davewantsmoore Posted January 20, 2015 Posted January 20, 2015 I thought drivers need around 100 or more hours to break in. A driver might very slightly change it's mechanical specs over it's entire life ..... however enormous changes can occur in the initial short "break in period". Eg. a drop from 100 to 80hz of Fs ... which is nearly half an octave (!!!!!) Think about the cone moving back and forth to xmax (a number of millimetres) ... the spider and surround material have never (or hardly) ever been stretched this far.... and their mechanical properties can change quite a lot
acg Posted January 20, 2015 Author Posted January 20, 2015 Ok...little experiment just started...if I can stand the sound of a 65dB 100Hz tone playing at my desk for half an hour. I will have to turn the music RIGHT up to drown out the buzz.
niss_man Posted January 20, 2015 Posted January 20, 2015 Nar.So what time frame would nar be exactly? 1
davewantsmoore Posted January 20, 2015 Posted January 20, 2015 Ok...little experiment just started...if I can stand the sound of a 65dB 100Hz tone playing at my desk for half an hour. I will have to turn the music RIGHT up to drown out the buzz. How far is the cone moving? ...... I would have expected tons more noise if you have the driver moving even anywhere near close to half xmax
acg Posted January 20, 2015 Author Posted January 20, 2015 How far is the cone moving? ...... I would have expected tons more noise if you have the driver moving even anywhere near close to half xmax To quote Scotty: "I'm giving it all she's got captain!" I'm just using the signal generator in DATS which is limited by the USB power rating of probably no more than 5 watts. The only other way that I can think of just now is to run a signal through my dac and then leave the premises. Don't have a signal generator.
davewantsmoore Posted January 20, 2015 Posted January 20, 2015 So what time frame would nar be exactly? The vast majority of the change (sometimes enormous change) will happen within a very small number of minutes of significant excursion. Depending on the driver, it may continue to move it's mechanical parameters a very small amount for its whole life..... however for most drivers this change is so tiny it cannot be measured. Contrast that with what we have here where the driver resonant might be almost half an octave too high (which is enormous).
davewantsmoore Posted January 20, 2015 Posted January 20, 2015 (edited) To quote Scotty: "I'm giving it all she's got captain!" I'm just using the signal generator in DATS which is limited by the USB power rating of probably no more than 5 watts. The only other way that I can think of just now is to run a signal through my dac and then leave the premises. Don't have a signal generator. I've done this before too .... I found that if I upped the output of the DATS probe like you have ..... that the signal had significant distortion. (Not that it matters in this case - as higher frequencies than Fs are perfectly safe) What I was expecting that you would do, is to use a signal generator on your computer (even just: http://onlinetonegenerator.com/) .... and connect the output of your computer to an amplifier, then to your driver. NB - Be careful. It doesn't take very much power at Fs to make the cone move (which is precicely why we are choosing to apply the power at that frequency - less heat) ..... but you do need to make the cone move significantly. Even a few millimetres of excursion will look (and feel if you were holding the driver in your hands) like a lot, and make a ton of noise. Anyways. Don't take me too seriously. Finish your "powered by USB" experiment for 30 minutes or so, and then sweep the driver and see what you see. I would expect that Fs would move some. Edited January 20, 2015 by davewantsmoore
hochopeper Posted January 20, 2015 Posted January 20, 2015 So what time frame would nar be exactly? Dave's answer is pretty good I reckon The folly IMO comes when counting hours of listening to music signals at 'polite' levels without much content around the resonant freq. A few minutes at or near the resonant freq, should be enough. Then sit back and listen to the music and forget about trying to 'listen' for 'break in' ... good people are missing good music while thinking about that other rubbish.
acg Posted January 20, 2015 Author Posted January 20, 2015 So after 20 minutes at 65 dB 100Hz sine wave Fs has risen 1Hz.
hochopeper Posted January 20, 2015 Posted January 20, 2015 (edited) Anyways. Don't take me too seriously. Finish your "powered by USB" experiment for 30 minutes or so, and then sweep the driver and see what you see. I would expect that Fs would move some. Yeah sometimes Good EnoughTM is the best approach. The amount of time I waste trying to do things The Right WayTM is a crying shame but hey it's a hobby and I'll do what I want (especially if it gives me an excuse to stay longer in the garage working on 'stuff' when the mother in law is visiting) Other times: So after 20 minutes at 65 dB 100Hz sine wave Fs has risen 1Hz. Give 'er more power captain! Edited January 20, 2015 by hochopeper
acg Posted January 20, 2015 Author Posted January 20, 2015 Give 'er more power captain! Preparing for warp factor How far is the cone moving? If I had to guess I would say a couple of mm peak to peak...certainly nothing significant or approaching 10mm 1
niss_man Posted January 20, 2015 Posted January 20, 2015 Have just double checked with Mr Lenehan re speaker break in. His recommendation was somewhere between 100hrs and nar hrs. 40-50hrs actually. 1
acg Posted January 20, 2015 Author Posted January 20, 2015 Have just made up some dodgey brothers speaker cable and set one driver buzzing away at 95dB 100Hz. There is some real excitation happening at this SPL so we will see what happens. I have moved to the other end of the house for half an hour.
acg Posted January 20, 2015 Author Posted January 20, 2015 Have just double checked with Mr Lenehan re speaker break in. His recommendation was somewhere between 100hrs and nar hrs. 40-50hrs actually. Interesting...the crossover would take longer I suppose with those enormous capacitors and inductors.
niss_man Posted January 20, 2015 Posted January 20, 2015 Have just made up some dodgey brothers speaker cable and set one driver buzzing away at 95dB 100Hz. There is some real excitation happening at this SPL so we will see what happens. I have moved to the other end of the house for half an hour. Interesting...the crossover would take longer I suppose with those enormous capacitors and inductors.Yep. Lenehan speaker's I think 300-400hrs for crossover burn in.
acg Posted January 20, 2015 Author Posted January 20, 2015 Interesting non-result right here. So after 30 minutes of 100Hz test tone played at 95dB the Fs has not moved at all. Still not loud enough perhaps? According to the spec. sheet for the 8M 95 dB at 100Hz will happen with a bit less than 1 watt. The cone was certainly more excited than the first try and it was easy to feel the basket resonating. It is impossible to tell how much cone excursion was happening, but it was definitely a more than earlier. Any ideas?
acg Posted January 20, 2015 Author Posted January 20, 2015 When I did the initial 95dB 100Hz "break-in" I noticed (but did not do anything about) that the tone was "dirty" with pops and probably all kinds of harmonics. It was just a file I found online but it did not sound 100% right to me. So I downloaded a few more online samples, listened to them and picked the one that sounded most "pure" (whatever that means!). So while I was doing something else outside I cranked 40 minutes at 85dB 100Hz with the new tone. Interestingly, the new tone did not sound anywhere near as loud as the original, and in fact I played it 10dB down, but what I did notice is that the cone behaved in a much more linear fashion. I could see the woofer behaving uniformly and used my fingernail to determine that it was uniformly rising about 2mm above the face of the basket, which when combined with its normal at rest position means the cone was extending outwards about 5mm. Excellent...I could not quantify this before. So how did it measure? Eureka!! We have movement...nearly 7Hz in 40 minutes plus maximum impedance has reduced 9 Ohm. Phew. 1
niss_man Posted January 20, 2015 Posted January 20, 2015 Will be interesting to see how long it takes to reach the 81hz manufacturers spec.
davewantsmoore Posted January 20, 2015 Posted January 20, 2015 Yes..... I see it is a naturally very stiff driver (cms=0.17mm/N) .... so it might take some bashing. Still .... 20 more hz is a lot, so it might not reach 80, shrug.
acg Posted January 21, 2015 Author Posted January 21, 2015 This morning I rode my daughter to childcare on the double-up bike and left both drivers playing a 80Hz tone at about that 85dB for exactly one hour (the time for the round trip). The driver that has had no test tone applied to it before dropped from Fs=106Hz to F2=99Hz . The driver that had already dropped to 100Hz dropped further to 94Hz, which seems like a fairly linear rate of change: 40 minutes 100Hz for a 6Hz drop and then 60 minute 80Hz for another 6Hz drop. At this rate it will take another two hours at 80Hz for this driver to reach 81Hz (its spec Fs) and say three more hours for the fresher driver. Interesting stuff indeed. A big thanks to @@davewantsmoore and @hochpeper for bringing this to my attention. 2
davewantsmoore Posted January 21, 2015 Posted January 21, 2015 Great! You can see that with the minuscule excursions that driver will get in a properly loaded horn, that it would take forever (if ever) for the driver to settle in..... and this would affect your system tuning (likely to put the lower passband of your horn right out of whack) That's quite the bashing.... however on reflection the specs for this driver basically say that it is very stiff (mechanical compliance is low), but has a lot of travel (xmax = 10mm) .... so perhaps not so surprising (you'd expect a driver with lots of travel might be "loose" - and vice versa) I'll be interested to see if the "linear" change continues.
acg Posted January 21, 2015 Author Posted January 21, 2015 Yes..... I see it is a naturally very stiff driver (cms=0.17mm/N) .... so it might take some bashing. Still .... 20 more hz is a lot, so it might not reach 80, shrug. Yes, you are right Dave, the suspension is very stiff. If I press on the woofer cone of the ML1's at my desk I reckon there is less than half the force required to move it compared to the cone of the 8M's. It was interesting but with the fresh driver and the one with the 40 minutes on it playing 80Hz beside each other on my desk I could hear the difference in tone between the two. Considering the wavelength of 80Hz is 4.3m I did move around to make sure it was not just an anomaly in one position, plus 80Hz is down in that grey area where directionality is debatable. Great! You can see that with the minuscule excursions that driver will get in a properly loaded horn, that it would take forever (if ever) for the driver to settle in..... and this would affect your system tuning (likely to put the lower passband of your horn right out of whack) Yes, that was really worrying me to be honest, especially when I initially measured the Fs and it was so far removed from the specs. I do wonder how many 8M's are out there sitting in a big upperbass horn that are not yet "free"...could be a few I reckon. I'll be interested to see if the "linear" change continues. I doubt it will, but I will find out.
damohpi Posted January 22, 2015 Posted January 22, 2015 have you tried bolting them face to face, or at least mount them close together, and playing them together but out of phase? it should cancel/reduce some of the the noise and help break them in evenly with respect to each other
acg Posted January 22, 2015 Author Posted January 22, 2015 have you tried bolting them face to face, or at least mount them close together, and playing them together but out of phase? it should cancel/reduce some of the the noise and help break them in evenly with respect to each other I have been tempted to do this, but in the true spirit of experimentation I have not. Wanted to play around a little more with what it takes to break in these drivers. So, another little experiment this morning. I replicated the lower 80dB volume that failed to get any results a couple of days ago and gave both drivers much more time than I was planning. In two hours neither one moved one iota regarding Fs even though there was plenty of cone movement. So I upped the SPL to about 85dB, gave another hour and ended up dropping Fs to 86dB and 89dB, drops of 8dB and 10dB in an hour. Seems like they are loosening up now. It is also obvious that these drivers would take eons to free up if placed fresh into a large horn where excursion is limited. 1
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