Twenty Watt Posted December 1, 2007 Share Posted December 1, 2007 I'm a little vexed over what impedance I should be targetting with my setup. Here's some background. I'm running a Dynaco Stereo 70 which has 4, 8, and 16 ohm taps on each side. I'm using a Dynaco PAS 3 as a preamp. There is no subwoofer output or center channel output available to drive a subwoofer so I must utilize the "speaker wire input and output" patch bay on the back of the sub to get a signal to my sub and then out to my speakers. I'm running a pair of Heresy II's which are 8 ohms each. I've got a JBL subwoofer driving a driver of unknown impedance. It's not anywhere on the literature. I used my meter to check the impedance of the subwoofer + Heresy "chain" and it registered 198 ohms!. My meter is fine...I checked the single Heresy and it registered about 5.8 ohms which is where it should be for a published 8 ohm speaker. Can anybody shed some light on this? Is this an acceptable way to drive a sub off of a Stereo 70 using the 4 ohm tap? Should I not do this? Anyhelp would be appreciated. Quote Link to comment Share on other sites More sharing options...
Guest " " Posted December 1, 2007 Share Posted December 1, 2007 the 198 ohm impedance you measured could be as a result of ... A passive subwoofer with an passive crossover intended to recieve output from your amp and them split the signal as lows to your subwoofer and highs to your normal speaker. In a 6db per octave passive crossover, The impedance value you measured included a high pass capacitor that runs from the subwoofer input to the output terminals that run to your Heresy chain. So your test circut actually consisted of a multi meter positive lead, capacitor, speaker, multi meter negative lead. Quote Link to comment Share on other sites More sharing options...
Twenty Watt Posted December 1, 2007 Author Share Posted December 1, 2007 So what tap should I use off my Dynaco ST-70...the 4, 8, or 16? Quote Link to comment Share on other sites More sharing options...
Guest " " Posted December 1, 2007 Share Posted December 1, 2007 Rule of thumb is the nearest tap setting above your speaker impedance. so for Heresy's with a sub woofer you could actually use the 8 or the 16 ohm tap. You will get+3db more output on the 16 ohm tap than you would on the 8 ohm tap. Your speaker impedance's change across the drivers. in the sub woofer range it's probally 3.9 ohms, the Heresy woofer 6 ohms, the mid driver 10 ohms, and the tweeter 6 ohms. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.