A Monster Construction Methods Shootout Thread

Versions 4 and 5 of the AugerPort are in!

AugerPort 4 results:

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AugerPort 5 results:

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Comparing the AugerPort 5 versus the Harman contour it is based on shows the huge improvement in knocking down the pipe resonances:

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The issue with all of these is much worse harmonic distortion. To add some data points I did a simple single tone spectrum analysis and you besides the harmonic distortion products, you can see broadband noise in from 500-5000hz that is not present in the Harman, and broadband noise in between the first 4 harmonics that only become an issue in the Harman at higher voltages. Making progress so I'll keep working the tap shape.

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@augerpro since you are on a port kick you might be interested in this Polk Audio Reserve Series Loudspeakers Press Event - YouTube Polk's new speakers have a resonator tuned to the resonance of the port in the throat of the port. Looks extremely good on the response charts they showed. May be a lot easier to implement and design parametrically when compared to a soft material method. Don't know the patent number or have technical implementation details, but I would guess that the 2 resonators are tuned around the 1/4 wave frequency of the first resonance to broaden the filtering notch and lightly damped with polyfil.

Not sure what your intentions are with your ports, but from what I have been seeing the Harmen port is ideal for a sub and shouldn't need the resonance reduction. Looks like there is still some opportunity to find a lower distortion port that reduces the resonance for woofers/midwoofers.
 
That Polk port idea is interesting, but I would totally disagree with a "ETF not needed on subwoofer as the resonance is out of band" It's not out of band for the listener who is listening - far from that, so reducing a port resonance would still make sense. They should just say it saves them on cost and maybe the effect is a bit weaker so they skipped it.
 
It looks to me to simply be a closed end pipe, with taps in the center, which is also aligned with the center of the port, I'm guessing it's dampening the 1/2 wave. When he shows all the pieces together it doesn't look like there is anything inside the resonator to damp the energy, just hollow? Certainly if anyone can explain what is going on there and how that might inform dimensions I could easily print something similar.

I do wonder that how the harmonic distortion looks, though he does say it chuffed later, so that is promising. That is my main issue, I'm quite happy with the pipe resonance dampening in this last round of designs, but it seems unavoidably to come with worse HD and chuffing.
 
Yeah, my take away is that you get the strong port resonance reduction with possible low distortion. My assumption on the damping is that they mention "appropriately damped" a few times when talking about the port resonators and the cabinet column resonator.

Looking at your figures lets assume there is a strong resonance centered at ~1900 Hz. If we want resonators at 1800 and 2000 at 1/2 wave they will be 8.5 cm and 9.5 cm. Judging from the images of the cutaway this seems to be more in the ballpark for the floorstander dimensions than 1/4 wave. I wouldn't be able to say on the diameter of port and resonator, by my eye the resonator looks to be ~1/4 the diameter of the port throat. If I were to damp it I would try at the point of reflection and at the inlet. At the inlet it could help to smooth the filtering like for the meta material absorbers. Should be light and not stuffed so as to not affect the tuning.

A thought I am having is they mentioned that the reduction in resonance peak gave a reduction in distortion because of the distortion in that frequency band. But, that would be with a flared ended straight port. The Harmen port does not have significant distortion at the resonance peak, so you may not get the benefits of both concepts here. Hopefully it won't distort as much as the slotted and damped port though.

Given that for a port you could 3d print the mount and inlet you could try a lot of different resonator lengths out with some thin wall pvc.
 
Tried a new CLD box using 1/4" Hardie backer board, a type of cement and paper composite board. Similar to earlier simple CLD boxes I did, the Hardie board was the internal layer, 1/4" MDF as the outer layer, glued together with Loctite PL300. I reran harmonic distortion for some earlier boxes that tested well because I couldn't remember how my test rig was setup. This time I included the THD% so you can just compare a value instead of the mental gymnastics of finding the difference between two wiggly lines.

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Tried a couple more ports designed to dampen the pipe resonance. While I've made some great examples that really do the job well, all of them suffer from much increased harmonic distortion and chuffing. Future designs will look into the newest Polk port that uses closed pipe in the center of the port that is tapped in the center to absorb that resonance. Polk claims it actually improved the HD performance even though that wasn't a goal. We'll see.

AugerPort 6
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AugerPort 7
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Comparing to best performer AugerPort 5 and the Harman port they are based on:
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Brandon - Just thinking, are the holes in sides of the port creating smaller air vortices within the main pipe, effectively damping the resonances because they cannot "flow" within the pipe, but creating distortion to the main air flow at the same time? Just picturing water trying to flow through a pipe, the same amount of water will still flow in and out overall (the port tuning), but it gets disturbed along the way by the little whirlpools on the edges.
 
Over the next few weeks I'll be posting more testing, but I wanted to share the two ports I'm working on. One is inspired by current Polk thinking and uses a resonator suspended along the the axis of the port. The second was inspired by a post from Nissep on microperformations of a sound absorber/resonator. They define microperforation as < 1mm, mine are .75mm.

Hi Brandon, this is interesting! Being a motorcyclist, the images you posted made me think of exhaust pipe designs that maximize flow and also tune the exhaust note to get the bike to sound a certain way... I used to have a SuperTrapp exhaust with disks that allowed the tuning of back-pressure - also when I took apart my current muffler, I realized it was simply a tube within a tube, with sound dampening around the inner tube. The answer is out there, keep on testing your ideas! Sixto
 
New port designs were measured today. AugerPort 8 is similar to my earlier designs, except that instead of large-ish holes in the wall, here I used microperforations, defined as being <1mm in diameter. Mine are .75mm. The hope was that with no large holes the chuffing and harmonic distortion would be closer to an untapped port. Similarly, AugerPort 9 is inspired by Polk's new X-port, which uses a suspended closed-end pipe along the port axis with taps in the center to again absorb the half-wave resonance of the port. Polk claims chuffing was actually improved.

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AugerPort 8 results:
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So damping of the pipe resonances was good, 2nd best to AugerPort 5. The hissy sort of chuffing was better too than prior attempts, but there was a distinctive "burrrr" sound at all power levels. You can see in the single tone spectrum plots how lit up it is. I don't see how I can improve this situation, so that's disappointing.

Next AugerPort 9:
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As far as damping the port resonance, this design did absolutely nothing. The resonator diameter is 1/4 that of the port, but watching Polk's video again it looks more like 1/3 or even 1/2 the diameter of the port. I'm going to resize to 40% of port diameter and try again.

Some comparisons, including with AugerPort 5, which had great damping, but poor chuffing as all these tapped ports do.

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Next are some new brace schemes. One is "matrix" style suggested by others. The other is similar to Kef's CLD brace where the place the damping material between the box and brace. I used the dowel brace here with 3M VHB tape as the constrained layer. But given the muted results vs Kef's simmed results, I wonder if using something like a window frame brace with the VHB tape would be better? More contact across the panel to absorb more energy? Also included are some comparisons with earlier tests: regular oak dowel bracing and CLD bracing where oak braces are overlapped 33% and glued together with Weicon 310M Flex.

Matrix bracing:
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CLD using VHB, Kef-style:
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Some comparisons:
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It might be good to recap where my cabinet testing has led. I started measuring just simple materials, ply, MDF, in 1/2" and 3/4" to establish a baseline. Moving on CLD construction, I now used 1/4" MDF "skins" joined by either the adhesive under test, or with an additional layer of foam, cork, etc. in between. From this the Nidacore construction was probably best, but the simple 1/4" MDF glued together with Weicon 310M Flex was so close and so much easier and cheaper to make, I would use that in the future. From my bracing tests (prior to the results just posted above) the CLD with Weicon 310M Flex made a decent improvement over solid braces. The next question is whether adding those CLD braces to the simple Weicon CLD box would retain the benefits if both. The following is just such box, compared to a simple 1/2" MDF box with solid braces, and a 3/4" plywood box with solid braces to represent the typical DIY boxes.

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I would say the rear panel measurement shows the Weicon CLD box to be superior to the others. The side measurement has it about the same as the MDF, with both being ahead of the 3/4" plywood box. I will say the addition of the CLD braces to the CLD box, didn't complement each other quite as I had hoped. Here is that CLD box with and without braces:

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You really have to match the construction method to the passband of the driver. If it was a (sub)woofer, plywood with a lot of bracing is perfect. For a pure midrange crossed at 300hz, I might go with the simple CLD box without braces. The real trick is when it's a 2-way. The choice isn't so clear to me at this point.
 
I also wanted to try a version of the simple Weicon CLD box (no braces) but using 1/4" MDF inside and 1/2 plywood on the outside. The idea being that the two materials would resonate at different frequencies and thereroe damp each other. I also did a version using 1/4" MDF & 1/2" MDF. I also switched from "box-within-a-box" construction to gluing the panels up ahead of time, then cutting to size and constructing the box. See pic to see what I mean. These are not braced and glued with Weicon 310M Flex. BTW, the Weicon can be found here.

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