On 6/2/2014 11:03 AM, Bill Frantz wrote:
I had this problem when installing a FTM-10 in my Mazda Miata. I placed the speakers in series so as not to overload the audio amplifiers. The output level is somewhat marginal when traveling at freeway speeds with the top down, but so is conversation with a passenger.
That was a mistake. Audio power amps have very low source Z, typically <0.05 ohms, and most are designed to drive a 4 ohm load. In other words, they are a constant voltage source. That means they will easily drive two 8 ohm loudspeakers. For all practical purposes, the power delivered to each loudspeaker is the same as if it were the only one connected. The limit on this is the power supply -- as you approach the minimum rated impedance and high signal levels, the power amp may clip a dB or so lower.
When you wire the loudspeakers in series, that constant output voltage divides between them as a function of their impedance AT EVERY FREQUENCY, and the impedance of ANY dynamic loudspeaker varies over a range of at least 50:1 with frequency. The rated impedance of a loudspeaker is the minimum value of the impedance, which occurs for most loudspeakers in its lower midrange. Which brings us to the second problem with your hookup -- unless the two loudspeakers are identical, and identically installed, the ratio between the two impedances at each frequency will modify (distort) the frequency response of the other!
73, Jim K9YC Retired Audio Engineer ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
