small micro speakers with a rich soundstage

i got a ebay package of 4 passive radiators (4"), sadly they didn't include a mechanism to add weight to them easily.

search ebay for the radiators with this term:
4 inch Horn Radiator Woofer Speaker Passive Radiator Auxiliary Bass 105x105mm

they cost about 8$ for a pair at max

since i wanted to test with and without extra weight, i decided to glue a 80g 0.75mh coil on one radiator on the inside to measure the differences.

without extra weight: a huge bump (about 10db) at 200hz and nearly no real bass response.

then i swapped to the radiator with inductor, and found out that the radiators glued in inductor was touching the TB speaker's magnet, which meant the enclosure isn't deep enough.

a temp solution i applied was mounting the passive radiator backwards.

then i measured, and found out that the speakers now have a very nice bass response, especially for their size, they sound like bigger bookshelf speakers in a room of 8*12 meter, and just one speaker (mono) can easily fill the room with a very rich experience sound (almost as if you were in the recording studios), they go pretty low as well: down to 55HZ with ease (lower than i expected)

the response at 1 meter distance, in the 8*12meter living room, please don't go lower than 40hz, as the distortion starts to increase by alot (average 10% at the rms wattage, where 45-25000hz is 2% distortion at the rms wattage)

and for the radiator depth issue, i ordered a new backplate, one which is 12mm deeper than the original, meaning i can mount it as it's designed when it arrives :) (should be 7th of june)

costs / speaker right now is: 160/piece (when ordering the enclosured at 3dhubs), which can be reduced alot if you're going for MDF wood instead of 3d printed (i printed the models in colorfabb ngen)

costs would then be more like: 110 a piece.

anyhow, i hope this'll be enough regarding this update :P

going to update project files right now.

i started sanding one enclosure to make it matte black instead of glossy black.
looks way nicer now, also sanded round corners and removes sharp edges.

i also applied the second 4" speaker to the back of the speaker to let it be a temporarily passive radiator.
then i measured the response at 1meter away, and found out that the bass response wasn't exactly what i hoped for.

but that's to be expected with such a small speaker in the middle of a 25 square meter room.
the measure showed a minimal rolloff above 15k when at 1meter distance, nothing too serious luckily.

the lower rolloff was lowered from 200hz to 100hz, but was a more steep one than the original measure (passive radiator effect?)
still, it goes as low 80hz with ease (-6db point) with the temp passive radiator.

overall very pleased with something as tiny as these speakers.

next steps are:
sand second enclosure
wait for the final passive radiators and mount them
screw the terminals in
solder the internal wiring
fill the internals a bit with dampening wool to help with possible resonances.

So i got the enclosures in, and decided to assemble one speaker (i don't have the passive radiators yet, so i laid the rearside flat on my bed)

luckily everything fitted in the first try, so no reprints needed! (saving costs and filament) :D

Hooked up to a 30W rms at 8 ohm amplifier.

Then i did a measurement from 45-20000hz, and here's the nearfield result:

As one can see, it starts to roll off slowly at 200hz, but it goes as low as 70HZ (without passive radiator!), the high end is very smooth and constant, no slight roll-off at all.

Okay, they're not the loudest (about 86dB @ 1W, 1M), but for a micro monitor they do exactly what's needed: deliver rich sound at a flat response, without too much distortion and staying low cost :)

Distortion is about 15% below 45hz on the 3rd harmonic (did a seperate 20-20000hz test). So i don't recommend them to play low at high volumes (the 4" fullrange speaker goes over it's xmax causing the distortion at those 30watts)

There is a slight peak in the distortion at 1500hz too (2nd harmonic), peaking at about 5.3% (possibly the resonance frequency of enclosure)

Overall the distortion stays at 2% average, which is OK.

Next up is to wait for the passive radiators and connection terminals so i can assemble the rearside of these tiny monsters :)