Quick test results, driver changes with heat

[mtrycrafts]

...Upper end frequency response is not shown due to inaccuracy of modeling. It is highly unlikely that there is any audible differences between 'warm' and 'cold' drivers even if there are minor measurable differences.

Please note even this set of data is far from statistically complete, but it is a more sufficient example than that offered by the OP due to larger sample size.

One also needs to know what the JND is at around that F3
I am willing to bet that the change is well below that threshold as the JND at the low end is kind of high

 

[mtrycrafts]

...

*Please note I cannot speak for the forum as a whole, but rather am making this statement based on my observations.

Ah, but you are a good psychic or is that a good observer

 

[mtrycrafts]

I disagree, the driver will change - in some cases dramatically - under operating conditions. Mids and tweeters it's not likely to matter nearly as much if at all compared to the bass end of a system, and in sealed systems it's not likely to significantly matter either. But in any form of a vented system the box tuning reacts greatly to driver parameter changes. Like I said earlier, a 20% change in Qts will make a 3db difference at the corner frequency ... and if Keith Larson is telling me he routinely sees 35% changes, then I'm going to try and find ways of tuning my box to perform how I want under realistic drive levels. These changes are due to a lot more than just heating of the coil and materials, chemical bonding and changes in compliance of the suspension are likely more a factor as hinted at by Keith.

Not sure how much SPL changes your testing shows either cold, under test or in actual use but one also needs to be aware of the human hearing capability, especially in the low frequency band.

http://www.provide.net/~djcarlst/abx_crit.htm

while the published paper is based on a small sample size, no reason that a large sample size would be much different. Please note the JND needed at the low band, say at 50Hz and below or at 80Hz and below. It takes a whole lot of SPL change just to be detected by the listener.
One reason why subs are tested at 10% THD

 

[Spkr_Bldr]

You guys sure are trying hard to say that you don't are about a +/- 5db variance in the lower octaves, which if so is just fine by me. Just don't tell me I'm stupid for caring. Some pretty incredible ego's here!

Would you tune a motor cold? Of course not ... I see no difference. A moving coil will reach a semi steady-state operating temp and mechanical compliance, and it's a pretty safe bet it's state immediately after playing 20 minutes of music is much more accurate representation of this than after being pulled from the closet.

 

[R-Carpenter]

Oh, it is very important but it's mostly important to a speaker designer not so much for your average guy, buying Polk or Boss. I am not sure if this was a correct forum to post this info.
This: http://www.diyaudio.com/forums/forumdisplay.php?s=&forumid=22
on the other hand is a fantastic forum for armature designers. Some DIY speakers that are posted here will blow away $150k exotics.

 

[bandphan]

 

[no. 5]

You guys sure are trying hard to say that you don't are about a +/- 5db variance in the lower octaves, which if so is just fine by me. Just don't tell me I'm stupid for caring. Some pretty incredible ego's here!

TLS Guy makes a very persuasive argument in post number 39. T/S specs change with heat, you have shown that and so has Avaserfi, and some drivers may change audibly (post 26), but the most important question remains; how do you design for it?

It's been shown how much three different drivers change after thirty minuets of operation, but how much would they change in five minutes? Ten? An hour? What about a higher input level? Or a lower one? Surely the results from any one of those tests would be different from another. If the half hour 'normal level' test shows a -0.4dB drop in bass response and the one hour 'high level' test shows a -3dB drop, which occasion are you to design for? To be optimum for rocking out or for mellowing out?

To paraphrase a few people, three samples do not a statistically relevant example make. In the end, what I get out of this thread is that if you're very detail oriented, you might want to know how the T/S specs of a driver you're considering change with heat; if only to decide if you can live with the amount of change, or that a driver that changes less needs to be found.

 

[no. 5]

Please note the driver I plan on measuring has been shown to be extraordinarily linear and well designed it also happens to be far more robust than the HiVi D10.8.

If you get a chance, can you do some extraordinarily nonlinear poorly designed drivers that are far less robust that the HiVi D10.8 as well?

Reason being I'm interested in knowing if the drivers typically present in mid-low to low end consumer speakers are any more effected. On more than one occasion I have seen a reviewer remark on how bass was "tighter" (as always ) after a fairly inexpensive pair of bookshelf's/mini system/etc was left to "warm up" for a few hours before returning, and I'm curious to see if the possibility is present that such a speaker's bass extension could actually change to an audible degree.

 

[Ketel1]

hmmm intersting

 

[A9X]

With a properly designed cone driver, at high SPLs, there is the possibility for minor power compression.

Define minor. Looking at the Beyma driver datasheets thermal compression is typically 2-3dB at half Pmax. For an efficient driver used domestically, it should not be an issue. However for an inefficient driver being given a workout with low crest factor source it may. Because most drivers use ceramic magnets, it's hard to get the heat out as easily as it is to get it in.

 

[bandphan]

Define minor.

As an adjective:
Main Entry:
1mi·nor
Pronunciation:
\ˈmī-nər\
Function:
adjective
Etymology:
Latin, smaller, inferior; akin to Old High German minniro smaller, Latin minuere to lessen
Date:
1526
1: inferior in importance, size, or degree : comparatively unimportant
2: not having reached majority
3 a: having half steps between the second and third, the fifth and sixth, and sometimes the seventh and eighth degrees <minor scale> b: based on a minor scale <minor key> c: less by a semitone than the corresponding major interval <minor third> d: having a minor third above the root <minor triad>
4: not serious or involving risk to life <minor illness>
5: of or relating to an academic subject requiring fewer courses than a major

 

[avaserfi]

If you get a chance, can you do some extraordinarily nonlinear poorly designed drivers that are far less robust that the HiVi D10.8 as well?

The only 'larger' drivers I own are the proven linear Kappa VQ 12" and unproven, but robust, HiVi SP10. I cannot bring myself to purchase a low quality driver. I think purchasing something that is poor quality is against my nature .

 

[no. 5]

The only 'larger' drivers I own are the proven linear Kappa VQ 12" and unproven, but robust, HiVi SP10. I cannot bring myself to purchase a low quality driver. I think purchasing something that is poor quality is against my nature .

Think of it as doing it for science.

By the way, may I ask what you're planning with the SP10?

 

[avaserfi]

Think of it as doing it for science.

I will see what I can get my hands on...I might be able to find something.

By the way, may I ask what you're planning with the SP10?

The SP10 is planned to be used as the lower module in my current speaker build [near field use computer monitors]. I actually just ripped the ply for the lower modules today [the upper modules are completed].

Pictures of the upper module and the SP10 can be seen here. I will likely update the album with pictures of the SP10 enclosure assembly as it progresses. Please note, the second constrain layer was not really needed, but due to a last minute change in materials used I had extra volume inside the cabinet that needed to be filled.

Define minor. Looking at the Beyma driver datasheets thermal compression is typically 2-3dB at half Pmax. For an efficient driver used domestically, it should not be an issue. However for an inefficient driver being given a workout with low crest factor source it may. Because most drivers use ceramic magnets, it's hard to get the heat out as easily as it is to get it in.

As an example lets assume we are talking about a single loudspeaker with average sensitivity of about 89dB using a 6.5" driver and dome tweeter both containing motors of quality and crossed over at about 80Hz to a subwoofer. If one took an averaged sweep [more representative of actual music than simply using pink noise, but still likely more demanding] at 96dB at 1 meter versus and an averaged sweep at 101dB [4 times the power] at 1 meter less than one decibel of compression is to be expected between the two in the lower band [less than 200Hz] and less than half a decibel in the higher band [greater than 200Hz]. Averaged distortion levels would still be inaudible for music playback.