Load Box vs Real Cab Dynamics?

[FractalAudio]

The impedance of a real speaker cab changes slightly with the excursion. The low-frequency resonance decreases and shifts slightly. The inductance changes.

The low-frequency resonance changes because the speaker suspension goes nonlinear and the B * l product changes with displacement.

The inductance changes because the voice coil moves in and out of the magnet gap. The more turns inside the magnet the greater the inductance.

The are papers by Klippel et. al. that quantify the effects. FWIW, our products model this.

However... Jay is 100% correct that the linear differences are far more audible. Even two copies of a speaker in an enclosure will measure differently due to manufacturing variances.

 

[James Freeman]

The inductance changes because the voice coil moves in and out of the magnet gap. The more turns inside the magnet the greater the inductance.

If I understood correctly, when the cone is moving a lot while playing low frequencies at high volume the inductance hence high frequency rise is lessened because on average there is less 'core' in the inductor?

Realistically, I have never seen a guitar speaker (Celestion primarily) move more than 1/8" at eardrum shattering volume, I did see 1/2" while feeding subsonic (5Hz) sine wave to break-in/loosen the suspension.

 

[Ed DeGenaro]

Clearly a perceptible difference, it starts with the amount of hair I notice.
Which I assume are the bumps I see in the midrange on graphs.

 

[FractalAudio]

If I understood correctly, when the cone is moving a lot while playing low frequencies at high volume the inductance hence high frequency rise is lessened because on average there is less 'core' in the inductor?

Realistically, I have never seen a guitar speaker (Celestion primarily) move more than 1/8" at eardrum shattering volume, I did see 1/2" while feeding subsonic (5Hz) sine wave to break-in/loosen the suspension.

Yes. Displacement is inversely proportional to frequency. As the speaker moves the voice coil moves in and out of the magnet gap. Inductance is proportional to permeability. The magnet is far more permeable than air.

It doesn't take much displacement to significantly change the inductance. A 5mm change can reduce the inductance by 50%.

 

[paisleywookiee]

I mean ..... again, that all rings true from my experience. I like my loadbox, but I'd rather mic a cab if I have the opportunity to do so.

Or run the DI from the amp, but keep it loaded down with a real cab.

 

[0XI0]

5mm change can reduce the inductance by 50%.

this is for a single driver? I'd love to see how this drastic effect translates to a sealed 4x12 with 4 drivers wired in various configurations, as it relates to what the amp sees at the single speaker out

 

[Richard_G]

Or run the DI from the amp, but keep it loaded down with a real cab.

Yeah. I’d be interested in a a high-quality reactive load box with solid attenuation that also allows using a real cab as the load while attenuating the signal going to it, and providing a controllable DI output. Perhaps the Two Notes Reload II is a candidate?

 

[Ed DeGenaro]

Yeah. I’d be interested in a a high-quality reactive load box with solid attenuation that also allows using a real cab as the load while attenuating the signal going to it, and providing a controllable DI output. Perhaps the Two Notes Reload II is a candidate?

That’b be an attenuator. Maybe Iron Man2 fits the bill for that.
But by definition a load is there to not have a cab involved.

 

[Richard_G]

I know. Perhaps my post was not clear. I'd like a combined load box and attenuator, with the option of using a cab as load. I'd still want the box the be able to provide the load on other occasions.

 

[Ed DeGenaro]

I know. Perhaps my post was not clear. I'd like a combined load box and attenuator, with the option of using a cab as load. I'd still want the box the be able to provide the load on other occasions.

As I said attenuator with load function.

 

[Richard_G]

Yeah. Thanks for reminding me of the Tone King Ironman II - I'll read up on that.!