New Cabinets for old speaker

Wayner · « **on:** 24 Feb 2009, 01:28 am »

I finally got the cabinets for the Dynaco A25XLs. I think the photos say it all

Nice to have them mirror image, and they do image quite well

Wayner

oneinthepipe · « **Reply #1 on:** 24 Feb 2009, 01:44 am »

Just gorgeous, Wayner. Absolutely beautiful. Even the front panel veneers are perfectly book-matched/mirror imaged, left and right. That is something you don't see too often.

gjs_cds · « **Reply #2 on:** 24 Feb 2009, 02:36 am »

Did you build / assemble these? I always loved speaker building, but the woodworking was always my downfall...

Wayner · « **Reply #3 on:** 24 Feb 2009, 12:13 pm »

No, I'm sorry I did not build the cabinets, but I did "engineer" their new looks, eliminating the grill, the front and back edges around the baffles and an inversion of the ugly vent, so the screen is on the inside. MY friend at work has these skills and the equipment to build very nice wood projects.

Wayner

bregez · « **Reply #4 on:** 24 Feb 2009, 02:40 pm »

Very clean and elegant Wayner. I always liked the sound of the A25 but disliked the looks. The look of vintage A25’s is too Wisconsin college dorm room for me.
Is there a difference in sound between the new cabinets and vintage cabinets?

Brad

Wayner · « **Reply #5 on:** 24 Feb 2009, 10:30 pm »

Thanks Brad.

There is a difference in sound first because the cabinets are now left and right hand insted of as before, the tweeter was always to the upper right of the woofer. That was great for the left speaker, bad for the right speaker and I had to aim them "crooked" to get the soundstage I was looking for. Also the lip from the old speaker is gone and perhaps that is helping the imaging, tho I haven't listened to them enough to say one way or another. The major factor in the cabiinet redo was symmetry with the drivers. Mission accomplished. This evening I will spin some vinyl and listen to soom HD FM (Classical) and see if I can't come up with a tangable oberservation or 2 if anyone else is thinking of doing this mod.

Wayner

oneinthepipe · « **Reply #6 on:** 25 Feb 2009, 12:03 am »

Wayner:

Is there any difference in the cabinet materials and does that have any effect on the sound? I assume, although perhaps incorrectly, that the new cabinets are veneered-MDF, and the old cabinets were some type of veneered-particle board.

Wayner · « **Reply #7 on:** 25 Feb 2009, 12:59 am »

I believe the old cabinets were an early form of MDF, but certainly softer as evident by the numerous corner digs. The new cabinets are made from 3/4" MDF with pre-finished teak wood. The inside is also backed by a non-expensive veneer to keep the MDF stable. My cabinet builder tells me that many people make the mistake of buying the MDF with just a front facing on it, but in that condition the MDF is unstable and can warp and change easily with the humidity which will eventually tear the cabinet apart.

For those unfamiliar with the Dynaco A25XL speakers, they were made in Scandinavia by SEAS and feature the SEAS H086 1" soft dome tweeter and the SEAS 10" Woofer (I think 25FW-TV) could be wrong on that and haven't had it apart to read the frame. If I do I will post the correct number.

Hearing a pair of these speakers will immediately strike a charm with most listeners as they will recognize a magical (musical sound) they haven't really ever heard before. That is because the A25XL tweeter crosses at a very low frequency and is a very simple crossover featuring a simple capacitor and induction coil. The woofer is rolled off naturally in a aperiodic cabinet.

The tweeter level is controlled by a Zobel network of resistors and has 3 settings (as opposed to it's earlier sibling, the A25 which had a 5 level tweeter control.

Imagining is the barn burner with these speakers, which they excel on in so many ways.

Wayner

rlee8394 · « **Reply #8 on:** 25 Feb 2009, 02:03 am »

Wayner,

So the overall dimensions are a bit larger due to the 3/4" MDF? That would be necessary to maintain the original internal volume of the speaker, correct. You are going to pull the woofer and give it and the interior the plasti-clay treatment aren't you? I did that to my A25XL's years ago and it made a positive difference. Too bad I sold them some twenty years ago.

Ron

mcgsxr · « **Reply #9 on:** 25 Feb 2009, 03:16 am »

Good point your cabinet maker raises, about the veneer on the inside - a hallmark of Totem in Canada, as they veneer the inside of the speakers too, for that very reason.

Nice work saving an older set of speakers - my kind of recycling!

boycephoto · « **Reply #10 on:** 25 Feb 2009, 03:42 am »

Hi Wayner,

Your speakers are beautiful!
Being fairly new to Audio Circle I am not sure if you have already commented about the crossovers in your "new" A25XL's. Have you updated them with modern parts?

It's lots of fun, isn't it!!

Enjoy,
Dave

turkey · « **Reply #11 on:** 25 Feb 2009, 02:48 pm »

Quote from: Wayner on 25 Feb 2009, 12:59 am

I believe the old cabinets were an early form of MDF, but certainly softer as evident by the numerous corner digs. The new cabinets are made from 3/4" MDF with pre-finished teak wood. The inside is also backed by a non-expensive veneer to keep the MDF stable. My cabinet builder tells me that many people make the mistake of buying the MDF with just a front facing on it, but in that condition the MDF is unstable and can warp and change easily with the humidity which will eventually tear the cabinet apart.

Applying veneer doesn't provide enough of a vapor barrier to make a difference in this case.

I also have never seen an MDF cabinet become "torn apart" from moisture under the conditions in a normal home.

TomW16 · « **Reply #12 on:** 25 Feb 2009, 06:30 pm »

I would tend to agree that the veneer would separate before a cabinet would be torn apart from only veneering one side of MDF, which is relatively stable.

Nice job on the speakers Wayner!

rcag_ils · « **Reply #13 on:** 25 Feb 2009, 06:59 pm »

I think applying veneer on both sides of the MDF does little to prevent the cabinet from separating. The air that is sealed inside the cabinet when it was built is unlikely would cause any problem, assuming the factory was environmentally controlled.

Moisture could still get in from the edge of the wood even after you put veneer on both sides, unless you put veneer around the edges too.

Workmanship of the carpenter, and the environment the cabinet is in contribute more to how long the cabinet will last.

I have many pairs of vintage speakers that are 30 to 40 years old and the cabinets are still fine, except for one speaker from a pair of AR 4x, but the 2" gap was there when I bought it.

turkey · « **Reply #14 on:** 25 Feb 2009, 08:23 pm »

Quote from: rcag_ils on 25 Feb 2009, 06:59 pm

Moisture could still get in from the edge of the wood even after you put veneer on both sides, unless you put veneer around the edges too.

Unless you're using vinyl-backed veneer, you're still not going to have much of a moisture barrier. Typical contact cements are permeable to moisture.

Quote

Workmanship of the carpenter, and the environment the cabinet is in contribute more to how long the cabinet will last.

Absolutely correct, although I'd say cabinetmaker rather than carpenter.

Wayner · « **Reply #15 on:** 25 Feb 2009, 11:16 pm »

Quote from: rcag_ils on 25 Feb 2009, 06:59 pm

I think applying veneer on both sides of the MDF does little to prevent the cabinet from separating. The air that is sealed inside the cabinet when it was built is unlikely would cause any problem, assuming the factory was environmentally controlled.

Moisture could still get in from the edge of the wood even after you put veneer on both sides, unless you put veneer around the edges too.

Workmanship of the carpenter, and the environment the cabinet is in contribute more to how long the cabinet will last.

I have many pairs of vintage speakers that are 30 to 40 years old and the cabinets are still fine, except for one speaker from a pair of AR 4x, but the 2" gap was there when I bought it.

The Dynaco A25XL is a ported cabinet design. Air can move freely inside and out, bringing in humidity (and it's changes) on a regular basis. My cabinet maker uses double sided MDF all the time on his projects. This is how he builds them and seeing his work, I'll not question his methods nor his construction techniques.

BTW, I have owned several well cared for speakers that eventually came apart at the seams that at the time, I thought were built well. One was a JBL-L100, the other a Marantz Imperial 7.

The effects of humidity change vary from zone to zone. Here in Minnesota the winter can easily put the humidity in the house around 20-25%, getting towards desert conditions. In the summer, it can be 100%.

I guess my point is if you DIYer's don't want to use double faced MDF, don't. If you think the need was not required for my cabinets, fine. It cost me really nothing extra, and I have relied on the talents and experience of a master builder. I don't have that big of an ego to tell an expert how to do his job.

Wayner

dB Cooper · « **Reply #16 on:** 26 Feb 2009, 01:42 am »

Great speakers, Wayner.

Tuning the cabinets will be interesting. To be 'aperiodic', the acoustic 'resistance' of the slot has to be carefully tuned to the driver and enclosure. Dynaco did this by feeding a low frequency square wave into the system, watching the output waveform on a scope and adjusting the amount of fiberglass stuffing in front of the slot to get the least overhang on the waveform. God only knows what that production method would cost today.

Or maybe World Audio Designs. Who the **** are they, you ask?

Well, for those feeling jealousy pangs over Wayner's awesome A-25XLs, you might want to check out this A-25 based reissue speaker. It is available kit or fully assembled. SEAS drivers chosen for this cabinet loading. There are also two tower versions. Not cheap, but not wild-eyed high-end expensive either, especially if you source the cabs locally (or build them yourself). Interesting.

I always thought that the aperiodic concept was brilliant- the bass definition was top-notch and they had a rep as easy to drive.

WorldDesigns WD25A

turkey · « **Reply #17 on:** 26 Feb 2009, 01:29 pm »

Quote from: Wayner on 25 Feb 2009, 11:16 pm

It cost me really nothing extra, and I have relied on the talents and experience of a master builder. I don't have that big of an ego to tell an expert how to do his job.

Hehe. You're a funny guy.

Wayner · « **Reply #18 on:** 26 Feb 2009, 11:10 pm »

We looked at the slot loading and decided that what we were doing was the same as the manufacturer. We could not determine any other method of controling wave form other than making the slot the same way, using the same piece of insulation the same way, placing it the same way and securing it the same way.

There is no adjustment means that we could detect that could alter the bass response, other than changing some of the physical characteristics dealing with the slot. It sounds the same as well (bass wise).

I am quite pleased and am looking forward to the weekend when I can get some time with them.

Thanks for the interest.

Wayner

Tom Alverson · « **Reply #19 on:** 27 Feb 2009, 03:38 am »

There is a nice free program you can use to measure the response of those speakers if you are a PC guy. Check out SynRTA on this site http://www.libinst.com/. It's by my friend Bill Waslo who wrote the full blown speaker analysis software used by Salk and Dennis Murphy (their crossover expert). It's a really neat idea where he uses a special noise-like test signal, but since it's not actually random noise he can quickly calculate the frequency response without taking a long time to average out the data. It's great for looking at room effects especially on the bass, and would probably be good to adjust the slot (damping?) on your speaker.