Help needed with choosing the optimal Dirac curve

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On 5/13/2019 at 9:54 AM, STC said:

 

Have you compared with one not sloping downwards for HF?  The recommended curve is based on concert hall acoustics which is the sum of direct plus reverbs. IME, even a slight slope kills the HF. 

 

There's a trend for speaker to exaggerate the treble either by shelving it up a few dB or by producing a rising response from the presence region onwards. This is probably market-driven, since audiophiles have become somewhat obsessed with "spaciousness" and "air".

But I would disagree that this sounds more natural/realistic. It's an effect, one that engineers use in their pop/rock mixes.

 

Perhaps the fact that many audiophiles listen to music at overly loud levels is helping with this trend as well by accelerating hearing loss at higher frequencies...

 

 

Here's the Olive/Toole target curve in red superimposed to the B&K target curve, showing the "ideal" in-room response of a speaker with a flat anechoic frequency response measured from the listening spot:

 

 

[semente]

On 5/14/2019 at 2:23 AM, STC said:

 

That is a myth. From the designer himself ( allegedly).

 

'

We're off walking in the Northumbrian hills today, so I have much time to relive and add to my comments.

One thing to be aware of which has direct bearing on your comments about the presence dip on the early Harwood-designed Harbeths (HL1, Mk2 etc.) is this: Dudley Harwood, unbeknown to me at the time I took over Harbeth, was a member of a fundamentalist Christian faith. He lived a simple life, and was disinterested in the trappings of modern consumer life. He was prohibited by the rules of his group to take any interest in entertainment, and that apparently included music of any and all types. Now, you may ask how a world-renowned loudspeaker engineer could evaluate loudspeakers, unable to listen to music on them - it is difficult to comprehend what work-arounds he used. But certainly speech recordings, which were permitted, became critical to his evaluatory process. Without the formal ongoing feedback from BBC users who you mention, it must have been very difficult for Harwood, now ex-BBC and running Harbeth, to be sure about what was a correct speaker response balance bwteen bass, mid and top. If you recall, in one HFC, he was criticised for having set the tweeter level too high (Mk3?) and this was surely a direct consequence of working alone, and not listening to music and natural hearing loss with age.

However, judging, controlling and shaping the energy in the presence region (say, 1-3kHz) and the position of musical performers front-back (z-plane) is much easier in stereo, and with music. Also, again this did come up in conversation with Harwood and is in the transcript, I asked him 'what is the purpose and function of the so-called Gundry-dip where energy is reduced in the (typically) 1-2kHz region'? His answer was unequivocal .... "to mask coloration in the polypropylene cones'. This was the first admission that even though he was the father and patentee of PP cones, they had known deficiencies - quite an admission.

The BC1 had a bextrene cone, where coloration in broadly that region was ameliorated with a thick coating of PVA 'dope'.

Alan A. Shaw
Designer, owner
Harbeth Audio UK

p.s. I was an active member of Harbeth forum then. That's why I remember.  

 

 

Shaw is a bit of a salesman, I'm affraid, so I'd take his word with a pinch of salt...

 

From the designer himself (not allegedly):

 

Some factors in loudspeaker quality

by H. D. Harwood, Wireless World May 1976

 

[semente]

Interesting post from @mitchco at ASR showing various target curves:

 

 

https://www.audiosciencereview.com/forum/index.php?threads/what-is-your-favorite-house-curve.2382/page-2#post-67187

[semente]

3 hours ago, STC said:

 Do you have the full text? As far as I remember the dip at that region is also where crossover is set. I do not have all the papers with me right now since I crashed three drives recently but I am sure there was another interview about the dip. Anyway, no one would happily admit their invention was flawed. 

 

If the dip is crucial then it would continue to exist even now in modern BBC inspired speakers such as Harbeth and Spendor. 

 

Also so please include the link for Toole room response. IIRC, it was the measurement at ear level. An UMIK mic measurement at LP and one at ear level varies greatly. 

 

I have had many interaction with Alan Shaw including one to one meeting and he is not a salesman not a snake oil peddler. He is straight forward and doesn’t toy with words to misrepresent. 

 

Here you go:

 

 

factors_harwood.pdf

[semente]

3 hours ago, STC said:

 Do you have the full text? As far as I remember the dip at that region is also where crossover is set. I do not have all the papers with me right now since I crashed three drives recently but I am sure there was another interview about the dip. Anyway, no one would happily admit their invention was flawed. 

 

If the dip is crucial then it would continue to exist even now in modern BBC inspired speakers such as Harbeth and Spendor.

 

All BBC designs show a dip in the presence region off-axis but some are flat on-axis (i.e my Stirlings).

 

Harwood says that the dip in the presence, which produces a perceived recession of the soundstage, makes orchestral music sound more natural.

And he, as well as the other researchers at the BBC RD should know because they could perform direct comparisons between the sound of the speakers and live orchestras.

 

3 hours ago, STC said:

Also so please include the link for Toole room response. IIRC, it was the measurement at ear level. An UMIK mic measurement at LP and one at ear level varies greatly.

 

The Olive/Toole curve has apparently been redesigned as per the Mitchco plot above.

 

3 hours ago, STC said:

I have had many interaction with Alan Shaw including one to one meeting and he is not a salesman not a snake oil peddler. He is straight forward and doesn’t toy with words to misrepresent. 

 

He is not a snake oil peddler but he does twist the truth somewhat if it suits his busyness... Just go on the HUG forum.