[rollei_list] Re: Completely OT- Loudspeaker info

You left out Mr. Bose.


On Wed, 16 Feb 2005 12:47:14 -0800, Jerry Lehrer <jerryleh@xxxxxxxxxxx> wro=
te:
> Thanks for the Audio 101 lecture, Mr. Vilchur and Mr. Koss.:-)
>=20
> Jerry
>=20
> Richard Knoppow wrote:
>=20
> > ----- Original Message -----
> > From: "Jerry Lehrer" <jerryleh@xxxxxxxxxxx>
> > To: <rollei_list@xxxxxxxxxxxxx>
> > Sent: Tuesday, February 15, 2005 6:48 PM
> > Subject: [rollei_list] Re: Completely OT- Loudspeaker info
> >
> > > Richard
> > >
> > > The people in the audio world refer to the planar
> > > speakers, such
> > > as the ones made by SME , Magnaplanar, and Martin-Logan,
> > > as
> > > dipoles.  Some "dipole" speakers have the backwave
> > > absorbed
> > > almost completely.  Then, are ribbon speakers "dipoles"?
> > > All
> > > that I have used, absorbed the backwave.
> > >
> > > Jerry
> > >
> > > Richard Knoppow wrote:
> >
> >   Loudspeakers of the diaphragm type are all dipoles. That
> > is energy is radiated from both sides with a 180 degree
> > shift of polarity from one side to the other. Ribbon and
> > electrostatic speakers are dipoles as or common moving coil
> > and cone speakers.
> >   The loudspeaker inclosure does two things. First, it
> > prevents destructive interference from the backwave
> > radiating into the hemisphere as the front. Because most
> > loudspeakers are small compared to the wavelength at low
> > frequencies each side is strongly non-directional. If the
> > speaker is placed in a baffle which is large enough the path
> > length around it will prevent this kind of interference down
> > to the frequency were the sound waves are able to bend
> > around it.
> >    A fully enclosed box will completely prevent destructive
> > interference by the back wave.
> >    The second purpose of at least some enclosures is to
> > provide a better acoustical impedance match of the air to
> > the loudspeaker. This is a somewhat complex subject. The air
> > has a characteristic impedance. Just as in an electrical
> > circuit the maximum transfer of energy takes place when the
> > source impedance matches the sink impedance, and both are
> > resistive. A small cone in air is both mismatched and very
> > reactive. A closed box will improve matters somewhat but
> > there is a still a rapid fall off of transferred energy
> > below a wavelength approximately equal to the circumference
> > of the loudspeaker. In order to improve this at low
> > frequencies some sort of impedance matching device must be
> > used. The two types most often encountered are the
> > bass-reflex and the horn. A bass reflex enclosure is the
> > analogue of an impedance matching filter section. A labrynth
> > type box is the equivalent of a 1/4 wave matching section as
> > used in radio frequency transmission lines. The Bass reflex
> > is essentially a lumped constant version of this. A properly
> > designed bass reflex enclosure will substantially improve
> > the match over a fairly narrow range of frequencies. An
> > acoustical horn is the analogue of an electrical
> > transformer. One can see it as enlarging the size of the
> > loudspeaker diaphragm to the size of the horn mouth although
> > this is a gross simplification. When used for mid or high
> > frequencies horns can be close to their ideal. This can
> > yield a very great increase in the efficiency of power
> > transfer and also be used to control distribution of the
> > sound. At low frequencies an ideal horn is usually too large
> > to be practical but a smaller horn can be used and still
> > have considerable improvement in efficiency. For the minimum
> > frequency possible a close box enclosure with a properly
> > designed loudspeaker and lots of equalization is superior to
> > the other forms due to size but is very ineffient.
> >    In the past large horn systems were use almost
> > exclusively in motion picture theaters because electronic
> > amplification was expensive. In more recent years large
> > closed box systems have taken over for bass reproduction
> > because power is now cheap and they deliver better, or
> > deeper, bass. Horn midrange systems are still used because
> > of their advantage in controlling distribution.
> >    Up to maybe the 1950's a typical 500 seat theater had
> > about a 10 watt amplifier. Amplifiers as large as 50 watts
> > could be found only in the largest theaters. Now one can
> > have kilowatts if desired so speaker efficiency is no longer
> > so important.
> >    All this takes me back to what seems like a previous
> > life.
>=20
>=20


--=20
Peter K
=D3=BF=D5=AC

Other related posts: