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swtuggle

Biamping the big ADS models

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After lusting over 710, 810, 910, 980, 1290, etc. for over 10 years, I finally got around to pulling the trigger a couple weeks ago on a pair of L980s I had a lead on for a few months. For the past couple days, I was adding my impressions to an old thread on AK, then asked about the biamp feature. That's probably not the target audience there, so I figured I'd post here, likely to get a more accurate and comprehensive response.

I've read just about every thread I could find on the biamping feature of these larger ADS models, and there is not an overwhelming consensus one way or the other.

I have become confused by reading reports from those who say they added an electronic crossover (dbx/Rane/Ashley/etc.) and the speakers woke up. Others have said adding the electronic crossover ruined the speaker's balance, sounding awful, and they went back to stock full range inputs. 

What I came away with from all these threads, is that the E-crossover is a deal-breaker for technical reasons, due to the slope imbalance that results on the high pass circuit. For example, the stock slope is 12 dB for both high and low pass. Adding a 12 dB E-crossover adds another 12 (or whatever its designed slope is) to the high pass circuit, but the woofer is only using the e-crossover's 12 or whatever dB, and that affects how the woofer to mid crossover point blends.

For those who love the sound of biamping these, do you not hear that technical imbalance? Is it not audible to human ears? Most of those opposed to the e-crossover say it is audible. Are we splitting hairs again as we so often do?

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Perhaps the reason I did not have that problem is my crossover uses a 24dB/octave rolloff.  I expect this allows full (relevant) bandwidth to each passive x-over in the cabinet.

It is not expensive to try - a used dbx 223 is pretty reasonable (and largely indestructible), you just need to be able to sort out your connectors.  All I had to do was adapt RCA to 1/4" TS, but some versions are XLR so make sure you know the back panel of what you're buying.

In my case I was not able to A/B my L980s, it was the 1590s that "woke up".  I had felt those were underwhelming beforehand, never had that concern with the 980s.

YMMV, and enjoy your 980s - room placement matters!

- Jeff

 

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I always felt the "bi-amp"  option that ADS offered to consumers was a mistake. There is more opportunity to screw up the sound than to improve it (I once owned a pair of 910's using just the built in passive crossovers).

Effective bi-amping requires pretty detailed knowledge of the raw drivers individual performance. It also requires test equipment to set amplifier gain levels, as well as the crossover frequencies and slopes.  Pro's use  bi-amping in sound reinforcement for increased output capability and reliability, and when the performance space has been defined. With pro use,the cost and complexity of additional amplifiers and electronic crossovers is justified over the long haul. With consumer use, I don't think it's justified,  from either a cost or performance point of view.

Let's assume the ADS passive crossover was properly designed, and yields what is generally acknowledged to be "good sound".  With bi-amping, audible changes to the system should be SUBTLE.  The primarily benefit should be less audible distortion as the woofer amplifier "clips" (overloaded) with heavy bass content. The distortion generated with this clipping is produced by the woofer(s) only, where it's mostly inaudible. It's inaudible because woofers naturally rolls off highs, and the passive crossover reduces the highs further.

The trouble with bi-amping  occurs when any additional filtering created by the electronic crossover upsets the INTENDED "blending" occurring between upper woofer frequencies and midrange lower frequencies. Not to mention any changes in the "radiation pattern" at the crossover frequencies.

 I'm not saying that bi-amping isn't a valid way of improving sound. I'm saying that in the hands of the average consumer, it's not likely to do so. 

Gerry S

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To swtuggle, I suspect you're considering the outboard and in-cabinet crossovers as additive, they are not.  If my post was not clear, my pre-amplification crossover at 24dB/octave rolloff ensures that the in-cabinet crossover gets all the signal that is intended for it, given a correct match in spectrum setting.

To Gerry S, I believe that reason for my change in perceived performance was not from amplifier clipping, as I have heard plenty of that in my time, but due to amplifier headroom - the high slew-rate/delta-A demands no longer need to contend between bands.  I will continue to believe these drivers like their current very very much, both low- and high-spectrum, and even though my amplifiers are extremely capable in that regard getting the channels to drive each in-box crossover independently allows "full service, no waiting".

And I will vehemently disagree that pro sound folks bi-amp for reliability - complexity, of any kind, will never improve reliability of a core path - failure mode management is the only exception to that rule and is not pertinent to consumer electronics.  Again, my upstream dbx presents more than required signal to each channel of in-box crossover, but in bi-amp configuration can deliver a dedicated 20A to each half of cabinet, and while delivering the same 40A in bridged full-range mode I believe splitting that spectrum is why my 1590s "woke up".  To your point on subtlety, there was no discernible change to my room correction curves before/after, only in my perceived soundstage.  Perhaps this is some limitation in my particular power amp, where the mains power supply can deliver the goods but the PA fets can't help but let the woofer's current demands impact those of the tweeters.

Cheers,

- Jeff

 

 

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