[Trevor]

On 27/01/2015 6:51 PM, Peter Larsen wrote:
"Trevor" skrev i en meddelelse
...
On 23/01/2015 2:16 AM, Scott Dorsey wrote:
Les Cargill wrote:

I have never had problems finding the manufacturer's published T/S
parameters.

Sometimes those published parameters are pretty fictional.

I'm not going to mention any particular manufacturers here, but a quick
sweep in free air to determine Fs by ear will tell you who they are.

And when they are not entirely fictional, they are often just ball park
figures which don't allow for individual and batch variations. If I'm
going to the trouble of designing and building a box, I'd rather take the
time to measure the drivers first, and then tune the finished box. But
each to their own.

I have a rebuilt white D123 made from original spareparts that has never
been used, it is as hard as guitar loudspeaker. Very nice sounding midrange
on home-coming test sans cabinet, seller suggested that a few days of
sinewave might do it good ... not gonna do that, just playing will be fine -
I don't want to loose the stability of the rear suspension but yes, it will
change in use. Fortunately what it means is only that the initial bassreflex
tuning will be on the lowish side.

I think the specs are where they expect(ed) a played in loudspeaker to end
up,

There were no T/S specs for that speaker when JBL designed it. (You were
lucky to find the Fs at the time) It was before Neville Thiele had
published his work I think, certainly before it was widely known and
accepted. And IME, and I think according to Dick Pierce's vastly
superior experience, "burn in" is not a one way street anyway. And
fortunately some variations cancel themselves out. What does happen and
is a far bigger problem these days IME is changes in design or materials
between batches that are not accompanied by new T/S specs. That will
*really* affect your box design if not careful. So measurement is always
a good idea IMO.

Trevor.