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In Reply to: RE: If we assume posted by pictureguy on May 14, 2015 at 15:23:21
No, I totally get it.The article compares passive single amp to active multi-amp, and does a fine job I have to say. (Nice explanation of how gain demands are reduced for individual amps in active configurations.)
But I was discussing differences between passive single amp and passive multi-amp. In the active/passive multi-amp comparison, active can get more watts per dollar/pound of amp compared to the passive equivalent.
In pro-sound environments, this is a no brainer since you want the most SPL for given dollar, weight and cargo space that gear takes up. In audiophile land these concerns may be a non-issue.
Case in point: Passive Tri-amp Versus passive tri-amp:
Passive 200W/channel amp x 3. Max potential output = 200W. (no gain in Max SPL).
Active 200W/channel amp x 3. Max potential output = 600W. Max used. 450W?** New max determined by reaching max output of any on driver or max output voltage of any one amp (clipping).
So, you have three choices how to use the increased efficiency of active:
(a) don't. You like passive multi-amp for other reasons than "more power".
(b) get smaller amps (less overall gain needed) for the same SPL as passive equivalent.
(c) use the same size amps and get more SPL than the passive equivalent - if speakers can do it.Nobody said active was not more efficient than active. I just said that max efficiency and max SPL per dollar are not necessarily design considerations for an audiophile. If a guy thinks (2) 200W amps sound better than (1) 200W amp and gets no additional efficiency or output capability (and doesn't care) then who's to bash his ideology if better sound was the *only* criterion for the upgrade?
The crux of my posts was that passive bi-amp is different from passive single-amp. Despite reproducing the full range voltage signal, they no longer reproduce the full-range signal current. Each amp only sees the current drawn by the respective low and high pass filter/driver combinations.
I did not say passive multi-amp offers the same benefits that active multi-amp does.
Passive multi-amp offers no voltage gain reduction, therefore does not make use of the increase in total available power.
Cheers,
Presto
Edits: 05/15/15 05/15/15 05/15/15 05/15/15 05/15/15 05/15/15 05/15/15 05/15/15 05/15/15 05/15/15 05/15/15 05/15/15 05/15/15 05/15/15Follow Ups:
The REFERENCE and starting point is a single channel of amplification and passive speaker level crossover per channel. A very large %age of stereo guys start and STOP right there.
Phase 2 is passive biamp using the speakers internal crossover
Phase 3 is either active or passive Line Level crossove which is where potential benefits REALLY pile up.
I think the 'efficiency' gain of a LL crossover comes from the out of band signals your amps are no longer asked to amplify. This, according to the ESP article, can amount to a maximum of about 3db. Roughly 2x the amp power, compared to the 'passive' biamped system. Given my panels low /mid 80s sensitivity, I'll take every watt I can get.
The drawings in the ESP article which show a HF and LF O-Scope 'trace' clearly indicate that the amp will Voltage Clip at about the same point as a single amp of the same power. I'll go with ESP on this.
I don't think we disagree about going to a Line Level crossover. That is my ultimate goal and the reason I went to a pair of stereo amps for my panels. And since my runs are short, I'm not overly worried about the PLLXO's inability to drive long runs of cable and its internal losses. Since each amp will have its own crossover, it will be locaed right AT the amp. From the crossover TO the amp may require 12" jumpers, certainly nothing longer. I can Duplicate, pretty closely, the crossover which came with the panels. Most of the Active crossovers I've see are high order and not generally to my liking. I'm not equipped to do a major crossover reengineering project for my panels. Most reports I've read say that 24db/octave filters don't necessarily sound 'right', anyway. I'd consider an active LL crossover using opamps, IF I could find a 6db / 12db octave schematic to evaluate.
Too much is never enough
I've been running DSP/ACtive for years now and I haven't looked back. Every time I try a different DSP crossover or an outboard active one, I start missing my DSP/Active (Thuneau) setup right away.
Maybe I'm just used to it... I don't know...
But all that rumination has me seriously wanting to play around with some passive bi-amping, for no other reason that I have bi-ampable two-ways here and a few amps kicking around...
I've never done a full-out PLLXO setup and I really want to try one... the upshot is the parts are small and not super expensive.
To the lab! :P
Cheers,
Presto
I think you've hit on one very good feature of a PLLXO setup.
You can basically build such a crossover into an ALTOIDS can and spend about 15$ EACH even buying the MOST EXPENSIVE components available. OK, add a few bucks for overpriced RCA jacks.
Too much is never enough
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