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Old 14th August 2008, 11:18 AM   #271
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Is it correct that series connection increases inductance, and lessens amplifier damping?
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Old 14th August 2008, 03:05 PM   #272
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Quote:
Originally posted by john k...


Click the image to open in full size.


Obviously the magnitude of the problem this creates will depend on the complete crossover design, not just the Z of the HP network. And the impact will depend on the amp used to drive the load. In any event, as you note, it's not really a problem unless the impedance is low as well.

That is an interesting set of plots. I have a significant overlap and more than an octave below X freq (500 Hz in your above example). It is partly because I use 1st order and also use the lower passband of the tweeter to fill in the off axis of the midrange below the X freq. This is more likely to be in the 3-5KHz range, I aim to have the tweeter to contribute to as low as 1500 Hz in some cases. Add to the fact that I don't do Butterworth filter and I sum at -6dB rather than -3dB. This -60 degrees vs -45 degrees. So I am more exposed.

I admit it freely, I have chosen this millstone myself, so I am not blaming anybody. But it does mean I have to look for solutions accordingly. But 100% vector summing I am achieving and at -6dB helps keep the tweeter's Z a bit higher, so it is not too bad. I tolerate the neg phase angle if the Z is correspondingly high.

Quote:
Originally posted by john k...


I generally try to keep the impedance phase between +/- 30 degrees if possible, with an upper limit of +/-45. Still, I don't think impedance phase is a real problem because, for example, you could correct the phase, and make the impedance magnitrude of your speaker more uniform though the mid/tweeter x-o region by adding a conjugate network...

Click the image to open in full size.

Classic example you show. Let me comment on that.

I do use conjugates to help a flatter overall Z, being tube conscious, to reduce the amplitude response being modulated with tube amps that may be as high as 3 Ohm output Z.

But in my case, to suit my approach, I don't use conjugate networks in this instance when it comes to tweeters. Not that I am not saying that it may happen sometime in the future when a good reason might arise.

As your perfectly good example shows, conjugates lower/reduce the Z, they also do reduce neg phase because they draw positive current. The point I am making is that they add to the load and thus reduces Z. So the conjugate only really works beneficially when (if?) we have a high Z to play with and high Z and low phase angle coinciding at the same frequency is pretty OK already. The conjugate really neither helps nor make things worse, as I see it.

This is the rule I follow: It is where the two coincide, low Z (say four and lower) and significant neg phase angle (say well above -30) at the same frequency, this must be avoided (but conjugates are still an important tool). But coming back to the example where I used series 5" mids, it helps when they are a high 16 Ohm Z and you have that XT25 tweeter, that series element helped overcoming the XT25 by avoiding that coincidence. When phase was bad the combined Z was still above 8R. I could have use a conjugate but ended up with 4R? The improvement in the phase was offset, so no real gain. In other instances your suggestion would have to be considered.

Quote:
Originally posted by john k...


So this is really a problem resulting from the choice of tweeter.

Ain't that the truth! Let's say you have an XT25 and has DCR of 2.80R and 91-92dB sensitivity. Your system sensitivity is also 91-92dB. See the problem? Add to that the approach I have take, and it's easy to see that I wrestle with this. But an 8 Ohm tweeter, DCR 5.6R (double) and 93dB sensitivity (I can even add a bit of series R), Peerless 810921, makes the job a lot more comfortable.

As I say, I've made the problems for myself, but I stand by the results I've been consistently getting and also getting tube friendly speakers to boot.

Cheers.

Joe R.
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Old 14th August 2008, 06:38 PM   #273
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Quote:
Originally posted by Joe Rasmussen

That is an interesting set of plots. I have a significant overlap and more than an octave below X freq (500 Hz in your above example). It is partly because I use 1st order and also use the lower passband of the tweeter to fill in the off axis of the midrange below the X freq. This is more likely to be in the 3-5KHz range, I aim to have the tweeter to contribute to as low as 1500 Hz in some cases. Add to the fact that I don't do Butterworth filter and I sum at -6dB rather than -3dB. This -60 degrees vs -45 degrees. So I am more exposed.
I really don't know how to reply. You comment was catagorically that 1st order high pass filters were bad because they have negative (impedance) phase. My reply was that all high pass filters have negative impedance phase. It is not unique to 1st order HP filters. And I don't think it's is an issue at all. What matters is the impedance (mag and phase) of the complete speaker. The amp isn't driving the tweeter network alone.

Quote:

But in my case, to suit my approach, I don't use conjugate networks in this instance when it comes to tweeters. Not that I am not saying that it may happen sometime in the future when a good reason might arise.

As your perfectly good example shows, conjugates lower/reduce the Z, they also do reduce neg phase because they draw positive current. The point I am making is that they add to the load and thus reduces Z. So the conjugate only really works beneficially when (if?) we have a high Z to play with and high Z and low phase angle coinciding at the same frequency is pretty OK already. The conjugate really neither helps nor make things worse, as I see it.
Well that is the point. Large negative phase with higher mag Z or lower mag Z with better phase. Which does the amp prefer? I think the beneficial aspect of one vs the other is dependent on the amp used, at least if it's a tube amp.

Quote:

This is the rule I follow: It is where the two coincide, low Z (say four and lower) and significant neg phase angle (say well above -30) at the same frequency, this must be avoided (but conjugates are still an important tool).
Well we agree that the phase isn't too important is the mag of Z is also high. But what does all this have to do with first oder HP filters? If you look at the different HP filter types you will find that actually 1st order is the least offensive. That is, if you look at the point where the phase is -60 degrees for various order HP filters, the 1st order filter has the highest impedance magnitude when thephase is -60.

Quote:

As I say, I've made the problems for myself, but I stand by the results I've been consistently getting and also getting tube friendly speakers to boot.

Cheers.

Joe R.
I guess we might differ on what the definition of tube friendly is. You have a relatively efficient speaker, I guess that makes it low powered amp friendly, tubes or otherwise. But at the same time, looking at you impedance curve, consider how the speaker will react to amps with different output impedance. Consider Z out = 0.1 ohm and 3 ohms (you mentioned 3 ohms). with 0.1 = Zout, the speaker will perform basically the same with and w/o a conjugate network. But when Zout= 3 the speaker w/o the conjugate network would show a rise in the response centered around 3k of about 1.3 dB with Q = about 0.5 (relative to the midrange level).

I'm not trying to be critical here, but I think you might look at that conjugate network. I realize it will draw more current from the amp, but assuming the amp can handle it I think it would make the speaker more "tube friendly". The network I computed was a series LRC across the input terminals of the speaker with L = 0.25 mH, C = 10uf and R = 14 ohms. Assuming that impedance curve is representative of the real speaker, you should give it a try. It all really 6 of one to 1/2 dozen of the other.

I, on the other hand, am not a low power kind of guy.
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Old 14th August 2008, 11:03 PM   #274
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Quote:
Originally posted by john k...


I really don't know how to reply. You comment was categorically that 1st order high pass filters were bad because they have negative (impedance) phase. My reply was that all high pass filters have negative impedance phase. It is not unique to 1st order HP filters. And I don't think it's is an issue at all. What matters is the impedance (mag and phase) of the complete speaker. The amp isn't driving the tweeter network alone.

Fair enough, but I was trying to paint a scenario, high sensitivity, too many good tweeters that are usually low Z that gets fully exposed because of that etc. Under those circumstances - and maybe you have to be there to experience it. Perhaps my initial comment came across a little too sweeping?

Quote:

That is, if you look at the point where the phase is -60 degrees for various order HP filters, the 1st order filter has the highest impedance magnitude when thephase is -60.

That is right and I made that comment if you looked back.

> This [is] -60 degrees... But 100% vector summing I am achieving and at -6dB helps keep the tweeter's Z a bit higher, so it is not too bad.

Quote:

I, on the other hand, am not a low power kind of guy.

I kinda gather that.

And that explains a lot and any differences that we may appear to have. The amps we typically use are typically 30 Watts or less and the current amps we make/sell to clients are 18 Watt (Vacuum State DPA-300B @ $16,000 built and $10,000 kit).

http://www.vacuumstate.com/various/d...ure_lo-rez.pdf

And a much less expensive 20 Watt (JLTi EL34 @ $1600), also no negative feedback triode designs and hence quite high output Z.

www.customanalogue.com/jlti_el34.htm

Gotta keep the customers happy.

Joe R.
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Old 14th August 2008, 11:15 PM   #275
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Quote:
Originally posted by Joe Rasmussen


<snip>

And a much less expensive 20 Watt (JLTi EL34 @ $1600), also no negative feedback triode designs and hence quite high output Z.

www.customanalogue.com/jlti_el34.htm

Gotta keep the customers happy.

Joe R.

$18,000 for an 18 w tube amp? That's rarified air for sure! How many of those things do you sell? I must be in the wrong profession (medical manager/electrochemist).

I recall my 12 watt EICO space heater from 1958 cost ~ $79.95 as a kit... 12AX7's and all....

http://cgi.ebay.com/ws/eBayISAPI.dll...m=140256646237

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Old 15th August 2008, 02:07 AM   #276
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Quote:
Originally posted by auplater



$18,000 for an 18 w tube amp? That's rarified air for sure! How many of those things do you sell? I must be in the wrong profession (medical manager/electrochemist).

John L.
Consider buying the kit?

The amp is pretty much designed to compete against the Audionote Kondo, have you seen what the that sells for. It's only 8W/ch.

How many DPA-300B? Not sure, the kits of parts are collected in Switzerland (they would know) and sent out to assemblers who get the fee locally for assembling, or the end user can try, but in the words of Allen Wright, it takes a skilled person to assemble, ain't no Dynakit and you have to figure out a fair bit yourself. No line by line instructions.

I use a pair for myself that is a bit less expensive and not the same flash metalwork etc. Sorta no frills version. Being a co-developer I am permitted this latitude.

But the newer JLTi EL34 has a much wider market potential, takes advantage of low Chinese costs and about the same power. It too has some unconventionality built in.

Cheers.

Joe R.
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Old 23rd August 2008, 05:17 AM   #277
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Elsinore construction.. but not the conventional way. Thats coming up next!
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Old 23rd August 2008, 05:18 AM   #278
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Old 23rd August 2008, 05:20 AM   #279
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Old 23rd August 2008, 05:21 AM   #280
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