Can a DCX2496 be a sustitute for Orions x'over?nt - Page 2 - diyAudio
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Old 21st January 2004, 01:15 PM   #11
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Again the answer is kind of. The Orion as it stands using the Peerles XLS needs a boost in the bass that reaches 40dB below 10Hz. This what SL feels is necessary for flat response and low group delay. 15dB of this is due to the low Q of the XLS10.

So you need a crossover that can provide this kind of boost. The DCX can by overlaying filters, but runs out of processing (the mids need 20dB on their own)

The dbx Driverack PA can't overlay shelving filters and has only two bands available in the bass so the maximum boost is 24dB.

The Driverack 260 has the processing power to do it, but you have to fiddle with parametric filters on top of shelving filters. I believe the Rane RP26z can do it too.

The more expensive processors (XTA, BSS, Ashly) may also be fine.

IMHO, you would be better off using a different bass driver, or crossing to a monopole sub below 40Hz as SL now recommends.

I use the Adire DPL12 and have a maximum EQ boost of 18dB at 20Hz, giving me flat response to below 20Hz. This may affect group delay but I can't hear it. The Driverack 260 gives me this boost, plus 9 bands of PEQ for room EQ.

However, this duplicating exactly SLs crossovers. You could probably cheat it with minor sonic problems. I've done all sorts of different boosts and still had great sound, it is just that my current one measures and sounds great.


Cheers
Steve
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Old 21st January 2004, 01:30 PM   #12
RHosch is offline RHosch  United States
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I'm very curious about this quote from SL: "It certainly is not just a matter of adjusting for similar magnitude response since the ASP is not minimum-phase."

My understanding of electronics and filtering theory is decent, but not complete. I admit that I am at a loss as to which part of the Orion "sound processor" is not minimum phase. I was under the impression that all filters created using analog components (by analog, I mean they operate in a continuous manner, not in an on/off manner) modeled an IIR filter, and were by definition minimum phase. I know that digital filtering using mult-tap topologies (the equivalent of a large group of mechanical relays as best I understand it) models FIR filters and may not be minimum phase.

Does the Orion crossover use any on/off switching elements (transistors used as switches...) that would cause it to not be minimum phase? Is it the addition of the all-pass time alignment circuit? I am very puzzled by this.

BTW, have others noticed that much of SL's site content has now been removed and archived, and is only available through the purchase of a $25 CD? Apparently this went into effect just a few days ago. I think that is certainly fair for the information he provides. I mention this so that any of you who have recently visited the site can check your web page cache and save pages that are important to you for future reference.
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Old 21st January 2004, 02:23 PM   #13
Ken L is offline Ken L  United States
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Default Question - for steve Doddsy

slightly off-topic _grin_

Steve, if I were to sell my Behringer DCX 2496 and put in a higher resolution (higher quality) digital crossover, what do you think would be the best candidates.

I would be using simply as an active digital crossover to bi-amp. In my current config, I have got to have delay. My main concern would be to go to more quality and higher resolution. I am using a tube preamp and at this point have no problems with gain matching.

Or do you think I would be better to mod the Behringer? I'm not prepared to spend BSS type of money _grin_

Thanks for your input.

Regards

Ken L
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Old 21st January 2004, 07:12 PM   #14
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Quote:
Originally posted by RHosch

BTW, have others noticed that much of SL's site content has now been removed and archived, and is only available through the purchase of a $25 CD?

I mention this so that any of you who have recently visited the site can check your web page cache and save pages that are important to you for future reference.
Try this instead


web.archive.org of SL's site
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Old 21st January 2004, 08:43 PM   #15
Ken L is offline Ken L  United States
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Quote:
Originally posted by Drew Eckhardt


Try this instead
It never ceases to amaze me as to how knowledgeable some of the posters here are.

Kudo's to Drew for this one

regards

Ken L
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Old 21st January 2004, 10:38 PM   #16
Vadim is offline Vadim  Canada
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I think that there is no way to use a digital crossover, regardless of its brand name, with a speaker system such as Orion in order to cover all necessary EQ points, and in the same time to optimize the S/N ratio of the A/D converters. I went through this exercise not too long ago.

There are 2 problems here than must be solved simultaneously. First, you must make sure that the analog input signal to DCX2496 is about 8-10 Volts. This need has been extensively discussed here. Secondly, assuming that you have boosted the input signal to those levels, you need to accommodate the rather high EQ requirements of the Orion XLS woofers. Those requirements are, as Steve indicated, about 35 dB at 10 Hz. DCX2496 does work to 10 Hz, although it only displays 20 Hz.

The problem arises when you notice that the headroom of DCX2496, and any other digital crossover that I am aware off, is about +/-15 dB. Considering than your input signal is already high at 8 or 10 Volts you have no ‘room’ left to boost the signal any further. Perhaps you can do a few dBs but certainly not anywhere near 35 dB that is required. Even if you decide not to use the entire 35 dB of boost and EQ your woofers at higher frequency you are still going to notice a rather hard clipping.

I really liked what DCX2496 can do and I was determined to keep it in my 3-way monstrous dipole system. By the way, my system uses stacked Phoenix woofers, 10-inch Scan Speak midrange in a Phoenix-style baffle and RD-75 in its own wing-type baffle.

My solution to this problem was to take the woofer and midrange open baffle EQ functions along with the woofer compensation EQ function out of the DCX2496 and use an analog circuit instead, - 6 op-amps for 2 channels, - not a big deal. So I end up with a kind of a hybrid crossover system.

This hybrid is unavoidable and it does not really add any more ‘boxes’ to the overall scheme of things. It is so, because you still need a Master Volume Control to deal with the 8-10 Volts that will be coming out from your DCX2496.

I ended building a remotely controlled 20-channel capable box using 10 dual 10K linear motorized pots from Alps. You can get them for $3.5 a piece. Add a motor control circuit with infra-red sensor and you are done. The pots must be linear because you want to turn them into ‘log’ by adding a resistor. This resistor will force the nearly 100% tracking pot to pot.

This Volume Control box can also ‘house’ the analog circuit that takes care of the EQ requirements. The DCX2496 is used for LR-4 filters, notch filters and most importantly the delays and limiters. You can time align your Orion with DCX2496 without the use of analog delay circuits with their associated phase problems. You can also protect your Orions by setting the limiters in the DCX2496 so that you will never blow a woofer.

Well, this my take on this problem. Comments?
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Old 21st January 2004, 11:12 PM   #17
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Ken,

The Rane unit is probably somewhat better, or the Driverack 260. How audible this is depends I guess.

Cheers

Steve
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Old 22nd January 2004, 12:01 AM   #18
Thunau is offline Thunau  United States
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Default If I may chime in

Quote:
Originally posted by Vadim
I think that there is no way to use a digital crossover, regardless of its brand name, with a speaker system such as Orion in order to cover all necessary EQ points, and in the same time to optimize the S/N ratio of the A/D converters. I went through this exercise not too long ago.

There are 2 problems here than must be solved simultaneously. First, you must make sure that the analog input signal to DCX2496 is about 8-10 Volts. This need has been extensively discussed here. Secondly, assuming that you have boosted the input signal to those levels, you need to accommodate the rather high EQ requirements of the Orion XLS woofers. Those requirements are, as Steve indicated, about 35 dB at 10 Hz. DCX2496 does work to 10 Hz, although it only displays 20 Hz.

The problem arises when you notice that the headroom of DCX2496, and any other digital crossover that I am aware off, is about +/-15 dB. Considering than your input signal is already high at 8 or 10 Volts you have no ‘room’ left to boost the signal any further. Perhaps you can do a few dBs but certainly not anywhere near 35 dB that is required. Even if you decide not to use the entire 35 dB of boost and EQ your woofers at higher frequency you are still going to notice a rather hard clipping.

I really liked what DCX2496 can do and I was determined to keep it in my 3-way monstrous dipole system. By the way, my system uses stacked Phoenix woofers, 10-inch Scan Speak midrange in a Phoenix-style baffle and RD-75 in its own wing-type baffle.

My solution to this problem was to take the woofer and midrange open baffle EQ functions along with the woofer compensation EQ function out of the DCX2496 and use an analog circuit instead, - 6 op-amps for 2 channels, - not a big deal. So I end up with a kind of a hybrid crossover system.

This hybrid is unavoidable and it does not really add any more ‘boxes’ to the overall scheme of things. It is so, because you still need a Master Volume Control to deal with the 8-10 Volts that will be coming out from your DCX2496.

I ended building a remotely controlled 20-channel capable box using 10 dual 10K linear motorized pots from Alps. You can get them for $3.5 a piece. Add a motor control circuit with infra-red sensor and you are done. The pots must be linear because you want to turn them into ‘log’ by adding a resistor. This resistor will force the nearly 100% tracking pot to pot.

This Volume Control box can also ‘house’ the analog circuit that takes care of the EQ requirements. The DCX2496 is used for LR-4 filters, notch filters and most importantly the delays and limiters. You can time align your Orion with DCX2496 without the use of analog delay circuits with their associated phase problems. You can also protect your Orions by setting the limiters in the DCX2496 so that you will never blow a woofer.

Well, this my take on this problem. Comments?

The SHARK processor (used in the DXC) is a 32bit floating point DSP device. It has a huge internal dynamic range- about 1500 dB. That's Fifteen Hundred, not One Hundred Fifty. You can achieve huge boosts internally and as long as you apply a corresponding level cut right before the D/A stage you will not run into problems with headroom be it analog or digital.
If you insist on feeding it (the DXC) analog signal then yes, you should use a +4dB nominal level which puts your peaks at +/- 12V or thereabout. But, feeding it digital stream takes care of this problem.
As to the possibility of reproducing the Orion crossover inside the DXC- it might not be possible due to use of allpass filters or cross feeding circuits which the Behringer lacks. It might be possible to come very close though to the point where some listeners will prefer one version over the other and vice versa.
The one "affordable" processor which addresses a lot of the challenges is the Rane RPM26z. It has freely configurable processing map, digital input, analog outputs with over 40dB of controllable gain and a decent library of processing blocks. I've used it in quite a few commercial installations - it works like a charm and it sounds very good. The volume control is a simple 20k linear pot wired to a contol port. The user just has to assign it to all the analog outputs in the software.

Another good one is the Symetrix Symnet. It's algorithm/processing blocks library is very extensive (much biggerthan Rane's) and the output stages are THAT VCAs also controllable in the software and by using a single pot. Much more money though- around $3k. But, you get 8 ins and 8 outs plus networking.

My money/hopes are on Multimedia PC though. A quiet Windows or Linux box with an RME interface running custom DSP program with all your CDs ripped to the hard drive and controlled wirelessly from a palm PC. It could live somewhere in the basement or a closet and be connected to the Converter by an optical cable. I've seen posts on this very forum about early versions of such system.
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Old 22nd January 2004, 03:08 AM   #19
Vadim is offline Vadim  Canada
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Jan,
Quote:
The SHARK processor (used in the DXC) is a 32bit floating point DSP device. It has a huge internal dynamic range- about 1500 dB. That's Fifteen Hundred, not One Hundred Fifty. You can achieve huge boosts internally and as long as you apply a corresponding level cut right before the D/A stage you will not run into problems with headroom be it analog or digital.
Yes I can see that. It is applying the signal cut before the D/A becomes a problem How do we do that?
Quote:
If you insist on feeding it (the DXC) analog signal then yes, you should use a +4dB nominal level which puts your peaks at +/- 12V or thereabout. But, feeding it digital stream takes care of this problem.
I do not see that using the digital input solves the problem. Perhaps I am missing something here. I plugged in my trusty Denon CD player to DCX using digital input-output ports and I observed input level meters on the DCX are doing about -3 dB maximum no matter what program material I throw at it. Now, it is my understanding that I am sending an 16-bit encoded signal to the DCX.

Anyway, I see no input clipping, - good. Now, if I introduce a shelving low-pass filter with 10 dB of gain I clearly see the output meters show clipping, - no good. Now, to fix this I attenuate the output digitally by 10 dB, and the DCX allows you to do this. The clipping goes away, - great. However, now what I have done is I reduced the signal resolution by almost 2 bits.

Considering that the DCX measures a little better then 16 bits in the real world environment this is a problem for me. I know that in the lab with A-weighting the DCX is specified at better then 18 bits, but in my lab I only see 16 bits and even that is rather amazing. Anyway, a loss of 2 bits is significant, don’t you think? Well, am I wrong about all this?

I understand that the internal processing of SHARKs has nearly infinite headroom, but how does it help me here. I think what might be happening is that the D/A is a delta-sigma type and as such it must collect all the charge pockets and convert then to analog voltage with an internal op-amp. This op-amp has defined saturation levels and fixed power rails and so the signal is hitting those levels due to its large amplitude. I do not see how we can help this.

With this in mind, although the DCX gives an ability to introduce at most 15 dB of gain, which is a significant amount, it is not advisable to use this facility liberally for the fear of possible clipping. The nature of dipole EQ requires the opposite. Perhaps this is why the DCX also provides limiters. I don’t know, perhaps I am wrong about this, but so far this is what I think.
Quote:
As to the possibility of reproducing the Orion crossover inside the DXC- it might not be possible due to use of allpass filters or cross feeding circuits which the Behringer lacks.
Well, the all pass circuits are analog delay lines and the DCX does provide them. I am not sure what the cross-feeding circuits are.
Quote:
The one "affordable" processor which addresses a lot of the challenges is the Rane RPM26z. It has freely configurable processing map, digital input, analog outputs with over 40dB of controllable gain and a decent library of processing blocks. I've used it in quite a few commercial installations - it works like a charm and it sounds very good. The volume control is a simple 20k linear pot wired to a contol port. The user just has to assign it to all the analog outputs in the software.
Yes I agree that the Rane 26z is a great unit. It must be controlled through a direct link to a computer, but I do not see that as a problem Its 40 dB of gain is a real plus. But even so I do not see how even that much of controllable gain will help with Orion-type open baffle EQ along with a low Q woofers boost. I think you will still clip. The VCA volume is handy, but somehow I would still prefer a much cleaner from THD perspective approach of a good attenuator. The cost naturally is yet another reason why 26z may have to be avoided.
Quote:
My money/hopes are on Multimedia PC though. A quiet Windows or Linux box with an RME interface running custom DSP program with all your CDs ripped to the hard drive and controlled wirelessly from a palm PC. It could live somewhere in the basement or a closet and be connected to the Converter by an optical cable. I've seen posts on this very forum about early versions of such system.
This would be the ultimate. In fact I would love to have a set-up with a total DSP-based PC-control and external sound card like M-Audio 410 Firewire. I think, however, that in order for this proposed rig to work and not to loose resolution the 410 Firewire output circuits may have to be modify to accommodate the Orion.
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Old 22nd January 2004, 04:34 AM   #20
Davey is offline Davey  United States
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Vadim has hit the nail squarely on the head.

DSP-based crossovers are highly compromised when asked to achieve something like the transfer functions required by the Orion crossover and still maintain a decent S/N ratio, non-linear behaviour, etc.

I've successfully programmed my DCX2496 to duplicate the curves of the Orion crossover....although the pure delay settings are not the same as an analog all-pass function. However, with actual usage it becomes a problem depending upon how the system volume control is implemented. If a normal two-channel volume control is used upstream of the crossover and the outputs connected directly to the power amp inputs you may find yourself with a serious noise problem that is clearly audible at low volumes. The alternative is to feed the DCX with a higher signal level input (either digital or straight from the CD output) and use a multi-channel volume control (or hybrid with fixed pads in combination with a control) downstream of the crossover. In this case the large equalizations and relative levels required will clip the internals of the DCX unless the levels are shifted downward. So, it's a compromise either way.

I've noticed this topic has been discussed a bit on other forums as well, but I fail to see what the attraction is to using a digital crossover for a highly specialized speaker system like the Orion. The analog crossover designed by SL is superior to any digital implementation and it also happens to be the least expensive. It's a no-brainer.

Cheers,

Davey.
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