Boswell , you have mentioned Bass units - look at mine,; I think i have been badly deceived by my seller . Do you or anyone else have the slightlest idea who could sell me a Roger Bass unit to replace the old one ? They do not sound the same !

I think I must be missing something here but I assumed you had bought 2 Quad 405's with an active crossover (presumably stereo but I don't know) and two Rogers LS5/8's.

If so, surely the internal crossovers in the speakers themselves are redundant and each driver should have it's own P.A. channel? Does one of the Quad's have a mono crossover on the input but the other doesn't? Not being familiar with the modified units it is impossible for me to advise but something seems to be amiss here.

Of course I may have it all wrong but this could just be some sort of wiring problem!

Mr Ease raises a very good point, and that is that we may all be getting confused about the crossovers. Your Quad amplifiers with the AM8/16 additional module installed already have active crossovers situated in front of the main amps, and these therefore should send separate low-pass and a high-pass power outputs to the two drivers in the loudspeaker enclosure. No crossovers may be necessary internal to the cabinets.

It's clear from your photos of the rear of the power amplifiers that you have both the outputs connected, so could you tell us exactly what the XLR cables plugged into the "left" and "right" outputs of each amplifier are connected to? Are the Rogers loudspeakers that you bought really LS5/8s and are they wired for bi-amplification? For example, assuming the speaker cabinets each have two separate inputs, what are the input connectors wired to inside the cabinets - crossovers or drive units?

I see that you have been getting some help from Hugh Robjohns on the SOS site, so I hope that our advice is complementary to that.

It is simple: one xlr connects the quad to the Rogers , the other xlr goes into my preampli ( at the moment a passive preampli).

I have no doubt that I have acquired the Rogers LS 5/8 - see pics. The only issue is that one Roger has a very old high frequency unit and main speaker ( that may have been re-conned in the past) . Replacing the tweeter is easy, finding a more recent speaker is harder. Apart from that I need to change the capacitors in the filter that hides behind the little blue board - you can just about see it on the photos next to the tweeter.

Therefore we are talking about fine tuning the Rogers.

Alexander

I'm certain it's not as simple as you think! I've just read up more on the Quad AM8/16 and Rogers LS5/8. Can you confirm that BOTH quads are the AM8/16 versions?(they need to be as the crossover is only Mono) The fact that you are worrying about the speaker's internal crossovers indicates that you perhaps do not fully understand what you need to be doing. Which is, I suppose, exactly why you asked for help! :

Also, what is certain is that the internal crossover in the LS5/8 is completely redundant and you certainly don't need to repair them. The two amp. outputs from the quad must be wired directly to each speaker unit (the right way round). If this wiring is not absolutely correct then it could easily explain the lack of tweeter in one of the speakers.

Both amps are the modified 405 by the BBc, and both are wired as you have indicated. It is not a Quad problem because selling the quad had no result on the "bad" Roger. How can the Roger filter be of no use when this active inductorless filter is part of the design ( p.5, "Design of the monitoring loudspeaker type 5/8", BBC. Paper ). ?

I am going to change the Audax and see what happens. Unless you have other ideas ?

Thanks very much for your help.

Alexander

First of all, I didn't suggest it was a problem with the Quad amplifiers, I was just checking that both were the BBC versions. Secondly, it may well be that a tweeter is blown.

However I think I should explain why the crossover units in the Rogers speakers are, I believe, redundant. The Quad amplifiers are modified with internal low level crossovers which drive the two amplifier channels, one channel with bass and one with treble. There is no subsequent need to try and filter the outputs into high and low signals - it is already done. Therefore the crossovers in the Rogers speakers are redundant and should be taken out of circuit. The wiring to do this should already be taken care of, but as your two LS5/8's are clearly not a "pair" and seem to have very different drivers then that alone surely brings in to question whether they are both correctly wired (or at least identically wired).

Before buying new units I urge you to carefully check that the wiring of both speakers is the same and that both Quad amplifiers drive the "working" speaker in the same manner. Then I would do a simple D.C. check on the non-working tweeter - if you have a multimeter, this is a simple test and the resistance should be around 6-8 Ohms - disconnect the speaker to do this in case any other parts are connected. If it is open or short circuit then it is definitely dead and needs to be replaced! A more basic test is to simply connect a 1.5V battery across the speaker and listen for clicks etc. as the power is applied and removed. This is only a basic test and there could of course be other problems.

This brings us on to the next potential problem which seems to be a characteristic of these speakers - they seem to rarely sound the same...

I suggest at this stage, if you have big differences, that you will need to be very careful in selecting replacement drivers and will probably need to replace units in both speakers unless the exact equivalent drivers can be found.

I hope this helps!

Thank you vfery much for your info, most informative.
I shall look into all the test you have mentioned. Thank you very much.

The wiring is identical in both Rogers and the passive cross over ( I would have thought) is part of the design. The Bass unit is fed directly from the quad, the tweeter is fed via the crossover. The crossover in both speakers are identical.
The obvuous difference is that the cone on the bass unit of one speaker has a slightly different plastic.

http://downloads.bbc.co.uk/rd/pubs/reports/1979-22.pdf

Kind Regards

Alexander

vonrozen, post: 435548, member: 49120 wrote: Both amps are the modified 405 by the BBc, and both are wired as you have indicated. It is not a Quad problem because selling the quad had no result on the "bad" Roger. How can the Roger filter be of no use when this active inductorless filter is part of the design ( p.5, "Design of the monitoring loudspeaker type 5/8", BBC. Paper).

I'm gradually getting the full picture of this.

My principal misunderstanding was to do with the connections between the two-channel amplifier and the loudspeaker box. I had expected that there would be two separate 3-pin XLR cables for this, but now realise from your saying that there is only one cable and that it must be a 4-pin or 5-pin XLR plug on the amplifier that carries the output of both amplifier channels to the two drive units in a loudspeaker cabinet. You haven't said what the connector is on the cabinet, but internet photos of the rear panels of Rogers LS5/8s show a Neutrik Speakon connector. I can't believe that was what was fitted to the originals. Either way, your units have one feed directly wired to the bass driver and the other apparently fed through a passive filter network (not a crossover) to the high-frequency driver.

In none of the descriptive information that I can find on the LS5/8s is there any mention of a filter network on the HF driver. That doesn't mean to say that the commercial versions (as opposed to the BBC versions) of the design did not have the additional filters as low-frequency protection, but I can't find any component data on them.

The circuit shown as Fig 8 on page 5 of the BBC paper is of the AM8/16 active crossover board that sits in the Quad amplifiers and not in the loudspeakers.

Hi Boswell -

It is a 5 pin XLR connection.
I have no reason to doubt taht it is the commercial verision , as it would seem crazy tha the seller would have gone at lengths and would have modified all the stickers to the extend.
Thank you very much for your comments. I am going to check right now with someone from the BBC , if this is the genuine version. In my opinioni there only ever existed one version of this speaker.

Again - many thanks for your kind help

Indeed, I agree with Boswell that the picture is slowly becoming clearer!

It could well be that a series capacitor is used to limit low frequencies that could arise from the P.A. stage due to switch on transients or imperfect crossover response. This would just be to protect the speaker itself. I'm more intrigued by what appears to be a transformer in the photo above. I would doubt that an iron core inductor would be used here for filtering and close inspection of the upper photo seems to show more than two connections. I think it is more likely then that this is a transformer, possibly stepping down the voltage to the tweeter to change the sensitivity. This is unusual as this is normally achieved with a series resistor if sensitivity needs to be adjusted. Unfortunately I have found no documentation on this but if it is a transformer then as I suggested earlier you will certainly need to disconnect the tweeter to test it for continuity.

If further tests show a problem with the transformer (maybe unlikely but possible) then you could also consider removing the transformer and just using a series resistor. After all we're not looking for efficiency at this point.

Well I have replaced the tweeter on the left Roger , but nothing has changed much. The problem still persists: one tweeter is only 30 % active. So, I assume , it is a problem of the filter and its 3 capacitors need to be replaced. That must be it, I hope. Changing g the Quads around did not have any effect.

I really don't get this at all? It's the subjective stuff hi-fi forums are full of. I remember my old BBC mentor letting me hear the Rogers speakers (can't remember which ones as it's a long time ago) he used at work, and I was kind of unimpressed, because at that time - late 70s - I was expecting to hear what Hi-fi shop speakers sounded like - and the Rogers were kind of unexciting. He introduced me to the lack of colouration that was the standard at that time for the BBC. Nothing wrong with the Rogers apart from they sound old. It's the same when you hear Quad Electrostatics. 60 years ago they sounded state of the art, now they don;t suit the music any longer. Everyone used to monitor on big and loud if they did rock or pop, and Auratones for checking for tranny radio listeners, and now we mix on tiny speakers in the near field, using perhaps our big speakers for the occasional check. The topic started all fluffy - and talking the usual 'warmness' - stuff and now we're thinking the speakers are faulty? That's a big journey.

On the serious side, I understand the thread far more than I understand your post! It has certainly been a journey finding out what the OP really wanted. My take on it is that the OP did not originally actually possess the Amp's/Speaker's mentioned but has since acquired them - only to find what he bought was a bit of a set of units with dubious history. We've now moved on to fault finding. What's not to get?

With regard to the subjective stuff. This was only the OP asking certain questions and there was no sort of "Subjectivism Love Fest" going on as you seem to infer.

Where you really amused me, having apparently berated the "fluffy" subjective stuff, were your of your own subjective comments -

paulears, post: 435617, member: 47782 wrote: Nothing wrong with the Rogers apart from they sound old.

Brilliant! I've never heard the subjective description of "old" to describe a sound before. Can you give me some idea of what it means?

paulears, post: 435617, member: 47782 wrote: now they don;t suit the music any longer.

Doesn't that entirely depend on what music you listen to, or have performances of Beethoven changed over the years? Maybe I should update my vinyl collection - it must be sounding old by now!

Considering that driver technology has changed very little over the years (with the exception of the electrostatics), the aim of any speaker design must be to be as neutral as possible. I've never known of any design intended to deliberately "colour" the sound - it certainly wasn't a design aim at Rank Leak Wharfedale when I worked there back in the 70's... Neutrality and fidelity were the order of the day back then. Definitely not "coloured"!

Whether this was serious comment or intended as satire, it's priceless!

Either way, thanks for bringing a smile to my face!

In the main, I was being serious. I'm not certain that it's ever been really possible to measure what we actually hear in terms of the 'overall sound', but the usual technical specs of speakers rarely give much of a hint as to if somebody will find them pleasant or accurate. The old Wharfedales are a very good example. It's taxing the brain bit but around that time, interesting stuff was starting to happen. The British sound, which had been firmly established was being eroded by foreign loudspeaker sounds. Before I mention these, even the 'British' sound had detractors, who were British too. Tannoy with their dual concentric designs. On paper in terms of frequency response and the other usual parameters, they were quite similar to the usual twin (or more) drive unit designs, but my ear can still hear Tannoys when I walk into a room. I haven't a clue as to how to explain this in words. The foreigners got in on the act, and Sony had a particular sound too (not that good of one, but certainly one applied right across the price band). In fact, when I used to sell them in one job I had, customers would comment and I described it as a result of them living in houses with paper walls. Seriously! All I knew of Japan was James Bond back then. The sound they had in my head, at least, equated to the sound I figured light weight houses would have - crazy now looking back. We also had another characteristic sound in the B&O brand. They had one model called the S35, and I always wanted a pair because I really liked the sound, but at that stage in my life were just too expensive. When I moved to professional audio, we were shifting Bose 802s, and the matching subs, and again, it was a unique sound that was like Marmite. You either loved it or hated it, but the paper spec told you nothing about that 'sound'. Celestion and Ramsa, Panasonic'c commercial brand had almost identical size speaker systems, but they sounded more 'normal'.

I am left wondering if 'neutral' has ever been a real design aim - flat, would seem to be the aim, but flat speakers to within a dB or so can sound radically different - almost like a kind of fingerprint?

When I said the speakers don't suit the music any longer this I feel is accurate. It isn't the performance, or the instrument, it's the recording. There are a few Buddy Holly recordings around that have been remastered from the originals and the quality is superb - the mic choice and placement being excellent, but they sound modern. These recordings were mastered to record in a very different way and those recordings sound much worse.

If you have a spotify account, search for well know tracks, and you will find many identical length versions, but often as part of compilations. If you pick a seventies recording, there are loads of different versions that sound radically different. I'm wondering if it's the re-mastering that makes the difference - different speakers and different ears?

I quite like the term 'old' as each decade does seem to have characteristics. 40's recordings are frequently very similar sounding and often very weak. The 50's stuff is very variable, as if some kind of quality medicine was sweeping through the recording industry. It started to get clever in the 80s, and the differences got less and less - so I think any recording made today using mics popular in the 70s, and monitor on the classic designs would probably sound realistic for that decade. The choices you would make during the sessions would reflect what you hear, and with so many contemporary musicians playing vintage instruments through vintage amps and speakers, recording with vintage mics and speakers would produce a proper, realistic vintage sound. What I cannot accept is any concept of the interconnections making differences. Back in the 70s, were enthusiasts not using their Quad amps simply because they were high quality - for the day, and NOT because of their particular style of distortion. Back then the aim was to minimise distortion, because distortion was BAD. Noise and distortion figures were the be all and end all in the reviews. Once amp designs became so good that measurement was difficult, people only then started to talk about sterility in sound.

I'm very stuck in ways. Although I can now hear the differences between preamps, having been successfully convinced they really were there not that long ago (in aspects other than noise), these differences are tiny compared to the difference swapping a pair of speakers makes. Swap a mic, a speaker or a guitar and you can hear it - very obvious. Swapping preamps is akin to making small changes with a 32 band eq - there are differences, but compared to the big ones - nothing for me to get worked up over.

Sorry Paul but having said this -

paulears, post: 435617, member: 47782 wrote: The topic started all fluffy - and talking the usual 'warmness' - stuff and now we're thinking the speakers are faulty? That's a big journey.

- I think we're now even further off topic.

Please take it as read that "neutrality" was and still is a definite aim in speaker design. While that does indeed infer a reasonably flat response, a flat frequency response is only a tiny part of the equation. What are apparently similar speaker designs (visually at least) does not imply that they would or should sound similar simply because of the huge number of variables beyond the size and veneer! Small High Q resonances that create only a fraction of a dB change in the response can completely wreck the sound of a speaker. This is why so much research goes in to cone design, spider design, suspension design etc. etc. Nowadays we also have much more advanced ways of analysing such things such as laser scanning of cones to measure resonances and "break up". Back then we tried to improve things more empirically. Just compare the Wharfedale and Leak brands of the era. Wharfedale speakers (the budget end) used almost exclusively paper cones (we tried stiffeners etc.) whereas the Leak branded speakers used a foil/foam/foil cone construction (at least for lower freq's) which did offer similar mass but much improved stiffness. Salespeople of the era used to love standing on an inverted cone to demonstrate how "tough" these cones were - altogether missing the point of the construction.

However, you have raised a very broad brush, now introducing almost every aspect of audio design.

paulears, post: 435630, member: 47782 wrote: distortion, because distortion was BAD. Noise and distortion figures were the be all and end all in the reviews.

I suggest we stop hijacking and leave the OP to his thread.

I didn't think there was a real topic here? Sorry to tread on toes. I'll depart and leave you to it.

Dear BOswell and dear Mc Erase and others -

Thank you very much for all your comments, they have been very oinstructive and I have learned a lot. Boswell - a huge thank to you for being a brilliant and patient moderator to suffer madmen like me !

THE TRUTH: After testing the tweeters and speakers generally it is now clear and without any doubt that I have a problem with the filter on one of the Quads ( on the 405-2) which needs to be revised / recapped because it does not filter enough information to the tweeter. This, in turn, results in the tweeter omitting to play half of the frequencies.

If any of you had experience with repairing/revising the BBC installed filters on the 405-2 I would be grateful to hear your comments.

And again , a huge thank you to all of you who have been so helpful !!!

Alexander (Paris )