference in price between using Solen FastCaps and the GEs with Dayton to fill in the small values is ~$100 per crossover.

I think that is well worth dealing with some extra size and buss bar fabrication.

Is there really no (or neglible for the price) discernible difference between using one or two large caps and using 25 smaller ones?

[ThomasW]

20+ smaller ones have a lower ESR than 1 or 2 large values. So the cheaper clusters actually create a better cap.

[seattle_ice]

Ok, I am getting ready to order the crossover parts. I have attached my list, so if anyone sees any problems with my order, please let me know.

I already figured that after assembling some of those big clusters the capacitance would need to be measured, and some small values supplied to trim them to the correct value. I tried to find a meter at RadioShack, but couldn't find one. Anyone know of a suitable supplier to get a decent low cost one?

Darryn

[Paul H]

Ok, I am getting ready to order the crossover parts. I have attached my list, so if anyone sees any problems with my order, please let me know.

I already figured that after assembling some of those big clusters the capacitance would need to be measured, and some small values supplied to trim them to the correct value. I tried to find a meter at RadioShack, but couldn't find one. Anyone know of a suitable supplier to get a decent low cost one?

Darryn

I think you're planning to already, but order some extra caps. The 10uF caps were typically 9.7, 9.8, 9.9, and not many were over 10.0, so when a bunch are put together you end up under-running the value you're after.

Parts Express sells meters that will measure capacitance and inductance. I have this one here and its been fine: http://www.parts-express.com/pe/show...number=390-513

I know the list you've assembled is for crossover parts but I don't see other speaker parts - ports, binding posts, internal/crossover wire, solder. You may want to get that stuff now to save time & shipping.

[seattle_ice]

I had planned on ordering some extras, particularly of the small values, and the .68 GE ones from madisound. And if need be, I can order any I need after assembling most of them.

I will check out that meter, I am always a little leary of ordering cheap no-name stuff from ebay.

I already have a large box full of high-quality binding posts, connectors, wire etc., but totally spaced on the port. I will get that now, thanks for the reminder.

[seattle_ice]

Does the distance of the top woofer to the top of the cabinet matter?

For example - can the cabinet be made taller to lessen the depth somewhat while keeping the tweeter height appropriate?

And when cutting ports to length - is the 12" the total length, flares and all?

[ThomasW]

Does the distance of the top woofer to the top of the cabinet matter?

No

And when cutting ports to length - is the 12" the total length, flares and all?

Yes

[seattle_ice]

All the crossover parts are ordered, and the wood is in my garage. Now I just need to clean the garage up from all the post holiday messes - when I clean the house by throwing everything out in the garage.

I decided to build the cabinets slightly different this time. Paint the sides, and stain the baffles. I added a removable panel to the back to allow installation of the crossovers.

I am going with the vent aimed down throught the plinths, with a hollow area in the plinths and spikes to hold the speakers off the floor.

[Hdale85]

Wow you sure go all out on the cabinet plans What did you use to draw all that up including the cut sheet and what not?

[seattle_ice]

Wow you sure go all out on the cabinet plans What did you use to draw all that up including the cut sheet and what not?

For most of my simpler hobby stuff, I use a nice little program called Smartdraw. The first perspective drawing is from Sketchup.

I designed the house we are living in now using Smartdraw. It doesn't do everything, but it is quite handy and quick for 2-d stuff, with small libraries of walls, windows, doors, etc.

Darryn

[TacoD]

Great project. If you're not so handy with a soldering iron, then you can better buy big caps, this reduces the number of joints you have to make. Then you also do not need a LCR meter.

[Hdale85]

Soldering is easy it probably won't take you long to get used to it.

[seattle_ice]

Great project. If you're not so handy with a soldering iron, then you can better buy big caps, this reduces the number of joints you have to make. Then you also do not need a LCR meter.

Thanks, I am actually not bad with the soldering, I do a lot of work on cars.

[seattle_ice]

I now have temporarily assembled one set of crossovers, and am posting the pics to verify that my wiring and locations are correct.

The 3 and 4 terminals on the Woofer crossover are flipped on purpose.


Zobel Prelim

Tweeter Prelim

Woofer Prelim


Thanks,

Darryn

[ThomasW]

I took a quick look things appear to be in order

[seattle_ice]

Which terminals are + and - on the M8a? I can find no markings on them and I don't know if the size (one is smaller than the other) is an indicator.

[Carl V]

use a AA battery + end of battery when connected to the + driver terminal
will yield an outward movement of the cone.

[Smokinghot]

Zobel Prelim

Tweeter Prelim

Woofer Prelim

Really nice layout... Sense the pride of a tradesman in you.

I appreciate nothing more than a person who builds with craftsmanship in mind.

:T

[ThomasW]

IIRC the larger terminal is (+)

[seattle_ice]

IIRC the larger terminal is (+)

That would have been my guess, and the voltage method confirms it.

[PMazz]

The last time I used them they had a black and red stripe either on the spider or right on a section where the voice coil is. Weird.

[seattle_ice]

And here they are. finished with a combination cherry veneer/maple edging finish. I haven't buffed them out yet, but they look good.



I haven't had a chance to listen to them yet, that will come in he next week or two.

[ThomasW]

Sweet...... :T :B

[Dean100]

Very Nice! You put those together very quickly.

[marchel]

Hi , Nice speakers you got,

I'm also considering the m8a for a dual 8 3 way project, I'm wondering how loud and deep do they go. How's the sound qaulity?

Thanks.

[ThomasW]

I'm throwing this link to Pete's build in for reference

http://mysite.verizon.net/buckswwkg/m8n_mtms.htm

[seattle_ice]

I finally got the time to hook them up and listen to them. The cabinets were built to ~125l internal volume, with 3/4" Sonic barrier lining all the internal walls and 6" of fiberglass at the back behind each woofer. The walls are 1 layer 3/4" MDF and 1 Layer 3/4" Baltic birch. The baffles are 2-1/4" thick where the drivers are mounted. The total weight is around 140 pounds each with the plinth. The vent fires out the bottom, and is ~2" from the floor. The crossovers are mounted on three boards, with two going through the woofer holes, and one through the access panel I put on the back.

Let me preface this by saying I am certainly no professional speaker reviewer, and this is only from a couple hours of listening. I have heard lots of mid range ($1000 - $5000/pr) speakers, but very few really high end sound systems. So that is what my opinions are based on. I am a musician however, with a degree in music theory, and I have been playing the piano since I was 7 years old.

The electronics are nothing special, just an pioneer SACD player and an Onkyo receiver (100w/channel) using the direct audio setting. The room is not optimal, as their final resting place is under construction. The floor is Marble, and the ceiling is a 20' high vault.

For comparison, I have a pair of Klipsch RF-63, a pair of North Creek Eska MTM Towers that I built a couple years ago, and a pair of Definitive Audio mini towers.

I listened to: Josh Groban Christmas album (Particularly Ave Maria with the Boys choir), Sarah McLachlan, Seal, Beethoven and Def Leppard.

I have never owned a set of metal-coned speakers, and was somewhat worried they might end up being a tad harsh for me. Not a problem at all, as these sounded more warm than I had expected. Let me say that I think the tweeters are a spectacular value for what they cost.

The speakers are plenty sensitive and will attain good SPLs without ridiculous amounts of power. They are quite close in volume to the Klipsch at the same levels, and slightly louder than the North Creek.

The vocalists voices sound extremely good. With the speakers about 10 feet from me, and about 2' from the back wall, I could not pick out the speakers in the sound field while sitting in the sweet spot. The voices were floating in the stage area. There was not too much brightness to the high notes (Sarah in particular can make bad tweeters sound horrible), yet there were times when shivers would run down my spine while listening.

The M8a MTMs were excellent on the Beethoven. While listening to the Chorale finale in the 9th Symphony, I was quite impressed with the power and presence of the music. You could easily pick out each instrument and different parts.

When listening to the older (non sacd disks) music, there are definitely times when the speakers exposed the lower recording quality. But the bass extension was certainly not lacking much. The bass guitar and drum sounded quite full with lots of impact.

These are now my new favorite speakers, especially for high quality recordings with a lot of emphasis on vocals.

My .02.

[evilskillit]

This is very interesting. I've been really attracted to the Natalie P design lately but I have the Vifa ring radiator tweeter in my current bookshelves and it is really sweet. I was wondering if anyone had made a Natalie P variant or dayton rs180 mtm that uses that tweeter. Granted this thing uses different woofers and seems to have a huge pain in the butt crossover to build bit it does use the vifa tweeter. I'll have to look into this design, looks substantially more expensive due to parts tho . Maybe someone will adapt the x-o in one of the current rs180 MTMs to use that tweeter. I would do it but I'm probably a year or more away from having the equipment and know how to even try that.

[ThomasW]

This is one of Jon's relatively early designs (for this forum). It's not as sophisticated, as refined, or as fine tuned, compared to the designs like the NatP, Modula MTM, etc.

I've built several designs using the XT25. To my ears they doesn't sound any better than a good quality soft dome tweeter.

[marchel]

HI ,

Have you tested the limits of bass loudness of your new speaker? How does the M8a behave with loud bass passage? Do they overload gracefully or with a bang. Are they clean in the bass?

Thanks

[Paul H]

HI ,

Have you tested the limits of bass loudness of your new speaker? How does the M8a behave with loud bass passage? Do they overload gracefully or with a bang. Are they clean in the bass?

Thanks

I built these a few years ago, (here: http://www.htguide.com/forum/showthr...&highlight=m8n) and continue to be very happy with their bass performance - for 8" mtm's. I've got them in a large tower, tuned low and they play clean bass for listening to music at any 'regular' volumes - say up to low 90dB. I would say they overload gradually but certainly benefit from a subwoofer at higher volumes and/or low movie frequencies.

Paul