La Scala Butchery

[Marvel]

Here are schematics for crossovers. The DHA2 is from John Albright. Take your pick.

Marvel

[ooteedee]

That makes sense. Thanks for explaining it.

Ok...I will make the slot bigger.

13x6....rectangular....but with straight lines? Or should there be a long radius on the longer vertical side?

Also, the wacky crossover I have is cutoff at 1200hz on the lowend.

Will a bigger throat help?

Also, again....You mentioned making a spare motorboard with the standard throat opening, in case I get a bigger driver or a K33. If I did, could I just mount the spare motorboard right on top of the wider one?

Or would that wack things out a bit?

PS: Marvel. Thanks for the schematic.

PPS: D-Man. Just noticed your mention of the convertable motorboard. I'll take a closer look. That thread is pretty interesting.

[ooteedee]

TO: Marvel and D-Man

Based on yours and D-Mans suggestions, which of the crossover schematics Marvel sent would be appropriate for the FrankenScala?

(Construction of which will require Dad's help. (Retired automotive engineer, electroncs engineer, audiophile since 1943........every crossover he ever had was hand made.)

[Marvel]

I can't help you out with the crossovers. I know that John Albright or his brother built the one set DHA2, and said they sounded really good. The automotive light bulb that is in the tweeter circuit is for tweeter protection.

The schematics were just what I had filed away.

Marvel

[D-MAN]

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On 12/28/2004 8:29:34 PM ooteedee wrote:

That makes sense. Thanks for explaining it.

Ok...I will make the slot bigger.

13x6....rectangular....but with straight lines? Or should there be a long radius on the longer vertical side?

Also, the wacky crossover I have is cutoff at 1200hz on the lowend.

Will a bigger throat help?

Also, again....You mentioned making a spare motorboard with the standard throat opening, in case I get a bigger driver or a K33. If I did, could I just mount the spare motorboard right on top of the wider one?

Or would that wack things out a bit?

PS: Marvel. Thanks for the schematic.

PPS: D-Man. Just noticed your mention of the convertable motorboard. I'll take a closer look. That thread is pretty interesting.

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The slot is typically straight lines. Some people cut a radius on the SHORT ends only (not the long dimension).

The slot opening on the baffle board is straight lines.

A 17" square motor board will effectively mount any 15" driver that you can get. Drill the mounting holes 1-1/2" from the corners using a 3/8" bit and counter-sink them with a 1" wide bit x 1/4" deep on the front. This will allow for the 1/2" jam nut and 1/2" washer to not interfere with a surface-to-surface mount on the baffle-mounted 2" carraige bolts. A gasket made from door-weather stripping foam should be run around each slot but LARGER than the 6x13" baffle opening to seal the driver board air-tight to the baffle!

To change slot sizes, cut another 17x17 board and make the same holes, etc. and remount the driver to the "new" board.

2 boards = 2 different throat cavity openings, for example 1 motor board with a 3x13" slot, the other 6x13", etc. That is what I meant by "convertable" motor boards, perhaps I should have said "interchangable" instead. Do not mount one driver mounting board over the other, unless you wish to experiment with cavity capacitance, however, this has been done in the past, especially for 12" drivers which actually had a small "box" built in front of the driver.

I would check out the ALK-A crossover; it is fine for a general Heritage horn application.

The inital crossover point for it should be less than 550Hz with the wide slot. 400Hz for the narrow using a K33E driver.

DM

[ooteedee]

Will do.

I'll let you know how it goes.

Probably fire up the table saw tomorrow.

Thanks!

[Rockets]

Marvel, I *think* there's an error in those LaScala plans. Part number (6) Bass Bin top, and Part number (7)Woofer door are both the same size @ 23 3/4" X 22 1/4". I think the Bass Bin Top needs to be 23" even...or at least the one I own is, then again I can't measure )

Also theres a part missing. I have a 2 1/2" by 22 1/4" brace that goes across inside the back and is fastened to the top.

[Marvel]

Rockets,

Andy would be the one to ask about this. I think you are correct though. You are talking the measurements front to back? If part 9 (H/F motorboard) goes in front of the top of the bass bin top then it should be the 23 inches.

For a brace, do you mean here (marked in red)?

Marvel

[djk]

"To change slot sizes, cut another 17x17 board and make the same holes, etc. and remount the driver to the "new" board."

And what am I supposed to do with this board? The motorbaord for a LaScala is only 15-1/4" wide.

"Choose your upper frequency drivers for a 104db sensitivity. The woofer should be approx. 96.5db eff to match that."

A K33E is 101dB/2.83V/1M as a direct radiator.

"2) the back chamber is sized based on the horn total cross-sectional area, not the woofer; the woofer HAS NOTHING TO DO WITH IT. Ignore the nay-sayers; they know not what they do."

The back chamber is sized based on the T/S parameters of the woofer, the cross sectional area of the horn HAS NOTHING TO DO WITH IT. The only other parameter you need is the Fc.

Vb=Vas/-1 Paul Wilber Klipsch, JAES, Vol.48, No.10, section 3.2.2 'Back Air Volume Requirements'

[Rockets]

Marvel, That's the one. Nice quick cut n paste btw!

[Marvel]

Rockets,

I don't think they had that on all the LS models. A friend of mine with LS doesn't have them on his. It would make the top a bit more stable though.

Marvel

[ooteedee]

Yeah, I'm hip to that inside brace in the mid/high area. that's easy.

Not sure about that "error" you mentioned.

Let me look again.

[ooteedee]

Rocket:

After studying the drawing, I think you may be right! Although I am wide open to any challenges on this.

The woofer door butts up to the backside board and the sides.

The bass bin top butts up to the backside board and the sides as well, but behind the mid range motorboard.

So it should be 3/4" shorter.

[ooteedee]

djk:

So based on your comments, what do YOU think about opening up the motorboard slot to 6x13 for my woofer?

The mighty k33 could easily push through the narrow slot, but my woofer may not.

[D-MAN]

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On 1/1/2005 5:56:25 PM djk wrote:

The back chamber is sized based on the T/S parameters of the woofer, the cross sectional area of the horn HAS NOTHING TO DO WITH IT. The only other parameter you need is the Fc.

Vb=Vas/-1 Paul Wilber Klipsch, JAES, Vol.48, No.10, section 3.2.2 'Back Air Volume Requirements'

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Djk, the traditional methodology for defining back chamber areas PRIOR to the invention of T/S parameters as described in the original 1943 Klipschorn patent # 2373692.

The simplified formula is A=V/2.9R where A=throat area in sq. in., V=back chamber volume in cu. in., R=exponential cross-sectional doubling point in linear inches, in the case of the Klipschorn, A=78 sq. in, V=4800+ cu. in., R=22.75 in. (from "How to Build Speaker Enclosures", Badmaeff and Davis, W.H. Sams Publishing, Az. 13th reprint 1978. This was simplified from PWK's patent, I believe.

DM

[D-MAN]

Here are the Eminence-supplied specs for the K33E as reported by Marvel. I don't see a 101db rating, so who is correct?

-----------

John,

I emailed Eminence and asked for the T/S parameters for the K33-E, and got this repsonse back from them. Maybe they would send out bogus info, but that wouldn't sem to benefit them very much.

SPEC 15162

PART # K-33

RE OHMS 3.39

FS HZ 34.46

LE MH .96

MMS GMS 78.59

QM 7.39 CMS

mm/N .2714

QE .410

RMS NS/M 2.3037

QT .390

VAS LTRS 301.66

XMAX MM 8.20

SD SCM 889.59

BL TM 11.88

EBP 84.4

EFF % 2.91

SPL dB 96.6

Wattage 150rms

-----

dm

[D-MAN]

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On 1/1/2005 5:56:25 PM djk wrote:

"To change slot sizes, cut another 17x17 board and make the same holes, etc. and remount the driver to the "new" board."

And what am I supposed to do with this board? The motorbaord for a LaScala is only 15-1/4" wide.

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Ooops, yes, you are correct (I was thinking Belle). However, the concept still applies, cut the board square at 15". The square corners is where to make the bolt-holes.

You could even cut one round as sort of a speaker gasket with the narrower slot in it.

I know that lot's of people put in extra spacer board in their LS's to allow for extended excursion without slapping the baffle board, so it can be done, of course.

P.S. PWK stated in the "little bastard" 1976 patent that the "correct" throat size for the K33 was 78 sq. in.

That's 6x13". I'd copy it in here, but it's a lot of work.

DM

[djk]

"Here are the Eminence-supplied specs for the K33E as reported by Marvel. I don't see a 101db rating, so who is correct?"

Those are the correct specs. Note that the 97dB/1W is into 3.4 ohms, with 2.83V it is 101dB.

"Djk, the traditional methodology for defining back chamber areas PRIOR to the invention of T/S parameters as described in the original 1943 Klipschorn patent # 2373692"

The old method is close, the new one is better, that's why they came up with it.

The flare rate of the main LF section on the old method is the Fc of the new method. The 2.9 was a constant (a fudge factor) that reflected the T/S parameters of drivers commonly used for horns. Subwoofer horns today use drivers with T/S parameters that would never have been considered 'back in the day'. The new method allows for computing of a back volume for these drivers, the old method didn't.

Some symbols in that equation looked like HTML so I am going to try it again.

Vb=Vas/:Fc/(Fs)(Qts):-1

Using : as a bracket, uing double brackers made stuff go away with HTML.

Notes on both front and rear chamber sizes: any equation is just to get you started, prototypes need to be built for evaluation. If you expect to drive below Fc you will not want to fully annull the back chamber, the response will be much smoother if you don't.

Tips on using McBean: reduce the rear volume until you get a peak close to the height of the main pass band. There will be a huge dip about a half octave wide just above this peak. Adjusting the front chamber volume will 'fill' in this dip. One you get close, play with both front and back volumes to get the smoothest response.

"The mighty k33 could easily push through the narrow slot, but my woofer may not."

The Qts on your woofer is too high to be of any use at all in this sized horn.

[D-MAN]

DJK, cool. I'm gonna add this to my bag of tricks.

DM

[Tom Mobley]

ooteedee,

I don't know what plans you're using, but watch out for the dimensions on the front baffle of the HF section. Many of the plans have the opening for the K-400 wrong. There needs to be at least 1.5" below it, not 3/4". I cut one with 3/4" below the opening and guess what? That 3/4" is taken up by the floor of the upper section (or roof of the doghouse) leaving no place for the flange of the K-400. There needs to be at least 1.5, maybe a little more to give room for the horn flange. Be aware that the fit is tight on the front baffle, there's very little room to spare vertically. the flanges of the K-400 and the K-77 more or less touch, there's very litte room above the tweeter and none below the K-400. If I were building these from scratch for my own use I would make the whole thing 1/2" taller in the top section, make everything easier. This wouldn't affect anything in the bass horn or the sonics of the upper section.