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General Asylum General audio topics that don't fit into specific categories. |
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General Asylum General audio topics that don't fit into specific categories. |
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In Reply to: Dumb Q'n how many filters has the signal driving a tweeter 'seen' (been affected by) before it gets to the HP posted by Timbo in Oz on August 6, 2012 at 20:16:38:
The XOs in 3-way, "true-ribbon" Maggies are engineered with:
* an external section (bass LP/mid HP) and
* an internal section (mid LP/ribbon HP).
The external section was housed in a little box which, in the older models like my IIIas, sat on the floor; the internal section sat in a rebate in the MDF frame, underneath the bass/mid driver.
So the ribbon signal already had to pass through a large series cap in the Mid/HP filter, before it got to the ribbon HP series cap. Magnepan set up the overall XO this way for good reasons but one good tweak was to use a wire for the ribbon that bypassed the mid HP filter and went straight from the external XO input, to the mid/ribbon input terminal. (So the ribbon signal only passed through the (relatively small) ribbon series cap - however, you had to adjust other compoenent values, as well.)
Re. your other Qs:
Active (line-level) crossovers, passive line-level crossovers. Or with series and parallel spkr level passive crossovers.
Any differences at all between these topologies?
Line-level active ... is what I use on my Maggies. It enables the amps - particularly the bass amp - to have an iron grip on the drivers (there being no series inductors "in the way"). It also provides gain to compensate for driver efficiency differences or different amp gains.
Line level passive (PLLXO) ... theoretically less signal degradation than with an active XO and enables the amps to be directly connected to the drivers. But it only has loss (no gain) and for slopes greater than 6dB, you get excessive loss.
Series vs. parallel speaker-level XOs. Again, series tend to only be used in a 6dB-slope XO. In a 6dB XO, I think the engineers would say that series would have identical sound to parallel (and, in fact, uses the same component values, just differently arranged) ... however, people who listen to the music would say series sounds better. :-))
I have read some exposition saying series deals with back-EMF from the bass driver better than a parallel XO.
Peter Gunn, on these pages, has made quite a career of using 6dB series XOs on all models of Maggies (including 20.1s), as he noticed that the old SMG/SMGa - which were the only models until the recent X.7s to use a series XO - sounded very musical.
Also, how effective are the high-pass elements at protecting a tweeter, or midrange driver from excess power, e.g. from a pulled IC when we forget to shut the amp down / turn it down?
Even one series cap used for a 6dB HP filter should protect the driver from amplifier "thumps" ... but, please note, I don't even use a series cap for my true-ribbons - the mid & ribbon amps are directly connected.
Regards,
Andy
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Follow Ups
- "how many filters has the signal driving a tweeter 'seen' (been affected by) before it gets to the HP" ... - andyr 14:37:14 08/07/12 (0)
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