[MarkB]

Hello all, newbie, so please forgive me if I'm covering a subject
which is old or obsolete...

I heard some time back of some speakers being made to create
ridiculously low-freq noise by effectively swapping the electro-
magnetic part of a large bass speaker for something that was servo
driven. Myths abound, but I'd heard that various armies may have used
this to recreate "real" bomb noises on firing ranges to test the
mettle of those in training...

Anyone know of a project, or even better some plans along these lines
so I might experiment with my own ULF speaker(s)...

Of course, if there's a better alternative then I'd be interested to
hear that too...

Cheers all, Mark.

[Arny Krueger]

"MarkB" wrote in message
ps.com

Hello all, newbie, so please forgive me if I'm covering a
subject which is old or obsolete...

I heard some time back of some speakers being made to
create ridiculously low-freq noise by effectively
swapping the electro- magnetic part of a large bass
speaker for something that was servo driven.

Servo can still mean electromagnetic, and often does. Hydraulics pretty
well fell out of favor for fast-responding servos (e.g., hard drive head
positioners) some decades ago.

Myths abound, but I'd heard that various armies may have used
this to recreate "real" bomb noises on firing ranges to
test the mettle of those in training...

I've heard that compressed air, actual explosives, or natural gas explosions
were commonly used for such things.

[Dirk Bruere at NeoPax]

On 15 Feb, 18:09, "MarkB" wrote:
Hello all, newbie, so please forgive me if I'm covering a subject
which is old or obsolete...

I heard some time back of some speakers being made to create
ridiculously low-freq noise by effectively swapping the electro-
magnetic part of a large bass speaker for something that was servo
driven. Myths abound, but I'd heard that various armies may have used
this to recreate "real" bomb noises on firing ranges to test the
mettle of those in training...

Anyone know of a project, or even better some plans along these lines
so I might experiment with my own ULF speaker(s)...

Of course, if there's a better alternative then I'd be interested to
hear that too...

Cheers all, Mark.

http://neurosis.mit.edu/mjolnir/

Dirk

[MarkB]

On 15 Feb, 18:26, "Arny Krueger" wrote:
"MarkB" wrote in message

ps.com

Hello all, newbie, so please forgive me if I'm covering a
subject which is old or obsolete...
I heard some time back of some speakers being made to
create ridiculously low-freq noise by effectively
swapping the electro- magnetic part of a large bass
speaker for something that was servo driven.

Servo can still mean electromagnetic, and often does. Hydraulics pretty
well fell out of favor for fast-responding servos (e.g., hard drive head
positioners) some decades ago.

Myths abound, but I'd heard that various armies may have used
this to recreate "real" bomb noises on firing ranges to
test the mettle of those in training...

I've heard that compressed air, actual explosives, or natural gas explosions
were commonly used for such things.

Should have been a little more explicit....I had hydraulic servos in
my head, but would guess you could get a faster response from an
electrical one...

If this idea is out of vogue, whats the current best thinking for
getting the lowest possible freq ? I want this for a music application
so real explosives may not be the answer ;-)

[MarkB]

On 15 Feb, 18:37, "Dirk Bruere at NeoPax"
wrote:
On 15 Feb, 18:09, "MarkB" wrote:





Hello all, newbie, so please forgive me if I'm covering a subject
which is old or obsolete...

I heard some time back of some speakers being made to create
ridiculously low-freq noise by effectively swapping the electro-
magnetic part of a large bass speaker for something that was servo
driven. Myths abound, but I'd heard that various armies may have used
this to recreate "real" bomb noises on firing ranges to test the
mettle of those in training...

Anyone know of a project, or even better some plans along these lines
so I might experiment with my own ULF speaker(s)...

Of course, if there's a better alternative then I'd be interested to
hear that too...

Cheers all, Mark.

http://neurosis.mit.edu/mjolnir/

Dirk- Hide quoted text -

- Show quoted text -

Brilliant Dirk....exactly along the lines I'm looking for, but maybe
there's a more elegant solution ?

[Richard Crowley]

"Dirk Bruere at NeoPax" wrote...
"MarkB" wrote:
Hello all, newbie, so please forgive me if I'm covering a subject
which is old or obsolete...

I heard some time back of some speakers being made to create
ridiculously low-freq noise by effectively swapping the electro-
magnetic part of a large bass speaker for something that was servo
driven. Myths abound, but I'd heard that various armies may have used
this to recreate "real" bomb noises on firing ranges to test the
mettle of those in training...

Anyone know of a project, or even better some plans along these lines
so I might experiment with my own ULF speaker(s)...

Of course, if there's a better alternative then I'd be interested to
hear that too...

Cheers all, Mark.

http://neurosis.mit.edu/mjolnir/

Yeah, those big solenoid positioners from the old
Winchester disc-pack drives would "walk" the drive
(the size of a dishwasher) across the room if you
did cylinder seeks at the resonant frequency of the
box mass. :-)

There is a commercial vendor (whose name I forgot)
who makes big sound-reinforcement subwoofers
with servo (stepping?)-motor technology driving the
cone(s). Don't remember any hydraulic (oil or water)
implementations.

[GregS]

In article .com, "MarkB" wrote:
On 15 Feb, 18:26, "Arny Krueger" wrote:
"MarkB" wrote in message

ps.com

Hello all, newbie, so please forgive me if I'm covering a
subject which is old or obsolete...
I heard some time back of some speakers being made to
create ridiculously low-freq noise by effectively
swapping the electro- magnetic part of a large bass
speaker for something that was servo driven.

Servo can still mean electromagnetic, and often does. Hydraulics pretty
well fell out of favor for fast-responding servos (e.g., hard drive head
positioners) some decades ago.

Myths abound, but I'd heard that various armies may have used
this to recreate "real" bomb noises on firing ranges to
test the mettle of those in training...

I've heard that compressed air, actual explosives, or natural gas explosions
were commonly used for such things.

Should have been a little more explicit....I had hydraulic servos in
my head, but would guess you could get a faster response from an
electrical one...

If this idea is out of vogue, whats the current best thinking for
getting the lowest possible freq ? I want this for a music application
so real explosives may not be the answer ;-)

Well, I just had gone upstairs in the building and the air handlers were
putting out some really heavy 7-8 Hz stuff. It would be hard to get a regular
speaker to do the same SPL.

The Servo Drive used a motor. Ther was a horn version.
http://www.servodrive.com/Download_f...ContraBass.pdf

greg

[GregS]

In article , (GregS) wrote:
In article .com, "MarkB"
wrote:
On 15 Feb, 18:26, "Arny Krueger" wrote:
"MarkB" wrote in message

ps.com

Hello all, newbie, so please forgive me if I'm covering a
subject which is old or obsolete...
I heard some time back of some speakers being made to
create ridiculously low-freq noise by effectively
swapping the electro- magnetic part of a large bass
speaker for something that was servo driven.

Servo can still mean electromagnetic, and often does. Hydraulics pretty
well fell out of favor for fast-responding servos (e.g., hard drive head
positioners) some decades ago.

Myths abound, but I'd heard that various armies may have used
this to recreate "real" bomb noises on firing ranges to
test the mettle of those in training...

I've heard that compressed air, actual explosives, or natural gas explosions
were commonly used for such things.

Should have been a little more explicit....I had hydraulic servos in
my head, but would guess you could get a faster response from an
electrical one...

If this idea is out of vogue, whats the current best thinking for
getting the lowest possible freq ? I want this for a music application
so real explosives may not be the answer ;-)

Well, I just had gone upstairs in the building and the air handlers were
putting out some really heavy 7-8 Hz stuff. It would be hard to get a regular
speaker to do the same SPL.

The Servo Drive used a motor. Ther was a horn version.
http://www.servodrive.com/Download_f...ContraBass.pdf


There is a horn model.
http://www.servodrive.com/basstech7.html

[Dirk Bruere at NeoPax]

MarkB wrote:
On 15 Feb, 18:37, "Dirk Bruere at NeoPax"
wrote:
On 15 Feb, 18:09, "MarkB" wrote:





Hello all, newbie, so please forgive me if I'm covering a subject
which is old or obsolete...
I heard some time back of some speakers being made to create
ridiculously low-freq noise by effectively swapping the electro-
magnetic part of a large bass speaker for something that was servo
driven. Myths abound, but I'd heard that various armies may have used
this to recreate "real" bomb noises on firing ranges to test the
mettle of those in training...
Anyone know of a project, or even better some plans along these lines
so I might experiment with my own ULF speaker(s)...
Of course, if there's a better alternative then I'd be interested to
hear that too...
Cheers all, Mark.
http://neurosis.mit.edu/mjolnir/

Dirk- Hide quoted text -

- Show quoted text -

Brilliant Dirk....exactly along the lines I'm looking for, but maybe
there's a more elegant solution ?

Cut a hole in the outside wall of your house and face the cone inwards?
Actually, this is the most practical and elegant solution I've come across:
http://www.hackaday.com/2006/09/27/rotary-subwoofer/

--
Dirk

http://www.onetribe.me.uk - The UK's only occult talk show
Presented by Dirk Bruere and Marc Power on ResonanceFM 104.4
http://www.resonancefm.com

[MarkB]

On 15 Feb, 20:29, Dirk Bruere at NeoPax wrote:
MarkB wrote:
On 15 Feb, 18:37, "Dirk Bruere at NeoPax"
wrote:
On 15 Feb, 18:09, "MarkB" wrote:

Hello all, newbie, so please forgive me if I'm covering a subject
which is old or obsolete...
I heard some time back of some speakers being made to create
ridiculously low-freq noise by effectively swapping the electro-
magnetic part of a large bass speaker for something that was servo
driven. Myths abound, but I'd heard that various armies may have used
this to recreate "real" bomb noises on firing ranges to test the
mettle of those in training...
Anyone know of a project, or even better some plans along these lines
so I might experiment with my own ULF speaker(s)...
Of course, if there's a better alternative then I'd be interested to
hear that too...
Cheers all, Mark.
http://neurosis.mit.edu/mjolnir/

Dirk- Hide quoted text -

- Show quoted text -

Brilliant Dirk....exactly along the lines I'm looking for, but maybe
there's a more elegant solution ?

Cut a hole in the outside wall of your house and face the cone inwards?
Actually, this is the most practical and elegant solution I've come across:http://www.hackaday.com/2006/09/27/rotary-subwoofer/

--
Dirk

http://www.onetribe.me.uk- The UK's only occult talk show
Presented by Dirk Bruere and Marc Power on ResonanceFM 104.4http://www.resonancefm.com- Hide quoted text -

- Show quoted text -

Thanks for the replies all....I like the fact that the last one can
get single figures in Hz (supposedly), the commercial horn-driven
thing is probably astounding but I'd imagine the shipping costs alone
(it weighs 920lb !) might be a little exorbitant....

I did run the idea of a large hole in the wall past "the long
suffering one" but strangely she wasn't overly enamoured with this
idea ....

[Eeyore]

MarkB wrote:

Hello all, newbie, so please forgive me if I'm covering a subject
which is old or obsolete...

I heard some time back of some speakers being made to create
ridiculously low-freq noise by effectively swapping the electro-
magnetic part of a large bass speaker for something that was servo
driven.

http://www.servodrive.com/contrabass.html
http://www.servodrive.com/basstech7.html

Graham

[[email protected]]

On Feb 15, 1:09 pm, "MarkB" wrote:
Hello all, newbie, so please forgive me if I'm covering a subject
which is old or obsolete...

I heard some time back of some speakers being made to create
ridiculously low-freq noise by effectively swapping the electro-
magnetic part of a large bass speaker for something that was servo
driven. Myths abound, but I'd heard that various armies may have used
this to recreate "real" bomb noises on firing ranges to test the
mettle of those in training...

Yeah, there are lots of myths, but at least one real
example of such was described in the JAES by Hilliard
back in 1965:

Hilliard, J. K., "High-Power, Low-Frequency Loudspeakers,"
J. Audio Eng. Soc, 1967 July

In it he describes a large tower-mounted horn driven by a
high-speed electro-pneumatic transducer. The purpose of
the device was to test atmospheric propogation of low
frequency sounds so that Saturn V engine tests could be
conducted at the Hunstville test site while minimizing
acoustic interference at nearby population centers:

"The velocity of sound changes with temperature
and wind conditions, and this variation tends to
refract the sound rays. If the velocity increases
with height, the sound rays are bent toward the
ground and an increase or focus will occur in
some areas - which may be at a factor of 10 db
or more. Though the development of missiles
requires almost daily firing of the engines, sites
which are adjacent to residential areas - such
as Huntsville, Cape Kennedy. Sacramento,
Houston, and Vandenberg-must assure that
firing is not made when an acoustic ray focusing
condition exists.

"At the Huntsville and Mississippi test sites, air
modulated loudspeakers have been erected on
60-ft high towers. They radiate several kilowatts
of acoustic power at low frequencies in the region
of 30 to 60 cps. The sound level at a distance of
10 miles or more is above the ambient noise and
so the propagation loss can be measured on a
steady basis. By this method, the normal
propagation is determined and firing is done only
at these times."

The remainder of the article goes on to describe the
development and deployment of a system based on
a linear pneumatic valve which permits the modulation
of an air stream at 40 PSI above ambient with a capacity
of 500 ft^3 per minute. The valve itself only requires
about 100 watts of electrical power, but the actual
acoustical output is derived from the air stream, not
the electrical actuator.

An air stream of 500 ft^3/m at 40 PSI represents
a power source of some 15 killowats. Assuming
Hilliards claims of 15% efficiency is correct (and it's
quite feasible) that suggest an acoustic output of
some 2300 killowats. And he states the design
bandwidth of the system extends from 30 to 60 Hz.
Given the size and resulting directionality of the
horn, it would be entirely reasonable to find sound
pressure levels in excess of 150 dB SPL in close
proximity to the device.

This pales, of course, to the acoustic output of a Saturn
V, which Hilliard states is in the realm of 50 million
acoustic watts, resulting in sound pressure levels
at 10 Hz (the peak in the device's output spectrum)
of 120 dB SPL, 5 miles from the launch site.

By the way, your use of the term "hydraulic" in the subject
is inappropriate, as this concerns the use of systems
based on liquid fluids, completely unsuitable for the
purpose you suggest. Rather, "pneumatic," based on
gaseous fluids, e.g., air is far more appropriate, I would
assert.

[Jerry G.]

What you are talking about is not done with conventional speaker drivers
as what are used for home or studio HiFi.

--

Jerry G.


"MarkB" wrote in message
ps.com...
Hello all, newbie, so please forgive me if I'm covering a subject
which is old or obsolete...

I heard some time back of some speakers being made to create
ridiculously low-freq noise by effectively swapping the electro-
magnetic part of a large bass speaker for something that was servo
driven. Myths abound, but I'd heard that various armies may have used
this to recreate "real" bomb noises on firing ranges to test the
mettle of those in training...

Anyone know of a project, or even better some plans along these lines
so I might experiment with my own ULF speaker(s)...

Of course, if there's a better alternative then I'd be interested to
hear that too...

Cheers all, Mark.