A Monster Construction Methods Shootout Thread

[augerpro]

I've set up a gofundme for this project! https://www.gofundme.com/f/a-monster...f+share-flow-1
Any amount helps, especially since I'm currently unemployed, having switched jobs at a most inopportune time. The initial goal will cover my current costs, plus the next round using CLD techniques. Speaking of that, got some Nidacore coming: https://www.marine.com/products/14-h...-h8pp-plain-14

[Bear]

Once I move on to CLD construction, I need recommendations on the adhesive. I've read silicone is not very good at dampening vibration, but would like cheap, common caulk to use as a baseline. To step it up a notch, the newer MS polymer adhesives are apparently the way to go:

https://www.amazon.com/WEICON-13305310-MS-Polymer-1-Component-Adhesive/dp/B004Z0MRU2/ref=sr_1_3?dchild=1&keywords=ms+polymer+sealant&qid=1596904242&sr=8-3

https://www.amazon.com/Red-Devil-0987-Advanced-Purpose/dp/B0843K399R/ref=sr_1_4?dchild=1&keywords=ms+polymer+sealant&qid=1596904242&sr=8-4

https://www.amazon.com/Rayt-1881-52-Sprint-Polymer-Transparent/dp/B017IPHREQ/ref=sr_1_5?dchild=1&keywords=ms+polymer+sealant&qid=1596904242&sr=8-5

https://www.amazon.com/Deka-FRA451072-Dekasyl-MS-2-White/dp/B00SYHMKV8/ref=sr_1_22?dchild=1&keywords=ms+polymer+sealant&qid=1596904242&sr=8-22

https://www.amazon.com/WEICON-Speed-...904242&sr=8-38

In the construction and architecture arena, Green Glue is relatively common.

https://www.amazon.com/Green-Glue-Noiseproofing-Compound-PACK/dp/B079S6WYVX/ref=asc_df_B079S6WYVX/?tag=hyprod-20&linkCode=df0&hvadid=312305907549&hvpos=&hvnetw=g&hvrand=9884659612128030032&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9061205&hvtargid=pla-568765555619&psc=1

"Better" practices for soundproofing a room is to stagger the studs, double-rock the walls and put Green Glue in between the layers of gypsum board. Oh, yeah, you also stuff the wall cavity with fiberglass insulation (which isn't done for interior rooms in a home). There may be something in that mess for construction of a little box vs a big box (room). We tend to use much higher cost materials than what even a custom builder would want to do.

[augerpro]

Harmonic distortion results up next. These are taken from the rear panel in the same manner as the first frequency response measurements.









The last two had holes routed for the dummy driver for lining/fill testing. I capped the hole with the respective material, but I'm not comfortable comparing these directly to the ones above.

[augerpro]

Bear> I know that Green Glue is pretty popular, but what is the data for that? Is it a good adhesive AND vibration resistant?

[augerpro]

Materials I have on the way: 4/5" wool batting, 1/4" NidaCore, Resonix CLD squares. Still deciding on CLD adhesives.

[gregrueff]

Materials I have on the way: 4/5" wool batting, 1/4" NidaCore, Resonix CLD squares. Still deciding on CLD adhesives.

FWIW I had researched CLD myself and read a lot of academic articles and thesis papers. What I got out of it was that constructing a true CLD system requires an adhesive with a high shear modulus, less the constrained layer be decoupled from the base layer by the adhesive itself and not provide the same effectiveness. In essence, an adhesive with too much compliance absorbs energy instead of imparting it into the constrained layer and placing it in shear as intended.

I’ve myself laminated hard rubber strip to wooden braces using epoxy ala the KEF method. The problem I had was the surface of the rubber strip was too smooth and I had to rough it up to get a solid bond.

Cheers,
Greg

[xandresen]

Bear> I know that Green Glue is pretty popular, but what is the data for that? Is it a good adhesive AND vibration resistant?

I have used Green Glue. It is NOT an adhesive if you mean something that hardens after application. It comes in a caulk-gun tube and has the consistency of Vasoline petroleum jelly but somewhat stiffer. And as their marketing says, it never hardens. It retains its original consistency (for at least many months in my experience).

Hope that helps.

[Bear]

I have used Green Glue. It is NOT an adhesive if you mean something that hardens after application. It comes in a caulk-gun tube and has the consistency of Vasoline petroleum jelly but somewhat stiffer. And as their marketing says, it never hardens. It retains its original consistency (for at least many months in my experience).

Hope that helps.

Yeah, I think someone would throw the phrase "viscoelastic damping material" in there. It's essentially the interstitial layer between two rigid construction layers to prevent them from being fully mechanically coupled, but also not fully isolated (one layer assists the other layer without making them a single resonating membrane). Is this any better than just sand? That's the testable hypothesis.

[wolf_teeth]

If you want NorthCreek "Glop" info, I have this saved below....
Wolf

[gregrueff]

I ran across this AES paper on the subject topic and found it extremely interesting:

https://www.aes.org/tmpFiles/elib/20200901/20758.pdf

Cheers!
Greg

[chrisn]

That link doesn't work for me:/

[DML9]

Greg:
Is this the proper link?
https://secure.aes.org/forum/pubs/co...ns/?elib=20758

[gregrueff]

Greg:
Is this the proper link?
https://secure.aes.org/forum/pubs/co...ns/?elib=20758

Yes, on metamaterials. Thanks for that.
An array of 1/4 length helmholz resonators if you will, tuned to cover a broadband of frequencies.

[bvbellomo]

What can I put in my cabinet to damp a 56.5 foot long 20Hz wave? Even 1kHz is over a foot long. This is an interesting thread, but I wonder if anything can be done from a practical standpoint as far as shearing or anything beyond the typical bracing, wall material choice and polyfill for the wavelengths we care about.

[augerpro]

I ran across this AES paper on the subject topic and found it extremely interesting:

https://www.aes.org/tmpFiles/elib/20200901/20758.pdf

Cheers!
Greg

That's interesting. Reminds me of this: https://journals.aps.org/prx/abstrac...sRevX.7.021034. A diffuser, not absorber, but still wonder if there is some benefit anyway. For example could be attached to the inside of the cabinet CLD-style, and covered with typical liner. The diffusive property may force more time contacting the liner and absorbing energy?

[augerpro]

That's interesting. Reminds me of this: https://journals.aps.org/prx/abstrac...sRevX.7.021034. A diffuser, not absorber, but still wonder if there is some benefit anyway. For example could be attached to the inside of the cabinet CLD-style, and covered with typical liner. The diffusive property may force more time contacting the liner and absorbing energy?

The lowest frequency that is diffused by this method is limited by the depth of the diffuser having a minimum of 1/20 wavelength. Which is still really good. Still, they say this "Indeed, to the best of our knowledge, the thickness of λ0=20 is the smallest that has ever been reported for acoustic metasurfaces manipulating transmitted or reflected waves with experimental verification (excluding the acoustic metasurfaces for absorption purposes)." Wonder what absorptive metasurface they are referring to? They don't have a citation here.

[gregrueff]

The lowest frequency that is diffused by this method is limited by the depth of the diffuser having a minimum of 1/20 wavelength. Which is still really good. Still, they say this "Indeed, to the best of our knowledge, the thickness of λ0=20 is the smallest that has ever been reported for acoustic metasurfaces manipulating transmitted or reflected waves with experimental verification (excluding the acoustic metasurfaces for absorption purposes)." Wonder what absorptive metasurface they are referring to? They don't have a citation here.

Very cool.
Much more dense than the one I posted.
I agree the important takeaway is f/20 is empirically verified, with a throat opening of f/2 for a helmholtz resonator.
Someone with a CNC router could potentially put some of these concepts in practice...

[augerpro]

I have a 3D printer and know my way around Fusion360. But I would need some help taking their formula and pulling that into F360 and could be scaled up or down in size as needed.

[gregrueff]

It is not clear to me how one would utilize these concepts and apply them into a mid bass or midrange driver enclosure.
They talk of impedance matching, and to me that means a gradual enclosure transition to a terminus where the array starts.
But then I’m also not clear on the helmholtz cross sectional area as related to wavelength. The one paper references f/2, but I’m intuiting this may be some of the secret sauce.

[augerpro]

It is not clear to me how one would utilize these concepts and apply them into a mid bass or midrange driver enclosure.
They talk of impedance matching, and to me that means a gradual enclosure transition to a terminus where the array starts.
But then I’m also not clear on the helmholtz cross sectional area as related to wavelength. The one paper references f/2, but I’m intuiting this may be some of the secret sauce.

I could see using this to widely disperse the sound, which -in my mind- would allow more time to contact lining to absorb more energy before it exits the walls or driver diaphragm. But maybe not.

Anyone know what kind of glue to use with this sort of foam roll (steel pipe insulation):



Also building the next round of boxes. Going to test bracing using oak trim, but also CLD bracing:

[xandresen]

Anyone know what kind of glue to use with this sort of foam roll (steel pipe insulation):

Assuming you are trying to glue the seam shut...

How about acrylic bath caulk/sealant? cheap, not so strong.

or strong: one part polyurethane construction adhesive? Locktite PL or similar.

If the foam is non-porous and you use a thin glue layer, these will set very slowly since only the edge of the glue line is exposed to air.

edit >> I forgot to mention duct tape.

[augerpro]

I've actually considered duct tape. So maybe that and I'll test the bath caulk also, got plenty laying around.

[augerpro]

Round 2 results! Couple issues make these results not exactly comparable to the first round. First, repeatedly disconnecting the source driver ended up with a terminal coming off, lead and all. I bought a couple more drivers, and of course the response isn't exactly the same. So I've taken a new baseline empty box measurement with the 3/4" mediocre ply identified before (AC Radiata pine plywood). Second, I already cut holes in that box for the previous fill testing, so built a new box. So new baseline is a new driver in a new 3/4" mediocre ply box.

On measurement conditions, remember that the amount is of signal escaping the box is relatively low, so low frequency noise can start to show up <200hz. So take that as the lower limit. The one exception is the fill testing where the amount of bass leaving the dummy woofer is actually pretty high, so you see a typical low frequency roll off there.

For the CLD enclosure, I used 1/4" MDF as the primary material. Why so thin? Well it seems to me that a proper CLD should be doing more with less - design smarter, not harder. I built box-within-a-box, minus the baffle, which was a solid piece of MDF left for last. I used a fine tooth trowel that made 1/16" beads to try to keep a consistent application. See pics below to get an idea. For the Nidacore and 1/2" XPS foam I used Loctite PL300 adhesive, since it is made to use with foam.

New baseline 3/4" mediocre ply box:



First up is fill/lining testing where the mic is placed at the SB15 dummy driver. Since I had the new source driver I decided to rerun the 1.8" denim insulation to get a good starting point.
1.8" Ultratouch denim insulation



Next up 1" melamine foam:





Lastly, .80" 100% wool for quilts from homeofwool.com. This looks the same as other wool batting for quilts, so I think any 100% wool batting for quilts you can find will behave similarly as long as the nominal thickness is the same:




Next is bracing. I used 3/4" x 1 1/2" oak braces from Home Depot. First up, solid brace vs empty box:





Next, Sikaflex 292i. This is a construction adhesive with claims of vibration dampening. Rather thick and tacky:





Next, Weicon 310M Flex Classic another construction adhesive made from MS polymer, a new-ish family of adhesives that supposedly has vibration dampening also. Very creamy and easy to work with:



Some brace comparos:





And now the full CLD construction. the first two are simply 1/4" MDF joined by either the Sikaflex or Weicon. The last pair use either 1/4" Nidacore or 1/2" XPS foam as an interior layer, glued with Loctite PL300.






Sikaflex 292i:



Weicon 310M Flex Classic:



1/4" Nidacore:



1/2" XPS foam:



And last, Resonix CLD squares applied to the 3/4" mediocre ply box above. The story of these is interesting. A hobbyist at diymobileaudio.com had done a very popular CLD test and one product rose to the top in overall performance and price: Sundown Solutions CLD tiles. The surprise was that there were other similarly constructed CLD tiles, but performance was surprisingly variable. Some years later SDS went out of business the hobbyist started his own line with the aim of being the same (or better) as the SDS tiles. I write all of this to alert you that just any butyl rubber and aluminum tile may not behave this well.

[augerpro]

Things I want to investigate in Round 3:

1) cheap adhesive in place of the Sikaflex and Weicon. Loctite PL Premium is being considered at the moment.

2) adding microspheres to the adhesive as recommended by Earl Geddes. This creates friction that bleeds off energy, helping the CLD do it's job better

3) test wall coatings like AcoustX

4) test additonal internal layers like the Nidacore, but maybe cheaper and more widely available

5) port testing. Square, straight tube with flared end at baffle, Powerport, and one based on a Harman paper

6) more wall materials like cement board, or maybe something like polyurethane



That said, I've spent about triple what my gofundme raised, so I won't be moving on to round 3 until I get the funds to do so. Thanks to everyone that has donated so far, this couldn't happen with out you!

[augerpro]

Some additional comparisons I find interesting. One thing to keep in mind about those main 200-1000hz resonances is that stiffer material pushes the frequencies up, but overall SPL may be the same. For example, comparing the 3/4" ply with Resonix tiles to the Weicon 310M which is basically 1/2" of MDF with an adhesive in the middle, the frequency differences are due more to the MDF vs ply, than Resonix vs 310M. You could see this clearly in the first results with simple woods where MDF is flexier so the main resonances would shift lower, but SPL is the same (or lower). Also 1/2" vs 3/4" showed the same thing due to the longer spans of material (I kept the external dimensions the same) for the 1/2" boxes pushed the frequencies lower. Putting that together you can see 1/2" MDF box vs 3/4" plywood box is basically two ends of a spectrum, where other combinations of material and thicknesses would fall in between. NOTE: for Round 2 and in the future, I have decided to keep the internal dimensions the same so at least one of the variables mentioned above is minimized.

[xandresen]

Things I want to investigate in Round 3:

6) more wall materials like cement board, or maybe something like polyurethane

I only got good CLD results when using a much stiffer inner wall than wood based products. I suggest giving cement board a try.

The Resonix tiles are interesting. I suspect they would also work better with a thicker(=stiffer) aluminum layer (website says it's only 0.004" thick!) but then they couldn't be form-fitted to car panels.

Thanks for all the work.

[augerpro]

Couple more comparisons:







In the last, remember that I said 1/2" MDF and 3/4" plywood are on opposite ends of a spectrum means that this is not a great comparison. I need to build another 1/2" MDF box to compare the 310M Flex CLD build to. I'll try to do that tomorrow and also get some distortion measurements done also.

[augerpro]

I'm thinking about how to combine techniques to cancel out weaknesses. Look at this, if the final response is simply an average (which it probably won't be since that is not quite the mechanics happening) this should provide quite a well behaved combo:

[augerpro]

Looking back at prior suggestions, I think cork and urethane sheets would be good candidates to test. Does anyone know much about casting urethane? Easy for a hobbyist? Cheap?

Another test I need to do is after identifying a couple good lining/fill performers, build a box with no dummy woofer hole and measure cabinet radiation like I am with the materials and methods testing above. The primary use of lining/fill is to dampen internal air resonances and reflections which then escape through the woofer cone, and some believe this has little impact on cabinet wall radiation. I'm not so sure anymore since it is apparent to me just sitting here listening to test signals that the lined boxes are quieter than a bare, empty box. Also, this difference might help prioritize similar lining performers. For example, my favorites so far are wool batting and melamine. Both widely available, cheap, and good dampening. I wonder if there is a difference between the two on how much radiation comes from the cabinet? Also, I've been using staples to attach the lining, it would be interesting when testing those two to do an additional test to the melamine where it is glued to the cabinet wall. If that dampens things further then melamine would probably become my go to lining over the wool batting. A last test though is to measure a woofers bass response and impedance, you can see the melamine sucks some energy out of the bass relative to the wool, so it night no be worth using it in some applications.

[Steve Manning]

Hey Brandon,

Looking at your box within a box, have you looked at anything like this stuff. https://www.lowes.com/pd/BLACK-JACK-...ealant/3013306. They actually have several different varieties of this stuff, depending on what your needs are. I would expect you could pour this between cabinet layers and then let it cure. An extreme example would be like what these guys do. https://www.youtube.com/watch?time_c...ature=emb_logo

[augerpro]

Now that is some pretty interesting stuff! I was thinking simply a wall coating until I watched that video.

[Concillian]

Reminds me a bit of the construction method used for this set, but they used concrete & epoxy mix:
https://www.diyaudio.com/forums/mult...ak-towers.html

Seeing the ribs like that with a "box in a box" supported by the meat of the sandwich seems like one of those "of course, why didn't I think of that" moments. Doesn't seem like it would be too difficult either, though with DIY friendly wood, the walls would end up pretty thick compared with the cast aluminum.

Wonder how well expanding spray foam would work (not the yellow stuff that dries super hard, the white softer foam.) Perhaps not structural enough.

[Steve Manning]

I try to keep up with what the big companies are doing with cabinet fabrication. I know I can't duplicate much of them, but they are a good source for ideas.

[augerpro]

Remeasured a 1/2" MDF box with the new driver, versus the CLD box using 1/4" MDF joined by Flex 310M:

[augerpro]

I wanted to return to the brace results for a moment:





It is interesting that the CLD braces showed almost no difference within the test's tolerance. I wonder if this is specific to this design: small driver, low SPL, or something like that? In this box/driver/SPL the CLD braces are effectively rigid? Perhaps a more robust woofer and bass signal would show more difference?

Another thought is that I have 95% overlap, I wonder if dropping that to 50% overlap would show differences then?

[gregrueff]

Does anyone know much about casting urethane?

I’ve wrapped an MDF cabinet in fiberglass bi-directional fabric in a 3K twill weave using wet-layup. The results were better than I imagined or expected. Granted wet-layup is a demanding endeavor. I had used the products from Fibreglast, but don’t see why the Home Depot stuff wouldn’t work.

If you’re considering a wet-layup of any kind or material, I have always wanted to try a composite plywood, fiberglass, rubber, fiberglass, wood panel. Even just a single layer of a fiberglass weave provides considerable strength, but I had considered using two layers placed with the weave perpendicular to each other. The resin, be it polyester or epoxy would provide the right kind of high shear bond to the constrained layer and the plywood. So you could construct it fairly easily from the bottom layer up, just stacking and then clamping. The outer shell of normal thin plywood would give you an ordinary working surface, while also encompassing the messy fiberglass and rubber composite.

I’ve had this idea for years and intend to try it eventually, but you have so much more drive to actually get to the work than I do. Bravo again for all your diligent work.

Cheers,

[augerpro]

I've updated my Soma Sonus website to include a condensed version of my results for an easier read.

[augerpro]

In the next round of measurements, I'm going to investigate ports. This was prompted by the Harman study (attached) and the Kef LS50 paper. I'll be testing against some typical DIY ports. Since the Harman port length is fixed, I'll verify its tuning, then cut the other ports to match that tuning. You might ask why I printed all of them. First I can standardize the mounting flange so I can swap them on the box quickly. Second, surface can have an effect, so I wanted the same surface finish on all of them to remove that variable. Starting at left the ports are: rectangle (1:4 ratio mouth, 3/4" roundover), straight port with 3/4" roundover at the baffle, Harman port, Precison Power Port, Kef port.

[augerpro]

ROUND 3!
I'll be rolling out results over the next week, but the first batch is the port performance. As mentioned before, the inspiration for this experiment was the Kef LS50 white paper and a Harman study by Salvatti, Devantier, Button (attached). The Kef port's innovation is using a foam center section to dampen the higher port resonances. The Harman paper looked at different port terminations and their impact on sensitivity, harmonic distortion, and power compression. Their own designs in the test were ports that were not straight walled, but a constant radius. They related this radius to the overall length via an equation, but the one labeled N=0.5 was the best balanced and the one that I selected to copy. Simply, the radius of the wall curvature is equal to the port length:



There is also a small 1/2" roundover on either end that isn't shown in that pic. What was interesting about Harman's results were slight sensitivity gain at low power levels vs the competition, and very good harmonic distortion and chuffing onset performance. I did not see the sensitivity gain, probably due to length, which I will address below.

For the Kef port I used common foam pipe insulation and also decided to print a version using TPU filament. I used Hatchbox TPU with a Shore 95A rating. I used 2 perimeter layers and 18% fill, which is about as low as I think a person could go. I copied the roundovers of the Precision port so it would just be the flexible center sections that were the variable.

The Precision port is just a 3D-printed copy of a 2" Precision port.

The "typical DIY" port is a simple 2" ID pipe with a 3/4" roundover at the baffle, as a DIYer would typically do. This would be the reference port.

The square port is similar to the typical port, except rectangle (it just now dawned me I labeled all the pics square, oops) with a 1:4 aspect ratio. The cross-section is equal to a 2" round port at 3.14 sq.inches. This also has 3/4" roundover at the baffle.

Speaking of diameter all of these are 2" nominal ID ports. For the Harman this would mean the very center of the port where it is skinniest.

The box is a 4th order bandpass tuned to 52hz. The driver is the SB15NAC-8. Front volume is 15L, rear volume is 10L (net, but see below). Front was lined with wool batting, rear was lined and somewhat stuffed with the same wool batting. I adjusted all the port lengths so the Fb was the same, as verified by impedance:



Length can give you an idea of how restrictive a port is. The less restrictive it is, the longer the port must be to maintain a given Fb. The lengths were: Harman 5.4", PP and Kef 4.25", and typical and rectangle port 3.75". This is where I deviated from the Harman paper. There they equalized the ports by length, which doesn't make much sense to me, in the real world you would want to know relative performance for a given tuning. For this reason, you might notice unexpected results vs the Harman paper. For example sensitivity, which was worst for the Harman in my tests, instead of the best in their paper.

This brings me to caveats. Since these are all different lengths, I had to add a little closed cell foam so the port volume was *roughly* equal. It wasn't exact, but I'm satisfied with my mitigation. Next caveat is that all of these are more or less close to the driver. A problem? I don't know. See pic for an idea:



Another caveat is surface finish. The Harman paper showed surface finish makes a difference and smooth is best. These are 3D printed and so not as smooth as PVC pipe you might typically use. A problem? I'm not sure, but I would say a necessary evil to keep the playing field level. Otherwise I would have just used the actual 2" Precision port I had. Another benefit was that I could make the mounting flange the same for all of them for quick attachment/removal.

Test setup> MLS measurements for the SPL: 500ms gate, 1/24 smoothing, mic at 1/4" from the baffle. I tested a number of distances and settled on 1/4". I had to change things up for the harmonic distortion measurements to not overload the mic and soundcard, here it is 20.5" from the baffle. On a related note, I could not use the MLS function for these high SPL measurements, so to judge power compression look at the level of the fundamental F1 in the HD measurements. Also when trying to get an idea of the onset of chuffing, you can see the harmonics starting to cluster. Why this is so is what you can't see in the plot: the entire spectrum is lit up with something almost like white noise, with other concerning sounds mixed in. You'll also notice the fundamental F1 goes from smooth to jaggy. I know the plots are limited, but I'll try to add subjective commentary to give clearer perspective. I added the drive voltage to the HD plots, if you are bored you can look at the impedance and calculate power and SPL.

Wow, lots of setup, let's just show the damn data!

Typical DIY port








rectangle port








Kef port w/foam








Kef port w/TPU








Precision port








Harman port








Some comparisons:









I need to delve into the results much deeper but here are some initial thoughts. The typical DIY and rectangle DIY ports were surprisingly similar in frequency response and sensitivity. I'll need to dig into the HD results to pic a winner.

The Kef ports didn't show their stuff as much as hoped. Foam looks better than what I printed, so chasing down high performance flexible materials will be the key to making the concept work. One thing I should mention, since the Harman port was the largest and not length adjustable, everything had to match that for Fb. This resulted in the Kef center section only being about 1 5/8" of exposed pipe for flexing. Perhaps if it was longer you would see a bigger impact on damping those port resonances.

The Harman was the most interesting to me. I was let down by the sensitivity being lower than all the others. But as soon as I did the HD measurements it clearly pulled ahead. I've only just glanced at the HD plots to confirm what I heard, but I can tell you sitting here running the test the difference was huge. Most of the others were having difficulty by 8.75V, and are downright scary sounding by 10-11V. The Harman was just so much cleaner. I remember thinking at 13.52V, yeah that's chuffing. But lower than that and you kinda had to listen closer to pick out audible distress, it just wasn't that noticeable, certainly not if I were actually playing music or movie to mask it. I need to compare it against the actual Precision port with smooth walls. If the 3D printed surface is not an issue, I would encourage anyone to try the Harman for any fullrange or subwoofer duty where ultimate SPL performance is important.

[augerpro]

Looking at the HD results closer for the first time, I see the rectangle and typical round port are basically the same in my implementation, with maybe a slight edge to the rectangle. The Precision port steps up performance with noticeably better HD and compression performance than the previous two DIY ports. But notice at the highest SPL it falls apart hard and actually falls a bit behind the the typical ports. Harman noticed this same behavior in their study where the straight port with no roundovers lagged all the competition until the point where they were all chuffing, where it actually was a bit better than the others. Still, they were chuffing, so sort of a pointless win. The Harman OTOH is just a beast. It takes another step up in compression performance from the Precision port, and the HD is just great until finally starts chuffing pretty good (to my ears) at 13.52V.

[gregrueff]

That Harmon port looks spectacular.

Since you already have the bandpass enclosure constructed with results, have you considered comparing the bandpass HD to regular infinite baffle HD? I’ve often wondered how they compare and wanted to do this comparison myself.

Cheers,
Greg

[augerpro]

That Harmon port looks spectacular.

Since you already have the bandpass enclosure constructed with results, have you considered comparing the bandpass HD to regular infinite baffle HD? I’ve often wondered how they compare and wanted to do this comparison myself.

Cheers,
Greg

You mean compare the bare driver (+port?) HD to the bandpass? I know the bandpass acts as a low pass filter so harmonic distortion should be reduced. Not sure if I have the time to do that test this week though.

[xandresen]

The Harman OTOH is just a beast. It takes another step up in compression performance from the Precision port,

What if we look at things a bit differently.
The Harmon port is the longest for this fixed tuning, that implies it has the largest effective diameter. This is confirmed just by looking at the interior diameter - it's only 2" for a very short length, larger elsewhere.

Perhaps a more accurate comparison would be a Precision style port whose diameter was increased until the port required the same length as the Harmon for the tuning frequency. The bigger diameter would allow more air to flow, similar to the Harmon.

We can't buy that port, but could you print one?
It could be made on the long side, then remove sections of the straight tube to hit the tuning frequency.

[augerpro]

Loctite PL300 CLD
In Round 2 I was impressed by the simple CLD of 1/4" MDF and Weicon 310M Flex adhesive, but wanted to check cheaper alternatives. I had plenty of Loctite PL300 on hand from the other CLD boxes and liked that it stayed softish when cured (acrylic latex). And it's super cheap. I also grabbed some polyurethane PL Premium adhesive. This cured quite hard, I really can't see it doing anything beneficial so I just built a box with the Loctite PL300. Here are the results:



1/4" cork CLD
Similar to the prior boxes made from 1/2" XPS foam and Nidacore, this cork is sandwiched between 1/4" MDF and glued up with PL300. Sorry forgot the pic, but it looks like the Nidacore build.



AcoustX
I've wanted to try this since a box I built years ago that seen improvement when judged by the old knuckle rap test. Problem with that is things can sound different but not better, and we have no way of knowing until we measure.







Some comparisons of the above with Weicon 310M Flex Classic:














On to bracing. Last time my CLD braces with 95% overlap behaved pretty much like a solid brace. So this time I used 33% overlap and the Weicon 310M Flex adhesive as before, and also added a version using 3M's VHB tape, which is a vibration dampening adhesive tape.

Weicon 310M Flex Classic 33% overlap



3M VHB 33% overlap

[augerpro]

What if we look at things a bit differently.
The Harmon port is the longest for this fixed tuning, that implies it has the largest effective diameter. This is confirmed just by looking at the interior diameter - it's only 2" for a very short length, larger elsewhere.

Perhaps a more accurate comparison would be a Precision style port whose diameter was increased until the port required the same length as the Harmon for the tuning frequency. The bigger diameter would allow more air to flow, similar to the Harmon.

We can't buy that port, but could you print one?
It could be made on the long side, then remove sections of the straight tube to hit the tuning frequency.

I could try that. I was following Harman's standard where they showed the smallest diameter defined the ultimate performance (via Reynold's number IIRC) even if only a portion was that diameter. I'll have to read their paper again.