Quick test results, driver changes with heat

[Spkr_Bldr]

I just wanted to try a quick test today to see how driver parameters change when they warm. For the test I used a Peerless HDS Nomex cone 5.25" driver. I think it's an OEM version, part number on the driver is 832794 which isn't listed in their product listing. Nevertheless it appears very similar to the standard 832873 Peerless HDS Nomex 5.25"

First set of numbers is driver parameters while cold tested with a Woofer Tester II, Delta Mass method used.

Re         =    5.5428 ohms
Fs         =   61.8861 Hz
Zmax       =   31.3244 ohms
Qes        =    0.5296
Qms        =    2.4635
Qts        =    0.4359
Le         =    0.4931 mH  (at 1 kHz)
Diam       =  105.8514 mm  (  4.1674 in  )
Sd         = 8800.0009 mm^2( 13.6400 in^2)
Vas        =    7.9259 L   (  0.2799 ft^3)
BL         =    6.1121 N/A
Mms        =    9.1799 g
Cms        =  720.4717 uM/N
Kms        = 1387.9796 N/M
Rms        =    1.4490 R mechanical
Efficiency =    0.3333 % 
Sensitivity=   87.2462 dB @1W/1m
Sensitivity=   88.8398 dB @2.83Vrms/1m

Next set of parameters are with a warm voice coil, about 30 minutes of music through it

Re         =    5.6941 ohms
Fs         =   58.5322 Hz
Zmax       =   33.2259 ohms
Qes        =    0.5166
Qms        =    2.4980
Qts        =    0.4281
Le         =    0.5004 mH  (at 1 kHz)
Diam       =  105.8514 mm  (  4.1674 in  )
Sd         = 8800.0009 mm^2( 13.6400 in^2)
Vas        =    8.5876 L   (  0.3033 ft^3)
BL         =    6.1960 N/A
Mms        =    9.4712 g
Cms        =  780.6261 uM/N
Kms        = 1281.0229 N/M
Rms        =    1.3944 R mechanical
Efficiency =    0.3132 % 
Sensitivity=   86.9763 dB @1W/1m
Sensitivity=   88.4530 dB @2.83Vrms/1m

This was just an exercise meant to show that when doing any enclosure modeling, it's best to get the coil up to operating temp before measuring.

 

[Djizasse]

Is one test enough to draw conclusions?
I'm just wanting to know

 

[Adam]

Ryan, thanks. Were the geometric sizes assumed to remain constant or were they measured?

 

[Spkr_Bldr]

Is one test enough to draw conclusions?
I'm just wanting to know

It's not like we didn't already know that params change as a voice coil warms, and spider/surround materials experience changes through mechanical excursion (heating, chemical bonding, etc). The conclusion is that parameters change, and potentially much more dramatically than this example shows. The lesson is not to test your drivers while cold, unless you only care how they perform on the first song played of the day

 

[Spkr_Bldr]

Ryan, thanks. Were the geometric sizes assumed to remain constant or were they measured?

You mean Sd? Yes, that's a measured constant ...

 

[Adam]

You mean Sd? Yes, that's a measured constant ...

I don't know what all of the variables are, but I was thinking the ones with geometric units such as "Diam".

I should clarify, though. Were those measured at both cold and warm, or just at one temperature?

 

[Spkr_Bldr]

I don't know what all of the variables are, but I was thinking the ones with geometric units such as "Diam".

I should clarify, though. Were those measured at both cold and warm, or just at one temperature?

Uhm, no ... I think it's a safe assumption that the cone diameter and moving area are constant, unless something catastrophic happens

It's a value that I input, and is displayed with these measurements. It's not measured by the Woofer Tester.

 

[Adam]

Thanks, Ryan. I was just curious. You had the diameter listed out to a tenth of a micron, so I figured that thermal expansion would play a role.

 

[Djizasse]

It's not like we didn't already know that params change as a voice coil warms, and spider/surround materials experience changes through mechanical excursion (heating, chemical bonding, etc). The conclusion is that parameters change, and potentially much more dramatically than this example shows. The lesson is not to test your drivers while cold, unless you only care how they perform on the first song played of the day

I've just learned one more thing, thank you
I'll be equalizing my speakers, I'll assume that it's better for them to be warm.

 

[Spkr_Bldr]

Thanks, Ryan. I was just curious. You had the diameter listed out to a tenth of a micron, so I figured that thermal expansion would play a role.

Haha, well I just input'd the spec'd 88 cm^2 ... not sure where the .0009 came from.

 

[Spkr_Bldr]

I've just learned one more thing, thank you
I'll be equalizing my speakers, I'll assume that it's better for them to be warm.

Well changes in measured FR will be minimial, except in the low octaves near box tuning.

 

[R-Carpenter]

I would probably question audibility and importance of this changes in the process of tuning.
Most of the people will try to tune by ear or with Rat Shack SPL meter which is less then linear.
I would say that your hearing changes much more dramatically during the day and it's important to give any speaker a chance and listen to it for a few days.
Just my 3C.

 

[Swerd]

OK, tell us whether any of those before and after values are significantly different. Especially for Fs, Vas, and Qts, would they make for a significantly different cabinet?

And while I'm being a such a pest , you can't really conclude that the T/S parameters change after 30 minutes of "warm up" unless you show that such variations in measurements are within the precision limits of Woofer Tester II. If you made 10 measurements under the same conditions, how much would they vary? And is that comparable to what you found above? And finally, would the measurements vary like that if you made several measurements without any warm up? Is 30 minutes enough warm up? Would the measurements continue to change with more warm up? What are the temperatures of the voice coil, and have they reached a steady-state?

 

[Spkr_Bldr]

I would probably question audibility and importance of this changes in the process of tuning.
Most of the people will try to tune by ear or with Rat Shack SPL meter which is less then linear.
I would say that your hearing changes much more dramatically during the day and it's important to give any speaker a chance and listen to it for a few days.
Just my 3C.

A 20% change in Qts makes a 3db change at the corner frequency ... that's significant.

 

[Haoleb]

Having never done testing like this myself I wouldnt really know, But I dont imagine every time you run the tests that the driver will measure exactly the same. To get any real idea I think you would need to do a number of cold and warm measurements and then average them and see what the differences are, if any.

 

[Matt34]

Were these tests done with the use of an enclosure or was it just the driver in the open?



Edit: I must have been really tired when I posted that mess before.

 

[ErinH]

This was just an exercise meant to show that when doing any enclosure modeling, it's best to get the coil up to operating temp before measuring.

good point

 

[ErinH]

Additionally, if you don't mind, I'm going to post your results on another forum I frequent. It'd be interesting to see what the car audio guys have to say...

 

[jaxvon]

A 20% change in Qts makes a 3db change at the corner frequency ... that's significant.

But your measurements only showed a 1.7% change in Qts...that doesn't seem very significant. You showed that driver characteristics change slightly when the temperature of the voice coil changes. This is not surprising or new, as the electrical properties would definitely change with changing VC properties. But given that the changes are very small, no real difference in performance should be noticed.

 

[avaserfi]

OK, tell us whether any of those before and after values are significantly different. Especially for Fs, Vas, and Qts, would they make for a significantly different cabinet?

And while I'm being a such a pest , you can't really conclude that the T/S parameters change after 30 minutes of "warm up" unless you show that such variations in measurements are within the precision limits of Woofer Tester II. If you made 10 measurements under the same conditions, how much would they vary? And is that comparable to what you found above? And finally, would the measurements vary like that if you made several measurements without any warm up? Is 30 minutes enough warm up? Would the measurements continue to change with more warm up? What are the temperatures of the voice coil, and have they reached a steady-state?

Having never done testing like this myself I wouldnt really know, But I dont imagine every time you run the tests that the driver will measure exactly the same. To get any real idea I think you would need to do a number of cold and warm measurements and then average them and see what the differences are, if any.

But your measurements only showed a 1.7% change in Qts...that doesn't seem very significant. You showed that driver characteristics change slightly when the temperature of the voice coil changes. This is not surprising or new, as the electrical properties would definitely change with changing VC properties. But given that the changes are very small, no real difference in performance should be noticed.

The previously quoted posters have good points. There is no actual evidence here just conjecture - simply taking one sample and one measurement will not give statistically significant results. Furthermore, there is no credible evidence that measured differences will result in audible differences when using the differing T/S found which is highly unlikely due to the small differences found that are most likely due to tester variance as opposed to actual found differences.

Wwe these tests done with the use of an enclosure or was it just the drive in then the open?

The tests are done free air by hooking up what is basically a sound card and using a measuring program that is bundled with this sound card. The WT software and hardware seems to be fairly accurate in my experience with the WT3.