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I must comment on a couple of things: Hi-Fi speakers have extended
range both ways. Hiss comes from extended high end but it may indicate
the speaker is resonant or peaky there. Not so good.
What you call "acoustic suspension" was a trade name for speakers
made by Acoustic Research (AR). The idea being that the restoring force
on the cone is made by compressing the air in the box. The box and
speaker are a unit and must be used together. It allows very low cone
resonance to be achieved with a relatively small box. The down side is
that the efficiency is necessarily low if the response is to be flat.
Despite being much maligned AR speakers were actually very good, if used
right, but take a lot of power.
A ported enclosure or "Bass Reflex" once a trade name of Jensen, is
another case where the speaker and box are a unit and must match. A
properly ported enclosure increases the efficiency of a speaker for a
given minimum frequency response but the enclosure forms something like
a lumped constant quarter wave matching network to the back of the cone
and for flat response and and best reduction of low frequency distortion
must be matched to the speaker. This is more than simply tuning the box
to the speaker free=air resonance. While some small ported boxes have
been made in general a ported enclosure must be fairly large to perform
well.
The Acoustic Labrynth, once a trade name for an enclosure patented
by Stromberg-Carlson, is another form of making a matching network for
the back of the cone, in this case a damped physical quarter wave
transmission line. Its performance is similar to a bass-reflex. The are
complex and therefore have never been as popular as the very simple
bass-reflex.
Direct radiator speakers are not very efficient, the limit is the
acoustic impedance match between the diaphragm and the air. The
acoustic load on a speaker, equivalent to the radiation resistance of
an antenna, varies with frequency. It is something like a Bessel
function. The important part is that below a mid frequency,
approximately that with a wavelength of about equal to the circumference
of the cone, the radiation resistance falls off quite rapidly. To
increase the low frequency output the cone resonance is raised to act as
a sort of equalizer. Low frequency response below cone resonance drops
like a rock. If the low end resonance is made lower the overall
efficiency must be reduced it the speaker is to have flat response. So
you are stuck. By using an acoustic impedance matching network one can
increase the overall efficiency obtainable for some low frequency
response cut off. This is the function of a bass-reflex or similar
enclosure. A horn acts like an acoustic transformer, increasing the
acoustic load over a fairly wide range of frequencies, at the cost of
size and complexity. The low range extension of the Acoustic Suspension
method is a matter of obtaining a low cone resonance in a small box but
does not improve efficiency, rather lowers it for the reasons stated
above for low frequency range vs efficiency of any closed box enclosure.
The Acoustic Suspension has an important advantage in that the
compressiblity of the air in the small box is more linear than the usual
"spider" and cone surround, which form the resoring foce in conventional
speakers.
The damping factor of the amplifier also comes into it especially
with the bass reflex enclosure, where it becomes a part of the total
acoustic impedance of the speaker (electrical to mechanical to acoustic
inpedance transformation which is accomplished by the speaker includes
the electrical properties of the amplifier). Most tube communication
receives have single ended pentode amplifiers with no feedback having
poor electrical damping. This can result in peaky low end response from
bass-reflex boxes. Mostly they do better with totally enclosed boxes
with some internal damping in the form of acoustical absorbent.
I didn't mean to post another essay, delete it if you like.

On 1/3/2025 6:39 AM, Floyd - K8AC via groups.io wrote:

I'd say that it all depends on how you're using the rig.? If your Drake
stuff falls into the "Shelf Queen" category, then the stock MS-4 is the
way to go.? My C-line is in daily use along with my other vintage gear
and the MS-4 is a loser for several reasons: It sounds terrible, it
takes up too much space and the fact that most folks house the AC-4 in
it restricts where you can place it on the operating desk.? I've found
that speakers designed for home theatre or music use are a far better
choice as they tend to sound great for communications use, are far
smaller and can be had for a fraction of what you'd pay for any speaker
offered for amateur radio use.? A few years back, speaker manufacturers
were convinced that everyone would be buying surround sound speaker
systems for their TV system, and cranked out zillions of "surround sound
speakers" to be used at the rear of the listening area.? These tended to
be much smaller than the main speakers, but with very good performance.
Today those speakers are sitting on shelves in Goodwill and Salvation
Army stores at giveaway prices.
I have a number of them with Sony and RCA logos on them, obtained from a
large "used stuff" store in Winston-Salem, NC.? A couple of them match
the Drake gear perfectly and are the right color and size.? Such
speakers are typically either ported or acoustic suspension, so have low
end response that produces a good sound for SSB.? ?Another good speaker
alternative are the ones made for use with a PC.? ?West Mountain Radio
makes a pair of powered speakers labeled "COMspkr".? While those are
powered speakers, one of the pair just has an RCA speaker connection.
I don't believe that wide range or hi-fi speakers are unsuited for
amateur radio use.? If you use them and are hearing unwanted hiss, fix
the audio source to eliminate it.? I use an old Timewave DSP-59+ between
the receivers and speaker to shape the audio to my liking and eliminate
power supply hum and high end hiss.? The LogiKit SCAF-1 filter is
another good choice for that purpose.
73, Floyd - K8AC

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998