BBC Dip

[kspv]

Is it true that some speaker manufacturers deliberately provide for what is known as "BBC dip" in their speakers' frequency response. What is the purpose of providing a "BBC dip" in a loud-speaker? Whether any research has been done on its effect on musicality of the speakers? Since fidelity is the acurate reproduction of the original recorded sound, is it not against the tenets of high-end audio to design speakers with a "BBC dip". Isn't the sound coloured this way?

[markp]

Yes there is a "BBC dip". It is a 'polite' dip in the midrange to make the speaker sound more to the liking of the average person.

[sreten]

The "dip" is a compensation for the sudden increase in off axis
response when the tweeter comes in above the usually large
midrange units in the BBC's case, nearly all are 8" or larger.

Its not needed and doesn't work well with small midranges.

sreten.

[markp]

Originally posted by sreten
The "dip" is a compensation for the sudden increase in off axis
response when the tweeter comes in above the usually large
midrange units in the BBC's case, nearly all are 8" or larger.

Its not needed and doesn't work well with small midranges.

sreten.

Yes, this increase in midrange brightness is what the BBC dip removes making the speaker less forward sounding, more 'polite' as it is said.

[sreten]

Originally posted by markp
Yes, this increase in midrange brightness is what the BBC dip removes making the speaker less forward sounding, more 'polite' as it is said.

The point is for "BBC" speakers it is more accurate.

sreten.

[Ap]

The BBC dip is a falicy.

Take alook at the response graphs...
http://www.harbeth.co.uk/images/35acurve1b.jpg

The problem arose from the Bextrene cone used in the LS3/5a, it had a pronounced breakup at around 1k due to either cone material or suspension.
My guess is the 'dip' was introduced to correct this, and the result was a flat response.

Note: one of the reasons why the 3/5a sounded polite was a very smooth 30deg off-axis response, something often over looked (or heard) in the majority of speakers around at the time.

[Gregm]

Originally posted by sreten
The "dip" is a compensation for the sudden increase in off axis

The idea was it seems, that even flat response @1,5-~3kHz is annoying to the ear, shrill and fatiguing, especially on classical. The solution was to introduce a small attenuation, dipping (1-2db) b/ween 300-3kHz -- better still, 2-3db between 100-10kHz.

I don't mind the idea, in fact I'd like it IF I could get a flatish extension thereafter...

[sreten]

Originally posted by Ap
The BBC dip is a falicy.

Originally posted by Gregm


The idea was it seems, that even flat response @1,5-~3kHz is annoying to the ear, shrill and fatiguing, especially on classical. The solution was to introduce a small attenuation, dipping (1-2db) b/ween 300-3kHz -- better still, 2-3db between 100-10kHz.

Hmm.......


AP, the LS3/5A doesn't need or have the compensation, as stated
it was used in BBC speakers with 8" or larger midrange units.

I'm sorry GregM but that is not the the classic "BBC dip" by any
definition, the dip is around the c/o point and very local to that
frequency range.

BBC speaker voicing on the other hand does prefer basically
a gently falling response, 2dB/3dB over the range, but this is
not the "BBC dip" phenomena, its just overall voicing.

This "voicing" is must less pronounced than the differences
in response of MM cartridges, and suits the brighter more
accurate examples of cartridges.
Budget cartridges often fall ~ 6dB across the frequency range.

Edit :

I'll just note that the dip was copied by some manafacturers
without apparently understanding its purpose, however the
technique is still in use today, reducing axial output if there
is a peak in off axis response, to give a balanced result.

sreten.