Speakerplans.com Homepage
Forum Home Forum Home > General > General Forum
  New Posts New Posts RSS Feed - Reversing drivers in BR.
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Reversing drivers in BR.

 Post Reply Post Reply
Author
Message
FOO View Drop Down
Registered User
Registered User
Avatar

Joined: 23 December 2018
Location: Denmark
Status: Offline
Points: 141
Post Options Post Options   Thanks (0) Thanks(0)   Quote FOO Quote  Post ReplyReply Direct Link To This Post Topic: Reversing drivers in BR.
    Posted: 10 January 2019 at 10:48am
Hi Guys.

Just a small question i cant find any Google answer to.

What excactly does it do to reverse mount one driver in a dual BR box enclosure?
I know it has something to do with elimination of 3th harmonic distortion.
But what else? Any other pros and cons on doing this?
We are talking a plain BR box with both drivers in the same chamber and on the same baffle. 
Back to Top
MattStolton View Drop Down
Old Croc
Old Croc
Avatar

Joined: 04 September 2010
Location: Walthamstow
Status: Offline
Points: 4044
Post Options Post Options   Thanks (0) Thanks(0)   Quote MattStolton Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2019 at 11:18am
Not that much!

In theory the movement of a cone away from basket, is ever so slightly different from its motion towards basket, as the air resistance of the basket will affect rearward motion. Also the basket can form (minor) disturbances to the rearward wave, forms of diffraction to the wavefront propagation. However, consider this resistance to motion of cone from basket, versus the resistance to motion from the cabinet, and port effects, and it all becomes a bit moot.

In a double BR box, I doubt you could hear it, maybe just about measure it. In other styles of box, the effect can be more pronounced, and often will have an inverted driver, but this is often for ease of loading and physical space considerations, as much as lowering distortion numbers.

Easy enough to try, and listen to try and hear a difference. Beware of emporer's new clothes syndrome when doing the listen, you may hear something because you want to hear it!

One good thing, may be improved thermal dissipation, by exposing the magnet structure to the open environment, rather than the closed box, it should run cooler, minimising power compression effects. However, exposed cabling/connectors to pissed punters may be a detrimental effect, and the speaker terminals may offer a point to get an electric shock off, at high powers/big amplifiers.
Matt Stolton - Technical Director (!!!) - Wilding Sound Ltd
"Sparkius metiretur vestra" - "Meter Your Mains"
Back to Top
Pasi View Drop Down
Old Croc
Old Croc


Joined: 25 April 2010
Location: Knutsford
Status: Offline
Points: 2721
Post Options Post Options   Thanks (0) Thanks(0)   Quote Pasi Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2019 at 12:12pm
Originally posted by MattStolton MattStolton wrote:

Not that much!

In theory the movement of a cone away from basket, is ever so slightly different from its motion towards basket, as the air resistance of the basket will affect rearward motion. Also the basket can form (minor) disturbances to the rearward wave, forms of diffraction to the wavefront propagation. However, consider this resistance to motion of cone from basket, versus the resistance to motion from the cabinet, and port effects, and it all becomes a bit moot.

In a double BR box, I doubt you could hear it, maybe just about measure it. In other styles of box, the effect can be more pronounced, and often will have an inverted driver, but this is often for ease of loading and physical space considerations, as much as lowering distortion numbers.
...


Since we are busting myths and false info here from now on:

So not. Not even remotely like that.

First and foremost: It depends on drivers used.

What push-pull does is reduce nonlinear distortion in the acoustical output of the said cabinet, excluding the port effects. Hence it depends on linearity of said drivers how much the effect ends up being. With lower quality (cheap) drivers the effect may be up to 50% reduction on both second and third harmonic distortion, it's not always like that.

Biggest reason for nonlinear distortion is suspension stiffness asymmetry and second is inductance variation. 3rd thing is the actual BL, force factor, variation depending on which direction the cone is moving. This is caused by the plateset assembly and non symmetrical structure of it.

As we can see on the pic below, there is a slight variation on Kms, the suspension stiffness and barely any change on BL. But Inductance varies quite a lot, which indicates that there is no shorting rings on this driver and thus doing a push-pull may have a slight benefit as it would make Inductance symmetrical. But on BL or Kms there is barely any benefit. So effect wouldn't be anywhere near 50% reduction.

When using a driver with aluminium or copper shorting rings, they already stabilize the inductance variations and thus push-pull would make even less sense. But on cheap driver where you don't have shorting rings, got BL symmetry issues and your suspension isn't symmetrical either, benefits can be huge.

And that's why you see / don't see it that much in the modern world as it's not always deemed necessary, unlike the olden days when drivers weren't as well engineered as they are nowadays.

And effect is very audible on drivers which actually benefit from the push-pull.

Drawback on push-pull is that spider flexing noise and cooling air noise can be severily audible from the driver with magnet pointing out. For example certain driver range from well known European manufacturer uses specific cooling method where air is compressed inside the plateset on a backward motion of the cone causing very loud bangs and noise even at low excursion rendering those drivers unuseable on push-pull design.

Edit: On the left and middle graph on both rows, right side is coil out = cone forwards and left is coil in = cone backwards.




Edited by Pasi - 10 January 2019 at 12:13pm
Back to Top
godathunder View Drop Down
Old Croc
Old Croc


Joined: 19 July 2004
Location: wicklow
Status: Offline
Points: 1737
Post Options Post Options   Thanks (0) Thanks(0)   Quote godathunder Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2019 at 12:35pm
and, of course, youll have changed the volume of the front and rear chambers

edit: whoops, misread it as bp, not br, so forget that there front chamber


Edited by godathunder - 10 January 2019 at 12:37pm
LOUDER THAN LOUD
Back to Top
MattStolton View Drop Down
Old Croc
Old Croc
Avatar

Joined: 04 September 2010
Location: Walthamstow
Status: Offline
Points: 4044
Post Options Post Options   Thanks (0) Thanks(0)   Quote MattStolton Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2019 at 12:45pm
Originally posted by Pasi Pasi wrote:


Since we are busting myths and false info here from now on:

Busted!

Principle is right though, cone motion towards basket is different to away from basket.

Nice to see some measurements of non-linearity, didn't think motor and magnetic side of things would be such a significant source of the variance?
Matt Stolton - Technical Director (!!!) - Wilding Sound Ltd
"Sparkius metiretur vestra" - "Meter Your Mains"
Back to Top
Pasi View Drop Down
Old Croc
Old Croc


Joined: 25 April 2010
Location: Knutsford
Status: Offline
Points: 2721
Post Options Post Options   Thanks (0) Thanks(0)   Quote Pasi Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2019 at 12:52pm
Originally posted by MattStolton MattStolton wrote:

Originally posted by Pasi Pasi wrote:


Since we are busting myths and false info here from now on:

Busted!

Principle is right though, cone motion towards basket is different to away from basket.

Nice to see some measurements of non-linearity, didn't think motor and magnetic side of things would be such a significant source of the variance?


One would think, wouldn't he?

Back to Top
MattStolton View Drop Down
Old Croc
Old Croc
Avatar

Joined: 04 September 2010
Location: Walthamstow
Status: Offline
Points: 4044
Post Options Post Options   Thanks (0) Thanks(0)   Quote MattStolton Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2019 at 1:05pm
So, for this driver, at -5mm X cone displacement, BL is 30, at +5mm X, BL 31.5.


5% ish? How "bad" was this particular driver, compared with others you have measured?

Edited by MattStolton - 10 January 2019 at 1:05pm
Matt Stolton - Technical Director (!!!) - Wilding Sound Ltd
"Sparkius metiretur vestra" - "Meter Your Mains"
Back to Top
corell View Drop Down
Young Croc
Young Croc
Avatar

Joined: 19 August 2013
Location: Berlin
Status: Offline
Points: 1153
Post Options Post Options   Thanks (0) Thanks(0)   Quote corell Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2019 at 1:14pm
Check out the voice coil magazine, plenty of klippel data on there.
Back to Top
Pasi View Drop Down
Old Croc
Old Croc


Joined: 25 April 2010
Location: Knutsford
Status: Offline
Points: 2721
Post Options Post Options   Thanks (0) Thanks(0)   Quote Pasi Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2019 at 1:19pm
Originally posted by MattStolton MattStolton wrote:

So, for this driver, at -5mm X cone displacement, BL is 30, at +5mm X, BL 31.5.


5% ish? How "bad" was this particular driver, compared with others you have measured?

Well, as Qes calculation has BL squared as divider, your 5% just became 10%. 30x30=900, 31,5x31,5=992.5

It is pretty typical chinese driver. First one originates from Mediterranean area :)



Edited by Pasi - 10 January 2019 at 1:20pm
Back to Top
FOO View Drop Down
Registered User
Registered User
Avatar

Joined: 23 December 2018
Location: Denmark
Status: Offline
Points: 141
Post Options Post Options   Thanks (0) Thanks(0)   Quote FOO Quote  Post ReplyReply Direct Link To This Post Posted: 10 January 2019 at 6:22pm
Well i think i got my answer 😁
Really Nice with such great answers. Thats going right into the wisdom vault 👌
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.01
Copyright ©2001-2018 Web Wiz Ltd.

This page was generated in 0.094 seconds.