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Vintage JBL for subwofer
Vintage JBL for subwofer
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Old 7th August 2018, 08:31 PM   #181
academia50 is offline academia50  Argentina
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I always thought that, one of the factors that make the quality of a speaker is the high BL factor. This is intimately related to a high damping factor, which in turn improves the transients by returning the cone to its position in less time.

Although I read there that in some cases (as in the cabinets of acoustic suspension, AR, for example) this can be counterproductive. I think that high BL is good for BR, but I can be counterproductive to achieve good compliance in the suspension of cabinet cabinets of "pneumatic or acoustic suspension". They are not exactly the same as "sealed" cabinets, although they look a lot like ...
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Old 8th August 2018, 01:22 AM   #182
GM is offline GM  United States
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It does not specify the PDF if the magnet is Alnico or ceramic ...
One of my all time faves, it's ferrite and the odds of needing re-magnetizing approaches zero. Ferrite/ceramic [AKA 'mud'] motors reject heat, hence VC 'cooking' whereas AlNiCo is a pretty good heat sink, but does need periodic re-zapping when subjected to a lot of continuous hot or hot/cold cycling. In typical HIFI apps, they last indefinitely.

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Old 8th August 2018, 01:29 AM   #183
GM is offline GM  United States
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I always thought that, one of the factors that make the quality of a speaker is the high BL factor.
Not really, you only want enough to track the signal, so one must look at the total system Q factor [sysQ]; any more and the leading edge of the transients are clipped off [over-damped, 'fast'] and too little results in overshoot ['ringing', under-damped].

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Old 8th August 2018, 03:15 PM   #184
academia50 is offline academia50  Argentina
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Hello GM


It is good to know that the Alnico under normal conditions of use, without sudden changes in temperature does not lose its magnetization. They have always been used in domestic use indoors.

I understand that the general quality of a speaker is not something that depends exclusively on high BL, yes, we have other factors there.

But, do you want me to tell you? I see those current neodymium magnets and I have to force myself to accept that that can work well !

Yes, they are prejudices, but they have their reason of being, they are many years thinking that "the bigger the better" .....
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Old 8th August 2018, 03:40 PM   #185
jjccoutcher is offline jjccoutcher  United States
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The JBL 2245H does use the ferrite magnet structure and I would agree the 20 to 30 year old drivers I have been working with, they have held up rather well. I feel the consensus here is I should leave well enough alone and move on. At this point I agree, I figured if I was able to get one of my drivers done I could compare before and after to see if it was worth the effort.


Dampening as GM eluded to is a balancing act and the target changes depending on the speaker design (closed box, 4th order. 4th order filter assist, TL, horn...). I mainly work with the first 3 and try to hit the following Qs. Closed box - .5, 4th order - .7 and 4th order filter assist - .6. But those numbers aren't etched in stone the driver being used will effect the final number.


I am using the term 4th order filter assist in place of 6th order as I don't want the confusion of it being an isobaric.


The main purpose of the cabinet dampening is to control the driver at a given frequency range. In the case of the 4th and 4th assisted, it's controlling frequencies above tuning. The 4th assisted you can get away with more dampening because the filter is cutting out the sub-sonics the driver can't do.


I find when you get it right a sub should not be disassociated from the rest of the system. That shows up the best in imaging, i.e. does the kick drum sound real and appear in the proper place.


Sorry for getting long winded on this, but it is an area I am very passionate about.
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Old 8th August 2018, 10:08 PM   #186
GM is offline GM  United States
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Me too since my first separate sub system after reading a 1970 Popular Electronics 'Super Woofer' article and being aware of time/phase issues from the pioneer's dealing with aligning short HF horns to huge folded [mid]bass horns gave me a head start on getting a good in-room system summation.

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Old 8th August 2018, 10:15 PM   #187
GM is offline GM  United States
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But, do you want me to tell you? I see those current neodymium magnets and I have to force myself to accept that that can work well !
Greets!

FWIW if I ever buy any more HE/prosound drivers they will be neodymium [or whatever outperforms it, if any] because it's the first magnet at reasonable cost that AFAIK can control a driver as well as the pioneer's field coils.

GM
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