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Old 18th April 2012, 06:52 AM   #4411
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Quote:
Originally Posted by ThorstenL View Post
Invariably worse than that of a passive one. That much should be abvious, assuming quality components are used for the passive crossover (so not ferrite cored chokes and bipolar electrolytics).
So then air-cored chokes? You don't count non-linear frequency dependent losses as distortion then?
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Old 18th April 2012, 07:38 AM   #4412
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Hi,

Quote:
Originally Posted by abraxalito View Post
Perhaps the FIR filters you've experienced haven't been 'correctly done' ? Care to share more details?
Could be they are not "correctly done", though fundamentally a FIR seems to designed "contra lex naturae". As to examples, 99% of all digital audio products. If they create such mayham as they do at frequencies at the edge or beyond hearing, what will they do in the Audio Band.

All digital XO's I have so far encountered where thankfully IIR. The old Yamaha one with PCM63 in the output's is worth hunting down and refurbishing, it is quite horrorshow and will knock any Behringer into a crocked hat. Sadly they seem mostly be bought for salvage, so they are rare.

Quote:
Originally Posted by abraxalito View Post
You use 'so' but I can't see how this (above) statement follows reasonably from your earlier ones.
If the digital XO does not deliver performance that is superior to passive crossovers (and it does not), the main reason one may wish to still employ one is because it is easy to adjust, unlike a passive, analogue crossover.

Hence my "So"...

Ciao T
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Old 18th April 2012, 07:49 AM   #4413
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Quote:
Originally Posted by ThorstenL View Post
Could be they are not "correctly done", though fundamentally a FIR seems to designed "contra lex naturae".
Curious - to me the IIR is like that and the FIR not.

Quote:
As to examples, 99% of all digital audio products.
Well, agreed that at least 99% of implementations aren't particularly good ones - half-band and linear phase, equiripple filters abound.

Quote:
If they create such mayham as they do at frequencies at the edge or beyond hearing, what will they do in the Audio Band.
I believe IIR is equally capable of that. You're speaking of ringing? Or only pre-rnging?

Quote:
All digital XO's I have so far encountered where thankfully IIR. The old Yamaha one with PCM63 in the output's is worth hunting down and refurbishing, it is quite horrorshow and will knock any Behringer into a crocked hat. Sadly they seem mostly be bought for salvage, so they are rare.
So you've never encountered a Behringer? They most certainly have FIR inside the DACs they use (AKM is it?).

Quote:
If the digital XO does not deliver performance that is superior to passive crossovers (and it does not)
TVR was asking originally about distorton performance, you broadened the discussion to sound quality. So by 'performance' here which are you referring to?

Quote:
, the main reason one may wish to still employ one is because it is easy to adjust, unlike a passive, analogue crossover.
Ah now you've qualified the 'so' with 'mainly' that's a material change.
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Old 18th April 2012, 08:20 AM   #4414
dvv is offline dvv  Serbia
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Thorsten, you are right, the chokes I have are rated for AC, not DC.

Damn! Back to the drawing board.
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Old 18th April 2012, 08:22 AM   #4415
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Hi,

Quote:
Originally Posted by abraxalito View Post
Curious - to me the IIR is like that and the FIR not.
FIR is zero/linear phase and so not found in nature, hence my "contra lex naturae" quip, IIR is minimum phase and hence mirrors nature.

Quote:
Originally Posted by abraxalito View Post
So you've never encountered a Behringer? They most certainly have FIR inside the DACs they use (AKM is it?).
I have used the DEQ, mine had CS ADC/DAC.

Quote:
Originally Posted by abraxalito View Post
TVR was asking originally about distorton performance, you broadened the discussion to sound quality. So by 'performance' here which are you referring to?
Depends on the definition of "distortion".

To me, if a deivce/process etc. alters the sound so that what appeared "good" before and "bad" after, it adds distortion, not necessarily measurable in the THD&N domain, but distortion nevertheless...

Quote:
Originally Posted by abraxalito View Post
Ah now you've qualified the 'so' with 'mainly' that's a material change.
Not really, except for hair-splitters. Prior I qualified with "seems"...

And I retain, I see no benefit to digital XO's (over analog solutions), except easy adjustability.

Ciao T
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Old 18th April 2012, 08:27 AM   #4416
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Quote:
Originally Posted by ThorstenL View Post
FIR is zero/linear phase and so not found in nature, hence my "contra lex naturae" quip, IIR is minimum phase and hence mirrors nature.
FIR is no more linear phase than red wine is Bull's Blood. PCM5102 has a min-phase FIR option.

Quote:
And I retain, I see no benefit to digital XO's (over analog solutions), except easy adjustability.
I don't mind at all if you're not looking for all the other reasons
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Old 18th April 2012, 08:34 AM   #4417
dvv is offline dvv  Serbia
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Regarding having or not having overall feedback, in my experience, I have never heard a device without a global feedback loop which sounded right to my ears. They do tend to have a warmis sound, it tends to be sweet and often a little too sweet, and they invariably leave me with a feeling of a job not finished, as if something was left over. Multiply everything said above by two if it uses tubes.

Which is why I don't much like tube audio, but hey - live and let live.

That said, in my experience, the quality of sound does not depend much on the amount of feedback, but does depend in my view heavily on how that feedback is applied. In this respect, I am totally with Thorsten, I also believe (based on personal experience) that devices with a lot of local but low overall NFB tend to sound better to much better than devices with low local and heavy global NFB.

The fact that those with heavy global NFB ALWAYS have better published specs means absolutely nothing to me (although it's easy to see why they mean so much to commercial manufacturers, people actually do read spec sheets, in fact they rely on them too much and certainly much more than on their own ears), I honestly don't give a damn if their published specs say 0.001% or 0.3% THD if it sounds good to me.

A great example is my own Harman/Kardon 6550 integrated. It's rated at 0.3% THD into 4 Ohms, 20-20,000 Hz at rated power, but it actually sounds a hell of a lot better than most other amps with specs like 0.01% under the same conditions. It uses just 17 dB of global NFB.
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Old 18th April 2012, 08:49 AM   #4418
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Has anyone considered using specialized amps for loudspeaker drive?

By that, I mean using a power amp for say the midrange driver (assuming a 3 way speaker), with classic analog first order filtering located at its input? In fact making it suitable for midrange reproduction only? Series low pass + high pass using simple passive components?

I realize first order filters are nothing to write home about, but in return, they have the least phase shift. You can't have it all.

For the bass and treble amps, you can be a little more ambitious and use the input stage as a second order filter, much like W. Marshall Leach used a second order filter on his first amp way back in the 70ies (in his case, it was used to remove ultrasonic signals).

Just a thought. If feedback can be localized to each stage, why not this?
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Old 18th April 2012, 11:25 AM   #4419
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Hi,

Quote:
Originally Posted by dvv View Post
Has anyone considered using specialized amps for loudspeaker drive?

By that, I mean using a power amp for say the midrange driver (assuming a 3 way speaker), with classic analog first order filtering located at its input? In fact making it suitable for midrange reproduction only? Series low pass + high pass using simple passive components?
I have done such things using Tubes.

In one case the system consisted out of two ESL Panels (appx. 100Hz - 500Hz and 500Hz to above 20KHz) per channel plus a dual 18"Dipole Sub.

The crossover filters and EQ was designed into the Amplifier, which where class A DHT Push-Pull, 300B for the Upper Mid / Treble and 845 for the upper bass / lower mid, non-lopped feedback of course. The Bass Amp was a 1KW Mosfet Module with the lowpass designed in as Sallen Key filter and the dipole EQ in the feedback loop.

The Tube Amplifiers employed normal output transformers and could be switched full-range & flat for driving more conventional speakers, but in system they drove the ESL Stators directly via capacitive coupling from the Anodes.

High pass filters combined the interstage coupling cap's and others to form a 3rd order HPF, while the lowpass & eq was done first order (assymetric slope XO).

Quote:
Originally Posted by dvv View Post
Just a thought. If feedback can be localized to each stage, why not this?
If your output stage is Class AB you will need some NFB.

So far my work leads me to believe that the correct number for NFB around a optimum or overbiased Class AB Output stage is around 12dB, this holding for Tubes as much as for Transistors.

More seems to lead to less favourable harmonic distribution and transient behaviour in technical terms and to a more edgy and constipated, subjectively, as NFB ratio's are increased, less seems to cause a sound that is overly soft & wooly and "inconsistent with level". My experimentation remains limited though and other means (like Feed Forward Error Correction) may be employed instead of NFB (and IME with benefit).

Class A Amplifiers can use local degeneration and/or loops only without negative issues, IME.

Ciao T
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Old 18th April 2012, 11:45 AM   #4420
tvrgeek is offline tvrgeek  United States
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I have a cheap ( Behringer) digital crossover because it is easy for quick testing on the bench for designing speakers. It is no where near a high fidelity unit. Not even close to their $100 analog ones which are surprisingly not as bad as one may think. Not what one can build though.

All drivers are non-ideal. Just some are a lot more "non" than others. In a perfect world, we could do all the filtering on the original bitstream before it reaches a D2A. Someday I will look at Bodzio's Ultimate Crossover. A big PC and several good DAC's does have some attraction. ( I use SoundEasy for speaker design) There is an entire world there to be looked at.

Yes, first amp is the modified Hafler 120, second Rotel 951. LTSpice models attached. Some liberties in devices due to limited models.

The above is purely LTSpice, not reality, and sure not using ones ears. So distortion added by an inductor is what the model does. When I model just a passive filter, I also get quite high distortion. What the model is assuming I have no idea.

It is completely practical for a DIY to design the speaker and amp together. The market has shunned powered speakers probably because so few were done well and if they were, the sticker shock would kill it. So this forces building amps that are immune to the load. Easier said than done. Powered subs seem to be the exception in market, but to my ears, none have been done well.

A lot of designs take some feedback before the outputs in that the drivers are not just tied together but the center point also tied to the output. Something I can plan on plying with when I build my test mule. The models seem sensitive to the driver current and the value of this resistor. I guess I am not following how to add local feedback to the outputs themselves. Larger emitter resistors? ( I am making the leap here that most consider DF to be of little importance) Some have tried to take the feedback after the output network including any fuse that may be there. I guess the extreme of that would be to sense at the speaker terminals. Maybe in a powered speaker, but would sure be looking for trouble in a conventional system. I thin I would only try it with disposable drivers and amps until some very aggressive protection systems were built.

This all comes back to the core of this thread. What makes it SOUND better, and then can we characterize it with a measurement? That is why I posted the differences in shape of the FFT as possible candidate rather than some absolute single number. I have no problem if the measured harmonics go from .0001 to .01 if it sounds better. (or 1% for those fond of glass) I am still leaning toward high order harmonics causing tweeter issues. I have parts on order to test adding steeper LP filters to the tweeters in my current build. (Seas T27-bfc/g) They break up at about 25K as do the tweeters in my Studio-20's. The Vifa's in my last pair break up even lower, and yes, my wife dislikes them more. The high energy is in the 2 to 4K range, so it is not that far a reach for the 5th and 6th harmonic being an issue. I am building two versions of the crossover, cheap parts vs. expensive parts for the tweeter side.
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