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JFHSQT

The physics of La Scala IIs and folded horns in general

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Last night my wife and I were enjoying some tunes on the La Scala II and SVS SB16-Ultra combo.

 

She was amazed when I explained that the bass we were hearing was not coming from the giant LS II cabinets, but mostly from the SVS at the back of the room. It really is an auditory illusion, as it sounded 100% like the sound was coming from the front soundstage, until I hit the Mute button on the SVS and the bass shrunk significantly down to the LSII's folded horns. I should note that we were just listening to a live George Michael recording (MTV Unplugged, "Older,") so the bass was essentially 60-80Hz bass guitar and soft kick - nothing that was really outside of the range of the LSIIs.

 

She couldn't understand why these giant speaker cabinets taking up her living room were not able to produce the same kind of bass as the SB16 – looking at the big folded horn woofers, it seemed like (to her) they would be capable of producing much more bass than she was hearing.

 

So I tried to explain that the speakers were that large not necessarily to produce "deep bass," but to produce distortion-free sound without resonance peaks... the speaker design was more about eliminating distortion and creating a deep and even sound field with smoother response than using up all that room to create tons of bass.

 

That being said, I realized I myself didn't have a good explanation as to the physics behind how and why these speakers are built. I know that the essential philosophy behind PWK's designs was to maximize efficiency, eliminate distortion, and as a result this sacrifices bass response. 

 

But is there a quick and easy primer someone could share on why these speakers were designed the way they are - what is the end-goal and how does this design serve that purpose?

 

Thanks!

 

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The design goal is efficiency.  A horn does it by trapping an air column against the driver cone so that its movement is tightly coupled to the air to produce vibration in the air.  That tight coupling allows for very small cone/diaphragm movement at a given loudness where the driver is very linear and mildly stressed reducing a myriad of distortions.  The low frequency limit (cutoff, fc) of a horn is defined by its length.  Compare the sound of the cheerleader's megaphone to one you make from a sheet of paper.  It is only the length of the a La Scala bass horn that prevents it from playing 30 Hz loudly.  The same woofer in a K-horn goes that low pretty well. 

 

Folding makes the bass horn occupy less space in a room.  Were it to be unfolded and built with a single path, it would be 3 feet long (with a mouth that is actually too small), compare to a K-horn's ~7 foot long horn path. 

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When first being introduced to horns, the following helped me.

 

'"A crude analogy of the direct radiator loudspeaker would be a "baffled" piston on the surface of a lake. It could agitate the waters but it would not be much of a pump. But put a cylinder around the piston, and it becomes capable of lifting the water. This is analogous to the driver unit coupled to a horn. The cone is forced to work at higher pressures with lower velocity. Another analogy is the gear ratio of the automobile which transforms the "low impedance" engine - low torque, high speed - to the "high impedance" drive wheels - high torque, low speed. The direct radiator speaker is a low impedance device - low pressure, high velocity. The gear box is an impedance transformer. The horn acts as a transformer to increase the pressure and reduce the motion of the driving system. Modulation distortion is directly affected by the amplitude of diaphragm motion, and would thus be greatly reduced by horn loading."'

 

Paul W. Klipsch, "Loudspeaker Performance", Wireless World, February 1970

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Here is a exploded view if the original LS, but the basic form is the same. And a set of plans to build the original done by a former member of the forums. It will give you the idea of the horn geometry.

 

Bruce

LS_wallpaper.jpg

LaScala11.pdf

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4 hours ago, JFHSQT said:

She couldn't understand why these giant speaker cabinets taking up her living room were not able to produce the same kind of bass as the SB16 – looking at the big folded horn woofers, it seemed like (to her) they would be capable of producing much more bass than she was hearing...But is there a quick and easy primer someone could share on why these speakers were designed the way they are - what is the end-goal and how does this design serve that purpose?

"They make miniature tubes and miniature loudspeakers, but they have yet to come up with a miniature 32-foot* wavelength."  PW Klipsch

 
* A 32-foot wavelength in air has a frequency of 35 Hz at room temperature. 
 
Most people don't know that they already listen to loudspeakers that are far too small to faithfully reproduce the low frequencies that they like to listen to on their music tracks and movies. 
 
The trend toward "small loudspeakers" in the home started in the early 1950s (Ed Villchur, et al.).  It's been downhill ever since--with everyone wanting smaller and smaller loudspeakers, but expecting the same performance as if the size of the bass section of their loudspeakers were actually some reasonable fraction of the size of the low frequencies being reproduced. Those original companies that first started making small loudspeakers have all bitten the dust--but Klipsch survives. 
 
I wonder why.
 
Chris
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When you hit the mute button on the subs was the bass you were sending to the subs redirected to the LaScalas? If not it wasn’t really a valid comparison. 

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3 hours ago, JohnA said:

The design goal is efficiency.  A horn does it by trapping an air column against the driver cone so that its movement is tightly coupled to the air to produce vibration in the air.  That tight coupling allows for very small cone/diaphragm movement at a given loudness where the driver is very linear and mildly stressed reducing a myriad of distortions.  The low frequency limit (cutoff, fc) of a horn is defined by its length.  Compare the sound of the cheerleader's megaphone to one you make from a sheet of paper.  It is only the length of the a La Scala bass horn that prevents it from playing 30 Hz loudly.  The same woofer in a K-horn goes that low pretty well. 

 

Folding makes the bass horn occupy less space in a room.  Were it to be unfolded and built with a single path, it would be 3 feet long (with a mouth that is actually too small), compare to a K-horn's ~7 foot long horn path. 

Thanks, this explains a lot!

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2 hours ago, Marvel said:

Here is a exploded view if the original LS, but the basic form is the same. And a set of plans to build the original done by a former member of the forums. It will give you the idea of the horn geometry.

 

Bruce

 

LaScala11.pdf

 

Thanks - this graphic kind of reinforces the way I have been looking at the La Scalas, which is to say as a "musical instrument" in and of themselves, as much as a speaker. I've owned lots of speakers over time, but having these sitting in the living room – and having been around lots of Ampeg bass cabinets, etc – really feels like the design of the speaker is fundamental to the reproduction of sound. Now I realize that's the case with all speakers, in a general sense. But with the LS IIs it does seem like they are more a part of the sound than anything else I've owned or listened to in the past.

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41 minutes ago, Kevin S said:

When you hit the mute button on the subs was the bass you were sending to the subs redirected to the LaScalas? If not it wasn’t really a valid comparison. 

 

Actually I am running the LS IIs full-range (with no crossover) from my Luxman/PrimaLuna rig out of an Oppo 205, and sending the analog signal into my Anthem which is processing the full analog signal through ARC and sending the low frequency content over to the SVS. So even without the sub, the LS IIs are always reproducing the full-range output of the Oppo.

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16 minutes ago, JFHSQT said:

 

Actually I am running the LS IIs full-range (with no crossover) from my Luxman/PrimaLuna rig out of an Oppo 205, and sending the analog signal into my Anthem which is processing the full analog signal through ARC and sending the low frequency content over to the SVS. So even without the sub, the LS IIs are always reproducing the full-range output of the Oppo.

OK. Sort of a “Double Bass” effect that many AVR’s offer. Then perhaps the overall level of the bass dropped quite a bit when the sub was muted. That would certainly make the bass seem to “shrink”. Try level matching the comparison at the listening position and see if your perception changes. 

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33 minutes ago, Kevin S said:

OK. Sort of a “Double Bass” effect that many AVR’s offer. Then perhaps the overall level of the bass dropped quite a bit when the sub was muted. That would certainly make the bass seem to “shrink”. Try level matching the comparison at the listening position and see if your perception changes. 

Kind of like that, but the input of the LS IIs is completely independent (a different source) than the subwoofer.

 

The Luxman & PrimaLuna tube rig is sending analog signal via USB DAC out of the main output of the Oppo (Oppo main L/R -> Luxman CL-40 -> PrimaLuna -> La Scala IIs)

The SVS Sub is getting bass from the Anthem AVR via the analog L/R pre-outs of the Oppo (Oppo preout L/R -> Anthem MRX -> SVS SB16 Ultra)

 

This way I actually can independently volume match/level adjust the bass from the subwoofer against the main L/R of the La Scalas. 

 

I normally level match by using my speaker switcher (both amps are connected to this). I listen to the Anthem output through the LS IIs, then hit the A/B switch and level match the Luxman preamp. 

 

It sounds more complicated than it is actually... But it sounds amazing. Best of both worlds!

 

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LSii's are small...

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Volti was kind enough to plot their performance vs the stock LS

IMHO the LS was optimized for the hearing sweet spot, the Mid Range.

If I read the post correctly, the LS is the Blue line and Volti is the red line.

 

"The picture below, shows a comparison of in-room testing of the Vittora prototype (labeled GR9) and a stock Klipsch La Scala I bass horn with a K33 woofer.  Exactly the same test was done on both horns, in the same location in the middle of a room at my shop (no walls or corners around either of the cabinets.  GR9/Vittora is the red curve. "

 

gr9curvedvsstockls.jpg

 

http://www.voltiaudio.com/newsletter/NL20.shtml

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I have always thought that the LS were inefficient from a bass vs size perspective. They take up a lot of real estate to still require a sub.Its performance  gives away its origin as a PA speaker from era requiring maximum volume from relatively low watt tube amps. Magnificent and very distinctive looking ( best looking of all Klipsch speakers IMO). 

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On 8/11/2018 at 9:20 AM, Bubo said:

Volti was kind enough to plot their performance vs the stock LS

IMHO the LS was optimized for the hearing sweet spot, the Mid Range.

If I read the post correctly, the LS is the Blue line and Volti is the red line.

 

"The picture below, shows a comparison of in-room testing of the Vittora prototype (labeled GR9) and a stock Klipsch La Scala I bass horn with a K33 woofer.  Exactly the same test was done on both horns, in the same location in the middle of a room at my shop (no walls or corners around either of the cabinets.  GR9/Vittora is the red curve. "

 

gr9curvedvsstockls.jpg

 

http://www.voltiaudio.com/newsletter/NL20.shtml

  That response curve looks very flawed. No highs above 1K Hz? Down 20 dB by 2K Hz does not match what I hear. 

  Is this maybe just the bass bin? 

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Compare this response of a Peavey FH-1 to the Volti above.  Note roll-off at 80, sag at 180 and return at 2k.  The FH-1 has corner reflectors, but is otherwise similar to a La Scala.  The similarities are striking to me.  

 

post-2142-13819263971418_thumb.jpg

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I don’t trust anything he measures. 

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On August 9, 2018 at 4:16 PM, Schu said:

LSii's are small...

 

--- as compared to -- Jubes? Yes ---- . RB75's --- no.

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9 hours ago, Schu said:

Squawker...

 I doubt the squawker is down 40 dB at 5,000 Hz. I can believe the woofer is down that much. 

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