I'm using a 4" woofer driver, which according to its manufacturer has a +/- 3 mm maximum excursion (Xmax).
I also use a DSP for this driver which has a limiter that I could use to limit the maximum excursion in accordance with the above specs.
My concern is, could it be safe for the driver to set the limit at a higher excursion, for example +/-5 mm, if the higher distortion is accepted.
Any experience on this issue?
I also use a DSP for this driver which has a limiter that I could use to limit the maximum excursion in accordance with the above specs.
My concern is, could it be safe for the driver to set the limit at a higher excursion, for example +/-5 mm, if the higher distortion is accepted.
Any experience on this issue?
It depends on the driver. It's often forgotten that there is (unfortunately) no industry-standard definition for what Xmax even is, let alone a standard method of generating a number for it. Like EBS, it's a simple 1st order approximation / guide to motor linearity, no more, and different manufacturers use different methods, some of which key off the physical coil & gap heights, some of which are on actual distortion measurements, and some which on first glance are not directly connected to either.
Which is a lengthy way of saying that in certain cases you may get away with the above. But not in others as rated Xmax may be rather closer to the mechanical limit of travel -either through the suspension bottoming out, or the rear of the VC smacking into the back-plate. Unless Xmech (Xlim) is also published or other details of the suspension, motor etc. limits, it's a bit of a guessing game.
Which is a lengthy way of saying that in certain cases you may get away with the above. But not in others as rated Xmax may be rather closer to the mechanical limit of travel -either through the suspension bottoming out, or the rear of the VC smacking into the back-plate. Unless Xmech (Xlim) is also published or other details of the suspension, motor etc. limits, it's a bit of a guessing game.
That depends on the mechanical construction of the driver. But generally speaking, +/- 5 mm for a 4" woofer should be doable in purely physical terms. But then you are literally pushing the driver (over) its limits: it is no longer a matter of "higher distortion", but a whopping 50% or more distortion.
Thanks Scottmoose for your response.
I see that the most important parameter for this is the "Xmech", the mechanical limit of travel.
Is there an easy way to measure somehow this ?
I see that the most important parameter for this is the "Xmech", the mechanical limit of travel.
Is there an easy way to measure somehow this ?
Thanks Boden for your response.
Yes the distortion is high, I measure 100% or more depending on frequency.
But in this case the higher Sound Pressure Level is more preferable, despite distortion.
Yes the distortion is high, I measure 100% or more depending on frequency.
But in this case the higher Sound Pressure Level is more preferable, despite distortion.
Take a bright flashlight and shine it into the side of the spider off at an angle. You'll have to get the angle just right, but I do this often and it works very well. The amount of VC winding visible above the pole plate is the actual real life xmax, not some embellished measurement via complex calculation.
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Goodness knows. As noted, there isn't even an industry standard for what 'Xmax' means, let alone a standard method of generating a number for it. It was never meant to be more than a 'quick & dirty' approximate guideline, dating from a time when measurement gear was not readily available / affordable to many builders.
As for Xmech -since it's simply the physical / mechanical limit of travel (irrespective of what the actual physical limiting factor is), then 'simply' deflect the cone until you reach said limit & measure that deflection from the resting position with ye trusty ruler or similar implement. It may be a little out depending on how accurate you are with it and eyeballing the quantity, but it should be ~'near enough' for purpose.
As for Xmech -since it's simply the physical / mechanical limit of travel (irrespective of what the actual physical limiting factor is), then 'simply' deflect the cone until you reach said limit & measure that deflection from the resting position with ye trusty ruler or similar implement. It may be a little out depending on how accurate you are with it and eyeballing the quantity, but it should be ~'near enough' for purpose.
You just have to have a feel for eyeballing it. At least you have some visual confirmation the driver has some amount of VC overhang. The best way to validate it indirectly is with IMD measurement.
Hi gdan,
in the ARTA Application Note Nr. 07 a procedure for the determination of Xlin based on the IEC 62458 (Chapter 15) is described.
https://www.artalabs.hr/AppNotes/AN7-Estimation_of_Linear_Displacement_with_STEPS.pdf
For this you normally need a laser for the excursion measurement. But there is a possibility to get a halfway real result for Xlin without a laser. To do this, one must use a simulation program (e.g. VituixCAD) to determine the „excursion constant“ in mm/volt for the driver at fs. With this information you can convert the excitation voltage at which the driver reaches e.g. 10% THD or IMD into displacement (Xlin = Volt * mm/Volt).
Regards
Heinrich
in the ARTA Application Note Nr. 07 a procedure for the determination of Xlin based on the IEC 62458 (Chapter 15) is described.
https://www.artalabs.hr/AppNotes/AN7-Estimation_of_Linear_Displacement_with_STEPS.pdf
For this you normally need a laser for the excursion measurement. But there is a possibility to get a halfway real result for Xlin without a laser. To do this, one must use a simulation program (e.g. VituixCAD) to determine the „excursion constant“ in mm/volt for the driver at fs. With this information you can convert the excitation voltage at which the driver reaches e.g. 10% THD or IMD into displacement (Xlin = Volt * mm/Volt).
Regards
Heinrich
Never saw the ARTA Application Note before. First of all of a somewhat cheaper laser would be great for diy.
Very interesting technique, that brings up the following question: could from the distortion profile the BL curve be derived?
Very interesting technique, that brings up the following question: could from the distortion profile the BL curve be derived?
Yes, I know, I have used ARTA to perform this procedure in the past.
I used ACH-01 with my accelerometer amplifier to measure the excursion, instead of the laser.
It is easy to do this, if you measure a large subwoofer like Peerless 12".
My concern here is how much excursion above Xmax is "safe" for the driver ?
For example, if you measure Xmax +/- 3 mm, is it safe to allow the driver up to +/- 5 mm, despite distortion?
Any experience on this?
Hi Boden,
the topic BL-curve seems to occupy you very much. I have already given you an answer in another thread. The suggestion is based on IEC 62458, section 10.3.2. There two possibilities are shown for setting a certain excursion: a) applying a DC voltage or b) a stationary air pressure.
Proposal a) leads to a not inconsiderable heating of the voice coil. Proposal b), on the other hand, is simple and inexpensive to implement. Simple electric air pumps are available for about 15 € and since it is a static displacement, no laser is needed, but a depth gauge is sufficient.
The measurement involves imposing a constant positive (pressure) or negative (vacuum) displacement on the loudspeaker inside the enclosure and measuring the TS parameters. This works quite well. However, the "auxiliary method" described here ignores the fact that one leaves the range of the small signal parameters.
Regards
Heinrich
the topic BL-curve seems to occupy you very much. I have already given you an answer in another thread. The suggestion is based on IEC 62458, section 10.3.2. There two possibilities are shown for setting a certain excursion: a) applying a DC voltage or b) a stationary air pressure.
Proposal a) leads to a not inconsiderable heating of the voice coil. Proposal b), on the other hand, is simple and inexpensive to implement. Simple electric air pumps are available for about 15 € and since it is a static displacement, no laser is needed, but a depth gauge is sufficient.
The measurement involves imposing a constant positive (pressure) or negative (vacuum) displacement on the loudspeaker inside the enclosure and measuring the TS parameters. This works quite well. However, the "auxiliary method" described here ignores the fact that one leaves the range of the small signal parameters.
Regards
Heinrich
Hi gdan,
with the procedure according to IEC 62458, you can see (and hear) very well with most drivers when it is overloaded. In some cases, it also leads to damage because the voice coil strikes.
If you are interested in the maximum sound pressure of your system, you have another possibility, which is described in the STEPS manual, section 3.5.
https://www.artalabs.hr/AppNotes/STEPS-HB-D2.4 Rev0.1.pdf
Regards
Heinrich
with the procedure according to IEC 62458, you can see (and hear) very well with most drivers when it is overloaded. In some cases, it also leads to damage because the voice coil strikes.
If you are interested in the maximum sound pressure of your system, you have another possibility, which is described in the STEPS manual, section 3.5.
https://www.artalabs.hr/AppNotes/STEPS-HB-D2.4 Rev0.1.pdf
Regards
Heinrich
Herr Heinrich,
Da sind Sie völlig richtig!
Yes, you are correct: I firmly believe the BL curve tells us much more about woofer qualities than "just" the VC lenght minus poleplate thickness. The Klippel plots are very revealing, clearly demonstrating i.m.o. many costly woofers simply fail. I would like to be able to make such plots in a diy setting. And yes there are diy methods. Still, deriving it from the distortion profile would be interesting. The pump option (David Clark) has crossed my mind.
Da sind Sie völlig richtig!
Yes, you are correct: I firmly believe the BL curve tells us much more about woofer qualities than "just" the VC lenght minus poleplate thickness. The Klippel plots are very revealing, clearly demonstrating i.m.o. many costly woofers simply fail. I would like to be able to make such plots in a diy setting. And yes there are diy methods. Still, deriving it from the distortion profile would be interesting. The pump option (David Clark) has crossed my mind.
As far as i know any reasonably well designed woofer will reach max linear excursion long before Xmech or even Xdamage.
I once did a very rudimentary excursion/current-measurement with DC that showed the max linear excursion:
https://www.diyaudio.com/community/...-the-bl-curve-of-a-woofer.386167/post-7034578
I once did a very rudimentary excursion/current-measurement with DC that showed the max linear excursion:
https://www.diyaudio.com/community/...-the-bl-curve-of-a-woofer.386167/post-7034578
All the above is reasonable, but what driver is it?
Unless the driver have well defined x-limit I would go with x-max + a fudge factor of 20%
note that MANY drivers don’t even reach their rated specified x-max, if we’re going by the Klippel definition.
The other thing is 4” driver with a manufacturer rated x-max (gap - voice coil height) / 2 of 3 mm is not really a high excursion driver to begin with,
so arbitrarily assuming it will make it to 5mm… well…unless you want to let out the magic smoke.
This use of a fudge factor is Engineering 101, for safe practice when when you have to deal with tolerances and unknowns.
Unless the driver have well defined x-limit I would go with x-max + a fudge factor of 20%
note that MANY drivers don’t even reach their rated specified x-max, if we’re going by the Klippel definition.
The other thing is 4” driver with a manufacturer rated x-max (gap - voice coil height) / 2 of 3 mm is not really a high excursion driver to begin with,
so arbitrarily assuming it will make it to 5mm… well…unless you want to let out the magic smoke.
This use of a fudge factor is Engineering 101, for safe practice when when you have to deal with tolerances and unknowns.
A single bass drum delivers a highly asymmetric signal ... so more Xmax headroom is better to avoid excessive distortion!
Dynamic resting position offset is also very bad for distortion and Xmax headroom ...
A low Xover freq relaxes the requirements for detecting distortions by ear , means 2way speakers are the most worse solution regarding sound quality vs input level!
Dynamic resting position offset is also very bad for distortion and Xmax headroom ...
A low Xover freq relaxes the requirements for detecting distortions by ear , means 2way speakers are the most worse solution regarding sound quality vs input level!