> "Yes, I know that it is a small speaker but I believe that this is more > than is caused by a small speaker. This restriction does not seem to be in > the exterior speaker jack, or the head phone jacks...I would like to > modify this to allow the response down to 100Htz or so. Any suggestions on > where the restriction is, or how to modify it?"
Dean, The K3's low frequency response limitation is not related to the speaker amplifier circuitry. It's capable of excellent low frequency response. The roll-off you describe is caused by an acoustical short circuit created by the wave cancellation of the forward and back acoustical waves. All speakers that allow for a short conduction path between the front and back of the speaker exhibit this behavior. You can prove this effect by removing the K3's speaker, laying it out on a table, then feed it from a high-quality source of your choice. Even from an audiophile-grade amplifier, you will hear substantial diminished low frequency content. Next, place the speaker in a small sealed box, and note the results. The low end response will dramatically improve. As a further experiment, you can take a full sheet of plywood and cut a hole in it exactly the same size as the K3 speaker. Place the speaker in the hole. The increase in low frequency content will also dramatically increase and you've not used an enclosure. Why? You've just increased the acoustical circuit path of the low frequency content. The longer the path between the forward and reverse acoustical wave, the larger the downward shift of the low frequency short circuit point. Back to the K3. To increase the low frequency content of the K3's internal speaker requires sealing and isolating its back side. The short circuit is presently being allowed through the many ventilation openings on the top cover, near the speaker. Of course, we cannot close those vent openings so to compensate, a small plastic cap can be added around the back side of the speaker. The more mass of the cap, the better. I used the top of plastic spray can and modified it to cover the entire back side of the speaker. Low end response through the speaker is excellent. Quite honestly, the best approach is to simply use a small external speaker with an infinite baffle (sealed box). I also use several Realistic Minimus 7 speakers for station audio. This is one of the few R/S products I will actually admit to owning. Back in the late '70s, they did a marvelous job with the Minimus series of speakers. They can be purchased on the used market for reasonable prices, although demand for them remains high today. 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
