[Vintage-Audio] Speaking On Speakers

[Bob]

One must also consider that the horns have a phase center
that moves with frequency and really messes up stereo's
sound field. This didn't bother people too much at first as
the source material really wasn't mastered for a sound
field, but to just place the various instruments around and
the vocals somewhere, The idea that vocals should be in the
middle didn't even occur for a while. Nothing was in the
middle at first. It took a good ping pong to really
demonstrate stereo...or so they thought. 

I don't agree with the idea that air or acoustic suspension
came after the big transistor amps came along. Kloss,
Lansing and Warfdale in England had very fine Acoustic
suspensions that required 50-60 watts for the average window
to break (Really, I broke a window with a Klipsch and 50
watt amp with Victory At Sea in about 1960 and it wasn't
even turned up to 20 watts.)

There are at least two fundemental problems with speakers,
low frequencies and high frequencies. In solving these
problems you generate problems with the middle frequencies. 

Starting with the low frequencies..if you can get the
speaker to act as a piston it will move air at the low
frequencies. But the air moving in the front of the speaker
cone and the air moving behind the speaker cone will cancel
each other and you will not have much sound a few
wavelengths away. So you need a "baffle" to block the rear
from the front. An infinite baffle is just that, a very
large wall so that none of the energy that is radiated from
the rear of the speaker can be heard. So mount you speaker
in a wall that is open into the next room, or better
outside. Some folk built speakers into fireplaces. You can
try to simulate the infinite baffle using a very very big
box and lots of absorber. Absorber doesn't work too well at
low frequencies and the closed box will create standing
waves if the energy rattling around inside is not absorbed.
That is why a big box. Wait..a little box full of absorber
will work if the box is small enough that the low
frequencies that cannot be absorbed are not bouncing around. 

This is the theory behind the acoustic loaded or air
suspension speaker. The low notes just load the cone with
back pressure, the high notes are absorbed and the middle
notes are now in trouble. Again with careful design, you can
solve the middle frequency problems. These baffled speakers
are less efficient than the horn or bass reflex, but they
can be made quite flat in frequency and have a reasonably
stable phase center. 

All speakers have a low frequency resonance. In general this
sets the low frequency where the cone acts as a piston. You
can move this resonance lower (or higher) by feeding some of
the rear energy, which isn't doing anything anyway to couple
with the front. Done carefully, this can lower the low
frequency by a factor of 2 or so. This is the theory behind
the bass reflex. The real problem is with the phase of all
this boost and the resulting ripple in the bandpass. It may
even sound worse that the same speaker in free space. Again
careful design of the enclosure can resolve these problems.

Bose speakers really sound great. No question, Bose has
captured what ever speakers need to do and packaged it. But
dont EVER run response curves on a Bose speaker. They will
never sound as good to you again. Sound engineers have a
saying, "No highs, No lows; must be Bose".

Gotta go..

WBob


JM/CO wrote:
> 
> There were several factors at work here. First, this must be viewed in the
> context of a timeline.
> When "Hi-Fi" was new ( post WW II ), it was very expensive, and therefore
> only affordable to a relatively few, relatively "sophisticated" listeners.
> The dominant music of choice was classical, and most people sat in one spot
> and listened. Audio was not an instant mass consumer success like TV was at
> the same time.
> The Klipsch corner horns were first produced in 1946. They are among the
> most efficient speakers ever produced. The dominant electronics of the time
> called for  power amplifiers which tended toward (very ) low power, thus
> making the high efficiency of horn loaded / bass reflex speakers desirable.
> A 12 watt amplifier, such as a Brook,  was considered "overkill". There was
> great debate in the Audio Press as to whether Triode or Pentode technology
> was superior.The best pentode vacuum tube audio amplifier circuit ever
> developed, the McIntosh, was first introduced in 1947. Early versions were
> only 15 watts.
> Wealthy folks also tend to live in large houses, and like to look at pretty
> furniture. Most of these early speaker cabinets fit this requirement nicely.
> As we moved into the 60's, and "stereo" began to dominate, audio technology
> became the technology of choice of the masses, who, for the most part, did
> not have critical listening skills, nor the large living areas required for
> the older, larger designs. Also, two speakers took up more room than one.
> Listening habits had also changed. FM Stereo began to broadcast in 1959, and
> stations that had, for years, been locked into a classical format, began to
> change. The music of choice had become Rock, and while some listeners wanted
> to sit and listen while imbibing their favorite substances, others wanted to
> dance to "punchy" bass, and "sizzling" highs.
> Another factor was the development of more powerful  amplifiers. The pentode
> "Williamson" and McIntosh designs gave way to solid state beasties, which
> could achieve a superior power to weight ratio. As power pushed up, speaker
> efficiency could afford to be lowered, and the "air suspension" or "acoustic
> suspension" speakers ( first designed by JB Lansing ) began to dominate. The
> overall system would equal, in loudness, the capabilities of earlier
> designs.
> As we moved into the '70s, these two consumer trends, toward smaller size,
> and more power available, led to speaker designs that were very in-efficient
> ( Bose 901, AR-3, Ohm "A" etc. )  but could be powered by relatively in -
> expensive large amplifiers to produce decent sound.
> By the early 1970's, power amplifiers of up to 350 watts per channel ( Phase
> Linear / Crown ) were being used in home audio systems.
> Unfortunately, the quality of the components in these "consumer grade"
> speakers left something to be desired. There are truck - loads of 60's and
> 70's vintage speaker systems showing up in local landfills these days
> because the foam suspension material for the woofers / midranges has all
> rotted. By contrast, many of those old "boatanchor" speakers made by such as
> Electrovoice, Bozak, Altec Lansing, Tannoy, J. B. Lansing etc, etc, are
> still working just fine, and are highly sought after and expensive today.
> Oh- one other thing. Electromagnets, as a speaker component, disappeared
> before WW II. ALNICO was discovered ( I think ) in 1938.
> Chuck N1LNH
>