Qu re: Tweeter LCR resonance compensation - Page 4 - 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 28th December 2012, 12:00 AM   #31
diyAudio Member
 
Moondog55's Avatar
 
Join Date: Jun 2007
Location: Norlane; Geelong: Victoria: Australia
Are you therefore saying that the DCR of the shunt coil is almost irrelevant?
__________________
QUOTE" The more I know, the more I know, I know (insert maniacal laugh >here<) NOTHING"
  Reply With Quote
Old 28th December 2012, 12:29 AM   #32
diyAudio Member
 
Join Date: Jan 2008
IF it is across a voltage source.....
  Reply With Quote
Old 28th December 2012, 12:37 AM   #33
diyAudio Member
 
john k...'s Avatar
 
Join Date: Aug 2004
Location: US
Quote:
Originally Posted by Moondog55 View Post
Are you therefore saying that the DCR of the shunt coil is almost irrelevant?
No. It has an effect on the shape of the transfer function (TF) created by the passive elements up stream and in that regard affects the system damping.

The original issues was whether or not the LRC affects excursion. The answer is that its presence alone does not. It affects the impedance the remainder of the filter net work sees, just as a simple parallel resistor across the driver affects the impedance the network sees, and in that regard it affects the TF which is what controls excursion.

You really need to get away from the idea that the LRC is something special. It's just more elements in the crossover filter and as such it represents 3 more degrees of freedom (three more things which can be adjusted) to get the response to match some desired target.
__________________
John k.... Music and Design NaO Dipole Loudspeakers.
  Reply With Quote
Old 28th December 2012, 12:47 AM   #34
diyAudio Member
 
Moondog55's Avatar
 
Join Date: Jun 2007
Location: Norlane; Geelong: Victoria: Australia
Much clearer now John.
I was very interested as I have never used any conjugate circuits apart from the occasional Zobel.
As a beginner it has always been easier to use drivers that work with simple cross-overs and I still consider myself a beginner.
Interested in where the trade-off lies tho, as using coils with a higher DCR is one area where money could be saved to spend elsewhere in the system where better components may have a greater effect.
Thanx again mate.
__________________
QUOTE" The more I know, the more I know, I know (insert maniacal laugh >here<) NOTHING"
  Reply With Quote
Old 28th December 2012, 12:52 AM   #35
AllenB is offline AllenB  Australia
diyAudio Member
 
Join Date: Oct 2008
The original quote is surely ambiguous.. the context is unclear and left to the reader to guess. Sure, if someone were to try to read it literally they'd probably end up OK but none the wiser. I tend to view this kind of spiel as a 'serving suggestion'.

I'd like to add yet another (effective if not over the top) way of looking at this issue. If you might imagine the driver's impedance as being a component(s) on its own, and the diaphragm as watching it (from afar) and moving according to the signal that it sees across that impedance component.

Of course the driver impedance will affect the Q of the filter (at least), and therefore affect the voice coil voltage. Following on, the diaphragm reacts to this as it sees it and the result is that with any modification to the impedance the diaphragm response will change also. By just putting, however, a signal into the amp and measuring the driver with a mic you wouldn't know where the change came from, in fact you could have modified the driver mechanically and left out the crossover and achieved the same end result.

The driver needn't be behaving any differently, as with our example. It is being driven at such a relative level (and phase) from the crossover as to appear to fake it so to speak.. ie at any given frequency, the diaphragm would be responding to the way it's being driven, just as it always did. It's only when you plot the response that the result becomes obvious.
  Reply With Quote
Old 28th December 2012, 06:29 AM   #36
diyAudio Member
 
wolf_teeth's Avatar
 
Join Date: Mar 2006
Location: Indiana
Blog Entries: 1
Wintermute- the reason your response did not change with the sim of with/without, is that it requires a voltage divider to become effective. If you place a series coil or cap before this LCR shunt, you will see the difference in simulation.

I agree that which JohnK has stated to be true in that there are multitudes of ways to get to a desired target, and lots of filter options can get the same results with differing components. All are means to an end.

(Now- speaking likely as my mind works here....)

The rising impedance of the rolloff using a parallel xover provides the voltage divider for this LCR-shunt to become effective. That's understood.

Given that- a design without an LCR compared to one with one utilizing a shallow slope as stated prior, you can see how it helps the impulse response in some cases, without going higher order in terms of slope.

Now- think in terms of damping... The LCR with HP suppresses the impedance peak to (if done properly and compensated fully) virtually a resistive load. Being that the Fs is the most easily excited frequency of a driver and that which causes the most Xmax with the least input voltage, reducing or shorting out this frequency area damps the Fs electrically, by attenuating/shorting the voltage to the driver at this point in the audible spectra.

An example- The XT25 is herendous for buzzing if not using a steep enough slope, or an LCR to damp the non-F/F driver at Fs. The Zmax at Fs is something around 25-30 ohms, and can buzz while causing a dip in the woofers' response if not corrected.

If the xover is not used- the XT will buzz.
If the xover is used- many ways will keep the driver from buzzing.
Does the XT25 buzz with the xover- not if the xover is adequate is what John is saying, no matter how it got there.
Does it have to have an LCR? sometimes yes, sometimes no.

Given that- an LCR is not the sole reason the Xmax is reduced to where the XT will not buzz.

It's almost a chicken or the egg argument depending on your viewing angle.
Later,
Wolf
__________________
Photobucket picture pages: http://photobucket.com/Wolf-Speakers_and_more
Writeups/thoughts/blogs: http://techtalk.parts-express.com/blog.php?u=4102
  Reply With Quote
Old 28th December 2012, 08:12 AM   #37
just another
diyAudio Moderator
 
wintermute's Avatar
 
Join Date: Aug 2003
Location: Sydney
Blog Entries: 22
Thanks wolf, I just did a sim with the same tweeter (morel DMS37) and just a series 3.3uf cap, with and without an LCR filter. This tweeter doesn't have much of a resonant peak, but it is still obvious the difference that it creates.

Black is just with the 3.3uF cap. Blue is with LCR filter added. red is a target 4Khz 2nd order bessel rollof.

Tony.
Attached Images
File Type: png LCR1.png (26.6 KB, 62 views)
__________________
Any intelligence I may appear to have is purely artificial!
Some of my photos
  Reply With Quote
Old 28th December 2012, 11:45 AM   #38
diyAudio Member
 
john k...'s Avatar
 
Join Date: Aug 2004
Location: US
Quote:
Originally Posted by wolf_teeth View Post
Now- think in terms of damping... The LCR with HP suppresses the impedance peak to (if done properly and compensated fully) virtually a resistive load. Being that the Fs is the most easily excited frequency of a driver and that which causes the most Xmax with the least input voltage, reducing or shorting out this frequency area damps the Fs electrically, by attenuating/shorting the voltage to the driver at this point in the audible spectra.

That all sounds very nice, but it is not exactly what happens. I've prepared a couple of sims to try and show what is actually going on. First of all, if the electrical damping of the driver changed, then it's impedance would have to change. Back in 2004 this was a topic of discussion on the Madisound board for the case of a series resistor changing the damping. My analysis showed that while the damping of the system (again note the word system, not driver) changes, the damping of the driver doesn't. Qes of the driver never changes. The impedance of the drivers is fixed.

Next, in the figures below, recognize that everything to the right of the capacitor represents some impedance load, ZL, that the capacitance sees. What happens without the LRC (which is a conjugate network) is that this load (the driver alone) has both resistive and reactive components (capacitance and inductance). The series capacitance of the 1st order crossover in combination with the inductive component of the driver's impedance at the impedance peak forms a LC resonance. You can see this in the first figure below where a cap is in series with a model of a driver's Z.
Next to it I have replace the model of the driver's Z with an inductor in series with a resistance. You can see similar behavior.

Click the image to open in full size.


In the next figure I have added a conjugate network which eliminates the the reactive components in the in the load, ZL, making it purely resistive. As you can see, there is no resonance peak in the response now because there is no inductive component in the load for the capacitor to resonate with.


Click the image to open in full size.

But the impedance of the driver model remains the same. Yes, the conjugate network has an impedance of 4.4 ohms at impedance peak of the driver model, and yes this does provide a current path to ground, but what suppresses the peak in the response curve is the elimination of the reactive nature of the load seen by the cap. This can be better observed by replacing the conjugate network with a 4.4 ohm resistor, the same value as that in the conjugate network. The last figure shows a comparison between the response with the conjugate network in red and when the shunt is just a 4.4 ohm resistor in blue. The resistor does add the same damping to the system at Fs as the conjugate network and therefore the LC resonance between the crossover cap and the inductive component of the driver's Z has a lower peak. But it is still present because the reactive components in the driver's Z have not be compensated for. (Note that the value of the series cap has been changed to compensate fro the difference impedance so as to keep the crossover point the same.)

Click the image to open in full size.

So it is not so simple as to say the LRC provides a current path to ground and therefore damps the resonance. There is more to it. Te correct conjugate network eliminates the cause of the resonance be removing the reactive components in the driver's Z around Fs. This is exactly the same as what a Zobel does to eliminate the effect of the rising impedance due to voice coil inductance. In neither case does the driver's impedance change. What changes is the impedance the upstream elements in the crossover network see, and how they interact with that impedance.
__________________
John k.... Music and Design NaO Dipole Loudspeakers.

Last edited by john k...; 28th December 2012 at 11:48 AM.
  Reply With Quote
Old 28th December 2012, 07:48 PM   #39
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hmmm......

This is using a sledgehammer to crack a walnut.

Its clear (to me at least) what the datasheet is going on about,
albeit very poorly precisely worded, and whilst JohnK's comments
are correct they are missing the point alluded to in the datasheet.

Which is the clueless don't take into account the drivers impedance
peak, and if your clueless your a lot better off including the LCR,
for the halfbaked crossover, as your clueless, you've come up with.

The problem in the explanation is reference to the impedance the
driver sees from the x/o, whist true, its glibly mentioned, and then
the following statement assumes your clever enough to work out
its not likely to be true, but implies its necessary when its true.

Which is wrong, as I and JohnK have both stated.

rgds, sreten.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
  Reply With Quote
Old 28th December 2012, 08:01 PM   #40
diyAudio Member
 
Moondog55's Avatar
 
Join Date: Jun 2007
Location: Norlane; Geelong: Victoria: Australia
I like the precision of Johns answer rather than the obtuseness in the Vifa spec sheet.

John has cleared and topped up what I found to be a rather murky half filled glass
__________________
QUOTE" The more I know, the more I know, I know (insert maniacal laugh >here<) NOTHING"
  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
Is LCR trap necessary even for ferrofluid cooled tweeter? Jay_WJ Multi-Way 10 13th September 2007 03:30 PM
series crossover with resonance trap for tweeter? madinoz Multi-Way 0 8th June 2005 02:03 AM
tweeter double resonance? leftnote Multi-Way 6 9th February 2004 12:36 AM
Tweeter Resonance Frecuency Higo Multi-Way 2 6th August 2003 10:41 PM
resonance in a LCR series Helix Everything Else 1 5th February 2002 12:00 AM


New To Site? Need Help?

All times are GMT. The time now is 12:36 AM.


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