What is Reddit's opinion of Walfront Resonance Speaker,1Pcs 50MM 2Inch All Frequency Resonance Speaker Vibration Strong Bass Louderspeaker (4Ω,25W)?

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Ive seen something as simple as a speaker with the cone cut off and hotglued to the plate.

This like this exist that wont break the bank.

Bear in mind the exciter should be sturdily mounted so that the energy goes directly into the plate.

You're going to need more of an AMP than a preamp to get the plate to move though. The pre would be if you also have a pickup on the plate that you're using to go back (in the case of a reverb effect). you would have a pickup or another transducer connected to just the plate for that.

An amp to excite the plate, and a pre connected to the pickup for the return trip.

A lot of these ideas will not work so be wary of the advice. I actually work and do rf test in shielded rooms for rf testing. Vibrational or resonance speakers vibrate the surface they are on and turn the surface into a speaker diaphragm. Most shield rooms are sheet metal laminated on some composite wood core. Those vibration speakers do penetrate as they oscillate both sides of the wall. I've used them with success. Here is one from amazon. You just stick to the outside of the room with some pressure and both sides will hear sound. Resonance Speaker,1Pcs 50MM 2Inch All Frequency Resonance Speaker Vibration Strong Bass Louderspeaker (4Ω,25W) https://www.amazon.com/dp/B074H4S71B/ref=cm_sw_r_cp_apa_KsoiAbDKMXN0H amps are easy to come by. You can even underdrive this one with a 10W amp and still meet your needs.

One can use a vibro speaker installed close to the neighbour's floor or walls.

https://youtu.be/rdtWxBpb3jw?t=142

i think best would be a loop pedal and play the backing tracks yourself, but unfortunately, they're not cheap for being standalone pedals

another option you might try, for playing pre-recorded audio, is a transducer speaker, or even more affordable, "vibration speaker" ... turn any surface into a speaker!