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

Joe Rasmussen Usher S520 "Current Compatible" Crossover
Joe Rasmussen Usher S520 "Current Compatible" Crossover
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
Closed Thread
 
Thread Tools Search this Thread
Old 10th January 2016, 07:34 AM   #1
Joe Rasmussen is offline Joe Rasmussen  Australia
diyAudio Member
 
Joe Rasmussen's Avatar
 
Join Date: Jan 2003
Location: Sydney, Australia
Default Joe Rasmussen Usher S520 "Current Compatible" Crossover



NO LAWS OF THE UNIVERSE WAS BREACHED IN THE DEVELOPMENT OF THIS PROJECT.


Joe Rasmussen Usher S520 "Current Compatible" Crossover

Subtitled: Can be used with the JR "Trans-Amp" - 40 Watt Transconductance "Current Amplifier"


Link:
Trans-Amp on DiyAudio

Click the image to open in full size.

This has been some time in the making. The Usher S520 has been available for some time and extensively reviewed including by Stereophile and with John Atkinson measurements, which correlates nicely with mine.

Link: Usher Audio Technology S-520 loudspeaker | Stereophile.com

Rightly, they were described as solid engineering at a bargain basement price. So what is the weakness that can be addressed? I was tempted, the price of these little buggers is hard to resist and I have been asked by the Elsinore Project builders for something along these lines, for a small satellite speaker. But in that case it had to be able to fulfill the same trick, that it could be driven by amplifiers with any output impedance in the same that Elsinore MK5 onward (now Mk6) can. This would mean that a number of things would need to come together and happily did. Those who have heard it say they can hear the family resemblance to the Elsinores, so must be satisfied by that.

My little "Trans-Amp" has an output impedance of 270 Ohm. So we are effectively talking about zero "damping factor" and for a speaker to rely on zero "damping factor"

The speaker would of course end up measuring somewhat different and also because the primary goal is not the flattest frequency response that can be achieved, but rather, in order to reach a goal that is primary even over frequency response, some small but acceptable trade-off has been made. The Elsinores does likewise. The primary goal can be seen in the electrical and phase measurements rather than the crossover. The design goals have a different order.

So what is the primary goal - the one that precedes others in importance? Basically it comes down to 'noise' that many conventional crossovers generate to varying different degrees. Now I don't intend to get into say too much except that every designer must have at least adopted some kind of philosophy before he designs anything, and that is particularly true of loudspeakers. Note that Dave Wilson now uses and "anti-jitter crossover strategy" in his up to $200.000 USD loudspeakers. This is basically saying the same thing that we are addressing here - it is 'noise.'

Edgar Kramer interviewed Dave Wilson and Edgar's three part interview is on YouTube.

Link: Edgar interviews Wilson Part 1

Before that interview, Edgar and I had lunch in Haberfield NSW and I was able to inform him that we too were working on this too and that it had to do with suppressing noise in crossovers. As I knew an engineer who has done work on Wilson speakers (to remain nameless), we indeed know how it is done (we had already guessed it and it was confirmed) and I was able to tell Edgar. Indeed the technique does work but is rather wasteful when it comes to drawing power from the amplifier - but as you can see this from the impedance and electrical phase angle measurement done by Atkinson.

Click the image to open in full size.

Note the flattened out peaks and troughs below 100 Hertz and a knowlegable person can figure it out. That compression can also be seen as a flattened, but not flat, electrical phase angle. This is always to be expected.

Now note what our respective measurements looks like for the alternative Usher S520:

Click the image to open in full size.
[Actual measurement, not the modelling.]

Compare the above and it's fair to say that something more, ahem... sophisticated is going on. The difference is that this approach achieves something that commercial speakers with crossovers can not do: Can be driven by current and hence any amplifier of any output impedance. We will show examples later to prove what the affect is from driving from zero Ohm (which is voltage delivery) and near infinite output impedance (which is current delivery).

Additional Notes:

Some of you may have heard of Esa Merilainen's book on Current Driving Loudspeakers. I have a copy and I recommend it. But Esa and I have possibly a different approach, one that I have discussed with him, about how to get current drive from a voltage source. He certainly recognised that as desirable and made some suggestions and we both agreed that a 5:1 ratio is a good target as a minimum. So 4 Ohm should be driven from 20 OHM min and 8 Ohm should be driven by 40 Ohm min. This can of course be achieved with series resistors, but now it means we can use only a small amount of available power from the amplifier - or get speakers that have very low sensitivity. Yet what are we trying to achieve? Simply this, give the drivers a chance to track "clean current" and avoid contamination of the current which is essentially, as Dave Wilson and increasingly others, have perceived as a higher noise floor (so anti-jitter is really anti-noise).

Dynamic drivers are current devices, motors are current devices, simple as that. Yet we insist on driving them from a voltage source. Then we make it even worse by inserting a crossover? It now becomes clear that the crossover needs to be looked at very closely.

Now I want to make a statement that I believe is an essential issue. The voltage source can produce current - no doubt about that - the problem is that it can also produce current of any phase angle. But a genuine current source can only produce a phase angle of zero since it sees it own output impedance as a series resistor of (ideally) infinite value. The voltage produced across the final load will always track current and voltage together without contamination.

What the above crossover does is comes to terms with those problems, and it produces the same (or extremely similar) results no matter what the source impedance is and also equalises the current. Some interesting things happens as not only will the bass alignment track well down to 30 Hertz, but also the crossover is also immune.

Please keep in mind, we are not really aiming to produce a loudspeaker that can only be current driven, and you can if you build a Trans-Amp of some sort, but the realisation that if it performs the same at both extremes and that current is the ideal way to go, that similar performance will intuitively tell you that we must be getting some of the benefits even when voltage driven.

Now for some pictures:

Frequency Response 15 degrees Off Axis:

Click the image to open in full size.


Crossing Over:


Click the image to open in full size.

The hump circa 1KHz was also indicated in the Atkinson measurements, it seems a reflection due to the mechanical layout of the driver.

The above are modeled.

Actual In-Room RTA Response:

Click the image to open in full size.


Additional Stuffing:

Click the image to open in full size.

Click the image to open in full size.


Remove Crossover & Links and Wire Directly External Crossover:

Click the image to open in full size.

Click the image to open in full size.


Later:

The above pictures speak largely for themselves and the rest should be easier to work out. I will also prepare some info on the modeling and how the modeling shows how the alignment fares when changing the source impedance of the amplifier. Typically voltage amplifiers have output impedances below 1 Ohm, many tube amps, especially those that eschew feedback, have typical impedances similar to speakers and 4-10 Ohm. Finally, current amplifiers should have an output impedance 5x greater at the very minimum.

Enjoy the fruits of my labour.

Cheers, Joe R.


Click the image to open in full size.

__________________
The "Elsinore Project" DIY Speaker System " & DIY "Trans-Amp" - 40 Watt Transconductance Amp
Soon: High Frequency Bias in Tube OPT - "Don't take anything I say as an affirmation but as a question."

Last edited by Joe Rasmussen; 17th February 2016 at 01:37 AM.
 
Old 10th January 2016, 07:35 AM   #2
Joe Rasmussen is offline Joe Rasmussen  Australia
diyAudio Member
 
Joe Rasmussen's Avatar
 
Join Date: Jan 2003
Location: Sydney, Australia
Part Two:

Two extremes, Red for voltage drive and Green for current driving (270 Ohm source impedance as per 40 Watt Trans-Amp):

Click the image to open in full size.


Now let's look at the current phase angle, same Red and Green:

Click the image to open in full size.


Next the Frequency Response Family, 0, 15 and 30 degrees of axis:

Click the image to open in full size.


Now comes the really interesting part, how does the crossover perform from a 270 Ohm source impedance (current drive):

Click the image to open in full size.


Now let us overlay that with crossover driven from zero Ohm (voltage drive):

Click the image to open in full size.

Note that the crossover performs almost as identically as can be.


Finally, we shall look at the minimum phase:

Click the image to open in full size.

Please note this is with 4 Watt input and indeed the minimum phase goes well above 10KHz when one Watt.

What the above shows is a remarkable immunity to any source impedance, the largest deviation is at 25 Hertz, low enough for a small speaker system as this (in the Elsinores it even better controlled and below 20 Hertz).


__________________
The "Elsinore Project" DIY Speaker System " & DIY "Trans-Amp" - 40 Watt Transconductance Amp
Soon: High Frequency Bias in Tube OPT - "Don't take anything I say as an affirmation but as a question."
 
Old 10th January 2016, 10:31 AM   #3
SY is offline SY  United States
On Hiatus
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Joe Rasmussen Usher S520 "Current Compatible" Crossover
Could you define what "noise in crossovers" means?
__________________
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
 
Old 10th January 2016, 11:54 AM   #4
Joe Rasmussen is offline Joe Rasmussen  Australia
diyAudio Member
 
Joe Rasmussen's Avatar
 
Join Date: Jan 2003
Location: Sydney, Australia
Quote:
Originally Posted by SY View Post
Could you define what "noise in crossovers" means?
I am not even sure if 'noise' is the right word.

__________________
The "Elsinore Project" DIY Speaker System " & DIY "Trans-Amp" - 40 Watt Transconductance Amp
Soon: High Frequency Bias in Tube OPT - "Don't take anything I say as an affirmation but as a question."
 
Old 10th January 2016, 12:31 PM   #5
Inductor is offline Inductor  Portugal
diyAudio Member
 
Inductor's Avatar
 
Join Date: Feb 2006
Location: Cascais
This can be done with any speaker? (crossover)
 
Old 10th January 2016, 12:43 PM   #6
Lojzek is offline Lojzek  Croatia
diyAudio Member
 
Lojzek's Avatar
 
Join Date: Feb 2012
Location: Croatia
What's stopping you from flattening impedance of the loudspeakers?
ARTA is free, simulation spreadsheets too. 2 hours worktime. Whether
you need one is a different story.
__________________
Mankind is created for eternity.

Last edited by Lojzek; 10th January 2016 at 12:47 PM.
 
Old 10th January 2016, 12:46 PM   #7
billshurv is offline billshurv  United Kingdom
diyAudio Member
 
Join Date: Mar 2014
Joe Rasmussen Usher S520 "Current Compatible" Crossover
Quote:
Originally Posted by Inductor View Post
This can be done with any speaker? (crossover)
Sure. Read here https://www.passdiy.com/project/arti...ssover-filters for a good introduction on the subject.
 
Old 10th January 2016, 12:58 PM   #8
Joe Rasmussen is offline Joe Rasmussen  Australia
diyAudio Member
 
Joe Rasmussen's Avatar
 
Join Date: Jan 2003
Location: Sydney, Australia
Quote:
Originally Posted by Inductor View Post
This can be done with any speaker? (crossover)
No, there are things that need to work together in just the right way.

The biggest gain is an obvious sense of clarity and resolution.

__________________
The "Elsinore Project" DIY Speaker System " & DIY "Trans-Amp" - 40 Watt Transconductance Amp
Soon: High Frequency Bias in Tube OPT - "Don't take anything I say as an affirmation but as a question."
 
Old 10th January 2016, 01:10 PM   #9
SY is offline SY  United States
On Hiatus
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Joe Rasmussen Usher S520 "Current Compatible" Crossover
Quote:
Originally Posted by Joe Rasmussen View Post
I am not even sure if 'noise' is the right word.
But you said:

Quote:
Basically it comes down to 'noise' that many conventional crossovers generate to varying different degrees.
So, what does it mean?
__________________
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
 
Old 10th January 2016, 01:36 PM   #10
billshurv is offline billshurv  United Kingdom
diyAudio Member
 
Join Date: Mar 2014
Joe Rasmussen Usher S520 "Current Compatible" Crossover
Quote:
Originally Posted by Joe Rasmussen View Post
No, there are things that need to work together in just the right way.

The biggest gain is an obvious sense of clarity and resolution.
What are these things?
 

Closed Thread


Joe Rasmussen Usher S520 "Current Compatible" CrossoverHide 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
Joe Rasmussen "Trans-Amp" - 40 Watt Transconductance "Current Amplifier" Joe Rasmussen Chip Amps 337 17th May 2017 02:49 AM
DAC Filtering - the "Rasmussen Effect" Coris The Lounge 596 13th February 2015 02:08 PM
Reducing tweeter volume on Usher s520 redrum.42 Multi-Way 28 19th December 2011 06:09 AM
Elsinore by Joe Rasmussen FrancoB Swap Meet 0 24th March 2009 11:23 AM


New To Site? Need Help?

All times are GMT. The time now is 08:51 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio
Wiki