[sfdoddsy]

In the interests of science (and since I have been one of the main doubters) I'm going to run a similar set of measurements on my OB woofers tonight. They have (according their T/S specs) slightly larger Sd, the same Xmax, and similar Qts. My H-frame is 330 wide and 350 deep. My room is much larger than Danny's at 10m x 10m opening into another similar sized space.

The mic will be 4m away.

Well, there is definitely some magic in those GR Research drivers. They sure stomped my poor Acoustic Elegance ones.

I wimped out for the sake of my drivers at around 85db. Poor babies were having a conniption.

[HAL]

The resistor with the lower temperature coefficient is actually creating less distortion in the feedback circuit.  The feedback voltage across the resistor creates heat.  This changes the resistance value that then changes the gain of the amp.  This creates intermodulation modulation distortion. 

The question is what is the audible threshold of the IM distortion.  This is actually easier to hear than THD.

The literature that I have read in multiple areas, like IEEE papers and opamp patents show that this is important.  Lower TC is always better in the feedback network.

Resistors like the Mills and Texas Components bulk metal foil are some of the best for low TC.

[THROWBACK]

Here I go again, jumping in when I don't know what I'm talking about. Seems to me the graphs--revealing as they are--are all based on steady-state sine waves. I know Danny's servos will go very low at high amplitudes with sine waves. I'm still hung up on the "jump factor." Is it possible to measure the effects of transients? If that has been discussed, I missed it.

Either my question was so ignorant that our esteemed posters are trying to save me some embarassment (if so, thank you); or it was so tough you are all shying away from it.

P.S. How the heck do you guys make those wonderful quotes in shaded blue?

[THROWBACK]

Oh. The shaded-blue thing happened without me entirely understanding how I did it. I guess that is the mark of genius.

[AJinFLA]

The resistor with the lower temperature coefficient is actually creating less distortion in the feedback circuit.  The feedback voltage across the resistor creates heat.  This changes the resistance value that then changes the gain of the amp.  This creates intermodulation modulation distortion.

Measurable, measurable, measurable...and measurable. Or to Rumsfeld you, known knowns. Trivial for a PhD EE to ascertain.
But that's not what Brian implied.
 

The question is what is the audible threshold of the IM distortion.  This is actually easier to hear than THD.

And measurable. Again, it is often the case that the DUT with lower _ distortion that is perceptually "drier" or "sterile", etc.
We seem to have the opposite here.

The literature that I have read in multiple areas, like IEEE papers and opamp patents show that this is important.  Lower TC is always better in the feedback network.
Resistors like the Mills and Texas Components bulk metal foil are some of the best for low TC.

We have a very restricted bandwidth system here, not going to be testing JNDs over headsets in Iso chambers....so I'm not sure how applicable what you're reading is. None the less, even if I have my doubts that the only thing changing in these listening sessions are resistors, I think we can move on to say that dipoles are definitely a good match for Maggies...and there are many ways to achieve high quality bass in room, Danny-Brians OB servo kit being one. Perhaps the easiest attainable one for the OP.

cheers,

AJ

[rythmik]

Well, there is definitely some magic in those GR Research drivers. They sure stomped my poor Acoustic Elegance ones.

I wimped out for the sake of my drivers at around 85db. Poor babies were having a conniption.

I am curious to know how much excursion you observe from your AE drivers and how much power is your amp.   

[JohnR]

Hm, yes, what do you mean by "conniption"?

[HAL]

Measurable, measurable, measurable...and measurable. Or to Rumsfeld you, known knowns. Trivial for a PhD EE to ascertain.
But that's not what Brian implied.
 And measurable. Again, it is often the case that the DUT with lower _ distortion that is perceptually "drier" or "sterile", etc.
We seem to have the opposite here.
We have a very restricted bandwidth system here, not going to be testing JNDs over headsets in Iso chambers....so I'm not sure how applicable what you're reading is. None the less, even if I have my doubts that the only thing changing in these listening sessions are resistors, I think we can move on to say that dipoles are definitely a good match for Maggies...and there are many ways to achieve high quality bass in room, Danny-Brians OB servo kit being one. Perhaps the easiest attainable one for the OP.

cheers,

AJ

AJ,
The distortion level change is measurable.  The questions are what does the distortion sound like and at what level is it audible. 

Here is a link to a paper on instrumentation to measure the effect in resistor designs.

http://www.barthelectronics.com/pdf_files/Application%20note%201%20Voltage%20Coefficient%20Products_Pulse%20Page.pdf

Sense circuits for feedback systems are the very sensitive to the effect.

Ok, back to OB subs.

[HAL]

A good reference for use for audio terms in J. Gordon Holt's Audio Glossary.  He put definitions to just about every term I have see used to describe a sound. 

This might aid in choosing terms for discussions on the sound quality folks are trying to describe and give everyone a starting point.

[AJinFLA]

AJ,
The distortion level change is measurable.

Great. Brian now has an EE type avenue to pursue, what was hitherto a complete mystery, or at least highly speculative in nature.

The questions are what does the distortion sound like and at what level is it audible. 

In a sensing circuit? Well, let's not put the cart before the horse...

Here is a link to a paper on instrumentation to measure the effect in resistor designs.
http://www.barthelectronics.com/pdf_files/Application%20note%201%20Voltage%20Coefficient%20Products_Pulse%20Page.pdf

I fail to see any relevance here. High voltage apps? The sensing circuit appears to be gap induced voltage levels. Not sure how high that's going to be. But once again, maybe you should be directing these wild speculations at Brian, as he is the designer and probably more privy to the parameters...yet he seems to imply the causes are far more esoteric and elusive in nature.
 

Sense circuits for feedback systems are the very sensitive to the effect.

More wild speculation here. It must be an audiophile thing  .

Ok, back to OB subs.

Indeed!!!

cheers,

AJ

[sfdoddsy]

I am curious to know how much excursion you observe from your AE drivers and how much power is your amp.

The amp is a 200 watt QSC pro amp. EQ is courtesy of a DCX2496. I stopped when the excursion made me fear for drivers.

[rythmik]

In a sensing circuit? Well, let's not put the cart before the horse...

The full function name of this "sensing circuit" related to resistor (a 0.22ohm MRA-10 10W resistor, in your amp we used MRA-12)  is "current sensing feedback".  It is a feedback circuit. Why do I have a sensing circuit and not feed back to the amplifier? 

AJ, this is really the last post we should have off-topic discussion on this thread. plz.

[rythmik]

The amp is a 200 watt QSC pro amp. EQ is courtesy of a DCX2496. I stopped when the excursion made me fear for drivers.

Do you have a visual of the 20hz excursion?  You don't want to use sweep to do that. You need a sine. If you need a pure 20hz sine, you can downloaded it from www.rythmikaudio.com/download/20hz_mono.zip. It is a wave file.

I know you are concerned about destroying another driver.  The power draw for OB driver at 20hz is very low.

[EDIT] pure sine wave and warble tone have different purposes. The former is for you to observe any audible noise and the latter is for SPL measurements. The are multiple tones in warble tone to cover 1/3 oct range.  So by nature, it already sounds flappy. 

[AJinFLA]

The full function name of this "sensing circuit" related to resistor (a 0.22ohm MRA-10 10W resistor, in your amp we used MRA-12)  is "current sensing feedback".  It is a feedback circuit. Why do I have a sensing circuit and not feed back to the amplifier? 

AJ, this is really the last post we should have off-topic discussion on this thread. plz.

Ok. I'll have HAL contact you directly to figure out how a 10w sensing resistor is creating enough distortion to dry out <200hz frequencies, cut out the middle man in the speculations. 

Do you have a visual of the 20hz excursion?  You don't want to use sweep to do that. You need a sine. If you need a pure 20hz sine, you can downloaded it from www.rythmikaudio.com/download/20hz_mono.zip. It is a wave file.

I know you are concerned about destroying another driver.  The power draw for OB driver at 20hz is very low.

Agreed. Maybe both Steve and Danny can download/use the same file and remeasure.
For s&g's, I just did using my old (not terrible accurate) RS digital meter and got 106db C weighted at 3.5m. Probably could have gone higher but that scared the bejeebs out of the cats already.

cheers,

AJ

[dBe]

So if I have this straight, the Mills is more "coherent" than the sandcast when used in your sensing coil?
Or is it simply passing less "distortion" (of unspecified variety)? Hmmm. Last I checked, it is often the case that the lower "distortion" DUT is the more "sterile" or "dry".
IIRC, wasn't there a test of opamps to find differences in "sound", where it was found that the preferred ones...had higher distortion (much like some tube amps with even order THD, etc.)?
What shall we call this, the "Inverse law of Dryness"?

cheers,

AJ

I like "The inverse law of dryness".  Could be you hit on something.

The Mills just sound cleaner.  Build yourself a test fixture that has a really, really good DPDT switch in it (you know - silver plated coin silver contacts) that you can use forever.  Put a Mills and a boat on the legs running to a tweeter.  You will hear the distortion as additional edge on transients like cymbal crashes, etc.  I know that this is Mr. Empirical talking to Mr. Theoretical, but it really is an interesting experiment.  Kind of like "Watch Mr. Lizard".   

Here is one of the long standing op amp links.  FWIW the most highly regarded opamps for audio at present are ones with distortion (THD + noise_ of around 0.00008% or below:

http://tangentsoft.net/audio/opamps.html

http://www.ti.com/product/opa2134

http://www.ti.com/lit/ds/symlink/lm4562.pdf

Dave

[sfdoddsy]

Do you have a visual of the 20hz excursion?  You don't want to use sweep to do that. You need a sine. If you need a pure 20hz sine, you can downloaded it from www.rythmikaudio.com/download/20hz_mono.zip. It is a wave file.

I know you are concerned about destroying another driver.  The power draw for OB driver at 20hz is very low.

[EDIT] pure sine wave and warble tone have different purposes. The former is for you to observe any audible noise and the latter is for SPL measurements. The are multiple tones in warble tone to cover 1/3 oct range.  So by nature, it already sounds flappy.

Thanks, I was using a 20Hz sine wave generated from REW,  and measured within REW.

I'm not sure that I'm game to push the drivers any harder, since what I measured is about what I was expecting based on the SPL spreadsheet on the Linkwitz site.

It's just reinforced the wisdom (for me) of crossing down to the sealed sub at 40Hz.

[dBe]

Thanks, I was using a 20Hz sine wave generated from REW,  and measured within REW.

I'm not sure that I'm game to push the drivers any harder, since what I measured is about what I was expecting based on the SPL spreadsheet on the Linkwitz site.

It's just reinforced the wisdom (for me) of crossing down to the sealed sub at 40Hz.

You have to remember.  This is all about what works for you, in your system, to your requirements.  Approaching great sound is pretty easy once you realize that you are the only person you have to please for your personal system.  Gets a LOT harder when you are designing for others. 

Dave

[studiotech]

It's just reinforced the wisdom (for me) of crossing down to the sealed sub at 40Hz.

Yup, or else you might end up like StigErik on DIYaudio with 8 21" in OB to get results.  Or Monte Kay with his nutty OB arrays of how many Dayton Refs per side?  No sense modulating the heck out of 150-200Hz with 1" P-P 40Hz, right? 

Greg

[Rclark]

Yeah, and StigErik doesn't get much lower than 20hz.  That's why whenever someone says they are getting low bass with their OB system, I never believe them.

[AJinFLA]

Thanks, I was using a 20Hz sine wave generated from REW,  and measured within REW.

Calibrated? What weighting are you using?

I'm not sure that I'm game to push the drivers any harder, since what I measured is about what I was expecting based on the SPL spreadsheet on the Linkwitz site.

What was the sim # for your 4x12 system? Freespace?

It's just reinforced the wisdom (for me) of crossing down to the sealed sub at 40Hz.

In multiples . Really comes down to music tastes...and whether your dipoles are capable enough. I subscribed to that method for the longest while, still for HT...but no longer music.

cheers,

AJ