Suhr Reactive Load Vs Fractal Audio X-Load

[Ed DeGenaro]

Another piece of information;
I expect the rising slope of a single 16 Ohm speaker in a 1x12 to be equal to a 16 Ohm 4x12 wired in series+parallel with the same speaker type and impedance, inductors behave like resistors so the L value theoretically should remain the same, 16+16 || 16+16 = 16.
2x12 cabs on the other hand will have half the inductance of a single speaker when wired in parallel, and double the inductance when wired in series.
That's why I'm curious about how the 8 Ohm Suhr RL actual frequency response from the amp compares to a more widespread 16 Ohm Marshall cabs from the same amp.

I think i recall Henderson say 8 ohm to mimic 2 16 ohm cabs

 

[2dor]

...now I'm really GAS-ing for a Marshall 1960BV lol

 

[James Freeman]

If anything, a 2x12 cab will sound better with two 8ohm speakers in series because more inductance = earlier slope rise = more high mids.
Two 16ohm speakers in parallel usually sounds bland, not enough high mids.

Here, switch between 8ohm and 16phm and see "Voice Coil - Inductance (1kHz)":

Eminence THE GOVERNOR - 12″ Guitar Speaker

12″ Guitar Speaker, 101 Hz, 150 W, 100 dB, 8 Ω

loudspeakerdatabase.com

8ohm:
Inductance (1kHz) = 0.41 mH

16ohm:
Inductance (1kHz) = 0.7 mH

2x12 Cab:
Two 16ohm speakers in parallel = 0.35 mH
Two 8ohm speakers in series = 0.82 mH

 

[James Freeman]

Thanks @Deadpan.

 

[James Freeman]

@Deadpan can you pop the lid off the Fractal LB-2 and post some gut shots?
I suspect it has a resonance limiting resistor, hence it doesn't sound as resonant as the the Suhr.

 

[MirrorProfiles]

why do most not get the bass resonance right?

Is it cost, reliability/safety, difficulty, size or something else?

 

[James Freeman]

Is it cost, reliability/safety, difficulty, size or something else?

None of the above.
If Suhr got it right, everyone can.
The components are off the shelf speaker crossover parts you can buy anywhere, including Aliexpress.

For example, a 8.5mH iron core inductor and a 220uF cap from Aliexpress will get you the exactly the same resonance response of the Suhr RL.
Throw in a 0.7mH air core for the main inductance, and a few power resistors, a project box, et voila.

https://www.aliexpress.com/item/32953092706.html

https://www.aliexpress.com/item/1005006163631723.html

https://www.aliexpress.com/item/32951716416.html

Suhr RL:

I built mine back in 2012, before Suhr or Fractal were offering their version.
I am no businessman, I probably could have made a fuck ton of money.

 

[James Freeman]

Here's a LTSpice simulation of both.
I don't own either, but I can probably mod the Fractal X-Load LB-2 to sound exactly like the Suhr and make the UK/US switch actually useful.

 

[Deadpan]

@Deadpan can you pop the lid off the Fractal LB-2 and post some gut shots?
I suspect it has a resonance limiting resistor, hence it doesn't sound as resonant as the the Suhr.

Sure thing:

 

[MirrorProfiles]

None of the above.
If Suhr got it right, everyone can.
The components are off the shelf speaker crossover parts you can buy anywhere, including Aliexpress.

For example, a 8.5mH iron core inductor and a 220uF cap from Aliexpress will get you the exactly the same resonance response of the Suhr RL.
Throw in a 0.7mH air core for the main inductance, and a few power resistors, a project box, et voila.

https://www.aliexpress.com/item/32953092706.html

https://www.aliexpress.com/item/1005006163631723.html

https://www.aliexpress.com/item/32951716416.html

Suhr RL:

View attachment 16869


I built mine back in 2012, before Suhr or Fractal were offering their version.
I am no businessman, I probably could have made a fuck ton of money.

View attachment 16870

View attachment 16871

View attachment 16872

Love it.

Design one that closely mimics a Mesa OS, Mesa Trad, and 1960TV and you’ll be basically printing money

 

[DrewJD82]

Copper French Crullers FTW. Needs some glaze.

 

[bikescene]

I always wondered how these cab impedance measurements were made. Are you guys wiring up two interface outputs to perform the impedance measurement on your cabs?

https://www.roomeqwizard.com/help/help_en-GB/html/impedancemeasurement.html

I built the Type M2 attenuator project from the Marshall Forum, and have thought about comparing it as a load to the Suhr Reactive Load.

 

[2dor]

I always wondered how these cab impedance measurements were made. Are you guys wiring up two interface outputs to perform the impedance measurement on your cabs?

https://www.roomeqwizard.com/help/help_en-GB/html/impedancemeasurement.html

I built the Type M2 attenuator project from the Marshall Forum, and have thought about comparing it as a load to the Suhr Reactive Load.

I've done it with some instructions from @MirrorProfiles :

- hooked up the amp to the loadbox (or loadbox with a cab in the THRU port)
- hooked up the loadbox to the audio interface
- shot a sine sweep into the FX Return of my amp
- I used the st.Rock React:IR software to deconvolve the sine sweep (Spectrum I) and amp signal (Spectrum II) and exported the resulting IR; you can use Voxengo but I found it finicky
- drag that IR into Room EQ Wizard (REW) and there you have it

 

[chicken]

What this big transformer for in the Fractal? It is not for impedance matching, right?

 

[James Freeman]

Sure thing:

View attachment 16883

View attachment 16882

Thank you.
Looks like three TO-220 resistors in series on the heatsink as main load and a bunch of ceramic resistors as resonance limiters.
Interesting design.

 

[James Freeman]

Fractals design appears to be engineered much better than Suhr but I don't see any "Dynamic Impedance technology" except maybe the small inductors are ferrite core so they might saturate more like a speaker does compared to air core inductors.

I don't see the Cap values but I think it is around 160-180uF (two 330uF in series to create non-polarized cap?) with the 15mH inductor to create the 95-100Hz resonance peak.
The US/UK switch adds another cap in parallel to move the resonance frequency lower.

The Suhr RL does not have limiting resistors for the resonance peak, so if you are courageous you might want to experiment by removing them from the LB-2, that should enhance the palm mute chug/bounce feel.

 

[PLX]

I built mine back in 2012, before Suhr or Fractal were offering their version.
I am no businessman, I probably could have made a fuck ton of money.

I copied yours (way back when, off the TGP thread) and beefed up the load to handle a cranked 100W amp & added an output transformer.

 

[James Freeman]

Here's my Fractal X-Load LB-2 sweep response going into the Metropoulos FX Return of my amp, NFB disabled.
My LB-2 resonance peaks measure lower than normal, UK is at 90Hz and US at 62Hz, not very happy about that, 4x12 cabs resonate at 115Hz.
High frequency slope measures very close to my 16 Ohm 1x12 Cab with a single Vintage 30.

 

[James Freeman]

Looks normal inside, like @Deadpan's, plenty of thermal paste on mine.
Also, I did not see the small fan active yet but the heatsink is hot to touch, both my amps are 50W.
Aside form the way out of spec resonance peak, I'm pleased.

 

[chicken]

If it doesn't approximate that well build quality doesn't matter.