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Old 11th September 2014, 07:46 AM   #1
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Default Woofers mounted from the inside

Hi, i have a curiosity
I was looking at some British classic speakers like the Rogers PM510 S2
Click the image to open in full size.
I have noticed that the woofer is mounted on the inside of the baffle
This is quite unusual .. is there a technical reason for this ?
Thanks and regards, gino
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Old 11th September 2014, 10:30 AM   #2
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by ginetto61 View Post
Hi, i have a curiosity
I was looking at some British classic speakers like the Rogers PM510 S2

I have noticed that the woofer is mounted on the inside of the baffle
This is quite unusual .. is there a technical reason for this ?
Thanks and regards, gino
In fact it's quite the other way

Most speakers in the World are inside mounted , for the technical reason that it's easier to do so and any one can be mounted that way.

"Front mounting" requires :

a) a speaker frame which allows it, meaning it has a relatively wide lip or mounting "ears" which to boot provides a flat surface, which can be back gasketed.
As you know, 99.99% of speakers provide both (a flat gasketed lip all around) at the front
Meaning practically all speakers are built so they can be mounted inside.

b) some frame to support a front grill on its own, which allows its removal for mounting/unmounting speakers.
Click the image to open in full size.
An inside speaker cabinet can have the front grill permanently stapled or glued, which is simpler and cheaper.

That said, front mounting is better, mainly because you lower edge diffraction, the resonance of the short tube you have in front (hole diameter and wood thickness), you improve dispersion a little, etc.

Not so bad in a woofer, but definitely hurts in a midrange or tweeter, so if you front mount 1 speaker ... you may as well front mount all.

Last edited by JMFahey; 11th September 2014 at 10:35 AM.
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Old 11th September 2014, 10:46 AM   #3
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Do Magico mount their speakers on the inside? They soften the front edges to avoid diffraction
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Old 11th September 2014, 04:55 PM   #4
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Quote:
Originally Posted by JMFahey View Post
In fact it's quite the other way
Most speakers in the World are inside mounted , for the technical reason that it's easier to do so and any one can be mounted that way.
"Front mounting" requires :
a) a speaker frame which allows it, meaning it has a relatively wide lip or mounting "ears" which to boot provides a flat surface, which can be back gasketed.
As you know, 99.99% of speakers provide both (a flat gasketed lip all around) at the front
Meaning practically all speakers are built so they can be mounted inside.
b) some frame to support a front grill on its own, which allows its removal for mounting/unmounting speakers.
Click the image to open in full size.
An inside speaker cabinet can have the front grill permanently stapled or glued, which is simpler and cheaper.

That said, front mounting is better, mainly because you lower edge diffraction, the resonance of the short tube you have in front (hole diameter and wood thickness), you improve dispersion a little, etc.

Not so bad in a woofer, but definitely hurts in a midrange or tweeter, so if you front mount 1 speaker ... you may as well front mount all.
Hi and thanks a lot for the very kind and valuable reply
So there is no specific technical reason
I was thinking that with the woofer inside the box the cone is more free to move ... there is more "air" behind it
Instead with the woofer outside the edges of the hole can have an impact on the movement of the cone ?
As i said i saw this technique used by Rogers, Spendor and BBC speakers
But i know very well that British like to be original
Thanks again, gino
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Old 11th September 2014, 05:31 PM   #5
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Quote:
Originally Posted by Bill poster View Post
Do Magico mount their speakers on the inside? They soften the front edges to avoid diffraction
Hi and yes it seems so
I was thinking that in this way the edges of the hole can create less turbulence when the cone moves forward and backwards
I think that another feature of the Magico speakers is the extremely stiff front baffle, another nice thing
Thanks, gino
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Old 12th September 2014, 09:27 PM   #6
system7 is offline system7  United Kingdom
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We've had this recessed bass question a lot of times. The reason you get away with it in BBC type designs is that if you wire negative polarity on the tweeter, and arrange the alignment error in the bass and tweeter at 2 to 3kHz crossover to be half a wavelength, which is 7.5 cm to 5 cm, the phase around crossover then aligns perfectly with big 8" to 12" drivers.

6moons audio reviews: Harbeth M30.1

Harbeth (and myself) still do it. It sounds good. If you look at old relevant KEF and Rogers 3rd order crossover designs, you will see that the tweeter IS always wired negative polarity. Let's consider the additional 90 degree phase difference in 3rd order butterworth an added complication, strictly for the enthusiast...
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Last edited by system7; 12th September 2014 at 09:40 PM.
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Old 12th September 2014, 10:09 PM   #7
sreten is offline sreten  United Kingdom
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Hi,

It requires a removable front or rear baffle, though some
BBC types have both. It allows a simple and thin grill.

FWIW most cheap boxes made nowadays have no
removable panels and drivers are front mounted,
usually, though exceptions through the bass
hole exist for for some mids, and rear press
fit tweeters in general - the latter usually
implying a 12mm thick front baffle.

Click the image to open in full size.

rgds, sreten.
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Old 13th September 2014, 08:55 AM   #8
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Quote:
Originally Posted by system7 View Post
We've had this recessed bass question a lot of times. The reason you get away with it in BBC type designs is that if you wire negative polarity on the tweeter, and arrange the alignment error in the bass and tweeter at 2 to 3kHz crossover to be half a wavelength, which is 7.5 cm to 5 cm, the phase around crossover then aligns perfectly with big 8" to 12" drivers.
6moons audio reviews: Harbeth M30.1

Hi and thanks a lot. This is difficult.
So it is a specific design choice this placement of the woofer.
Very interesting.
Actually when i saw such a big woofer with a small tweeter i remained perplexed
Not a common choice ...

Quote:
Harbeth (and myself) still do it. It sounds good.
If you look at old relevant KEF and Rogers 3rd order crossover designs, you will see that the tweeter IS always wired negative polarity. Let's consider the additional 90 degree phase difference in 3rd order butterworth an added complication, strictly for the enthusiast...
Very interesting. Actually these speakers have got very good reviews.
I tend to prefer paper for woofer cones ... but the answer is in the listening
I guess they are special polymeric cones ... i do not know
Thanks again, gino
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Old 13th September 2014, 09:05 AM   #9
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Quote:
Originally Posted by sreten View Post
Hi,
It requires a removable front or rear baffle, though some BBC types have both. It allows a simple and thin grill.
FWIW most cheap boxes made nowadays have no removable panels and drivers are front mounted, usually, though exceptions through the bass
hole exist for for some mids, and rear press fit tweeters in general - the latter usually implying a 12mm thick front baffle.
Click the image to open in full size.
rgds, sreten.
Hi and thanks and yes i asked because the mounting is quite unusual
As you say the vast majority of woofers (not only in cheap speakers) are front-mounted (Wilson Audio for instance, amd i would not call them cheap)
I did not understood completely the "phase" issue
But i have never understood phase in general ... i get lost with phase ...
Thanks again, gino
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Old 13th September 2014, 09:38 AM   #10
system7 is offline system7  United Kingdom
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Good phase matching, or at least control of, makes for the drivers reinforcing each other at crossover, rather than cancelling each other out and creating a hole in the power response on axis.

I had a look at a flat baffle 8" woofer plus small tweeter on a BW3 (Butterworth 3rd Order filter) here:
8"+1" two-way DIY speakers

On the following page I looked at some other filter choices like LR4.
8"+1" two-way DIY speakers

The negative polarity principle applies to bigger woofers too, which otherwise would have lousy phase matching due to the deepness of the woofer and its acoustic centre.
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Last edited by system7; 13th September 2014 at 09:45 AM.
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