Passive Speakers

[oldric_naubhoff]

It's quite possible that a 6db passive crossover may will be the best compromise for overall system clarity and lack of distortion.

(this one goes to Stevie)

not to mention there will be other benefits too. no problems associated with group delay, phase coherence and perfect transient response to boot... all you have to provide is some capable drivers.

one more point about passive xover measurements submitted by Stevie. that guy was deliberately using cored coils because he new that at high power levels cores will saturate and it will cause the coils to induce distortion, i.e. the coils will no longer be linear. but if he used air cored (ribbon) coils the results wouldn't be even remotely that severe.

 

[steve_1979]

Can you please tell me which hi-fi and speaker engineering test books you are referring to?

There are plenty of good speaker engineering text books around for anyone who is interested.

Gilbert Aurther Briggs has wrote several good ones (they're 50 years old but the science is just as relevant now as it was then).

High Performance Speakers by Martin Colloms.

Loudspeaker Design Cook Book by Vance Dickenson is good too (make sure you get a recent edition because apparently the old ones have a lot of errors).

I've also been told that Loudspeakers by Ted Jordan is good but I haven't been able to find a copy of this one.

 

[steve_1979]

It's quite possible that a 6db passive crossover may will be the best compromise for overall system clarity and lack of distortion.

Consider it this way.

Almost all passive speakers use a shallow filter 1st or 2nd order crossover because they have to. But with active speakers the designers are able to use any filter slope they want. Shallow 1st and 2nd filters upto steep sloped 3rd or 4th filters can all easily be used, yet active speaker designers always choose to use the steeper 3rd or 4th order filters. :?

Steep filters sound better because they allow each of the the drivers to stay in their frequency comfort zone which means that they will distort less.

 

[lindsayt]

Steve, the Bozak N-106 active crossover uses 6db slopes.

As I've already explained in my previous post from which you've quoted my last paragraph, a 6db crossover slope is sufficient for keeping system distortion due to the drivers being taken outside of their comfort zone well under 1%. Op amp based active crossovers, on the other hand, introduce distortion of more than 1% to the system at lower volumes. The more efficient the speakers you are using, the higher the volume will be at which the op amp based active crossover introduces distortion to the system of more than 1%.

Also, remember that the distortion due to passive speakers being taken outside of their comfort zone will only happen at certain frequency bands between 20hz and 20khz. The distortion due to the op amps in the active crossovers will happen at all frequencies with it increasing above 1khz.

 

[lindsayt]

Can you please tell me which hi-fi and speaker engineering test books you are referring to?

There are plenty of good speaker engineering text books around for anyone who is interested.

Gilbert Aurther Briggs has wrote several good ones (they're 50 years old but the science is just as relevant now as it was then).

High Performance Speakers by Martin Colloms.

Loudspeaker Design Cook Book by Vance Dickenson is good too (make sure you get a recent edition because apparently the old ones have a lot of errors).

I've also been told that Loudspeakers by Ted Jordan is good but I haven't been able to find a copy of this one.

Can you or anyone else confirm that these text books do contain the results of measurements of passive crossover distortion for all power levels equating to in room volumes of 30dbs to 110 dbs? If so on which pages of which edition is this information contained? Do any of them also have the results of equivalent measurements for any active crossovers?

 

[hoopsontoast]

Oh and you can do 3rd and 4th order passive crossovers, my Acoustic Energy AE2's have 4th Order 24dB/Octave I believe.

If you are really interested, a PDF comparing distortion in a mix of Active and Passive monitors, including the AE2 and AVI passives -

http://www.google.co.uk/url?sa=t&rct=j&q=acoustic%20energy%20ae2%20distortion&source=web&cd=5&ved=0CF0QFjAE&url=http%3A%2F%2Fwww.soundonsound.com%2Fpdfs%2Fns10m.pdf&ei=S6rLT7ryEoeg8gPS9iE&usg=AFQjCNEk6Dts2l25mj52E-CltxHQgZ9IWA&cad=rja

 

[John Duncan]

That does indeed look interesting. What does it mean?

 

[hoopsontoast]

Absolutley sod all, low distortion, IME does not always mean they actually sound good. :rofl:

I was using a tube amp at 2wpc, and it measured something like 1% 2nd Harmonic at 0.7w (one channel driven), and got a lot worse going higher. Sounded very very good though despite the 'distortion'.

Distortion will be audible but only at the levels around 90dB/1m and higher, which the majority of people will never get them that loud ever. Low distortion is good for Studios where you need it, but in the home, I doubt it.

 

[bigblue235]

Any chance of a quick explanation of what those graphs show for simpletons eejits laymen like myself?

Y'know, just in a 'who's talking cobblers' kinda way.

*edit: beaten to it!*

 

[hoopsontoast]

Look at the original frequency response trace, then the lower traces at 1st, 2nd, 3rd and 4th harmonic.

I think If the distortion cuve is around 20dB below, its around 10%, -30dB is 3% and -40dB around 1% and -60dB is around 0.1%

http://www.audioheuristics.org/primers/nonlinear_distortion_testing.htm

 

[bigblue235]

I understood "Look at", but after that... not so much.

 

[hoopsontoast]

On the graph of each speaker, you have a trace up around 90dB, this is the frequency response of the speaker, usually at 1w (or 2.83v) input.

The lower traces are the distortion measurements for each 1st, 2nd, 3rd and 4th harmonic. The Lower the traces (Bigger the gap between the traces), the lower the distortion.

 

[bigblue235]

Ta, muchly. I get it now. But having looked at them, I'm still somewhat baffled. That's nothing unusual, though.

Do the graphs back-up or invalidate Steve's Active accuracy assertions?

 

[hoopsontoast]

Well in this case, you could say yes, as the two lowest distortion speakers tested were active, BUT in general, the others were much the same, with the AE2 and two AVI passives (being the only passive speakers in this test) not really being any better or worse than the other Active speakers measured.

It would be easy to make a passive speaker with lower distortion, by having larger, multuple mid bass drivers, higher power tweeters, like a compression driver. It may not sound any good but distortion would be lower, and that aparently is all that matters! :silenced:

 

[bigblue235]

So, overall, no real obvious, startling differences? Jolly good.

So it's just another factor, much the same as drivers, cabinets, cables (eek!), room interaction, wind direction, ley lines, time of the month, etc?

 

[hoopsontoast]

 

[bigblue235]

Thought and hoped as much, as I've been making that point despite being rather poorly informed!

Seems that certain Actives are just good speakers, rather than them having some magical 'Active ingredient' (Boom, boom! Ahem, sorry).

 

[steve_1979]

So, overall, no real obvious, startling differences? Jolly good.

The differences aren't huge but they are there and they are noticable. Try visiting a pro audio shop and have a listen to a range of different speakers yourself. I'm sure that you'll be able to hear the extra clarity and bass control that many active speakers have.

So it's just another factor, much the same as drivers, cabinets, cables (eek!), room interaction, wind direction, ley lines, time of the month, etc?

Correct. The crossover is just one of several important factors.

 

[steve_1979]

Can you or anyone else confirm that these text books do contain the results of measurements of passive crossover distortion for all power levels equating to in room volumes of 30dbs to 110 dbs? If so on which pages of which edition is this information contained? Do any of them also have the results of equivalent measurements for any active crossovers?

Reading one of Gilbert Aurther Briggs books are a good place to start reading for anyone who's interested in understanding the real facts about active and passive crossovers. Unfortunatly I can't tell you exactly which page to look at for the relevant infomation bacause I've returned my copy of the book to the library (and they had to order it specially because they don't normally keep it in stock).

It's also worth mentioning that everything I've said about active crossovers isn't my own subjective opinion. I'm just repeating facts which have been established for several decades in the professional audio industry and are scientifically proven to be the best way to reproduce music with the least amount of distortion.

Don't take my word for it - try reading a book on the subject if you're interested. It'll teach you much more about our hifi hobby than any magazine or forum will.

 

[John Duncan]

So what do those graphs add to our knowledge of passive and active speakers? I'm too lazy to work it out and I know how you like this stuff.

 

[oldric_naubhoff]

So what do those graphs add to our knowledge of passive and active speakers? I'm too lazy to work it out and I know how you like this stuff.

maybe; a good speaker is one that measures well. and not if it's active or passive.

 

[John Duncan]

So what do those graphs add to our knowledge of passive and active speakers? I'm too lazy to work it out and I know how you like this stuff.

maybe; a good speaker is one that measures well. and not if it's active or passive.

Do those graphs bear that out? Can you tell me where and how if they do?

 

[John Duncan]

So what do those graphs add to our knowledge of passive and active speakers? I'm too lazy to work it out and I know how you like this stuff.

maybe; a good speaker is one that measures well. and not if it's active or passive.

Do those graphs bear that out? Can you tell me where and how if they do?

 

[idc]

So what do those graphs add to our knowledge of passive and active speakers? I'm too lazy to work it out and I know how you like this stuff.

maybe; a good speaker is one that measures well. and not if it's active or passive.

Do those graphs bear that out? Can you tell me where and how if they do?

I would be interested in an answer as well. Is there any correlation between how a speaker measures and subjective reports of sound quality?

 

[John Duncan]

There's a report out there that suggests a strong correlation, yes, but I'm interested first to find out what these measurements tell us about actives vs passives. On a brief glance I don't think it tells us anything but am interested in others' interpretations.