Cellos from 2012 MWAF

[tomzarbo]

This is a small write-up of the "Cello's" speaker design my wife and I brought to the 2012 Midwest Audio Fest.
This project spanned several years since we sold our house and lived several different places in between the start and finish of this project. The build threads are all over the place, so I thought I'd consolidate the whole shebang here. Not that anyone would want to try to duplicate this exact cabinet design, but here is the journey I took to finish these...

First design sketches...

Cabinet Dimensions...

Laying out the drivers on the baffle...


The tweeter is as close to the two midwoofers as possible.

In order to get the spacing as close as possible I did lay out this part out very carefully on the computer after taking close measurements:

To modify the tweeter, I put the tweeter in the baffle then placed the midwoofers in their holes, then scribed the two arcs with an X-acto knife. Then I removed the tweeter and re-scribed the lines several times to make a nice indent. Then I just covered the tweeter and ground the plastic down on a stationary belt sander until I was within a 32nd of an inch and hand sanded the rest with a bit of sandpaper glued to a length of plastic pipe.
Working on the top...

That was the trickiest part of the cabinet. When you look at the sides of the cabinet from the front, the width tapers as it rises to the top, this means that the top is wider near the back since it slopes downward. The only way to cut this and have it mate up with the sides was to orient it just as it would be when mounted on the cabinet. I probably spent half a day trying to figure out how to do this correctly, but that's half the fun!

Cabinet starting to take shape...



Nice shot of the before and after on the nice curve at the bottom of the cabinet, purchased online from a vendor recommended by one our Tech Talk members.

Sides glued on...

Now on to figure out how to attach the back panels...

After breaking several pieces of 1/8" MDF, or at least hearing nasty crunching sounds, I decided to try 1/8" hardboard to make the curve, it took the bending just fine without any distress. The jig helped to pull down the back panels in the deep recess. The hardboard I used is smooth on one side and dimpled on the other side.
The first time I applied only one layer at a time, then I realized that two thicknesses of 1/8" material would better hold its shape against the clamps and shims than gluing up one at a time, yielding a closer tolerance on the finished joint.
Cabinets completed and testing in our other house a few years ago...

Without any gasket material on the drivers or bottom stand to contain the air leaks it still sounded pretty good to me. I gave Chris Roemer's crossover several weeks of good listening including several tweaks based on his suggestions which were based on what I told him I was hearing. It's a heck of a way to refine a crossover, but patience paid off eventually; the end result was good to my ears. Thanks Chris. I actually learned quite a lot from him during this process about what components do what and what to look (or listen) for.
Crossover...

A rendering done early on in the process...

It followed pretty closely the eventual cabinet design...

Back to building. Veneering going well...

One area just wouldn't stick when ironed. Drastic times call for drastic measures. This did the trick...

Iron-on method on paper backed veneer. I love this method of veneering; it's almost therapeutic. The back curvy panel I did have to use contact cement on, however.


Something I forgot to take pics of is the additional veneer that was added to the top and front to mitigate the "joint creep" that can take place on the end grain. This shows up as raised areas under the veneer and it doesn't look so nice. Several folks mentioned that I may want to add a sacrificial layer of veneer -- 1/16" maple in my case -- to these areas before I put my final veneer on. I think it will keep those areas from showing through the finish veneer... thanks for that tip! These cabinets had sat for a few years so the end grain was a bit proud of the rest of the cabinet... I sanded that smooth, then veneered those panels with the 1/16" maple veneer, then let that sit a bit before sanding and finish veneering.
Lots of work to be sure, but I think these will look beautiful for years to come. Little stuff like this tip is what's so great about Tech Talk in my opinion.
Almost ready for a listen...

Trying them out in the family room before packing them up in the car to head to Ohio...

A few more fancy shots of the completed speakers...





I really enjoyed designing and building these. As I said, these took several years to finish. After completing most of the cabinet and voicing the crossovers, my wife and I decided to sell our house and move in with my mother and father while we looked for another home... so into storage these went. Everything seems to take longer than you expect... so a few years later, I finally finished these just in time for this year's Midwest Audio Fest. Had it not been for wanting to get these ready for this year's MWAF, these may have been sitting unfinished in the basement for who knows how long. Nothing like a deadline for a little motivation!

Here's a little technical info on the system...The drivers used are all Dayton; the RS 180-8 Shielded woofer, RS 100-8 Shielded midwoofer, and ND20FA tweeter. The crossover points are 450 Hz on the woofer, 525 and 4500 Hz for the midwoofers, and 5500 Hz on the tweeter. It is a 4 ohm design and has a 87 db. efficiency. The mid box volume is around .75 cu. ft. The lower woofer box is around 2.3 cu. ft. and it is tuned to 38 Hz with a 4" x 11.5" port with a 1/2" radius on both ends. These sound like the subwoofer is on with some types of music. Not bad for a couple of woofers that only measure 5" across from the centers of the surround.

Thanks to everyone who helped me with suggestions along the way and especially to Chris Roemer who kindly and patiently helped me with the crossover and further tweaks after the fact. As I said, I doubt anyone would actually want to try and duplicate this cabinet madness, but hopefully these pics can help answer a few questions on how to handle a few of the trickier aspects of dealing with bending wood.

[gowa]

Beautiful!
What's the MTM in the background?

[tomzarbo]

Beautiful!
What's the MTM in the background?

Thanks! Those are my curvy D-3's, my reference system!
TomZ

[Dirttracker73]

Nicely done. What an extraordinary example of craftmaship. Those belong on a magazine cover.

[greywarden]

Those look amazing! I too am very ready to finish up my 2 year long build!

[LouC]

Darn impressive. Wish I had the patience and physical ability to build and finish an heirloom like those.
I take it the RS100 is a satisfactory mid. Looking to use that down the road.

[johnnyrichards]

Well Tom, you have done it. You have taken my ambition away Very beautiful, very well done and a nice, succinct write-up with just the right pictorial information covering the stuff that is most difficult to figure out.

[donradick]

Very ambitious build, and you pulled it off cosmetically and acoustically.

Couple of observations and questions.
Is that mahogany veneer on the main box? Did you use any stain or tint? Very beatiful.
Did you use a different veneer on the base? Sure looks different.

I'm very surprised at the NS20 - I would have thought one needed a RS28 to match
the quality of the mids.

I'll file the mid crossover tip of using the LP coil before the HP cap.
Never would have thought of that - Chris is the guru again.

thanks for sharing.

[tomzarbo]

Very ambitious build, and you pulled it off cosmetically and acoustically.

Couple of observations and questions.
Is that mahogany veneer on the main box? Did you use any stain or tint? Very beatiful.
Did you use a different veneer on the base? Sure looks different.

I'm very surprised at the NS20 - I would have thought one needed a RS28 to match
the quality of the mids.

I'll file the mid crossover tip of using the LP coil before the HP cap.
Never would have thought of that - Chris is the guru again.

thanks for sharing.

Don,
About the veneer...
I ordered it so long ago that I don't really remember what kind it is. I had thought I ordered maple, but someone at the MWAF (can't remember his name) suggested it may be Sapele... I don't really know at this point what it is. I used the same veneer from the same two 4x8 sheets to do the base. My flash in the pics was on auto, and some pics flashed, others didn't; I think that's the difference in appearance in the photos.

I had plans to use tung oil and/or rub on poly on the cabinets, but due to time constraints I went with the rub on poly only. I didn't want the tung oil softening and possibly sticking to the cloths that were in contact with the cabinets on the long 10+ hour ride to Springboro, Ohio. No color was added, just poly, 3 coats if I remember correctly.

The ND20 tweeter is a pretty decent performer. If the RS series tweeters were smaller, I probably would have went with those to stay with the Reference series theme, but these did the trick fairly well. I don't think they have quite the 'sparkle' that some of the big boys have, but unless you were to listen side-by-side, not many would probably notice. And getting the ultra-close spacing was a priority to me; using a Reference tweeter would have changed the appearance considerably. I've been thinking lately how nice it would be to have a Reference Series tweeter in a smaller form factor for closer CTC spacing.

And thanks a lot for the kind words, I appreciate them. I spent a ton of time trying to get these as close to perfect as I could, I didn't cheat or 'skimp' on anything, no regrets with these.
TomZ

[RINNAV]

Tom,

Just amazing! Beautiful and original cabinet work. Unlike Johnny , you have inspired me to build a grand project... I just fear it may take me two years before I can even start.

[fastbike1]

What do/would you think of the ND-28F as a step between the ND20 and the RS28? I liked it in Paul's Swope TM. Not too big a faceplate and seems to be closer to the RS28 tahn the ND 20 in performance.


And Tom, really really wonderful work on the cabs.

Very ambitious build, and you pulled it off cosmetically and acoustically.

Couple of observations and questions.
Is that mahogany veneer on the main box? Did you use any stain or tint? Very beatiful.
Did you use a different veneer on the base? Sure looks different.

I'm very surprised at the NS20 - I would have thought one needed a RS28 to match
the quality of the mids.

I'll file the mid crossover tip of using the LP coil before the HP cap.
Never would have thought of that - Chris is the guru again.

thanks for sharing.

[donradick]

What do/would you think of the ND-28F as a step between the ND20 and the RS28? I liked it in Paul's Swope TM. Not too big a faceplate and seems to be closer to the RS28 tahn the ND 20 in performance.
.

I've never heard or used the ND28, but someone I respect a lot called it the "poor man's Morel" - which
is high praise. If I didn't have half a dozen pairs of tweeters on the shelf (including a pair of
vintage Morel MDT29s) I'd pick up a pair of NS28s. I love Morel tweeters.

[Wolf]

I've never heard or used the ND28, but someone I respect a lot called it the "poor man's Morel" -

It's easy on the ears, polite and smooth. A really nice cheap tweeter!
Later,
Wolf

[ReissM]

This is one top notch design. Congrats!

[Thezeek]

I have to say that is very nice.

[feltrider99]

These are some beautiful speakers! Excellent work!!

[Jay1]

Those seriously look like $10,000-20,000 commercial speakers. Awesome job!