Monolith B5 bookshelf speaker measurements and mod

[roci_big_ear]

I bought the Monolith B5 bookshelves from Amazon, aiming to use them as surround speakers to complement my HT system with Monolith subs. The manufacturer makes impressive frequency response claims:

That's +/- 2dB, outside of that dip around 10.5 kHz! Naturally, the first step was to measure them:

Here's what I got:

Not bad, but much more smiley face than the claim. I guess my "reference angle" wasn't right...

The wide dip at 1.6 kHz is -5 dB and I was determined to fix it. Time to do surgery:

The long inductor is in series with the woofer. All other components are filtering the tweeter.

My strategy was to lift the woofer cut off, for more overlap around that cross-over to counter the dip. Everything is covered in goo, so my best path of action was to tap onto the inductor around 1/3 the way. This way I could short the 1/3 tap point to either terminal, allowing me to try different inductances.

What the image shows I deemed optimal. This flattened the middle, though caused a narrow bump 6 kHz.

Overall much better result in my opinion. A capacitor in parallel with the woofer might have fixed the bump, but I did not have appropriate values handy. Good enough.

With the mod, I think the speakers punch above their weight. It's sad they didn't come like this out of the box.

 

[SlowJim]

Thanks for sharing. I have been really impressed by my Monoprice DT-5BT speakers for nearfield use. Bought them for $90 shipped brand new

 

[SlowJim]

How is the low end on these, btw? Look like it falls off quite sharply below 100hz. Comparable to similarly sized speakers or worse?

 

[Ktacos]

Thanks for sharing. I think this could be improved a lot with little effort or money.

Was this mod developed with individual driver responses or just the speaker response as a whole? I would definitely notch out the woofer break up, assuming that is where the peak is from. That peak is going to messing up more than just the speakers on axis response, the dispersion the waveguide provides is probably ruined for instance.

 

[norman bates]

maybe add a notch near 6.3khz on the woofer ?

 

[Putter]

I suspect that for the average listener who is doesn't use tone controls, this dip in the midrange becomes a form of loudness compensation since most people don't listen at 'reference levels'. For the listeners who do use tone controls a small reduction in the bass and treble will make it reasonably flat. Those with home theater amps may have automatically corrected. All things considered, it seems like a good value for a sub $200/pr speakers notwithstanding some apparent fudging on the specs.