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Hi folks, my first appearance in this forum, and many thanks to Robert and Bill for introducing me to the Apollo at the RMAF - my favorite room at the show, no matter whether it was the Allen Wright modified SACD player or the Stellavox tape machine.I've been listening to a Prometheus going through its burn-in process at a friend's house, and I've had some thoughts on ways to improve the break-in process for the unique Bastanis drivers. I understand the break-in of the spider, as typical for most drivers, takes only a day or two. This is typical for most dynamic drivers, where the cone material is stable and doesn't change with time or use - it's the spider that changes, and results in the well-known lowering of Fs, as well as improvement on dynamics and tonal qualities.
What's different with the Bastanis drivers is the *cone* requires a break-in as well - and a much longer break-in than the Lowther or Fostex. This can try the patience of Americans - especially the folks around here in Colorado, who are a more go-go, hurry-up kind of crowd than the people I knew in the Pacific Northwest. So I've been thinking about not only a quicker break-in, but also better, more thorough, one that would result in symmetric properties and a quicker arrival at the chemical/mechanical steady-state condition (the tail end of the asymptotic break-in process).
My thoughts so far - and I would welcome comments from anyone who knows more than I do, especially Robert - are this:
1) Get an analog signal source that puts out very fast rise-time square waves, 1 microsecond or less rise-time (not a sound-card or CD player). There are plenty of old analog sig generators that put out very fast square waves. Get one that runs as low as 20 Hz - you'll see why later.
2) Get a decent-quality transistor amp with a bandwidth of at least 100kHz and anywhere from 20 to 50 watts output power.
3) Face the two Bastanis widerange drivers towards each other - maybe an inch apart or less. Connect one to each channel of the amplifier, but connect one driver out of phase. Get a "Y" splitter for the signal source so both channels of the amplifier are driven together.
4) Set the generator anywhere from 20 to 30 Hz, adjusting the frequency for maximum displacement of the cone - the third harmonic should land on the resonant frequency of the driver, and it should be obvious when it does.
5) Increase the power level until the cone is moving about 3 to 4mm - Robert would know what a safe long-term level would be, but these are basically PA drivers, so they should absorb a few watts with no problem.
6) Leave it on for 24 hours, with a blanket over it if the sound is annoying (and it will be). I would recheck every few hours, adjusting the frequency downward as the spider and cone break-in together, which will gradually lower the resonant frequency of the driver. Sweep the frequency up and down to find the new resonant frequency, and leave it there for a few more hours, then repeat until the 24 hours are over.
7) my best guess is 24 hours of this treatment will be equivalent to hundreds of hours of music player at a fairly high level. Why? Loudspeaker drivers are constant-acceleration devices - a theoretically perfect driver with a flat acoustic frequency response also has a flat acceleration vs frequency curve.
This implies that the cone and voice coil former, and most of all the cone/voice-coil-former junction, experiences extremely high G levels in normal use. It is this area that is changing in sound as the driver breaks in - the spider is what responds to the large excursions of the bass (displacement), but the cone and junction area that experience the high G levels in music playback.
If we want to encourage the process of re-forming the fibers of the cone, and remove small stress fractures in the cone/VC glue region, we want to give it lots of acceleration, not displacement. We don't want to destroy it - obviously 200 watts of square wave power is too much - but do want to take the cone assembly to a reasonable fraction of its maximum acceleration. If max acceleration is 100%, we'd like maybe 10% to 20% of that for 24 hours, so the driver is well within its limits, but working at a reasonable fraction of its potential.
The problem with music is the duty cycle - 95% of the time far below peak modulation - and rather low peak acceleration, except for very loud percussion, or maybe trumpet sounds. There's lots of variety, but the peak energy, especially peak acceleration, is only happening a very small percentage of the time, even if you are feeding the driver with a 200-watt amp at full power.
Anyway, that's where we come to the test generator, which can be an old surplus instrument. The high rise time generate the maximum possible G-force, as well as maximizing the fourth derivative of motion (jerk), which should relieve stresses in the fibers of the cone and the materials used to assemble the driver. The key concept is to carry it out at levels that are well within the thermal and mechanical design limits of the driver, but using a signal that efficiently - and completely - removes the artifacts of manufacture.
Hi all,This is my first post to Robert's forum. First I'd like to thank Robert for using my new amp to demo the Apollo's in his room at RMAF. On to current business...
I was reading Lynn's break-in ideas and the requests for break-in signals. Started playing around with the tone generator in Cooledit 2000. Cool edit can make some pretty strange sounding tones! You can choose the wave type, base frequency, how much to modulate it by and the modulation frequency. You can also add a start and stop frequency and sweep the whole mess.
I also discovered that my cats really don't like the sound of low frequency squarewaves played through the crappy little PC speakers on my desk. It's turned out to be a most usefull tool for removing my cat from the space between me and the monitor. Just click the preview button in Cooledit and watch the ears go back then the cats leave the room. Works very well even at at low volume.
I was thinking that a base frequency of 20 hz modulated by 5 hz with a modulation periode of 10 seconds would cover all the frequencies of interest quite nicely. This would give us a square wave sweep that ramps up and down every 10 seconds between 15Hz and 25Hz. If we made the modulation 10Hz so the fundimental ranged from 10 to 30 hz we would then cover all frequencies of the spectrum directly as the 3rd harmonic would come down to 30Hz and go up to 90Hz.
This test signal would cover the whole spectrum of frequencies while delivering a high G load to the driver. Recorded at a 96K sample rate we would have output up to 48Khz. This could be burned onto a DVD-V disk that any DVD player could play back. I'm not sure of the high frequency capabilities of most DVD players though...
If there are any takers I could burn a 96/24 DVD-V for the extended frequency version or put it on 44/16 CD for a more frequency limited version and send it to someone to try.
Hi Gary,thank you for sharing the forum and also for your kind burn in- CD offer, i will come to you by a p.n.
Regards
Robert Bastani
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If the woofer driver has the same cut out dimension as the wideband, why not install the widebands in the sub cabinets and drive with the sub amps with low freq test tones?
Thanks Lynn - a much needed consideration of the break-in issue.
How about some testing? Is it possible for someone to make a CD with a square wave program of 'music' and try it out? If it works it would be a great thing to include with every Prometheus.
A couple of customers here in Hong Kong (where there are no garages, basements or remote locations for noise generation) would certainly welcome the chance to speed up the break-in. I have a square wave generator and will try it here on my own set.
I did a very similar treatment when building mine; although I have a decent sweep generator capable of doing square waves, I burned a CD-R with fast rising warble tones from 18-40Hz and ran that hard as described by you (facing each other, out of phase, LOTS of blankets).
I did that 24x7 for about 5 days (loved ones wanted me killed ;-) ). Then, with the same setup, I ran a mix CD with lots of different types of music (percussion oriented, classical, 80's synth pop dance mixes etc.) for another 2 - 3 days.
The end results were good and I would agree with Robert's approximate numerical breakdown, maybe even a bit better, say 90+% near full musicality. The "rest" just took elapsed time, albeit enjoyable time!
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Hi Lynn,thank you for your in- depht thoughts about the burn- in of the widebands, i agree we have to do a pre- burn- in for the widebands.
The two aspects of burn- in you named can be solved by your method, i will discuss this with Bill. The maximum power- input to the widebands
depends on the signal. When you allow frequencies below 30Hz the voicecoil is cooled by it`s movement, then only the maximum- excursion is important for not- destroying the driver. The maximum- excursion for a 48 hours burn- in (imho better than 24 hours) should be setteled at around 4-5mm max. in each direction (max. 1 cm total), the cone can move more than 2 cm without mechanical crashing the voicecoil but better stay in a save range on permanent signal. Also the woofers need a burn- in to soften the suspension, maybe using the second channel of the power- amp for this is fine.
The re- forming of the cone- and glue- structures is also done by this method and i am shure that Prometheus can play music (also the cap, tweeters, cables and soldering- points need some signal and the mechanical de-stressing of mounting needs also some time)after a few hours when the assembling is finished. This method will help to make it much easier for customers.
There is a third aspect of burn- in regarding the Prometheus- widebands which can`t be solved by on a short string, doesn`t matter which method: The cones are flexing over a wide frequency- range, the re- forming of the structures can be done by your method but not the softening of the cone- structures in the microscopic range which is also very important for listening. This microscopic flexibility is needed for all the fine informations which doesn`t result a movement of the whole cone- surface. When the cone is too stiff in this range it can not follow the microscopic signals, like violins or guitars when new. It takes around 6 month until this cone- behaviour is stable and there are many customers who report that they get music out of the speakers relatively quick and then they thought there is no more change in sound until "the one day" they listened to the music and there was only music left, no more hifi- sound at all and every customer who reported this rated the change in sound very high.
My method of cone- treatment to achieve the flexing behavoiur is matched to this point to get 100% out of them.
Following my experiences i would rate the sound- quality of a new Prometheus wideband- driver at 40%, when the high- level burn- in is done they are at 85%, to achieve the 100% it needs time, i haven`t found a method to speed up the fine burn- in but the drivers don`t need high levels for this and also with your method for the high- level burn- in customers can listen to their music on a satisfying level after a few hours.Thank you again for your thoughts and working out a method on this string, it will be a big step ahead!
Regards
Robert Bastani
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Square waves are composed of the fundamental and a series of odd harmonics (no evens anywhere) - and to have it even be recognisable on a scope the harmonics have to go out to at least the 9th, preferably a lot further than that for a really pretty one.(In passing, triangle waves are spectrally identical to square waves, the only difference is the phase of the harmonics. This is said as a reminder that spectrum analyzers discard time and phase information, since triangle and square waves have very different behavior with respect to how fast the equipment has to slew in order to follow the rise-time of the square wave. Do square waves and triangle waves sound different, even though spectrally identical? I leave that as an exercise for the reader ... )
Anyway, returning to the topic at hand, we can exploit this harmonic structure of the square wave in order to cool the voice coil while we break in the driver. If we want to voice to really be moving, we select the FIFTH harmonic to be the same as the Fs of the driver - so, for example, if the free-air Fs is 60 Hz, then we tune the square-wave generator to 12 Hz. If we want the third harmonic, we tune the generator to 20 Hz. Simple.
I do feel the key concept is a waveform with extremely high acceleration. This will get the attention of the cone, and assist the chemical re-bonding and re-arrangement of the paper fibers in the cone. A square wave is nothing more than a repetitive series of step functions, which is exactly what we want to stimulate the break-in process.
Going along with that thought, hmm - maybe a test DVD-V recorded at 96/24 would be a good idea after all, since it could contain a series of test tones that gradually ramp up and down in level, maybe over a 60 dB range. Set the DVD player to "repeat" and leave the thing alone for a several hours.
But failing that, I would manually crank the generator up and down in level to let the thermal cycling do its work - a heat/cool cycle would probably be desirable. Maybe full power for five minutes, forty-five minutes at -40dB, and ten minutes at -20dB? (Full power, cool-down, and pre-heat cycle.)
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Hi guys,Do I see any volunteers to produce a CD ?
Cheers,
Thom (150 hours and counting)
|
| Galibier Design
| ... crafting technology
| in service of music
| http://www.galibierdesign.com
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Modified piano
To infinity and beyond!!!
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To infinity and beyond!!!
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Careful with this puppy
To infinity and beyond!!!
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Burn in..
To infinity and beyond!!!
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with HiFi News..there was no copyright mentioned anywhere..It had various burnin tracks...one was sub 20Hz...with a level adjustment...I used them for my Prometheus..If I put it too loud..the gainclone shut itself down...
The last track was a burnin track with modified piano notes..
I'll see if I can put up some mp3's on my site. Or if not too many people want a copy..I can make some copies.
is the Purist Audio burn in- CD but i don`t know if it is still available. I had one (somebody has stolen mine) - very expensive but worth the money. There are high- energy signals similar to what Lynn described, sweeps and pink noise on it, simply play it in repeat- mode for two days at high level and the first burn- in is done. Also the amps and all signal- touchíng components take profit from this CD, even when they are burned- in with normal music- signals. The amps will get much hotter than with normal music- signals...Regards
Robert Bastani
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Used the Purist Audio Design CD (REV-B)
(six-+++ hours as prescribed)Not sure where the improvement came from,
tubes, cap's, wires, drivers, or my just expecting them to ...Needed a second opinion....recruited ...
the "Sig-Oth" ....After a glass of wine
and an hour and a half-hour or so ... she said ..."Wow ... what did you get ... NEW ... how much did it cost ???
it sounds GREAT ..."My opinion too ... and the cost was about a hundred bucks...
After this "run-in", my system seemed to demonstrate a little more synchronicity ... to repeat an over-used term.It just keeps getting better ... back to tube "rolling" ...
and maybe ... putting the "caps" back on the MK II AirForce horns ...
GGGGGGGGGGGG
Robert,The Purist Audio Design CD is still available but is a revised edition (revision B). Retails for $99USD. I'm still wondering whether or not to buy it as I can't find any reviews of it on the 'net and I'm worried it may not be as good/effective (advertising hype aside) as the original.
I want to try this disc too, but had the same reservations...BUT....it's Christmas time and I have a very deep stocking above the mantle...Maybe Ms. Santa will be kind to me.
Dogs will be DAWGS...
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