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Boomzilla

How to treat Cornwall 3 cabinets for better bass?

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When Klipsch came out with their "new" MDF cabinets, they (wisely) took the step with the La Scala 2's of making all cabinet walls significantly thicker for vibration control. With the Cornwalls, however, the original 3/4" thickness was used. The results, in my opinion, are insufficiently stiff cabinets that resonate and "sing along" with the music, particularly in the bass. My Cornwall 3s (henceforth "Cs") sound very loose and boomy in the bass frequencies.

This is not a room artifact. The same location where the speakers are placed has worked well with many other speakers (including Cornwall ones) without the bass issues that the Cs have. This is not a result of slap echo - the room is treated with ATS panels and has worked well with many other speakers.

This is not an amplification artifact. The Cs have been tried with a half dozen different amps, none of which adequately control the boomy bass. Some amplifiers do seem to be slightly better than others. The "tightest" that I've tried so far is an Emotiva XPA-2 (300 wpc, solid-state). Although the boom is not gone, it is somewhat reduced with this amp.

Assuming, therefore, that the remaining looseness and bloat in the bass is a result of cabinet vibration, my question becomes: Without damaging the resale value of the Cs, what modifications are feasible with the speakers that will reduce cabinet vibration? Ideas that I've come up with (but have not yet tried) include:

  • Screwing a small ATS pad to the back of the speaker - foam to the cabinet, for panel control
  • Taking some open-cell foam and making plugs for the port openings
  • Using self-adhesive lead wheel weights to add mass inside the cabinet
  • Using poly fill to stuff the cabinets
  • Damping the woofer struts with adhesive material and using a felt sheet to attenuate the woofer's back wave for higher frequencies

So the point of the thread is to ask: Will any of the proposed mods improve the bass of the Cs, or do I need to consider other choices? If the latter, what choices might be effective?

Thanks - Boomzilla

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Have you tried placing your CWIIIs in the corners of your room within 18 inches (445 cm) of the corners? You might be surprised that some of your "box resonances" are actually room placement modes.

You will also need to move any furniture, racks or equipment away from the speakers for at least 3 feet in radius around the speakers, or place absorption material on the sides of these acoustic reflectors. The room's walls should be smooth, and the fewer reflective objects between the speakers, the better the bass response and imaging, even to the point of moving all equipment racks from between the speakers.

Chris

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Hi Chris -

No, corner placement is not an option in my room. My room is exceptionally kind to bass - all four corners are vented by WIDE openings into other areas of the house (foyer, kitchen, hallway, and stairwell). Having lived here for 20 years with a WIDE variety of loudspeakers and subs, I know the room's characteristics well. With the ATS pads that I now have behind the speakers and behind the listening couch, and with the side walls six and twelve feet from the speakers, reflections are not an issue.

Summarizing - I appreciate your comments, but the room is NOT the cause of the Cornwall's bass performance.

Cordially - Boomzilla

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I noticed that you didn't show a picture of your room setup, and the detail around the speakers. I assume that don't want to discuss this part of the problem space since you've already determined that this isn't an issue.

You're also the first person that I've seen to say that CWIIIs have bass problems. CW bass bins sound like bass reflex boxes to me and that sounds different than horn-loaded bass bins. I've also noticed that this characteristic sound can't be minimized unless the speakers are in room corners (due to dramatically decreased bass modulation distortion by taking advantage of the free 1/2*pi steradian room loading). But it sounds as if you've identified what the problems are already, and have ruled these factors out already.

Please let us know the solution to your issues when you find them: I would like to know...

Chris

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Hi Chris -

I have full confidence that the room is no longer the issue. Prior to putting up the ATS pads, then yes, the reflectivity was an issue. Having run at least two other speakers in the treated room in the exact same positions as the Cornwalls, and having not had bass issues with either of them, I'm convinced that the room is NOT a contributing factor.

"Bass reflex boxes" are too diverse to be thrown into a single category, IMHO. I've heard ported boxes (some with just ports, others with passive radiators in place of ports) NONE of which sounded like the Cornwalls. I would agree that all of the reflex and passive-radiator boxes sounded significantly different than horn-loaded La Scalas, but beyond that, there is very little commonality. Because some of the other vented boxes that I've used in my room DID provide taut and pitch-accurate bass, I think that one of two things may be preventing the Cornwalls from doing so as well:

Either the design is optimized for high efficiency at the expense of bass accuracy (possible) or the economies taken in the manufacturing process have resulted in insufficient cabinet rigidity and allowed the cabinet to vibrate along with the signal (likely).

Either problem should be "solvable" with a bit of reverse engineering. I'm willing to invest the time to do a bit of "tweaking," and should that fail, I'm also willing to encase the entire Cornwall cabinets with another 3/4" layer of plywood to prevent them from vibrating. The latter option, obviously, has resale implications for the speakers, but if that's what it takes to make them stop vibrating, then I'm willing to do it.

Cheers - Boomzilla

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Boomzilla I would rethink wrapping another layer of 3/4 plywood around your 3's. You would be better served building new speakers.....

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i had 4 cornwall 3's in a 16x16 room and it was awesome sounding. have now gone to 79 corns and 79 heresys in the same room and its quite different

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...have now gone to 79 corns and 79 heresys in the same room and its quite different.

Could you describe the difference?

Chris

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not much sound coming from the rear heresys as with the big cornwalls

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Boomzilla I would rethink wrapping another layer of 3/4 plywood around your 3's. You would be better served building new speakers.....

Normally, I'd agree with you. My particular speakers, however, were purchased "half-price" because of some corner damage. Covering the damaged cabinets would not only improve cabinet rigidity, but also improve cosmetics.

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hi boomzilla, sorry to see your issues are still with you, as you try to solve the boomy bass , i am not sure if you have already tried and disregard

this option , since you are unable to place speakers in current corners , why not create temporary false corners to see if this may solve the issues you're

having.if it does you can work on a more permanent solution.

this might eventually be resolve with amplification, or even reconfigure sound panels, some times to move forward we need to start anew.

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The largest panel in the Cornwalls is the rear. This is true regardless of Cornwall I, II, III.

I've seen mods in the past that doubled the rear panel with another 3/4 piece of plywood. I would think that 2 or 3 vertical pieces of 1" oak or maple on the outside rear would serve the same purpose and be pretty much invisible as they don't need to come right to the edge.

If the Corwall IIIs are like the Heresy III you don't have access except via the woofer cutout, so putting a large number of additional braces would be difficult. I might try for a side to side brace and a back to front.

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The largest panel in the Cornwalls is the rear...If the Corwall IIIs are like the Heresy III you don't have access except via the woofer cutout, so putting a large number of additional braces would be difficult...

I believe you're right, CF. I was looking at the back panel of my CW3s and noticed that (unlike previous models) there are NO attachment screws visible. This means that I either excavate the back panel looking for screws or I abandon ideas of work inside the cabinet.

The "add some stiffening to the back" sounds like an option. I have plywood to spare. I also have a spare ATS panel in need of a home. Would bolting the ATS panel to the back of the Cornwall (foam against the current back) be effective? Would it be as effective as adding a 3/4" layer of plywood?

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Glenn,

I don't think that adding the ATS panel would do much. Stiffening is different than absorbing. It's more proactive vs reactive. Stop the cabinet vibrations before they happen! It can also be best to apply this type of reinforcement asymetrically.

Chuck

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I believe you're right, CF. I was looking at the back panel of my CW3s and noticed that (unlike previous models) there are NO attachment screws visible. This means that I either excavate the back panel looking for screws or I abandon ideas of work inside the cabinet.

I believe the front and back panels are set into a groove/dado cut into top/bottom and sides. See the attached pic of Cornwall III being assembled. You will notice there are two 2x4 pieces running front to back between the woofer and the mid horn.

Bruce

post-7149-1381985418475_thumb.jpg

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...Stop the cabinet vibrations before they happen! It can also be best to apply this type of reinforcement asymetrically...

Thanks - I'll get my saw on!

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Dumb question coming up....

If the back panel was resonating,it would happen at a specific frequency or perhaps range of frequencies that (I presume) would be fairly narrow??

Couldn't you place your hand on the back and play a test tone sweep to see if there is a sudden vibration in the back?

Sure would be frustrating if you went to lengths to 'fix' something that might not be in need of fixing.

Also... were the other speakers that were in the same location capable of similar output to the Cornwall? In other words, could the problem have been there before, just not as pronounced?

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I believe the front and back panels are set into a groove/dado cut into top/bottom and sides.

I think you're right about the motorboard being set into a dado, but the rear appears to be a removable, screw-in panel.

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That’s an interesting picture Marvel. My comment was only conjecture as I've never seen a Cornwall III, only the Heresy III. Those 2x4 braces should go a long way in stiffening the front to the rear, but unless there are screws on the back at that position, I would assume they are glued in place.

Glenn, how about a picture of the back of the CWIII?

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There may be a article still floating around online about internally bracing the inside of a Cornwall...can't recall the name of the article...

Cross braces from front to back and side to side will stiffen up the cabinets, using the acoustic panel material you are mentioning wouldn't hurt on the side and front/back panels.

Forget about stuffing with poly-fil. Damping the boomy bass by stuffing with poly-fil only really works with cabinets/enclosures up to 3 feet in internal volume. Trust me, I tried it with my Cornwalls, which are around 6 feet internal volume. It didn't do much at all, and takes a ton of poly-fil.

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