Tweaking the K-400 Horn Lens

[HDBRbuilder]

Ok, folks...time to give some of you this little "tidbit of tweakdom":

If you have LaScalas, or Klipschorns with the old metal K-400 mid-horn-lenses...and you have the time to do this...you may want to consider it!

Next time you remove the horn lenses from your speakers, just pull(unscrew) the driver...and look down into the mouth of the K-400 lens. About half-way down you will likely see a change in its INSIDE surface...here it is NOT smooth, but instead has a sort of proud ripple all around it or a "step-up" or a "step-down" all around its inside there. This was caused by the fact that when they cast these horn lenses, they used a two-piece core in the casting process. The core was two pieces that were likely hot-glued together to form one continuous core. The core was responsible for supporting the metal from the inside of the lens as it cooled so that the lens would not collapse inward while the metal was still molten. That being said...these two piece cores seldom are an exact continuous smooth unit when assembled together. In addition to that, they tend to erode at their junction point during the casting process as the molten alloy reaches the joint. This causes an uneven place within the horn lens...that can be smoothed out by you to better the horn's performance. Just look upon this as removing a "speed bump" from the sound pathway within the horn lens!

OK...first determine whether your lenses need this by carefully looking into the mouth of them. If you see what I described, then get yourself a set of inexpensive riffle files, some various rat-tail files of differing grades, and a mill bastard file that is easy to work with.... and smooth this area out to where it is nice and continous in its flare rate at that point. This requires some "elbow grease"...so be ready to take some time doing this.

In order to keep the files from "loading up" with the aluminum alloy, dip them in kerosene on occasion...this will allow the cleaning of them to be easier so that you can use a "file card" and keep the work progress moving along more easily.

When you have finished smoothing-out this area...then look down the lens from its throat area. You may see some flashing within that area...or other spots with "proud" points from the intended inner surface of the lens. Again...use those files to smoothe that area out.

After using the files, you CAN use a "sanding stick" to smoothe out the rougher file marks, but if you used riffle files, since they are normally pretty fine-cut anyway, that sanding will likely not be necessary.

When you are all finished with your work, rinse the whole lens down with acetone (inside and out!)...blow it dry...and then repaint it in flat black. Please be SURE that you have no filings in the threads at the throat of the lens(where the driver mounts)...and that all metal filings are COMPLETELY removed from the lens prior to mounting the driver back up!

This inexpensive tweak may actually surprise you in how well it adds to the performance of those horns!

If you have other models of Klipsch speakers with other models of the metal horns on them...you can also check to see if there are any abnormally "Proud" areas within the inner part of the lens and do the same thing to eliminate them.

EDIT: One minor additional tweak for the K-400 horn lens....The supporting bracket near throat of the horn lens....take a couple of rubber faucet washers and put one on EACH side of the horn's cast-in mounting point for the bracket before installing the bolt that secures the SUPPORTING bracket to the lens...this will provide a bit of additional damping in that area...this horn is designed to be damped by its SNUG mounting to the motorboard at the front of the lens and the supporting bracket's mounting to the wood of the cabinet at the rear of the lens. Some of you feel a need on your particular speakers to add additional damping, and that is sometimes necessary...but it is NOT necessary to add damping material all along the outer surface of the horn lens...because that will give TOO MUCH damping...so find where it is needed first...then apply your preferred damping material only in those places.

[Jim Cornell]

No one seems to have ant interest here, i guess they just replace the horn!

Just thought id reply LOL

Jim

[fini]

Are there any other horns that will benefit from this treatment (the ones in the Cornwall, or the Heresy)? I guess the smoother the better here, so if someone was ambitious enough (or bossy enough with their kids), a polished finish would be the ultimate? Just curious...

fini

[j-malotky]

I always thought about smoothing the inside of the K400 horn. There are so many pits and peaks from the sand cast.

I always thought I might try to fill in the pits with auto body filler or something, before sanding and polishing the surface smooth.

The 400 is so deep, it would really be hard to get down to the driver side of the horn.

JM

[HDBRbuilder]

Fini,

The K400 lens is the only one of the metal horn lenses that uses a two-piece core in its casting, sometimes giving it those soundpathway "speed-bumps" on the inside of its lens about halfway down it. The other metal horn lenses are either cast-up in two halves which have been welded together or they are cast up as one unit with just a one-piece core...so they will not tend to be as rough inside as the K-400 CAN be.

JMalotky,

I was just referring to smoothing-out the above-mentioned casting irregularities that protrude into the soundpathway of the K-400 horn lens. It would likely have very little impact, if any, on the K-400's performance to fill in tiny porosities of the lens' surface, but IMHO it would definitely help to remove any irregularities that PROTRUDE INTO the soundpathway of the lens.

[jt1stcav]

Now I would never doubt anything Andy would advise us on, or on any of his cabinet construction methods (he is, afterall, a living God, who'll one day be seated at the right hand of PWK himself), but I am curious...

The inside of my Cornwall squawkers have these verticle pits that run along most the entire length of the inner verticle walls (not so on the inside top and bottom, or horizontal ends). Do these pits really effect the sound quality, as opposed to a fine, smooth surface? Wouldn't Klipsch R&D have known this to cause a less than ideal performance when these horns were cast, and wouldn't they have done something to eliminate this effect?

I know I don't see any rough pits inside the bells of a trumpet, trombone, sax, or any other horned musical instrument, or even inside the resonators of all individual pipes of any pipe organ. My Cornwalls sound fantastic to me just as they are...if I was to file down these pits as you describe, would I really notice an improvement in my squawker's sonic quality?

I just have a hard time believing that the sound characteristics of a filed-down horn lens will be sonically superior to an original cast horn lens from the manufacturing shop.

Hope I didn't make the great HDBRbuilder upset or angry...

[HDBRbuilder]

jt1stcav,

OK...what did I just write in my answers above? Did I mention anything about filing down a surrounding surface to make it even with casting pits? OR>>>>did I instead mention to remove any of the things PROTRUDING INTO the soundpathway? Read what I said again, and then think about it for a minute!

If you are in an alleyway between two tall buildings, and there is a RECESSED doorway into one of those buildings, and you are standing WITHIN that recessed doorway....

And somebody at the end of the alley yells something...will you hear it better if you poke your head out into the alley from that doorway???...OR will you hear it better with your head remaining within that recessed doorway? Think about it!

Now, take that SAME alleyway, but instead of a recessed doorway, there is are walls protruding out into it somewhat from each side. You are standing by one of those walls...and the same person is yelling from the end of the alleyway...if you tuck your head in behind one of those walls will the sound you hear be as loud or will it be louder with your head NOT tucked in behind one of those walls?

Remember...soundwaves are movements of air...and air flows along like water...now if a creek is flowing along and hits a washout...it slows some and creates an eddy, but it continues to flow...but if it hits a wall...it backs-up until it can get high enough to flow over it. Both of these situations create DISTORTION in the smooth continual flow of the water...but ONE of these causes the water to REFLECT BACKWARDS until it rises enough and creates enough pressure to either push the wall down or flow over it! Think about it!

Look on the pits as the doorways...the sound will travel past them ...right over them and continue onward. Look on those things that protrude into the horn's soundpathway as the walls...the sound wil hit them, and then have to flow around them to continue on...creating some distortion in the process.

Now...BOTH pits AND things that protrude CAN cause distortion, BUT things that protrude INTO the soundpathway will cause MORE distortion!!

No production speaker you get from ANY company will be the "ideal" of that particular model!! Plain and simple! There are just too many slight variables that can occur in the production of the parts that go into the speaker and the cabinet itself! The best any company can do is to establish MINIMUM STANDARD guidelines for the testing of each speaker before it is shipped and ensure those speakers fall WITHIN those guidelines...and those guidelines are the performance REQUIREMENTS of the speaker. Just because a speaker tested meets its MINIMUM performance REQUIREMENTS to leave the plant, does NOT mean it CAN'T be tweaked to EXCEED those MINIMUM requirements!

[tubelion]

Hello HDBRbuilder,

I think you have a good point here.

"The K400 lens is the only one of the metal horn lenses that uses a two-piece core in its casting"

As I own a pair of belle and La scala, does the belle horn have the same problem ?

I am going to check my La scala's horn.

Thanks very much for your sharing.

Tubelion

[danno]

If the ridge inside the K-400 lens can degrade the horn's performance, then what about the tweeter horn, which is mounted on the inside surface of the cabinet? Doesn't the 3/4" plywood overhang a fair bit into the sound wave's ideal trajectory?

danno

[jt1stcav]

HDBRbuilder, thanks for pointing out the obvious with a full and detailed explaination! You went well above and beyond the call of duty with your answer, and I'm sorry if I had you repeat yourself!

[HDBRbuilder]

Danno,

PWK said the mounting of the horn lens mouth to the inside of the cabinet as opposed to mounting the lens flush with he outside surface of the cabinet "didn't make a dime's worth of difference"...and he should know. He was, of course, referring to HEARD DIFFERENCES, and NOT to testing equipment differences.

The point I am trying to make here is that on the K-400 horn lens, this ridge that is often found inside the lens is located over halfway down the depth of the inside of the lens itself...IOW...at a point where little of the flare-rate of that lens has yet been achieved...and the soundpathway there is still quite constricted, thereby making this ridge even MORESO of a problem in producing distortion on the soundwaves due to the SMALLER VOLUME OF AIR within the lens at that point.

In an exponential horn lens, which has a CONTINUAL flow of its curvature(ie, flare-rate)towards the mouth of the lens...it would seem to me that having any constriction on the soundpathway at a near-midpoint of that flare-rate would HAVE TO provide SOME amount of distortion. In every K-400 I have encountered, this anomoly as a part of the casting process is present in them ALL to some extent or the other...and with my 7 years of recent past experience in the casting industry as a pattern-maker/corebox-maker...I understand the process by which this occurred. I also understand why it occurred, and how to compensate for it so that it will NOT occur. In addition to that, I understand about all the other anomolies generally found in aluminum alloy(and other metals) castings due to the processes used. I am quite sure that the K-400's COULD have been cast using techniques that would have eliminated these anomolies, but the cost of using those processes would have driven the prices paid by the company for these to more than triple what the company was paying at the time...and that is not even taking into account the higher scrap-rate the foundry would have been dealing with by using those processes...further driving up the individual cost of these as paid for by the company.

As for the company not taking the time needed to "detail" the inner surface of these lenses in order to eliminate thesee casting irregularities, it should be obvious how extreme the labor cost of doing such would have been...further driving up the cost to the company of each horn lens used...and thereby driving up the MSRP of the speakers themselves...by at least 200 bucks a pair!...in 1970 dollars!!

One of the reasons the company eventually went to thermoplastic horn lenses in the first place was the much lower cost per unit incurred AND the better consistency of the product! But, at the time of the original procurement of the metal horn lenses, the types of plastics available for this were not conducive to a low-cost, and sonically feasible alternative to metal horn lenses for the purposes intended...so the company stuck with the metal lenses until things in the plastics industry evolved to a point where thermoplastics could do the intended job as well as metal horn lenses could.

[AndyKubicki]

WOW! And to think I have not visited this part of the neighborhood! This is really great Andy! Those are real nice "private proof" directions too! LOL! But I can't help thinking, I paid about $1800 for an unfinished pair of Khorns in 1980 or so...$7000 today...THEY should have been done by hand at Klipsch that back then! But what you say here makes perfect sense.

You mentioned something else...

Some of you feel a need on your particular speakers to add additional damping, and that is sometimes necessary...but it is NOT necessary to add damping material all along the outer surface of the horn lens...because that will give TOO MUCH damping...so find where it is needed first...then apply your preferred damping material only in those places.

It was posted here a couple years ago as a tweak to Dynamat/rope caulk your horn and tweeter and I did the WHOLE horn and tweeter. I thought I liked what I've been listening to for a couple years. Now you tell me this! What's the result of too much damping?

[Randy Bey]

I went from "too much" damping with dynamat, etc. to no damping (tore it all off one rainy Saturday).

Hated the result. Spent weeks agonizing over the difference.

Finally did something in between, rope caulk all over the narrow throat area, and 1 1/2" wide strips of rope caulk running from the throat out to the mouth area in a symmetrical fashion.

Not near as much damping as before, but the results are back to a pleasing level.

Hard to say how to decide where and how much to damp the horn. It's my opinion that a horn should not vibrate at all, so too much damping is impossible, even if you cast the darn thing in cement (which I heard one person did do).

[HDBRbuilder]

OK, Let's look at horn lens "damping" for a few minutes.

One can remove the metal horn lens and its driver, and simply hold it to his mouth like a megaphone and check it for damping positions....by adjusting WHERE...along its LENGTH...that its being held BY ONE'S HAND...gives the proper desired damping effect. Now...One must take into consideration that the mounting of the horn lens' mouth to the wooden motorboard ALSO provides some damping effect...as does the rear support bracket for the K-400 metal lens...so...since both the front and the rear of the lens ALREADY receive some damping effect at these points...the position of your hand along its length should STILL be about the right place for the damping to be done...make sense?