BBC inspired loudspeakers - discussion

No its not a BBC design, Robin Marshall paid lip service to them to be politically correct. I have spoken to him more than once, he knows his onions and his crossovers are simple.

 

The 405 deserves to be maligned, it is an abortion of an amp IMO, it is a current castrated flannel box, that has little chance of recognising what good music is. It is the last legacy of the idea that voltage was king. Although I much malign them at times, within the hi-fi market Naim signalled the death knell of that idea and many others have continued the theme of current being king.

 

From an amplifier manufacturers point of view this is just complete nonsense. I don't think they even thought about amplifiers, they just had their own ideas and just went merrily along without a thought apart from their own narrow minded view point. Yes of course you can build amplifiers to drive anything, even a short circuit if you want. But if your priority is fidelity to music and not some BBC voice parameters then you would *not* design amplifiers just for driving these abortions.

EDIT :- And I was using Royd as an example of a different and better approach, yes light paper cones but heavily doped. I could just as easily named Ed Vilchur or Roy Allison as different approaches again. We seem to be infatuated with this BBC thing, maybe because it is *British* well we can't play football and apart from a few notable exceptions (mostly in the past like Tannoy) we don't make that good speakers either.

 

Are the JR149s just LS3/5s in a cylindrical cabinet, or is the crossover different?

 

So you think the cabinet makes no difference

 

Depends what you want it to drive.

It has enough current to drive most speakers to the levels most people require in their homes, and many professional require in their studios come to that.

If you pop one on the test bench and try driving a 4 ohm resistor with sine waves it'll get hot and the protection circuits will limit current. You effectively have a 70w/4 ohm RMS amplifier.

So what?
You need enough current to do the job.

The job has nothing to do with recognising music - it needs to do a job of work which is to provide a magnified replica of the input on it's output while driving a load.

 

Rob.

Have you heard any of the modified 405s that remove the current dumping?

 

I've tried removing the current limiting and it makes no difference whatsoever - though it clearly would if you needed to exceed the current demand set by the limiter.

It is important to realise that the 405 has a large PSU perfectly capable of letting the amplifier drive low impedance loads. The limiter circuit exists to protect the output transistors from excessive current draw and short circuit.
It is also a physically small amplifier and high current draw for long periods make it run extremely hot.

Even with the limiter in place a 405/2 will give you 150w into 5 ohms, and it progressively limits as impedance drops, but it stills has enough reserve for many people.

The designers Walker & Albinson were at pains to explain that this was not a lab amp designed for continuous use with test tones. It is designed for use with music signals - dynamic use.

 

Hmm.

Not sure the PSU is that big.
But back OT enough to drive loads of BBC speakers for many years. And don't forget the BBC was, well, the BBC! They knew their shit!

 

150w continuous RMS into 5 ohms x 2 without clipping needs something pretty meaty.
Take the limiter off and you can have 200w into 4 ohms x 2 - for a while, after which the heatsink makes a great waffle pan
Remember that a 405 is little larger than a NAP140.

 

OK Rob.

I'll take a look but I suspect the traffo is less then 200VA and what's it like into 2 ohms? I stand to be corrected though.

 

2 ohms....... about 20w RMS for Mk1
Higher on peaks naturally.

But again that is due to the limiter circuit and not a PSU limitation.

How much of limitation that is depends on where the impedance dip occurs.
So for example Quad's own ESL falls to about 1.5ohms above 15khz.
Not a problem because power demands up that high are incredibly small, so even a mk1 405 plays fine into them.

I wouldn't want to drive Saras though!

 

Richard - (dunn) -

you mention that you don't like the elaborate nature of the crossovers in BBC loudspeakers.

Is this because you prefer the sound of a simple 1st or 2nd order crossover (following your philosophy of using as few parts in the signal chain as possible)?

Also, does this follow through to an appreciation of other simple designs in audio - I am specifically thinking of 'NOS' dacs.

I am trying to appreciate where you are coming from..




for my own perspective I have a foot firmly in both camps. I like horn loaded speakers with simple first order crossovers, simple amplifier circuits and high quality passive parts here and there.

I also appreciate the unneringly neutral sound of speakers made by companies such as Revel - which are designed with different parameters (very flat responses, elaborate crossovers to achieve it, whatever works, works).

They sound very different but I enjoy both.

 

One plays music the other plays hi-fi (BTW horns do not make it simple they introduce just about the biggest mechanical acoustic filter circuit possible). It seems a lot of people want hi-fi.

*Everything* in audio is a compromise, yer pays yer moneys ands yer takes yer choice.

My favourite DAC at the mo is a highly modified and re-PSU-ed QED digit from the mid 90's, but I am listening to others at my computer audio bake-off and I have an open mind.

 

Just by way of clarification:

Are you saying that in playing music a speaker may be less faithful to the recording (but more faithful to the music if that's not a complete contradiction) and in playing hi-fi a speaker may be more faithful to the recording (higher fidelity) but less faithful to the music.?

Or are you simply using the term 'hi-fi' to cover the train-spotter artifacts that some folk are attached to?

Just trying to understand.

 

Hi Richard

I know horn's aren't to your liking - you prefer the diffusive sound of omni-directional speakers I believe?

If so I understand a difference of opinion - the very direct, engaging and dynamic presentation of horns (they also have vices I'd readily acknowledge) have a very different sound to the omni-directional speakers I have heard to date.


Incidentally I haven't heard the speakers you make, and wouldn't dream of commenting on them - there is too much of that on internet forums.

 

Amen to that

 

Nope, I am saying that complication puts blockage / constipation in the system. Quite simply *anything* in the signal path cocks it up, so put in the minimal to do the job. The differences are musical in nature not hi-fi, both are needed to a degree but unless you can find the musical experience amoungst the image and all the other hi-fi guff in my terms you are wasting your time. Now it is this ellusive music thing that is causing most of the problems between the objectivists and subjectivists, as the music thing cannot be spec-ed it is there or it isn't. I have my own ideas that I have linked to articles and interviews many times on this forum and others, and normally it fires of the ad hominem and the dissers.

 

They are not omni- directional, they are semi omni, there is a lot of difference. The sound is not diffused, there is direct and in-fill. Every speaker does this to a degree but these are designed to use the room not fight it. Normal speaker aren't designed to drive the room they try to create a room within the room or are so direct as to try and take the room out of the equation (which is impossible) as you are refering to. It is just carrying on the work of Roy Allison.

My speakers are nothing to do with this discussion and I am not interested in discussing them, I am not here for that, I am talking principle not specific. There are some horns I like and some complicated crossover speakers I could live with. I am saying the principle has problems and complication just for engineering sake is pointless in the pursuit of music.

 

One of the things I find the most interesting about audio is trying to understand what others listen to. A friend worked in an audio shop in London for some years and I sometimes used to sit-in on dems at weekends or when I was between IT contracts. The thing I found the most fascinating was listening to people attempting to articulate what they were hearing and to try and understand they were seeking. I came to the firm conclusion that there is no 'correct' here, the whole audio reproduction thing is so imperfect that the best one can possibly hope for is to find a basic match between a listener's personal taste and some audio kit. To slag off specific technologies or ideologies merely indicates agenda IMO. In reality there is a happy listener for pretty much everything, and that's what makes it all so interesting.

Tony.