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jwgorman

DIfferent woofer or AL-4 circuit more effective for taming 140Hz bass hump in lascalas?

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The difference between your quoted number for cutoff and the number that I quoted is the boundary gain on bass bin cutoff frequency.  This is missed by a lot of folks, including some "horn designers". 

 

See the following article by PWK describing low frequency extension due to room boundary gain on a prototype Cornwall bass bin:

 

https://community.klipsch.com/applications/core/interface/file/attachment.php?id=54362

 

Chris

 

EDIT: here's the full article.  Note that first two figures are switched in this version: https://community.klipsch.com/applications/core/interface/file/attachment.php?id=66006

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4 hours ago, Chris A said:

The difference between your quoted number for cutoff and the number that I quoted is the boundary gain on bass bin cutoff frequency.  This is missed by a lot of folks, including some "horn designers". 

 

See the following article by PWK describing low frequency extension due to room boundary gain on a prototype Cornwall bass bin:

 

https://community.klipsch.com/applications/core/interface/file/attachment.php?id=54362

 

Chris

 

EDIT: here's the full article.  Note that first two figures are switched in this version: https://community.klipsch.com/applications/core/interface/file/attachment.php?id=66006

First to the OP's initial remarks about the woofer replace and the filter to solve a "hump" at the 140 Hz region. This appears to be addressed  as to a fill of not loose material in the bin, addressing and measuring resonance before and after a stiffen of the bin, a shunt filter inline on the crossover to lessen/solve the hump in frequency. Using a dedicated equalizer(EQ) on the woofer at the crossover. A room null point with a Cornwall as well. And then of course the upstream digital EQ. Sortof a recap then as I have been reading. Looking at the graph in line curve 3, instead of a hump, as in an upwards camel back for instance, I see a drop down or reversed hump.

 

Question 1 for anyone, is the idea of a filter, or any of the aforementioned methods, to attenuate this hump/null or, to emphasize it?

 

Question 2 is more of a takeaway from the PWK articles you last presented. An upright cornerhorn speaker or a box speaker using the size parameters mentioned, both greatly benefit from corner placement of a room, in order to enable a listener to audibly discern a lower frequency, that is, lower bass.

Using curve 3 of the graph and having in this case, the speaker directly sitting on the floor, this appears to be the case.

 

Have read here from members what appears to be some cardinal considerations of PWK and the understanding of them.

Know there are much simpler ways of stating what I have read, yet I appreciate the nutshell simplicity with how others

can explain this. Still learning what others seem to know first hand without having to process.

Thanks!

Edit: drop in woofer

        

 

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In my opinion, using upstream EQ to flatten the response is the best approach.  Using a notch filter in the passive can lead to other issues--like a 2 ohm load on the driving amplifier at 140 Hz--although this analysis doesn't include the reactance of the woofer in the bass horn since I didn't have that data.  This may not be an issue for the amplifier, but the values for the inductor and the capacitor are fairly large ($).

 

Your description of the PWK corner speaker placement article appears to be correct.  The better loaded the bass bin is by the mirror reflections from the walls, floor (or perhaps ceiling instead), the smoother and deeper the response with less distortion (harmonic and modulation distortion, that is). 

 

Chris

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with a lower Q woofer and back chamber volume reduced you might effectively tame the peak but LF cutoff will move upwards (see M151 sim below) - I'd say parametric on a media player if your source are mainly digital files.  You could try making Belle's back chamber smaller.

G3gTHzg.jpg

 

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Ok, I found Dennis' notes...

 

Just some notes for both the stock and the (vented) ported LaScala.
Porting does not reduce the basic efficiency of the LS, it does however reduce the massive
140hz peak
, porting also smooths out the overall response above 100hz, and reduces the dip at
200hz in the stock LS.


To get the most out of the ported LS mod you need an EQ similar to the EV Interface A box, it
has 6dB of boost at 35hz. You can boost a sealed LS, but that increases the cone motion, EQ at
Fb (port tuning frequency) does not increase cone motion. Less cone motion, less distortion.
Any equalizer with a subsonic filter can be changed to do this as well, usually it's just a matter of
changing two resistors per channel. I buy used Audio Control EQs from eBay when they go for
cheap, the 520 is a nice 5-band piece that is designed to complement standard tone controls and
be easy to use.


Foam
Both versions of the LS benefit from a 2' x 2' x 1" piece of foam behind the woofer. It really
smooths out things above 100hz.


If you are using subs all the time, you can leave the stock LS sealed and reduce the back volume
by about 1/3, and use the foam. This totally reduces the bottom octave, but smooths things out
above 100hz. Use non-porous fill to reduce the volume.


On axis, the above modified LS will measure flat to about 800hz, and very smooth too. You may
use a 650hz or so crossover point on a good horn and driver combo for a nice two-way at this
point (or retain the stock Klipsch setup).


Thanks are due to Carl Huff for his extensive work and measurements.

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3 minutes ago, Marvel said:

Ok, I found Dennis' notes...

 

Just some notes for both the stock and the (vented) ported LaScala.
Porting does not reduce the basic efficiency of the LS, it does however reduce the massive
140hz peak
, porting also smooths out the overall response above 100hz, and reduces the dip at
200hz in the stock LS.

This indicates to me that the 140 peak isn't a "bass bin sidewall resonance".  If this is occurring (lessened resonance peak at 140 with porting) then the porting is bleeding the resonance acoustic pressure away from the horn and into the ported cavity, where the "Q" of the horn/driver/back chamber resonance is smoothed out.

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If my memory is any good at all (doubtful), I thought that peak was from the short, parallel sidewalls. in the horn.

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I was under the impression that the 140Hz hump was a mouth resonance issue and that the braces or the double side wall thickness dealt with that?

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^ So the LSii deals with that hump?

 

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