Speaker ports
"Trevor" skrev i en meddelelse
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On 27/01/2015 6:51 PM, Peter Larsen wrote:
I have a rebuilt white D123 made from original spareparts that has never
been used, it is as hard as guitar loudspeaker ....
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 when it was known nobody in their sane mind would design the white D123
version, according to the specs that come with winisd it should have a 200
liter box, according to the guidelines Duelund taught me - I don't know if
they were his own or had some source - it is a unit for a closed box with
its Qt around 0.45. With a room friendly box version it almost invariably
ends up with a 4 dB boost around 60 Hz or - in a closed box - quite lame
sounding. All assuming those specs are valid of course.
And IME, and I think according to Dick Pierce's vastly superior
experience, "burn in" is not a one way street anyway.
Yes, quite well matching that speakers that have been left unused should
have a play in before being evaluated, he did write about this over in
~.tech.
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.
Oh yes, most designers would prefer "loudspeaker unit" to be a constant
rather than a variable!
Trevor
Kind regards
Peter Larsen
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