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#390170 - 02/25/13 12:54 PM Re: Customizing Axiom M80's(audio jewelry) [Re: Mad_Chesser]
Socketman Online   content
connoisseur

Registered: 07/12/09
Posts: 1154
Loc: Whitehorse YT
Fred i dont think he wants to alter the impedence. Impedance is the sum of all connected parts. If only the tweeter's ,mids and associated crossover parts are seperated from the woofers ,the overall impedance seen by the amplifier would change.If someone was to run 2 wires from the same amp ,the impedance seen by the amp would remain unchanged. I will run some impedance sweeps on my M80's tonite and see what the difference is.



As can be seen here,takeing out the bridgeing would result in two seperate crossovers.


Edited by Socketman (02/25/13 12:56 PM)
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#390190 - 02/25/13 06:37 PM Re: Customizing Axiom M80's(audio jewelry) [Re: Socketman]
Mikesk Offline
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Registered: 02/14/13
Posts: 18
Originally Posted By: Socketman
Fred i dont think he wants to alter the impedence. Impedance is the sum of all connected parts. If only the tweeter's ,mids and associated crossover parts are seperated from the woofers ,the overall impedance seen by the amplifier would change.If someone was to run 2 wires from the same amp ,the impedance seen by the amp would remain unchanged. I will run some impedance sweeps on my M80's tonite and see what the difference is.



As can be seen here,takeing out the bridgeing would result in two seperate crossovers.

Yes this is what I am getting at.

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#390196 - 02/25/13 09:20 PM Re: Customizing Axiom M80's(audio jewelry) [Re: Mad_Chesser]
Socketman Online   content
connoisseur

Registered: 07/12/09
Posts: 1154
Loc: Whitehorse YT
Go HERE and read what Kal Rubinson has to say. He basically says no , impedance should not change. I plan to run some impedance sweeps on my M80's hopefully tonight depending on whether I can get near them. Kids watching tv atm.
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#390201 - 02/25/13 10:05 PM Re: Customizing Axiom M80's(audio jewelry) [Re: Mikesk]
JohnK Online   content
shareholder in the making

Registered: 05/11/02
Posts: 10360
Mike, I thought that my brief previous reply was adequate to point out the principles involved, but I'll go into greater detail to help out more. Yes, as you question, the impedance is partly the result of the crossover circuitry, not the impedance or number of the individual drivers alone. When loads(such as speaker drivers)are connected in parallel the combined impedance is such that its reciprocal is equal to the sum of the reciprocals of the impedances of the individual drivers. So, if an 8 ohm mid-woofer and and an 8 ohm tweeter were simply connected in parallel without intervening crossover circuitry, the combined impedance would in fact be 1/X=1/8+1/8, 1/X=2/8, 2X=8, X=4(ohms). The crossover circuitry changes this, however. For example, on a bass frequency the impedance of the low frequency section of the crossover would be 8 ohms, but the capacitor and other components in the high frequency section would make the impedance the amplifier "sees" there for bass frequencies far higher than 8 ohms. For a relatively simple calculation, say that the impedance of the high frequency crossover section on the bass note is 160 rather than 8 ohms. The resultant combined impedance would be 1/X=1/8+1/160, 1/X=21/160, 21X=160, X=7.6(ohms). The point therefore is that a 4 ohm speaker impedance isn't the result of two 8 ohm drivers connected in parallel.


The other point previously mentioned is that the high and low frequency sections of the crossover are always separate. They have to be or they couldn't send the separate frequency ranges to the low and high frequency drivers. This is the case regardless of whether the speaker inputs are single or dual, or if dual, regardless of whether the connecting link is or isn't removed. As was pointed out previously the only difference(when removed)is that the wiring separates at the receiver output rather than inside the enclosure.
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#390208 - 02/25/13 11:39 PM Re: Customizing Axiom M80's(audio jewelry) [Re: Mad_Chesser]
Socketman Online   content
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Registered: 07/12/09
Posts: 1154
Loc: Whitehorse YT
John, I will admit I don't know all the fancy formula's since I hold no electronics degree of any sort, though I do mess around a bit building speakers and crossovers. I purchased a Dayton Audio test system, with this, I can take many measurements of raw drivers etc. It also allows me to take an impedance frequency sweep . I took 3 different sweeps, one of the tweeter/mids, one of the woofers and another of all the drivers. I include a screen shot of all three purely for reference purposes.









Sorry you may have to save the pic and open it with paint. Its a screen capture.

It seems clear to me that 2 separate amplifiers will each see an entirely different impedance when bi-amped (bars removed) than will be seen by a single amp (jumper bar in) .
None of this really matters imho since bi-amping or bi-wireing passively is for all intents and purposes of no use.
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#390249 - 02/26/13 05:59 PM Re: Customizing Axiom M80's(audio jewelry) [Re: Mad_Chesser]
dakkon Online   content
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Registered: 02/08/04
Posts: 1842
john, the load would not be a constat 8ohms. you are using dc equations to explain an AC circuit... your freely interchanging resistance and impedance. resistance is a term used to explain DC circuits, impedance is used for AC circuits. the impedance will change, as it is a function of frequency within a curcuit. this is the whole reason mafacturers publish impedance graphs, to show the impedance across a range of frequencies.. the "nominal" or reported impedance is what the resistance is at a constant voltage. as the frequency changes, the voltage changes, both in volts and in vectors.. it becomes a 3 dimentional eqn, where the equns your using are 2d eqns that are used for DC circuit analysis....

i'm on my phone, so i am not going to google ac voltage eqns... Also, please forgive any typos, as i'm on my phone... smile

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#390253 - 02/26/13 08:27 PM Re: Customizing Axiom M80's(audio jewelry) [Re: Mad_Chesser]
Socketman Online   content
connoisseur

Registered: 07/12/09
Posts: 1154
Loc: Whitehorse YT

I found a better way of displaying my graph's for anyone who is interested.






The bottom graph is Axiom's impedance curve and it is virtually identical to the impedance graph that I generated.
Once the jumpers were removed from the speakers, I measured the impedance of the tweeter/mids and the woofers. The impedance changed dramatically once the the crossover was separated.

Sunfire amps have some interesting feature's for bi-amping. They allow you to bi-amp using either current or voltage depending on speakers and configuration. Using one of their 7 channel amps you can run it 5 channel and use the extra 2 channel to bi-amp. Each amp channel has 2 inputs so you can jump one amp channel to another with a simple patch cord.

Cary Audio has some interesting insight to bi-amping as well.
_________________________
DOG is GOD spelled backwards.
I blame my terseness on my keyboard. smile

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#390255 - 02/26/13 08:44 PM Re: Customizing Axiom M80's(audio jewelry) [Re: Socketman]
Mad_Chesser Offline
veteran

Registered: 01/11/13
Posts: 195
Loc: B.C., Canada
Quote:
the impedance changed dramatically once the the crossover was separated.


So from a technical standpoint it makes a difference?

There seems to be quite a split group on this.

My dad has Cerwin Vega XLS 215's and his Pioneer Elite 57 has a biamp/bi wire configuration. I believe you hook one speaker wire into the front main and another into the front height on the back of the amp. Then he has to go into the amp's menu and switch it to "biamp/biwire" mode. You can hear something in the amp click over.

I haven't had a chance to directly compare, but he swears there is a difference, but only at very high levels. My dad and me like to sometimes partake in hearing damage levels. lol Again, he says it's only noticeable at those very high levels.

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#390257 - 02/26/13 09:11 PM Re: Customizing Axiom M80's(audio jewelry) [Re: Mad_Chesser]
Socketman Online   content
connoisseur

Registered: 07/12/09
Posts: 1154
Loc: Whitehorse YT
Lots of opinions all over the net, some pooh pooh it while other praise it. I suggest you read the article linked at carey audio, it very informative then you can form your own opinion and decide if it is something worth trying. I don't have the coin to try it though I may do so one day since the M80's have the feature. A 7 channel sunfire amp is 3500 so that's a no go lol. Maybe another Emo 2 channel .

Still with using a powered sub to do the heavy lifting I am on the fence whether it would be beneficial.

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#390261 - 02/26/13 10:07 PM Re: Customizing Axiom M80's(audio jewelry) [Re: dakkon]
JohnK Online   content
shareholder in the making

Registered: 05/11/02
Posts: 10360
Alex, the point wasn't that the impedance would be a constant 8 ohms. A previous post appeared to suggest that a 4 ohm speaker was the result of two 8 ohm drivers connected in parallel, and that separating the wires in the manner described would increase the speaker impedance substantially above 4 ohms. It's certainly recognized that impedance isn't a constant and varies widely with frequency.

The purpose of the simplified calculations was to show the effect of the crossover circuitry on the impedance. The formula used is the basic one for calculating impedances in parallel. An 8 ohm impedance(without the crossover effect)for both drivers was selected for convenience and familiarity, not because it was a fixed value. The well-known effect of the crossover circuitry to increase the "seen" impedance of the driver not playing the particular frequency by a very large amount results in the speaker impedance(at that particular test frequency)being just slightly lower, not cut in half(two 8 ohm drivers forming a 4 ohm speaker).
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