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Old 20th October 2012, 11:40 PM   #1
system7 is offline system7  United Kingdom
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Default Upgrading Mordaunt Short MS15 Bookshelves

These were a fun buy. 20 year old MS15 speakers, designed by Robin Marshall at a guess. They have his style.

Click the image to open in full size.

Inside is a simple 1st order bass, second order treble filter with those polyfuse things. Elac 180NS10 paper bass unit and small (ferrofluid?) polycarbonate tweeter. Lots of stuffing and a 3.3uF non-polar electrolytic capacitor which I replaced as a matter of course with polypropylene and got a cleaner sound straightaway.

Sound is a bit muffled and it tends to sibilance at high frequencies, which I would think is cone breakup from the bass around 5kHz. I'm going to get rid of some stuffing and damp the side and top panels next in BBC style.

To this end, I've got some 4.5mm Regupol rubber and cork floor underlay and some rubber sheeting. Bass cutout is 147mm, PCD 185mm, tweeter cutout is 50mm with room for up to 72mm diameter replacement. Cabinet is 325mmx230mmx160mm, 7 Litres in golden ratio internally. Been modelling a second order crossover which looks much better too.
Attached Images
File Type: jpg Mordaunt_Short_MS15_Loudspeaker.jpg (76.5 KB, 318 views)
File Type: jpg Mordaunt_Short_MS15_Rear_View.jpg (102.1 KB, 307 views)
File Type: jpg Mordaunt_Short_MS15_Disassembled.jpg (88.0 KB, 315 views)
File Type: jpg Loudspeaker_Damping_Pads.jpg (134.8 KB, 308 views)
File Type: jpg MS15_Crossover_FR.JPG (60.9 KB, 129 views)
File Type: jpg Mordaunt_Short_MS15_Crossoverr.jpg (20.7 KB, 136 views)
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Old 21st October 2012, 12:06 AM   #2
sreten is offline sreten  United Kingdom
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Hi,

Stuffing works fine for sealed, not that good for vented, but vented
lining style has no advantages for sealed, just stuff sealed. You
don't need a foam lining for sealed. You can vary stuffing density.

I can't find anymore the cheap industrial solid self adhesive vinyl
floor tiles that are excellent in layers as cabinet wall damping.

If the tweeter is twist removable from the front plate, its the classic
and best by far Audax original, ferrofluid and edgewound formerless.

similar bass mid driver :
ELAC 5 inch hifi bass speakers woofers PAIR KEF JPW | eBay

rgds, sreten.
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Old 21st October 2012, 12:29 AM   #3
system7 is offline system7  United Kingdom
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Well, you know me, sreten. I just like trying stuff. If panel damping is used by the BBC for closed box, it must do SOMETHING! The rolled up stuff is more light self-adhesive expanded foam.

These bass units are remarkably like the ELAC ones you quote from eBay. Just bigger dustcaps as far as I can see.

Only marking on the tweeter is TW6x9 and it's a one piece moulding AFAIK. Sound very smooth, so will persevere with them. All units are 6 ohms resistive.

Edit. Oh wait. The tweeters twist apart into two pieces of faceplate and motor/diaphragm. Hope I haven't broken the wires! LOL
Attached Images
File Type: jpg Elac, 180NS10.jpg (104.5 KB, 112 views)
File Type: jpg Elac, 180NS10,speaker 002.jpg (101.2 KB, 68 views)
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Last edited by system7; 21st October 2012 at 12:43 AM.
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Old 21st October 2012, 12:47 AM   #4
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the original 10mm Audax were coded something like 'TW10**' so its possible they are OEMs made by Audax. These speakers certainly have something ovdar the models that followed them.

Id agree that 2nd order maybe good for the woofer but the round bezel version of the audax i bought back when maplin sold them, had a fs of something like 2.5khz. I understand the motivation to maintain simplicity, but maybe 3rd order on the tweeter, OR a zobel (i know you like these) will help. Although i liked my old audax i found that the resonance was very noticable. This was mainly due to me using textbook values for a 2nd order at 4k. My only grace was that i did use the impedance plots, and a table of values to rough it out. I dont recall the frequency response but i just remember the resonance showing through unless i crossed at 5k
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Old 21st October 2012, 01:35 AM   #5
system7 is offline system7  United Kingdom
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Yup, it does look like an Audax TW6X9 plastic tweeter. I guess that is good.

I tried to allow for acoustic centres of 50mm and 10mm here. A bass Zobel worked out best on phase and flatness with more inductance. Didn't change much else apart from increasing attenuation on tweeter and tweeter Zobel for 0.1mH. Might work. Should get rid of some sibilance with more bass riolloff, and up the bass a tidge which won't be a problem.

Now must get on with ordering the parts. The crossover board has lots of room.
Attached Images
File Type: jpg Test_Crossover_MS15.JPG (23.1 KB, 76 views)
File Type: jpg Test_Circuit_MS15.JPG (59.4 KB, 59 views)
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Old 21st October 2012, 01:51 AM   #6
sreten is offline sreten  United Kingdom
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Hi,

The much copied Audax tweeter is the eponymous cheap tweeter.

Click the image to open in full size.

The original and still near the best twists out for different faceplates.

The original has a formerless edgewound voicecoil in a ferrofluid gap.

rgds, sreten.

Fs is high and they are designed for a 3rd order roll-off with a single capacitor.
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Last edited by sreten; 21st October 2012 at 01:58 AM.
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Old 21st October 2012, 02:01 AM   #7
system7 is offline system7  United Kingdom
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Yup, it looks like the one. Good ID work, sreten, on both drivers.

The square bit twists out.

There's a tiny little blob of solder on the domes for some reason.
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File Type: jpg Audax_TW6x9_tweeter.jpg (38.8 KB, 84 views)
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Old 21st October 2012, 02:34 AM   #8
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With past experience in Carnival 5 series for my AV 5.1 system, the British speaker brandname “Mordaunt Short” is my favor brand with high value-added (i.e. low cost with high performance). This brand is highly recommended.
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Old 21st October 2012, 11:09 AM   #9
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3rd order acoustic at 5k or beyond makes perfect sense Sreten. Back when i was a teemager these tweeters were good value, but a little difficult to use. I remember thinking that they would work better in a 3way crossed high. I found them to sound pretty good as long as their resonance was far enough out of band. However i did cut out the part in front of the dome, and that couldve made things worse. Also from recall these domes had a small nipple at the apex of the dome.
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Last edited by mondogenerator; 21st October 2012 at 11:12 AM.
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Old 21st October 2012, 12:13 PM   #10
system7 is offline system7  United Kingdom
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Interesting remarks on the tweeter. It looks like it has sharp natural rolloff at 3kHz and at 0.03mH vc inductance and flat won't need a Zobel.

This is the Audax TW010F1, but very similar apart from the faceplate. This could work very well with the woofer which will peak around 1.4kHz on a second order. A question of suck it and see, I think. I'll leave the tweeter crossover essentially unchanged. Happens it looks very good with the Visaton TW70 too, if this all goes pear-shaped.

I enclose some data for future reference.
Attached Images
File Type: jpg Audax_TW010F1.JPG (56.2 KB, 97 views)
File Type: jpg Audax_TW010F1_Parameters.JPG (96.7 KB, 68 views)
File Type: jpg Audax_TW010F1_Tweeter.JPG (36.4 KB, 75 views)
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