Bass shaker - as a substitute for Sub

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I was wondering if a bass shaker could be a substitute for a subwoofer.

my reasoning being - my speakers no matter what will not reach 20hz, they even might not reach 30hz (i don't know yet as i'm waiting to source original woofer drivers - as for now i use substitute), regardless 20hz they will not reach.

so my first idea was to take upon myself a first diy speaker project - building a subwoofer capable of 20hz or even lower.

but - i have no experience, sub will probably be big 250L+, if i succeed - it will shake the whole room probably with the whole building, while the response might not be great - i don't know if my room will even allow such low frequencies (i have acoustic treatment, but currently my treatment is effective in 40hz and upwards range probably. and really i'm not ready yet to build helmholtz resonators or advanced acoustic treatments...

so, i stumbled upon Bass shaker idea - its seems reasonably simple to implement, it will operate from maybe 30hz and lower only (i will see how my speaker performs with original woofers), vibrations will be isolated to the couch...i mean, it seems like an interesting solution to me.

My concerns that come to mind -
1) what are the frequency response of those devices? or in other words - can such a device have somewhat flat frequency response? (or at least smooth response) - or do they have a sharp peek in a very narrow frequency?
if its the later, then i would say its a bad idea for music.

2) i will need some kind of time delay, as the distance will be different (though i will need this with subwoofer as well, as i will not be able to position the woofer next to speakers - space constrains)

what are your thoughts?

I know that what i'm asking might be considered a blasphemy, but if that's the case i would like to understand 'why'. also i'm not looking for reference level yet - im looking for 'reasonable' and practical.

Thank you
Just speculating, but it might be OK for sound effects but not natural for music. Depends on your music tastes.

Really not much below 32 Hz in organ music and anybody would guess on hearing 32 Hz that it is 16 Hz that's playing.

Run RTA on your sources and see if you have anything any lower. Really really hard to pump enough air below 30 Hz to be audible without heroic measures. But with some EQ, 15-inch drivers can go to 30 Hz.

It will work down low, but like a speaker, the bass shaker is going to have a resonance and roll-off. Multiple options shown here with manufacturer's specs:

Tactile Transducer Comparison

The graph toward the bottom with force vs. frequency is interesting. Unfortunately, they don't have them for all units. Both units they show are rolling off the lower frequencies though.

One thing you haven't mentioned is room gain. Most designers are counting on that to offset some of the natural roll-off of a typical speaker. You can wind up with flat in-room response even though the anechoic response is rolling off.

Graph here assumes 7 dB/octave gain below 40 Hz. Obviously this is going to be room dependent, so in your case will likely be different.

Sealed vs. Ported Subwoofers | SVS

Many subwoofer designs use DSP-based equalization to boost the lower frequencies. It makes for a smaller package, and with excursion, power, and DSP more affordable these days, it's often an easier solution if you want flat output to 20 Hz.

If you don't like those ideas, infinite baffle is another way to go. Those will get you down to the range of the driver's natural resonance, which can be quite low with the right speaker. Some people put them in a closet. I've seen others in ceilings or floors. You often see multiple woofers used in these configurations, as the users are going for extreme output.
I mounted a bass shaker under the front seats of a Land Cruiser and used a car amp with adjustable crossover/gain/eq to drive them in addition to the standard four speakers plus after market powered sub box.
This worked out to be a lot of fun but be warned with the right programme the shaking blurred one's vision.
In a sofa home situation I expect you will need EQ to get it to sound/feel right.
Try it out and have some fun with it, it is guaranteed to add the tactile bass that only big speakers/high power can deliver.

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