potential speaker problem

[Guest Douglas Wright]

I came across a pair of "Linn Isobarik" speakers - the Sara model.  I need some advice before I make an offer.  It seems like they could be a pretty nasty thing to drive without the right amp.  They can dip down into some really low impedance.  I'm wondering if they could smoke a 6250.  Any thoughts ?

[musinteg 5]

Could you define " really low impedance"...Loudspeaker impedance varies with frequency. A loudspeaker with an "8 ohm" rating can dip as low as 4 ohms at certain frequencies. Certain speakers drop to 1 ohm ( Martin Logan ).

 

I have never owned a pair of Saras', but looking at a few google images, the tweeter looks like a scanspeak d2008 ( shouldn't give ANY impedance problems here ), the woofers are KEF SP1004 8" units in parallell. ( true isobaric ) wiring. You will get some dips into the 2-3 ohm range, but unless you are driving test tones through them, I wouldn't be too concerned.

If you want to see the worlds most USELESS owners manual, go here : http://www.linn.co.uk/owners_manuals

and look up the SARA manual.

I'm quite familiar with many carver products, but not so with a 6250. Anyone else care to wade in ?

Rob

[Guest Douglas Wright]

Thanks for your reply Rob.  It pretty well squares with the little bit of (useless) info I've been able to find.  It seems that Saras are  nominally  4 Ohms - lower in the treble region - as the amp is driving one tweeter (on one crossover) and a resistor (on the second crossover).  They do have a dip at about 4khz to 2.6 ohm.

 

Numbers for the 6250 receiver are 8 ohm/125w - ch, and 4 ohm/140w - ch,  and 2 ohm dynamic power/ch  is 145w.  That being said, real world experience suggests 6250 power transistors are susceptible  to over-heating  to the point of failure  if they are pushed too hard. Therein lies my concern.  The Linn Isobaraks are unknown territory for me, and I tend to err on the side of caution.  But I really want them if they will do no harm.

[BillD 239]

You typically don't need nearly the power at 4kHz that you do at, say, 40Hz.  I'd certainly risk the low impedance at that frequency rather than a frequency demanding a lot of power (to move lots of air).