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  • 03-11-2009 3:37 PM

    • BeoMatt
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    Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Design concept failure

    As we all know, after about 15 or so years the foam used in B&O & many other manufacturers speakers turns to mush, cones fall away, speakers become seemingly useless.

     A market has arisen providing a readily available supply of replacement foam rubber rings, and appropriate glue that breaths new life into these majestic wonders of 20th century design. This is great, but ABR's (Auxiliary Bass Radiators) are rectangular.

    Mushy foam rot on a rectangular bass radiator found on Red Line Bang & Olufsen Speakers

    Bang & Olufson speakers seem to suffer badly, and in the case of the Red Line series, the design concept fails completely after about 15-20 years.

    A rectangular metal plate supports a foam/rubber material that is glued across a metal diaphragm, it radiates a resonance, as the air contained within is distorted from the traditional drivers to the right of the speaker cabinet. This concept provides a good bass output.

    Background

    The foam had perished in my newly acquired Red Line 45’s, and after visiting the wonderful B&O fan site, www.beoworld.org members advised that B&O aware of this failing, released a tuned port conversion that sadly is no longer available. So my challenge was to replace the sticky mushy foam with new, perhaps longer life foam. I scoured many DIY shops, building merchants, only managing to find carpet underlay, which is made of a very similar grade of rubber but quilted and attached to a canvas or fabric back.

    Fishy Inspiration

    Laminate floor underlay also seemed to have similar properties, but alas at only 1mm thick, and quite week, it was no good. Almost giving up I took my daughter to see rabbits at our local pet shop. Eureka!! The foam rubber used to lay at the bottom of fish tanks was perfect, although a little thick, approximately 4-5 mm; it was the best I had found for the purpose. It’s tough, resistant to heat, oil, water obviously, and light, it also happened to be black unlike underlay which is brown or white. So my mini project is off to a good start.

    On removing the foam from the plastic I noticed it had properties very similar to memory foam, found in expensive mattress toppers. I am yet to find if this has any additional value but it would certainly enable me to man handle it. It also cuts very well, with a knife gently heating the blade tip, it go’s through like butter. So forming two gaskets was easy. There are several holes so I simply used the end of drill bit, warmed in a candle and then pressed to form holes where required.

     

    Template drawn on the rubber/foam gaskets surface then cut using craft knife, drill bits, scissors & candle

    To dismantle the speakers I removed the 10 retaining screws at the rear of the cabinets. Carefully prising the fronts away, and removing the green and black wires from the rear terminals. There are 6 cross head screws holding the ABR's metal diaphragms. If you look carefully you can see one end of the diaphragm is narrower, allowing easier removal.

    Once removed I vacuumed the old residual foam and lifted the dislodged ABR's from the speakers. Using a credit card! and tooth brush most of the mushy foam was removed from all metal surfaces. Finally I pasted them all with Nitro Mors, left for an hour then rinsed in cold water, wire wool took the remaining stubborn foam/glue off. I placed each part in the oven on high to dry and all the stubborn glue burnt off. You don’t have to do this I am just finicky about preparation, plus its quite dangerous with toxic fumes.

     

    Using a credit card! and tooth brush most of the mushy foam was removed

    Now the ABR's diaphragms, plates and gaskets are ready for reassembly. I used Araldite Rapid, about £4.99 from Home base. Very strong and tough, I tested an off cut of foam on my steel ruler and left for an hour. It was fine just very slight deformation nothing to worry about, more then enough to support the ABR's.

    After cutting the gaskets, I mixed the glue spreading evenly over the ABR's diaphragms, the glue gives you about 4-5 minutes to adjust.

    I then placed the foam gaskets onto the ABR's diaphragms. I placed quite a bit of weight on top evenly spread, and left for an hour.

    Tricky Rads

    The ABR's centre plates (Radiators) proved quite tricky, when aligning to ensure equal space around the edges it was more guesswork than a precise science.  The glue again was applied in a similar pattern to the original shadow left on the metal radiators surface. I carefully placed Weight equally across the surface by placing upturned cups and a flat surface where weight is then applied for an hour.

     

    Reassembly is a reverse of above, although be careful when replacing all the screws, if you use an electric driver make certain its torque setting is at about medium, as the cabinets screws can be brittle.

     

     Proof is in the pudding; my authentic repair is almost complete

      

    Before & after repair measured frequency levels displayed using Adobe Audition 

     

    A fully repaired and beautiful sounding Red Line 45's

    Fully reassembled I tested both speakers at various volume levels using a Beomaster 3000, 3500 and Beogram CDX/2. I am personally happy with a good solid bass reflex, perhaps too much deep tone at low volume, only a trained ear would pick up, but as the Redlines tweeters provide such clarity it is a happy balance. I am still on the look out for B&O replacement ABR's so if anyone out there has any or a pair of good RL45/60's drop us a line, thanks to all Big SmileBeomatt

    If you have any questions then you can contact me via Beoworld.

  • 03-11-2009 3:57 PM In reply to

    • Puncher
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Very well done (and very quickly too I must say).

    Regarding the bass performance - if they are stood directly on the floor the bass is definitely more prominent. I think they sound better (and more controlled) on the floor stands - if you don't have them they do crop up fairly regularly on ebay, the RL60 versions are the ones to look out for, the RL140 stands are much too large and won't fit).

    There are two styles of RL60 stand, the earlier "double leg" type and a later chrome pole riser type - depending on your taste (the pole types seem to crop up slightly less often).

    Generally speaking, you aren't learning much if your lips are moving.

  • 03-11-2009 4:05 PM In reply to

    • BeoMatt
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Big SmileThanks for the advice, as for the timescale I am used to fast effective repairs goes with my job as an engineer, Beomatt 

  • 03-11-2009 4:17 PM In reply to

    • Puncher
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Beomatt:

    Big SmileThanks for the advice, as for the timescale I am used to fast effective repairs goes with my job as an engineer, Beomatt 

     

    I too am an engineer - my ABR frames are underneath my piano upstairs (and have been for a good while) waiting for me to do something with them. (My RL60's currently have the tuned port conversion)

    Generally speaking, you aren't learning much if your lips are moving.

  • 03-12-2009 4:50 AM In reply to

    • BeoMatt
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Stop tickiling the ivorys and repair them or send them to me and I will do them. I have offered my refoaming services to another fellow member, I am going to look around for thinner foam/rubber. If you have any suggestions drop me a line cheers again Beomatt

  • 03-12-2009 2:16 PM In reply to

    • BeoMatt
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Big SmileHey everyone I have found the perfect foam rubber replacement for ABR's Its Neoprene foam on Amazon at about £6.70 incl p&P in various colours A4 sheets at only 1mm thick !! I've ordered some, so if anyone has any spare ABR's out there give me a shout cheers everyone BeoMatt

    Here's the link

    http://www.amazon.co.uk/Funky-Foam-Sheets-Assorted-Colours/dp/B000UCUL48/ref=sr_1_1?ie=UTF8&s=toys&qid=1236881705&sr=8-1

  • 03-13-2009 1:25 PM In reply to

    • Puncher
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Pardon me if I appear a bit thick but aren't the ABR's longer than A4?

    Generally speaking, you aren't learning much if your lips are moving.

  • 03-13-2009 2:46 PM In reply to

    • Dillen
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Yes, the ABR's are longer than A4.
    I tried neoprene but gave it up because the required glue is very hard to find
    and difficult to handle (very toxic if I remember correctly).
    The replacement ABR mats that Anthony Garza in Texas made were extremely precise
    repro parts but unfortunately also neoprene. I tried these too - and had to give up.

    Martin

  • 03-13-2009 3:55 PM In reply to

    • Craig
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Very impressive repair Matt, thanks for sharing the details with us.

     

     

    CraigSmile

    For millions of years, mankind lived just like the animals. Then something happened which unleashed the power of our imagination. We learned to talk and we learned to listen..

  • 03-14-2009 7:42 AM In reply to

    • Puncher
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Dillen - are you saying you don't refoam ABR's anymore or just that you don't use Neoprene?

    Beomatt  - RS Components has a selection of both natural rubber and synthetic rubber (Silicon and Neoprene) sheets of varying thicknesses. One of the Neoprenes is even self adhesive, although I wouldn't know if the adhesive would be up to the task.

    I have no idea which material would be the most suitable - but maybe you can experiment and report backLaughing

    Generally speaking, you aren't learning much if your lips are moving.

  • 03-14-2009 12:28 PM In reply to

    • BeoMatt
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Yes you are correct, my mistake sorry Embarrassed never mind, I could sell them on ebay as memory foam for small pets !

  • 03-14-2009 12:32 PM In reply to

    • BeoMatt
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Superb link Puncher, cheers. Big Smile

    I think i'll offer my services as an ABR repair man ! Satisfaction guaranteed, just send your faulty ABR's by post email me here mattybrillo@hotmail.com

     

  • 03-15-2009 5:41 AM In reply to

    • Dillen
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Puncher,

    Yes, I still refoam many ABR's (not using neoprene).
    Still, it's nice to know that there are a stabile and guaranteed ABR refoam
    service available in the UK.

    Martin

  • 03-15-2009 5:48 AM In reply to

    • Puncher
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Obviously refoaming them with anything is better than having no ABR's but the originals have a particular resonant frequency, I would like the material used to match the original's compliance. Without an original to compare I guess this is all but impossible.

    Generally speaking, you aren't learning much if your lips are moving.

  • 03-15-2009 6:05 AM In reply to

    • Dillen
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Certainly, Puncher.

    It seems Matt did exactly that if you look higher up in this thread.
    Though I must admit not being able to see much in those little pics.
    However, it does seem to me that, if the "after" shot is the one to the right,
    the repair seems to have introduced some kind of hump in the lower midrange
    if you look at the light blue curve, or maybe I'm reading it wrong, I never
    used Adobe Audition.
    He doesn't tell us where he got the "before" shot from. Safe to say that he
    didn't have access to an original and yet complete RL60 ABR, I haven't seen one
    myself for many years (and I've seen many RL's) and won't ever see one again I'm sure,
    so maybe it was merely a shot of the speaker with no ABR installed
    though obviously, that would be useless for comparison.

    Matt, you will have to tell us a little more about your measurements if possible.

    Martin

  • 03-15-2009 12:51 PM In reply to

    • BeoMatt
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Hi Dillen, I took shots before and after the repair, using a mic, laptop and Adobe software. I don't think it was very conclusive. The shot on the left is without an ABR, and the other after my repair.

    I have since written to B&O asking them for advice on the material to use. Their reply was that any appropriate material can be used

     ?!Unsure

  • 03-15-2009 3:25 PM In reply to

    • Dillen
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Brilliant answer from B&O. Laughing

    In other words; They don't know and/or they don't care.

    Martin

  • 03-15-2009 4:50 PM In reply to

    • Craig
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    For a while I had some RL60's in my garage/workshop. These had the ABR's removed, have to admit they still sounded good. Although I was not able to compare them to a pair with the ABR's.

     

    CraigSmile

     

    For millions of years, mankind lived just like the animals. Then something happened which unleashed the power of our imagination. We learned to talk and we learned to listen..

  • 04-20-2009 1:55 PM In reply to

    • shwaya
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Hi... or could I say "Hej"? Er du dansker?

    I'm from Denmark, Humlebæk north of Copenhagen. I've just had a pair of Redline 45 for free together with a Beocenter 7700 and a Beogram CD 3500.

    I'm having the same trouble as everyone else with the rottening foam in the bassport of the 45's. I'm not a wizzard with electronics, but I've managed to remove all the smuldered foam without damaging the speakers.

    Now I wonder can you help me with a good solution for replacing/rebuilding the 'woofers'? Or can you offer any good advice if I have to do it myself?

    Hvis du fx taler dansk og kan hjælpe mig med at oversætte/forklare noget af det tekniske lingo, som BeoMatt bruger i sin forklaring af 'how to do it', ville det være en kæmpe-hjælp!!

    Glæder mig til at høre fra dig...

    Mvh Mikael

  • 04-20-2009 4:09 PM In reply to

    • Dillen
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Mikael,

    Welcome to Beoworld !  Yes -  thumbs up

    You have a PM (in danish) - check your inbox in the upper right corner of this page.

    Martin

  • 08-01-2009 1:50 PM In reply to

    • abdank
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

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    Hi BeoMatt!

    I'm from Sandvika, Norway. I have a pair of Redline 45. I'm having the same trouble as everyone else with the rottening foam in the bassport of the 45's. I have problem to open the case. I removed 10 screws at the rear of the cabinets, but I have problem with opening and will not damage frontplate. Please help me!

    Wladek.

  • 08-01-2009 2:13 PM In reply to

    • BeoMatt
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Hi Wladek,

    I hope I can be of help, if my memory serves me correct it does require a little confidence to prise the rear section away, I think I removed the central part aswell with the screws that hold the rear stand on. Matt

  • 08-01-2009 2:18 PM In reply to

    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    abdank:

    I'm from Sandvika, Norway. I have a pair of Redline 45. I'm having the same trouble as everyone else with the rottening foam in the bassport of the 45's. I have problem to open the case. I removed 10 screws at the rear of the cabinets, but I have problem with opening and will not damage frontplate. Please help me!

    Did you get the two screws under the strap holders as well as the one in the bottom of the connector bay?

    If yes, it might just be tight (there's a foam gasket in there), or you're trying to pull at the wrong place. The "red line" will stay with the front plate, you have to pry between that and the rear part of the case.

    -mika

  • 08-01-2009 3:43 PM In reply to

    • abdank
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    Thank You for help!

    Everything is OK now!

    Wladek.

  • 11-01-2009 9:41 PM In reply to

    • mfishmike
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    Re: Bang & Olufsen Red Line Authentic DIY ABR (Auxiliary Bass Radiators) Successful Repair

    I have come up with a great ABR repair/modification and many folks in several countries have used my advice and love their finished speakers.  Many are original owners and didn't want to loose them after enjoying them for so many years. 

    I use twin 5.25 passive radiators with an Fs of 23 hz in place of the ABR plates.  The bass is outstanding.  I don't have any testing software but my ears have worked well for me for years.  I do have a track history of building some fine speakers.  My B & O Redline modification can be found at: http://www.speakerhobby.com/bangolufsen.htm

    I have provided a fully detailed photo of the modification for your convenience.  I also rebuilt the crossovers to get rid of the 63 volt electrolyte caps. 

    Unfortunantly, Tymphany has discontinued the passive radiator, so I've ordered 1,000 of them specially built for me by Tymphany to have them available to those who want to rebuild their Redlines using my method.  I'll also be using them in some other projects and will be selling them retail.  The build completion date is November 30th, and I expect to have them by December 15th.

    These resonant free B & O cabinets are so well built and sound so good, I would hate to see them go to the dump because of the failed ABRs.  I've bought several pairs of attempted repairs with various rubbers, carpet underlayments, and unusual foams, all which didn't work at all.  I have a nice inventory of drivers available.

    Mike

    http://www.SpeakerHobby.com
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