TH THE BOX 12-280/8W

[Djim]

Greets! Thanks!
Where did you find it? I found several different sets of specs, all with the same '283965' document #, but only the one I listed had anything at all WRT Xmax, so a 15.1 mm VC height and 10 mm gap depth = [15.1-10]/2 = 2.55 mm and while not 100% accurate, it's a good approximation; though I've noticed in recent years that some manufacturers have been 'padding' it with various formulas, but 6 mm seems a bit of a stretch and still be at the <10% distortion the industry has historically considered acceptable.
GM

Hi GM,

With the formula (Hvc-Hg)/2 + 1/4Hg it is 5 mm but 6 mm has been measured for this driver . At that point more than half of the power will be gone in losses but it has good cooling properties. The mechanical suspension, cone and even the basket are excellent for its class.
Not sure if 10% THD values are worth looking for in ‘budget’ low frequency PA drivers but I share your view that lacking standards seem to have become a standard on its own.

Cheers,
Djim

 

[tetrapol]

hi Gm

You think that the movement is 3mm?

https://www.youtube.com/watch?v=MqknzdRjyw8

 

[bjorno]

Hi All,

FYI:

Paramètres de THIELE et SMALL des haut-parleurs

Paramètres haut-parleur de THIELE et SMALL, sans filtre ni ampli

Paramètres haut-parleur de THIELE et SMALL, sans filtre ni ampli


b

 

[weltersys]

You think that the movement is 3mm?

Tetrapol,

The excursion certainly exceeds +/-3mm, but from the sound of the distortion, excursion is also probably greatly exceeding the linear range of operation (Xmax). There are many drivers capable of excursion double (or more) of the Xmax rating without experiencing damage, which is called Xlim or Xmech. Xlim or Xmech is the the limit where the suspension is stretched to full extension, or in the case of many drivers, when the voice coil former hammers the back plate, which can cause instant mechanical damage.

If you have a RTA, you can see the harmonic distortion content when running sine waves through a speaker. When the harmonics rise above -20dB of the fundamental frequency, distortion has exceeded 10%, or by definition, the excursion has exceeded Xmax.

In the example below, the fundamental frequency is 45 Hz at 124.8 dB (using 46 volts into a 4 ohm speaker), the second harmonic is 98.2 dB, -26.6 dB, about 5% distortion.

Art

 

[tetrapol]

HI...

I totally agree, theory is theory. But I doubt the data that gives me the manufacturer.

else are field tests ... and I can assure that the keystone TH modified the sound is good without appreciable distortion by the ear at a high spl above 125dbs

 

[tetrapol]

Hi..bjorno

18LB100-8BA-Beta Three

xmax=0?

 

[djk]

The people doing data entry make mistakes all the time, even at JBL.

That's just one problem with using people with no technical knowledge for data entry, they can't spot a mistake.

 

[tetrapol]

weltersys
xmax concept is relative. JBL was the first to make a definition 80s . Today every manufacturer uses different formulates for calculation. For example



Faital

Xmax= [(winding depth - magnetic gap depth)/2] + (magnetic gap depth/3)

RCF

Xmax= (Hvc - Hg)/2 + Hg/4 where Hvc is the voice coil depth and Hg the gap depth.


the concept of harmonic distortion(10%) is also relative . LABORATORY formulas is clear , but ultimately it is the human ear determines

 

[tetrapol]

weltersys
xmax concept is relative. JBL was the first to make a definition 80s . Today every manufacturer uses different formulates for calculation. For example



Faital

Xmax= [(winding depth - magnetic gap depth)/2] + (magnetic gap depth/3)

RCF,B C, 18 SOUND

Xmax= (Hvc - Hg)/2 + Hg/4 where Hvc is the voice coil depth and Hg the gap depth.


the concept of harmonic distortion(10%) is also relative . LABORATORY formulas is clear , but ultimately it is the human ear determines

 

[bjorno]

Hi..bjorno

18LB100-8BA-Beta Three

xmax=0?

Agree with weltersys and djk...It doesn't hurt to do consistency check for incomplete Driver data by cross checking all data there is, including estimation of apparent displacement capability derived from simple measurement on the Driver cone....

b