Biamping the big ADS models

[swtuggle]

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?

[batchman]

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

 

[Gerry S]

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

[batchman]

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

 

 

[tysontom]

On 6/20/2019 at 10:53 AM, Gerry S said:

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

I agree with Gerry 100%. 

Bi-amping is somewhat of a solution to which there is no problem.  Years ago, with under-powered amplifiers, audiophiles often resorted to bi-amping speakers to get higher output levels with lower distortion.  However, with the ADS L1590-2 -- as with most modern loudspeaker systems -- the passive crossover is an integral part of the design of the loudspeaker, and to bypass the crossover can be problematic.  In fact, ADS spent about two years researching improvements in the design of their tower speakers (the 1090, 1290 and 1590 in the Series II version) to make them even better, and most of the improvements came in the crossover itself with driver enhancements.  Therefore, removing or bypassing the crossover altogether can lead to serious spectral-balance issues, when using an outboard active crossover, which could result in some frequencies favoring others along with a serious issue with the shape and slope of the acoustic-power response into a room.  Many times, audiophiles feel that they know better than the designers, and they can improve on the original design, but this is usually a false premise.  In other words, the engineers at ADS knew very much what they were doing when they designed and improved these speakers; why screw with their professional work?  Place the speakers in an acoustically "proper" listening room, large enough to appreciate the bandwidth of the speakers and a room properly damped with furniture and floor treatment.  Again, use an appropriately powerful and stable power amplifier.  

If the crossover is left in place, however, separating the woofer section from the treble section does not accomplish much of anything, and to get the proper balance is sometimes difficult.  There is always the issue of getting the two section out of phase along with the relative balance of the output.  With an adequately powered amplifier; i.e., an amplifier with 200-300+ watts output, the sound of the 1590 should be fine without the need to bi-amp.

I drove my ADS L1590-2s with several different high-powered amplifiers over time, but mostly I used a Threshold 500-watt amp or McIntosh MC2500, and there were times when the Mac "Limit" lights flashed on peaks, meaning that peaks were greater than 1kW into each channel.  I did have a good friend with a pair of L1290s, and he chose to biamp his setup with the crossover in place.  He struggled to get the sound properly balanced, and ultimately he returned it to a single-amp operation. 

With my ADS L1590-2 system, I never once detected any weakness, distortion or lack of clarity from these speakers, a hallmark of the excellent design of the ADS speakers.  I did mount them back within about a foot of the front short wall and away from the room corners in my large, well-damped listening room of about 15' x 23' or so.  I was always amazed at how clean and effortless these speakers sounded, with clear, balanced output and low-distortion deep bass. 

--Tom Tyson

[batchman]

All that said, I'm not going back ;).  I will however agree there are ways to screw up bi-amp implementation, even though it really is not difficult "people can find a way".

First is the outboard crossover, which must be set to the center frequency of the internal crossover.  To do this correctly requires knowing that frequency and using a crossover set specifically to that.  The crossover should have a steeper rolloff than the internal one (12dB/octave).

Second is the power amplifiers themselves.  All the channels must be identical.  Preferably with no gain adjustments - just amplification, yes-or-no.

With those aspects in place, setting the bi-amp switch simply provides a direct path for the woofer (bypassing the low-pass filtering) and leaves the high-pass as-is.  When driving a magnet (the drivers), doing so through other magnetics (in the crossover) will reduce the signal - no matter how good those internal components are they cannot be 100% efficient.  I believe in my case the bass filled out slightly (no measurements, sorry).

The depth of the sound stage certainly increased.  I attribute this to reduced contention in the amplifier, quite possibly in damping behavior.  That is one spec that is a standout in my power amps, and may be what plays very very well with my ADS boxen - and may explain why it works so nicely for me, and perhaps me alone.

Your mileage will apparently vary,

- Jeff

 

[Saabstory]

Back in the 80’s I had two friends each running systems with L-1230’s in biamped setup with ADS C2000 crossover & pairs of Apt1 power amps in bridged mode. The sound was phenomenal & made me a believer in bi-ampflication, but qualified by implementation. I have wondered if it might be possible to get (Emulate?) crossover character of the PA1 modules with outboard amps - low end direct to woofers & midrange/tweeter share other amp using internal passive crossover for L1290’s & L1590’s. I think biamping can be game changing, but as Tom observed above, in concert with how ADS engineers designed them to perform. 
Cheers, Paul

[batchman]

Hi Paul,

The Apt1s were awesome amps, even more so bridged.

That's exactly how the 980/1290/1590 and xx30 in-cabinet passive crossovers work in bi-amp mode.  I think there is much misunderstanding of how to do this.

With the crossover switch set to bi-amp, the low input goes directly to woofer; mid/high to the midrange/tweeter integral crossover.

To get the benefit in terms of amplifier headroom you need to split the spectrum before amplifying though.  I use dbx pro-sound pieces, 223x if I recall correctly, set to split at the frequency of the ADS internal low/mid-high break, this varies by box.  There is much discussion and debate on here, I'll spare re-opening the argument beyond saying "It's worked spectacularly for me".

Best,

- Jeff

 

[TD1]

Hi all,  I'm new to this forum.  I'm presently renewing my interest in high fidelity sound, using vintage components.   I live west of Boston and recently retired after 40+ years working in computer systems and telecom equipment engineering development.  I hope the pandemic is giving everyone a chance to enjoy their music that much more.

Last year I picked up a pair of L1290/2.  The speakers I wished I'd owned (and wished I could afford) as a youth.  I've had a pair of L700 II since 1980 or so and owned a pair of L810s for a while (which I bought opportunistically, 2nd hand at the now-defunct Music Box in Wellesley, with stands, for $250).

So, I'm a fan.

I'm considering bi-amping the speakers.  There's some really good information here.  Thank you very much for that, it will be helpful if I move forward.

Amplification would be an Adcom 545 II for the lows, and a B&K ST-1400 for the uppers, which happen to be what I have   The speakers sound great with either amp right now.  I'd probably use a dbx 223/224 crossover, since they can be had for under $100.  The spec'd voltage gain of the two amps is quite close (1 dB delta), but clearly there is a risk of some deterioration of tonal balance w/o gain adjustment.

One question that sticks in my mind is, why would the developers include the ability to bi-amp the L1290/2 if they didn't think doing so might provide an advantage? 

And why did they choose the unusual design for the bi-amp support in the crossover (straight through on the woofers but through the internal crossover for the mid & tweeter when in bi-amp mode)?

There is of course the usual reason developers add features - namely, they sell more stuff, in this case C-2000s!   But there are some other putative advantages outlined on page 8 in the C-2000 manual (https://www.manualslib.com/manual/1019271/Ads-C-2000.html), some of which are discussed here.

Thoughts?

Thanks!
Tim

 

[Aadams]

6 hours ago, TD1 said:

One question that sticks in my mind is, why would the developers include the ability to bi-amp the L1290/2 if they didn't think doing so might provide an advantage?

Search for posts by Tom Tyson in this ADS forum.  The short answer is you should biamp the 1290 with identical amps using the speaker's designed crossover.  There is plenty of relatively inexpensive monster power today that wasn't available in the 1980s so biamp capability was provided.  

[TD1]

Will do - thank you!

[Alkaloid]

The owners manual for the L1230s has a really good description on page 7 that is the most thorough explanation I have seen yet on benefits of bi-amping. I will post a link of a PDF and navigate to pg, 7 and read it. Has what the C2000 says and a tiny bit more about the distortion reduction when you separate the high and low signals.

 

https://documentcloud.adobe.com/link/review?uri=urn:aaid:scds:US:ae3a4cea-4490-4bcc-9faf-5b546d7fbfb9#pageNum=1

 

The 12db slope crossover designed by Linkwitz Riley is the finest design for a 3 way passive crossover. No phase shift. I have a pair of CM5s that use a 24db slope on a 2 way. I hope this helps everyone.