[aceinc]

What is your opinion on adding dynamat or something equivalent to the exterior of "plastic" horns to keep them from resonating?

If it is a good thing, is doing each panel of the horn partially enough, or should all of the largish surfaces be covered?

My use case is a pair of Klipsch Cornwall IIIs. If I do open them up I may choose to make other physical changes such as bracing. Does anyone have much experience with the CW III cabinets and whether bracing is beneficial?

[Hobbsmeerkat]

I like the idea! Esp since it's a lot more pliable than norez & you can also wrap the horns with a sheet of polyfill or a similar recycled absorptive fabric to help reduce any hard reflections off the plastic as well.

As for partial or full coverage, it's really down to how much dynamat you have or want to use, as any mass added would be helpful.

I know Tyson upgraded his Klipsch Forte IIIs, including the crossovers along with adding norez & several braces throughout the cabinet and chunks of norez to the horns and drivers as well to help control resonances. (Pages 3&4)
https://www.audiocircle.com/index.php?topic=166996.msg1773331#msg1773331

[Tyson]

All speaker cabinets need to be well braced and damped.  Damping the horns is good too but less important than bracing and damping the speaker walls.

For my Forte III's I used a combo of angle braces and NoRez on the cabinets and then a combo of NoRez and modeling clay on the horns as well as the driver frames.   Very nice improvement in bass punch and clarity. 

[aceinc]

Does anyone have first hand knowledge regarding the internal structure of the Cornwall III vis-a-vis bracing & acoustic insulation?

I ended up with the CW III speakers in one of those too good a deal to pass up scenarios. My main system has a pair of "W" OB servo woofers laid horizontally with Magnepan MMGs on top of them.

[aceinc]

As for partial or full coverage, it's really down to how much dynamat you have or want to use, as any mass added would be helpful.

I would be buying what I need. My thought is, if all we are trying to do is to tame resonances, would adding a small amount of mass on the panels which resonate change the frequency they are excited by to outside the bandpass of the driver?

Adding mass to all of the surfaces should absolutely do what needs to be done, but if I don't need to do the additional work and the additional expense it's a win-win (work smarter not harder).

[S Clark]

I have no experience with Klipsch horns, but I do with the Altec 811 horn in the Valencia speakers.  These are cast Al and have resonance issues.  Adding slivers of open cell foam on the inside of the outermost cells resulted in significant smoothing.  By trial and error we changed foam shape and locations, measuring each time to finally get the best results. 

[aceinc]

I have no experience with Klipsch horns, but I do with the Altec 811 horn in the Valencia speakers.  These are cast Al and have resonance issues.  Adding slivers of open cell foam on the inside of the outermost cells resulted in significant smoothing.  By trial and error we changed foam shape and locations, measuring each time to finally get the best results. 

I actually have a pair of Flamenco's in the garage with very rough cabinets, waiting for me to do something with.

When you say inside, do you mean in the mouth/throat area? I can't tell from the picture.

[Hobbsmeerkat]

Does anyone have first hand knowledge regarding the internal structure of the Cornwall III vis-a-vis bracing & acoustic insulation?

I ended up with the CW III speakers in one of those too good a deal to pass up scenarios. My main system has a pair of "W" OB servo woofers laid horizontally with Magnepan MMGs on top of them.

I dont have any first hand experience sadly, & I couldn't find many pictures of the Cornwall III internals, but I have found internal pics of the Cornwall I, 1.5 & II, and there's very little bracing, if any, in them, mostly just some small braces in the corners that aid in assembly. There is a video looking inside the Cornwall IVs tho.

The Cornwall III & IV seems to have 2 large braces just above the woofer, and some pics of the CWIII's being built show the same braces. And there's likely a shelf just above the ports similar to the ones in the CWI & II.




Inside of a Cornwall "1.5"

I would be buying what I need. My thought is, if all we are trying to do is to tame resonances, would adding a small amount of mass on the panels which resonate change the frequency they are excited by to outside the bandpass of the driver?

Adding mass to all of the surfaces should absolutely do what needs to be done, but if I don't need to do the additional work and the additional expense it's a win-win (work smarter not harder).

You likely wouldn't be needing more than 2 10"x14.5" sheets (depending if you oder by sheet or by roll) per speaker, and it'll be most effective on any large/flat surface area. Plus anything left over can be used to dampen the woofer frame. I ordered a pack of 10 sheets off Amazon for about $20 and have used it for several different projects, and I still have some left over for future projects.
https://www.amazon.com/dp/B01KZ5X7KO/ref=cm_sw_r_cp_apa_fabc_spa7FbRXXFHJJ?_encoding=UTF8&psc=1

[Tyson]

Looks like the Cornwall has slightly more bracing and damping than my Forte's did, but that's still pretty piss poor.  That cabinet needs MUCH more bracing and NoRez.

[aceinc]

Hobbsmeerkat Thanks for the pictures...

I believe starting with the CW III they mount the drivers from the front and the back is not removable, I will look more closely when I get home.

The panel I think would have the most stored energy if not properly braced is the back panel. It would probably have the lowest resonant frequency.

I saw in the Tyson Forte mods the braces from the side to the rear, however this cabinet is not as deep front to back, so I am thinking baffle to back as well as a few side to back & top braces.

Alternatively would just adding 1" x 2"  edge mounted pieces on the large flat panels increase the resonant frequencies to the point they would be high enough not to be excited by the woofer? A non symmetrical (quasi-random) layout so there would be less chance of multiple section's resonances reinforcing each other.

[Tyson]

I was talking to Danny about brace location because I'd planned to do the same thing you are, which was a front to back brace and some side braces.  He said that you shouldn't do that because it eats up too much airspace inside the cabinet which will affect bass tuning.  A better approach is to use the angle braces.  These take up airspace too, but a lot less and you'll compensate for that by using some rockwool or fiberglass stuffing inside the speaker. 

The braces do push the resonances upward but they also reduce them in volume quite a bit too.  Using NoRez on the inside of the speakers soaks up the rest of this left over resonance.  It's a very cheap/easy/elegant way to end up with a very inert box.  Speaking from my own experience with the Forte's, it took the bass from 'good' to 'world class'.  And it really cleaned up the lower mids, while actually INCREASING punch and power.  That's because the acoustic energy the large drivers produce was not getting muddled by a vibrating box. 

[aceinc]

I was talking to Danny about brace location because I'd planned to do the same thing you are, which was a front to back brace and some side braces.  He said that you shouldn't do that because it eats up too much airspace inside the cabinet which will affect bass tuning.  A better approach is to use the angle braces.  These take up airspace too, but a lot less and you'll compensate for that by using some rockwool or fiberglass stuffing inside the speaker. 

I read through the first 8 or so pages of your "build" thread. What I see as a difference is the ratio of side to back width are quite different. The Forte is 13" deep by 16.5" wide vs the CW is 15.5" deep by 25.5" wide. This would mean on the Forte the 45 degree brace ended up place about 40% of the width of the back panel (assuming it was centered in the middle of the side panel). A 45 degree brace centered in the side of a CW would only make it to 28% of the back panel. To me this seems to leave a largish un-braced section of the back panel.

I am really considering adding the 1" x 2" ribs/battens I mentioned above, rather than the angle or front to back bracing, unless someone can tell me my concept is messed up.

[Hobbsmeerkat]

I definitely thought about the ribbing idea as well, and it might not be a bad idea in combination with angle braces and rockwool or fiberglass. Plus the ribbing will also act a bit like a diffuser since its no longer just a large, flat surface for the sound waves to reflect off of.

[corndog71]

Seems like it would make more sense to just build a better box with proper bracing and airspace.  But then again, that’s a lot of work.

[Hobbsmeerkat]

Seems like it would make more sense to just build a better box with proper bracing and airspace.  But then again, that’s a lot of work.

I found more pics of a DIY Cornwall III project than i could find any internal pics of the speaker itself. 

Even then, it only really had one main brace that surrounds the woofer and the shelf for the ports.

[rajacat]

Seems like it would make more sense to just build a better box with proper bracing and airspace.  But then again, that’s a lot of work.

+1

[aceinc]

What I stated earlier appears to be true. The drivers in the CW III are mounted to the front of the baffle and the rear panel is not removable.

I spent the $26 and bought the "Noico 80 mil 10 sqft car Sound deadening mat, Butyl Automotive Sound Deadener, Audio Noise Insulation and dampening" recommended by Hobbsmeerkat. it was $26 because I bought a roller to use for the installation.

I am not particularly good at documenting what I do, but I'll try. I know the steps needed to document everything properly, I'm just not very disciplined. Also I've never done waterfall plots which would be important in measuring the results of the cabinet mods.

Going to Danny's from S Florida with a pair of CW IIIs is impractical.

[S Clark]

I actually have a pair of Flamenco's in the garage with very rough cabinets, waiting for me to do something with.

When you say inside, do you mean in the mouth/throat area? I can't tell from the picture.

Yes, the inside surface of the outer wall of the outer cell.  I cut a wedge about an inch at the thickest and tapered to about a 4 inch wedge.  That worked the best of what we tried. 

[aceinc]

I have started the analysis phase of the project.

I moved one of the CW IIIs into the center of the room and using REW did a scan. I had the microphone about 39" from the baffle and about centered in the mid range horn.

From that I was able to get the following graphs. A few things surprised me;

• How smooth response was.
• The boost below 100hz.
• The dropout at ~5Khz.
• The waterfall plot seems too clean.

The boost below 100 hz is probably room gain/node. I have never worked with waterfall plots, but this one looks too consistent. Either everything is decaying too much at the same rate, everything is perfect, or I don't know what I am doing or looking at. I'm going with the latter.

Comments are welcome.

[aceinc]

I believe I answered the the reason for the cutout at 5 khz. It would appear that it is driver cancellation. The CW has two crossover points, 800 hz and 5 khz. Based on some of the knowledge gleaned from Danny's Tech Tuesday videos i decided to measure a few times from the same distance from the baffle and centered on the horizontal plane adjusting the height in 4" increments from the center of the mid range horn (31") to the center of the tweeter horn (35") to 4" above that. The results show the cutout frequency shifts. Based on Danny's explanation I believe this is because the relative distance from the two drivers changing causes the cancellation frequencies to change. It can be seen in the 800 hz frequency range as well.

It's really cool to see with my own eyes stuff I learn. Thanks Danny.