jquin's M8ta build thread

[jquin]

I hope your home life is not in any way necessitating truly dent resistant speakers. :E :W

Yes I have a three year old and a five year old that love to damage anything slightly valuable.

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Now on with the show.
I did not have the correct MDF for the 1/4" inserts for the walls.
Checking out the local H/W store it would have cost $30.
I took issue with this as all the wood to date cost $120 as it was purchased wholesale.
Instead I had the idea of making ribs, well a grid in this case.
I did some back of the envelope calculations to show that it would have a neutral impact on the enclosure's volume.
So I got to use scrap 1" MDF instead of pay $30.
Its seems fiddly but hasn't been too bad so far.
Now as far as I can see this technique should be stiffer than the original 1 1/4" walls.

[Gir]

I've heard it called a torque box, since it stops the box from twisting. This should really help keep everything solid, I like the idea! :T

[JonW]

Yes I have a three year old and a five year old that love to damage anything slightly valuable..

Ahh, I see.

The support grid inside looks great. We've got to give you a tip o' the hat for your ingenuity. :T

Come to think of it, doesn't this symbol ":T" mean something obscene in Oz? Sorry about that. Let's just say nice work! :B

-Jon

[jquin]

It's getting close now.

At least two more of these clamps would have been nice

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Now this is interesting. Although I have some SS6600 I will be using RS28 until I trust that novelty has worn off (see last photo in this post).
Anyway I made a jig to use in conjunction with a jasper jig to machine the front of the RS28 down to the size of the ss6600.

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Finally in one piece

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Testing out some grille ideas

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The grille design I settled on.

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A better mouse trap?

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I finished machining the grille yesterday and I am waiting for the magnets to finish gluing (damn "slow curing epoxy").
Anyway I'll have some more photo's to post soon.

[Jed]

Wow, now that is a lot of work! How do you move them?

They must weigh a ton.

Jed

[Hdale85]

Hmm thats a sexy speaker....

[chrisn]

Lookin' good

I like the grille design you chose. Are you using threaded inserts to mount the drivers? I see darkish/silver colorations in that area...

Could you detail how you cut the tweeter flange? I didn't know the RS28 had an aluminum flange... I have two of them in my closet I haven't opened yet.

I don't have any kids around my house, but I do have cats so I can understand needing to dent proof things. I recall watching my just completed red oak finished mini transmission line cabinet flipping end over end before hitting the tile-over-concrete floor with a sickening thwack. Not to mention coming home to find floorstanding speakers with the wrong end on the floor... I think your cabinets have enough weight to prevent that, at least until the little ones get into football

[jquin]

Lookin' good

I like the grille design you chose. Are you using threaded inserts to mount the drivers? I see darkish/silver colorations in that area...

Could you detail how you cut the tweeter flange? I didn't know the RS28 had an aluminum flange... I have two of them in my closet I haven't opened yet.

I don't have any kids around my house, but I do have cats so I can understand needing to dent proof things. I recall watching my just completed red oak finished mini transmission line cabinet flipping end over end before hitting the tile-over-concrete floor with a sickening thwack. Not to mention coming home to find floor standing speakers with the wrong end on the floor... I think your cabinets have enough weight to prevent that, at least until the little ones get into football

Yes they are inserts. They are cast aluminum but I wish they were steel to reduce the threat of cross threading.
I got them at http://www.profhdwr.com/55008.htm but I am sure there are equivalents elsewhere.
I used #8-32 for Tweeters and #10-24 for woofers.

I have CAD models if anyone is interested.

I have not managed to perfect inserting them accurately yet.
In spite of meticulous marking, centre punching, pilot hole drilling and reaming they seem to be just off enough to be annoying.

Any hints from you pros out there? ;x(

I intend to glue them in place once I coax them into position.

As far as the flange is concerned I removed it from the driver and mounted it on a scrap piece of MDF
( you can see it bottom right of the first photo in the last post)
then you drill a 1/8" hole in the centre and used the jasper jig.
Measuring and drilling the hole is critical if you want the cut to be concentric. I think I got to within 0.5mm so I am happy.

[jquin]

Hi Again
I completed this work a couple of months ago but have only just gotten around to posting it.

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I had to resort to hand carving to get the diamond for the tweeter cutout but it all worked quite well.

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There is a bit of distortion due to the wide angle lens but this is what it sort of looks like.
I have since increased the height of the plinth and put spike feet on it.
I'm not to sure about the spikes, they make it very hard to move and I think the science behind them is dubious, of course just like speaker cable they add more aesthetically than sonically.

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These measurements were taken quickly but are probably a good indication of the current performance.
The near field was taken about 1' away and I didn't record the port separately and add it in.

The port was tuned from the impedance response to around 25Hz.

The far field obviously show how poor the speaker placement is in my room.
Interestingly I took measurements after running the EQ on my HT amp and the lumps in the bass region were intensively the same.

I have only constructed one of these to date so I can not comment too much on the sound quality, only that the bass is far superior to my Modula MT, but then you would expect that.

Any comments/suggestions are welcome.

[Jed]

Looks like that grill is causing a diffraction peak at 2k. Looks almost like waveguide loading. I'd remove it when listening or try some felt because the treble is going to sound a bit bright.

[ThomasW]

The felt wrapped piece of MDF has to go. It should be replaced with a piece of thick high wool content felt, sized and cut the same as the piece of MDF you remove.

[Paul Ebert]

Now this is interesting. Although I have some SS6600 I will be using RS28 until I trust that novelty has worn off (see last photo in this post).

Speaking from personal experience, that should be, oh, about 20 years from now.



I'm encouraged to see the progress you are making. My M8tax2 NeoCD variant (I need a better name) is stalled awaiting completion of my Pearl phono stage. But that will be completed 'any day now'. I can't wait to get back at them.

I've also had trouble with the inserts. I can't seem to get them to go in exactly perpendicular to the baffle, despite using a drill press. Hmm, it just occurred to me - maybe using the drill press to thread them in somehow will correct this problem. I'll give that a try and report back.

[jquin]

The felt wrapped piece of MDF has to go. It should be replaced with a piece of thick high wool content felt, sized and cut the same as the piece of MDF you remove.

Hmmm I seem to have completely misinterpreted this photo from ColoradoTom

I'm not exactly sure what I am doing now with the grille.
A layer of felt glued to the front baffle covered by a grille with a large circle cut out for the tweeter?
I thought circle cutouts would be bad for diffraction.
I'm guessing my magnets might have trouble sticking the grille if the felt gets too thick.

I do NEED a grille, those SS6600 wouldn't last 10min with my children around.

[ThomasW]

What you see in that picture is a wool felt pad. I don't remember if he used 3/8" or 1/2" thick.

No one is using a circular tweeter cutout for anything.

Avalon makes a grill cloth covered frame that snaps over their felt pad.

[Dennis H]

Yeah, Tom's is all thick felt, no wood. To save your grill, I'd cut as big a trapezoidal hole as you can around the tweeter area. Glue felt of equal thickness into the hole to replace the wood. Cut the diamond shape into the felt.

[ThomasW]

. Glue felt of equal thickness into the hole to replace the wood. Cut the diamond shape into the felt.

Felt really should cover the entire area as shown.

One fix is to make self supporting grill cloth frame out of smallish angle iron (say 1/2" legs). Stretch and glue the grill cloth over the metal frame, like a painter stretches a canvas. Attach with rare earth magnets. The frame would be open everywhere except the edges. Use a cross piece of metal just above the woofer if the frame wants to bend.

[jquin]

Thanks Heaps everyone
I may modify the current grille in the short term.

Modifying the grille completely would require repositioning the magnets in
the front baffle. Something I will defer for a bit.

I guess it's an artifact of the "paint by numbers" approach I have to speaker building at the moment but it's not obvious to me why the felt covered MDF diamond I made would act like a waveguide any more than a pure felt diamond.

Anyhow they say you learn through your mistakes, so using that logic I must be getting close to being a genius.

[ThomasW]

but it's not obvious to me why the felt covered MDF diamond I made would act like a waveguide any more than a pure felt diamond.

It's a function of the thin felt over MDF not aborbing much energy

[kvardas]

I built the M8tas, used rare earth magnets, but not big enough ones. After making sure the grills fit perfectly and performed well, I used hot glue to attach them to the speaker fronts. Only used a very minor amount of glue, such that I could remove them easily if I wanted to.

[jquin]

After a long pause I have a new photo.
I built these boxes for the x-overs specifically to put on the back of the M8ta
I think of them as the humpback configuration.
I can supply drawings if anyone wants

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I'm planning to spray these soon with black two pack paint.

[Bear]

After a long pause I have a new photo.
I built these boxes for the x-overs specifically to put on the back of the M8ta
I think of them as the humpback configuration.
I can supply drawings if anyone wants
[..]
I'm planning to spray these soon with black two pack paint.

Looks good! I'd love to see drawings. Were you ultimately able to use the Air Circ, or did you have to fall back to a Millenium? (Some of the pics have "expired")

Bill