What is meant by "BBC rise"?

[Javachip]

I see this phrase once in a while. I surmise that it refers to an intentionally non-flat frequency response. How much, over what range, and why? Is it achieved by crossover design, driver matching, or both? Does it have any merit today, or is it merely of historical interest? Thank you.

[infinia]

Can you be thinking of the "BBC dip" instead? Google is your friend.

[Scottmoose]

It was done across the vocal range to increase the presense slightly, mostly, as I understand it, achieved by allowing the rise through careful crossover filtering. The classic example of this is the earlier 15ohm model of the LS3/5a, which contrary to popular belief were not flat: remember, these were mobile monitors for mixing purposes, and therefore needed this slight presense lift to aid mixing etc. The later 11ohm version of the LS3/5a with it's computer designed crossover did not have (as much of) a lift (though there still was a little I seem to recall). If you feel this would be of merit to you, then fine. If not, just as fine. Depends on what you listen to, the rest of your system & room, and how you listen / what your preference is I suppose. It might appear to add a touch of sibiance to female vocals, i.e it'll be merciless if there is any on the recording, but useful for the recording studio, or if you prefer increased presense in this region.

Best
Scott

[Javachip]

Hmm ... I found another relevant thread within this site, and I now, including the preceding post, have 3 different explanations to choose from:

a) It is a gentle wide dip across the midrange to compensate for uneven response of early phono cartidges, thereby reducing listening fatigue.

b) It is a narrow dip around the crossover point of early BBC speakers to compensate for the increase of off-axis response as the tweeter takes over.

c) It is a rise (not a dip) across the vocal range to increase presence.

Any more votes?

[infinia]

Googled speakers+"BBC+dip" = 1000 hits
then speakers+"BBC+rise" = 3 hits

let's start reading first

[sreten]

Originally posted by Javachip

Any more votes?

Hi,

If there is such a thing as BBC rise :
d) I'd say its the top end excess built into LS35/a's.
This was intentional to make poor hiss performance apparent.

The classic term is BBC dip. b) is the nearest. a)+c) simply wrong.

/sreten.

[bear]

Dip.


But I suspect that it was to compensate for the on-axis response of the "midrange" becoming narrower as it neared the xover point to the tweeter, IF that sort of thinking played a role at all.

In reality I think that someone came up with it just to make things sound "better" and without any direct technical research or purpose behind it. If they came up with some sort of technical justification I'd bet it was after someone decided it "sounded better"!

Pretty sure the LS3 had a dip built in, not a rise.

_-_-bear

[reins]

Hi,

to my knowledge the BBC dip is around 5k, 2dB deep to suppress hissing with 's'-syllables.

I also remember the concept of a 2dB difference between 100Hz and 10kHz (at 10kHz 2dB down). But I'm not sure if that was in connection with BBC.

Stephan

[Scottmoose]

We're probably looking at different things. There's both. The dip is typified by designs such as Spendors etc. The rise, on the other hand comes from the infamous LS3/5a. It does / did exist. I quote Alan Shaw of Harbeth (knew I could find the article somewhere -been looking for it for an hour) Hifi News, November 2004.

'The computer optimised LS3/5a (i.e. the 11ohm version) reshaped the frequency response to that of the original 1974 BBC specification except in high frequency output above 10KHz. In the 1970s, pre-digital, a considerable lift at the top end was considered a desirable characteristic to 'pre-emphasise' the contribution of hiss from analouge tape to a recording and hence to alert the sound engineer how best to maximise the dynamic range. This characteristic, however, is completely inappropriate for digital recordings, for which the MK 2 LS3/5a is a much better match.

'A peak in output at around 1-2KHz was not a characteristic of the original BBC Design Report RD 1976/29 -although the HF boost is evident - and is probably not present on the very first production LS3/5As, but is in evidence with a vengence by the mid/late 1980s, if not rather earlier. It is typically +6db above the average pass band output... That the "raw" bass unit is at its most efficient in that region was taken into account in the design of the network at the BBC, and energy was sucked-out between 1-2KHz by judicious use of a series notch filter comprising coil L2, capacitor C5 and damping resistor R2 in the crossover feed to the bass unit.'

There you have it, from a man who probably knows more about BBC speakers than anyone else alive. So it depends which one (the dip many 'BBC' designs, or the lift the LS3/5a had) you were refering to.

[infinia]

Dip or rise depends what your point of reference is, but dip if you believe google.
Link for story of BBC speaker development. Seems like they had supplier problems with mid bass units. Looks like they ran it (mid bass) with a elliptical LPF and a fair amount of BSC.
http://www.ls35a.com/