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Greg Woods
Reply with quote  #1 
So I've recently gone off the deep end and purchased a pair of Altec Lansing VOTT A7-500 speakers, with 16 ohm 515C woofers and 8 ohm 802D drivers on 511B horns. I'm seriously thinking about trying active crossovers, which would of course require another amplifier in addition to the Mini Beast that I currently use. 

My question is this... Would I be ok in using one Mini Beast per speaker as quasi-monoblocks? Using one channel of each amp, for instance the left, for the 8 ohm horn driver and the other channel, the right, for the 16 ohm woofer of each speaker? Basically would it cause undue strain on the amplifier to drive two different loads, 8 ohm on one channel, 16 ohm on the other, simultaneously? 

Or would it be better to use one amp to drive the horns and the other to drive the woofers? If so would a Son of Beast be the way to go for the woofers? As is, with stock passive crossovers, the Mini Beast is plenty powerful, but if I'm gonna spend the money more power is always nice. 

Reply with quote  #2 

it would be an "undue strain" as one psu feeds both channels of one amp and they would have to drive different loads at different volumes. How much this would be audible in the end I cannot say. But I can say that the same OTL amps sound really different with 8 and 15 ohm loads and need very different volume settings for the same SPL. So better use one amp for the same loads.

The sound you know from listening with passive x-over will also change dramatically and will be a lot better, more refined, clearer, the amps will sound more powerful and with better transients. Ideal for OTLs, basically as good as using a single driver speaker concept.It also takes the harshness/brightness  out of the midrange horns, especially with fine tuning them to the rest of the speaker (for example tri-amping the La Scala II with the Behringer and 3 OTLs).

I would recommend to use a very versatile active x-over like the Behringer Ultradrive Pro. You won't hear the "digital" but it gives you so much more freedom and possibilities than with any analog x-over.  There are some really good analog x-overs out there but at 10 times the price, with less options, and not better sounding. I woudn't use a cheap analog x-over for only adjusting the x-over frequencies (max. 12-18dB/octave) and volume. The cheap electronic circuits will eat up most of the benefits which you would otherwise get from going active. The Behringer on the other hand has almost the same "sound pattern" as an OTL: open, very good transients, the opposite of "dull and lazy", revealing every tiny detail of the music, very good balance between width and depths of the virtual sound stage.

I hope you have fun going active and adjusting those speakers to the perfect sound which you have in mind. They must sound dramatically open and revealing with OTLs and active.

Greg Woods
Reply with quote  #3 

Thank you for your insight! Based on everything I keep reading, active is the way to go. It does however seem to go against the KISS principle, which I guess I'll just have to get over. I suppose it's really not that complex though since I'm using a two way speaker, just trading passive for active and adding one amp. 

Bret Miller
Reply with quote  #4 
I use Marchand Electric active 3 way crossover. Mine is solid state balanced and I use the now defunct SE OTL monoblocks for my conical horn/super tweeters from 400Hz up. If I had the money I would love to build Bruce's 300B amp. I use Legacy monitors ( from right here in Springfield,IL) from 60Hz to 1150Hz, and I have some subwoofers from 60Hz down. I use Nuforce amps for the mids and lows (these are digital switching amplifiers) . Phil Marchand makes any kind of filter slope you want and he has these little cards (with resisters and capacitors soldered in) that slide right in to a slot inside the 3 way crossover. You can put up to 3 of these cards in each spot- low/mid/high for each channel left/right. Phil makes great stuff but can be a little slow getting stuff done. His stuff is very dependable and sounds top notch. I had to do some trial and error to find the right filter slope and am very happy. Boozhound labs had a solid state active crossover kit, but he took it down now. I built his pre-preamp to boost my tt cartridge voltage and his kits sound really great, but they are not finished with boxes - just the circuit board and parts and manuals. Good luck, I am sure you will find much happiness with biamping with horns. Use Ed's sub in a bucket if you want to go 3 way!
George Ollapally
Reply with quote  #5 
I'm using Mini Beast on 515s and 288 Hollywoods,both 16 ohms, with passive XOs.
Reply with quote  #6 
Check your present passive crossover to see if it has shelving or any other corrective circuits. It most likely does. If so only the digital crossovers like Wolfgang mentioned will work as they have the ability to be configured to correct other problems. I do not use an active crossover but in the past I have tried standard electronic crossovers and didn't care for the sound.
Example why digital my horn tweeter is crossed over at a different frequency than the woofer, lowered 12 db  from about 800 to 2500hz bell curve. The woofer is boosted 12 db at 40 hz and rolled off at 32 to 0 hz. None of these things can be done with an analog electronic crossover.
Personally I would stay with the passive.
Greg Woods
Reply with quote  #7 
Currently I'm using the N-500-F dividing network, which uses a Zobel across the woofer. I have the HF padded down by 4db to match up with the LF, which seems to match up pretty well in my room. My next step will be to try the Altec 30923 attenuator circuit in an attempt to flatten the midrange hump and effectively extend the treble. This will be an inexpensive tweak that oughta buy me some time until I can buy a calibrated mic and miniDSP so that I can try different crossover settings and eq, as well as more accurately measure and see results. 

I like the KISS principle, but must admit to a desire to try an active 4 way system at some point, finances permitting. As things stand, I would like to wring whatever performance gains I can out of one amp and 2-way passive speakers. 


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