Jump to content
Sign in to follow this  
Ricci

JTR Speakers Captivator 212Pro Discussion

Recommended Posts

Any discussion of this speaker or the measurements should go here. Enjoy. 

Share this post


Link to post
Share on other sites

Very impressive results for such a small cabinet, driver size, and low cost. Of particularly noteworthy aspect of the performance, which Jeff kinda pointed out already, is how little difference there is between the long term output and burst output. I've never seen a passive system driven by a K10/K20 report such small differences. I wonder what's going on. In one way it can be seen as excellent design that maximizes long term output, in another one could wonder what's going on with the drivers that they can barely handle 100V during burst testing. Anyone wanna chime in?

  • Like 1

Share this post


Link to post
Share on other sites

A pair of 3" coils can handle as much power as a 6" coil. However, design goal was for max efficiency and output with 1200w (69v) which we need to add to the website (up to 1200w amplification).

Share this post


Link to post
Share on other sites

I have a theory that some of the lighter cones start to flex due to extremely high forces placed on them during the burst testing. It is something I have noticed on those types of drivers over the years. At the 80 to 125Hz bands the driver may not be able to reach xmax or even the THD limitations for the testing before something starts to sound wrong. This will usually be noted as mechanical noise on the burst chart. I stop at that point because it is a clear indicator not to proceed further as damage may occur. It is just a theory and could be any number of things though. 

In this case it really doesn't matter that the cab wouldnt take more than 110v. It means a less powerful and costly amp can be used and get all of the available performance.

  • Like 1

Share this post


Link to post
Share on other sites
13 hours ago, Ricci said:

I have a theory that some of the lighter cones start to flex due to extremely high forces placed on them during the burst testing. It is something I have noticed on those types of drivers over the years. At the 80 to 125Hz bands the driver may not be able to reach xmax or even the THD limitations for the testing before something starts to sound wrong. This will usually be noted as mechanical noise on the burst chart. I stop at that point because it is a clear indicator not to proceed further as damage may occur. It is just a theory and could be any number of things though. 

In this case it really doesn't matter that the cab wouldnt take more than 110v. It means a less powerful and costly amp can be used and get all of the available performance.

I kind of doubt it's cone flexure.  That's what cone break-up is all about, which doesn't set in until much higher frequencies.

As a guess, you could be encountering strong inductance or actual flux-modulation effects.  Strong IM distortion may sound a bit like mechanical noise if it's bad enough.  Being IM distortion, I guess it might not show up as THD, depending on the analysis being used.

Share this post


Link to post
Share on other sites
11 hours ago, SME said:

I kind of doubt it's cone flexure.  That's what cone break-up is all about, which doesn't set in until much higher frequencies.

As a guess, you could be encountering strong inductance or actual flux-modulation effects.  Strong IM distortion may sound a bit like mechanical noise if it's bad enough.  Being IM distortion, I guess it might not show up as THD, depending on the analysis being used.

Those are different things. Breakup modes due to bending forces in the cone geometry and composition are basically resonances. These occur even at very low volumes and are a separate issue IMHO. Basically they are inherent to the driver. This is something that does not occur until the speaker is driven extremely hard. Usually harder than any user scenario would ever push it. If things are continually pushed harder and harder the forces on the speaker increase and eventually something will break or start to behave very badly.  Have you ever looked at the forces involved to produce some of the burst output numbers recorded? Acceleration or velocity for example?  The forces involved are way beyond the scope of normal use. Lighter more flexible materials will tend to give more. What happens to the mass at the edge of the cone when the voice coil acceleration at the center of the cone is constantly increased?

I doubt it is IMD or flux modulation effects I just don't see them making the sorts of noises I've heard. In some examples a driver will go from producing a relatively clean pure sounding tone to a clearly mechanical almost bottoming out sound in the 63-125Hz bands with only a small increase in the input signal. However it is not actually bottoming out or hitting suspension limits and the amplifier is well below clipping. That is easily verified. The signal captured goes from a normal looking reproduction to a complete unnatural mess.

Share this post


Link to post
Share on other sites

I think the noise we are hearing is a form of mechanical non harmonic noise. At the end of the stroke, in a well designed driver, the suspension has to stop the voice coil or any other part to hit another part of the driver. It is doing this by getting harder and harder to stretch until it stops completely. Before it does, some  mechanical clipping noise can be heard but it's not really a square wave because the diaphragm is bending a little also at those displacements.

In the image one can see what one Powersoft X8 channel can do to a pair of 18TBX100 drivers in an 340 BR enclosure where the maximum excursion allowed was 1.5 mm more than the maximum Klippel recommended protection of 15.4 mm, which is already 4.4 mm over XVar (50% KMS) and where the people using it completely neglected that powerful noise

2017-09-09-PHOTO-00000004.jpg

  • Sad 1

Share this post


Link to post
Share on other sites
6 hours ago, Ricci said:

Those are different things. Breakup modes due to bending forces in the cone geometry and composition are basically resonances. These occur even at very low volumes and are a separate issue IMHO. Basically they are inherent to the driver. This is something that does not occur until the speaker is driven extremely hard. Usually harder than any user scenario would ever push it. If things are continually pushed harder and harder the forces on the speaker increase and eventually something will break or start to behave very badly.  Have you ever looked at the forces involved to produce some of the burst output numbers recorded? Acceleration or velocity for example?  The forces involved are way beyond the scope of normal use. Lighter more flexible materials will tend to give more. What happens to the mass at the edge of the cone when the voice coil acceleration at the center of the cone is constantly increased?

I doubt it is IMD or flux modulation effects I just don't see them making the sorts of noises I've heard. In some examples a driver will go from producing a relatively clean pure sounding tone to a clearly mechanical almost bottoming out sound in the 63-125Hz bands with only a small increase in the input signal. However it is not actually bottoming out or hitting suspension limits and the amplifier is well below clipping. That is easily verified. The signal captured goes from a normal looking reproduction to a complete unnatural mess.

Cone flexure occurs at lower drive levels too, but it should remain linear at low drive levels.  Many materials with elastic properties (metals, polymers, composites) exhibit some mild non-linearity at higher stresses, but this should manifest as a gradual increase in distortion with drive level.  Where the stress-strain relationship changes abruptly, the material is usually permanently damaged.  This is could involve elastic deformation (i.e., bending of metal, which does not return to its original shape afterwards) or fracture.

You say that the driver is not hitting suspension limits, but if it's being pushed "close to Xmax", maybe it actually is, even if you don't expect that it is based on simulation data.

3 hours ago, radulescu_paul_mircea said:

I think the noise we are hearing is a form of mechanical non harmonic noise. At the end of the stroke, in a well designed driver, the suspension has to stop the voice coil or any other part to hit another part of the driver. It is doing this by getting harder and harder to stretch until it stops completely. Before it does, some  mechanical clipping noise can be heard but it's not really a square wave because the diaphragm is bending a little also at those displacements.

In the image one can see what one Powersoft X8 channel can do to a pair of 18TBX100 drivers in an 340 BR enclosure where the maximum excursion allowed was 1.5 mm more than the maximum Klippel recommended protection of 15.4 mm, which is already 4.4 mm over XVar (50% KMS) and where the people using it completely neglected that powerful noise.

Let me suggest a mechanism for why this could occur even if one believes the driver is being operated within its limits.

More typically, driver excursion is only high at low frequencies.  At frequencies well below resonance, the motor force primarily acts in the direction of the driver motion and is primarily opposed by the suspension (including box air spring, in a sealed box).  When pushed to the extremes, the drop off in motor force tends to limit the excursion vs. power applied.

In contrast, at high frequencies the motor force acts opposite to the direction of driver motion.  It acts in conjunction with the suspension forces to slow the driver down and reverse its motion.  As excursion increases and BL drops, this part of the opposing force also drops, and depending on the suspension properties, the driver is likely to exhibit *more* excursion than expected for the power input.  This does not mean that the output increases because output depends on acceleration, not excursion.  Physically speaking, acceleration describes both rate of increase in velocity (positive) and rate of decrease in velocity (negative).  Sound comes from oscillation (positive and negative) of the cone acceleration.  So paradoxically, increased compression and distortion will be observed at the same time that excursion increases.

At some point, the coil can literally fly out of the gap, and it's up to the suspension to restrain its motion, or else.  It's likely at that point that the sound may abruptly change from mildly or moderately distorted to very heavily distorted.  As I discussed in previous posts, if driven hard at resonance, it may exhibit very little distortion right up to the point that it suddenly bottoms (soft or hard).  This occurs because at resonance, motor force  has only minimal effect on the driver motion at its extremes, so any BL distortion may be inaudible even if the coil is flying out of the gap.  This is especially true for high Qtc alignments.

Share this post


Link to post
Share on other sites
On ‎9‎/‎22‎/‎2017 at 7:53 PM, SME said:

Cone flexure occurs at lower drive levels too, but it should remain linear at low drive levels.  Many materials with elastic properties (metals, polymers, composites) exhibit some mild non-linearity at higher stresses, but this should manifest as a gradual increase in distortion with drive level.  Where the stress-strain relationship changes abruptly, the material is usually permanently damaged.  This is could involve elastic deformation (i.e., bending of metal, which does not return to its original shape afterwards) or fracture.

You say that the driver is not hitting suspension limits, but if it's being pushed "close to Xmax", maybe it actually is, even if you don't expect that it is based on simulation data.

Let me suggest a mechanism for why this could occur even if one believes the driver is being operated within its limits.

More typically, driver excursion is only high at low frequencies.  At frequencies well below resonance, the motor force primarily acts in the direction of the driver motion and is primarily opposed by the suspension (including box air spring, in a sealed box).  When pushed to the extremes, the drop off in motor force tends to limit the excursion vs. power applied.

In contrast, at high frequencies the motor force acts opposite to the direction of driver motion.  It acts in conjunction with the suspension forces to slow the driver down and reverse its motion.  As excursion increases and BL drops, this part of the opposing force also drops, and depending on the suspension properties, the driver is likely to exhibit *more* excursion than expected for the power input.  This does not mean that the output increases because output depends on acceleration, not excursion.  Physically speaking, acceleration describes both rate of increase in velocity (positive) and rate of decrease in velocity (negative).  Sound comes from oscillation (positive and negative) of the cone acceleration.  So paradoxically, increased compression and distortion will be observed at the same time that excursion increases.

At some point, the coil can literally fly out of the gap, and it's up to the suspension to restrain its motion, or else.  It's likely at that point that the sound may abruptly change from mildly or moderately distorted to very heavily distorted.  As I discussed in previous posts, if driven hard at resonance, it may exhibit very little distortion right up to the point that it suddenly bottoms (soft or hard).  This occurs because at resonance, motor force  has only minimal effect on the driver motion at its extremes, so any BL distortion may be inaudible even if the coil is flying out of the gap.  This is especially true for high Qtc alignments.

Perhaps you are right. The point about mechanical damage happening due to a stress or strain overload of the cone is likely true. You would almost expect a catastrophic failure or fracture somewhere.

 I still don't think this is related to "normal" over excursion. Those things can surely happen, but I would expect them to happen in the low bass register as well. Assuming a sealed cabinet, in order to produce xmax at 80Hz we would expect output roughly 12dB higher than at 40hz. There can be some differences of course due to real world signal reproduction and other variances but this is close. So if a driver produces 110dB at 40Hz at 15mm excursion we would expect it to produce roughly 4dB higher output each 1/3rd octave up when driven to the same 15mm excursion. 114dB at 50Hz, 118dB at 63Hz and 122dB at 80Hz etc. Velocity and acceleration forces increase accordingly as well. reaching the same excursion an octave up requires 2x the cone velocity and 4x the acceleration.  In some cases there is some form of distress or other "bad" noise that occurs well prior to this 4dB per 1/3rd octave expected increase.

You mention that a dramatic drop off in motor force or "control" of the moving assembly is lost at the excursion extremes which is true. This could result in an overshoot effect where excursion would increase as the moving assembly is not "grabbed" and returned. Sort of like a loss of traction on the voice coil. However for the SPL to not increase with the greater cone displacement it basically has to behave in a manner that is not following the waveform of the drive signal. It would be a sort of clipping almost. Sort of like the speaker jumping out of the track provided by the electrical waveform. Indeed when I experience this it often is accompanied by a captured waveform that is completely different than expected and utter garbage. If the output waveform is not the 80Hz or whatever expected and is instead some terrible distorted mess with squared off components it would reduce the measured SPL. Perhaps it doesn't appear at lower frequencies is because the velocity and acceleration forces are lower and the suspension can better deal with controlling the assembly.

Hmmm. I'd never quite thought of it like that. That may just be a possibility. I do seem to see it more often with lighter weight moving assemblies and softer suspensions though.

We are way off topic and none of this pertains to the Cap212-Pro exactly, but this is a fairly common occurrence using the K20 for burst testing.

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×