A Monster Construction Methods Shootout Thread

[augerpro]

Here are the results of the new port test. Here I wanted to investigate a few things. One was abandoning the Kef method of flexible center sections to reduce pipe resonances, and go to tapping the center of the port and then dampening that energy. I also wanted to investigate whether the performance of the Harman port was inherent, or whether it was simply due to the average port diameter being larger than the others (thus it being longer than all the others also). I did this two ways.
First by downsizing the Harman port so it matched the overall length of my Precision port clone. Port ID ended up at 1.756". Since I hadn't yet determined an end correction factor, I had to make an educated guess and the final port tuning was high by about 2-3hz. Not bad.
Second, I upsized my Precision port clone so that the overall length was the same as the original Harman port. Port ID is 2.28". Tuning was virtually identical.
I also measured an actual 2" Precision port to see if surface finish made a difference. If you recall I 3D printed all of these to remove the surface finish variable, since that is known to have a measurable impact on performance.
Additionally I added a 2.38V harmonic distortion plot to better capture typical listening conditions.

Harman port (shorty)








Precision port (jumbo)









Precison port (factory smooth finish)








Tapped port

I should note that I heard (and measured) a "flapping" sound during the harmonic distortion tests. No doubt the taped cavity being pumped back and forth. So treat these HD results as preliminary until I can print the dampening cavity, so it is sealed with hard material.

[radule]

I tested with neoprene, it sealing so keeping LF port response, and flexing enough to notch down first port resonance.

[augerpro]

Some observations...

The Harman port is superior. It's a bit ahead in distortion performance for the original vs jumbo Precision port, and more definitely in the shorty Harman vs the original Precision port. Behavior at the very highest levels is where the difference is pretty large.

Surface finish matters. Quite a bit. The harmonic distortion of the actual smooth finish Precision port is cleaner than my clone, and is really noticeable at the highest power. Not enough to catch up with the Harman though, but close. Close enough that smoothing the Harman print is well worth the effort. I've seen if you print with ABS you can smooth the finish with acetone.

For some reason the F1 was not quite as smooth in the distortion plots this time around so it is not as obvious when chuffing starts when just looking at F1. The higher harmonics are still indicative though. Because of the difference in F1, power compression vs the earlier testing is a little harder to see.

[augerpro]

Just wanted to share a fantastic paper. Harman's must be based on it. I actually like this paper's method better than Harman's for exactly the reasons that I diverged from Harman: normalizing based on tuning, not length, and later on length but with varying diameter so tuning was still the same. Curiously Roozen's worst performer (D) superficially looks like mine, BUT Harman did several variants where the changed ratio of length vs wall curvature radius. The one I selected was called N=0.5, which was sort of in the middle. At the high end of N there was much more curvature, and at the low end it looked pretty similar to Roozen's E. So I'm guessing his D was more like the N=1 port from Harman's paper. Still he specifies the optimal contour as like Harman (and his own D) but where curvature from port center to exit is not faster than 6 degrees. I'm going to try that, and tapping the port at 1/2 and 1/4 length.

[augerpro]

EDIT: N is actually NFR in Harman's paper

[454Casull]

Stupid question - did you try to stuff any of the ports with a light fluffy material?

[augerpro]

Nope

[jzagaja]

Originally Posted by augerpro

I know these are sort of data dumps, and unless you open plots in separate browser tabs to flip back and forth and comparing them, not so east to digest. So maybe a summary of what I'm seeing so far. I should add my observations apply to any woofer duty that is not a subwoofer. For subs, it seems to me 1/2" or 3/4" plywood well braced is all you really need.
1) MDF is actually pretty good. I would use it over plywood for anything except a subwoofer
2) simply gluing two pieces of MDF together with a softer adhesive like Weicon 310M Flex Classic or Loctite PL300 works really well as a simple CLD
3) a sandwich of MDF and Nidacore or cork works well too (again glued with the 310M Flex or PL300) but I'm not sure most people will want to deal with the hassle
4) CLD bracing with 33% overlap has a small edge over solid bracing, but any bracing at all really drops that main box resonance
5) melamine foam or 100% wool batting is the way to go for lining the box
6) Resonix is a nice cherry on top if you can swing the extra cost

Things that were not impressive: XPS foam in a CLD, hard polyurethane adhesives like PL Premium, crappy plywood, coating the interior with any supposed vibration absorbing compound.

Sorry if already asked - have you tried alu-buthyl used in windows industry? Shore A value for soft glue ? I'm thinking about printing CLD using Shore A40 plastic.

[augerpro]

Originally Posted by jzagaja

Sorry if already asked - have you tried alu-buthyl used in windows industry? Shore A value for soft glue ? I'm thinking about printing CLD using Shore A40 plastic.

Never heard of it. Know of a US source?

[454Casull]

Just sounds like aluminum foil laminated with butyl rubber.