Multiway Impedance Load Question

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If you're reading this you are either confused regarding this issue too or know enough to advise or lastly fall into the third category: a unique brand of DIY sadist who preys on ignorant folks like myself to inflate their egos. I'll take anything I can get! Here's my problem: I have a 4 way open baffle. Wharfedale w15 15ohm LF crossed below 150hz. Goodmans Mid. Run full range 15ohm. Goodmans 2" tweeter 4ohms crossed at 6k. Lastly a realistic super tweeter crossed at 10k built in passive xover. Preamp is Dynaco pas2. Available amps: dynaco st70, Motorola el84 6bq5, topping tp20 mark 2, another chip amp 50w maybe smsl. I have a Sony active dividing network that can run 2way high and low, 3way and 4 way. I think it sound s best when I use it as a 2way low to isololate the LF. It has some bass boost features as well. Crossover points run: 150-2.5-3.5-4.5-6-8. I am having trouble summing my impedance to match the amps. I usually run the el84 to the mid and Low. I use the Topping for the Tweeter and super tweeter 8ohms. Does anyone see a better combination. I would prefer to do this whole mess passive as I think it might sound better. I have the coils and caps for the low end and usually use once cap for the tweeter. Sorry for the rambling post. Cheers.
 
Rockaway,

Sounds unnecessarily complicated.

However, if you are going to stick with those complications, grab XSim and simulate your various alternatives. Ideally you should measure the individual driver impedances and use that data in XSim for perfect accuracy.

You can use something like SPL Copy to copy impedance data from spec sheets. This won't be 100% accurate as the enclosure and baffle affect it, but it should give you a very good idea of your minimums.

Best,


Erik
 
Rockaway,

The problem is that your question is complicated. :) If this was a simple set of questions, it would be easy to go with a simple answer. However, since all of your options are pretty complex, it's best you have a tool that can deal with the complications.

XSim will allow you to simulate the driver and crossover components so you can see the final impedance plot of each of the sections you might put together, giving you the most accurate answer.

Best,


Erik
 
I have a 4 way open baffle. Wharfedale w15 15ohm LF crossed below 150hz.
Goodmans Mid. Run full range 15ohm. Goodmans 2" tweeter 4ohms crossed at 6k.
Lastly a realistic super tweeter crossed at 10k built in passive xover.

Is this Wharfedale W15 an RS version that used to be built in Airdale?
If I were you, I'd first try a 3 way without the midrange unit, passive or
active, whatever at hands. Cross the 2" tweeter low, probably around 800 Hz
and the super tweeter in the 5kHz region. Have you got any measured TS
parameters of W15? Dynaco looks best to me for the passive application
of the speakers.

p.s.Gotta run back or nurse Ratched is gonna kill me! What category do I fall in?:D
 
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I have used online impedance calculators but i have read that they are unreliable. I gather that the software you recommended is better.
Absolutely it is.

What is your question? With a voltage amp, ie one with a minimal output impedance the main concern is probably with the performance of the amp..current limits, distortion and stability.. although none of these would be an issue if the amp were ideal. None are of course. Sometimes you can treat the ratings as guidelines, it's amp dependent. What are you trying to do?

The valve amps might have a less insignificant output impedance which of course may impose an effect on the response based on the 'signature' of the impedance. Some amps may also not perform as well into a reactive load.

You can apply Zobel compensation of a load to make it appear resistive. Typically with passive components this means RLC filters at a crossover or other peak (sometimes two, ie where the peak isn't symmetrical), and RC to deal with a rising impedance with frequency although it depends on what you have to work with, and you would typically bring the impedance down to flat to meet the lowest existing magnitude.
 
It is the W15RS. I find it too boomy above 200hz. It may be a mechanical compliance issue given its age. Also I would suspect it to function better in a large sealed cabinet like the Airdale. Mine are in a folded baffle. I really want to keep this a mostly full range driver with helpers. The Super tweeter could be sacrificed. I was shocked at how much better the tube amp sounded compared to the chip amps. The chips do detail well but suffer in the punch and drama department. I use them because I thought they had more flexibility in terms of matching impedance (specifically the 4ohm tweeter) where the tube amp would need to be closer to spec. I am assuming that the el84 was set up with an 8ohm tap. It came from a console and was converted by the person I bought it from. Can this be done with a parallel/series passive configuration? If not, where can I divide with the active xover and use passive components for the other cover points?
 
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You can use any combination of active and passive crossover, including adding passive components within the amp and whatever you can think of.

If the impedance isn't flat with frequency, the finite output impedance of an amp can change the frequency response as heard. This may be representing a lot of what you are hearing as a difference between amps, and the tap you choose affects this influence.
 
That explains a lot. I have been running in circles for about a year with this setup playing audio Whacka-a-Mole. ( a game where you hit a mole on the head and another one pops up from a different hole. No moles are injured, just fake moles) The impedance issue makes sense and may explain what's been going on. I know that Roger Russel and others believe that all amps sound good if used within their parameters. I am hearing pretty distinct differences not entirely bad but different.
 
Maybe it would be more productive to design a fully passive
loudspeaker using a wealth of information available here, then
flatten impedance to make it more tube amp friendly and
drive it with the best and most powerful tube gear you have.

A lot of work, but I'm confident it would have payed off.
 
I agree. That's was my intention when I started the thread. Sorry if that wasn't clear. One thing is clear, however, I will have to figure out a way to plot impedance curves. I thought I had gotten sophisticated when I got a multimeter to check the dcr of my drivers and check the capacitance and inductance values of my crossovers! These speakers are loosely based on the Lampizator Open Baffles. I will go back and see how he powers his 4 driver beasts.
 
I thought I had gotten sophisticated when I got a multimeter to
check the dcr of my drivers and check the capacitance and inductance
values of my crossovers!

It's a start. Check this free measurement suite and if it's not too much,
learn to use it so you can make modifications that will mean a night to
day difference. Once measurements properly executed, can be loaded
to a simulator for trying out different XO filters. You will find many
threads covering free simulation programs.

ARTA Download
 
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