Signal modulated inductance in speaker drivers is worth mentioning.
It's a major source of distortion, especially in passive xover apps.
Overview:
AE Speakers Design Philosophy
Some measurements of AETD12M and others including Alnico mag Altec 414.
12" driver comparisons
The 414 is not bad for a 40 YO driver - but the TD12M is better. I'd be
interested in seeing direct comparison of Alnico vs Neo vs Ceramic all other
things being equal.
T
Shortening rings from copper, aluminum or even silver prevent inductance modulations.
More sofisticated contructions with two ore more shortening rings like the Scan Speak SD system raise inductance again at high volume to prevent harmonic distortion ( and not so pleasant types too) by simply cutting of high frequency output.
Unfortunately even a basic copper shortening ring takes about 15% of the BL away. We did a FEM anaysis on that. it´s not that simple.
More sofisticated contructions with two ore more shortening rings like the Scan Speak SD system raise inductance again at high volume to prevent harmonic distortion ( and not so pleasant types too) by simply cutting of high frequency output.
Unfortunately even a basic copper shortening ring takes about 15% of the BL away. We did a FEM anaysis on that. it´s not that simple.
This is a tough decision. We really don't design loudspeakers here, BUT I am really personally interested in any SPECIFIC data on magnetic structures. I have heard that there are differences, but I have never seen any specific information. When I make an amplifier design, I try to make the OPEN LOOP output impedance as low and as wideband as possible. I do not use an output coil. I do use a simple RC Zobel network on the output, and my peak currents are 32-135A. I do all this, because loudspeakers are so difficult to drive, and I don't want the amplifier to be effected by this difficult load.
This is a very popular tweeter and inductance is typical for a non compensated magnet system with high BL. Making the magnet very strong, that it saturates makes a shorting ring obsolete in a way. The inductance is 50uH. Of cause there is the crossover.
Two types are popular:
1: One resistor ( typical 20 Ohm) in parallel and one ( 2.2Ohm to 8.2Ohm) in series
That lowers problems with tolerances of Fs and makes the impedance more linear
2: One resistor in series. I prefer that because i can use a smaller cap. Makes QC mandatory.
Two types are popular:
1: One resistor ( typical 20 Ohm) in parallel and one ( 2.2Ohm to 8.2Ohm) in series
That lowers problems with tolerances of Fs and makes the impedance more linear
2: One resistor in series. I prefer that because i can use a smaller cap. Makes QC mandatory.
Typical and popuar tweeter:
http://www.seas.no/images/stories/prestige/pdfdatasheet/h1189_27tdfc_datasheet.pdf
http://www.seas.no/images/stories/prestige/pdfdatasheet/h1189_27tdfc_datasheet.pdf
I found this article on the Back EMf toppic.
Active Crossovers Vs. Passive Crossovers
John, i try to find my measurements.
Unfortunately my lab is not set up because we move in a new building.
I get a new lab, and they just build up the walls.
Active Crossovers Vs. Passive Crossovers
John, i try to find my measurements.
Unfortunately my lab is not set up because we move in a new building.
I get a new lab, and they just build up the walls.
I am comming to the rescue.
I found the data on my old home computer.
I measured two midrange drivers with carbon membrane.
One had an Alnico and the other a Neodym magnet.
Black is the backround noise and distortion of the amp. colour is the sparce spectrum multitone signal and grey is distortion.
When you look carefull the Alnico has much lower distortion in the current.
Alnico is conducting so there may be some beneficial eddy currents at work.
I found the data on my old home computer.
I measured two midrange drivers with carbon membrane.
One had an Alnico and the other a Neodym magnet.
Black is the backround noise and distortion of the amp. colour is the sparce spectrum multitone signal and grey is distortion.
When you look carefull the Alnico has much lower distortion in the current.
Alnico is conducting so there may be some beneficial eddy currents at work.
John,
You need to clean your PM boxes out, I tried to send PM but failed due to
lack of space.
Terry
Well, we look stopped again. No new info, for some reason. However, I am concerned today with hi fi fuses that are going to be tested in a highly modified JC-1 pair of power amps. I am sending them to my associate to try. They are the right value, made of silver rather some other combination of materials. We hope for 'sighted' progress. I hope to report back on this, when some evaluation is done, by people younger than me.
I might comment on what I have been doing in recent months. I have been working on a new phono stage with no holds barred, so to speak. What then can I do to make a better preamp than, let's say a Vendetta Research SCP-2 phono stage?
Well, not much, but I elected to design in a remote controlled input load, that is composed of a triple gang motor driven precision wirewound pot. My employer just about gasped at the prospect, but I insisted that we at least try. Can we make it flawless? Should we use hybrid rather than just wirewound pots? Only time will tell.
Well, not much, but I elected to design in a remote controlled input load, that is composed of a triple gang motor driven precision wirewound pot. My employer just about gasped at the prospect, but I insisted that we at least try. Can we make it flawless? Should we use hybrid rather than just wirewound pots? Only time will tell.
, but what's a hybrid pot?
Obviously you do not use potentiometers in a professional way. A 'hybrid pot' or hybrid potentiometer is a wirewound potentiometer with the wires filled in with a conductive material in order to improve electrical, and perhaps mechanical smoothness. Many industrial grade wirewound potentiometers offer this option. Of course, you might have to 'Google' in online in order to find out more.
A hybrid potentiometer has design elements of both a conductive plastic potentiometer and a wirewound potentiometer. It is a multi-turn wirewound potentiometer with a conductive plastic overlay. This design provides ease of manufacturing of the wirewound potentiometer with the long-life, low-noise, high-resolution characteristics of the conductive plastic potentiometer.
An externally hosted image should be here but it was not working when we last tested it.
Seems the only thing the wirewound element brings is "ease of manufacturing." All the other desirable characteristics appear to be brought to the table by the conductive plastic.
So why not just go with conductive plastic?
Are any of the wirewounds made using non-magnetic resistance alloys? This is for loading a phono cartridge, right?
se
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Actually I am playing with some this weekend as part of my resistor testing. Although the classic ten or more turn pots were wirewounds, I have never trusted then not to degrade when left in one spot for a few years.
As to motor driven pots, I have toyed with using stepper motors to tune circuits. They are easier to control and keep in calibration.
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