[ST86]

Hi,
I have a couple of questions about my Supertower/R speakers.

I am looking to update my 15" passives.  The current ones are at least ten years old, brand and characteristics unknown, purchased from Brian.  I have the Misco 12" woofer LC12W-8A and Goldwood 15" woofer GW-15PC-8.  What passive would be a good match for these woofers? I know people have used a few different models and I would prefer to not have to modify the cabinet.  What weight is used for the recommended passive? 

Also I did an impedance sweep using Dayton Audio DATS (shown below, and by the way, what's up with the 20 ohm impedance peak at 2.4K?) .  I do not get the double impedance peak that you should get with a passive radiator setup, not sure what is going on.  The only peak that shows is the woofer impedance peak, there is no "saddle", and no peak from the passive.  I tried different mass loads on the passive without much change. 




The other question I have is regarding insulation in the cabinet to damp standing waves.  Currently I have the top 3/4 or so of the cabinet loosely filled with fiberglass insulation.  Looking for recommendations regarding how much insulation is "typical" and if other wave damping materials would be better.   Don't know at this point if the amount of insulation is part of the reason for the missing passive impedance peak or if there is a problem with the passive where it isn't responding.

Appreciate any help with this.

Thanks,

Ed

[RSorak]

You are gonna have to buy whatever 15" passives you can find....I know Parts Express sells one. But ATM that's the only one I know of. I have some passives that were sold by Creative Sound Solutions but they only sell the smaller versions now.

As far as the cabinet stuffing, it sounds like yours are about the same as mine. I have made no changes.

[ST86]

Thank you.  You must mean this one:

https://www.parts-express.com/dayton-audio-rss390-pr-15-aluminum-cone-passive-radiator--295-504

I've used it in a homebrewed subwoofer, with this driver:

https://www.parts-express.com/dayton-audio-rss390hf-4-15-reference-hf-subwoofer-4-ohm--295-468

Two passives, one driver, 8 cu ft cabinet.  With this setup I get the typical two peak impedance trace.  Don't know why it is missing with the Supertowers.

Anyway, the Supertower/R cabinet is somewhere around 7.5 cu ft if I have measured correctly.  I am concerned about matching the cabinet volume, two woofers and one passive.  Any advice on what I should look for?  I may not have a choice and end up buying this one just because it is the only option but it would be good to know if it is OK for the application.

Thanks,

Ed

[ST86]

Hi,

I did more impedance measurements but first some background.  The original parallel twelve inch and fifteen inch woofer had a twenty-five ohm ten watt resister in series with the twelve inch.  When I updated the twelve inch with the Misc woofer and the fifteen inch with the Goldwood I kept the original configuration with the twenty-five ohm resistor in series to the Misco woofer. 

I measured the impedance with the resistor (original trace above) and without the resistor (below).  You can see without the resistor the impedance looks much more as expected. I removed the resistor. The bass is back!  I have not heard low bass from these speakers until now and the overall balance is much better.





I ordered the passive replacements from PartsExpress.  They arrived yesterday....and they are a tiny bit too big for the opening.
Looking for suggestions on how to widen the opening for the passive.  I have a router and could use a rabetting bit but would prefer to find a way that doesn't make clouds of sawdust.

Regards,
Ed

[RSorak]

I had the same problem when replacing the 15" woofer in my Towers. I just used a rasp that was driven by a drill. I think the router would be neater. They make vacuum cleaners for the dust.

I was told the crossovers are a series design and to change anything in them, would totally mess them up.....Your experience seems to state otherwise. I was told this in my thread where I inquired about possibly converting my towers to be bi-amped, but in a different way from that which the designer intended. Biamping them by the orig configuration drives everything but the tweeters w one amp, and the tweeters w their own amp. I wanted to seperate the 15 on its own amp and drive the rest of the drivers w the other. In the end I did not, because of the advice I got regarding the crossovers. Maybe I need to revisit this idea.

[ST86]

-->I had the same problem when replacing the 15" woofer in my Towers. I just used a rasp that was driven by a drill. I think the router would be neater. They make vacuum cleaners for the dust.

Thanks.  I may try a sanding drum with coarse grit paper in a variable speed drill.  Maybe the lower speed won't let the dust fly around as bad as a router.  My router does not have an attachment for dust collection.

-->I was told the crossovers are a series design and to change anything in them, would totally mess them up.....Your experience seems to state otherwise.

Well, yes and no.   With a series crossover changing any component affects the performance of all of the others.  For the original components (including the original mids) the 25 ohm was required, the inductor was 1.0mH, and the capacitor was 48uF.  I forgot to mention when I changed the woofers I also bought new mids from Brian.  When I changed to the newer drivers Brian had me change the inductor to 2.8mH and the capacitor to 54uF.  I don't remember if he told me to remove the 25 ohm or keep it, but I ended up keeping it.  So when you look at it, I bought from Brian a whole new series crossover section of the Supertower, drivers and crossover components (two woofers, two mids, one inductor and one capacitor for each cabinet). It turns out changing the impedance of the Misco driver by putting the 25 ohm in series with it, and having that impedance in parallel with the Goldwood fifteen changed the impedance of the woofer section of the series crossover enough to muck up the whole network and kill the low bass, and also change the impedance of the midrange, if you compare the two traces.  Removing the resistor brought everything to where it should be, including the midrange impedance.

Here is a good article on series crossovers:

https://www.tubecad.com/2017/11/blog0402.htm

Because the woofers and mids are connected with the series crossover the biamp split is the point where the mids cross to the domes, which with my speakers is 4.5KHz.  The only way I can think of to biamp close to what you want would be to remove the series crossover and drive the two woofers in parallel with one amp.  Then you'd drive the mids and tweeters with another amp.  You'd need a woofer-to-mids crossover point (mine are around 600 Hz) and either divide the frequencies with active DSP or a passive network.  Seems to me either way you are getting away from the original design.  Weather or not you want to do that is your call.

Thanks,

Ed