[Elecraft] Use of external speakers/amp

[Jim Brown]

  On 10/4/2010 6:40 AM, Rick Staley wrote:
> In connection with the second topic, I wonder what other K3 owners 
> might have done.
> Have you gained any improvement by using external speakers, PC-type 
> speakers with audio
> amps built in, or even something like a stereo amp with hi fi speakers? 

The K3 is a very compact rig, which requires that the loudspeaker also 
be compact. That limits its performance, both in terms of output LEVEL 
and frequency response.

The most important characteristic of a loudspeaker is the SMOOTHNESS of 
its frequency response. The LIMITS (how low, how high) don't matter 
nearly as much. One of the major differences between a good speaker and 
a poor one is that smoothness. Bumps in the frequency response add both 
amplitude and phase distortion, which makes speech much harder to 
understand. One of the few shortcomings of the K2 on SSB is that the 
narrow RX filter settings use the multi-stage CW filters, re-tuned to 
stagger their response, and the total response is VERY bumpy. The K2 
sounds great when the TX filter is used for RX (the full width setting), 
but sounds just awful when those narrower settings are used.

Another important characteristic of a loudspeaker is its VOLTAGE 
SENSITIVITY.  That is, how much voltage does it take to achieve a 
certain loudness. Most hi-fi loudspeakers have pretty LOW sensitivity -- 
they are designed to be driven by 50-200W power amps. The K3 has a 1-2W 
power amp, so it needs a speaker with fairly high sensitivity (unless 
you also add an outboard power amp).

And yes, as others have noted, amplified loudspeakers are notorious for 
having bad RFI problems. When I attend audio trade shows, I wander the 
exhibit floor with a Kenwood TH-F6A (2M/220/440 talkie) and use it as a 
signal injection probe to test for RFI. So far, I've found only two 
amplified loudspeakers that didn't have RFI problems. Both cost more 
than $3K.

Bottom line -- if you're going to add an external speaker to any ham 
rig, choose one with very smooth (flat) response in the speech range 
(400 - 4,000 Hz), and with reasonably high sensitivity.

73, Jim Brown K9YC