# 6 ohm vs 8 ohm in crossover.



## aceinc (Oct 24, 2006)

I was about to buy some parts to build an inexpensive HT (5) speaker system. Being lazy, and unskilled in the design and construction of crossovers, and not wanting to pay a substantial amount to have someone design and build my crossovers, I thought I'd buy some prebuilt from PE. The bass and mid speakers are fairly wide range, the tweeters need to crossover above 3.5khz.

This is a 3 way system that will use multiple drivers in each section, the Bass and Mid section should each net 8 ohms using a series/parallel configuration, but the tweeter section will net 6 ohms. My question is, how will this affect the crossover frequencies? The xover's freq's are 500 & 4khz.

Paul


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## aceinc (Oct 24, 2006)

I have done a little research, and it appears that if the capacitor value in a Linkwitz Riley 2nd order xover stays the same, and the impedance goes down, the xover frequency goes up. 

I have found calculators tha allow you put in the impedance, and xover freq, and it will provide the values for the caps and coils, but what I really need is a calculator that will allow me to put in the cap impedance & coil values, and have it tell me what the xover would look like.

If anyone knows of such a program please let me know.

Paul


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## kano32 (Sep 14, 2006)

Check out this site. It has alot of free programs, maybe you'll find something to help.

http://www.pvconsultants.com/audio/frdgroup.htm


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## aceinc (Oct 24, 2006)

Thanks for the link...

The folks at PE have L-Pads that they say will make the drivers appear 8 ohms to the xover, so even though the load is 6 ohms, once it goes through the L-Pad it will present an 8 ohm load to the xover.

Unfortunately my understanding of electronics is limited, and I do not know if this is possible, but if the folks at PE says it's so, it must be.

Has anybody used the PE 260-154?

If so how did it work out?

Paul


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## BoomieMCT (Dec 11, 2006)

aceinc said:


> Thanks for the link...
> 
> The folks at PE have L-Pads that they say will make the drivers appear 8 ohms to the xover, so even though the load is 6 ohms, once it goes through the L-Pad it will present an 8 ohm load to the xover.


Really? I thought the L-pads were designed to maintain an 8ohm load while varying the attenuation, not produce one from a 6 ohm load. I'll have to do some testing!


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## aceinc (Oct 24, 2006)

This is a copy of part of an on-line conversation I had with a PE technician named Chris about PE part # 260-235;

===========================================
Paul: 
OK, I am looking at a 3-way design, and the tweeter section is 6 ohms, the mid 8 ohms, and the bass is 8 ohms. How will this affect tha L-Pad & vice versa? 

Chris: 
it will show an 8 ohm load across the board 

Paul: 
Irrespective of the speaker load? 

Chris: 
the 6 ohm is not going to affect it enough to make a difference 

Paul: 
In designing the xover, should I use a 6ohm load for the xover, or an 8 ohm load? 

Chris: 
8 ohm 
===========================================

So now you know from where I get my information.

Paul


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## BoomieMCT (Dec 11, 2006)

:scratchhead:


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## JCD (Apr 20, 2006)

Let me preface this with "I have no actual crossover design experience", so please take the following accordingly..

Crossovers are far more than assembling caps and inductors and resistors -- you also have to take into account the electrical properties of the drivers themselve, certan nodes you need to flatten out, etc. Getting a crossover right for a 2-way system is difficult and subject to much experimentation. Jumping to a 3-way system is exponentially harder. Granted, the crossovers will work in that one driver will stop working at some point while another starts, but the end sonic result is likely not going to be optimum.

I wish it wasn't so hard, because I'd be doing the same thing, but everything I've read leads me to the same conclusion: designing an effective crossover is almost as much black magic as it is science.

Given that, that's why I usually recommend kits for folks getting into DIY (myself included). There are several kits out there that are inexpensive and already have a pre-designed crossover.

JCD


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## BoomieMCT (Dec 11, 2006)

I guess I'm kind of confused as to how a variable L-pad made to preserve an 8 ohm load can present a 6 ohm load as 8 with the same topology. Here is an example say you wanted to cut a driver by 6 dB. 

If you had a 8 ohm driver and wanted to keep the load at 8 ohms you would use a 4 ohm resistor in series and an 8 ohm resistor in parallel. If you had a 6 ohm driver and you wanted to present an 8 ohm load (with the same attenuation) you would use a 4.5 ohm and 8.2 ohm resistors. 

I guess they are close but still . . . .


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## aceinc (Oct 24, 2006)

Confusing is one word for it

Paul


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