[Boatanchors] [AMRadio] Dreaded D-104

[Richard Knoppow]

----- Original Message ----- 
From: "Todd, KA1KAQ" <ka1kaq at gmail.com>
To: "Discussion of AM Radio in the Amateur Service" 
<amradio at mailman.qth.net>; "Boatanchors" 
<boatanchors at mailman.qth.net>
Sent: Thursday, October 06, 2011 8:07 AM
Subject: Re: [Boatanchors] [AMRadio] Dreaded D-104


> On Thu, Oct 6, 2011 at 10:18 AM, Bob Macklin 
> <macklinbob at gmail.com> wrote:
>
>> Most of the measurements hams could do would be 
>> subjective.
>
> Bingo. Few take the time to properly assess and compare. 
> It's more a
> case of 'This one is my favorite, so it's better' for the 
> most part.
> Along the same lines as the endless Best Receiver 
> discussions. Without
> proper testing, aging ears will give different preferences 
> as will the
> intended service.
>
> I've never heard a 664 or 444 on AM that didn't sound 
> rather muffled
> or muddy without some additional compensation, compared to 
> the
> crispness of the D-104. They both work better on SSB than 
> AM by far,
> where fidelity isn't an issue. The presence rise of the 
> crystal D-104
> is designed that way for a reason, which is why they 
> penetrate the
> noise so well with more recoverable audio. They are indeed 
> "peaky"
> (mid-range to high peak). If they sound tinny, something 
> is wrong.
> Unless it's SSB, of course.
>
> True, they don't have a big low end, but that wasn't a 
> concern until
> the last couple decades when folks focused more on 
> 'broadcast quality
> audio'. It was wasted energy in the communications field.
>
> There's a reason there are so many of them out there. This 
> was the
> case long before the CB scene, too. Just look through old 
> QST photos
> and other publications. It's not my favorite mic, but it's 
> hard to
> argue with success. The rebuilt RCA-77D ribbbon sounds 
> much fuller
> after it's been properly equalized and preamplified to the
> transmitter. I can't just plug it in and go though, nor 
> can I move it
> to the next transmitter and enjoy similar results without 
> readjusting
> the additional box needed to make it sound good.
>
> ~ Todd,  KA1KAQ/4

     The "tinnyness" is typical of crystal and ceramic 
microphones. They look like capacitors; the impedance seen 
by microphone acts like an RC high pass filter so the input 
must be very high if the low end is not to be attenuated. 
OTOH, research by Bell Labs into speech characteristics some 
eighty years ago, and confirmed many times since, shows that 
most of the power in male speech lies below 500hz but 
contributes only about 2% to articulation. where bandwidth 
or power is limited the low end should be rolled off. The 
most important frequency range for intelligibility is 
between about 1khz and about 3khz. Microphones designed for 
high intelligibility speech generally boost this range and 
roll off the low end. Naturalness requires more of the low 
end which is why Bell System transmitted down to about 250hz 
for telephone service.
     I am puzzled as to why an EV 664 would sound muffled, 
it actually has a slight rise in the intelligibility range. 
The 77D and DX have a frequency response which varies with 
the directional setting; for bi-directional it drifts down 
toward the high end, for non-directional it has a definite 
peak around 4500hz and in unidirectional the two combine to 
a curve with a slight rise at 4500. If you use the mic in 
non-dirctional and set the roll off switch on the bottom for 
2 you will get a pretty good communicaions type response.
    I was trained on RCA mics by the head of microphone 
production at Camden and know the 77 series pretty well. 
They should not sound muffled and should not need 
equalization. If your mic doesn't sound smooth and fairly 
wide range the ribbon may have been damaged (easy to do) or 
not installed correctly. The 77D/DX was never my favorite 
for music recording but is a good voice mic.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com