SpeakerTalk

[KefHeir]

Hello Kef Community

I'd appreciate your thoughts / guidance / wisdom on the benefits, or not, of bi-amping as I read conflicting opinions on it. I can possibly get my hands on a couple of Quad QSP stereo power amps and in the longer run plan to move to an active configuration, so I'm thinking about bi-amping now as an intermediate step. I'd appreciate any thoughts on the pros and cons.

One view seems to be that bi-amping is entirely redundant now modern amps can comfortably drive the full range. Others I've read claim there are audible benefits from the extra power and headroom.

I also had a couple of technical (for me) questions:

- Using a Y splitter from the pre-out into two power amps I believe you need to ensure the correct impedance ratios (at least 1:10 from source to load). Firstly is that correct, and secondly how would I discover those impedance values?

- Currently I have a couple of homemade kef 'Concertos', with a crossover from Wilmslow Audio. As the XO is already configured for bi-wiring am I correct in thinking that no alterations would be necessary to the circuitry in a bi-amp configuration?

Thanks, and a very good xmas to all

[SaSi]

Bi-wiring is different to bi-amping.
Bi-wiring is just a (silly in my view) way to use two set of wires in parallel. Better use a single set of thicker gauge wires.
Bi-amping requires the low pass and high pass sections of the crossover to become isolated so that each amplifier drives one section. Such loudspeakers usually have dual binding posts that are bridged with a spade and by removing the spades, you isolate the two sections. Not familiar with these crossovers so I can't say if they are suitable for bi-amping.

Bi-amping is the easy way to isolate the low frequencies from the high frequency range. There is a benefit to that because low frequencies usually suffer from compression due to peaks in the music content, unless the amplifier is really (really) hefty, perhaps 5-7 times as powerful as the nominal power required by the loudspeakers.

And with bi-amping you can use a much less powerful amplifier for the tweeter. 20-30WRMS would be pretty enough for most tweeters, while the low pass section would need a much more powerful amplifier.

Having said all that, I think that your Concertos are not two way speakers. IIRC, the B139 is active woofer, not a PR, so these should be 3 way speakers, so I wonder what kind of bi-amping would / could be used with them.

Going active is a very interesting and rewarding adventure, especially if you plan on retrofitting existing speakers. You are actually called upon to design a crossover for them. Even if you use a sophisticated dsp based crossover unit, you will need to tweak and select quite a few parameters and settings in order to get to a working solution to drive a three way speaker system.

In principle, active is the best design option for an amplifier-loudspeaker system, as the loudspeaker designer can design a crossover at low level signals (before the power amplifier) and not introduce a whole set of passive components between the amplifier and the speaker drivers. But it's not easy. Not impossible, but in order to get decent results, you need to do a lot of studying and tests. The results, if successful, would be rewarding.

[KefHeir]

Thanks @SaSi

You remember right, the Concertos are three-way units with the B139 an active driver, along with the B110 and T27. The Wilmslow Audio crossover is sold as a replacement / upgrade on the original Kef DN12 (www.wilmslowaudio.co.uk/concerto-upgrade-crossover-with-mundorf-capacitors-pair-2330-p.asp) and the one I have is configured with dual binding posts.

[SaSi]

Having a look at the picture of the crossover you posted, it appears that it doesn't have separate input for low - high section. This means that whether you have two separate binding posts in the back, they are hard-wired in parallel and connecting two amplifiers to them would short their outputs together causing magic smoke to escape.

If you want to pursue the active setup, a decent active crossover to use would be a Behringer DCX2496. It can be configured to provide output for three way speakers and by using three separate amplifiers, you get a fully active setup with plenty of contours to choose from and even phase correction.

The B139 doesn't need more than 50-75W, the B110 would be happy with 30-50W and the T27 would not require more than 10-20W. All that means is you need a decently powered amplifier for the woofers and any consumer level amplifiers for the midrange and tweeter. You can even use more powerful amplifiers - if that's what you have - and adjust levels either on the crossover or the amplifiers themselves.

Once you wire the setup, there are endless possibilities in configuring the crossover. It can be made to sound great all while having a lot of fun, if that's your cup of tea...

I would reverse engineer the passive crossover and make a schematic, calculate the crossover points and slopes and start from there as a baseline.

[KefHeir]

Thanks again @SaSi

I'll check in with Wilmslow on their XO as that doesn't sound like a desirable kind of magic smoke. I know they offer the XO in standard and bi-wired configurations, but not sure what's showing in that picture.

That's very helpful info and guidance on the active set up. I knew about active speakers but had always assumed that was limited to loudspeaker companies developing their own proprietary amps. I hadn't appreciated it was also a fundamentally different way of managing the frequency filtering nor the benefits which that opens up. All very fascinating and something I will definitely pursue in 2021, pandemics and brexit permitting.

Thanks again, and wishing everyone a good xmas and a vaccine-enabled 2021

[speakerguru]

A word of caution; multi-amping with passive xo filters is a lot of complication for not much gain. With passive xos all the amplifiers have the same full range input signal. Therefore if a large high frequency spike causes clipping, all the amplifiers will still clip, not just the hf one. i.e. you are not gaining any headroom, which would be the case with active filters between pre and power amps.

[KefHeir]

Thanks SpeakerGuru. Yes that all makes sense I think; with the XO in an active setup being upstream of the amplifiers, so to speak, the input signals going into the amps are already narrowed in range. And if I read correctly this is where you get benefits in headroom, as well as more direct coupling of amps to drivers.

I may have spread confusion when I mentioned greater headroom in the earlier post: I was referring more to the increased power of a QUAD QSP over my current 50w NAIM amp rather than any anticipated gains from passive multi-amping as such.

If I were to parse all that with my non-technical language, I think the message is:

- there are benefits from passive bi-amping (but they're marginal)
- bi-amping in itself doesn't increase headroom (but bigger amps do)
- passive bi-amping doesn't reduce the potential for clipping
- don't go to the effort unless a couple of amps land in your lap

It all starts to make the double slit experiment seem quite intuitive

Happy winter solstice one and all

[audiolabtower]

For a different perspective bi-wiring can be worthwhile but there are so many variables involved you can't predict whether it will work for you or not. My experience is that it works best with flat, tight tolerance, low colouration speakers such as BBC types, Spendor BC1, LS3/5a, and Kef References, especially if you have high quality amplification with no discernable noise floor.
The main advantage is a more strict star earth connection back to the feedback point on the amp, and the current demand on the amplifier(s) supply(s) is band limited. However the most advantage can be obtained by taking the crossovers out of the cabinet and connecting direct to multiple amps, the clipping possibility is much reduced. Removing vibration on the crossover has advantages, as has connecting the drivers to the crossover via the speaker cables. The driver side may have a better defined or easier load for any cable reactance, and the shortest connection from the complex crossover input to the amp is obviously good.
In short I have multi-amped, bi or tri-wired all the above speakers with external crossovers by the amps and there is an improvement in solid stereo, front to back depth, and "blackness" of the silences of already very good speakers. But obviously all of that is the next steps beyond just using one amp and 2 sets of speaker cables.
Years ago almost everyone was adament there were advantages in simple bi-wiring, and 4 sets of terminals were everywhere, it just shows how hi-fi is a fashion industry.

[KefHeir]

@audiolabtower, thanks for the other perspective. I have some DIY constructor series Concertos, and not conspicuously high quality amplification, so probably not going to benefit my setup, but interesting nonetheless - esp taking the crossovers out of the enclosures.

I was considering bi-amping only really as a staging post until I could overcome some hurdles to converting to an active setup, but I've now found someone who can do the diagnostics and build me an electronic crossover so I may be able to skip straight past the bi-amping stage. I'll keep a journal of the process. I don't know if it would be of interest here but if it is I can upload it later; might be helpful for anyone thinking of going on the same 'active' journey but who [like me] lacks the technical skills to do it themselves.