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Multi-Way Conventional loudspeakers with crossovers

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Old 1st October 2008, 06:42 PM   #11
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Like your site, a lot of info to shew on there!
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Old 1st October 2008, 10:54 PM   #12
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You would do very well if you could bring down the number of opamps from 22 to 3 or 4.

I guess 4 or 5 might be OK for the tweeter and the midwoofer but 3 would be extremely challenging. For the lower bass, who cares how many opamps are used?

I have not built the Orion but built its "counter-part" John K's NaO and like it a lot.

The NaO has 10 opamps instead of 22 for its active EQ/XO. I have reduced it to 7 opamps while maintaining 100% of its transfer functions. For the tweeter and the midwoofers, they go through only 4 opamps.

I remembered that I also spent about an hour or so trying a completely different topology with 2 opamps for the tweeter and midwoofers, while trying to maintain the same transfer functions. The NaO uses a modular approach with dipole EQ, notch filter and LP/HP filters. I tried to use a high Q (Q>1) Chebyshev filter which could create the "notch" and dipole EQ at the same time. I got fairly close (up to 90%?) but was not happy with it so I ditched the plan. But even with 4 opamps in the signal path the NaO still sounds very clean without any harshness.

With the Orion, I am not sure if it is possible to use 3 or 4. The delay network (all pass filter) would require that many. Unless you make a passive crossover between the tweeter and the midwoofer.
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Old 1st October 2008, 11:26 PM   #13
cuibono is offline cuibono  United States
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Although I'm only part way through it, it looks like each driver will only go through 2 opamps each - the input goes to an opamp that does all the eq'ing, then the signal is split by three opamps, one for each driver, high, mid, and low. So the signal will only go through two opamps before it hits the amp and then driver (I hope..). I might have to add more, but we'll see. To delay the tweeter I'm just going to do physical offset after measuring the drivers phase.

The reason I'm going to this trouble is due to my experience with SL's Pluto and Orion speakers - IME, both speakers had a similar sonic signature, I felt like there was some softness in the treble, kind of a lack of clarity. While there are many possible explanations, including my own poor judgment, I feel it will be worth while to go to the trouble and see what happens..

I'm hoping someone will speak up if there is some problem with the single opamp 4th order circuit posted above, it'll save me a lot of trouble
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Old 1st October 2008, 11:36 PM   #14
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Quote:
Originally posted by cuibono
Although I'm only part way through it, it looks like each driver will only go through 2 opamps each - the input goes to an opamp that does all the eq'ing, then the signal is split by three opamps, one for each driver, high, mid, and low. So the signal will only go through two opamps before it hits the amp and then driver (I hope..). I might have to add more, but we'll see. To delay the tweeter I'm just going to do physical offset after measuring the drivers phase.

The reason I'm going to this trouble is due to my experience with SL's Pluto and Orion speakers - IME, both speakers had a similar sonic signature, I felt like there was some softness in the treble, kind of a lack of clarity. While there are many possible explanations, including my own poor judgment, I feel it will be worth while to go to the trouble and see what happens..
Distort the tweeter and you'll get all the clarity you want, hehe.
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Old 2nd October 2008, 12:01 AM   #15
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I have just had a look at your simulation. I don't think it can do it without matching at least 95% of the original transfer function. When I modelled the NaO with 2 opamps, I got result closer than that but still would not dare to use it.

1dB difference at the knee would constitute unacceptable response which is highly audible.

Have you simulated both the Orion and your circuit and got the transfer functions? Which simulation software do you use?

Regards,
Bill
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Old 2nd October 2008, 02:44 AM   #16
cuibono is offline cuibono  United States
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In my first post, there is a link to the circuit simulator program I'm using. Its the one SL recommends. I'm not actually doing anything with the Orions, I'm trying to make an analog duplicate of the digital crossover I'm currently using. I have only just started, and haven't constructed the whole transfer function yet. I also haven't yet checked if the complementary high pass and low pass 4th order crossovers (based on a single opamp each) sum flat. I'm going to guess they do, but we'll see..
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Old 2nd October 2008, 12:53 PM   #17
infinia is offline infinia  United States
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Quote:
Originally posted by cuibono
Here is the simulation. There is something interesting going on - each filter has a slightly different 'knee', the passive circuit having the softest knee, and the single opamp circuit having the hardest knee. Y axis is in decibels..

(the green line is the passive circuit, the yellow is the double opamp, and the blue is the single opamp)
The "soft knee" freq response is due to the circuit Q. So unless they all 3 track well near the HP cutoff freq (-6 dB point for 4th order) they cannot be considered equivalent.
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Old 2nd October 2008, 05:00 PM   #18
cuibono is offline cuibono  United States
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Thanks - I had been suspecting that. I'm not sure what effect it will have on things yet.... I guess I'll have to build it and see. Maybe soon I will post a preliminary XO/EQ circuit.
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Old 2nd October 2008, 09:21 PM   #19
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What I believe is that text book LR2, LR4, BW3 responses work with the acoustic slope of the drivers, not the electrical one.

Drivers are not completely flat so if we apply text book electrical crossovers the result would not be as intended.

For example, if the tweeter is naturally rolling off towards lower frequencies at 12dB/oct, applying a 2nd order electrical crossover may yield a 4th order acoustic slope.

It is the correct acoustic slopes that allow summing correctly.

You could possibly use Speaker Workshop and design a passive network first and derive the network response out of it. Your active circuit can then mimic the same network response to obtain the correct filters.

Regards,
Bill
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Old 2nd October 2008, 10:35 PM   #20
cuibono is offline cuibono  United States
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I'm currently using a program called Allocator which allows you to import a .frd files for each driver, then apply crossovers and EQ. Allocator is then applies the filters to the output of my media player, in my case Winamp. I've gotten my desired acoustic function (mostly), and am going to try and make an electrical analog of the digital function in Allocator, so right now, I'm mostly worried about how the electrical signals will work when combining multiple filters around a single opamp. Later tonight I'm going to check that the XO's do electricaly sum flat.
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