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Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!hound!rfg
From: rfg@hound.UUCP (R.GRANTGES)
Newsgroups: net.audio
Subject: Re: Speaker Sensitivity
Message-ID: <1451@hound.UUCP>
Date: Wed, 30-Oct-85 23:37:19 EST
Article-I.D.: hound.1451
Posted: Wed Oct 30 23:37:19 1985
Date-Received: Sat, 2-Nov-85 01:48:14 EST
References: <480@uvaee.UUCP> <601@bonnie.UUCP>
Organization: AT&T Bell Labs, Holmdel NJ
Lines: 29

[]
Well, one more bit of information.  Its not the type of box, so much,
folks (horns aside) but the sound pressure level the designer is
aiming for. If you're not using a horn and you want loud sound at
low frequencies, then you have to move a lot of air. For a given
diameter cone, louder means more cone excursion (in and out).
Speakers designed for big excursions (so called "long throw") have
the problem, "How do you keep a long travel linear?"
1) You have to keep the suspension linear - solutions discussed
earlier.
2) you have to keep the voice coil seeing a constant magnetic field
throughout its travel.  For long travels, the easiest most economical
way to do this is to make the voice coil much longer than the magnetic
field. That way however it moves the coil still sees the same field.
However, it means that only a small part of the field of the voice
coil is being used at any time. Hence, a loss of efficiency.

If you decide to live with not so big excursions then you can still
get your frequency response and efficiency in the small box, only 
don't play loud. 

Horns act like transformers and couple the speaker to the room. You can
get loud sounds, large air motion, with small speaker excursions, hence
no need for long throw design (but watch out for the speaker suspension
when you drive the speaker below its cutoff frequency. 

-- 

"It's the thought, if any, that counts!"  Dick Grantges  hound!rfg