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Old 4th January 2003, 03:25 AM   #1
Ilianh is offline Ilianh  Canada
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Default crossover network impedance question

Ok, I aquired this panasonic 5.1 amp, it sais that speakers that are 6 to 8 ohm only should be used.

The speakers i wanna use with it are kindof special, they have a 4 ohm woofer, a 6 ohm mid and a 8 ohm tweeter to match their sensibility.

So that means that at 0 to 200 hz, the speaker impedance will be 4 ohm, from 200hz to 2000hz 6 ohm and from 2000hz and +, 8 ohm.

Evrything is second order too.

Could that cause problems to the amp? Its a class H, and i'd guess they use premade ic's like stk's, and those have like tons of protections..

Any ideas on this one?
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Old 4th January 2003, 07:28 AM   #2
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Default Re: crossover network impedance question

Quote:
Originally posted by Ilianh
I aquired this panasonic 5.1 amp, it sais that speakers that are 6 to 8 ohm only should be used.
This is one way of saying that the amp has limited capability of providing the current needed to drive lower impedances -- the power supply has been skimped on to get the price down.

It could well have some significant problems driving your 4 ohm woofers.

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Old 4th January 2003, 09:11 AM   #3
Ilianh is offline Ilianh  Canada
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oh well.. that greatly sucks...
ok... so what i'd do is... hum...
add a 2 ohm resistor to the woofer, the mid and the tweeter?

I dont see how a too high impedance (the amp is 6ohms to 8ohms and if i add a 2 ohm to the tweeter is gets 10ohms) could do something to the amp unless its a tube amp, but its not...

but that still sucks... bah...

think it'll work?
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Old 4th January 2003, 09:46 AM   #4
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Quote:
Originally posted by Ilianh
add a 2 ohm resistor to the woofer, the mid and the tweeter?
Not a good idea. Have you actually tried the amp out with your speakers? Are you using all 5 channels of the amp? Are the speakers your own DIY?

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Old 4th January 2003, 06:35 PM   #5
Ilianh is offline Ilianh  Canada
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Quote:
Have you actually tried the amp out with your speakers?
not yet.. im still trying to figure out what to do


Quote:
Are the speakers your own DIY?
yhea.. my own diy


So here comes a question.
On a crossover network, lets say a 3 way, when you have a frequecy that in the LP section, its the woofer's impedance, when its in the BP section, its the mids impedance, and when its in the HP section, its the tweeters impedance.

But audio isnt only one frequency at a time, its alot of frequensies at the same time, and if you have mids, bass and highs, your total speaker impedance (if evrything is 8 ohm) goes down to like 2.67 ohm.

Ive seen comercial speakers having a "3 way" crossover thats simply 2 caps, one for the mid, one for the tweeter and the woofer is left to his natural rolloff, they are all 8 ohm drivers. and the speaker sais its 8 ohm on a sticker in the back. same thing here, its basicly never 8 ohm, its almost always under that...

The speakers I made have an external crossover so I can change stuff on it and make tests easily.
For now its a second order LP, a first order BP and a second order HP. I wanted to try simple a cap on the mid, to see whats his natural rolloff and how does it perform.

So, all this may sound stupid but its one of those things that bugs me off...
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Old 4th January 2003, 07:08 PM   #6
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Okay, just for the heck of it, can you give us details on your woofer, the Thiele-Small parameters, which sized box, ported or sealed, and tuned to what frequency using which sized port?

I want to run your speaker in Subwoofer Simulator, a freeware program, (written by F4ier, a member here), which gives impedance curves when it has that information.

Also, can you give us details of your crossover from woofer to mid?

Some 4 ohm speakers end up having fairly high impedances. If you are near 6 ohms anyway, who knows, maybe you can pass.
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Old 4th January 2003, 07:30 PM   #7
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Quote:
Originally posted by Ilianh
So here comes a question.
On a crossover network, lets say a 3 way, when you have a frequecy that in the LP section, its the woofer's impedance, when its in the BP section, its the mids impedance, and when its in the HP section, its the tweeters impedance.

But audio isnt only one frequency at a time, its alot of frequensies at the same time, and if you have mids, bass and highs, your total speaker impedance (if evrything is 8 ohm) goes down to like 2.67 ohm.
You only need worry about the lower impedance in the woofer section. Because of various factors, but mostly because of the XO, the other speakers have very high impedances out of their band and don't significanly impact the impedance of the in-band speaker.

get that info to kelticwizard and he will curn out some pictures with MUCH more meaning than the simple 1 dimensional nominal impedance number.

dave
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Old 4th January 2003, 07:32 PM   #8
Ilianh is offline Ilianh  Canada
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ok, well its in a 1.771 cu ft box tuned at 31 hz.

thats the woofer part, its separated form the mid and tweeter part.

the crossover is a second order LP at 200 hz fx.
and the mid has a simple first order BP from 200 hz to 2000 hz

heres the woofer tiele-small params
Attached Images
File Type: jpg woofer 8inch specs.jpg (37.6 KB, 400 views)
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Old 4th January 2003, 08:12 PM   #9
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Quote:
Originally posted by Ilianh
heres the woofer tiele-small params
Re= 4 ohms would imply a nominal impedance of 6-8 ohms.

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Old 4th January 2003, 08:24 PM   #10
Ilianh is offline Ilianh  Canada
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The Re I measure now gives me around 3.8 ohm.
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