Plastic Horn Buzz Control

[HalM]

The cellular telephone construction industry has suppliers everywhere such as Kenwood, Tessco, GrayBar, etc.

One of the most commonplace items is a Universal Weatherproofing Kit, "Type WK-U." This kit has

one roll of two-inch wide, thick vinyl electrical tape, two rolls of 3/4-inch vinyl insulating tape, and six rolls

of butyl rubber between wax paper separators.

All this for a couple of bucks. What is usually done with this stuff is to cover coax connectors on

"flexible" hard lines from 1/2" diameter to 2-1/4" diameter.

The plastic horns on my newly-acquired Forte-II's and Chorus-II's are resonant somewhere in the

audio spectrum. I guess if they were made out of concrete I might be able to keep the buzz down, but

plastic they are, and buzz they do. Using a second generation H-P audio oscillator going into the

audio chain at 0.1 volts P-P is a great way to sweep cabinets. If they are going to push out all the speaker screws

and walk around the floor like an old washing machine, an audio oscillator will find out how soon. However,

back to the plastic horns. Yes, they buzz.

Using the butyl rubber portion of the WK-U kits, pieces of rubber about three-inches square are cut, leaving

one side of the wax paper attached to the butyl so it doesn't get to be too bad a chocolate mess. The squares are

simply laid on to the plastic and also on to the flat metal magnet surfaces. Next, the 3/4" tape covers the outside

of the butyl rubber (which is naturally sticky). The finishing layer is the two-inch-wide, thick electrical tape, over

the 3/4-inch-wide tape, which imparts a smoother finish. With just the thin diameter tape covering, fingers can

be used to squish-in the butyl into corners where the ribs are, etcetera. One WK-U will really do a midrange

squawker well, and the left-over material can goon the woofer and tweeter magnets to break up the hard

surfaces, and even using some of the material on the bare wood inside the cabinet will affect its vibration

reaction.

Lastly, and this is an old Klipsch trick, is to put a board across the speaker stand bottom, seal the gasket surfaces with

RTV, drill a filler hole in the side and fill with pool filter sand, tamping it down by hitting the bottom slab lightly with

a dead-blow hammer. The hammer really helps because the bases will accommodate thirty percent more sand

by volume if reasonably tamped.

Hal

[STL]

I think a much easier way to fix this is to use $2 box of rope caulk from your local hardware store. The stuff is super easy to apply and can easily be removed if you change your mind. I tried it first on one of the K-85-K horns in my KG5.5s. After some lengthly A-B testing, I decided to do the other horn as well.

[mas]

Ordinarily I avoid these debates...

But just a couple of ideas.

First, do not use a kit for externally exposed coax that employs electrical tape! Electrical tape simply does not resist the elements for any length of time. In fact, with the exception of being a mess, we could argue that it does few things well.

The industry standard that has worked without fail for 30+ years is a small sealed pack with a flooded section of 3 inch shrink tubing, whose activation occurs upon exposure to the air, and the flooded quality is akin to maintaining the junction in a silicone bath that remains sealed in a liquid state.

Regarding the 'buzz'. If this is what is occurring, you have a vibration rather than a resonance. A vibration ocurs when incomplete coupling occurs between two surfaces, such as the horn lens mouth and the cabinet. But the horn lens itself will not 'buzz', although there may be a persistence in time at a particular fundamental frequency.

In other words, if you indeed hear a 'buzz', you need to figure out where it is buzzing. And I suspect that it will be due to something else making contact with the horn lens or with the horn lens mouth not being adequately secured to the cabinet. This is easily done in a variety of ways, ranging from carefully tightening screws to installing a small gasket between lens and cabinet.

Horn lens resonance is a very simple issue to address. It does not require tons of goo applied,but rather mass applied at a 'strategic' point (or possibly, but also more rarely) on several points on the lens. (A good place to segue off into the subject of eigenvalues...) A glob of adhesive caulk is usually sufficient.

Have fun.

[DrWho]

Adding mass to a resonating surface actually lowers the frequency of the resonance. In which case, you are relying on increased damping to keep it inaudible. However, I believe the approach Klipsch takes is to move the resonance of the plastic out of the audible passband. In other words, if it does resonate, it's going to resonate above 20kHz...the further above, the less audible it will be.

I'm with mas on this one...a buzz is rarely caused by the vibration of the walls in the horn. I would first check to make sure the driver is properly screwed into the horn. The next thing I'd check is the mounting flange and adding a gasket).

So did you ever run a sweep to determine the offending frequency?

[kevin Rao]

That is another kind of weatherproofing kit, make the installation much easier.

It is called gel seal closure. It is one-step, reusable

Huijia co ( www.cn-huijia.com ), Tyco (www.tyco.com), they can supply this material