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Old 4th January 2013, 05:05 AM   #381
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Quote:
Originally Posted by Bruno Putzeys View Post
The data word length in the TAS3108 is 56 bits (48 after the point) and its accumulator is even longer.
Eh? I'm looking at instruction set and see no mention of a 56 bit word. 54 bit instruction word, 48 bit data word for the DSP. 76 bit accumulator, yes.

I agree the TAS3108 is a nice part and also fail to understand why TI is discontinuing it. Guess not enough folks understand the value of having more than 32 bits.

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Originally Posted by Bruno Putzeys View Post
You don't need a lot of DSP for that. The LS1 has a 6000 tap filter correcting the 70Hz subwoofer crossover, and it's done in a hundred cycles or so.
Thanks for mentioning this. I'd wondered about using delay to offload phase shift computations but hadn't gotten around looking into the synthesis.
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Old 4th January 2013, 07:14 AM   #382
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Originally Posted by ds23man View Post
I also think linear phase is overrated....
We have to see everything in it's perspective. Only a loudspeaker with 1 driver hase a linear phase,
Except concentric (coaxial) drivers like Tannoy, TAD, Cabasse, Beyma or Altec Lansing. Not to forget the APPOLITO 's configuration.
But, at this time no digital delays where available to recover the physical delay due to the non horizontal alignment of the coils. Nowadays, we can correct this in a nice way.
We have to notice this delay problem is important at the crossover. This argue (once more) in favor to 2way horns systems, where the crossover is at low frequency (<1000Hz) , so, phase correlation will not change a lot with vertical misalignment, because the wave length is 0.34m.
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Old 4th January 2013, 09:46 AM   #383
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Quote:
Originally Posted by Esperado View Post
Except concentric (coaxial) drivers like Tannoy, TAD, Cabasse, Beyma or Altec Lansing. Not to forget the APPOLITO 's configuration.
But, at this time no digital delays where available to recover the physical delay due to the non horizontal alignment of the coils. Nowadays, we can correct this in a nice way.
We have to notice this delay problem is important at the crossover. This argue (once more) in favor to 2way horns systems, where the crossover is at low frequency (<1000Hz) , so, phase correlation will not change a lot with vertical misalignment, because the wave length is 0.34m.
Of coarse coaxial drivers have lesser problems, I owned several Tannoy's. But most of the time they also need time alignment because their high drivers are not in the same acoustical centerpoint of the woofer due their construction.

But you can also overcome this vertical misaligment by using steeper slopes, the higher the order of the filter the smaller the frequency band where problems occur. I think using 48db filters has more effect than chasing the Fir filter holy grail.
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Old 4th January 2013, 10:02 AM   #384
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Hi ds23man,

What would be the benefit of using asymmetrical slopes for time alignment of drivers vs. a delay on the tweeter? I can see the downside (bad phase tracking) but not the upside..

Taking inspiration from the Grimm Audio LS1 I would (am) use(ing) FIR only for phase EQ and IIR filters for the crossovers. Resulting in a linear phase sytem. (rePhase and a miniDSP openDRC are my weapons of choice for phase EQ at the moment, combined with Hypex PSC2.400d based IIR XO).

Just trying to understand why you make such a choice.

Edit: (Big) typo
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Old 4th January 2013, 10:42 AM   #385
ds23man is offline ds23man  Netherlands
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Originally Posted by Mark.Clappers View Post
Hi ds23man,

What would be the benefit of using asymmetrical slopes for time alignment of drivers vs. a delay on the tweeter? I can see the downside (bad phase tracking) but not the upside..

Taking inspiration from the Grimm Audio LS1 I would (am) use(ing) FIR only for phase EQ and IIR filters for the crossovers. Resulting in a linear phase sytem. (rePhase and a miniDSP openDRC are my weapons of choice for phase EQ at the moment, combined with Hypex PSC2.400d based IIR XO).

Just trying to understand why you make such a choice.

Edit: (Big) typo
I do not use asymmetrical slopes, it is mentioned in the article. What I want to point out is the fact that even if you use a phase linear xover, the problems with vertical misallignment still exists and is clearly shown in the polar plot. A lot of people make the mistake that if you use a linear xover, you will get a phase linear system. Well you can actually, but only in one listening position and you will need to strap your head to a headrest!
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Old 4th January 2013, 11:19 AM   #386
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Originally Posted by ds23man View Post
I do not use asymmetrical slopes, it is mentioned in the article. What I want to point out is the fact that even if you use a phase linear xover, the problems with vertical misallignment still exists and is clearly shown in the polar plot. A lot of people make the mistake that if you use a linear xover, you will get a phase linear system. Well you can actually, but only in one listening position and you will need to strap your head to a headrest!
Yupz, you`re quite right, all the usual design parameters have to be taken in account, time alignment being 1 of them, dispersion / lobing is another big one. The phase EQ (making the system linear phase) is just the icing on the cake.
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Old 4th January 2013, 11:34 AM   #387
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Originally Posted by ds23man View Post
I do not use asymmetrical slopes
Most of the time, the loudspeaker adds its own slope to the one of the filter. Not in the same way on the basses and trebles units. So, searching for symmetrical acoustical slopes drive-you most of the time to asymmetrical electronic/electric slopes.
You want to use bass speaker in the range where it does not fractionate. By habit, you will see a peak of its response curve just where you will cut-it. So your filter will have to cancel-it. No rules: each driver need a dedicated filter for the same cut-off slope.
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Old 4th January 2013, 11:37 AM   #388
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Originally Posted by Esperado View Post
Most of the time, the loudspeaker adds its own slope to the one of the filter. Not in the same way on the basses and trebles units. So, searching for symmetrical acoustical slopes drive-you most of the time to asymmetrical electronic/electric slopes.
You want to use bass speaker in the range where it does not fractionate. By habit, you will see a peak of its response curve just where you will cut-it. So your filter will have to cancel-it. No rules: each driver need a dedicated filter for the same cut-off slope.
In principle this is true, but with the current DSP's it's not difficult to first EQ the driver flat well beyond the XO points and apply an XO after that. This solves the problem you descibe here .
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Old 4th January 2013, 11:52 AM   #389
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Originally Posted by Mark.Clappers View Post
In principle this is true, but with the current DSP's it's not difficult to first EQ the driver flat well beyond the XO points and apply an XO after that. This solves the problem you descibe here .
How can-you EQ a horn slope ? Better use-it, no ?
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Old 4th January 2013, 11:52 AM   #390
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Quote:
Originally Posted by Mark.Clappers View Post
In principle this is true, but with the current DSP's it's not difficult to first EQ the driver flat well beyond the XO points and apply an XO after that. This solves the problem you descibe here .
And is the advised way of working by Hypex and other dsp manufactures.

Using asymetrical slopes is implementing the old way of working with passive xovers.......
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