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RE: An added complication is the non-linearity of the "Phenomenon of the 'Weak Fundamental' "

158.222.164.209

John Atkinson

In Reply to: RE: An added complication is the non-linearity of the "Phenomenon of the 'Weak Fundamental' " posted by John Marks on July 21, 2024 at 07:56:50

>One example: The lowest string of a 4-string electric bass guitar is E,
>usually tuned to around 41Hz (the numbers to the right of the decimal
>point don't make a difference). 41Hz has a wavelength of 27.5 feet. To
>begin to do full justice to the frequency, you need a string length of
>6.7 feet. Not gonna happen!!!
>
>So, in real life, the low E of an electric bass is a "Weak Fundamental,"
>which means that the octave harmonic of Low E, E = 82Hz, is 6dB louder,
>which is perceptually twice as loud.

Fig.3 at the link below and the table below the graph show the levels of
the harmonics of the bass guitar's open E string. The second harmonic is
almost 12dB higher in level than the fundamental.

>So, engineering a BSC network is as far as I know a trial and error
>iterative process, with lots of measurements. The designer of the final
>crossover for my current project put more than 50 hours work into it.
>JA, please comment!

The baffle step compensation can be achieved in a second-order low-pass
crossover filter by using an inductor with a relatively high series
resistance. However, this reduces sensitivity. But yes, optimizing BSC
is very much a matter of trial and error.

John Atkinson
Technical Editor, Stereophile

https://www.stereophile.com/features/338/index.html (Open in New Window)

Follow Ups:

"However, this reduces sensitivity." Aye, there's the rub! - John Marks 12:54:44 07/21/24 (3)
Thanks, John

Sorry for the memory glitch. I don't have time to fact-check it, but I vaguely now remember that it was the Stand-Up Acoustical String Bass that had the octave harmonic 6dB louder. And yes, the electric bass's harmonic series is even more sharply divergent.

My crossover designer Curt Campbell told me that the BSC on my current design was -6dB.

So, if the efficiency had been 84dB before BSC, after BSC it was... 78dB.

I can't imagine any magazine doing that measurement, and then not making a major issue of it.

Which is to say, that can be Reason #4 why a loudspeaker designer might make the Executive Decision not to implement BSC.

john
- Are you sure you understand any of it? - Doug Schneider 20:03:24 07/21/24 (0)
  "I can't imagine any magazine doing that measurement, and then not making a major issue of it."
  
  "Which is to say, that can be Reason #4 why a loudspeaker designer might make the Executive Decision not to implement BSC."
  
  Are you sure you understand "baffle step"? From the comments above, saying "that measurement," perhaps no. It has to do with frequency response and simply shows up as a rise on the frequency response if not dealt with in the crossover.
  
  Also, in another post you talked about the money involved in compensating for it -- and companies not seeing it being worthwhile because of that. It becomes part of the crossover network, and if you know how much a crossover takes to make, well, it's not exactly all that much money.
  
  Did you say you "design" speakers?
  
  Doug Schneider
  SoundStage!
- Not quite understanding sensitivity? - Doug Schneider 18:49:22 07/21/24 (0)
  Hello,
  
  I came back to this comment and realized it indicates that you might not understand sensitivity well. If not, you're not alone, I made a whole video about it when Robert Harley got it wrong.
  
  How "sensitive" a speaker is depends on the frequency or, preferably, frequencies at which you measure. The baffle step varies per speaker, and in the case of that Franco Serblin speaker, it starts happening just shy of 1000Hz. So if someone where to take a sensitivity measurement at, say, 400Hz, it would be unchanged. Instead, the rise of 6dB would be at its fullest by 1000Hz. So the entire speaker didn't change by 6dB if you compensate for the baffle step -- 400Hz remains the same, the frequencies just below, at, and above 1000Hz get reduced.
  
  We average sensitivity over a range -- 300Hz to 3000Hz -- so by doing so, once again the sensitivity wouldn't change by the full 6dB.
  
  Finally, if you have a speaker that's 78dB, you've got a real problem with it -- that low sensitivity will likely mean it'll blow up if someone plays it loud. It's too low.
  
  Doug Schneider
  SoundStage!
  - Speaker Sensitivity Explained - "4-ohm/2.83V" is Not a "Tric (Open in New Window)
- The reason is... - Doug Schneider 13:03:21 07/21/24 (0)
  The usual reason for not eliminating the baffle step typically completely is because you don't even know it's there. As soon as you measure something properly -- anechoically -- it sticks out like a sore thumb.
  
  Furthermore, if you understand the interaction of loudspeaker and rooms -- read any version of Floyd Toole's book -- you'll know if has to be ironed out to get a respectable response.
  
  Otherwise you'll have one of the worst sins a loudspeaker can commit: NO BASS. And if you do further reading on the importance of bass response based on the research of Toole and later Olive, you'll find out that, all things being equal, the speaker that produces deeper bass is the one favored by listeners.
  
  In fact, Toole talks about that very thing in our latest podcast episode, linked below.
  
  Doug Schneider
  SoundStage!
  - Dr. Floyd Toole: An Oral History Part 2 (Open in New Window)

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