A Monster Construction Methods Shootout Thread

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)
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Precision port (jumbo)

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Precison port (factory smooth finish)

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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.

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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.
 
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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.
 

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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.
 
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I assume it is something like this, https://www.amazon.com/ROSEROSA-Professional-Waterproof-External-Aluminium/dp/B07Z32Z8WB

Though what is more typically used in speakers is the same stuff as cars, https://www.amazon.com/Noico-deadening-Automotive-Insulation-dampening/dp/B00URUIKAK/

That is the 80mil version, there are thinner butyl layers like 50mil out there as well. I have yet to build a speaker box with the butyl, but cars and right behind my headboard of my bed outside is the water heater box. Really thin galvanized metal that just made an incredible racket in the wind and rain. Use that to fix it up right. Sound is reduced and what is left is lower pitch.
 
Newb(ish) suggestion...

I've been going off this for designing a new system: https://qualia.webs.com/newdampingfactors.htm

Which, when the info is put in order (and taking out anything over 300hz) looks like this:

material frequency damping factor
tungsten loaded putty 80 0.725
'Permali' 18mm 220 0.688
'Permali' 6mm 250 0.671
'Newplast' 160 0.635
bentonite filled resin 48 0.618
'Panzerholz' 150 0.599
lead filled resin 100 0.592
bentonite powder filled resin 100 0.518
glass 'Butacite' laminate 150 0.391
'Pyrotek' 6mm 100 0.376
recycled rubber crumb 109 0.348
glass 'Sentryglas' laminate 247 0.317
Page Lacquer' acrylic over mdf 100 0.315
Plasticine' 77 0.304
...

Tungsten loaded putty is available at fishing supply places but too expensive for a bulk coverage. Good for small area decoupling though! Similarly, Permali and Panzerholz is very expensive - not to mention tough to source. So I don't think they are worth considering given the parameters of this testing.

However, bentonite filled resin looks very interesting (and goes looooww), resin (isophthalic, in this case) is relatively cheap and the bentonite for the non-powder version is standard cat litter. Also cheap, and available everywhere. If it's possible to pour a reasonable thickness in the gap of the enclosures, or even make a quick box out of it, that'd be fascinating to see the results. I've ordered some resin anyway, so I'll be trying it out soon...

If I can find a cheap source of tungsten powder, I'm tempted to try a resin with that in as well.

Anyone else have experience with these materials?
 
Newb(ish) suggestion...

I've been going off this for designing a new system: https://qualia.webs.com/newdampingfactors.htm

I've seen a similar list, which included more composite materials than this one. My main take away from it was that ANY hybrid material is much much better than the base material. e.g. MDF with a thin laminate was truckloads better than basic MDF.

That is: a cheap complex material can be better than a simple expensive one.

Also note that a complex shape (a box, with holes and bracing) probably has massively different damping compared to a flat test panel. e.g. a bell and a gun will ring very differently, even if they are made of the same metal.

Tungsten loaded putty is available at fishing supply places but too expensive for a bulk coverage. Good for small area decoupling though! Similarly, Permali and Panzerholz is very expensive - not to mention tough to source. So I don't think they are worth considering given the parameters of this testing.

Also: a 31 litre box using 2 litres of cheaper kitty litter goo will probably work better (and be less wasteful of a valuable material) than a 30 litre box using 1 litre of tungsten goo.

Unless you are after exoticism for its own sake, or in a bling competition with a millionaire, I can't see any situation where the expense would be worth the marginal volume reduction.

However, bentonite filled resin looks very interesting (and goes looooww)

Anyone else have experience with these materials?

I've tried a basic bentonite loaded mix (kitty litter and gloopy glue mixed in a slurry like concrete) to line a cheap ABS plastic PA speaker. In this application, it didn't make much / any difference when compared to an identical untreated speaker.

...but I'd rather be disappointed by $10 of materials than by $500 of materials :)

I've also done some building with a ply / bamboo laminate, because

1) bamboo has really good damping properties
2) it looks really good
3) it is good to work with (really hard surface, machines very cleanly).
4) the stuff I like comes as 2400 * 1200 * 5mm sheet. It is a single layer that is designed to be laminated to a base layer
5) that 5mm thickness is very forgiving of sloppy workmanship
6) it isn't crazy expensive like Panzerholz (I got 4 sheets for $500 Australian)

I like the aesthetics so much, I've done non-audio projects the same way (e.g. stripped old furniture and re-skinned with bamboo).

The only downsides are
- its hardness (and silicon content) makes it more work to cut, and it probably dulls tools more quickly
- it doesn't respond to tools exactly how wood does (e.g. you can't plane it with hand tools)
- the splinters are different to most woods (they can be really fine and really strong, so they go in deep and break off).
 
HiFiCompass talks about a method to reduce the port resonance here:

Puri Bliss - BeWg | HiFiCompass

Do a Ctrl-F for "N.B. Rozen"

So the last paper I referenced is that Rozen paper, which is the inspiration for the port(s) Harman developed in their paper, which is the basis for my Harman port here. hificompass utilized a rectangle port, and only used Rozen's curve in one dimension. I would like to try in a rectangle port also (but curved in both dimensions) since these ports look ideal for subs, and a rectangle port made with bender board should be easy enough to fabricate.

hificompass doesn't say much about how he tapped the port and dampened the energy, maybe he will chime in.
 
I hope to have some new testing soon of new ports and CLD cabinet construction. I'll have one port using the Roozen profile mentioned from the paper above. Assuming that does not outperform the Harman inspired port (if it does I'll use the Roozen profile instead) I'll have a new hybrid combining the Harman profile with taps at 1/2 and 1/4 wavelength that will be filled with stuffing and sealed using some plastic strips to absorb the primary port resonances. I dub thee: AugerPort!!

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