How can I build a better pulsed pressure generator?

ure.

I doubt automatic braking is done with a electrically activated piston, I would imagine it consist of a pump and some proportional valves

for abs I believe it is called a modulator, I think it is just valves and a pump

-Lasse

Possible but a pump would have to come on darn fast or run all the time. Running all the time makes it prone to wear and failure.

ABS is easier, that just takes pressure away from the individual brake lines so that the corresponding wheels do not lock up.

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with an accumulator it only need to run until the pressure is up, it not li ke you need a continues flow and the volume involved is small

I think it has a pump/accumulator so it can get the pressure back up if you only bleed pressure you'd run out of pedal travel or not brake enough on a changing surface

-Lasse

Yes, true, I was still thinking in terms of my old Citroen 2CV which did not have any brake assist.

Well, I guess that idea won't fly then either :-(

For quiet you need a different sort of pump. perhaps scroll or Roots. unlikely to be cheap.

OTOH it may be possible to muffle the intake with the right sort of accoustic ducting (car exhaust muffler?) and perhaps soundproof the compressor room.

Unfortunately I do not have a compressor room. The compressor has to live in the office for those tests.

AIUI The "doof-doof car" builders just wire them in series or parallell.

Air looses 1/8 of it's volume if compressed 2PSI you could add a passive comonent to the driver on the high pressure end to compensate for the shorter throw and therefore lower innertial load.

But in my opinion 12% is not a large mismatch, simple is probably better.

Later Citroens had full hydraulic brakes.

You could look at electric trailer brakes, that seems to be an electric-hydraulic system, judging from the appearnce of the hardware I'd guess ballpark 100W.

The 1960s DS model had pumped hydraulic brakes, suspension, steering, and gearshift.

If the pump stopped pumping, you were left with a mechanical emergency brake, steering that needed two people, no gearshift, and bottomed suspension.

Hailed as "The Car of the Future".

De Gaulle was in one that was ambushed, and managed to get away.

Only the DS series, and maybe XM and GS. For the smaller ones that is way too expensive.

I did look. They are unfortunately fully electric, no hydraulic fluids there.

Sounds like a construction project. Wooden box about 18" square, two hand wound solenoid coils with an iron bar between them, and a sheet of plywood mounted on the center of the iron bar the same size as the box.. You power one coil, the sheet of plywood is pulled to one side and you get a high pressure pulse. Power other coil, and you get a low pressure pulse. Apply different power levels to each coil, and you can get interesting waveforms!

Charlie

IIUC the series assembly of such speaker still won't solve the problem that the front speaker has to do full excursion for the require pressure of 4psi. So its surround would still fail after some time, like it did on mine. They had enough power, they just could not stand the pressure.

I can almost see the C.L. Stong illustration of that setup.

Found his entire 1960 650-page book here:-

Best regards, Spehro Pefhany

Perhaps the easiest solution to your problem is simply a better quality speaker. Look for something with a high XMAX. The LAB 12 is a good bang for the buck. If you need more, they are made. They crank out the pressure all night.

Kevin Gallimore

But I can't spend a kilobuck just on the speaker :-)

I'm not sure that you're using those physics terms ( "power" "pressure" ) correctly because putting them in (mechanial) series halves the pressure.

not to scale

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Ah, thanks, now it becomes clear. The speaker behind creates some pressure that helps the membrane of the front speaker not to see the full pressure differential.

Adjustment would be better by series resistors because pegging introduces a hard non-linearity.

Have you looked into horn-driver off-the-shelf speaker components? The back pressure problem should get easier if you use that kind of specialized drive module instead of a foam-surround woofer.

Mainly, though, why can't you just use a limited volume, flow-limited (capillary tube) fill, and A/B your trial sensor against a standard? It'll make a ramp, and adding a burp valve will make that into a sawtooth. Dunno how much 40 Hz harmonic you could make, though.

Or