La Scala Bass Bin Frequency Response

[ClaudeJ1]

quote]

I've actually set in front of my speakers with my head in the front of the mouth of the bass bin and applied inward pressure with my hands to the outside walls of the bins. You can actually hear a difference in the quality of the bass. It gets louder and clearer. It's not a huge difference, but it's definitely noticeable.

Yes, after much searching I found the same thing......I already had braces fitted to my cabs, but they didn't come all the way to the front of the cabinet.....so I used an additional layer of 3/4" ply on both the external sides & the rear with a viscous glue, sound deadener, between them....problem cured.....and now the bottom end is ultra clean & powerful.....cleaned up the mids as well. The standard cabinet is simply not rigid enough to handle the forces generated by the woofer. Once you get rid of all the resonances all you get is pure, clean sound.

Just get a couple of Peavey FH-1 cabs for $100 each. Sell the Black widow woofers and put old square magnet K33's in there, or get Crites 1526c woofers. Then refenish them as pretty as you like. the cabinets are rock solid and the bass horn is smoother than the LaSala by a teeny bit. With PEQ, you can get 30 Hz. out of K33's in a small room. They are 30" wide rather then 24, so a bigger mouth and no straight section, so it's a bit longer horn, effectively. I have owned many older LaScalas, some of them newover the years, and I prefer the more rugged bins with braces for sure.

[DrWho]

If you look at the PEQ's for the JubeScala, there is a -7 db at 148Hz, Q=8.

I've got a little voice in the back of my head that says this was to kill that resonance. I think it was Pat that mentioned this long ago how he no longer has that issue now that he's biamping.

Panel resonances usual show up as dips in the frequency response, not peaks. They way I conceptualize it is that the acoustical energy that would otherwise be moving the air, is now moving the panel instead...

The peak in the Lascala bassbin is a function of the short horn with a small mouth. Basically, the driver has a better impedance match at that frequency than at the other frequencies. It should be minimum phase (or mostly minimum phase) so EQ'ing it down is simply going to reduce distortion in that passband, while yielding a flat phase response at the same time...

[ClaudeJ1]

Panel resonances usual show up as dips in the frequency response, not peaks. They way I conceptualize it is that the acoustical energy that would otherwise be moving the air, is now moving the panel instead...

The peak in the Lascala bassbin is a function of the short horn with a small mouth. Basically, the driver has a better impedance match at that frequency than at the other frequencies. It should be minimum phase (or mostly minimum phase) so EQ'ing it down is simply going to reduce distortion in that passband, while yielding a flat phase response at the same time...

Corretomundo. This is what I did with my Peavey FH-1 bins with the Behringer/EVDH1a/960 combo. I had a square magnet K33 in there, and that 2-way setup sounded great and got to an amazing 30 hz. via room gain and PEQ in my old office.....

[CECAA850]

Allrighteee then. back to my original question. Does anyone know the frequency that the cabs have the bad vibration?

I've got to agree w/ Doc and Claude. When I hold the cabs with my hands the bass seems to increase.

I'm currently conceptualizing (thanks for the word Doc) a brace for my Lascallas to reduce the vibration. The trick is that it has to be completely removable and leave no marks whatsoever on the stock cabs. I have it constructed in my head, but need to actually build a prototype. I'm also going to highpass them at 70 Hz and see if that helps also.

[ClaudeJ1]

Allrighteee then. back to my original question. Does anyone know the frequency that the cabs have the bad vibration?

I've got to agree w/ Doc and Claude. When I hold the cabs with my hands the bass seems to increase.

I'm currently conceptualizing (thanks for the word Doc) a brace for my Lascallas to reduce the vibration. The trick is that it has to be completely removable and leave no marks whatsoever on the stock cabs. I have it constructed in my head, but need to actually build a prototype. I'm also going to highpass them at 70 Hz and see if that helps also.

Is there a non-stick rubber edgerd pressure fit plywood triangles in your future?

[CECAA850]

Is there a non-stick rubber edgerd pressure fit plywood triangles in your future?

More like felt lined oak clamps.

[Islander]

Panel resonances usual show up as dips in the frequency response, not peaks. They way I conceptualize it is that the acoustical energy that would otherwise be moving the air, is now moving the panel instead...

That same principle applies to engines. Part of prepping an engine for maximum performance is balancing it. If it's balanced, all its energy is available to propel the vehicle instead of shaking the engine and everything attached to it.

Since that bass peak is caused by the dimensions of the La Scala bass horn, it explains why the EQ settings for the JubScala are the same, whether the La Scala II or original La Scala bass horn is used, since their inside measurements are the same.

Doc, your description of the side panel resonance absorbing energy (which doesn't necessarily occur over the same range as that bass peak) also explains why the LS II, with its stiffer horn walls, is perceived to have stronger and deeper bass, although I've read that the measurements are not that different.

Thanks for clearing that up. [Y]

[ClaudeJ1]

Is there a non-stick rubber edgerd pressure fit plywood triangles in your future?

More like felt lined oak clamps.

the point of bracing is to move the point of resonance up into the crossover slope, so that it gets filtered out. So a 1Khz. cabinet resonance in a LaScala is better than at lower frequencies, where the sound generated flops to the sides instead of forward where it belongs.

[Coytee]

Thanks for clearing that up.

x2

[sfogg]

" The trick is that it
has to be completely removable and leave no marks whatsoever on the
stock cabs. "

You could do something like what John Allen did in his smaller HPS-4000 speakers which should look familiar....

http://www.hps4000.com/pages/525_.html

I think the panel vibration is at a fairly low frequency. When I kick in a high pass on the LaScala's (at 70 or 80hz) it greatly reduces the vibration.

Shawn

[sfogg]

"Panel resonances usual show up as dips in the frequency response,
not peaks. They way I conceptualize it is that the acoustical energy
that would otherwise be moving the air, is now moving the panel
instead..."

I guess that depends on where you are measuring. Most any panel resonance test I have seen are measuring the motion of the panel itself, in that situation it looks like a big peak. But if that panel is out of phase with the acoustic output of the speaker then it might show up as a dip elsewhere.

The real test of a resonance is to look at the decay. A resonance will have a very long decay relative to the frequencies around it. That is why a resonance down low in the bass can be heard as muddy midrange... you literally are getting sound output when it isn't supposed to be there that is masking other details in the recording.

Shawn

[CECAA850]

" The trick is that it has to be completely removable and leave no marks whatsoever on the stock cabs. "

You could do something like what John Allen did in his smaller HPS-4000 speakers which should look familiar....

http://www.hps4000.com/pages/525_.html

I think the panel vibration is at a fairly low frequency. When I kick in a high pass on the LaScala's (at 70 or 80hz) it greatly reduces the vibration.

Shawn

Shawn, are those braces removable? That's my goal, to leave the cabinets unaltered yet still braced if desired..

I plan on crossing it over at 70Hz as soon as I'm done building my sub. Should be in about another week or so.

[DrWho]

"Panel resonances usual show up as dips in the frequency response,
not peaks. They way I conceptualize it is that the acoustical energy
that would otherwise be moving the air, is now moving the panel
instead..."

I guess that depends on where you are measuring. Most any panel resonance test I have seen are measuring the motion of the panel itself, in that situation it looks like a big peak. But if that panel is out of phase with the acoustic output of the speaker then it might show up as a dip elsewhere.

The real test of a resonance is to look at the decay. A resonance will have a very long decay relative to the frequencies around it. That is why a resonance down low in the bass can be heard as muddy midrange... you literally are getting sound output when it isn't supposed to be there that is masking other details in the recording.

Shawn

In the cases where I've seen dips, I've actually never seen it show up in the decay...I'll have to go take a closer look at some old measurements some time. Hurd and I just did a before and after with bracing on a different speaker recently with an outdoor ground plane. I don't recall looking at the waterfalls though.

I think the accelerometer tests you're referring to are probably the best way to identify the resonances...I should rig one of those up sometime.

[ParisK]

I don't know if this will help you too with the resonances of bass bin in LS (as I use stands), but that is what I found to be very effective in my speakers, reducing significantly the coloration in low frequency: Metal rings for better stability in the 16 screws of the removable bottom panel (bigger ones on axis, front and back). As I understand it, this panel was vibrating a lot, making things much worse for the rest of the bass bin.