Amplifier's impedance effect on XO - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 29th December 2006, 09:28 PM   #1
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
Default Amplifier's impedance effect on XO

I have been playing around with some series and paralell crossovers... However in order not to inadvertantly blow my power amp (as I switched wires and caps around) I installed an 8 ohm resistor in series with the amp's ouputs.

What now I am unsure of, and has not been covered in the readings i have done on the forum is the effect of amplifier output impedance on the XO or even the XO point/freq.

In this case the crossover see's the amplifier having an OP imp. of around 8 ohms.... since the circuit (amp + crossover + tweeter) has an 8 ohm in series with the crossover... I cannot but think it affects the XO point.

There is no resistance once the crossover circuit begins (to eliminate L-Pad type variables in the response I am looking for).

What about tube amps?

What do you guys think?
  Reply With Quote
Old 30th December 2006, 12:24 AM   #2
Davey is offline Davey  United States
diyAudio Member
 
Join Date: Dec 2001
Location: Bremerton, WA.
8 ohms is a significant amplifier output impedance. It will most likely skew the transfer functions of your crossover by quite a bit and also add a significant insertion loss. Any crossover design that you might perform with this resistor in place would be invalid.

Cheers,

Davey.
  Reply With Quote
Old 30th December 2006, 12:37 AM   #3
diyAudio Member
 
Join Date: Apr 2004
Location: 12km off the alaska highway in northern BC
http://sound.westhost.com/biamp-vs-passive.htm


did you read this re actual value of amp. impedance as seen from the speaker/xover system?
  Reply With Quote
Old 30th December 2006, 02:40 AM   #4
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
Quote:
Originally posted by Davey
8 ohms is a significant amplifier output impedance. It will most likely skew the transfer functions of your crossover by quite a bit and also add a significant insertion loss. Any crossover design that you might perform with this resistor in place would be invalid.

Cheers,

Davey.
Thanks... how can I factor the XO point or calculate it based on the 8 ohm series resistor. As far as insertion loss, let's disregard that for now...

so lets say a simple 1st order cap HF crossover for a 8 ohm driver at 3kHz is for example 2.2uF, then how will a resistor afftect the XO point (and maybe phase) if placed:

1) Inside the cap/driver loop (this is ez... the Xo will be 1.5kz with about 3db loss) but what about the following.
2) Outside the cap/driver loop.
  Reply With Quote
Old 30th December 2006, 02:53 AM   #5
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
Quote:
Originally posted by audio-kraut
http://sound.westhost.com/biamp-vs-passive.htm


did you read this re actual value of amp. impedance as seen from the speaker/xover system?

Nice read, though does not answer te question (unless you want to rid me of using passive networks altogether.
  Reply With Quote
Old 30th December 2006, 05:13 AM   #6
diyAudio Member
 
Join Date: Apr 2004
Location: 12km off the alaska highway in northern BC
Quote:
unless you want to rid me of using passive networks altogether.
one can always try, can't one

I like active....
  Reply With Quote
Old 30th December 2006, 05:18 AM   #7
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
Well so did I... till I got audible noise and hum in my system by inserting it in. i have behringer CX-3400.
  Reply With Quote
Old 30th December 2006, 05:23 AM   #8
diyAudio Moderator Emeritus
 
roddyama's Avatar
 
Join Date: Jan 2002
Location: Michigan
If you assume the output impedance of the amp is very low and purely resistive, the series resistance will just be a frequency independent voltage drop. However, as the output impedence increases, and if there is capacitance and/or inductance in the output, it will become more frequency dependent and began to have an affect on the crossover.
__________________
Rodd Yamashita
  Reply With Quote
Old 30th December 2006, 05:26 AM   #9
K-amps is offline K-amps  United States
diyAudio Member
 
K-amps's Avatar
 
Join Date: Nov 2003
Location: Indiana
Quote:
Originally posted by roddyama
If you assume the output impedance of the amp is very low and purely resistive, the series resistance will just be a frequency independent voltage drop. However, as the output impedence increases, and if there is capacitance and/or inductance in the output, it will become more frequency dependent and began to have an affect on the crossover.

Thanks.

Will the affect only be attenuation at that freq? Or will it affect the XO point, thats all I need to know, Will it change the XO frequency?
  Reply With Quote
Old 30th December 2006, 05:30 AM   #10
diyAudio Member
 
Join Date: Apr 2004
Location: 12km off the alaska highway in northern BC
Never had a problem this way. Started with a marchand xover, wenr from there all digital to behringer deq/dcx. Total quiet when no signal.
Never had a hum in active - I ran both three and two way fully active. Neither in analog, nor in digital.
The only problem is the crackling that a few dcx can exhibit - see the thread at diy.


To stick with your question - looking from amp to speaker, the network sees the speaker impedance. The amp impedance does not play a role being below 1 ohm anyawy (maybe not with tubes)

The impedance that the speaker sees through the network towards the amp only influences the back emf, that now can flow towards the amp, no damping factor stopping it.

But from what I can see, that does do nothing to influence the xover point.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Effect of amplifier slew rate on planars..... ashok Planars & Exotics 4 8th March 2008 12:43 AM
Effect of tweeters on ohm impedance? Flyin11 Car Audio 3 28th February 2008 05:46 AM
Effect pedals vs amplifier EQ. moo Instruments and Amps 4 26th November 2007 03:01 AM
Tweeter impedance and crossover effect - Wharfedale Evo 30 lastig Multi-Way 1 29th January 2007 01:54 PM
Shunt Feedback - effect on input impedance gingertube Tubes / Valves 12 6th December 2004 11:04 AM


New To Site? Need Help?

All times are GMT. The time now is 09:15 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2