Altec Biflex for OBs?

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iansr
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#1 Altec Biflex for OBs?

Post by iansr »

I want to try making some OBs as some folks reckon that well implemented OBs can outperform ESLs, which I currently use. I'm thinking of some vintage Altec Biflex for the "full range" drivers supplemented by my Velodyne DD12 sub and a quality ribbon tweeter such as the Raven 2.

Anyone got any experience of, or thoughts on, the Biflex drivers?
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Paul Barker
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#2

Post by Paul Barker »

Sorry no, but I've had a lot of trouble trying to get three drivers to integrate passively. Gave up a while ago. The ribbons don't have the sensetivity of the full range drivers, I found them a waste of time in this application.

Quite a few here have had reasonable success with OB, Nick's were probably the best allrounders. James' were the best with the right amp behind them, but fickle in their choosiness.

But then Steve Shiels came to join the party.....
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#3

Post by Darren »

I changed the transformers in my ribbons to up the sensitivity.

it's a simple job and they are cheap enough, about £17 each from memory.

Worked a treat for me as my other drivers are quite sensitive and they now work fine together.
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Nick
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#4

Post by Nick »

I guess that would work to reduce the impedance the amp sees with the ribbon, what xover are you using?
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#5

Post by Darren »

Hi Nick,

I'm using the standard 3 way that came with the original speakers, only the 12" base drivers are still in the box, the other two I changed.

No doubt the crossovers could do with tweaking, but they are working fine as they are to my/other ears. Besides i wouldn't know how to do it and would have to enlist in some help should I wish to go down that avenue.
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#6

Post by Paul Barker »

but your drivers aren't the same sensitivity as we use in ob's afaik I don't think you could obtain the sensetivity required to match high efficiency single drivers, but I'd be happy to be proved wrong..
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#7

Post by Darren »

Whilst I'll admit I can't find the sensitivity of my drivers I can tell you they go quite loud with just 2.5W or even to a reasonable level with 1W 6EM7.
That tells me, coupled with comparing them to another known set of speakers that they are quite sensitive.

90db is easily managed before the PX4 runs out of steam.

The ribbons keep up just fine. With the standard transformers they are pathetic.
I do wish people who have never heard my set-up would stop telling me what my system can and can't do.
It is a known fact that I listen to it and do have some idea of what I'm on about.
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#8

Post by Nick »

Darren wrote:The ribbons keep up just fine. With the standard transformers they are pathetic.
I do wish people who have never heard my set-up would stop telling me what my system can and can't do.
It is a known fact that I listen to it and do have some idea of what I'm on about.
I just wanted to point out that changing the ratio wasn't a free lunch, that there was other effects from doing so that may or may not have undesired results.
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#9

Post by Darren »

Whilst I can't claim to know if there is any undesirable effect of changing the ratios of the transformers, I can only tell you that in my situation the benifit was quite large.

I make no claims to inventing this idea. In fact alternative transformers for the London Ribbons have been around for a very long time and at least one person still produces them today.

I didn't go down that route, instead I stole a pair of trans from a set of Decca Kelly ribbons. They'll have to be returned at some point, but at least they showed me a way forward.

The Decca Kellys don't seem to suffer the same low sensitivity as the Londons. The transformers are nothing complicated and some people wind their own or modify the secondary of the originals. From memory you have to remove some of the secondary turns.
Don't quote me on that, I could have that the wrong way around.
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Paul Barker
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#10

Post by Paul Barker »

I'm not suggesting it isn't working for you Darren.
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#11

Post by steve s »

Darren wrote:Whilst I'll admit I can't find the sensitivity of my drivers I can tell you they go quite loud with just 2.5W or even to a reasonable level with 1W 6EM7.
That tells me, coupled with comparing them to another known set of speakers that they are quite sensitive.

90db is easily managed before the PX4 runs out of steam.

The ribbons keep up just fine. With the standard transformers they are pathetic.
I do wish people who have never heard my set-up would stop telling me what my system can and can't do.
It is a known fact that I listen to it and do have some idea of what I'm on about.
I too have not heard your system.. nearly did...

to get the sound levels into prespective i can get 115db peaks with less than 4 watts.. with out sounding distorted.. the det25 played at those levels at owsten..

the px25 would give me 120db peaks on the horns, my baffles are slightly more efficient.

my normal listening is around 90 dbs so there no clipping ...
not that px4's do that sort of thing you know ..

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#12

Post by Paul Barker »

Amaising you get more efficiency from obs than from horns.

I really like the sound syou are geting out of your speakers from low powered amps these Days Steve.

I might just have to go full circle myself.

think I'll try the one good pm6a and see where we go from there.

Not sure there is any benefit to the ex range over the dx range when using ob. Not convinced the extra control of the powerful nib magnets over the Alnico magnets which Brucie loves yields the "better" overall sound.

After you've spent a morning trying to keep up with Bruce Edgar as he talks with a slow drawl about such issues it's hard to get the prejudice towards Alnico out of your bloodstream.
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#13

Post by steve s »

thanks Paul.. after years of practice and you realise you need to do something when nobody like the sound of your system...

so.. thanks to you all....

interestingly, I read a bit about the difference between high power magnets and lower powered ones...
you will all know this i suppose..

lower power motors need current 'source' to control them as they have less self control?... yes i know you know that..


but higher powered motors only need voltage source..so is ideal for you low wattage/ low current amp.. .
sorry...

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#14

Post by Paul Barker »

I didn't know that Steve, you have been doing quite some reading about speakers and are way ahead of me.

I really liked your p2 on the lowther the other day, I also remember when I was using lowther ex3's the lower the powered the single ended amp the better the lowther sounded. Likewise I remember James speakers at their best on Jonothan's 45 amp.
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#15

Post by Nick »

Hmm, I wonder. We are all familer with the "first watt is the most important" mantra that is all over the place, and its often worried me, why is the first watt from a 45, into 100dB speakers better than the first 3 watts from a 211 into 94dB speakers (ignore the numbers, its just the general idea I am talking about). Maybe thats actually rubbish, maybe it what Steve almost said there, it sounds best when you use speakers that only need 1W to be loud enough, nothing to do with low power amplifers. just with the speakers.

its late, but something in that feels to be correct (IYSWIM).
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