On Thu, 17 Jun 2004 00:33:23 -0400, Don Wilhelm wrote: >I have always thought the K2 to be a bit 'wimpy' on the audio >output - but I have found it is really adequate when driving the internal >speaker, just not a lot of reserve to overcome a high ambient acoustical >noise level.
Wayne has done a really good job of engineering the audio chain on the receiver to provide enough loudness (and good quality) without wasting battery current. Part of that good engineering was finding a really efficient loudspeaker to go inside the K2. When you want to add an external loudspeaker to the K2, you must do the same level of good engineering. That means NOT grabbing whatever cheapo loudspeaker you have in the junk box, but rather looking for a loudspeaker with relatively high efficiency (and, as you correctly observed, a 4 ohm loudspeaker has an inherent 6 dB advantage). You have a very big advantage over Wayne though -- in general, the larger the loudspeaker, the easier it is to find one with high efficiency! The spec you are looking for is dBSPL for 1W at 1 m. (that is, dB sound pressure level at 1 meter away from the loudspeaker with 1 watt electrical power). The higher the number, the louder it will be. Hi-fi loudspeakers are generally LOW efficiency. PA loudspeakers are generally HIGH efficiency. A good number for an 8-inch loudspeaker is in the high 80's or low 90's. To translate this, the K2 puts out 1 watt sine wave at clip. Speech typically has a 10-14 dB peak to average ratio, so if your loudspeaker is putting out 90 dBSPL at the peak of that sine wave, the average level will be 10 dB below that (80 dBSPL). Few of us listen 1 m (39") away from our radio -- half that distance is far more typical, (19"), and gives us 6 dB more level, so we're back up to 86 dB. And that assumes no sound is reflected from nearby walls, shelves, etc., which can also add a dB or two to the loudness. The bottom line is that 86 dB is plenty loud unless you've got severe hearing loss or are in a very noisy environment. And, of course, if you listen closer, it will be even louder. On the other hand, let's say you hang an 8 ohm hi-fi loudspeaker (you bought it at Radio Shack or your local hi-fi shop) and it has a sensitivity of only 80 dB for 1w at 1m. The same math puts you 10 dB lower in level for the lower sensitivity, and anothe 6 dB lower because it's an 8 ohm loudspeaker. That's only 70 dBSPL, which is only marginally loud enough in a noisy room (or if you have a lot of hearing loss). Jim Brown K9YC http://audiosystemsgroup.com _______________________________________________ Elecraft mailing list Post to: [email protected] http://mailman.qth.net/mailman/listinfo/elecraft You must subscribe to post. Subscriber Info (Addr. Change, Unsub etc): http://mailman.qth.net/subscribers.htm Elecraft page: http://www.elecraft.com
