Guest echesky Posted November 2, 2006 Report Share Posted November 2, 2006 I owned a pair of New Large Advents that I traded in a pair of Small Advents for in April of 1978. I really liked the way the NLA’s sounded in the ‘normal’ position of the tweeter control switch. Being a college kid at the time I periodically blew a tweeter because the Sherwood 7910 receiver used to power them had one of two settings…off or full blast (rated at 60w RMS @ .1 THD 20-20K…actually tested at 75w RMS at those specs by an electrical engineer where I worked at the time). In 1983 I blew a woofer right before the warranty went out and the newer woofers had round magnet structures…so I opted to get another to have a matched pair of woofers. I also ‘upgraded’ to the newer soft dome tweeters. In time those tweeters got blown, too. Over time I tore-down the speakers and discarded the cabinets, blown tweeters and x-over networks…keeping only the woofers. The woofers were re-foamed by me in the early 90’s with surrounds bought from Parts Express…easy to do and worked great. I have since built new, solid as a rock, cabinets out of ¾” MDF and covered them in plastic laminate and built acoustically transparent grilles for them…they look quite nice. When I built new boxes the tweeters were centered above the woofers at approximately the same distance they were originally. FWIW, what was ‘up’ with the ‘off-set’ placement of the tweeters in the original speaker?? I did take the time to record what the values were for the original x-overs…for the most part. There were resistors on the tweeter switch/crossover which I did not record the values for. I went to a local electronic shop and used an inductance meter to measure the original woofer inductance coils: .3 mH. The capacitors were labeled at 13 uF. Now I am trying to re-set-up a decent (read ‘killer’) pair of NLA speakers. I bought a pair of the orange ‘ferro-fluid’ ‘fried egg’ tweeters off of ebay as originally equipped in the NLA’s. Using a simple digital ohmmeter the tweeters measured at 2.4 ohms each. The Advent (Jensen ?) woofers I have measured at 4.7 ohms each. I realize that once a speaker is put under a load that the resistance value does increase. Potentially considering slightly elevated resistance loads with power applied I hypothetically ‘assumed’ the tweeter to be 4 ohms and the woofer 6 ohms. That would make the x-over points at ~3300 Hz for the tweeter and ~3000 Hz for the woofer…per the x-over network design chart in 'Building Speaker Enclosures' by David Weems (distributed by Radio Shack). I then went to the 'Loudspeaker Design Cookbook' by Vance Dickason to figure new crossover networks and opted for the second order (12 dB) Linkwitz-Riley formulas which ended up with a .47 mH coil and a 3 uF capacitor for the woofer and a 6 uF capacitor and a .37 mH coil on the tweeter…’crossing’ at 3500 Hz and the tweeter being wired in reverse polarity. The speakers are now somewhat lacking in the midrange area…they basically sound ‘dead’ or ‘muddy’. I’m thinking I need to simply go with a 6 dB slope on the woofer to ‘bring it up’ a bit and then for the tweeter…I’m dumbfounded?? I have read that the orange ‘ferro-fluid’ ‘fried-egg’ tweeters crossed at 1500 Hz as built by Advent ‘back then’. Yet…when I look at the newer tweeter specs I got from them (Advent/Jensen) long ago, the response for the tweeters is 3500-23,000 Hz. Typically, I like to use Solen 400 volt capacitors, 18 gauge coils and 16 gauge oxygen-free copper wires to wire the insides of speakers.Bottom-line…Without using a three-way switch on the tweeters…’normal’ position is good for me…what can I do to get these guys sounding like they used to without using inordinate amounts of equalization circuitry to make up for any shortcomings?I’m not looking for rocket-science here…just a simple solution to a simple problem.Any and all help would certainly be appreciated…thank you for your time!Yeah…BTW…I do try to use all settings of the volume control these days…older and wiser. I still would like to ‘crank them up’ on occasion though. Link to comment Share on other sites More sharing options...
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