Dayton CX150-8 Coaxial Project

[4thtry]

I mounted an RS270P in one of my unstuffed cabinets and did some near field FR testing of the cone with several port lengths. The final port used had dimensions of 1.85 x 3 x 11 inches. In the graph below, I added the port to cone in OmniMic, reducing the port level by 9.4dB to account for the size difference. I also delayed the port by 1.3ms to account for the distance difference (roughly 17 inches). (This delay only affected the higher frequencies on my graph). The glitch at approx 180Hz is the top to bottom reflection. The multiple bounces from 450Hz to roughly 1KHz are side to side reflections, which vary with the curved side. Adding a couple inches of poly to the top partition eliminates the 180Hz glitch. I have not done it yet, but my hope is that adding about 1 inch of fiberglass to all the other internal walls will dampen the other reflections as well...

[4thtry]

A little progress:

I dropped one of my input cups on the concrete basement floor when making a template for it. The corner hit the floor at just the right angle and "pow," the plastic corner went flying across the floor. Took me about an hour to find the broken pieces so that I could super glue it back together. Not the best repair job, but it appears solid. They were only a buck each at the MWAF tent sale; I should have grabbed a few extras while I was there!

[4thtry]

I shot the first coat of high gloss almond yesterday. Went on just as smooth as the primer, with a good flow and creamy texture, just the way I wanted. The almond does not appear as dark as I would like, but this might just be the white primer showing through on the first coat. After the 2nd or 3rd coat I should be able to see the almond color darkening up a bit. If not, I will have to mix in a small amound of Rustoleum's deep brown leather to get the sort of look that I am going for.

[KEtheredge87]

Hi Bill, looking good so far! What kind of spray system do you use? Any recommended guns you like? I'm scheming an HVLP setup in my garage sometime after I move, so I'm looking for any cost-effective options.

[4thtry]

Hi Bill, looking good so far! What kind of spray system do you use? Any recommended guns you like? I'm scheming an HVLP setup in my garage sometime after I move, so I'm looking for any cost-effective options.

Thanks, Keith. Funny you should ask. I just purchased a new HVLP setup for my garage to replace my failing 40+ year old high pressure system. My old sprayer was a hand-me-down Binks Model 7 with a 1.8mm tip, which I used to shoot the thicker, old based type paints at roughly 50 to 60psi. I have a 5HP 20 gallon compressor, which, as I recall, is rated at 8.7cfm @ 40psi and 7.1cfm @ 90psi. It can just barely keep up with the Model 7.

My new HVLP sprayer is the inexpensive Central Pneumatic combo 2 piece HVLP spray gun system (sorry, no link, but it s/b easy to find). I picked this one up on John H's recommendation, and I am really glad I did. I have had a few problems with clogging initially. This was my fault because I failed to thoroughly clean all internal parts the way I was suppose to. But once I got it all cleaned up, it began spraying as smooth as can be. I found out the hard way that you need to completely disassemble and thoroughly clean all internal parts and passageways before using it for the first time. I thought I had everything cleaned out well, but it started spitting on my second job, so I completely disassembled and found several fairly large pieces of manufacturing shavings lodged deeply within the sprayer.

This sprayer includes interchangeable 1.4 and 1.8mm tips and needle valves. I had trouble initially removing the 1.4mm tip; had to take the needle valve out first and then it turned out easily. There is also a smaller sprayer with a 1.0mm tip for detail work. So far, I have only used the larger sprayer with the 1.8mm tip & needle valve installed.

The bodies are made of aluminum. The tips & needle valves appear to be stainless steel. So this system should be OK with waterborne using the 1.4mm tip. The build quality, however, is not the best and it will probably only last a few years. I would say that this is a good sprayer for the part-time hobbyist who wants to save money on equipment.

Oh, I forgot to mention, I am now spraying at 30-35psi instead of 50-60psi. But the new sprayer takes more air from the compressor. I find that I have to pause occasionally to let the compressor catch up. I had to pause a little with the old sprayer, but not quite as much.

Bill

[4thtry]

As promised, here are a few attachments showing my crossover design and measurements.
See photo captions for additional detail:

[4thtry]

Impedance:

Overall system impedance model with drivers and crossover installed. Impedance drops to about 3 ohms at 460Hz which relates directly to the lower midrange crossover point of 460Hz. Moving this crossover point up and down causes the impedance to move up and down as well. This should be OK since the phase angle is only -15 degrees at this point.

Crossover: 460/4000Hz

Total of 12 parts with all drivers connected in phase. The tweeter gets a 12dB/octave electrical filter and a 4.3 ohm padding resistor. The midrange gets a 12dB/octave electrical filter at both ends, but no padding. C5/R1 form a tank circuit to further dampen a 9kHz midrange breakup mode. R1 is an amplifier protection resistor. The woofer gets a steeper 18dB electrical filter in an effort to further dampen a 700 to 1Khz internal woofer cabinet cancellation/reinforcement mode caused by my odd shaped cabinet design.

[4thtry]

I created a set of temporary upper and lower baffle boards from 3/4" particle board. They will eventually be replaced by solid 3/4" thick walnut. I did this because I was waiting a very long time for my walnut order to be processed and I wanted to mount my drivers and take some measurements.

I finished the temporary baffles with 3/8" round-overs, bondo, two coats of primer and several coats of high gloss leather brown enamel (see pics). These temporary baffles will become permanent in the event that I mess up badly when gluing & routing the solid walnut.

[4thtry]

There will be a nameplate on the front of the speaker between the upper and lower baffle boards. Tentative name: "Asymmetrax". Suggestions? After I complete the walnut baffle boards, I plan to have a local CNC shop engrave a piece of contrasting hardwood to fit this space.

[4thtry]

Constrained layer damping experiment:

Edit: Actually, this is a "mass loading" damping experiment; not CLD. See post 137

[4thtry]

For those that wish to experiment with my design using other software packages, I am posting a cabinet layout drawing, a set of on-axis FRD's and a set of three "in-box" ZMA files.

All FRD's were measured 1 meter on tweeter axis. OmniMic was 37.6 inches above the floor in my great room, which has a sloped ceiling leading to a loft area. The speaker was set on the carpeted floor for all the on-axis tests to keep the woofer near the floor. This eliminated a nasty 100-300Hz floor bounce that occurs when I place the speaker on top of my horizontal polar response turntable.

All measurements include raw OmniMic phase data, so you will need to replace this with minimum phase data to use other software packages. The on-axis Xsim model delay (Z offset) is -0.88 (in) for the tweeter and 10.18 (in) for the woofer. No model delay was applied to the midrange.

T alone.frd
M alone.frd
W alone.frd

EDIT: A 33uF polypropylene protection capacitor was in series with the tweeter for all measurements. All OmniMic measurements were sine sweep, blended, 5ms gate, 1/48th octave smoothing.

[4thtry]

Here are the rest of the on-axis FRD files:

T+M.frd
T+M+W.frd
T+W.frd
W+M.frd

[4thtry]

And here are the ZMA files, all measured with DATS V2. The woofer was mounted "in-box" with fiberglass, steel bars, and final BR port installed. The coaxial midrange driver was also installed in the final 0.25 cu. ft. sealed cabinet with Acousta-Stuf, fiberglass, and steel bars installed.

CX150-8 tweeter in box.zma
CX150-8 midrange in box.zma
RS270P-8 woofer in box.zma

[jhollander]

Did you grab a near field of the woofer and mid?

[4thtry]

Did you grab a near field of the woofer and mid?

John, I did a NF on the woofer and the port, but not the mid. I'll do a NF on the mid later tonight and post both of these files tomorrow.
Do you also want the NF on the port? I was originally going to post all these files, but forgot about the NF stuff. Bill