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Choosing an active 3-way crossover
Choosing an active 3-way crossover
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Old 29th August 2012, 07:02 PM   #21
Davey is offline Davey  United States
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Quote:
Originally Posted by AndrewT View Post
You don't want different voltage gain.
I agree, but that's not what I said. I said, a possible audible difference in a passive biamping configuration might be explained by some variable......one of which might be power amps with different voltage gains.
I assume in your case you matched gains....if they weren't the same. So, what other variable in your Tannoy Berkley experiment explains the night and day difference?

Cheers,

Dave.
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Old 29th August 2012, 07:07 PM   #22
ashok is offline ashok
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Choosing an active 3-way crossover
Quote:
Originally Posted by Davey View Post
In theory, passive bi-amping shouldn't make much difference.....unless the power amps utilized were different in some way. Different voltage gain.....different output resistance.....etc, etc.
Cheers,
Dave.
Yes, but in practice it does make an audible difference. But like Andrew said the improvement could vary between systems.

However if there is some active crossover built in , just a general HPF/LPF set such that the passive crossover still works in it's range, it will make a big difference and the system will sound cleaner and go louder than expected with just a stereo amp. The ultimate solution will be to remove the passive crossover and make it fully active. This isn't as straight forward as it might seem. Lots of hard work is involved !
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Old 29th August 2012, 10:29 PM   #23
CopperTop is offline CopperTop  United Kingdom
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Originally Posted by Davey View Post
I assume in your case you matched gains....if they weren't the same. So, what other variable in your Tannoy Berkley experiment explains the night and day difference?
I'm definitely an active evangelist, but presumably it is conceivable that one amp goes unstable with the combined load, while separate amps behave well with the individual loads.
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Old 29th August 2012, 11:16 PM   #24
sreten is offline sreten  United Kingdom
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Hi,

Claiming passive bi-amping makes a "night and day" difference
is way off any sensible mark for a typical two way speaker.

Its very amplifier, and then speaker dependent to be worthwhile.

A classic case is the Quad 303 stereo amplifier with
its shared regulated supply for both channels that
is somewhat current shy by modern standards.
Passive bi-amping works well with tougher load 2 ways.

In many cases its a complete waste of money, e.g.
if you roll-off the treble amplifier 1st order well below
the x/o frequency you can use a much smaller amp.

rgds, sreten.
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Old 30th August 2012, 12:20 AM   #25
Charles Darwin is offline Charles Darwin  United Kingdom
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Originally Posted by AndrewT View Post
I find that bi-amping makes a difference.
The speaker that responded most to this was the Tannoy Berkley.
It was not bi-wireable. I had to go in and alter the crossover PCB slightly. Drilled a couple of tracks and cut another. Brought the extra wire out to the new 4 terminal board.
The change was night and day. The combination of bi-wireabale and bi-amping created a new sound environment that was so good in comparison to what was before that I did not change my system for about 6years, even though I was still going around the good retailers listening to good equipment and "wanting" to spend some money. There was nothing in my price range that I thought could compete.
I will certainly admit that other speakers have not reacted as much, but then I do have some quite good amplifiers. But all sound better when bi-amped, (not active).
My Tannoy Little Red Monitors have 4 terminals at the back from the factory.
I have come across people claiming vast improvements from just bi-wiring them. This came as a surprise to me since the extra pair of posts is internally NOT connected to anything!

That said mine do sound a lot better since I've gone completely active but then I expected this as I have done that before to other speakers.
The eq function of the high pass in the xover is now being done by a parametric equalizer.
I have yet to come across speakers costing under 20k that I would swap them for and there aren't many over 20k neither.
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Old 30th August 2012, 07:40 PM   #26
Davey is offline Davey  United States
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Originally Posted by Charles Darwin View Post
My Tannoy Little Red Monitors have 4 terminals at the back from the factory.
I have come across people claiming vast improvements from just bi-wiring them. This came as a surprise to me since the extra pair of posts is internally NOT connected to anything!
Awesome!

When bi-wired the second set of non-connected speaker wires acted like antennas and picked up some soothing RFI and fed that back to interact with the feedback loop of the amplifier? Easily a vast improvement and audible change.

Dave.
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Old 31st August 2012, 04:25 AM   #27
ashok is offline ashok
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Quote:
Originally Posted by Charles Darwin View Post
My Tannoy Little Red Monitors have 4 terminals at the back from the factory.
I have come across people claiming vast improvements from just bi-wiring them. This came as a surprise to me since the extra pair of posts is internally NOT connected to anything!
I have a small Tannoy bookshelf speaker with bi-wireable connections and it IS connected separately to the woofer and tweeter through their own crossover.
Did you check if the crossover board has provision for conversion to a bi-wireable scheme ? If so I wonder why they would have not done it themselves !
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Old 31st August 2012, 11:18 AM   #28
Charles Darwin is offline Charles Darwin  United Kingdom
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Originally Posted by Davey View Post
Awesome!

When bi-wired the second set of non-connected speaker wires acted like antennas and picked up some soothing RFI and fed that back to interact with the feedback loop of the amplifier? Easily a vast improvement and audible change.

Dave.
The second set of binding posts is not connected to anything at all internally.

The set of speaker wires came separately in a little bag together with an allen key to remove the driver if you wanted to use the optional active xover Tannoy made. They were not fitted inside by the factory.
This is all very clearly described in the manual but if one bought them s/h sans manual it might look as if they would be bi-wirable.

Incidentally many moons ago I came across an article in which they assessed the benefits of bi-wiring using blind testing.
The result was that the only reason bi-wiring sounds marginally better is because it gets rid of those connecting plates one finds on bi-wirable binding posts not because of the extra cable run. The best results were achieved by using one run of good cable into the treble posts and then using short bits of the same cable as jumpers to the woofer posts.

Similarly Tannoy themselves found possible improvements when hard-wiring the xover rather than using pcbs as they did and by removing the acoustic control switches. Tannoy did just that when the Super Red Monitor series became the Super Gold Monitor series in '89. They replaced the switches with gold-plated pins.
These two things are the only difference between Super Reds and Super Golds. Visually they changed the baffle colour from walnut to black.
Drivers remained the same.

Later on (after '91) Tannoy bowed to market pressures and installed bi-wirable xovers.
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Old 6th September 2012, 04:23 AM   #29
foodchain11 is offline foodchain11  United States
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Thanks for all the feedback, guys. I purchased an old Ashly SC-77 3-way stereo crossover for $80 (I understand they are pretty decent, albeit perhaps not audiophile quality), found an old NAD 906 multichannel power amp, and I'm going to try cutting the passive crossovers out of the speakers in such a way that they can be re-wired in a jif, if necessary.

I made an inquiry to Polk and their customer service was very helpful (in addition to encouraging me in this project). The tech guy sent me a bunch of graphs, etc., but summed it up with this comment: "The stock crossover frequency between tweeter and woofers is right around 2k (electrically) w/ a 2nd order high pass & a 1st order low pass." He did say he didn't think there was any fancy stuff going on as far as equalization, etc. in the factory passive crossover.

The Ashly is 2nd order all the way (i.e., the slope is 12db/octave and it's non-adjustable), but I'll have to make do with that even though they had a gentler slope for the high pass. At least I have a starting point.

I also use a Polk powered subwoofer. The L/R speakers go down to 35 hz; the subwoofer goes up to 200 hz. I think if I cross the subs/mids at ~90hz that should work. (I don't keep the subwoofer too near the front speakers; therefore, I don't want to go up too high for fear of "localizing" it.) Mids will initially cross to tweets at 2khz and we'll take it from there.

The NAD 906 power amp has 3 independent amps, consisting of L&R channels in each, of which and pair can be bridged together into mono. So I think what I'll do is bridge two of them, each assigned to one mid, and use the third in the conventional fashion to do the tweeters.

Anyhow, it will be a fun experiment. If it doesn't work, I'll just reattach the passive crossovers, eBay the Ashly unit, and chalk it up to a fun waste of time.

One thing I don't understand about the Ashly: it has adjustable "Q", or rolloff -- what the heck izzat for?


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Old 6th September 2012, 02:13 PM   #30
puppet is offline puppet  United States
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The adjustable Q changes the response curve at the target frequency. A higher Q value will boost the response incrementally ... a Q of .07 is basically a flat response with a 12db octave slope ... a Q of 2.0 will give a 6db boost also with a 12db octave slope.

Does the Ashley do LF time alignment? Being away from the mains ... the subs will benefit with some adjustable here.
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