# Tried to add a subwoofer to the B&O, hit a brick wall.



## James cole (Sep 3, 2007)

I dont mean literally, the install went fine I tapped under the seat the cables for the left t38/9 and t38/ also t38/21 and t38/22 then fed the amp...



It all worked but I was not getting a full blown low signal, frequencies under 60hz were missing, so they are crossed over but with a brick wall of crossover, nothing absolutely under 60hz plays...which makes the install a bit worthless since you are not getting anymore than what your current door woofers output...

So... the only solution I can think off is that somehow tweak or eliminate this crossover with VCDS... Any ideas?

Thanks!
JC


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## GrantTTS (Mar 18, 2016)

Try an Audison Bit Ten

This will take the high level existing signals strip them back to basic signals de-equalise and then feed the outputs to whatever amps you want. It is possible to output to a sub from a cut off and you can tune it with a laptop via USB. Not cheap but I have used before on my BMW and my son uses one for his hi hifi. Excellent bits of kit.

www.fourcaraudio.co.uk/brands/audison/a ... n-bit-ten/


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## jonstatt (Mar 30, 2017)

No after market solution will help if the output channels from the amplifier have a fixed crossover in place. If nothing below 60Hz is there, it can't be recreated with any EQ etc. I can't see from the wiring screenshot shown above how it was determined these were left and right channels? There may be a pair of output signal level channels somewhere (full bandwidth) or it may be you are tapping rear left and right amplified channels which have a higher crossover?


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## GrantTTS (Mar 18, 2016)

There are unlikely to be any cross overs installed on an OEM basic system other than maybe on the dual coil speakers. Having been into this with BMW systems they artificially equalise the system to be compatible with the cheap speakers they squeeze into the spot that the fashion designer provides. I doubt anyone is actually cutting off these frequencies It would sound very poor if they did cut them off.

You are right to suspect that the diagram doesn't tell the whole story and there are other feeds


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## Dino_Donis (Apr 19, 2004)

I currently have a MK2 TTS with Bose, I added a subwoofer pretty quickly as I was very disappointed with the LF response. All the reports I read state that the B&O system is very good? But the fact that you are adding a sub would suggest otherwise! Is the low frequency reponse not very good??? I looking to upgrade to MK3 in the near future...


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## James cole (Sep 3, 2007)

This is the B&O full schematic for the TT...


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## noname (Aug 20, 2015)

these wires, 9-10 and 21-22 are not low signal..so I assume you did send this sign signal to an high input to the amp? is that right?
the subwoofer is mono or stereo?


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## James cole (Sep 3, 2007)

ManuTT said:


> these wires, 9-10 and 21-22 are not low signal..so I assume you did send this sign signal to an high input to the amp? is that right?
> the subwoofer is mono or stereo?


The signals are high level indeed, My amp is capable of receiving low/high level signals. Sub is Mono...

It all works perfectly except 60hz and below is not there.

JC


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## noname (Aug 20, 2015)

why did you take left and right signal then?


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## James cole (Sep 3, 2007)

ManuTT said:


> why did you take left and right signal then?


Because the amp has inputs L and R and converts to Mono... Tried with only one input but its the same only lower volume.


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## noname (Aug 20, 2015)

It can't be so.. send me some pics of the amp...
Try sending to the L and R input, both left woofer channels


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## jonstatt (Mar 30, 2017)

Just to be clear only the connections at R21/R23 should be used. Only the bass lines should be connected. If they do have a forced High pass filter then I can't see a way around it. What are the second pair of wires at R21 and R23 for though?


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## Rev (Nov 17, 2015)

ManuTT said:


> It can't be so.. send me some pics of the amp...
> Try sending to the L and R input, both left woofer channels


Usually the high level inputs are taken from the L+R speakers on a factory headunit, it then merges them to get a mono output, otherwise you'd only get bass from the L or the R.

If you want a bodge solution, you could use an ipod to listen to all your music, and just feed the amp with the ipod line out. Not sure if it'd work being plugged into the car as well though. But if it did it would give you a full signal. Sorry thats all I can think of since I don't know how the B&O is set up.



jonstatt said:


> Just to be clear only the connections at R23 should be used. Only the bass lines should be connected. If they do have a forced High pass filter then I can't see a way around it.


Are you sure though? The B&O subs could be stereo, in which case you'd want to take one +/- from each one (a +/- from R21 and a +/- from R23).


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## jonstatt (Mar 30, 2017)

Rev said:


> jonstatt said:
> 
> 
> > Just to be clear only the connections at R23 should be used. Only the bass lines should be connected. If they do have a forced High pass filter then I can't see a way around it.
> ...


I submitted by accident before I had finished so went back to edit my post. I meant both R21 and R23...but what I couldn't figure out is why are there 4 wires and not 2 at each of R21 and R23?


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## noname (Aug 20, 2015)

Woofer are double coil, 2channels each to reach lower Hz


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## James cole (Sep 3, 2007)

ManuTT said:


> Woofer are double coil, 2channels each to reach lower Hz


Yes woofers are DVC, wiring seems to be fine because the woofers sound cut off clearly in the low HZ range!

Only solution is vcds... any ideas? ManuTT?


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## Rev (Nov 17, 2015)

You're wiring from the amp, which may be where the cut off is happening. I don't know for sure, but there may be some kind of MMI adaptor you can use which will allow you to connect RCAs to the MMI unit, so you're wiring from a full signal.


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## James cole (Sep 3, 2007)

Rev said:


> You're wiring from the amp, which may be where the cut off is happening. I don't know for sure, but there may be some kind of MMI adaptor you can use which will allow you to connect RCAs to the MMI unit, so you're wiring from a full signal.


Thanks Rev... you are right but that involves a much more complex install that would be suitable only if you are scrapping the whole system

Thanks anyway!
JC


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## noname (Aug 20, 2015)

I need to check available pin from the MMI and from another Audi with B&O with real subwoofer and find the difference..


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## macaddict111 (Jun 13, 2018)

James cole said:


> It all works perfectly except 60hz and below is not there.


This isn't surprising. Driving a small woofer with low frequency sound is pointless. It simply can't reproduce frequencies that low, so trying to drive it with them just adds more power, heat, and distortion. So they've put a high-pass filter probably onto every speaker so it's not being driven with frequencies it can't handle. This is a GOOD thing normaly as it helps avoid distortion on small speakers, especially as the volume is increased. It's not a good thing for trying to add a sub.

Frankly, I'm beginning to realize the only way to add a proper sub to the B&O is to skim the audio signal off of the incoming fiber-optic MOST bus. I'm an electrical engineer and could probably make this happen, but it would be a lot of work.


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