Steve, Someone else responded to me in private with the same question. Here's my answer:
"The K3 speaker output has something like 470 uF of C in series with the speaker output amp. That's reasonably adequate. The problem with the K3 speaker's bass frequency response is not the electrical circuit. Rather, the K3's speaker has low-end response limitations due to the fact that the speaker is in not encased by an adequate baffle. The back wave of any speaker driven by a coil is 180-degrees out of phase with the forward wave. Although the K3's speaker is mounted to a metal surface, too many openings near it allow for the short circuit of the acoustical front and back waves at low frequencies. The degree to which acoustical wave cancellation occurs is a function of distance. At low frequencies, quite a bit of isolation distance is required. Typically, commercial speakers are encased (although some are ported to a resonance) to produce a virtual infinite distance through the use of the so-called infinite baffle. We've all done this experiment before at some point in our electronics education: Simply place an open speaker driver on a desk just sitting there and listen to low frequency tones. Then, take that same speaker and place it in an enclosure, or behind a large surface. The speaker placed by itself on the desktop sounds vastly inferior in bass response when compared to the same speaker enclosed in a box or placed behind a surface like wall or ceiling. For the K3, the fix is relatively easy. Simply enclose the back of the speaker driver with a solid substance like plastic. I used the top of a spray paint can and modified it slightly to fit around the K3's support truss." Incidentally, there's another interesting acoustical mechanism that assists our brains with bass content. If it were not for this effect, our perception of low-frequency content would be worse than it is when we listen to small speakers whose low-end response is restricted. In effect, our brains create a missing fundamental when it detects the presence of multiple harmonics of a single fundamental that should be there in the first place. Among auditory professionals, this effect is referred to as "Phenomenon of the Missing Fundamental." http://www.phys.uconn.edu/~gibson/Notes/Section7_4/Sec7_4.htm Paul, W9AC ----- Original Message ----- From: "Steve Ellington" <[email protected]> To: "Paul Christensen" <[email protected]>; <[email protected]> Sent: Monday, April 06, 2009 9:31 AM Subject: Re: [Elecraft] My K3's hissy and noisy audio > Paul > I can see how this mod would improve headphone audio but what about low > frequency audio for the speaker(s)? > Steve Ellington > [email protected] > ----- Original Message ----- > From: "Paul Christensen" <[email protected]> > To: <[email protected]> > Sent: Monday, April 06, 2009 6:54 AM > Subject: Re: [Elecraft] My K3's hissy and noisy audio > > >>> Perhaps the band noise is more obvious in the K3 because the low >>> frequency >>> audio is restricted causing the noise to be distributed over a more >>> narrow >>> range. This lack of bass tends to induce for ear fatigue. >>> Steve Ellington >> >> I agree with Steve on this one. Once more low-end was rolled into my >> audio >> hardware changes, I noticed a significant reduction in my own listener >> fatigue. >> >> Others have noted the K3's audio frequency response variance across >> different headphone models, most notably the Heil product. The K3's >> headphone circuit uses 10 uF of series capacitance from the headphone amp >> to >> each of the headphone coils. >> >> For the moment, assume that your headphones are 32-ohms (ref 100Hz). >> What >> is the best possible low-end response from the K3? The answer is 500 Hz >> @ -3dB. That part of the circuit needs some help. With a headphone Z >> even >> lower toward 8-ohms, the attenuation of bass response is worse. >> >> Now upgrade the series caps to 330 uF and re-run the calculation. With >> 32-ohm phones (ref 100 Hz), the frequency response improves to 15 Hz. >> Now >> that's t real Hi-Fi on par with what Icom delivers and the difference is >> immediately noticeable to anyone -- not just the folks with "golden >> ears." >> >> Finally, compare the result of the modified K3 with the Icom '7700 or >> '7800. >> >> Paul, W9AC >> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[email protected] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
