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Danieln

My new LaScala crossovers.

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29 minutes ago, Danieln said:

I see Deang, L2 is about 2.5mH. The point is that part of this is in the voice coil.

Else, how can I explain my measured point is 430?

When you say "measured", are you passing a 430 hz signal to the speaker, checking the voltage across the crossover input, then checking the voltage across the woofer output?

 

The woofer out should be the input times .707.

 

Mike

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Mike, exactly as you describe.

I have a two channels oscilloscope. Channel one on the woofer, channel two connected to mid range before attenuator (Output of 300uH inductance). I then use "online tone generator" and find at which frequency the two channels reads the same peak to peak amplitude. This is the crossover frequency. I then measure the crossover input level. My measurement were 2.0Vpp (Woofer and midrange) with a 2.75Vpp input @ 430 Hz.  20Log(2.0/2.75) = -2.8Db  very slightly off the -3.0Db  (.727 vs .707)

 

Dan

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in the next couple of days, I will revert one of my crossover to 2.5mH and measure the crossover point again.

Quite curious to see how this will compare to my simulation.

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1 hour ago, Danieln said:

Mike, exactly as you describe.

I have a two channels oscilloscope. Channel one on the woofer, channel two connected to mid range before attenuator (Output of 300uH inductance). I then use "online tone generator" and find at which frequency the two channels reads the same peak to peak amplitude. This is the crossover frequency. I then measure the crossover input level. My measurement were 2.0Vpp (Woofer and midrange) with a 2.75Vpp input @ 430 Hz.  20Log(2.0/2.75) = -2.8Db  very slightly off the -3.0Db  (.727 vs .707)

 

Dan

Not to create more work, but I'm curious what the voltage drop across the 1.3 mh inductor is at 430 hz.   Maybe 1.3Vpp???

 

Mike

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So I rewired my crossover to use a 2.5mH inductor and precisely measured using my scope and also confirms with an AC voltmeter.

I  re-simulated both the 1.25mH and the 2.5mH design.

The results are not surprising:

 

Using the 2.5mH, the crossover point is lower.

Simulation shows 338Hz @ -4Db

Measurement shows 300Hz@ -4.8Db

 

Using the 1.25mH, the crossover point is higher.

Simulation shows 417Hz @ -2.8Db

Measurement shows 430Hz@ -2.8Db

 

It is clear that  my crossover requires the 1.25mH woofer inductance.

Joined are two pictures, showing equal low and mid levels and the measured period and frequency.

One channel on the woofer, the other on the mid, before attenuation.

 

Dan

430HzCross125mH.jpg

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Interesting!  Someday I'll re-install my ALK Universals into my K-horns and experiment.  I have a pair of 1.0 mh inductors that I can put in series with the 1.3 mh in the crossover.

 

I assume the yellow graph is the woofer, with the woofer current lagging the mid driver current by 90 degrees?

 

Thanks for the info!

 

Mike 

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Very nice work and PROOF Dan..........which we usually don't see from the forum network advocates. You selected a great design for your lascalas.  I have sworn by ALK's for many years.  Enjoy.

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Thanks Mike, i don't remember exactly which one is which, but as you noted it shows the phase shift.

i strongly encourage you to try and confirm the measurement. You don't really need a scope, just an AC voltmeter.

Use "onlinetonegenerator dot com" to drive your amp.

I'm jealous of your K-horns , but in my case haven't corners to put them in.

 

Dan

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Mark, I consider the ALK crossover in high regard. 

Mine is inspired by his work. But as you noted, I slightly modified, simulated, constructed and measured the result. 

My hearing is not so good, so i will trust a good design methodology and measurement over my hears anyday :-)

 

I cannot stress enough that you need a constant impedance network with Single Ended Triode (SET) amplifiers or even more so with pentode (without feedback). The key is the damping factor, or say another way the amplifier output impedance. The worst offenders are the original Klipsch networks. The midrange is boosted by several DB without controlled impedance, but is flat with a constant impedance network. been there, done that!

 

Dan

 

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8 minutes ago, Danieln said:

The key is the damping factor,

Wrong amps to choose then 😂.  Damping factor above 0 is awesome then? 

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On 2/4/2019 at 2:21 PM, Danieln said:

My spice simulation models the woofer as a 6.2 Ohms in series with a 1mH voice coil inductance. Adding my 1.25mH (Essentially two 2.5mH in parallel taken from the AL type crossover) brings the total to 2.25mH for my simulation. The resulting crossover is simulated at 417 Hz. Now, when I look at the actual electrical response of the crossover, I measure 430 Hz which matches quite well the simulation. Increasing the inductance lowers the crossover point in fact. Which crossover frequency is optimum from your point of vue?

 

The total *impedance* of a K-33-E averages about 6.3 ohms, or a little more, in the bass horn.  That includes the reactance of the voice coil.  The impedance at the nominal crossover point of 400 Hz is about 10 ohms.  This graph is for an LSI, but the regular LS should be about the same.

 

Impedance of LaScala Industrial.jpg

 

What is the measured output of the speaker, outdoors, preferably?   A La Scala's bass horn has significant output from 600 to 1200 Hz.  A lower simulated electrical crossover frequency is needed to tame that output so the speaker's acoustic response is flatter.  This is especially true when using first order filter slopes.  

 

A voice coil's inductance will affect the driver's acoustic output, but should not be added to the filter. 

 

Look at the response curve of this woofer.  It has a common response curve, though maybe a little worse to illustrate the point.  If you wanted to cross this woofer to a tweeter at 1k with a first order filter, where would it need to be?  If it could be done at all the electrical crossover would be nearer to 500 Hz so the acoustic crossover would be near the desired point without a bump in the response curve. 

 

 

 

 

woofer.jpg

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John, thanks for the factual post. My goal is to understand.

Basically you state that in order to get rid of the big 2000 Hz bump, the crossover must be lower in order to get enough attenuation at 2000.

You propose around 500 Hz, which make sense.  But in this case, the crossover will be stated to be @500Hz.

 

Speaker's acoustic output is proportional to electrical signal that drives it. 

So when I measure voltage at the electrical crossover, that must be reflected in the acoustical response. 

The fact is that I measure a lower electrical crossover with the 2.5mH on my crossover.

It is quite an easy measurement to do using an AC voltmeter and tone generator.

 

So do you propose that electrical and acoustic crossover frequency are not the same?

 

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Deang, ever heard about a Zobel??

Hint...it is used to nullify the VC inductance when required.

If I remember, ALK used one of them in his Forte crossover , and other design.

On the other hand, in another one, he states that he utilizes this inductance as part of his filter.

 

It's there and cannot be ignored.

 

https://www.trueaudio.com/st_zobel.htm

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43 minutes ago, Danieln said:

So do you propose that electrical and acoustic crossover frequency are not the same?

 

No, they are not. 

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What’s a “zobel”?  Better explain it to me ...

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19 hours ago, Danieln said:

Mark, I consider the ALK crossover in high regard. 

Mine is inspired by his work. But as you noted, I slightly modified, simulated, constructed and measured the result. 

My hearing is not so good, so i will trust a good design methodology and measurement over my hears anyday :-)

 

I cannot stress enough that you need a constant impedance network with Single Ended Triode (SET) amplifiers or even more so with pentode (without feedback). The key is the damping factor, or say another way the amplifier output impedance. The worst offenders are the original Klipsch networks. The midrange is boosted by several DB without controlled impedance, but is flat with a constant impedance network. been there, done that!

 

Dan

 

 

The thing to watch with the ALKs when using with a very low power amp is how much power the swamping resistor consumes.

 

I have ALKs in my lascalas but have 60 watt KT-88 based mono blocks.

 

I have ALK ESNs on my Jubs.  But I have an MC-402 powering those.  :) 

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