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Bass speaker facing backwards in cab. How does this work


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 I am presently refurbishing a pair of  Kef 104/2  Speakers, new doughnuts / dust caps and complete rebuild of one of the bass speakers.

During this process I have noted that one pair of the bass speakers face back in to a sealed cabinet. Top speakers in the picture.

How can this be better than facing out in to the cabinet ,with sound exiting the port ,as the other pair do ?

 

I also have a pair of 15''  PA  Bass bins that are set up the same way.

 

KEF.png

 

Edited by EV Cali
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When dealing with low frequencies the shape of the cone has no impact other than for stiffness etc.. So it doesn't matter if it faces in or out it is still moving air.  The only impact you may see in that scenario is the slightly smaller radiating area on the back of the cone due to the voice coil former taking up some of the surface area.

 

Does the lower driver go into a sealed chamber as well?

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Thanks luke325 

 

No the bottom pair of drivers face the other way and are close to the port ,as can be seen in the picture.

If as you say it does not really matter what way they face I suppose the upper driver is also in the ported part of the cab.

Just appeared odd to me that they do not both face the same way especially as you mention this would give  a slightly smaller radiating area on the back of the cone due to the voice coil former taking up some of the surface area .Why not the other way round with a bigger radiating area.

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1 hour ago, Sub Sonic said:

It would be to help cancel out distortion. M&K subwoofers also use this principle, have a look on pages 8 and 9 in the link below.

 

http://www.mksound.com/wp-content/uploads/2013/01/XSERIESWHITEPAPER.pdf

 

Regards,

 

SS

 

Definitely a possibility.  A bit like an Isobaric setup, unusual having both firing into the ported chamber.  But there are so many different styles of enclosure configurations.

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Isobaric enclosures usually have the two woofers closely coupled (often face to face) so they act as one. The end result is that the enclosure volume can be halved compared to a single woofer, for the same response.

 

The enclosure in the original post is a 4th order band pass, where one side of the woofer is in a sealed enclosure and the other is in a vented. This one is a slight variation where two woofers are used, but the principle is the same.

 

SS

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A fundamental property of all waves (sound, light, water etc) is that they don’t ‘see’ objects that are much smaller than their wavelength but largely pass by them.

 

Hence AM radio waves, whose wavelengths are of the order of 100 m, can be received in places where FM signal, whose wavelengths are of the order of 1 m, cannot.  And there are limits that ultrasound waves, of the order of 1mm, can resolve.

 

In the case of subwoofers, where the wavelength is around 3m at 100Hz and around 10m at 30Hz, the soundwaves effectively don’t ‘see’ the cabinet (dimensions around 0.3m) but largely pass around it.

 

However, there will be a small time delay of around 1 ms putting the driver on the back compared to the front.  At 100 Hz the phase change will be around 36 degrees but only around 10 degrees at 30 Hz, the latter probably not hearable.

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