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Heritage_Head

La scala mid driver

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7 hours ago, ricktate said:

I just saw this post and when I re-veneered my Scalas I put some screws or brad nails I cant remember now in the side wall top and bottom and then veneer over that. Before I did that I could move side walls with my fingers in and out now you cant even move them with a knee on one side and 2 hands on other side.

I had a set that used slightly thicker side wall plywood. It was not all that much but it was enough to be visually thicker and they were much better sounding than the other LS's that have gone though here.

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17 minutes ago, mark1101 said:

Have you seen the ALK transformer based attenuators?

I assume these are like Bob's autoformers with 12 tap values or is it something different?

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2 hours ago, Dave A said:

OK guys when you have questions the internet is your friend and you do not have to wonder and wait for an answer. Type in "what does a speaker L-Pad do" and you will find more info than you know what to do with. For instance.......

 

http://www.bcae1.com/lpad.htm

 

 

" An L-pad is a passive device which lets you control the output level of speakers without changing the impedance seen by the amplifier. A constant impedance is not really necessary for the amplifier but if you are using passive crossovers, a constant impedance is necessary to prevent the crossover frequency from changing. The following image shows what typical L-pad looks like. This L-pad is relatively large (~3" in diameter) because it's rated at 100 watts. L-pads rated for higher power have to be larger than ones rated for lower power because they have to dissipate more heat. This one has an unusually long shaft. This would generally be installed directly into the wall of the speaker enclosure. If you were using a terminal cup, you could use this (using nuts to allow only a fraction of the shaft to protrude through the terminal cup but it would be better to use one with a proper/short shaft. "

Thanks. I did research it a bit. Surprised Ive never come across l-pad before (probably have read it on here but never was something for what ever reason peaked my interest). 

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On 6/7/2019 at 12:49 PM, mark1101 said:

But I would replace the exponential horns with tractrix before I would change drivers.  I got lucky and wound up with a pair of Dave Harris Fastracs.  Those made a big difference IMHO.

Of course it is only a modification not an improvement or upgrade:). But I have the same HO.

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1 hour ago, Dave A said:

I assume these are like Bob's autoformers with 12 tap values or is it something different?

 

Something different.  Used in ALK networks.  These work great.

 

dscn2017.jpg

 

 

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After all these years I recently became aware that transformers do weird things with impedance.  Especially with tube amps L-pads would be the superior implementation and I just don't get why transformers would (have) be(en) used.  Surely a transformer is so much more costly to produce than an L-pad that it would more than offset the cost of the higher-value capacitor(s) required with the L-pad.

 

Re: resistance vs. impedance, it doesn't matter whether it's AC or DC, if the load is purely resistive, it's resistance.  With AC only, if the load has complex components (inductance and/or capacitance) then it's termed  impedance.  If the complex load is fully corrected by adding capacitance or inductance in the proper amount needed to maintain the current and voltage being in step, then the source would see, effectively, resistance.

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So, you've tried these and they don't work well for you?  What experience do you have with the picture I posted?

 

Here is what is stated on ALK website about these.

  • Stable attenuation settings of 0, 3, 5, 7, and 9 dB by a movable plug.

    set12db.JPGEnlarge

    Two additional setting of 10.5 and 12.5 dB available with an optional plug and cable.

    This is intended for very high sensitivity tweeters. You will likely never need this!

  • Flat 8 Ohms impedance load to amp at all settings.
  • Virtually flat frequency response from 20 Hz to over 50 Khz.
  • 10W continuous power handling.
  • None of the reduction in amplifier damping factor caused by resistive "L-pads". Tweeter sees a source impedance of about 0.4 Ohms for a damping factor of about 20 compard to damping factor of about 3 for a 4 dB resistive "L-pad".

Pricing (Set of two): $89.00

 

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While the voltage level in-to-out of the transformer is a direct function of the turns ratio, the impedance as seen by the source is a function of the turns ratio squared.  Without seeing what else is going on in the network it's hard to say just what he's doing, but with the transformer by itself it's utterly impossible for the amplifier to see "Flat 8 Ohms impedance load to amp at all settings."  At a turns ratio of 1:1 an 8-ohm driver would appear as an 8 ohm load.  At a turns ratio of 2:1 (50% reduction in output voltage) an 8-ohm driver would appear as a 32 ohm load.  If the crossover elements are before the transformer, the crossover point would change as well as driver output level when different taps are used.  If the elements are behind the transformer then only the output level would change, though the amplifier would still see the drastically different load.  Modern solid-state amps shouldn't care, but those with output transformers will behave differently.

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2 hours ago, mark1101 said:

Virtually flat frequency response from 20 Hz to over 50 Khz.

I wondered about this. So you could use this on your mids OR tweets as long as you don't exceed 10 watt levels. 10 watts into a BMS 4592mid would blow you across the street:)

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13 hours ago, Cinema_head said:

Mine seem pretty sturdy. I Havnt put any real force (would hate to break them lose). Not sure how hard I would need to go to reach the same pressure?

 

8 hours ago, ricktate said:

Did not take much before to make them move I could see it move with very little pressure. You wont break them apart. I think veneer on the outside did a lot to stiffen them up. It was also Iron on veneer I used contact cement type on my K-Horns and wanted to try the iron on type. It was just as good maybe even a little easier.

So gave them some really good force. They aren’t moving man. I put pressure from high up middle and bottom. I can’t move them. I guess if I put my foot on them and grabbed a side they would probably move. But it feels like something would snap first. 

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19 hours ago, glens said:

Surely a transformer is so much more costly to produce than an L-pad that it would more than offset the cost of the higher-value capacitor(s) required with the L-pad.

An autoformer doesn't waste power by changing it into heat, and it allows you to use a much higher quality capacitor(s) in the signal path. I would rather use a 12uF film and foil than a 50uF metallized.

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Those ALK attenuators are nice, just keep in mind they're for 8 ohm loads only (like most tweeters we use anyway). ☺️

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Regarding the Fastracs, I don't know what you guys are talking about them REDUCING volume a couple of dB compared to the original horn.  My experience was that they were slightly louder and needed to be reduced a few dB.  Or maybe I'm just remembering the K600's in the Cornwalls but I think I remember a similar experience with the La Scalas when I swapped them out.  BUT either way, using Fastracs made me alter the networks.  Is there anything I didn't try?  

Now I'm settled on the Eliptracs and I'm pretty happy but with the BMS drivers they required a larger drop.  

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Don't know anything about the Cornwall version - this is for the Fastrac LaScala. 

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