# Conversion of B&W 805 to active - help



## rjpcardoso (Oct 23, 2013)

Hi everyone,

In order to try improve my system I had this crazy thought of "upgrading" the crossover of my B&W 805s to active crossover. After seeking for the available options on the market I have decided to order the Marchand XM44 which seemed to be flexible and reasonable priced in comparation with others.
I have ordered 3000hz and 4000hz cards (1st and 4th order) as B&w states 1st 4000hz cross point.

After doing some measurements I have found that the bass is not behaving as I expected so would like to ask your help on the solution that usually speaker developers use to cure this issue, as I dont want to do wrong things..

You can see on the following graph in yellow the bass response and the full speaker response with XM44 4000hz 4th order card and in red you can find the matching graphs for the original crossover. Measurements were made 1m away from the speaker. There was no aditional eq on both.



Is the bass raising because of the impedance? What is usually implemented to cure this?

I have set in my processor a Q filter that seems to fix the problem but dont know if its the right way to do it. 

Next image (purple )is full graph equed in the processor.
Can someone please help?


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## rjpcardoso (Oct 23, 2013)

think I got this in the wrong section of the forum.
Can a moderator move to DIY speakers if more appropriate?
Thanks


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## theJman (Mar 3, 2012)

You're in a bit of a gray area regarding which might be the best area for this post. On the one hand it's a manufactured speaker, but you're attempting to modify it in a DIYish manner.

I'll leave it here for now, but if you don't get much assistance and want it moved let me know.


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## rjpcardoso (Oct 23, 2013)

thanks Jim


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## robbo266317 (Sep 22, 2008)

Is this measurement at the listening position? If so it could be a room interaction rather than a driver issue.


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## rjpcardoso (Oct 23, 2013)

robbo266317 said:


> Is this measurement at the listening position? If so it could be a room interaction rather than a driver issue.


No all measurements were taken 1m away from the speakers. In red you can see the measurement made for stock analogue crossover and in yeallow at the same mic position the active crossover.
Problably i was not clear but my concern in the difference between red and yellow and not the dip in the beggining ( at least for now ).
Its clear that there is same sort of eq implemented in the analogue crossover. Just wondering which type and if this is normal?
How is people with active crossover dealing with this?
Thanks


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## robbo266317 (Sep 22, 2008)

Ah, ok. 
Are you able to plot the results, using the active crossover, for each driver independently ie, just the bass and then just the tweeter so we can see what the response is of each.

Also are these the speakers you have? http://www.soundandvision.com/content/bowers-amp-wilkins-805-diamond-speaker-system-ht-labs-measures


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## rjpcardoso (Oct 23, 2013)

Hi its the previous generation of those speakers, the 805s without the diamond tweeter.
Let me grab my pc and I will add the plot tweeter and bass separate for both crossovers without eq on the active crossover. I actually also did a test of connecting the bass to the amp with crossover in between and the result was similar to the active crossover, which again leads me to believe there is something tamming thr bass in the analogue.


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## rjpcardoso (Oct 23, 2013)

top yellow plots are from active, bottom reds from original analogue. Active only with crossover 4th at 4000hz 
Any Suggestion?


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## robbo266317 (Sep 22, 2008)

Going by those results I believe you are correct in assuming they have added filters to the crossover to change the response.
Personally, I would go with the setup in your first post (purple graph) using EQ in the processor and see how you like them after a week or two of listening.
After that I would investigate what is causing the anomaly in the bass region.


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## rjpcardoso (Oct 23, 2013)

Hi Robbo,
Thanks for the help. It currently is like in the purple and I like the sound of it. I'm Just wondering if could do better by fixing the woofer problem the right way.
Im sure that some speaker developers face this problem and there should be a common practice for this type of situation? Maybe not?

Anyone with active or analogue crossover experience can comment? Is this happening because woofer impedance changes across the freq?

Thanks


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## robbo266317 (Sep 22, 2008)

The woofer impedance, within reason, should not affect the output since modern amplifiers are capable of handling it.


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## Orange55 (Jul 20, 2009)

Have you thought about contacting b and w and pose the question to them for guidance?

When I first started measuring my speakers for EQ I contacted linn as the response I was seeing seemed to have way to much high frequency. One of their speaker designers confirmed to me that they give their speakers a slight smiley face response curve. Which tied in with what I was seeing and allowed me to be confident in my actions to cure that issue. 

Hope that helps?


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## rjpcardoso (Oct 23, 2013)

Hi Orange,
I don't have much experience with measuring speakers without the original crossover, and thought this was a "normal" behaviour of some sort of speakers when connected directly to a power amplifier.
It's a good idea to contact B&W just wanted to captured the most information possible before,because again, thought it was a normal behaviour.

@theJman: Do you think we can move the thread to DIY just to check if any crossover DIYer can help ?

Thanks


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## Orange55 (Jul 20, 2009)

rjpcardoso said:


> Hi Orange,
> I don't have much experience with measuring speakers without the original crossover, and thought this was a "normal" behaviour of some sort of speakers when connected directly to a power amplifier.


I think you have entered a very specialist area and I you may well be right in asking this to be moved to the DIY section.

Good luck, sounds like a very good anorak!


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## robbo266317 (Sep 22, 2008)

I have moved the thread to the DIY Speaker forum for you.
If, as I suspect, it is a related to the port tuning then it should show up on a close mic scan of the driver and port outputs. 
Place the mic 25mm (1") from the port and do a scan and then do another scan with the mic close to the center of the bass driver.


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## aktiondan (Feb 18, 2007)

I think the word crossover is misleading in speaker design and oversimplifies the purpose of all those caps/inductors/resistors in between the amp and the drivers. While it appears as though you've done a fair job of mimicking the crossover point of 4kHz, you haven't corrected for other characteristics of the "crossover" such as baffle step compensation, notch filtering, padding, phase correction, crossover slopes/types, etc. You just don't know what the true transfer function of the original passive crossover is, which your active crossover would have to duplicate in order for it to have a similar sound, or at least produce a similar FR plot. 

Fortunately you have REW! I would take the passive crossover and run it through REW and see what it "looks" like. This can be done with a simple loop-back into your computer and a resistive load comparable to the drivers' nominal impedance. You can create a similar plot with your active crossover. That will at least show you what you need to do to get the in-room measured response plots to overlay, assuming that is what you're trying to do. I'm not familiar with the active crossover you mention. What kind of response shaping can it perform? I think it's cool you're taking a consumer speaker and trying to make it active. Haven't heard of too many people attempt that especially on such a nice pair of speakers. 

Edit - just re-read that you were able to EQ the response and get it to look flat (purple graph looks pretty good), so it sounds like that crossover has some pretty good shaping properties. I wouldn't be worried about the dip in the bass region, most likely a room mode. As was mentioned, measure each driver at 1" and see what it looks like.


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## natehansen66 (Feb 20, 2011)

If the yellow response is what you get with your active xo I'd say you're way off. Standard fixed slope crossovers rarely work well with real drivers in my experience. Gated measurements of the tweeter and woofer would show you what's really going on. The purple trace is nice and flat but if that's in-room it probably isn't correct and will change with position. You need to see what the speaker is doing without the room influence.


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## rjpcardoso (Oct 23, 2013)

robbo266317 said:


> I have moved the thread to the DIY Speaker forum for you.
> If, as I suspect, it is a related to the port tuning then it should show up on a close mic scan of the driver and port outputs.
> Place the mic 25mm (1") from the port and do a scan and then do another scan with the mic close to the center of the bass driver.



Hi,
sorry for the delay on replying but been impossible to take measurements.

You can find in red the woofer plots with the mic close and in yellow the port plot.
Any conclusions? With the mic close it seems more linear but still some rising in dbs..


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## rjpcardoso (Oct 23, 2013)

aktiondan said:


> I think the word crossover is misleading in speaker design and oversimplifies the purpose of all those caps/inductors/resistors in between the amp and the drivers. While it appears as though you've done a fair job of mimicking the crossover point of 4kHz, you haven't corrected for other characteristics of the "crossover" such as baffle step compensation, notch filtering, padding, phase correction, crossover slopes/types, etc. You just don't know what the true transfer function of the original passive crossover is, which your active crossover would have to duplicate in order for it to have a similar sound, or at least produce a similar FR plot.
> 
> Fortunately you have REW! I would take the passive crossover and run it through REW and see what it "looks" like. This can be done with a simple loop-back into your computer and a resistive load comparable to the drivers' nominal impedance. You can create a similar plot with your active crossover. That will at least show you what you need to do to get the in-room measured response plots to overlay, assuming that is what you're trying to do. I'm not familiar with the active crossover you mention. What kind of response shaping can it perform? I think it's cool you're taking a consumer speaker and trying to make it active. Haven't heard of too many people attempt that especially on such a nice pair of speakers.
> 
> Edit - just re-read that you were able to EQ the response and get it to look flat (purple graph looks pretty good), so it sounds like that crossover has some pretty good shaping properties. I wouldn't be worried about the dip in the bass region, most likely a room mode. As was mentioned, measure each driver at 1" and see what it looks like.


Hi,
I have realized that the crossover is not only separating freq from bass and tweeter and that it actually adds some corrections to the speaker. The reason why I have converted to active was to get the most I could from this speakers, so I don't need to replicate what I have and instead and I want to learn how to this compensation the best way possible. The original crossover is first order and currently Im running 4th order crossover in active.
The eq I have done was actually not in the crossover but instead on the processor (Tag mclaren av192) where I can have Q filters to reduce or boost freq. My first question is: is this the correct way to it ? Or is it better to implement it in the crossover? The second is: Which type of correction is being applied in the original crossover? Is it baffle step compensation ?

I will definitely try to measure the crossover, just need to investigate how to do it.
Thanks


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## rjpcardoso (Oct 23, 2013)

natehansen66 said:


> If the yellow response is what you get with your active xo I'd say you're way off. Standard fixed slope crossovers rarely work well with real drivers in my experience. Gated measurements of the tweeter and woofer would show you what's really going on. The purple trace is nice and flat but if that's in-room it probably isn't correct and will change with position. You need to see what the speaker is doing without the room influence.


Yss the yellow is what I get with the active xo without any EQ in the AV and at 1m distance in my room.
How can I measure without the room influence? Would it be better if in an open space (like the garden)?


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## natehansen66 (Feb 20, 2011)

You need to gate the impulse before the first reflection. Easy to do in REW. Outdoors and gated would be good because it would give you good data lower in freq. You should be able to get at least 3ms of good data which is sufficient for your xo.


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