bi-amping, passive, active or analog crossover?

What kind of cross over should i choose?

I am looking to bi-amp a pair of b&w nautilous 805 2 way spakers, and also connect a 12" sealed bass speaker(have seperate amplifier, but no xover) for low end extention.

I am after transparent and honest sound.

the system concists of:

Speakers
B&w 805 nautilus 2 wayspeakers
12" sealed bass speaker

power amps
2 x 110w 8ohm newclassd green(tweeters)
2 x 150w 8ohms diy power amp(midrange)
2 x 150w 8ohm diy power amp(for bass speaker)

Source:
Holfi xsara cd player with vol. control. only analog rca outputs.


Crossover options:

1) passive biamp for the b&w speakers and a digital lowpass filter for the bass 12inch speaker.

+ easy to get it correct, as pross rd the filter for this speaker.
+ cheap as i have a behringer dcx 2495 for lowpass and offcourse the original passive filter.

- not getting full advantage of bi-amp.
- No Hi-pass filter to to remove freqencies below 100-150hz from b&w speakers.
- need to level match tweeter to midrange level.

2) 3-way Active crossover
Using b&w original xover frequencies for tweeter/midrange xover and adding a hipass ot the midrange driver at 150hz to let the 12inch do all the work below that frequency.

+ full advantage of bi-amp.
+ Transparence of no passive filters?

- dont really understand the theori of active filters or how to design them or where to buy them.
still need to match tweeter to midrange and bass speaker level.


3) 3-way Digital xover with behringer dcx2496.

same as in the active filter above, just with options to roll of much steeper and so on.
can easylie mach levels on all drivers.

I tryed to pass the stereo signal though the behringer and to my poweramp driving the b&w speakers, grany and agressive sound, not nice.

If i decide to spend 500-800euro to upgrade it(fx jan diddens upgrades), will it gett good enoughf or will it still be the weakest link.

+ "endless" options

- alot of work getting it all to play together.
- can all those components create a transparant sound, or will it influence the sound to much?


sorry for the way to long post and thanks alot to all that read this far:eek:

what do you think?

best regards

panduro
 
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I cannot recommend any mucking about with a B&W Nautilus that cannot be returned to as new condition!!!!

Adding a high pass filter to the amplifier/s feeding the Nautilus will do no harm. It will simply cut the quantity of lower frequency information that you ask the Nautilus to reproduce.

Adding an amplifier to drive a low bass speaker cannot do any harm to the Nautilus.

Use Linkwitz Riley to guide you through the bass speaker project.

Why did you choose amplifiers with different voltage capability to bi-amp your Nautilus? Both sets of speakers terminals expect to see the same signal voltage, NOT different signal voltages.
 
Hi, and thanks for the replies.

Hi Jan i have already read that, but i think i need to read it again:eek:. have you heard your speakers with another xover? and if so what are your impressions compared to the other filter?

Hi Andrew
That may be a good point, my resale would drop if I coudnt take them back to original finish.
just mucked about:D, just to see the connections. Its two mini "banana" plug into the tweeter and spadeplugs to the mid/bass driver.
only fidling around woud be at the main binding post where i would have to desolder the original wires and solder new ones in. woudnt be hard to reverse if I leave the wires and passive filter in there.

well, mostly because it was just offered to me used four days ago at a good price and its designed to be tweeter/midrange supply.
I dont know if they are in different in output voltage yet, as i wont get it before next week. just assumed that it would either be the amps voltage that would differ or that the drivers sensitivity wasnt the same..



best regards

panduro
 
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if the speakers are designed to be driven by a single amp and alternatively passive bi-amped, then the voltage sensitivity at the terminals must be the same.
This requires both the bi-amping amplifiers to have precisely the same gain and for their peak output voltage to be similar.

I would be more than tempted to keep the passive bi-amping of the Nautilus and introduce the active stage only for the low bass unit. Then experiment with the active HP and LP filters and some active EQ to try and get a good balance between the three drivers.
 
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In passive bi-amping that makes good sense.

why? less work or a better result?

maybe the layout of the filter is very good, but the cross over doesnt seem to have been made with such high quality components(dont se any mundorf m-lytic as i would in a 802 diamand, the powerresister is the one i can get at the local partspusher for 1,5euro).

im not saying youre wrong, just asking why thats your appinion?

best regards

panduro
 
Andrews suggestion of passive bi-amping the 805s and adding a woofer with low level hi-pass (for the 805) & lo-pass (for the woofers) is most expedient. This is easiest to achieve with 2 identical amps for the 805 (one channel for mid/one for tweeter. This approach does not have the potential of full activem but will likely work better as the passive approach removes the need to re-egineer what B&W have done in terms of EQ and driver matching in the XO, a daunting task requiring knowledge of filter design and measuring kit.

One could fiddle with something like the DCX2496, but that unit would need extensive modification to bring it up to sonic level equal to the 805s requirements.

dave
 
Why did you choose amplifiers with different voltage capability to bi-amp your Nautilus? Both sets of speakers terminals expect to see the same signal voltage, NOT different signal voltages.

Isnt that only true if the tweet and woof (in the box) have the same sensitivity?

If I were doing this the first thing I would do is measure the x-over in the speakers. Plug a tone generator (sine wave) into an amp and set so the amp output is 1 volt. If the speakers have any adjustment set them to flat. Then measure the voltage right at the driver terminals (after the crossover) as you sweep (or step) the generator thru an appropriate freq range (concentrate around the crossover freq eg 1k ). ( 40 200 500 750 1k 1.5k 2k 5k 15k )
This should show you the relative levels between woof and tweet (use measurements far from the crossover point, 200hz compared to 5k ), the crossover freq, and how steep the filters are ( if the woof is -3db at 1 k and -9db at 2k its -6db/oct )
 
Isnt that only true if the tweet and woof (in the box) have the same sensitivity?
it is very likely that the two drivers do not have matched sensitivity.
The cross over corrects for that and for any frequency anomalies as well as filtering the signals to the two drivers.

Consider the speaker driven by one amplifier connected to both sets of speaker terminals.
Both sets of speaker terminals see the same voltage drive.
Now separate the terminals and drive them with separate amplifiers. Both sets of terminals expect to receive the same voltage drive to sound as balanced as they did with a single amplifier. Any sound improvement that accrues should be due to separate cables and an easier load on each amplifier.
 
Consider the speaker driven by one amplifier connected to both sets of speaker terminals.
Both sets of speaker terminals see the same voltage drive.

We need to talk about the drivers. In this case the drivers see the after x-over voltages, which will not match due to the drivers differing sensitivities.

Now separate the terminals and drive them with separate amplifiers. Both sets of terminals expect to receive the same voltage drive to sound as balanced as they did with a single amplifier.

This is confusing, you should say take out the speaker crossover and drive the drivers each from there own amp. The drivers should see the same voltages as in the first case (after the x-over)

And the main advantages are: the crossover is now low power, which is a lot easier to make low distortion, and easier loads for the amps.
 
In the simpliest case, which Andrew is describing, passive bi-amping, each amplifier is driving the passive XO plus its driver. 2 identical amplifiers are recommended.

If you remove the passive XO, then you need to reverse engineer all of the EQ, fiddling, driver matching that B&W put into the XO, which can be a daunting task and is not for the faint of heart. It is, in the long run, the option that offers to get the most out of the speakers. Badly done thou, you will end up with something not as good as a single amp driving the 805s. IMHO if you are going that route, you might as well start from scratch instead of living with the expensive compromises inherent in a store bought loudspeaker.

dave
 
ok it seems like the generel consencus is that one should stick to passive biamping in commercial made passive designs, allthough it it doesnt offer the highest possibilities.

if i was to do that and ad a active highpass to the woofer section of the 805(get 100hz and below out of the 805), would that be possible without degrading the sound of the midband?

quote: expensive compromises inherent in a store bought loudspeaker. what are those?


best regards

panduro
 
Hi,
as a first stage in experimenting to find if there is a way to improve the sound you are currently hearing, then adding a low bass speaker and removing the low bass content of the signal sent to the main power amplifier and speaker, is the easiest experiment to carry out.
Tuning those two active filters with possibly some EQ to get the sound right will give you an insight into how difficult a job that is and show where your skills are adequate or not and can be improved with practice.
Then decide whether you can provide the resources to turn the Nautilus into an actively driven speaker.

Start with steps that give you a chance of success.
Many on this Forum start off with ambitions that are way above their resources and they have insufficient knowledge to even recognise that.
 
if i was to do that and ad a active highpass to the woofer section of the 805(get 100hz and below out of the 805)

100Hz seems a little high and won't be making the most of the LF performance of the 805's bass/mid as well as losing some directionality in the bass. I'd aim for a second order slope with turnover between 50 and 70Hz as B&W quote the bass roll-off -3dB at 49Hz.

You can achieve the required high pass and low pass to the bass unit with a three opamp configuration - a low-pass, an all-pass and a subtractor. I could even post up a schematic if you're interested because I've been designing one for my own system.:D

would that be possible without degrading the sound of the midband?

So long as your active filter's designed to be transparent, yes. No mean feat though getting that.
 
we all wanna fly before we can walk:D. that sound like a good way to gain further skills without to much frustration.

I know that 100hz is a bit high, but the speakers loose their focus and their lush sound in the midband when the driver simultanious has to handle both bass an midband when playing loud, thats why id like to try taking the thumb out ou of them.

By the way, its the on wall version of the 805, same crossover, same drivers, just different tuned cabinet, so it has -3 db at 60hz.


I'd love to se your schematic.

thanks fore all the replyes, especially from those continuing to follow the thread!

best regards

panduro
 
Here's the three opamp schematic with values calculated for 100Hz. Its lower Q than Butterworth but higher than Bessel. Right scale is group delay, unfortunately not shown with dotted lines, so perhaps a tad confusing.
 

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