Ardent Speaker Camp

[JonMarsh]

I've heard that you need something like 300 or 400 psi of clamping force for a good bond when glueing up speaker cabinets. I don't know if this is really true. But some of my clamps are rated to do 1100 psi. How would you get this kind of pressure with vacuum clamping? Also, is there a point where the bonding agents need air to cure properly? Waiting on this project. :Z It's going to take too long to get my shop properly equipped. :T

These are valid points. You can't get anything lose to that kind of pressure with vacuum clamping. But then, you usually don't need it. Another point that has been raised on vacuum bag sites is not to leave the work in the bag too long (more than a few hours) to setup, as in some climates, mold starts growing.

The "serious" guys use two part glues like Unibond for vacuum veneering, so setup is not an issue. PVA glues start setup due to exposure to the air when you're applying to the substrate.

As with most things, it's a sensible combination of techniques that will get the job done- so while I use clamps, I also use additional panels for force spreading for working with anything thinner that 3/4" MDF, for example. This is very desirable/necessary just when gluing up 1/4" MDF to 3/4", for example.

[Hdale85]

Jon I was curious if you've tested the replacement for the C79 I believe its the C90-6-79. Just curious if it measures identical or if like other brands there may be slight differences and if they would matter and what not. I imagine you've thought of this though.

[Face]

As for the veneer, what's wrong with contact cement? I've only used it on a few projects, but have never had an edge peel, any bubbling, etc...

[JonMarsh]

Jon I was curious if you've tested the replacement for the C79 I believe its the C90-6-79. Just curious if it measures identical or if like other brands there may be slight differences and if they would matter and what not. I imagine you've thought of this though.

It's just a different (new) part number for the same driver. Being an old fashioned kind of guy, I'm still using the old number, even though the number you cite is on the box of drivers I ordered for this project.

[JonMarsh]

As for the veneer, what's wrong with contact cement? I've only used it on a few projects, but have never had an edge peel, any bubbling, etc...

If you have a technique that works for you, then by all means go with what works. I've used contact cement in the past, but more successfully for synthetic laminates. My experience is that it's hard to get the cement application consistent in thickness to where it doesn't affect the surface flatness, especially when using thin veneer (paper backed).

As I mentioned before, I've seem quite a few veneer jobs with unfortunate surface ripple and issues at DIY meets, and they were all contact cement jobs.

Some guys don't like iron on with PVA glue, but I have pretty good technique for that, and it works OK with paper backed veneer. But for this project, to get the quality and specific effects I wanted, I needed to use select solid veneer- which doesn't work well with iron on technique, nor, IMO, contact cement. So far using PVA cold press glue and mechanical press things are working quite nicely.

I wouldn't talk anyone out of using a technique that they've mastered and are comfortable with, though.

I'll be following up with a PM to you later today- by this evening, on the other topic. Need to do some CAD work and make more sawdust today!

[Face]

If you have a technique that works for you, then by all means go with what works. I've used contact cement in the past, but more successfully for synthetic laminates. My experience is that it's hard to get the cement application consistent in thickness to where it doesn't affect the surface flatness, especially when using thin veneer (paper backed).

Understood.

As I mentioned before, I've seem quite a few veneer jobs with unfortunate surface ripple and issues at DIY meets, and they were all contact cement jobs.

That describes my first experience with CC.

I'll be following up with a PM to you later today- by this evening, on the other topic. Need to do some CAD work and make more sawdust today!

No rush, priorities first!

[Jed]

Jon I was curious if you've tested the replacement for the C79 I believe its the C90-6-79. Just curious if it measures identical or if like other brands there may be slight differences and if they would matter and what not. I imagine you've thought of this though.

Its not a replacement. Same driver... new name.

[Hdale85]

Ok was just curious and wanted to make sure

[JonMarsh]

Coming to you from my music server... :W

Just putting together piece part sheet drawings and thought I'd post another teaser screen shot... :B

Yeah, I'm fixing up my music server/speaker tester Mac Mini to also use for work and work/work, as I have to go into the office more often, and want to run full dual monitors, not a laptop and second monitor. So this is from my Mini, bless it's little heart.

As noted earlier, the midrange is in a tunnel, but not open back, though the sides do extend to the back for front to back bracing and for the assembly process.



And now, as ThomasW would say, more sawdust and less pixels. :W

[brucemck2]

Edit : oops, too slow to post, already answered

[CraigJ]

Just putting together piece part sheet drawings and thought I'd post another teaser screen shot... :B

You keep letting out those little teasers, and I'm gonna have my Ardent speaker done before you. :W O.K., you'll hear about it soon enough, here it is.

Have fun and as always, enjoy.

Craig

[Paul Ebert]

I've turned this portion of the cabinet work over to Evil Twin, who is convinced that he can do all the veneering with mechanical cold press techniques (can't complain about how the front panel worked out).

I'm considering doing the same for the (very) front of my Trilliums. I would iron-on the facets. I'd be interested in any more details about this (what glue? any details about the press and techniques, etc.).

I've done some practicing with ironing on raw veneer (birdseye). I get some cracks, but less than I feared and nothing that a mixture of maple sawdust and epoxy can't make pretty much unnoticeable. But, I think the very front will be too large a surface and should be pretty easy to cold press.

[JonMarsh]

Well, I've already done my fronts, Paul, but I'll be doing the sides and backs about the same way you describe, I think- if you're not in a hurry, you might as well wait and see if it works for me!! If so, you're good to go- if not, you'll know what won't work!

The basic concept is using clamping boards to distribute force, and using my copious quantity of Bessy style clamps.

I've also fabricated some slightly pre-warped MDF plates to use on the sides and back for clamping- in that the center bow in will sit in the middle of the cabinet panel. That was done by gluing up some high quality 1/4" MDF to 3/4" MDF; just like veneering a flat panel, if you don't veneer both sides, it will warp somewhat.

I should be getting to this stage by the first week in August when I have to take off another week without pay from work.

Facets will be done using Bessy cable clamps and cut blocks- at least, that's the plan. So the whole thing will wind up being cold press veneer with solid veneer, except the back which will be paper-backed (yeah, I'm cheaping out there.... sheessshhhh! You'd think I'd have some standards or something....)

[JonMarsh]

You keep letting out those little teasers, and I'm gonna have my Ardent speaker done before you. :W O.K., you'll hear about it soon enough, here it is.

Have fun and as always, enjoy.

Craig

Sigh.... you're always beating me to the punch, Craig- somedays I don't know why I bother.... Oh yeah, wait, it's so I'll have a pair to listen to, too. Or two pair- my RS180 versions are trailing a bit, doesn't really matter as I could measure any of the drivers in the prime set, since I'm using a midrange mounting plate adapter for the RS100-4. For now I must focus on the primary pair so they'll be ready to go to Denver late September.

When I started this, I didn't really appreciate how much work this would be... my ability to conceptualize outpaces my ability to actualize. :W

[Johnloudb]

Jon, really been enjoying seeing this project progress. Right now, what speakers do you usually listen to in your main system? Just curious.

[ThomasW]

Jon, really been enjoying seeing this project progress. Right now, what speakers do you usually listen to in your main system? Just curious.

NeoDcc

[JonMarsh]

Oh, we've been having fun... made some sawdust, too, more today




As Thomas notes, the SDX-1 NeoD CC (in a stereo pair as mains) are my "daily driver". Best "little" box I've ever done. Not having the linear distortion and accompanying energy storage (think SL and MarkK testing) above 800 Hz that most cone drivers has does wonders for midrange resolution with good source components- that RS52 is a great driver, as is the D26NC55- they just get out of the way of the music.

[ColoradoTom]

No, I don't own stock in Bessy, but maybe I should. I don't think a vacuum clamp for assembly operations would work well for what I'm doing; I'm actually using clamps at some points to line up work pieces initially, then moving them to more conventional positions after other clamps have been installed. And the clamping force on heavy pieces is much higher than what a vacuum bag can generate; plus, there's the heavy angle iron stock I use at times to insure the glued up piece is perfectly straight.



:W

Well.... I should probably own "clamp stock" as well. Since a project doesn't exist unless there are pictures - here is the "rough wood", clamping the arch for the bed frame, and final product from this weekend.... I'm keeping up with you!!!

Tom

[Evil Twin]

Impressive, most impressive.



Now, if you could produce that curved piece with the power of the Force instead of all those clamps, that would be the mark of a true Sithlord.

[Hdale85]

Did you have to put the wood in a steam box for that?

[ColoradoTom]

Impressive, most impressive.



Now, if you could produce that curved piece with the power of the Force instead of all those clamps, that would be the mark of a true Sithlord.

No kidding..... you should see how fast I can get the laminated pieces onto the form and get all the clamps attached. I'm guessing I can reporduce everything you see in the picture in under 5 minutes. 8O

I was using my power of the Force to overcome the pain in my back from doing too much with this ancient body over the weekend! :rofl:

Tom

[fjhuerta]

Jon, why did you decide on a closed-back midrange? Care to argue the merits of each approach? (open vs. closed back)

[ColoradoTom]

Did you have to put the wood in a steam box for that?

Nope.... I took a 12/4 piece of cherry (seen in the picture) and cut it into 4 inch by 80 inch strips using my bandsaw. The strips were evenly sanded to 3/16ths of an inch with a drum sander and then glued up with a urea glue and bent around the form. When they came off the form there was a slight amount of spring back... ~1/2 inch but it was already accounted for in the design of the form. Steam box would have been a PITA .... although given the temperatures over the weekend I might have been able to do it in the backyard! :rofl:

Tom

[Hdale85]

So they went in the form with wet glue and then removed when the glue was dried?

[JonMarsh]

Jon, why did you decide on a closed-back midrange? Care to argue the merits of each approach? (open vs. closed back)

This is monopole speaker with minimal baffle width over a range of frequencies (the narrowing front baffle) in order to support greater off axis dispersion. Did my first system trying that as a 4 way in the late 70s.

I'm not a subscriber or fan to the notion of a low pass tunnel for rear wave out of phase radiation of the midrange. It adds another variable to room dependent issues, and requires some special work in the crossover region. It's also possible that depending on rear boundaries and frequency ranges, you may get early reflections with out of phase products which can cause combfiltering in the response. Others like that approach for their own reasons and do it; I'm not about to "steal their thunder". :W


I have done dipole designs and have some ideas to re-visit the Arvo Part some day, but right now the only ideas I have for drivers are more expensive than I want to use while getting the necessary radiating are and Xmax for sufficient output.

I don't usually mix the two approaches, though helping Tom with the original Whisper we had dipole bass and sealed midrange. Sort of the opposite of what you're experimenting with now! :W

[cjd]

When they came off the form there was a slight amount of spring back... ~1/2 inch but it was already accounted for in the design of the form.

See, this is something I don't know how to figure out - is there a standard amount you can anticipate? How do you calculate this?

I know how to figure out how much silver to use by weight instead of wax, how to calculate how much a casting will shrink given material... springback from laminating like this? No idea.

[ColoradoTom]

So they went in the form with wet glue and then removed when the glue was dried?

Yup........

[ColoradoTom]

See, this is something I don't know how to figure out - is there a standard amount you can anticipate? How do you calculate this?

I know how to figure out how much silver to use by weight instead of wax, how to calculate how much a casting will shrink given material... springback from laminating like this? No idea.

There is a general calculation I've seen somewhere that goes (for my arch):

springback = (height of arch) * (1/number of laminations squared).

the height of my arch is 18 inches and the number of laminations was 6... so pluging in the numbers:

18*(1/6^2) = 0.5

Since my units are in inches the answer is 1/2 inch. THIS IS JUST AN ESTIMATE... I ran a test on scrap wood and the number was correct. Obviously thickness of laminations, radius of curve...etc can change the estimate so I always run a test but the formula works for a guestimate.

If my laminations were 1/16th of an inch thick the springback would have been insignificant..... but I would have had to cut and sand 18 very thin sheets and not the 6 kinda thin sheets that I used. :B For most woods cut to 3/16ths the formula is pretty close if the radius isn't too tight.

Tom

[fjhuerta]

This is monopole speaker with minimal baffle width over a range of frequencies (the narrowing front baffle) in order to support greater off axis dispersion. Did my first system trying that as a 4 way in the late 70s.

I'm not a subscriber or fan to the notion of a low pass tunnel for rear wave out of phase radiation of the midrange. It adds another variable to room dependent issues, and requires some special work in the crossover region. It's also possible that depending on rear boundaries and frequency ranges, you may get early reflections with out of phase products which can cause combfiltering in the response. Others like that approach for their own reasons and do it; I'm not about to "steal their thunder". :W


I have done dipole designs and have some ideas to re-visit the Arvo Part some day, but right now the only ideas I have for drivers are more expensive than I want to use while getting the necessary radiating are and Xmax for sufficient output.

I don't usually mix the two approaches, though helping Tom with the original Whisper we had dipole bass and sealed midrange. Sort of the opposite of what you're experimenting with now! :W

Thanks Jon!

I was wondering whether it is possible to assure an open baffle / tunnel in the midrange. I love the sound, but the speaker is basically tailored to the room it's in - the crossover, space from wall to baffle, etc., was taken into consideration. If I took it somewhere else, it would sound far too different - something I dislike about the design.

[JonMarsh]

Then too, there's a big difference between a dipole baffle midrange like you have and a low pass midrange tunnel with damping like the Statements.

While mixed metaphors work fine in literature and joke telling, I'm not so sanguine about in speakers.

But that's just for me- YMMV. Everyone marches to the beat of a different drummer...

To bad there's not some way to have a humungous HT Guide DIY event with all the guys getting together for a few days and sharing and playing their designs with their favorite music.

[chasw98]

Rmaf 09? :t

[JonMarsh]

Well, likely as close as we'll ever come. So are you bringing your line arrays? :W

Carry on? :rofl:

[Hdale85]

When is RMAF? I'd kind of like to come out to listen to some of yours and Tom's designs. Probably wouldn't go to the show. Not sure I could make it though.

[kirknelson]

http://audiofest.net/2009/index.php

[Face]

I'm on vacation...oh boy.

[Hdale85]

Only 3 months away, not sure I can swing that.

[JonMarsh]

Bits and pieces...

Last night I "glued" together the first pair of midrange enclosures, or rather, "epoxied" them together- mostly because they would be awkward to setup to clamp. I use "50 minute" epoxy as I really like to take my time- none of those five minute quickies.




If I get done with work quickly enough today, I'll probably dado the front panel groove for the brace and clue up the mid enclosure and brace, after checking a dry assembly. Or not, knowing how things have been at work- yesterday started at 5:30 in the office, and finished at 7 with the end of an hour long conference call to Singapore.

[brucemck2]

What's the purpose for the tunnels, aside from cabinet bracing?

[JonMarsh]

The extension to the back means that the midrange enclosure is not reliant on resisting tearing forces with the glue to come off the front panel- it is braced in position by the wings extending to the back on either side.

Good mechanical design means using materials in ways that they are strong, not ways that they are weak. If you just had a box glued on to the back of the MDF front panel, it could be relatively easy to shear the glue bond, splitting off a thin lear of MDF. MDF has good compression strength, mediocre bending strength, and poor tearing/delaminating strength.

I have been a product designer in a past life (decades ago), but I still tend to think like one- robustness should be a given.

[cjd]

You must have designed portable bomb shelters based on that front panel assembly!

[JonMarsh]

And the military definition of portable is anything that two strong men and a boy can lift off the ground- at least for a little while! Mobile has an even broader definition.... :W

I'm enjoying hefting and looking over my front panels... it gives a certain satisfaction. :B I may almost regret putting them in a cabinet! I probably won't be so keen on hefting and inspecting the cabinet. During the planning I had drawn in a top center to center brace above the midrange enclosure. After hefting the top panel plates, I realized bracing them was rather redundant. So, even I have a point at which some vague notion of commonsense kicks in.

Still have some design details to work on for the base, but will probably do dado'ing and stuff this evening if I get home soon enough. (since I got into the office at 5:30, I have a generous notion of when I should be ready to leave....)

[Dave Bullet]

So Jon - what is your estimated total weight per enclosure (incl. drivers and crossover) when finished?

Out of interest - is it worth putting an accelerometer (sp?) on the front with some 30Hz sine waves to see what level of baffle resonance / movement (if any) you get?

I'd love to see the results of this speaker compared to a commercial in that regard.

[JonMarsh]

Estimated weight is 110 to 120 lb. Depends partly on how the crossover comes out... :W

Usually 30 Hz is not problem- for conventional baffles the issues are usually in the midbass area or midrange. Low in level, but large in area for a floor standing speaker.

As mentioned earlier, this is not a new thing for me; first speaker like this (4 way 10" system) with uber thick faceted baffles was done in the 70's. (that one also had a rounded back- half circle... don't ask. MB 3/4" tweeter, Audax dome mid, Audax 6" mid, 10" woofer (a special "long throw" CTS part if I remember correctly).

That speaker used 1st order crossovers and was "transient perfect", i.e., it would reproduce square waves. But it had the off axis lobing that results form 1st order Butterworth networks with phase quadrature and non coincident drivers.

Some day I'll get this right.

[bigg]

Ardent SDX-2

120 pounds!!! I'll have to add a fork lift of some kind to my work shop :g> shopping list. Otherwise, I won't be able to move the speakers from the shop to my hi fi room. Maybe I'll just tell my wife that she needs to start bulking up. :T

[cjd]

That doesn't sound all that heavy to me for some reason...

I should weigh my towers.