BBC dip

[boxerfan88]

Recently I reconfigured the gain staging of my entire system to support 100dB SPL. During loud testing (~90dB SPL avg) I realized some "busy" rock tracks sounded a little bit harsh and fatiguing to my ears after a while. If I bring the volume down to (75-80 dB SPL avg) it is sounds much better. Maybe I am not used to listening so loud.

And so I thought ... maybe there is a way to make it more enjoyable even at loud levels. So I went and started researching about harsh and fatiguing sound. Somehow I landed on the "BBC dip" topic.

Here are some interesting snippets that I came across...

Our perception of loudness is slightly different for sounds arriving frontally versus sounds arriving from random directions at our ears. The difference between equal-loudness-level contours in frontal free-fields and diffuse sound fields is documented, for example, in ISO Recommendation 454 and in E. Zwicker, H. Fastl, Psycho-acoustics, p. 205. Diffuse field equalization of dummy-head recordings is discussed in J. Blauert, Spatial Hearing, pp. 363, and headphone diffuse field equalization by G. Theile in JAES, Vol. 34, No. 12. Reference to a slight dip in the 1 to 3 kHz region for loudspeaker equalization is made in H. D. Harwood (BBC Research Department), Some factors in loudspeaker quality, Wireless World, May 1976, p.48.

Around 3 kHz our hearing is less sensitive to diffuse fields. Recording microphones, though, are usually flat in frequency response even under diffuse field conditions. When such recordings are played back over loudspeakers, there is more energy in the 3 kHz region than we would have perceived if present at the recording venue and a degree of unnaturalness is introduced.
This applies primarily to recordings of large orchestral pieces in concert halls where the microphones are much closer to the instruments than any listener. At most listening positions in the hall the sound field has strong diffuse components.
I use a dip of 4 dB (x1.gif, 2760NF) to equalize for this. [...]

I have found through my own head-related recordings of symphonic music that the dip adds greater realism, especially to large chorus and to soprano voice and allows for higher playback levels.» - Siegfried Linkwitz

https://linkwitzlab.com/models.htm#H

To make the connection to the speakers of classic pros. Here is a snippet from an interview with Joachim Kiesler of Geithain about the way they deal with the directivity around 3 kHz.

"What's important is tonal neutrality, correct localisation and a correct sense of distance. This is achieved, among other things, by not splitting the radiation of a loudspeaker across drivers that are more or less far apart, as is often the case with multi-way systems [ME Geithain uses coaxial systems that are close to the ideal point source, the author]. In addition, the effect of the directional characteristic of a loudspeaker is often underestimated: Compared to other frequency ranges, the human ear rates direct sound between 2-4kHz about 2.5dB higher than diffuse sound, which must be taken into account when developing loudspeakers. Depending on the loudspeaker model and the associated optimum listening distance, we make sure, for example, that the loudspeaker is less focussed in the range between 2-4kHz. Otherwise, there would be an overemphasis in this range, which would not be conducive to sound colour fidelity or distance detection - the sound image would appear more present and subjectively closer to the listener."

Translated with DeepL.com (free version)

The actual BBC dip was deliberately applied to reduce listener fatigue. I suspect one reason was that engineers needed to use these for prolonged periods in a noisy environment (portable studio for broadcast) and so listened at high volume levels to overcome background noise. The dip at 2-4K takes the edge off any nasty vocal effects or forwardness.

From a hifi perspective the dip is often used to give a sense of a deeper soundstage, particularly in placing vocals behind the plane of the speakers. Some people like that.

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[boxerfan88]

And a video about the BBC dip...

 

[boxerfan88]

So, I went about experimenting with the BBC dip.

Looking at the KH310 frequency response, it is relatively flat through the 2-4kHz region at the listening postion.

I tried two configurations:

A. PEQ @ 2600Hz, -1.0dB, Q=1.4142 Simulation

B. PEQ @ 2800Hz, -1.0dB, Q=1.0000 Simulation

Listening impressions (no measurement liao):

• At lower volumes (~75-80dB SPL) the "center image" on the soundstage moves backward a little bit with the BBC dip PEQ
• At higher volumes (~90dB SPL) the harshness is lesser now.
• I prefer the Q=1.414 setting

Very interesting observation indeed! I have turned my studio monitors into a "HiFi" speaker

I just love the ability to tune my system at will.

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[boxerfan88]

After playing around with/without the BBC dip over this weekend, yup it does take the edge off the upper region, and also pushes the soundstage back a little bit. It’s nice.

Am pleasantly surprised that a small -1dB cut makes a nice difference.

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[boxerfan88]

With the current day technology, I guess designing a flat speaker isn’t too difficult, but the tweaking/voicing is where the magic is.

Projecting it system wide, it’s my opinion that starting with a flattish system as a baseline, lays a nice foundation for system tweaking/voicing to one’s preference.

Hence for myself, using a PC as the source is the most flexible.

As a next step, I should build a few EQ profiles for different moods or use cases, like relaxing listening, critical/analytical listening, tube wooly warmth, etc…

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[boxerfan88]

Interesting tid bit ... from the EPOS designer ... he adds a small "BBC dip" ...

Hi,

I published the measurements of ES-14N and I made them with the Klippel NFS. So I think I did everything to be as transparent as possible. I can't see what would be different with a different Klippel NFS. The other measurement I saw above looks a bit strange, so I cannot comment, as I don't know how it was made. I trust my NFS .....and my ears.
Even so, I like Audiosciencereview and Erins Channel, it does not mean I always agree with what both conclude from the measurements. With a lot I'm OK, but a small valley in the 2-3kHz area for example is very easy to straighten out with a crossover, but sometimes you add it to avoid the speaker sounding aggressive and too forward. Designing a waveguide for a tweeter is not very complicated, but I like the way it sounds in the room without it and with an exposed dome. The speaker is a compromise in most cases, so my speakers are the result of my idea of a compromise. I can accept if somebody thinks a speaker only has to be so and so......as long as I have the freedom to do it the way I like.
We have a lot of equipment around and we use it a lot......but in the end, we have to listen to it and so, final adjustments are done by ear.
So far, we have not established a distribution for EPOS in the US. it's a difficult market, as it is so large and the time is not very good for a new brand, even so, it's old. So we have to wait for better times and the right distributor.

Best regards

KHF

Ref: https://www.audiosciencereview.com/...isation-without-subwoofer.48559/#post-1740359

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[Spunky]

I went to the ASR thread above and this is funny!
I dunno who is matty but now I am curious!

Dear Karl you talk with matty, you're new here and you don't know.

 

[boxerfan88]

New bbc dip tweak ... this time targeting the KH310 measured Sound Power DI ... to make it a little flatter in the 2.5kHz region.

Revised PEQ: 2500Hz, -1.0dB, Q=2.0

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