Plywood thickness for K-Horns

[Erland]

I am in the process of building a pair of K-horns.

I am living in Norway, and the dimentions of all building materials avaliable is in millimetres and not in inch. However I have found a supplier that has premium quality birch plywood from Russia.

The dimentions given for the K-horn is for the front and sides 3/4' and the horn itself 1/2'
This dimentions is not avaliable.

For the front and top I can get18 mm (equals 23/32') or make a special order of 20mm (equals 25/32).

For the horn I can get 12mm (equals 15/32) or up to 15mm (equals 19/32).

I am most tempted to go down to 12 and 18mm, but I like the hear if any comment or experience on this?

Will make much difference if the horn is 1/32' off on each side? Is the factory made horn that accurate in the first place?

I will use the K33E woofer, K55V driver monted on Al K's trachorn, and the C125 tweeter from Bob Crites. Crossover will be Al K's ES400/ES5800.

As the trachorn is quite high, I consider to place the tweeter below to get it in heads listening position. Does this make sence? I have seen them placed vertically on the side of the squaker. I do not find this a good solution, as this may result in a very narrow sweetspot.

Any suggestion or experience is welcome.

Regards
Erland

[Guest " "]

I was in Germany from 86 thru 89 and made numerous sets of K-horns from different stock, including the stock you list.

Which plans will you be using. Some of the plans floating around do not include the modifications to connect the internal volume of the ramp chambers to the innternal volume of the woofer. There are different views on the motorboard woofer mounting hole size. Are you going to include attached false corners? There is also a mod to dove tail the horn corner baffle at the horn exit to reduce wave bounce back.

[Erland]

The only plans I have been able to get hold of is some with German text on, and converted to millimeter. Tho hole size of the woofer motherboard is 335millimeter (equals 13.188 inch)

[Guest " "]

this one or the eckhorn from ACR Swiss?

klipschorn.pdf

[Erland]

I have one that consists of 5 pages describing all parts in detail with spesific angles

I have enclosed the first page for reference. Does it look familiar?

[Guest " "]

Those are eckhorn k-horn plans. I have used them and they work out fine, with out any adjustments. I have those in both original print and electronic copy.

[Erland]

Thank you very much.

So I am on the right track then...

By the way, I looked at the wooden midband horns you posted a pic. of in the "Idiot question" thread. What kind are they? I understood that the Trachorns was only avaliable in black paint, and tried to make a pair, but after several attempts of bending layers of ply, I gave up and ordered a set from Al.
After all, a black horn is better than no horn at all, and I rather spend the time working on the basshorn.

[Guest " "]

Here are a couple of mod's

on page k_horn2, look at part 14. This is the baffle that causes wave bounce back into the bass horn. Add a dove tail 90 degree peak to part 14 to prevent wave bounce back.

on page k_horn3, look at part 2. This is the woofer front motor board. There is quite a bit of internal volume created by the ramps that guide the sound waves to the first turn. You can connect this volume of air to the woofer chamber by drilling 2 holes in the board. The holes should be about 2 inches in size. Make sure you don't drill the ramps, or go thru the front of the cabinet.

Depending on the driver you will be using, you might want to use a 6X13 slot and use an adapter plate to switch to a 3X13 slot. PA type drivers need a 6X13 slot, whereas the k-33 will use the 3X13 slot.

[Guest " "]

""By the way, I looked at the wooden midband horns you posted a pic. of in the "Idiot question" thread. What kind are they? ""

I need the link, doing a search did not return anything.

[Erland]

Thank you very much for the advise.

The woofer I am going to use is a pair of new K33's

[Erland]

This ones

[Guest " "]

those are plastic with veener laminates.

I think AL's horns are better. Al's are wood, not compoite.

I thought you were refering to the patrician IV 300HZ bass horn construction plans that I posted a few months ago. The Patrician IV bass horn, is a very easy build. The patrician IV bass horn, however does not have much curb appeal.

[Wrench722]

I build mine out of 3/4. It make a big diffrents. Here is a good set of plans on E Bay

(330006681411)

[Guest " "]

Erland

you already have the metric plans indicated in listing 330006681411. But the general info indicated in the speakerlab K plans may be useful. For example, the speakerlab K plans shows the cut layout of what you should get out of your 4x8 boards.

[JJkizak]

With all of the written retoric and mathematics by PWK on bending a 30hz wave around a corner, how does bending it around a 1/2" and/or 3/4" plywood edge affect this bending?

JJK

[Erland]

Nothing of couse.

My quiestion is related to the following:

All manufactorers of horns in general, and in this case PWK in special calculates the dimentions of the horn in accordance to the frequency range of operation.

Since this is my first DIY horns, I like to build the basshorn as close to the original spec as possible.

By changing the the thickness of the building material, (even by 1/32') the size of the horn will be slightly altered. So effectively by using a building material that is like 1/3 thicker than the original construction, you are building a horn slightly narrower than the original. In my case the the alternative is not as thick as 3/4 but 19/32'. Would this reduction in horn size be audible/measurable?

By using a thinner building materia, the horn gets slightly larger. In my case with 15/32' plywood, the enlargement is minimal, and I find it hard that building accuracy even at the factory is that precise. Anyway, the question still stands...

The other side of the same question is ridgity (does it spell this way?) of the horn. With like a 3/4' horn section, you get a much more ridgid construction that will be more resistant for internal vibrations. Is this a more important issue? Will a slightly reduced size of building material like 15/32' make the horn more exposed to internal vibrations?

Anyway, when writing this, I recieved an email from a capenter I know, hwo told me that the Russian Birch grade A (in Norway referred to as Premium q) that is sold as 12mm (15/32') actually is the same as sold in US as 1/2, so that makes the choice easy for me, but in relation to the posters who claims that it does matter if you alter the size of building material, the question of experiences still stands.

Regards
Erland

[Erland]

Is my conserns here just "nitpicking lunacy" that I should push to the side, or does it make any sence?

[DizRotus]

PWK probably would have said, "It doesn't make a dime's worth of difference." You would never identify any audible differences.

[JJkizak]

DizRotus:

I do not think PWK would say that, he was too precise an individual.

JJK

[DizRotus]

I met him and heard him use the exact phrase more than once, under similar circumstances. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

When I specifically asked him why the tweeter and midrange horns were mounted to the backs of the baffle boards rather than flush mounted to the fronts, he said, Not a dimes worth of difference. The precise craftsman in him would have done the aesthetically more pleasing and technically desirable flush mounting, but the practical businessman determined that listeners could not perceive any difference and the production costs would have been much greater, i.e., the often repeated phrase, . . . not a dimes worth of difference.