How can I build a better pulsed pressure generator?

[Joerg]

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.

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.

 

[Spehro Pefhany]

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

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

Found his entire 1960 650-page book here:-
http://www.sciencemadness.org/library/books/projects_for_the_amateur_scientist.pdf



Best regards,
Spehro Pefhany

 

[axolotl]

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.

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.

http://www.usspeaker.com/lab12-1.htm

http://www.usspeaker.com/B&C-21SW152-1.htm

Kevin Gallimore

 

[Joerg]

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.

http://www.usspeaker.com/lab12-1.htm

http://www.usspeaker.com/B&C-21SW152-1.htm

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

 

[Jasen Betts]

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'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

########
/| /| #
[ |[ | ===[] <-- DUT
\| \| #
########
^ ^
| |
p/2 p

Each driver sees only half the pressure differential.


If you're having problem related to the drivers moving too far you may
need to fill some of the voids with something rigid - Say, a wooden cone
that the driver's cone almost meets at full extension. any unused
volume in the pump chanmber should not be filled with compressible gas
as that just reduces the pump's efficiency.

 

[Joerg]

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'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

########
/| /| #
[ |[ | ===[] <-- DUT
\| \| #
########
^ ^
| |
p/2 p

Each driver sees only half the pressure differential.


If you're having problem related to the drivers moving too far you may
need to fill some of the voids with something rigid - Say, a wooden cone
that the driver's cone almost meets at full extension. any unused
volume in the pump chanmber should not be filled with compressible gas
as that just reduces the pump's efficiency.

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.

 

[whit3rd]

John Fields wrote:

That's exactly what I am looking for, but as a nice reliable unit with a
metal piston, rings and the ability to run oil-less for some tens of hour.

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.

 

[Ralph Barone]

Tom Danley is the guy to go to for high SPLs. The Servodrive subwoofer
was a product of an earlier company, Intersonics.


Here's a picture:

http://www.cstone.net/~dk/servodrive.jpg

Here's a link to the patent. Mr. Danley has several for high SPL generators.

http://www.freepatentsonline.com/4564727.pdf

Kevin Gallimore

Or http://www.rotarywoofer.com

 

[Joerg]

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.

I have seen some from Peavey, Eminence and others but they didn't seem
to have the travel needed.

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.

There you lost me. You mean a long stand pipe where a water column
ratchets down a bit by its weight and creates an air pressure pulse?

Maybe that could work but I am trying to work without fluids here.
Because that could make a huge mess.

 

[Greegor]

Do the old type Wagner vibratory paint sprayers
only eject paint? I always thought that they
pushed a lot of air to carry a small bit of paint.

You described how much paint they move but
are you 100% certain that they don't move
any volume of air to convey the paint?

 

[Joerg]

Whups... missed a word there. The paint cup is *not* pressurized by
the gun... only by exterior atmospheric pressure. You can use longer
suction tubes to pull paint directly from a gallon or 5-gallon
can... I think the painter will pull paint upwards 3-4 feet or more,
once the pump has primed and the suction has started.

But those things clog up a lot if you use sturdy paint, plus the
cleaning is such a lengthy hassle. Those are the main reasons why my
Wagner sits parked in a cabinet for around 15 years now and we have gone
back to brush and roller.

 

[[email protected]]

But those things clog up a lot if you use sturdy paint, plus the
cleaning is such a lengthy hassle. Those are the main reasons why my
Wagner sits parked in a cabinet for around 15 years now and we have gone
back to brush and roller.

+1

Mine has been sitting on a shelf, in its original box, unused, for
over thirty years.

 

[Joerg]

+1

Mine has been sitting on a shelf, in its original box, unused, for
over thirty years.

I was tempted to use it when we painted our house earlier this year but
then decided to use ye olde brush and roller. I think the Wagner would
have had a hard time with the rather thick Sherwin-Williams Duration
paint. 9 gallons later ... done

 

[[email protected]]

I was tempted to use it when we painted our house earlier this year but
then decided to use ye olde brush and roller. I think the Wagner would
have had a hard time with the rather thick Sherwin-Williams Duration
paint. 9 gallons later ... done

I don't think I've ever had mine clog up during a project. On the
other hand, almost every paint I've ever used it with, has had to be
thinned at least slightly to meet the Wagner's viscosity
requirements. I've sprayed oil-based primer, latex primer and finish
coats, and Kelly-Moore "Dura-Poxy" waterborne acrylic enamel
successfully.

I understand that some paints are of the "Do not thin before
application - really!" They probably wouldn't be a good choice for
this sort of sprayer.[/QUOTE]

Those tend to be the best paints for the house, though.

 

[Joerg]

I was tempted to use it when we painted our house earlier this year but
then decided to use ye olde brush and roller. I think the Wagner would
have had a hard time with the rather thick Sherwin-Williams Duration
paint. 9 gallons later ... done

I don't think I've ever had mine clog up during a project. ...[/QUOTE]


I did exactly one project with this Wagner, a lattice fence. It clogged
up about every 20-30 minutes. The Wagner may be good for thin paint but
IMHO not for robust outdoor Latex paint.

... On the
other hand, almost every paint I've ever used it with, has had to be
thinned at least slightly to meet the Wagner's viscosity
requirements. ...

Well, that's just the point. I do not wish to compromise the
specification of the product just to make a tool work.

... I've sprayed oil-based primer, latex primer and finish
coats, and Kelly-Moore "Dura-Poxy" waterborne acrylic enamel
successfully.

I understand that some paints are of the "Do not thin before
application - really!" They probably wouldn't be a good choice for
this sort of sprayer.

The Sherwin-Williams can be thinned but they recommended not to do that.
Plus it might compromise the warranty. In the end doing the whole house
with roller and (small) brush was less onerous a job than I thought.
Considering that the pros want $6-7k for this job we came out ahead
financially as well because that would have been after-tax money.

We wanted the best paint there is and this one seemed to come really
close to that requirement. Of course, we waited for the 40% off sale

 

[Joerg]

So, didja get it working yet? Wha'd you do?

(Please let the curious know what your solution was, once you get there).

I will. Right now a much more pressing issue has come up plus a client
needs support, so the pressure generator will likely be on ice for 5-10
days. It is not something super urgent, I won't need it until spring
2014. But then I am really going to need it and it has to work.

So far I am still using the rat-tat-tat-tat compressor and a makeshift
valve for the pulsing (excenter in drill chuck hits valve switch handle).

 

[John K]

So far I am still using the rat-tat-tat-tat compressor and a makeshift
valve for the pulsing (excenter in drill chuck hits valve switch
handle).

Joerg, go to Home Depot or Grainger and get a 26dB Multi-Position
Earmuff.

They are lightweight and the headband is adjustable so you can get the
optimum position for maximum noise reduction and comfort. I got a pair at
Home Depot and was amazed at the attenuation they provide. They are light
and very comfortable and you can wear them for long periods with no
problem. They should really help with the impact noise from the air
compressor.

Here's a link. Note how the headband presses against the center of the
earmuff. This allows it to tilt properly to fit your ear and the side of
your head.

"http://www.grainger.com/Grainger/CONDOR-Ear-Muff-2AAG4"

$11.77 is very cheap for the comfort they give.

Contrast that with the Leightning Hi-Visibility Earmuffs. They use a
steel band which may be hard to adjust when the earmuff is on your head.
Almost 3 times the price, although you certainly can spend a lot more and
get a lot less. Note also they do not state the amount of attenuation
provided:

"http://www.walmart.com/ip/Leightning-Hi-Visibility-Earmuffs-
1013941/25561720"

JK

 

[whit3rd]

whit3rd wrote:

I have seen some from Peavey, Eminence and others but they didn't seem
to have the travel needed.

Titanium piston, and they specify the throat to be a little under an inch.
Can you connect a dozen of them to a single plenum to make up enough
volume moved?

There you lost me.

Yeah, it's a long shot: basically, I was suggesting a slow-filling tank followed
by an abrupt loss-of-pressure, and trying to get high frequency harmonics
from a fast-release-of-pressure valve. You'd get a pressure rise as the tank
filled, and a pressure drop as the tank vented, and you could servo it
to make a sawtooth, with F, 2F, 3F... harmonics.

Even a longer shot, use a tuned organ pipe on the outlet, and let the
ventpipe resonance be your pressure modulation.

 

[Joerg]

Titanium piston, and they specify the throat to be a little under an inch.
Can you connect a dozen of them to a single plenum to make up enough
volume moved?

Yes, but at some point the whole enchilada will get too far in the
direction of yet another science project. I was looking for something
simple.

Yeah, it's a long shot: basically, I was suggesting a slow-filling tank followed
by an abrupt loss-of-pressure, and trying to get high frequency harmonics
from a fast-release-of-pressure valve. You'd get a pressure rise as the tank
filled, and a pressure drop as the tank vented, and you could servo it
to make a sawtooth, with F, 2F, 3F... harmonics.

That's essentially what I am doing right now. Slow filling reservoir
tank, abrupt pressure loss via a switch turned into a makeshift
motor-driven valve. That works. But it isn't very exact and repeatable.
Plus the compressor for the tank replenishment is very loud.

Even a longer shot, use a tuned organ pipe on the outlet, and let the
ventpipe resonance be your pressure modulation.

The next church with a pipe organ is around 40 miles away and they
probably won't let a Lutheran mess with the innards of their organ

 

[Joerg]

Joerg, go to Home Depot or Grainger and get a 26dB Multi-Position
Earmuff.

They are lightweight and the headband is adjustable so you can get the
optimum position for maximum noise reduction and comfort. I got a pair at
Home Depot and was amazed at the attenuation they provide. They are light
and very comfortable and you can wear them for long periods with no
problem. They should really help with the impact noise from the air
compressor.

Here's a link. Note how the headband presses against the center of the
earmuff. This allows it to tilt properly to fit your ear and the side of
your head.

"http://www.grainger.com/Grainger/CONDOR-Ear-Muff-2AAG4"

$11.77 is very cheap for the comfort they give.

Contrast that with the Leightning Hi-Visibility Earmuffs. They use a
steel band which may be hard to adjust when the earmuff is on your head.
Almost 3 times the price, although you certainly can spend a lot more and
get a lot less. Note also they do not state the amount of attenuation
provided:

"http://www.walmart.com/ip/Leightning-Hi-Visibility-Earmuffs-
1013941/25561720"

Then I'd also need earmuffs for all the others in the house, tell people
not to call between 8:00am and 6:00pm, put a note on the doorbell to
forget about ringing it, and get custom-made earmuffs for two labarador
retrievers

Anyhow, it's also that the current scheme does not produce a very
repeatable pressure pulse. Often I need umpteen attempts to get it close
to what it was yesterday.