SergeAuckland

A Winter's Project

121 posts in this topic

With winter approaching, I’ve been thinking about a new project. I’ve thought about building a new pair of ‘speakers, but lack the space and tools to do much woodworking, and anyway, woodworking isn’t my strong suit, so although anything I build might work OK, it won’t look pretty.

As many of you know, I’ve always said that the best sound I’ve ever heard has been B&W 801s at Danmarks Radio, where they had a number of IEC listening rooms with 801s driven by unknown amplifiers. I also heard 801s at Abbey Road and elsewhere, and have always liked them.

Anyway, to cut a long story short, I’ve just bought a pair of 801s from fellow ‘Wammer Solidsonics. Thanks Ben, it was a pleasure doing business with you.

Before anyone thinks that I’m abandoning active ‘speakers and “downgrading” to passives, here’s where the project comes in:- The passive 801s are very fine loudspeakers just as they are, but I think they could be improved by changing the passive crossovers to digital DSP crossovers and a six pack of amplifiers – or more likely a three-pack of stereo amps.

First things first:- I’ve only just brought them home, so I’m going to listen to them just as they are for a short time before doing anything. I'm currently using my old Yamaha CR1000 receiver, and it's doing a decent job of driving them. I have details of the existing crossover, so I'll disconnect the crossover, bring out connections to the three drive units, and replicate the passive crossover in DSP. Measure and listen and compare with the reference. With something like the Behringer DCX2496 and DEQ2496, I should be able to improve on the 801’s frequency response, with steeper crossover slopes may be able to reduce distortion around the crossover points and with no series inductors on the bass unit, hopefully also improve the bass.

When I’m happy with what one loudspeaker is doing, I can then replicate it on the other. If it all goes to plan, the end result should be better than the original 801 and the Meridians but I’ll be keeping both until I’m sure. John Bowers himself believed in Active Speakers, but commercially presumably thought the 801 was expensive enough without the additional cost of electronics. He went on a few years later to manufacture the Active One, which was a superb loudspeaker.

That’s me sorted for the next few months!

S.

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Sounds like a great project. Let me know if you want the thread moving to the DIY section.

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That would be something to hear at Scalford if they are done by then & you have the room to transport them.

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Sounds like a good plan, keep us updated as you progress.

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Moderator

Interesting project Serge, we need measurements, lots of pretty graphs and data! :^ Distortion, Freq.Resp etc comparing passive Vs active would be good :geek:

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I would be interested to hear an A-B comparison of the original XO modelled using the DSP versus a higher order one that measured better. Maybe you could do a trial at Scalford, Serge, that wouldn't be scientific (it would have to be a "which do you prefer") but could be interesting.

But yeah, improved bass on 801s would be fun to hear :)

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I you like Serge I could bring the Multi channel version of the box we used last Scalford, you could use that to implement your crossovers digitally, it is capable of two times four way.

Kind regards

Keith.

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I don't have any practical experience with crossovers but my basic understanding (and that's all it is) is that the overall circuit performance depends on the combined properties of all the impedances, including those of the drivers themselves. So when you 'move' the crossover from after the power amps to before them you will, in practice, leave some of those impedances behind. They're 'trapped', if you like, in the drivers. Is it straightforward to deal with this when you recreate the XO in the DSP ? Are the effects of the speaker impedances in fact too small to worry about ? Is the nonlinearity of the speaker impedances a problem (speaker suspensions are nonlinear aren't they ?) ? Do you need to worry about the interaction between the drivers and the effective output impedance of the amps (I imagine not since you'll probably use chunky solid state so it'll be really low). I can easily see how this is going to be a winter's work :) and I'd really like to keep in touch with how it goes. Please do post reports when you get the time. I'll declare an interest too - I'd like to look at doing the same thing with some of my Quad IIs. 15 W/ch isn't much and even being able to double it (one pair of amps handling the bass, one the mid/treble) might give my system useful additional headroom.

Valvebloke

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Should be an interesting project, Serge, and I look forward to seeing (and maybe hearing!) the results. However I can't help thinking that using 801s as the candidates for modification is a bit like buying a Ferrari and then tweaking the engine to make it faster!

;-)

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With something like the Behringer DCX2496 and DEQ2496, I should be able to improve on the 801’s frequency response, with steeper crossover slopes may be able to reduce distortion around the crossover points and with no series inductors on the bass unit, hopefully also improve the bass.

Don't forget the new http://www.behringer.com/EN/Products/NU6000DSP.aspx monster power amp with programmable DSP crossover. Too bad it's only two channels, but perhaps they can be daisy-chained.

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A good project Serge I look forward to seeing just how bland they can be made to sound..... ;-)

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I would be interested to hear an A-B comparison of the original XO modelled using the DSP versus a higher order one that measured better. Maybe you could do a trial at Scalford, Serge, that wouldn't be scientific (it would have to be a "which do you prefer") but could be interesting.

But yeah, improved bass on 801s would be fun to hear :)

Having different crossover rates should be easy with the DCX2496, as it has several memories, so doing one as a replica of the original crossover (24 dB/octave), and another with 48dB/octave filters shouldn't be difficult. I will be doing that anyway to see what the effect of higher filter rates will be.

As to the bass, looking at the circuit diagram of the crossover, there's a 1000uF capacitor in series with the bass unit which has an impedance of some 3 ohms at 50 Hz and 8 ohms at 20Hz. With a resonace of 37Hz, the bass driver has little amplifier damping, although being a sealed box rather than vented, the air load will offer resistance. There are also two coils in series, which although they will have a small DC resistance, it would be better to have none. Nevertheless, I'm expecting that active bass will be different to the original passive bass.

More when I get inside the boxes.

S.

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I you like Serge I could bring the Multi channel version of the box we used last Scalford, you could use that to implement your crossovers digitally, it is capable of two times four way.

Kind regards

Keith.

Thanks Keith, kind as always. However, it's going to take me the best part of the winter to get this right, and as I'll never be able to afford one of your boxes, there's probably not much point in doing the design work with one.

S.

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Should be an interesting project, Serge, and I look forward to seeing (and maybe hearing!) the results. However I can't help thinking that using 801s as the candidates for modification is a bit like buying a Ferrari and then tweaking the engine to make it faster!

;-)

Although I've always loved the 801s, there was always a nagging feeling that they could have been so much better as actives. (But then I would say that wouldn't I) The problems of very high power crossovers (The 801s have an "unlimited" power rating - although looking at the manual, the protection comes in at 144w for LF, 250 w for MF, 32 w for HF nevertheless, still pretty high power) is that the coil wires have to be sufficiently thick to take the current, but thin enough to be wound in the space available. If they are air-cored, they are then pretty big, if ferrite cored they can be smaller, but they can overheat. Also, probably for loudspeaker protection against DC, all three drive units have series capacitors, the bass unit especially having 1000uF which increases radically the effective output impedance seen by the bass driver. Going active should remove these limitations.

As to Ferraris, there's not a lot of point modifying a Fiesta!

S.

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