Chris A Posted December 7, 2017 Share Posted December 7, 2017 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 2 Quote Link to comment Share on other sites More sharing options...
billybob Posted December 7, 2017 Share Posted December 7, 2017 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 Quote Link to comment Share on other sites More sharing options...
Chris A Posted December 8, 2017 Share Posted December 8, 2017 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 1 Quote Link to comment Share on other sites More sharing options...
karlson3 Posted December 9, 2017 Share Posted December 9, 2017 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. 2 Quote Link to comment Share on other sites More sharing options...
Marvel Posted December 9, 2017 Share Posted December 9, 2017 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. 2 Quote Link to comment Share on other sites More sharing options...
Chris A Posted December 9, 2017 Share Posted December 9, 2017 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. Quote Link to comment Share on other sites More sharing options...
Marvel Posted December 9, 2017 Share Posted December 9, 2017 If my memory is any good at all (doubtful), I thought that peak was from the short, parallel sidewalls. in the horn. Quote Link to comment Share on other sites More sharing options...
moray james Posted December 9, 2017 Share Posted December 9, 2017 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? Quote Link to comment Share on other sites More sharing options...
Schu Posted December 10, 2017 Share Posted December 10, 2017 ^ So the LSii deals with that hump? Quote Link to comment Share on other sites More sharing options...
geoff. Posted October 28, 2020 Share Posted October 28, 2020 @Tizman ...for your consideration Quote Link to comment Share on other sites More sharing options...
moray james Posted October 28, 2020 Share Posted October 28, 2020 On 12/6/2017 at 8:45 AM, jwgorman said: Gentlemen, I thought some of you might be up on the latest 15" woofers out there and might know of a drop in woofer upgrade for a lascala that might both tame the dreaded 140Hz hump and maytbe provide a little more output at 300HZ. Alternatively, maybe some of you have tried the AL-4 woofer circuit with the older lascalas like mine (looks like an 18db/oct low pass filter) with good results. I know I could do this actively if I split the woof from the horns in the xover and ran a dedicated amp/para eq to the woof. And that's an option, just wanted to see if there's a passive fix. that hump is a mechanical resonance which has been identified and dealt with you can either thicken and stiffen the side walls as in the LaScala ll or you can install braces between the side walls and the doghouse. Problem solved either way. There should be lots of threads in the archives. Quote Link to comment Share on other sites More sharing options...
Blvdre Posted October 28, 2020 Share Posted October 28, 2020 MJ, I remember reading a post about the hump, and that it is not caused by sidewall vibration. I'll try to find the post.... Edit: forget it. The forum search is not the best. Anyway, I believe it's caused by other design issues. 2 Quote Link to comment Share on other sites More sharing options...
billybob Posted October 28, 2020 Share Posted October 28, 2020 27 minutes ago, Blvdre said: MJ, I remember reading a post about the hump, and that it is not caused by sidewall vibration. I'll try to find the post.... Edit: forget it. The forum search is not the best. Anyway, I believe it's caused by other design issues. Might not help with finding more but, some: Quote Link to comment Share on other sites More sharing options...
billybob Posted October 28, 2020 Share Posted October 28, 2020 More in this thread around page 66 of 67 (null): Quote Link to comment Share on other sites More sharing options...
Tizman Posted October 30, 2020 Share Posted October 30, 2020 On 10/27/2020 at 8:07 PM, geoff. said: @Tizman ...for your consideration Thanks Geoff. Quote Link to comment Share on other sites More sharing options...
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