Again on Jubilee...

[Batmans Robin]

Some of my latest reading has indicated that a perfectly linear Bl might not produce as many IMD products as might otherwise be implied from direct extrapolation of PWK's findings (which were based on measuring very imperfect drivers)...I'm not sure if perfect would yield zero or not, but that's more just an intellectual problem rather than a practical one. I guess what I should say is that non-linearities in the driver's suspension and motor are major sources of IMD and some of the modern drivers address that quite remarkably.

Thanks for the info but what do you mean by BI? What is your take on the claim that IMD is the most noticeable kind of distortion? I am suspicious because it may have just been a claim to make "cone and dome" speakers out to be worse than they actually are, to the advantage of marketing horn speakers.

[Blvdre]

The reason IM distortion is so objectionable is because the distortion frequencies generated are not harmonically related to the fundamental, unlike THD.

[Don Richard]

The fact is, the little BBC monitor must have a lot of IM Distortion to it if we are to accept PWK's DATA, not speculation. The fact is, the LS 3/5a is a very very highly regarded speaker with many web pages run by fans of it that I have discovered and looked at last night.

The BBC monitors control IMD by limiting excursion. They start rolling the bass off at 90Hz, and they are intended for near-field use in small control rooms. Near-field use reduces input power requirements. Near-field use causes room gain to reinforce the bass. The highs have a dip in response centered around 4KHz which further increases apparent bass output.

What these little monitors does very well is to create a 3 dimensional image of the soundstage. Properly installed, they will be located out into the room, allowing one to "hear around" the speakers. That, and the low diffraction caused by the small cabinet allows for pinpoint imaging.

Newer variants of the LS3/5A employ low frequency drivers that have copper shorting rings that improve IM performance. For a shoebox sized speaker they are absolutely amazing.

[bhendrix]

Hey, Don,

How does the copper shorting ring work?

Thanks . . . .

[Don Richard]

http://www.audiogroupforum.com/csforum//showthread.php?t=5166

http://www.diymobileaudio.com/forum/diy-mobile-audio/80-purpose-copper-shorting-ring.html

http://www.martinsoundpro.com/upload/item/5643.pdf

http://www.audioheritage.org/html/projectmay/technology/1500al.htm

So, in short, a shorting ring makes the loudspeaker motor more linear (less distorted) by preventing the permanent magnet's magnetic field from being modulated by the current flowing through the voice coil.

[Batmans Robin]

The reason IM distortion is so objectionable is because the distortion frequencies generated are not harmonically related to the fundamental, unlike THD.

I have read that somewhere before but I wonder if it is true so much with music in a real life situation. There are different types of distortion and I don't know that I for an example could hear it, let alone distinguish it from some other kind of distortion.

[Batmans Robin]

The BBC monitors control IMD by limiting excursion. They start rolling the bass off at 90Hz, and they are intended for near-field use in small control rooms. Near-field use reduces input power requirements. Near-field use causes room gain to reinforce the bass. The highs have a dip in response centered around 4KHz which further increases apparent bass output.

OK I guess that should have been obvious to me that you'd have less IMD if it wasn't playing louder than it was designed to play. When PWK wrote about large amounts of IMD, was he measuring a speaker inside its design parameters or was he driving the gosh darned thing too loud?!?! Because I think we can all agree that the BBC mini monitor in question sounds dang good. I remember being impressed as all heck years ago hearing a pair in a showroom. Cone and dome but what's the problem other than you can't play it loud? Maybe LS3/5a-heads have less permanent hearing damage than Klipschheads!?!?!

[fini]

nevermind

[DrWho]

Some of my latest
reading has indicated that a perfectly linear Bl might not produce as
many IMD products as might otherwise be implied from direct
extrapolation of PWK's findings (which were based on measuring very
imperfect drivers)...I'm not sure if perfect would yield zero or not,
but that's more just an intellectual problem rather than a practical
one. I guess what I should say is that non-linearities in the driver's
suspension and motor are major sources of IMD and some of the modern
drivers address that quite remarkably.

Thanks for the
info but what do you mean by BI? What is your take on the claim that
IMD is the most noticeable kind of distortion? I am suspicious because
it may have just been a claim to make "cone and dome" speakers out to
be worse than they actually are, to the advantage of marketing horn
speakers.

Bl is the amount of magnetic flux times the
length of wire seeing that flux....so basically it's the strength of
the motor. As the voice coil moves up and down, the number of windings
in the gap and the intenstity of the magnetic field change. In other
words, the strength of the motor changes with excursion. The stiffness
of the suspension also changes with excursion. It should also be noted
that the temperature of the voice coil changes the electrical damping
and series resistance. The inductance of the voice coil also changes
with excursion, but that's kinda tied in with the strength of the motor
- however it can cause HF modulation which doesn't sound too nice.

While
I think PWK was certainly trying to make a marketing point, I don't
think he was trying to stretch science to make it. But I like a lot of
Klipsch speakers so it's probably the case that I just have similar
tastes. I think it's fair to say that smaller percentages of IMD are a
lot more audible than larger percentages of THD.

[ZAKO]

Thats always been the case,,,,IMD has always been more noticeable and annoying than THD,,, Thats why in tube amps people like the sound of the uphonic THD sound. even when reaching up to 8%

[NOSValves]

Thats always been the case,,,,IMD has always been more noticeable and annoying than THD,,, Thats why in tube amps people like the sound of the uphonic THD sound. even when reaching up to 8%

Not all of us....

[Don Richard]

OK I guess that should have been obvious to me that you'd have less IMD if it wasn't playing louder than it was designed to play. When PWK wrote about large amounts of IMD, was he measuring a speaker inside its design parameters or was he driving the gosh darned thing too loud?!?! Because I think we can all agree that the BBC mini monitor in question sounds dang good. I remember being impressed as all heck years ago hearing a pair in a showroom. Cone and dome but what's the problem other than you can't play it loud? Maybe LS3/5a-heads have less permanent hearing damage than Klipschheads!?!?!

PWK was referring to Frequency Modulation Distortion, and the other speakers that he tested were at the same output level as the Klipsch speaker to which he was comparing. I have seen a comparison he ran between a Heresy and a BoSe 901 ansd there were higher amplitude sidebands displayed on the spectrum analyzer for the BoSe than there were fundamental frequencies!

[Batmans Robin]

Everybody keeps mentioning THD but there are lots of different distortions other than intermodulation and THD.

[Audio Flynn]

Thats always been the case,,,,IMD has always been more noticeable and annoying than THD,,, Thats why in tube amps people like the sound of the uphonic THD sound. even when reaching up to 8%

Not all of us....

Quite the odd statement. I suppose I can buy that statement if we are talking about 45 year old poorly maintained vintage amps or flea powered tube amps trying futilely to fill a larger room.

[ZAKO]

Ive takin new amps,,measured them,,,Low distortion at first,, 6 momths later,,, measured higher distortion,, They dont make good quality tubes i guess.

[hobie1dog]

Ive takin new amps,,measured them,,,Low distortion at first,, 6 momths later,,, measured higher distortion,, They dont make good quality tubes i guess.

Tubes are not for people who don't like to tinker and adjust them all the time. It looks alluring and plays with the ego to own tube equipment, but it's hard to understand some of the theory behind the small wattage, and being able to produce uumph for transients(some have humongous power requirements). I've heard several systems lately and when we switch from tubes back to more powerful SS equipment, the SS just has more balls. Brings me back to the old days of Bob Carver's amplifier challenge proving he could mimick the sound of the ultra expensive Class A tube amps.

[Marvel]

Tubes are not for people who don't like to tinker and adjust them all the time. It looks alluring and plays with the ego to own tube equipment, but it's hard to understand some of the theory behind the small wattage, and being able to produce uumph for transients(some have humongous power requirements).

Different strokes for ...

I haven't tnkered with my 2A3 amps since I got them, and the sound is wonderful on my LS. Everyone who has heard them has been amazed at how good they sound. Granted, I don't have a large room, but I do turn it up every once in a while. [] It doesn't have a thing to do with my ego, either. If it did, I would be using fancy wires... and... pretty much every thing would be different.

[seti]

I check bias on my tube amps once every couple of months or after tube rolling.

[hobie1dog]

Tubes are not for people who don't like to tinker and adjust them all the time. It looks alluring and plays with the ego to own tube equipment, but it's hard to understand some of the theory behind the small wattage, and being able to produce uumph for transients(some have humongous power requirements). I've heard several systems lately and when we switch from tubes back to more powerful SS equipment, the SS just has more balls

Hi Hobie dog--

One thing many people forget is that not everyone cares so much about making big BoomBoom thumping sounds with their speakers, and thus don't need megawatts of power. I sure do remember the time when the first and only important question I had about a system is "how much boom boom can she make?" The Bass-O-Rama days. As for worrying about "big balls" for instance, I am frankly more interested in the face, the hair, they eyes maybe, and not so interested in the "junk." In that case some smaller wattage tube amps like 60W or 25W or even 2W might sound "prettier" than some "hairy beast" if you get my drift.

Yep, it does heavily depend on what type of music you are trying to reproduce in your room. I just read where all SS equipment produces 3rd order harmonic distortion which our brain tells us is not good and that tubes produce 2nd order which is what our ears are used to in normal life....ever heard that?