The drift varies from driver to driver, box or not. Audibility most likely also varies with drift. A sine sweep proves lowering of Fs of some drivers. Dynamics will be cut with a stiff spider(s) and will most likely be audible until sufficiently broken in.
At this point I think it's prudent to say that break-in is real in some drivers and can be expected to be audible in some speakers. Your post above don't prove anything in this case. Klippel's data provide evidence for break-in. The audibility of break-in a speaker could be recorded with a mic when new and after break-in with sufficient cooling time in between.
Have a look at the graph again.
View attachment 118658
The spiders break in layer by layer. Dynamic music will be heavily clipped, less so with many of the modern compressed recordings.
Clipping of the dynamics by up to 40%, maybe more if the driver needs more break-in, is so far the best piece of evidence of break-in I've seen so far. Claims to the contrary will need to backed up by evidence.
Yes, that single piece of evidence weighs much heavier than the claims by Floyd and placebo oriented HiFi veterans. Bear in mind that Floyd already had his mind made up and didn't investigate break-in and quoted some anecdotes from the industry.
I'll do you one better. But first you have to separate evidence from speculation. You have:
- Evidence for driver change. But only stiffness of suspension, not the dominant audibility parameter, frequency response.
- No evidence for speaker change.
- No evidence of audibility.
- An unreasonable line of thinking implying that Harman never did time based driver tests. This is absurd. They design their own drivers. Keele had already written about driver compliance vs. fitting in his 1970s papers about vented loudspeakers.
- "As stated by Keele, [4 p.254], typical batches of drivers have a 10-20% variation in T-S parameters, and this is largely due to differences in suspension compliance, but luckily for the speaker designer this has little effect upon the frequency response in a given box because of the insensitivity of this to alignment." Link
From Klippel's own presentation in 2011, test setup:
Response from Loudspeaker A:
Loudspeaker B:
So it's shown clearly that stiffness of a new woofer changes when in a box, over time, in long term tests, with differing power levels moving the loudspeaker driver closer to its nomimal mechanical behaviour.
But the caveat is in the context. Klippel did these tests from the manufacturers' perspective. The overall goal of the test was to determine how to separate break in from mechanical fatigue, the former showing that the driver has overcome its initial stiffness and the latter showing that the driver is has weaknesses and may get damaged. He modelled it as so, with another main research question being how to select good parts and what measurements will show quality:
The model shows an initial sharp dip, which is break in, but the implication is that only a well designed speaker will show that kind of behaviour. A lesser driver will show less initial decline in stiffness, but the decline will continue persistently and more quickly reach the area where it is at risk of damage.
Klippel does more to show that the time based model is somewhat abstract because it does not reflect the amount of work the loudspeaker is asked to perform.
Measurements of Loudspeaker B a few charts above show just this behaviour, although I would assume that P2-P4 in the chart directly above are models of poor behaviour specifically, meaning either bad driver design or excessive work.
There was not a word in this presentation about audibility or frequency response. I couldn't find any Klippel literature linking audibility to these features. What this means for me is that you have another example of measured values what are only important for designers and manufacturers, not listeners, which makes sense. There will always be some physical difference that is more easily measurable than heard.
To recap:
- Driver stiffness changes when measured in free air and inside an enclosure, but:
- There is no evidence that this matters or is important for speaker frequency response until the driver fails.
As such, for which qualities does measuring stiffness provide evidence? Driver quality and durability.
