Dayton CX150-8 Coaxial Project

[4thtry]

Not sure, I just assumed since both are from the same line, so I could be wrong. PE photos aren't much help. Maybe 4thtry could verify?

Yes, I can see vents.

[4thtry]

Looks good Bill.

How do you like particle board to work with compared to MDF. It's a lot nicer, right? I need to use it more often, it doesn't make dust like MDF and it doesn't smell so funny.

I like the idea of using the scraps to make a clamping fixture, great call there. Not sure if I did that or not on any of my projects, but I probably should have if I didn't!

TomZ

Thanks, Tom. For this project, I changed from MDF to particle board for a number of reasons:

1) Particle board is roughly 1/2 the cost per 4x8 sheet
2) Particle board is slightly lighter than MDF (not much, maybe 10% or so, based on my crude bathroom scales measurements). I wanted to keep the cabinet from getting too heavy, as I intend to do a double thickness 1.5" baffle board. It will be a composite of 3/4" particle board and 3/4" solid walnut. Solid walnut is very dense and heavy stuff.
3) As mentioned, MDF is very dusty stuff.
4) This is subjective, but recently the MDF that I have purchased has tended to be somewhat flaky. I remember years ago using 3/4" MDF and when I routed the baffle recesses, the recess was very clean. Recently, my baffle recesses using MDF have been very flaky looking. At first, I thought I had a dull router bit, but installing a new bit produced the same results. Not sure why this happened to me, maybe I just got a bad batch of flaky MDF or something.

[4thtry]

It's all I used when I was a kid doing speaker building, but I remember it was pretty crumbly, MDF holds a very sharp edge and is very machinable (though it's weak as heck if you bump or hit it), the dust is horrible though which is why I'm a plywood and solid wood guy for the most part these days. I noticed Bill is good with the bondo though, interested to hear your thoughts Bill.

I must have gotten some bad MDF. In the past MDF was always very machinable with a sharp edge. And I always use a good dusk mask with MDF.

[4thtry]

Bill, I think you'll be surprised how much stronger a laminated, curved side is. I built a pair of stentorians a few years back and used 6 layers of 1/8" HDF on the sides. In hind-sight, I could have easily gone with 3-4 layers and the cabinets would have been significantly lighter and the side walls would have been more than stiff enough. Of course you're more than welcome to use 6 layers, but I'm just letting you know that I don't think it will be necessary to go with that many.

Also, I built a "Dr. Seuss" bookshelf for my sister recently and made the curved sides with 3 layers of 1/8" hardboard, just like you're doing. I scuffed each layer by hitting it quickly with some 40 or 60 grit on the random orbit sander, just to take the shine off the smooth faces and make sure the glue has a chance to soak in. I used Titebond Extend wood glue, which has an extended working time for applications such as this. When I made my forms for gluing/clamping, I put some weather-stripping on the edge and left the paper attached to the "outside" of the weather stripping. This gave a smooth surface that would flex a little as it gets clamped down. Otherwise, as you add layers, your curve actually changes shape slightly and you're no longer applying clamping force to all the areas necessary. The weather-stripping helps keep clamping force on the entire area. It's not a perfect solution, but it works better than just using the cutoff piece as your clamping surface. For some reason I chose to use weight, which was barely enough. If I build another, I'll use ratchet straps.

Attached are a few pics of my jig setup, but you cannot see the weather-stripping in these pictures. If you want to see it, I can take pictures tonight that show the detail of the weather stripping. Even though it's not speaker building, I might make an OT post on that bookshelf and show how I went about it, because some of the techniques I used are applicable to curved cabinets, and sometimes it's always fun to see a wood-working project other than a speaker box

Thanks for all the great suggestions! I knew I was copying my curve shape from somewhere, but couldn't place it. My curve, however, is a little wider toward the bottom.

My tentative plan is to line my compression fixture edges with self-stick felt. And as you suggest, I think I will add a thin 1/16" thick self-stick layer of foam rubber underneath the felt, to fill in the gaps created by the multiple layers. I am going to do several "dry" runs, bringing the clamps down slowly, without glue, to see how the first 3 sheets of 1/8" material tend to squirm under pressure. I may need to add a number of "alignment" clips along the edges to keep the panels in place as I apply the pressure.

I will be using 3 layers on the first clamp up. As you suggest, maybe this is good enough. I'll give it the knuckle rap test before adding the second 3 layers. My plan is to lightly sand the smooth side as you suggest. Good tip on the Titebond Extend wood glue; I will check for this locally. Will post some pics of my "sandwich" clamping fixture when I get that far.

How thick was the weather stripping that you used? Was it the spongy open cell type or the denser closed cell type?

[4thtry]

For my pair of CX150-8's, I played a series of sine wave sweeps and individual test tones at various power levels to determine if the vented VC former would cause a problem in my design. I set things up so that I could switch back & forth quickly between listening to the driver in free air and then listening to the driver again at the same frequency in a sealed 0.25 cu ft test box. The test box was filled with fiberfill at a rate of 0.75 lbs per cubic foot. I was able to obtain a good seal on the mounting gasket when I switched back & forth from free air to sealed box.

The test tone on the video was 80Hz, so I started with this frequency, playing at roughly the 90-95dB level at 1 meter. I was unable to hear a difference as I swapped the driver in and out of the test box. No chuffing or buzzing noises. As I lowered the driver into the mounting hole, there was a temporary chuffing noise around the driver gasket as I lowered the speaker into position, but once the driver was sealed into position, the chuffing disappeared. Also, the low frequency output increased somewhat as the front to back driver cancellation disappeared.

Then I varied the frequency up and down at very low frequencies. From 20 to 60Hz, a slight chuffing noise through the VC could be heard when I sealed the driver onto the box. This chuffing disappeared as I raised the speaker off the box. I was varying the playback level in the 85 to 90dB range, trying to stay within xmax for these tests, as I did not want to damage the driver. The chuffing was noticeable but not severe, and I had to move my ear close to the VC to hear it clearly.

From 80Hz and above, however, I could hear no chuffing when I sealed the driver onto the test box mounting hole. I varied the input level up and down from 85 to 95dB at 1 meter and the results were the same. No chuffing.

I then ran several 45 second sweeps from 100 to 1000Hz in 100Hz bandwidth intervals. I could hear no chuffing either in free air or when mounted in the test box. I did the same from 1000 to 5000Hz in 1000Hz bandwidth intervals. Again, I could hear no chuffing or buzzing noises of any kind.

After spending several hours testing both drivers in free air and then in my test box, I came to the conclusion that this driver should work just fine in my design. With a crossover of 400Hz at 12 dB per octave, the response should be roughly 30dB down before any chuffing begins. And even as low as 60Hz, the chuffing is barely audible compared to the fundamental frequency.

[4thtry]

A little progress:

I built a custom clamping fixture from the baffle board remnants. To keep the fixture from sliding left as I tightened the clamps, I bolted a horseshoe shaped end cap on the right side of the fixture. The end cap allows the three 1/8" curved panels to stick out the right side slightly, by about 2 inches, yet provides a very rigid brace for alignment. I also added four alignment gauges along the sides to keep the 1/8" panels centered on the cabinet as I tighten the clamps.

I've been working on this fixture for about a week now, dry fitting and tweaking again and again. I added wax paper to the end cap to keep the fixture from becoming a permanent part of the enclosure. I added long strips of black felt to the edges so that the fixture slides smoothly into postion as I tighten the clamps. I think I am now ready to apply some glue!

[4thtry]

I just glued up my first set of 3 curved 1/8" thick panels. For those with experience gluing up these type of curved panels, how long do you normally wait before taking the clamps off? I used quite a bit of glue, flattening it out along the panels with a squeegee. If I take my clamping fixture off too soon, I am afraid that it might fall apart. I was thinking maybe 24 hours, but maybe I should wait 3 or 4 days. Any suggestions?

[PWR RYD]

Just overnight (~12 hours).

[TN Allen]

I usually use Epoxy for curved panels, and check the left over Epoxy in the can I mix it in for hardness. 6-8 hours is usually sufficient time depending upon the shop temp., but frequently it is the following morning before I remove the clamps.

Just out of curiosity, is there an acoustic advantage to the enclosure shape you chose?

[1100xxben]

For wood glue, overnight should be plenty long. When I built up multiple layers, I would clamp up a set in the evening, and then put the next layer on the next morning before work.

[kenrhodes]

TN Allen, Curved walls are typically stronger than a flat panel they can also help with internal standing waves and panel resonance. Typically the biggest gains are in WAF.

[4thtry]

Thanks for the quick responses. I apologize for my slow response. This is the first chance that I have had to check my thread since I posted my clamping question. It has been over 48 hours now and the clamps are still on. Looks like I can save quite a bit of time by cutting this back to 12 hours or so.

Regarding the curved panel shape, as pointed out by Ken, they will help with standing waves. Flat parallel walls will tend to concentrate the low frequency reinforcement and cancellation effects at certain frequencies, based on the internal dimensions. Curved panels help to distribute these peaks & dips over a wider range of frequencies.

Another reason for the shape is an attempt to replicate the sound of a small bookshelf type speaker placed on a stand. I started out wide on the bottom to give the 10 inch woofer some space. Then I quickly reversed the curve to a very thin shape near the center. I widened it out again near the top to allow room to mount the 5.25 inch coax. This creates the effect of placing a smaller type bookshelf speaker on a two foot stand because the center area has less reflective surface area.

But my main reason for the curve was to give my speaker a different look. I deliberately avoided making the speaker symmetrical from top to bottom. Doing so would have significantly reduced the slopes of the curve and would have made it look quite conventional. By sloping just one side, the curves, and thus the impact and drama created by the curves, are doubled.


Bill

[TN Allen]

Thanks for the explanations.

[JavadS]

Here in California where humidity is typically below 40%, wood glue dries fast, I'd say a few hours would be enough, maybe 6, but I was shocked at how long Titebond took to dry in Ohio this summer at MWAF, overnight it was still nowhere near dry. I'd say 24hrs to be safe if it's humid, or maybe haul the setup into a dehumidified AC part of the house if you have it.

[Paul K.]

I live in Ohio near Columbus and always use Titebond glue, type 3 and Extend, and both dry quite nicely overnight. But, my workshop is in the basement and benefits from the HVAC.
Paul

Here in California where humidity is typically below 40%, wood glue dries fast, I'd say a few hours would be enough, maybe 6, but I was shocked at how long Titebond took to dry in Ohio this summer at MWAF, overnight it was still nowhere near dry. I'd say 24hrs to be safe if it's humid, or maybe haul the setup into a dehumidified AC part of the house if you have it.