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.!

 

[2dor]

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.

I think that's what the st.Rock React:IR2 does when used in the attenuation mode. You could still see the cab resonance frequency (albeit much more tamed) when the attenuation is used and if you run some sweeps in the FX Return.

 

[Chocol8]

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

There are two ways to look at it. With 4 drivers, at the same volume level each one will move less so the change in inductance will be much less. OTOH, if you keep the 5mm excursion the same across 4 drivers, the change will be the same, other than the serial/parallel impacts on effective load. The other thing is the sealed enclosure is going to impact the drivers in the lower frequencies and will change that part of the curve.

 

[jay mitchell]

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

5mm is a lot. It exceeds the linear travel range of most 12" guitar speakers by a large margin. It is extremely unlikely that a guitar speaker will ever be driven to that great a displacement, because it would drive most or all of the voice coil clear of the magnet gap. It's unlikely that there would be enough motor strength to push the speaker that far. Were you to manage to do so, you'd almost certainly hate the sound, and there's a good chance you'd cause permanent damage, both thermally and mechanically.

Here's a partial list of Xmax values for Eminence guitar speakers. Unlike other manufacturers, Eminence publishes complete specifications for their products. Other manufacturers' guitar speakers Xmax values fall into a similar range.

CV-75 - 1.23mm
Man O' War - .8mm
The Governor - 1.24mm
The Wizard - .8mm
Legend 1258 - .4mm

 

[paisleywookiee]

It’s interesting because I often read people saying they find the Suhr too bright - compared to Fryette, React IR, and especially Driftwood it can be but compared to a real cab it’s a bit closed off. I think it maybe exaggerates the 2-5kHz area a bit which is maybe where it sticks out to real cabs a bit.

Totally forgot I did this test too - several amps and load boxes but only comparing to a couple of cabs (otherwise the permutations just goes mad).

The Driftwood sounds like shit with pretty much every amp. Cool test though!

 

[MirrorProfiles]

The Driftwood sounds like shit with pretty much every amp. Cool test though!

Agreed. Knew instantly it was going straight back within a minute of trying it. Super disappointed after so many friends were hyping it up to me.

 

[paisleywookiee]

Agreed. Knew instantly it was going straight back within a minute of trying it. Super disappointed after so many friends were hyping it up to me.

I mean, ultimately I can’t tell because I’d have to play it, but it actually sounds even worse than the Captor X does.

How are you liking the Fryette as a load? It sounded pretty good in your comparisons. Seems to kill many birds with one stone.

 

[MirrorProfiles]

I mean, ultimately I can’t tell because I’d have to play it, but it actually sounds even worse than the Captor X does.

How are you liking the Fryette as a load? It sounded pretty good in your comparisons. Seems to kill many birds with one stone.

I like it a lot, but more so as a jack of all trades way. I think it sounds best when used to load down an amp before amplifying it again. Purely as a load, I prefer Suhr and React IR.

It can be quite context dependent too.

 

[paisleywookiee]

I like it a lot, but more so as a jack of all trades way. I think it sounds best when used to load down an amp before amplifying it again. Purely as a load, I prefer Suhr and React IR.

It can be quite context dependent too.

Good to know. I LOVED the Suhr RL when I had one. Sold it to get the Suhr RL/IR, but bought the Captor X like a dummy, when the RL/IR was back ordered.