Yeah he "did not mean it" (some good info in there!) If he likes pies, lets not set a fresh one nearby...lol WB0IQK Mark, has the right idea. I too used a dual cone speaker, I wanted to stay away from other types of boxes in order to keep the system unity complete. I was not aware of that one shown by Surplus Sales and instead used a common "bulk" speaker used in factory car stereo installs. I think it was like (embedded link) yet mine is 8 Ohm. When you use some additional power, you can boost/cut to suit, compensate for cabinet issues too. There is just enough room (barely) to use dynamat throughout. Discard the cardboard inside and use more proper hardwood ply version, and go. I used contact adhesive to glue black speaker cloth to the hardwood, so when assembled it looks beautiful through the metal grill.? It takes some fiddling around, yet worth it. It sounds a bit better than my SP-20 for sure, and that one is excellent. Oh, I used a thin layer of open cell foam on the back of the AC4 also which is cut to allow ventilation also. Make no mistake, a stock MS-4 sounds terrible, yet does work.
On Friday, January 3, 2025 at 10:39:54 AM EST, n4buq <n4buq@...> wrote:
Richard,
The next time you "don't mean" to post something like this, please post it anyway!? I found this very interesting.
Barry - N4BUQ
> 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
>
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>
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