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Behringer Truth B2031A - how truthful is it? (review / modding)

roci_big_ear

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I bought one speaker out of curiosity. I wanted to see the value the speaker delivers for just $199.

front.jpg


What a great first impression unboxing and taking it apart!

These things are designed (thanks, Genelec!) and built (thanks, Behringer!) really well: the cabinet is dense and solid, the driver frame is cast, the circuits have good layout and soldering. Speaking of circuits: 3 TDA7293 chip amps power it, fed by a toroid transformer. At the +/-42V supply voltage, the power these chips can deliver is over 300W. This is not the 20-year old B2031A design you see reviewed online: on the outside it looks the same, but the PCB is a new revision of the now discontinued B3031A (which I have had for 10 years and like a lot).

internals.png


I particularly like the front facing bass ports and the down facing rear connectors that make placement easy.

But then you turn it on... Right out of the box, my B2031A sounded very bright. Sure enough, a sweep confirmed the tweeter is 4-5 dB too loud above 4 kHz. They say it is factory calibrated... Did the technician stick the microphone in the woofer?

Thankfully, Behringer has put 2 hidden trimmers to change the level of the tweeter and adjust a ~17 kHz booster.


MOD 1

Using the factory trimmers, I decreased the tweeter level, and added a bit of a high boost to flatten it (as much as possible). This ended up in an overall flatter response, but also with a wide ~4 dB dip around the crossover frequency, which is at 1.85 kHz. Each driver is at -10 dB at that point. So overall, factory calibration was bad, but even after manual calibration, I am left with a smiley-face response.

response-initial.png


I am starting to think the woofer cut off frequency is too low due to a wrong component value, which messed up the rest of their factory calibration.


MOD 2

It was time for more drastic measures. I removed the main PCB, took out the soldering iron and increased the woofer's low-pass filter cut off frequency a bit, so that the cross over is at 1.95 kHz vs 1.85 kHz originally. I didn't want to take out existing components (they are also glued), so I decided to solder a 47 kOhm resistor in parallel to R86 like this:

B2031a-mod.jpg


This increased the overlap of the two drivers and bumped the frequency valley by ~2 dB. Still not ideal, but better.


MOD 3

The response above 5 kHz bugged me. Not only is it not flat, but then the sudden drop off. The only reasonable course forward I could think of is to modify the 17 kHz booster. My plan was to move it to 25 kHz and counter that steep fall off. After another couple of hours of studying the board and simulating the circuit, the mod was to solder a parallel 10k resistor to R80.

pcb-mods.jpg



Conclusion

As you can see, all the mods I did cost absolutely nothing (other than a weekend of my effort). I am dumbfounded why Behringer doesn't tune their speakers better. With all the mods, the speaker is quite nice actually.

Final response, 37-20kHz +/- 3dB.

response-final.png
 
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roci_big_ear

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You made the frequency response flatter, but what about phase and off axis response?
Mod 2 changes the woofer phase by less than 1.5 degrees around the crossover, so I'd expect the impact to vertical off axis response to be quite small, but likely measurable.

Mod 3 has a more pronounced phase effect, but it's far from the woofer.

Made homepage on the first post! Congratulations @roci_big_ear, that’s quite an achievement. Welcome!

Nice mods! Would love to see off-axis measurements as well.
Thanks, and I am happy to share my findings and tinkering. I am glad you find the mods interesting!
 

Eetu

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Nice mod but an 80dB scale makes everything seem a lot flatter than it is. 6dB difference from 2k to 10k doesn't seem that impressive, considering that with a higher resolution measurement rig like the Klippel high Q peaks/dips would show up more.

Here's No Audiophile measurements/review btw:
Behringer_Truth_B2031A_On_Axis_Frequency_Response.jpg

Doesn't seem to have such a pronounced crossover dip. He also did a tweeter mod including removing the grill and 'diffuser'. Ah someone just mentioned it as well.
 

YSC

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nice and a budget option!

but as a sidenote I did impress more by Genelec after seeing this, you have Genelec to deisgn the whole thing ground up, and even with the great cabin and waveguide copied Behringer can't get nearly close to the original Genelec, yet Genelec usually don't cost an arm and a leg to buy
 
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roci_big_ear

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Great Post! Do you have any measurements for your B3031a?
Here are my 2 B3031A, along with the single B2031A. They are all moded now in a similar way and measured in exactly the same place and way.

Unfortunately, I don't have plots before modifications, but it seems the B3031A tweeter is just flatter.

All Behringers.png


you have Genelec to deisgn the whole thing ground up, and even with the great cabin and waveguide copied Behringer can't get nearly close to the original Genelec
I thought the same, but then looked at the frequency response of the Genelec 1031a and it is not super flat either. I haven't seen a teardown, but I guess the circuit is completely different based on pictures of the back panel. And to Behringer's credit, I think they've improved on some things, such as the downward-facing connectors on the back and the 3 times more powerful amps. But regardless, unless they licensed it somehow, the copying is apparent.
 
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Bennyboyph

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Here are my 2 B3031A, along with the single B2031A. They are all moded now in a similar way and measured in exactly the same place and way.

Unfortunately, I don't have plots before modifications, but it seems the B3031A tweeter is just flatter.

View attachment 188791
Very nice! What mods did you make to the 3031a? How are your dip switches set for the above trace?
 
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roci_big_ear

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Very nice! What mods did you make to the 3031a? How are your dip switches set for the above trace?
The dip switches are all set to 0. B3031A has an additional "smiley" trimmer, and the trimmers were enough to flatten the curve. I didn't do any soldering on them.
 

Ajax

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Impressive work - thank you.

This is what it is all about for me. Hearing a problem (too bright), confirming the problem is real (via measurements) and then addressing / fixing the problem.

This is where Amir and ASR offers a valuable service to manufacturers, should they choose to avail themselves.
 
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