Welcome to AH. Is this your first try at building or re-building a speaker? If so, I want to encourage you. Keep that in mind as I poke some holes in your ideas
.
I bought a pair of
Advent Heritage towers without woofers. I'm going to re-cap the crossovers and put in
new woofers, and replace the extremely thin leads with heavier gauge wire. This'll be a bits-and-pieces project that I'll buy for as I have a little spare money freed up. I've researched and mapped out the crossover (attached) and a couple questions need answering before I buy anything though.
How did you choose those replacement woofers? Simply Speakers claims they work, but I don't see any further info indicating that they actually would be suitable replacements for the Advent 8" woofers. For any new woofers to work, they have to match the electrical and mechanical properties (known as Thiele/Small, or T/S, parameters) of the old woofers. That's not impossible to find for replacement woofers, but it is extremely rare. It is essential to know the T/S parameters in order to match the low frequency response of the woofers to the volume of the cabinet, and to match the the high frequency response of the woofers to the crossover network. If they are off, your old cabinet, crossover network, and tweeter are useless.
The T/S parameters of the new woofers are shown by Simply Speakers (below). The question is, what were the T/S parameters for the original Advent, and how well do the new woofers match? Because Simply Speakers say it works great for
all those speakers, I have to wonder.
- Le: .28 mH, Fs: 39 Hz, Vas: 1.39 cu. ft., Qms: 4.07, Qes: 1.23, Qts: .94, Xmax: 4.5mm
- Great replacement woofer for many speakers, including Advent, AR, EPI, Fisher, Genesis, Infinity and many more!
1) it's a 2.5- way speaker. One woofer is low-passed through a 1.2mH inductor, and the other through a 2.3mH. What do these values translate to in cutoff frequency? I assume that the higher cutoff woofer will need to be the upper one, but I'm not sure which that is. Also, the OG woofers were 6-ohm, but the replacements will be 8-ohms. Will that shift the crossover points? And if so, should I go with new inductors of a different value?
The crossover schematic you attached shows two drivers (S2 & S3) with single inductors, 1.2 mH for S2, and 0.5 mH for S3. It does not show a 2.3 mH inductor. I'm confused.
2) 6uF capacitors don't seem that common anymore. On Parts Express there seem to be plenty of 5.6uF and 6.2uF. Which should I replace C1 on the tweeter with? It doesn't seem to calculate into much overall difference with either, but I'd like to be certain. The tweeters are also 6-ohms.
This is the least of your problems. A good rule-of-thumb for most crossovers (especially older designs as this one appears to be) is that parts have a tolerance of ±10%. If the design calls for 6 µF, any capacitor in the range of 5.4 to 6.6 µF will work. If you can find a 6.2 µF cap at a reasonable price, get it.
My final comment is a more general one. Let's assume you find successful replacements for those woofers, and build the crossover board. The design is intended to cross between the 8" woofers and the 1" dome tweeter at 3500 Hz. I'd bet that there is a large drop in response between the woofers and tweeter. Despite Advent's popularity decades ago, that problem was common in all of their models with 8" woofers.
I don't know of any 8" woofer, old or new, that can go as high as 3500 Hz without a significant drop in response (leads to a hole in the mid range sound),making unwanted break up noise (leads to audible noise at higher volumes),or at best, a significant loss in off-axis response (leads to poor imaging and sound stage in stereo). That's why you don't find many modern 2-way speakers that combine 8" woofers with a small dome tweeter.
In short, I think these speakers might not be worth the effort to re-build them. They'll be bass heavy and have a large suck out in the all important mid range.
