High Efficiency Speaker Asylum

Ergs, Gauss, and the Jensen P15LL

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Thermionic27609

A

I ran across an old Jensen Professional Series datasheet that listed the "gap energy level" of a Jensen P15LL as 13.6 Millions of ergs.

I was hoping that someone more familiar with the units and systems used to measure magnetic field strength might be able to tell me how ergs convert to the Gauss or Tesla figures you see on JBL datasheets.

For example, the JBL E-130 is listed as having a flux density of 13.5k Gauss.

Any assistance helping me up this learning curve is appreciated. I'm curious about these things.

Follow Ups:

RE: Ergs, Gauss, and the Jensen P15LL - Thermionic27609 12:22:04 08/01/14 (1)
I consulted a friend who's a university researcher in Electrical Engineering, and his take on it was that I'm not crazy in being confused here because the units used on the promotional sheet don't really make sense.

We're thinking that either by accident or on purpose, something was lost in translation between the engineers and whoever was writing and producing these promotional materials. In other words, the document I'm getting this from was an early 50s advertisement, not a datasheet. Maybe "gap energy" sounded better than "flux density."
- RE: Ergs, Gauss, and the Jensen P15LL - Thermionic27609 13:27:52 08/01/14 (0)
  Or maybe not...
  
  I found an article from the 1950s on speakers that gave the formula:
  
  W8π = B[squared] * V
  
  Where
  
  W = Gap energy in ergs
  B = flux density
  V = gap volume in cubic centimeters
  
  Since I recone P15LLs, I have one that's just a basket, so I could measure the gap. I calculated gap volume as 4.89 cubic centimeters. That gave me a flux density of 8.36k Gauss. Of course, that seems somewhat low to me compared to data I've seen on other speakers, but Jensen never seemed that interested in publishing detailed specs on its speakers.
  
  At this point, I give up.
RE: Ergs, Gauss, and the Jensen P15LL - lokie 11:22:58 08/01/14 (0)
Sorry I can't contribute any technical specs although I am very interested in any specs generated from this thread.

I currently use a pair of P15LL's in a 2 way with an altec 802cd w 32b horn and am more than happy with the results. Wonderful tone and dynamics. I would guess the efficiency to be floating around 100db. I'm getting good bass down to around 40hz (no port... yet) and xing over on the top end at 1200hz.

I'm getting peaks but may be room related. I need to take better measurements to figure out what's going on and modulate the crossover accordingly.

Overall, a real winner and great bang for the Alnico buck.
RE: Ergs, Gauss, and the Jensen P15LL - Paul Joppa 16:44:30 07/31/14 (1)
The energy per unit volume in the gap is (1/2)B^2/mu - B is in gauss or tesla, and mu is permeability, which is 1.0 for air. If you know the dimensions of the gap, you could calculate the field strength.
- RE: Ergs, Gauss, and the Jensen P15LL - Thermionic27609 10:28:01 08/01/14 (0)
  I'm still not seeing a formula that states the precise relationship of ergs to Gauss, but I'll do my best to make sense of this.
RE: Ergs, Gauss, and the Jensen P15LL - weltersys 13:06:36 07/31/14 (0)
Convert away!

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