Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multi-Way Conventional loudspeakers with crossovers

DC Bias in Crossovers (mostly Tweeters)
DC Bias in Crossovers (mostly Tweeters)
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 8th April 2009, 01:21 PM   #11
Joe Rasmussen is offline Joe Rasmussen  Australia
Sin Bin
 
Join Date: Jan 2003
Location: Sydney, Australia
Quote:
Originally posted by danieljw
hopefully get to it on the weekend. so busy at the moment !

is there anty thing to watch out for with tweeter and amp safety

i dont particulary want to damage my hiraga amp

-dan
Should be quite safe. Don't forget the 1K resistor. Make sure of your wiring and check with a DC meter, should read zero across the Tweeter and zero on the input to the crossover that interfaces with the amp.

Today connected my Elsinores up to a gainclone amp (SS) and no drama at all. Didn't expect any.

Joe R.
  Reply With Quote
Old 8th April 2009, 01:31 PM   #12
AndrewT is offline AndrewT  Scotland
R.I.P.
 
Join Date: Jul 2004
Location: Scottish Borders
Default electrolytic only?

does this polarising voltage apply to all capacitors? i.e. both polar (electrolytic) and non polar (metallised film/foil+film/PIO/mica)?
__________________
regards Andrew T.
  Reply With Quote
Old 8th April 2009, 02:02 PM   #13
Joe Rasmussen is offline Joe Rasmussen  Australia
Sin Bin
 
Join Date: Jan 2003
Location: Sydney, Australia
Default Re: electrolytic only?

It basically refers to all coupling capacitors of any type. But I would think primarily metalised film and some foil+film types. Occasionally you will still see non-polar electros and same applies.

Joe R.
  Reply With Quote
Old 8th April 2009, 02:20 PM   #14
woody is offline woody
diyAudio Member
 
Join Date: Jan 2002
Location: Tyrone Ga. U.S.A.
No electrolits benifit the most by being battery biased. If you look at the old article Picking Audio Capacitors by Walter Jung he has some test using biased elecrolits. I replaced the large cap in a solitstate amp the one that helps null the dc offset with a pair of battery biased caps and was rewarded with a LOT more clarity. I used a 500k resistor and a 9v battery.
  Reply With Quote
Old 8th April 2009, 11:09 PM   #15
mcmahon48 is offline mcmahon48  United States
diyAudio Member
 
Join Date: Aug 2008
Location: Orange California
Default capacitance balancing

I noticed an additional cap in 2nd order XO, so does this still equal the the capacitance value of the X0 in series and any specific ratio
  Reply With Quote
Old 9th April 2009, 03:24 AM   #16
Robh3606 is offline Robh3606  United States
diyAudio Member
 
Robh3606's Avatar
 
Join Date: Nov 2002
Location: Destiny
Hello Joe

Do you realize JBL has been doing this for years on their SOTA designs?? All my DIY networks are Charge Coupled only difference is they use a 2-3meg as the resistor value.


http://www.audioheritage.org/vbullet...ead.php?t=3555

Rob
  Reply With Quote
Old 9th April 2009, 06:59 AM   #17
Joe Rasmussen is offline Joe Rasmussen  Australia
Sin Bin
 
Join Date: Jan 2003
Location: Sydney, Australia
Quote:
Originally posted by woody
I replaced the large cap in a solitstate amp the one that helps null the dc offset with a pair of battery biased caps and was rewarded with a LOT more clarity. I used a 500k resistor and a 9v battery.
Sound like a good application to me. I think, and I am repeating myself, that the idea is to keep the 'attractive force' - phrase used by both Menno and also Paul Doods IMSMR - from reversing polarity. The moment the cap has to do that, the force is interrupted and has to reset again. The force remains the same even if the polarity has changed, but what happens at the moment it does reverse? The resetting of the plates and dialectric tension as well as potentially setting off mechanical resonances etc. So we should hear an improvement and, as you say and it's one of my favourite words, more clarity.

Quote:
Originally posted by Robh3606
Hello Joe

Do you realize JBL has been doing this for years on their SOTA designs?? All my DIY networks are Charge Coupled only difference is they use a 2-3meg as the resistor value.


http://www.audioheritage.org/vbullet...ead.php?t=3555

Rob
Hi Rob

Very well spotted. The R value just needs to be high and MOhm would do it too. Isn't it interesting they came up with a phrase that's saleable - "Charge-Coupled" - but any tech would call it just plain DC bias. No need to invent new when the old is still OK.

But is it 'crossover' distortion a la Class A vs Class B as they say? I suppose we could end up with a semantic discussion about that, but again it's just clever/good ad-speak. But I think we now have better ways of explaining what's going on - but they managed to get it right in execution, so that recognition is deserved. But Menno has now tackled the maths on this. I simply read hi paper and it occurred to me right there and then that this was the obvious thing to do. Others have to, but coming from a different point.

But why is it not more common? Maybe we can help it become so as this is the sort of edge and challenge DIY'ers love.

Joe R.
  Reply With Quote
Old 9th April 2009, 07:21 AM   #18
mcmahon48 is offline mcmahon48  United States
diyAudio Member
 
Join Date: Aug 2008
Location: Orange California
Default It is kind of simple idea

a capacitor is a bucket with water splashing back and forth and losing charge with each splash so just making sure that it is full when it has to splash in the forward direction, I am surprised some one has come up with using metal hydride and using redirected energy into a charging system in the network
  Reply With Quote
Old 9th April 2009, 11:58 AM   #19
john k... is offline john k...  United States
diyAudio Member
 
john k...'s Avatar
 
Join Date: Aug 2004
Location: US
"... capacitance is not a constant, it depends on the charge on the capacitor. Charging the capacitor will result in an attractive force [tension] acting on the conducting plates. As no material is infinitely stiff, this force will reduce the thickness of the dielectricum and thus increase the capacitance. The force is always attractive, reversing the polarity will result in the same attractive force [now in the opposite direction]. "

Joe,

I don't disagree with the statement as form the paper, but your edit is incorrect. The force does not change direction. That's not a big deal but let's look at the effects of bias. The force between two plates of a cap is proportional to q^2, the charge of the cap squared. If the cap is ideal except for the compression of the dielectric then when the a positive voltage, +V is applied the cap will have a charge of +q. When the voltage is -V, the charge will be -q. In both cases the force is of the same magnitude and direction such that it pulls the plates together. Since q = proportional to V, for V = sin(wt) then q^2 (thus F) goes like (sin(wt))^2 = (1 - cos(2wt))/2. Thus the force varies between 0 and 1 but varies at twice the frequency. This results in a perfectly symmetric system where the change in C is the same for a + or - swing in voltage about 0 volts. This symmetric system will have only odd order distortion. Now, if we apply a DC bias the voltage across the cap is V = sin(wt) + DC and since q^2 goes like V^2, and V^2 = (sin(wt))^2 + DC^2 + 2 DC sin(wt) = (1 - cos(2wT))/2 + DC^2 + 2DC sin(wt). This is a highly non-symmetric system and while I can see that it will introduce even order distortion I can not see how it would reduce odd order distortion, at least not by the argument that the capacitance changes due to the force pulling the plates together. The figure below shows the variation of the force between the plates of a parallel plate cap over one cycle, with and w/o bias. This does not include the effect of a resulting change in C, however, including it would only make the force more asymmetrical since if the capacitance increased as the force increased the charger would increase for a given voltage across the cap further increases the force. I know the application of a DC bias is used in this way, but I can't see a positive effect arising from the force argument.

Do you have the full reference to the AES paper? I'd like to take a look.

The arguments I have heard for biasing cap has centered on dielectric absorption, i.e the JBL argument, well part of it.

As an after though, if the DC bias were much, much greater than the AC signal magnitude, then the AC variation could be viewed as a small perturbation and in such a case greater linearity could be achieved. But we aren't talking abut high bias levels. But it would still depend on the elastic nature of the dielectric.

An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.
__________________
John k.... Music and Design NaO dsp Dipole Loudspeakers.
  Reply With Quote
Old 9th April 2009, 12:30 PM   #20
john k... is offline john k...  United States
diyAudio Member
 
john k...'s Avatar
 
Join Date: Aug 2004
Location: US
Thinking about this a little more, I failed to consider the properties of the gap between the plates. If the dielectric is elastic as a linear spring, then my previous post makes sense. However, if the gap can not be considered as a linear spring, but rather as a car suspension with bump stops, then an applied bias of sufficient magnitude can compress the plates against the bump stops and hole it there. But in this case the DC bias must be high enough so as to maintain the required minimum voltage across the cap so that the plates are against the bump stops. This means the bias must be sufficiently greater than the peak to peak voltage swing of the applied signal.
__________________
John k.... Music and Design NaO dsp Dipole Loudspeakers.
  Reply With Quote

Reply


DC Bias in Crossovers (mostly Tweeters)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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Using Batteries to Bias crossovers into Class A, how does it work? pjpoes Multi-Way 34 18th March 2018 07:51 PM
Stray hum pickup *preamp* cathode R-bias vs. battery bias & 12AU7vs.5687 awedio Tubes / Valves 2 19th April 2008 02:30 AM
Boston Acoustics Rally RC620 6.5" Woofer and tweeters and crossovers for sale NicolasGaal Swap Meet 0 31st December 2003 10:10 AM
Questions regarding piezo tweeters, crossovers Splork Multi-Way 7 6th December 2003 01:42 PM


New To Site? Need Help?

All times are GMT. The time now is 10:39 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki