I posted this to another list, for what it's worth, be interested to hear from others if they try it: There was talk sometime back about large Advent speakers and I'm always surprised when people comment about how good they are, I suppose they might be good for their day or good for the low price point. I noticed fairly serious midrange coloration from the first listen. Still, they had the best bass and a real tweeter when compared to the competition of the day, Dyna A-25, EPI 100, AR2. The Dyna A-25 and EPI100 both had much better midrange smoothness. I happen to have a pair of large Advents here where one was reconned about 10 years ago and the other needs to be reconned. These are otherwise original, never had any tweeter problems. I've always thought the Advent (about $250/pr in the 1970s) would be a good candidate for mods since it seems as if the basic components are good. I hooked the good one up in my main system with an A/B switchbox to compare it to my commercial floor standing 3 way reference (about $2000/pr). The reference was 3ft out from the wall and I first placed the Advent on top. The Advent was much louder in the tweeter range, very bright sounding, there's a 3 position tweeter level control and in the "increase" position it sounds like a shrill transistor radio with bass, not even a good transistor radio, shouty sounding to an extreme. The other positions sounded better but still something drastically wrong in the midrange. My kids gave a big thumbs down for the Advent and thought the A/B switch was very cool. I guessed that the coloration was midrange peaking and there was also a boxy quality to the sound. Definitely like sound from a speaker rather than music in the room and I thought they'd need a lot of work. The A/B switch also provides line level switching so I inserted a volume control to match levels. Matching was hard due to the frequency response differences. Next I put them on the floor which helped bring up the mid bass to some extent, still not right, not even convincing on vocals. I happen to have a passive line level circuit that provides baffle loss compensation (6 dB) with also some high end boost, mostly above 10 kHz. Boost this high tends to add air to the sound rather than brightness and as I recall these older tweeters start to roll off above 15 kHz. I didn't think it would be this simple but now they were very close at least at moderate levels and with the tweeter switch now in the "extended" position. The Advent runs out of displacement capability with any demanding bass material and higher listening levels. Now the reference required some level reduction due to the 6 dB of loss in the baffle compensation circuit. The Advent was now heavy in the mid bass, and elevating them 10.75" was a bit too much, sounding thin, 4.75" was about right overall. The two sound very similar with this setup, the reference is a touch cleaner, smoother, and more transparent but they're very similar at moderate levels, as I said the Advent runs out of steam in the bass, and the reference also has more extended very deep bass but these are design differences. The difference is much more subtle having to listen for it rather than being in your face. I believe that the baffle step compensation is a bit too much, 4-5 dB is probably about right, still much better even at 6 dB. I thought the speakers would require much more work, they're not perfect but the difference is dramatic. Advents have never had that disappear, music in the room quality, they do with this shaping network. I'll probably do some driver measurements, don't expect to do full measurements of the Advents, just don't have the time. Might work up crossover mods so the line level circuit is not needed. These are bookshelf speakers that one might think should not need baffle step compensation when used in bookshelf applications but I've heard similar colorations even on the floor against a wall. Actually, on an ear level shelf they'd see only one close boundary, the wall behind. Placed on the floor out in the room should provide a similar one close boundary response and therefore the compensation is probably about right even for elevated bookshelf applications, adustments to this circuit are easy: Here's the baffle step and HF compensation network: --------- R 2.2 K ---------------------------- |---- C.01uF -----|.....| ...........................C.1uF ............................| ..........................R 2.2K ............................| ------------------------------------------------ ignore these: ..... they're needed because spaces are removed on this board Pre should have < 100 ohm output Z, power amp > 22K input Z.
