Mission 760i Bass extender (poor man’s AB1) - diyAudio
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Old 25th September 2014, 06:30 PM   #1
diyAudio Member
 
Join Date: Jan 2012
Location: Leersum
Default Mission 760i Bass extender (poor man’s AB1)

I am planning a nice (and cheap) project for the coming winter. I have a lot of projects which I could start …or finish, but they are a bit costly or they just take time to bring to a nice end.

But I want to go with a very old idea. I have pair of nice Mission 760i, I first thought of selling them but for the 25-60 euro’s I will keep them myself.
Every time I hook them up to my old (refurbished) Quad 33,303 I am surprised by these little cheap speakers. I think they sound wonderful but after a while I am missing the lower regions.

I like to own a pair of LS3/5 speakers but they are too expensive for me. But then it hit me! Could I build a AB1 like “Bass extender” (see attachments) for my 760i speakers?

This is not my territory of knowledge…so there a “few” questions. I also don’t have software to see if it would even work.

The dimensions I (now) have are: Height 570mm, Wide 180mm, Depth 200mm and I want to use 18mm MDF so that would result in 20,5 litres.

I have sketched some ideas in the attached picture, “A” is like the original AB1, “C” is like the Harbert version. The other versions are just ideas but I must admit that the idea of a passive radiator is high on the “try it out list”.

I had a look at some 5 inch (130mm) speakers but it is a bit pointless if I don’t have a clear idea of the design and final dimensions or vice versa.

So the questions are:

Which speaker do I choose? (looked at Tangband, Peerless, B110 and others)
Which dimensions (I like to keep the width and depth at 180mm and 200mm).
Which type of enclosure type goes with the above.
And there are some filter questions like..
- (depending of the speaker) where do I cross etc…
- How do I control the overall resistance
- And maybe I missed some questions...

Or is it just a weird idea?? Or must I post this at the subwoofer forum?
Attached Images
File Type: jpg Mission-extender.jpg (148.3 KB, 75 views)
File Type: png xtender.png (186.3 KB, 72 views)
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Old 25th September 2014, 07:29 PM   #2
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

The AB1 and clones incorporate filters for the mains and
a precisely tuned high pass in the the style of A and C.

B and D are both useless without the low pass ports of A and D.
A and C are 4th order - 2nd order, sealed high pass.
B and D with top ports are 6th order - 4th order reflex high pass.

Its doable but complicated with a vented top speaker -
that would probably need to be converted to sealed.

The bass driver is 60-lfc13/bk, and given its vented
in the 6.5L 760i, 20L is plently for a 6th order.

TBH adding a powered sub is a lot easier, along the
lines of E or F (which is E vented) with a plate
amplifier in one of the boxes driving both.

Alternately just bite the bullet and accept the
760i is a cheap speaker, not worth the effort,
and simply build something like these :

https://sites.google.com/site/undefinition/diy/amiga

They would certainly sort out the bass issue, though I
personally I'd tune them lower than 39Hz to improve F6
and give tighter bass, say 34Hz, at the expense of F3.

rgds, sreten.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

Last edited by sreten; 25th September 2014 at 07:50 PM.
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Old 25th September 2014, 08:02 PM   #3
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Hi,

Re powered towers :
The TB 6x9 sub would be good in 20L tuned to 33 Hz.

rgds, sreten.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
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Old 26th September 2014, 08:31 AM   #4
diyAudio Member
 
Join Date: Jan 2012
Location: Leersum
Hi Sreten,

Well that is maybe not what I hoped for but it is very clear. A plate amp to drive both speakers is an idea to think about! Thanks for your comments and ideas.
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