Mission 73AS sub upgrade (if possible) - diyAudio
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Old 6th February 2007, 11:57 AM   #1
DAMIC is offline DAMIC  Seychelles
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Default Mission 73AS sub upgrade (if possible)

For a couple of years I have Mission 73AP subwoofer (btw made 1997) and since last year when I upgraded my main speakers with double bass reflex enclosure (hybrid 26 inch ribbon and 6,5 inch mid woofer in 26l cabinet), it appear that present sub do not goes down enough. There are some information of the sub I found from the manual:

LF response 27Hz (-6dB) ???
X-over freq. control 50 150 Hz
Phase adjustement 0 180 deg.
Acoustic radiating area 450 cm sq. (equivalent to 12 inch)
Amplifier 120 Watt (100 Watt)
Internal volume 32l (about 1,13 cf)
Cabinet dim: 428 x 611 x 248 mm, bass reflex type

Last week I dismantled the sub and find on the bottom, two 20cm drivers with markings on the magnets as follows: Mission, 3A-LFGDN. A friend of mine said that they are probably made by Audax, and they indeed look like some 30cm Audax drivers I found on the internet, the type with inverted dust cap. The cones are made of black plastic, look alike. Both drivers are connected parallel to the amp output, although there are two separate inputs what surprise me a bit.There are also two flared duct ports, diameter 5cm and 21cm length. I put ducts dimensions and cabinet volume in the formula and it seems that the sub enclosure is tuned to 39Hz, what surprisingly corresponds to the same tuning point of my upgraded main speakers. Now it is clear to me why sub is almost not noticeable im my room when switched on.

Well, I am wondering, does anyone knows some more informations about a/m drivers, T/S parameters etc. Secondly, I would like to upgrade the sub. I want sound to be deep as possible with a/m drivers and amp, while the loudnes is not so important. Making of any size and type of enclosure is not problem for me.

Any suggestions?

Thank you in advance.
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Old 6th February 2007, 12:04 PM   #2
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You would have to entend the vent length (which might not be physically possible) and add electronic equalisation (boost). That is assuming the design has not been done in this way already.

Basically it would be quite a major project.
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Old 6th February 2007, 01:01 PM   #3
DAMIC is offline DAMIC  Seychelles
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Yes, I know that with extension of duct port length and increase in cabinet size should lead to lower freq. but I do not know what are the limits as driver parameters are not known.
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Old 6th February 2007, 01:31 PM   #4
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You can measure them.
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Old 7th February 2007, 05:10 AM   #5
DAMIC is offline DAMIC  Seychelles
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Unfortunately, I do not have neccessary equipment for measuring the driver parameters and this is one of the main reasons I posted the topic.

One think I forgot to mention on the first post is that I have a pair of very old KEF B-139, type 6171, nominal power 30 Watt , fundamental resonance 20Hz. They are still in good working order. Rubber surround is for sure a bit more stiff, but that would lead only to lower the resonance, I assume.

One of my earlier idea was to use Mission amp and drivers together with two KEF B-139 as a passive radiators all in one box. B-139 piston area is about 50 percent bigger than Mission 20cm woofer, and as I sow on other PR threads, that ratio is adequate to work properly.

If neccessary, the dditional weight could be easy attached on flat KEF surface. But the main question, what would be the sufficient size of the cabinet to cover the range starting form to app 20-24 Hz, again still remains.

Any thoughts?
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Old 7th February 2007, 09:44 AM   #6
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All you need is two resistors, reasonable power amp, and a millivolt meter and ohm meter. You already have a computer.
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Old 7th February 2007, 10:20 AM   #7
DAMIC is offline DAMIC  Seychelles
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Maybe it sounds funny but I do not have PC at home. Looking to buy something new with LCD screen in near future.
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Old 16th February 2007, 12:15 PM   #8
DAMIC is offline DAMIC  Seychelles
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Finally, I found the driver which looks totaly the same like the woofers employed in my sub, Audax HT210G10. The only difference is DC resistance. I measured 6,6 ohm what means that they are 8 ohm drivers. I think that as both drivers are conected to work in paralel, the Mission made special order to Audax for 8 ohm version.

Here are the links from official Audax site

http://www.hautparleur.fr/_audax/ht210g10.pdf

http://www.hautparleur.fr/_audax/ht210g10.jpg

As the freq.graph shows, 8 inch driver although defined as a woofer, do not show spectacular response bellow 100Hz, IMO.

Are there any suggestions for new enclosure which could give me deeper bass?

Thank's in advance
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Old 16th February 2007, 12:46 PM   #9
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If the drivers you have are 8 ohms it's safe to assume the Thiele-Small parameters will also be different from the 6 ohm spec driver.
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Old 16th February 2007, 01:14 PM   #10
DAMIC is offline DAMIC  Seychelles
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Well, I am now really not sure what is actually the nominal impendance of the driver. On the first link it is quoted Z as 4 Ohm, while on the second link is quoted as 8 Ohm. The other parameters seems tobe the same on both links.
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