Phil Allison wrote:
"Rob"
Phil Allison wrote:
"Arny Krueger"

The cone works against a relatively large mass - the speaker and its
enclosure.


** The mass ratio of a whole speaker box to the woofer cone is around
500: 1, or more.

The conservation of momentum principle ( Newton's "every action causes
an equal and opposite re-action" ) requires that the momentum of the
moving cone and whole box remain equal and opposite. So, the box moves
about 0.2% of the cone's movement in the opposite direction.

Typical woofers move at most 6mm forward and back when producing the
lowest bass frequencies.

The box, in compliance with Newton, then moves 12 um back and forward.

12 um = 0.5 thou = one quarter the thickness of a page in the phone
book.



Why bother with spikes and cones at all?
Because it sounds better.
Only in sighted evaluations.

** Of course.

IME it doesn't always work like that.


** Long as the box is not bolted down - it IS how the box reacts to the
woofer.

Newton is not to be messed with.


Not by me, certainly - but Einstein had a thing or two to say :-)


My Dynaudio 1.1s sit on some stands with a smallish top plate. After an
hour of fairly spirited listening, they'd moved about 4cm forward.


** Bet your floor is vibrating in sympathy with SPL at low frequencies.

Then the speaker stand vibrates - cos it is supported by it.

Then, the un-secured box drifts forward.


It is a suspended timber floor.



I'd usually use blutack for that reason - it's all in the movement of air.


** Low frequency sound pressure waves shake the whole room - floor,
ceilings, windows, cupboard doors - every damn thing. And by exactly the
same amount even of the speaker boxes were hung on long coil springs from
the roof.


I thought it was more to do with air being pushed out of the rear reflex
port and hence proximity to a wall. I don't know if it makes any
difference to sound (I've never done an A-B), but the fact remains the
speakers move about if I don't 'tack them down, and they'd eventually
fall off the stands.

Rob

"Rob"
Phil Allison


** Bet your floor is vibrating in sympathy with SPL at low frequencies.

Then the speaker stand vibrates - cos it is supported by it.

Then, the un-secured box drifts forward.


It is a suspended timber floor.


** QED - end of story.



I thought it was more to do with air being pushed out of the rear reflex
port and hence proximity to a wall.


** Err - the air goes in and out, same air, over and over.


I don't know if it makes any difference to sound (I've never done an A-B),
but the fact remains the speakers move about if I don't 'tack them down,
and they'd eventually fall off the stands.


** That must be very funny.


Woof , woof, woof, woof ........ thump !!





......... Phil

Rob wrote:

Phil Allison wrote:
"Arny Krueger"

The cone works against a relatively large mass - the speaker and its
enclosure.


** The mass ratio of a whole speaker box to the woofer cone is around 500:
1, or more.

The conservation of momentum principle ( Newton's "every action causes an
equal and opposite re-action" ) requires that the momentum of the moving
cone and whole box remain equal and opposite. So, the box moves about 0.2%
of the cone's movement in the opposite direction.

Typical woofers move at most 6mm forward and back when producing the lowest
bass frequencies.

The box, in compliance with Newton, then moves 12 um back and forward.

12 um = 0.5 thou = one quarter the thickness of a page in the phone book.



Why bother with spikes and cones at all?
Because it sounds better.
Only in sighted evaluations.


** Of course.


IME it doesn't always work like that. My Dynaudio 1.1s sit on some
stands with a smallish top plate. After an hour of fairly spirited
listening, they'd moved about 4cm forward. I'd usually use blutack for
that reason - it's all in the movement of air.

Actually it's down to 'microvibrations'.

Graham

Phil Allison wrote:

"Rob"

I don't know if it makes any difference to sound (I've never done an A-B),
but the fact remains the speakers move about if I don't 'tack them down,
and they'd eventually fall off the stands.

** That must be very funny.

Woof , woof, woof, woof ........ thump !!

LMAO ! .............. thump !!

Graham

On Sat, 09 Sep 2006 09:10:18 +0100, Rob
wrote:

I thought it was more to do with air being pushed out of the rear reflex
port and hence proximity to a wall.

It's sucked in precisely as much as it's blown up. Otherwise your
speaker enclosures would either implode or blow up like a balloon.

Laurence Payne wrote:

On Sat, 09 Sep 2006 09:10:18 +0100, Rob
wrote:


I thought it was more to do with air being pushed out of the rear reflex
port and hence proximity to a wall.


It's sucked in precisely as much as it's blown up. Otherwise your
speaker enclosures would either implode or blow up like a balloon.

Air blowing out of the port is more directional than air sucked in.
The forces may be measurable but are too small to propel a cabinet.

I have had a speaker without rubber feet slide down a shelf that wasn't
perfectly level and jump off the edge. It may have been driven to suicide
by the volume and the quality of the music. :-)

--
Eiron

No good deed ever goes unpunished.

On Sat, 09 Sep 2006 11:14:24 +0100, Eiron wrote:

It's sucked in precisely as much as it's blown up. Otherwise your
speaker enclosures would either implode or blow up like a balloon.

Air blowing out of the port is more directional than air sucked in.

Justify, please?


The forces may be measurable but are too small to propel a cabinet.

I have had a speaker without rubber feet slide down a shelf that wasn't
perfectly level and jump off the edge. It may have been driven to suicide
by the volume and the quality of the music. :-)

Indeed. It's the shelf not being level that matters.

Laurence Payne wrote:

On Sat, 09 Sep 2006 11:14:24 +0100, Eiron wrote:


It's sucked in precisely as much as it's blown up. Otherwise your
speaker enclosures would either implode or blow up like a balloon.

Air blowing out of the port is more directional than air sucked in.


Justify, please?

Measure it yourself. Get a straw and blow through it. Feel the airflow
or hold a strip of paper. You can see how directional it is. Then suck.

--
Eiron

No good deed ever goes unpunished.

On Sat, 09 Sep 2006 11:32:14 +0100, Eiron wrote:

Measure it yourself. Get a straw and blow through it. Feel the airflow
or hold a strip of paper. You can see how directional it is. Then suck.

That's measuring the effect some distance from the orifice. Aren't we
interested in the effect AT the orifice? Unless the wall is very
close.

"Eeyore"

** That must be very funny.

Woof , woof, woof, woof ........ thump !!

LMAO ! .............. thump !!



** So Graham Stevenson FINALLY falls off his OWN pedestal ??

Like Cocky falling off his perch ......





....... Phil