In fact , these are older than previously posted – Sonido , Woland Edition
These were first , proof of concept , so – kudos to HiFish (David , member of Baby Diyaudio) for bravery and trust in my choices .
What’s already written regarding previous ones , applies here too – motor run caps , hefty iron for bass helper etc.
Pics are little smaller this time , maybe I’ll change them in time (just to visit David again , and remember to take non-shrinked files from him) .
Gallery comprised of old pics and last few recently made , when I changed test xovers for proper ones . Positioning motor-runs on top of box is David’s wish .
Well , these two yellow-ish drivers are Hungarian Sonido – FR 8″ as main , baffle-less mounted , plus 12″ in folded MLTL box .
Tweet Helper is Fountek ribbon.
Xover is simple – 8,2mH Torobar for 12″ , 58uF (47+10uF Icar motor-runs + 1uF MKC) for 8″ , 1uF MKC for Fountek tweet helper . All drivers in phase electrically.
I’ll put exact driver types later here .
Concept , same as plans for box ( well known MathCad MLTL software my MJK of http://www.quarter-wave.com/ ) , xovers and their execution, are mine , while boxes are work of local Wood Meister .
Woland is that handsome (even if already old fart , as me) guy visible on last pic ….. member of our Baby Diyaudio.
As title sez – boxes for Mr. Vladimir Simovich’s (AKA AR2 , AKA Master Burner ) office 😉
Finally I got him to buy a pair of not so expensive Tanns ….. after more than a year of me harassing him with numerous Tann links …..
Box plan is sort of my job – done with MJK MathCad MLTL sheets – http://www.quarter-wave.com/ , while xover will be , hopefully , other Aleksandar’s work – http://www.raalribbon.com/
Mr. Simovich and Mr. Aleksandar Radisavljević RAAL are friends …. and these gorgeous Eternity pics at RAAL home page are work of Mr. Simovich 😉
So , world is ……. small
Taken from here : http://tinyurl.com/kjyup7u
Here’s the Scoop
Ferrite magnets do not demagnitize with time or drive. They are affected by temperature but that is reversible. They will return to normal when they return to room temperature. Ferrite is basically a lousy magnet material for speakers but it is cheap and readily available. JBL has done a ton of things within the magnetic circuit to make the material behave in a more stable manner. At 100 degrees F, a Ferrite motor will be down about 1.5 dB in level which means the midband of the woofer will be lower by that much and there will be increased output around the system resonance. The TS parameters will be completely different – as though the BL was reduced by about 18%.
Alnico magnets, by their nature are easy to demagnitize with drive. They will not change with time and their dependence on temperature is really small – maybe 1% at 100 deg.F. Alnico stability and resistance to back EMF is really good. This is why they make the best sounding magnetic structures. Unfortunatelly, given a big enough pulse of magnetic energy, they will demagnitize by up to 3 dB. The sensitivity to demagging is dependent on the specifics of the magnetic circuit and the length of the coil providing the field. Underhung woofers (LE15 and such) midranges, tweeters and compression drivers do not have sufficient back EMF fields to push the operating point of the structure below the knee. They are essentially stable regardless of input signal. The short gap-long coil speakers are the ones that have a problem. A 2235 can take a hit of up to 3 dB if a big enough hit of current takes place. 1.5 dB to 2 dB is more common. The effect does not get better or worse with time, it solely depends on how much current is driven through the coil. The more current, the more field. Once the field is bigger than a certain number, some amount of demagnitizing occurs. It is perminent (until externally recharged) and will only increase if a larger sustained current hit occurs.
Therefore, if you have a qualifying alnico woofer and you have played it loudly you have some damagging. You can have the unit recharged and it will be fine until you play it again. Exceed the critical level and it will start happening. If you never do, it won’t ever demag. Most of these designs trace back to the 50’s and 60’s where 15 – 30 watt tube amps were the rule. They didn’t have the current capability to hurt anything. With the advent of big solid state amps, the current levels went up and the problems started to surface.
Most of the qualifying 4″ motors will loose 1 – 1.5 dB unless they are pummeled. Some of the older 3″ with really short magnets, like the 2213A and 123A will typically be around 3 dB down. They go really easily. The old decade woofers (116A and 127A) only had to see an amplifier in the room and they got really nervous. FYI, the new 1500Al used in the S9800 can take continued pulses of 5000 watts and loose no more than 1%. The test can only be done a few times before the coil is destroyed, but the magnetic assembly is totally stable.