[Listening test/DIY] Lonpoo LP42M - active minimonitors, a simple tweak to make them passive

Product: Lonpoo LP42M - active bookshelf loudspeakers
Manufacturer: Lonpoo - China
Suggested retail price: circa €/$110/pair, depending on offers and shipping
Reviewer: Lucio Cadeddu - TNT-Audio Italy
Reviewed: May, 2025

A few weeks ago I reviewed the new LP42M active mini speakers, with results that were not exactly flattering. In fact, these new speakers from Lonpoo were a bitter disappointment, so much so that they deserved a resounding failure without appeal. However, the new cabinet and the new drivers left some hope and so I decided to go hunting for the real culprit for such a disappointing performance. In that review I suspected that the internal electronic section was largely to blame for the compromised performance. So I decided to eradicate it completely and make the LP42M completely passive.

A 10 minute tweak

The LP42M are active speakers, with one that acts as master and therefore contains all the electronic parts (DAC, power supply and amplifier) while the other, the slave, is a completely passive speaker. Let's modify the master and make it practically identical to the slave.

Accessing the inside of the speaker containing the electronic section is very easy: just unscrew the 6 Allen screws that fix the metal plate to the speaker cabinet. The internal amplifier has two outputs: one connected to the external terminals that connect the slave speaker and one that goes to the internal drivers. Two small white plugs (see pic above) perform the task of connecting everything. It is sufficient to unplug them from the board and join them together with the method you prefer. I opted to cut the two pieces (the cable is long enough to allow this operation) join them and then secure everything with heat-shrink tubing. In this way the mod is easily reversible. If you want, you could put fast-on type terminals, but it is an additional contact on the signal path: the bare cable is better, in my opinion.

It is impossible to make a mistake, because the cables are of the red-black type, so just join the same colours and you're done. In this way the output connectors that carried the amplified signal to the slave speaker become inputs for an external amplifier for the master speaker, while the slave speaker is ready to be amplified and does not need to be modified. If you want to avoid having to join the two pieces, you could solder the cable that goes to the drivers directly to the input terminals, but the short length of the internal wiring makes the operation not exactly easy.

Finished! There is nothing to solder, it is really a 10 minute job (even for those who are completely new to DIY!) including disassembly and reassembly. The external appearance of the speakers does not change. At this point you have two (almost) identical passive speakers that you can connect to your favourite amplifier. Why do I say almost? Because one speaker (the master) still contains the electronic boards, which take up a bit of space inside. If you wish, you could remove it completely and close the back of the speaker with a small MDF panel of the same shape and size.

While you're at it, wrap some thin foam around the internal wiring that carries the signal to the master speaker drivers, so you make it more similar to the slave one. The foam (thin, mind you!) has the effect of limiting any vibrations of the cables inside the cabinet, solicited by the air moved by the mid-woofer.

I would also eliminate all the other internal wiring, now useless: just remove the connectors from the board and the front of the cabinet. The less there is that can vibrate with the air moved by the midwoofer, the better. If you want to restore everything to its original condition, take pictures of the positions of the various cables or, better yet, label them with writings, such as "cable that goes to the front LED", "cable that goes to the volume" and so on.

If you wish, you could completely eliminate the internal electronics and replace it with a good integrated circuit (say, a Fosi V3) so as to turn the LP42Ms into active speakers that should finally sound as they can.

N. B. Just to be clear: all these operations must be performed with the master speaker disconnected from the power supply and, once the mod is complete, you will no longer have to connect the LP2M to the power supply! Just connect the speakers to any external amplifier and you're done. The modification is reversible, but in any case it invalidates any warranty on the product. Since the second generation LP42X also suffered from similar problems caused by the internal electronic section, it would be a good idea to make these passive too, if necessary.

Was it worth it?

Absolutely yes! The LP42M, as I had guessed, sound much better this way. First of all you can use an external amplifier and make them play as loud as you want, without the electronic limitation provided by the internal amplifier. And they can play loud, very loud. Moreover, the dip in the mid-range disappears and the bass re-emerges, as if by miracle. Even the dynamics increase significantly, a sign that the drivers had much more to give.

Of course, I performed a direct comparison with the old passive LP42s. These are two completely different speakers, so it is normal to expect significant differences. First of all the sensitivity: with the same volume knob position the old LP42s sound louder, almost +2dB more. In any case, any amplifier of 20 watts will be able to drive them without problems.

Moving on to the differences in tonal balance, these passive LP42Ms sound sweeter and less aggressive and brilliant in the medium-high range. Less shrieking, so to say. The typical characteristic of the old LP42s - that is, a certain aggressiveness in the medium-high range - has disappeared; the overall sound is more refined, musical and enjoyable. Voices benefit from this, being more natural, and string instruments less pungent. In the low range the new passive LP42Ms do better than the old LP42s: the bass goes deeper, with increased impact and authority. This allows you to move the speakers away from the rear wall, also benefitting the midrange, which is now cleaner. Not only that, but 50 cm of distance from the rear wall is enough to improve the image as well, which opens up a little in all directions, becoming more realistic.

From the point of view of speed and dynamics, however, the LP42s take a small revenge: the impulsive sounds, especially in the mid-range, are clearer, faster and more powerful, but this is the only area where I can say that the new LP42M (passive) give way to the old LP42s: it is not enough to tip the scales towards the old speaker. If I had to choose, I would have no doubts and I would say that, overall, the LP42Ms are more complete, musical and pleasant. The fact that they can be kept away from the rear wall, then, is a very important plus.

Now the main question: I assume whoever designed the LP42Ms listened to them as passive speakers at least once before inserting the electronic section. The choice of drivers, the design of the cabinet and of the filter, the choice of reflex alignment must be performed when the speakers are passive, right? If so, how could the designer not have noticed that the sound got much worse once the electronic section was inserted? Or, perhaps, he was told: make a new speaker but stay within this budget. He took one of the many ready-made boards found on the Web (e.g. Aliexpress) and stuck it in, without worrying too much.

Conclusions

If you have purchased the LP42M (or even the second generation of LP42X) and are not satisfied with their sound, now it is possible for them to sound as they should, making them passive and amplifying with an external amp. Alternatively, you can still make them active simply by installing a small amplifier such as the Fosi V3 or something similar inside the master speaker. The possibilities are endless, of course, you could even still have Bluetooth, digital inputs and remote control if the chosen amplifier had them. Lonpoo, informed of the positive outcome of this modification, should have been convinced to market the LP42M as passive, simply by taking two slave speakers (that is, without the electronic part) and putting them in a single, new package. A zero-cost operation, which could repeat the sales success of the first, incredible, LP42, especially if the elimination of the electronic part allows - as is logical - a significantly lower price.

Update December 2025: Lonpoo listened to me and released the LP42 MX, a passive version of the aforementioned LP42M. The link takes you to the review here on TNT-Audio.

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Lonpoo LP42M - active mini-monitors

A simple mod to make them completely passive

A 10 minute tweak

Was it worth it?

Conclusions