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jwgorman

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

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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.

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I believe you can add some fill to the woofer chamber (solid.. not stuffing) , reducing the volume, and it will flatten the response somewhat. It will also lower the efficiency some, but may be what you are after. I don't remember the amount offhand, but Dennis (djk) has mentioned it in the past.

 

Bruce

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2 hours ago, jwgorman said:

tame the dreaded 140Hz hump

Dreaded?  That's a little over top...how about "corner frequency?"

2 hours ago, jwgorman said:

 ...just wanted to see if there's a passive fix.

Re-design the cabinet.

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The Mini DSP worked wonders with mine without the need for an extra amplifier (besides the subwoofer amp).

 

 

 

 

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Or add the blue-shaded shunt filter across the woofer crossover outputs:

 

5a284d902adf0_140Hznotch.jpg.0b5324e64912973eee2c65ab8810e31c.jpg

 

With the resulting frequency response looking something like this:

 

5a284d5066260_140HznotchFR.jpg.d70f0c6afb59031a3c228cd0c25a6e3f.jpg

 

and the resulting impedance looking like this:

 

5a284cf4a4bf0_140Hznotchimpdance.jpg.3080fcc86e5f8b69f4a7b1136d0c126e.jpg

 

 

 

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I have some old lascalas that I run a graphic EQ on tape monitor loop of preamp and handle that issue plus other general EQ for that setup.  I am using ALK Super X, Jr. Cum Laude passive networks.

 

Edit:  Just to clarify, the correct name for the networks in my 1977 Lascalas are Super AA.  They are not the nonsense name above.  Sorry for any confusion.

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19 minutes ago, Chris A said:

...nevermind...

 

 

What about an EQ?

Thanks!

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4 minutes ago, mark1101 said:

I have some old lascalas that I run a graphic EQ on tape monitor loop of preamp and handle that issue plus other general EQ for that setup.  I am using ALK Super X, Jr. Cum Laude passive networks.

Thanks!

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3 hours ago, billybob said:

What about an EQ?

Thanks!

Yes...I'd use a good upstream parametric EQ, perhaps on the source or via Windows/Mac while still in the digital domain (no added noise or losses).  Really good lossless EQ is also available in DSP crossovers between the preamp and amplifier. 

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7 hours ago, babadono said:

@ClaudeJ1 what woofer is it that you recommend for the La Scala, Eminence Kappa 15?

Eminence Kappa 15C. What I like about it most is the extra 4 db of output at 400 Hz. to mate up with the K-400 Horn. Way more detailed midrange vs. the K33 and doesn't thin out the bass as much as a K43 does. Either way, a good sub takes care of the below 100 Hz. stuff better than any other method, including porting.

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14 hours ago, jwgorman said:

woofer upgrade for a lascala that might both tame the dreaded 140Hz hump and maytbe provide a little more output at 300HZ

You're dreaming if you think you can tame the inherent peak in the HORN itself by replacing the woofer alone. An Eminence Kappa 15C is a great replacement to get the midrange detail up between 300-400 Hz. yes, but all you have to do is use a sub below 100 hz. to mate UP to that peak.

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Dumb question (since I don't know much about driver peaks/resonances and stuff like that.....)

 

Isn't the cabinet itself part of the problem?

 

Fix the resonating sidewalls first, then go to part 2??

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I think you're probably correct Coytee. Claude, yep, that's proven to mitigate the peak to a large extent in my room.

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4 hours ago, Coytee said:

Isn't the cabinet itself part of the problem?

I believe that the culprit in this case is the undersized mouth of the bass bin which results in the peaks and nulls in response near the horn cutoff frequency, which is around 100 Hz (full space) in the case of the La Scala bass bin. 

 

The flexing of the sides of the La Scala bass bin will create a resonance or two close to cutoff...but basically just robs the output of SPL and is typically much less frequency dependent than a high-Q 140 Hz resonance described above.

 

Chris

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Your room could be creating more peaks and nulls than anything but I'm not arguing with Chris... just that I had similar issues when I had Cornwalls where the La Scala's are now.

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One way to tell the source of the problem: measure the frequency response of the bass bin, then stiffen the sides of the bass bin, then measure again.  If the 140 Hz peak gets bigger--you've got a small horn mouth size issue.  If it moves up in frequency, then it's a wall-resonance issue. 

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1 hour ago, Chris A said:

believe that the culprit in this case is the undersized mouth of the bass bin which results in the peaks and nulls in response near the horn cutoff frequency, which is around 100 Hz (full space) in the case of the La Scala bass bin. 

 

Know am not understanding this part but cutoff around 100 Hz when the low output of the bin goes down to around 50 Hz?

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9 minutes ago, billybob said:

...but cutoff around 100 Hz when the low output of the bin goes down to around 50 Hz?

Where is your La Scala located (relative to the floor, ceiling, and walls) when you quote 50 Hz?  It's not hoisted into the air 10-20 feet high outside, away from other surfaces...right?

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