LaScala VS Belle

[mboxler]

3 hours ago, avguytx said:

I've had it mentioned that the very large 160 - 200hz hump on my Belle clones...

 

Although I can't find the AB-3 schematic, I did find a document describing a 162 Hz notch filter across the woofer in the AB-3 crossover.

It's composed of a 12mH inductor and a 80uf capacitor, but the series resistor value is missing.  I assume the purpose of this filter was to tame this hump?

[avguytx]

16 minutes ago, mboxler said:

 

Although I can't find the AB-3 schematic, I did find a document describing a 162 Hz notch filter across the woofer in the AB-3 crossover.

It's composed of a 12mH inductor and a 80uf capacitor, but the series resistor value is missing.  I assume the purpose of this filter was to tame this hump?

 

I used to have a copy of that somewhere but I can't find it now.  I'd saved the link to where it was before but the info is gone from the link.  There were definitely more parts in the AB-3.

 

Edit:  I just found it.

 

@Chris A  I remember chatting with Roy about this crossover back when I built my clones.  At first he thought there were some of them left at the plant but found out there were none left.  It would take a bunch of parts to build this for sure.  But, with fairly inexpensive polyester caps, it might be doable.

 

AB3 Crossover.pdf

[Marvel]

2 hours ago, Max2 said:

The Belles were like Mini K's.   Tell you what though, I would take a pair of these over them both.  Unicorns here and may be my favorite of all as far as looks go

 

Those are beautiful!

[OO1]

3 hours ago, Max2 said:

, I would take a pair of these over them both

 

--now  for the specifics --- the cabs were BB  -- 7 plys -

-https://drive.google.com/file/d/1CKqv01YKLfhEhB9FW0B7YR1i7d-EiUGW/view

 

 

[geezin']

4 hours ago, Max2 said:

Without doubt.  The Belles were like Mini K's.   Tell you what though, I would take a pair of these over them both.  Unicorns here and may be my favorite of all as far as looks go.

 

 Please forgive my ignorance. But what am I looking at...........other than gorgeous speakers.

[Frzninvt]

Those are raw wood professional La Scala's with split cabinets and the triangular shaped HF/MF section.  Must have been a custom order but they are awesome.  I have had both and would take the La Scala each time.  Had 1980 Oak Lacquer Belle's with cane grills and 1981 Walnut Oil Belles.

[Islander]

On 5/17/2021 at 10:16 AM, Chris A said:

No, it's really related to the dimensions of the horn itself.  Here's a figure from Beranek's Acoustics that illustrates the effect of a smaller horn with a finite-sized (too small) mouth that doesn't fully expand the emerging sound waves (the solid black line corresponds to SPL output from the horn mouths, and the Belle and La Scala bass bins are both exponential expansion horns):

 

 

More discussion on this effect here: https://community.klipsch.com/index.php?/topic/161404-a-k-402-based-full-range-multiple-entry-horn/page/30/&tab=comments#comment-2263347

 

This is why horn-loaded loudspeakers benefit from in-room measurement and EQ compensation. 

 

Chris

 

Chris, the K400 midrange horn is obviously an exponential design, but I was under the impression that the La Scala bass horn is a conical design.  The straight sides of the horn would appear to confirm that.

[Chris A]

7 hours ago, Islander said:

Chris, the K400 midrange horn is obviously an exponential design, but I was under the impression that the La Scala bass horn is a conical design.  The straight sides of the horn would appear to confirm that.

No, it's a modified exponential horn (just like the Khorn bass bin) with a "rubber throat", meaning the expansion is greater than exponential near the throat, but it continues to a taper rate of 70 Hz (from PWK's 1965 JAES preprint #372, pg. 2).  The folded horn construction is made up of a series of expanding straight-sided segments which approximate an exponential expansion.

 

If the bass horn were merely "straight-sided" (a.k.a., "conical" expansion), the SPL response would look like the following impedance plot for a conical horn:

 

 

Exponential horn expansion SPL looks like the plot that you showed, above. Here is a Hornresp area expansion profile put together by Greg B (Edgar) on the La Scala bass bin, showing its modified exponential expansion profile:

 

 

A conical or straight-sided expansion would appear as a straight line on this type of plot.

 

For those not familiar with basic shape of an exponential horn profile (cross section), here is a little snippet from the exponential impedance plot (above) showing that basic shape:

 

 

You can see the difference in the throat (small end) areas of the exponential profile vs. the actual La Scala profile with its "rubber throat" expansion.

 

Chris

[Chris A]

For reference (and before questions might arise), here is a fairly well-known diagram of the various acoustic straight horn profiles used in loudspeakers (i.e., not folded or curved):

 

 

The tractrix and the exponential horn profiles actually share the exact same geometries at their throats, but differ as the horn expands toward its mouth, with the tractrix always flaring out to 90 degrees from its central axis.  Indeed, the tractrix formula starts at its mouth instead of its throat, and always starts with the mouth perpendicular to the central horn axis.  Typically, tractrix contours are actually about 85-90% as long as exponential contours for the same throat size in practice.

 

Chris

[Goldenear67]

Hey everyone:

 

Original Klipsch La Scala K-33 woofer frequency range starts at 47 Hz

 

Eminence Kappa 15C woofer is 63 to 2,800Hz  https://www.parts-express.com/Eminence-KAPPA-15C-15-Driver-4-Ohm-290-459?gclid=Cj0KCQjwk4yGBhDQARIsACGfAetqN1ctJTSiuoJtilclZaFs9RwDwchTxtUsqBsVA2FHFlVmKAywy9MaApPbEALw_wcB

 

Goldwood GW 15PC is 25 Hz - 2500 Hz https://www.midwestspeakerrepair.com/shop/home-audio/woofers/15-1-woofers/goldwood-gw-15pc-15-heavy-duty-woofer/

 

It appears that using the Eminence Kappa 15C  you'll loose 20 Hz on the bottom end.  The La Scala's need as much low end as possible so why are these  replacement woofers so highly recommended?

 

I can't speak for the Goldwoods clarity or performance because I have never used/heard them installed in a La Scala but did notice their specs on paper look better than the  Eminence Kappa 15C. 

 

Wouldn't the Goldwood GW-15 PC be a better choice for a replacement woofer?

Edited June 17, 2021 by Goldenear67

[Chris A]

54 minutes ago, Goldenear67 said:

It appears that using the Eminence Kappa 15C  you'll loose 20 Hz on the bottom end. 

 

Free air resonance is not the same as horn-loaded F3 (the frequency at which the output of the bass bin is down 3 dB from "nominal").  While higher free air resonance will typically raise the horn-loaded F3 point slightly, it's not nearly as pronounced as your statement.  In fact, the real limitation of both the Belle and La Scala Bass bins on their F3 is the designed-in "cutoff frequency" of their exponential horns--and not really the woofer's free air resonance.  See the following figure that shows the horn normalized throat resistance (i.e., horn loading) vs. frequency for several horn profiles, showing the effect of the exponential horn volume expansion profile, with its definite "cutoff" frequency due the horn profile itself:

 

 

Chris

[KT88]

double post.

[KT88]

1 minute ago, KT88 said:

On the contrary, regardless of the resonant frequency issue (which obviously is not an issue when such a higher resonance driver is mounted in a horn compression chamber) I think that such a soft and floppy hung driver like this (quote) "Goldwood GW 15PC is 25 Hz - 2500 Hz" performs very poorly in a horn and is too unstable to work like a stiff piston.