Dampen Khorn cabinet

[Colin]

After advice from BobG on the Klipsch forum, I wrote about sandbagging my super-sensitive walnut-oiled Cornwall 1, with B2 crossovers, with bags of sand, then 60 lb. paving stones

http://www.enjoythemusic.com/magazine/equipment/1299/sandbagging.htm

Now I have one paving stone on each of my classic Klipsch corner Khorns, on a thick rubber kitchen pad of course. But at preacherman Daddydees May 2004 Klipsch gathering in Little Rock, Arkansas, youthful looking Trey Cannon said such dampening was NOT need for the Klipschorn because of the adequate internal cross-bracing. I know a listening test is barley more work than just getting up from this PC, but what does everybody, who is NOT guzzling and grilling for Memorial day, think about dampening the Khorn cabinets in this manner?

what about the Reference towers then?

[HDBRbuilder]

I think Trey is correct. Between the much heavier weight of the K-horns, AND the fact that the build of the Bass bin itself IS an internal cross-brace, damping (as opposed to DAMPENING) of the K-horns by adding weights atop them is more or less an excercise in futility.

For adding bracing to the Cornwalls, the simplest method would be to just cut out pieces of 3/4" baltic birch plywood exactly the same size as the Cornwall backs, then run a rabbet around the edge on one side of these replacement back panels that is approximately 7/8" wide by 1/4" deep. Using the original back panels as a template, drill the new back panels for the screw holes, and install the new back panels made of the baltic birch, with the rabbet to the inside of the cabinets (IOW the rabbet will be against the glue/screw blocks). NOTE: It is important that the rabbet be CONSISTENT and not have any "proud" points in it so that it lays flat against the glue/screw blocks!

Baltic birch is heavier than regular 3/4" birch cabinet-grade plywood, and it is stiffer, too. With the rabbet facing to the INSIDE of the cabinet, the rear panel will not project past the rear edges of the cabinet, and it will not detract from the interior dimensions enough to make any real difference in sound you hear. You can store the original rear panels against a wall in a closet (or whatever) for posterity's sake, since they have the original labels on them.

[ZAKO]

On the Khorn some of the guys have replaced the woofer access door with a thicker one. From the 1/2" to a 3/4". Can you hear the difference? Nahh. But it,l make you feel better.

[3dzapper]

Colin,

You might like the effect that some asphalt sheeting (Dynamat) makes in the bass bin. A 10X10 piece on each of the 3 sides, another on the woofer door, and enough to dampen the woofer basket seems to reduce any 'flubbiness" in the bass.

Rick

[artto]

I think Trey is correct.

Years ago, Richard Burwen published his awesome 20,000 watt five channel (before there was 5.1) system in Audio Magazine. It was fully horn loaded. The bass horns were made of cement block & concrete. He was amazed at how much vibration there still was. http://scrounge.org/speak/burwen/

I tried a similar thing, but used a different approach. I made a corner plate out of 2x12 which I lag bolted (10 ¼ lag screws) to the heavily reinforced wall corners which are tightly braced against the house foundation. The Khorns tail board is lag bolted to this corner plate (8 ¼ lag screws). The idea was to allow any excess vibration to be drained off to the point of least resistance, in this case, the earth itself! Guess what. They still vibrate, albeit far less than they did. The interesting part of this exercise was that it didnt seem to do much for the bass response. However the mids & highs became more focused & defined. Its almost as if the diaphragm motion, due to the speakers efficiency, is so small, compared to the vibration of the overall speaker structure, that the diaphragm movement is a relatively large percentage of the speaker structures vibration. Its as if the vibration caused a smearing of the mids & highs. Yes, Im having difficulty explaining this. I hope its not too confusing.

[pierceb]

Not confusing at all Artto, in fact I have suspected the same thing with my Khorns that do not have any added extra bracing.

I noticed when playing at loud levels that the top of the high frequency sections have quite a lot of vibration compared to the low frequency sections, and I wondered if this might be effecting the sound. Then I thought this might be a problem with lots of speakers, so I kind of left the issue alone.

I might try your corner plate idea sometime.

-PB

[scriven]

Wouldnt it be easier to disconnect the HF cabinet from the base and mount it on to the wall? Or am I missing something?

[artto]

The bottom of the mid/high frequency unit forms the top of the bass horn. Also, there is still substantial vibration induced into the wall. So wall mounting at that point would not produce any better results than simply coupling the whole structure to the most massive & largest object you can find, in this case, the earth.

[artto]

----------------

On 6/1/2004 7:05:02 PM pierceb wrote:

I might try your corner plate idea sometime.

-PB

----------------

Just to be on the safe side, seal the angled edges that go flat against the wall with some closed cell foam weather stripping.

[scriven]

Ok, now I see the error in my thinking. Once you have the bass coupled to the earth, by whatever means, it does not matter what the HF section is connected to since it all goes back to the earth, by whatever means. Therefore, there is no point in even trying to isolate the two. (What on the moving earth was I thinking?)

[ZAKO]

If you,d turn the damn thing down you wouldnt shake the Earth. Your effecting my Khorns Now I,ll have to crank mine up to out shout yours. Get off my planet.

[D-MAN]

Did somebody really try to "drain" off vibrations as if it was a moving fluid? Hmmmmmm... that was a unique approach.

My current understanding is this: After it's vibrating, it's already too late. Prevention is key. Any vibration in a cabinet is technically lost energy to the soundpath, that is, it goes elsewhere than it should in a perfect world. We, of course, all realize that VIBRATION HAPPENS.

The point is to dampen vibration in any or all of 3 ways,

1) structure

2) absorbtion

3) cancellation by opposite vibration

The easiest approach to employ is absorbtion, followed by structure and then the seldom used cancellation by opposing waveforms exactly 180 degrees out of phase. All of these have their strengths (especially structure) and weaknesses (absorbtion).

Don't know of any other way around the problem, but I liked the idea of looking at the problem in a new light.

That is worthy of attention.

DM

[michael hurd]

Even if you add bracing to an enclosure, you are not fully eliminating vibration and resonance, just moving it up or down in frequency. I used to think along the lines that any cabinet vibration at all was lost energy. No matter if the enclosure walls are 1" thick, they will still vibrate, albeit at a different frequency, and with much less amplitude. As the panels that make up the enclosure get larger, the more apt they are to vibrate.

As long as the enclosure is reasonably braced, with adequate mass, the resonance should be low enough that it will not be audible. Think about this: if a panel is constucted so that practially all energy is absorbed ( constrained layer, braced, etc. ), this still will not provide any more electromotive force to move the cone outwards. As a result, the energy is still in essence "lost".

If the resonance or vibration of the cabinet falls within the frequency range of the speaker enclosure, then steps should be taken to reduce the amplitude of the vibrations below audibility.

For example, in a subwoofer cabinet that reproduces 20 - 80 hz, does it matter that there is a sharp resonance peak at 150 hz? If the example peak was 30 db down, would you hear it? Anyone think along this line, or have more thoughts?

[michael hurd]

As you can see by this picture of the incomplete k-horn, the panels are well braced, and quite small, in comparison to some large direct radiating ported enclosures.

[michael hurd]

[D-MAN]

Mr. Hurd brings up a good point about the resonant frequencies of the enclosures in question. I think he's right. Also, achieving 30db's down would be a rather good dampening effect.

As far as a Khorn, I would pay particular attention to the back reflector panel (typically 1/2" ply) as being a particular culprit as it takes the brunt of the horn output directly onto its face. I would add at least another 1/2" strip (preferably as full width as possible) behind it to dampen vibrations.

The other area of concern would be the back chamber upper and lower panels, again needing a strip on each.

That would be all that I would do to strengthen it against excessive vibration. I have seen this mod before, and some clones actually came that way. It doesn't appear to be a Klipsch approach.

DM

[HDBRbuilder]

The VERB is DAMP!! NOT DAMPEN!! Unless you are planning to wipe them down with water! Get it?? Damp, damped damped...NOT dampen dampened dampened!

[D-MAN]

I beg to differ, in this usage, I believe that "we" are correct.

DAMP as a noun implies a certain degree of wetness.

to DAMPEN something (verb)

DAMPENING something (adjective)

Look it up.

DM

[Colin]

Damp means to restrain or check; discourage, to put out, as fire; to depress or deject; to DEADEN; to cloud; to check or restrain, as action or vigor; to make dull; to weaken; to discourage.

Dampen means to make damp; to deaden, restrain, or depress, to SOUNDPROOF.

Dampened means to depress; to check; to make dull; to lessen.

I'll write the book Andy, you tell the stories.

[HDBRbuilder]

Like I said...DAMP means to DEADEN, NOT to SOUNDPROOF. You WANT sound, you just want to DEADEN unwanted sound...right?