LaScala build question

[Islander]

Whatever the cause of that peak in the LS bass response, the Dx38 settings in the JubScala conversion cure it and the sound of the speaker is improved noticeably.

[ClaudeJ1]

Since some, if not all, of that peak comes from the bass bin's sidewalls resonating, the stiffer 1" MDF of the LS II may address most of it, so there may not be as much "taming" in the new crossover as you might think.

Well, I have gone to old Peavey FH-1 bins, which have a larger mouth. The peak is more inherent in the horn design because those have the braces, are built like tanks, and still have a similar peak as the Klipsch LS bin.

So I"m not convinced about the LS II bin because of this observation. However, when you put a K33, knock down that peak with a PEQ at 180 Hz., the FH-1's will go down to 30 Hz. in a small room according to RTA readings., but I'm not using them there anymore.

[ClaudeJ1]

Whatever the cause of that peak in the LS bass response, the Dx38 settings in the JubScala conversion cure it and the sound of the speaker is improved noticeably.

Right. So, this leads me to believe that if you want the BEST perfomance from ANY 2-way horn system, you have to go to bi-amping with Digital Xover so you clean up the humps and bumps that have been there all along in the bass bin while cranking up the inherent rolloff of compresson drivers and CD horns by about +12 db @ 12-13 Khz.

This is what all of the Pilgrimage 2007 grads are doing with Jub, LS, and MWM bass.........except me. I'm just using only the flat portions of all the drivers with natural rolloffs and good old 1st order networks with efficiency matching via driver attenuation (only the EV DH1A).

[DrWho]

"....

Since some, if not all, of that peak comes from the bass bin's sidewalls resonating, the stiffer 1" MDF of the LS II may address most of it, so there may not be as much "taming" in the new crossover as you might think....."

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I am not so sure about that. As I understand it, if the cabinet was vibrating you not get a peak in freq response. Rather you would get a loss of energy (SPL) at that frequency. Essentially the engery is not being converted to SPL, rather it is being converted to cabinet vibration. However, stiffening up the cabinet via thicker material or bracing is a good idea.

That has also been my experience...cabinet resonances show up as dips in the frequency response.

However, I'm not convinced that there is any loss of energy...if there was energy lost into the vibration, then the walls of the cabinet would start heating up. This is certainly happening to an extent, but I don't think it would account for the majority of the amplitude drop.

I wonder if the behavior isn't more like a capacitor where the energy is being stored up and then released over time....and the "charging of the cap" is creating an amplitude drop because it's effectively "shorting out the output"- or basically the wall is expanding to prevent any air pressure from transmitting into the air. Or from another perspective, you're getting a velocity of the cabinet wall that is out of phase with the velocity of the air - so basically most of the amplitude drop is a result of phase cancellation. And then of course, there is energy left over that slowly is removed from the cabinet walls as the resonance subsides over time.

As far as the crazy huge peak around 110Hz (I don't remember the actual frequency off the top of my head), I wonder if it doesn't have more to do with the area expansion of the horn...for example, there are sections where the cross sectional area is constant...things like that start to behave like tuned pipes (in fact, you could almost think of a horn as series of pipes tuned to different frequencies). And tuned pipes have an oscillating type nature to the frequency response.