Active crossover question

I'm planning on making a preamp and 4 monoblocks (courtesy of ESP no less) driven through a Linkwitz-Riley type active line level crossover network.

My question is do I have to do major surgery on my speakers for this to work - they are rather expensive (for a student at least)B&W DM603 S3s?

I understand this is the best thing to do - i.e. remove as many components from the high level line as possible, but is it completely necessesary?

If I run two sets of cable per speaker and remove the bridging bars will this arrangement still work (provided I use the same crossover point in active and passive circuits)?

Will this approach lose the gains of using 4 monoblocks to drive different frequencies?

Any response will be helpfull.

All praise must go to ESP for the incredibly informative site, http://sound.westhost.com



:D
 

MRehorst

Member
2002-05-17 8:48 pm
The existing networks in the speakers will affect the signal driving the speakers. A Linkwitz-Riley crossover is used to insure that the signals from the drivers will remain in phase at all frequencies. If you have a bunch of reactive components still tied to the drivers, at the very least you can expect the phase to get screwed up, and probably the frequency response as well.

You should completely disconnect the crossover networks inside the speakers, or at least short them out by jumpering directly from the connectors to the drivers. The crossovers probably connect to the terminals and drivers using push-on terminals anyway, so it shouldn't be a big deal.

If there is any sort of protective device for the tweeter in the crossover network, you should try to reuse it. Connecting any amp capable of more than a couple watts directly to a tweeter is asking for trouble. Check the amp for DC at the output before you connect it to the tweeter. Also watch out for turn-on/off thumps from the amp. While they are harmless to a speaker with a crossover, they can send your tweeter diaphragms across the room with no high pass network to protect them. It is best to use an amp that has output relays to allow power-on transients to die out before connecting the output to the speakers.

Once you have the system up and running with the active crossover you'll forget all about the passive crossovers that used to be in the speakers.

MR
 
If I may piggyback for a minute...

I am working on a pair of active speakers and will biamp in a similar fashion. Are there any suggestions for DIY tweeter protection? I was worried about that, having toasted a pair of KEF tweeters once in my car stereo when an electronic crossover failed. I used 0.25A fuses for the replacement tweeters, but I have a feeling that is not the best for a home speaker.

Thanks! Dan
 
You have to take out the passive crossovers. If you don´t then the whole thing will probably sound worse with the sound going through all those filters. If you don´t want to take the passive crossovers out than you don´t need to use an active crossover at all. Just biamp the system.
If you can work your way around electronics you can take the pasive crossover out and rewire you speakers for active. You can allways put the passive crossover back if you ever need to sell your speakers.
 

roddyama

diyAudio Moderator Emeritus
2002-01-19 9:25 am
Michigan
Hi Dan,

I went to the B&W site and had a look at your speakers. Very nice looking speakers

http://www.bwspeakers.com/products/...peaker_id=FE212946-C0D6-4DCF-89AF645E767EAB8F

The bass and the mid ranges are handled in parallel by the 2 - 7" drivers. There will be some sort of electro-mechanical filter utilizing the manipulation of the mechanical parameters of these two drivers as well as conventional filter components.

B&W does provide the terminals for bi-wiring, but I would get the ok from B&W before I tried to bi-amp using these terminals. You might end up connecting the outputs of the two amps together in some unknown fashion.

If B&W says yes, then you're all set, but you won't need an electronic xover. I would assume the hi-pass and lo-pass elements to be built into the speaker.

If they say no, than you can still add a sub-woofer. In which case you would then need an electronic xover between the sub-amp and the main-amp.

Hope this helps.
Rodd Yamashita
 
Thanks for the help...

...thanks for all the response.

I wasn't expecting so many replies!

There is a slight problem with my speakers as previously mentioned in one of the replies. Currently they operate in a 2.5 way configuration - the high frequencies to the aluminium tweeter, mid and bass to the kevlar cone and bass only to the aluminium cone (mushroom).

If I was to "modify" the crossovers would it be best to set the Linkwitz-Riley to around 300Hz (as suggested in ESP) and use the high/mid pass section of the crossover to seperate the high/mid signal to the tweeter and kevlar cone?

Thanks for the help so far guys!
 

pinkmouse

diyAudio Moderator Emeritus
2002-04-03 7:15 pm
Rotherham, England
From what I understand of the 603s, it sounds like the crossover point between the low pass for the mushroom driver, and the high pass for the mid driver is not the same, i.e. mushroom is driven below, say, 500Hz, but the low mid is not rolled of till 300Hz, (purely hypothetical figures...).

I don't know why, but B&W make damn fine speakers, so I'm sure it makes sense somehow.

I think you need to look at your aims, are you just trying to replace your passive crossovers because it is the thing to do, or do you have the measuring kit to work out which driver is doing what at a given frequency, so you can calculate your active crossover properly.

Sorry to put a downer on your project, but I would suggest trying something a little less complicated than a 2.5 way speaker as your first attempt at DIY active...
 

roddyama

diyAudio Moderator Emeritus
2002-01-19 9:25 am
Michigan
One possibility

I don't know why, but B&W make damn fine speakers, so I'm sure it makes sense somehow.

One possibility is that the bass is tuned with a bump in the response near its lo cut-off and the mid is subject to the baffle step boost up in the ~500Hz area. Then, if both the mid and the bass drivers are operating together between the bass bump and the baffle step, the theoretical result is a flat response.

Just a thought,
Rodd Yamashita
 

pinkmouse

diyAudio Moderator Emeritus
2002-04-03 7:15 pm
Rotherham, England
I think, like all companies, B&W have their marketing weanies, but lets face it, they are the only company that I am aware of that can sell you an excellent loudspeaker at £100, or at £30,000!

B&W do their own thing, and are one of the few companies that will spend huge amounts of money on top end systems, and use that R&D to beniefit budget buyers.

Yes, you can be cynical, ( and 90% of the time you have to be), but I suspect in the 603s, they were trying something different, which is why I suspect trying to duplicate their passive crossover might be difficult..
 
after some research...

...I discovered the frequency allocation:

4 kHz < Tweeter < 22kHz

44Hz < Mid/Bass < 4kHz

44Hz < Bass < 150 Hz


The large overlap (between 44Hz and 150Hz) that is covered by both mid/bass and bass drivers is the reason for them being 2.5 way.

I'll have to give B&W an email as to whether they can be actively bi-amped or just passive, thanks to everyone for the feedback!





:cool: :cool:
 

MRehorst

Member
2002-05-17 8:48 pm
In a speaker with a passive raditor, the passive radiator does little for the upper bass and works primarily at low bass frequencies, which sounds a lot like the description of "2.5 way" operation.

There really is very little new stuff around, especially in loudspeaker boxes. The designs were thought of many years ago and maybe a few wouldn't work with drivers made when they were first thought of, but modern materials have now made them possible. But whether they have any truly new stuff or not, the marketing department wants to sell "New, improved!" stuff every year, so guess what? They come up with some new way to describe something old and voila! the money rolls in.

I'm not saying that that is the case here- it will take someone opening up the speaker and looking at the wiring to know for sure, but B&W is a business like any other, subject to the same pressure as everyone else to keep coming up with new stuff. Don't be surprised if a "2.5 way" speaker is really just a 2 way plus passive radiator.

My 9th grade science teacher, Ralph Vena, taught me the most valuable lesson of my life- "a good student is eternally skeptical".
I can't even remember any of my other teacher's names. I want them to engrave "here lies a good student" on my tombstone.

MR
 
...I'm prety sure it's not passive

The actual speak cabinets are in two halves - the top half contains the tweeter and kevlar mid/bass and the lower half contains the mushroom sub cone.

Both halfs of the cabinet are independantly ported one to the rear and one to the front and looking through the rear port the two halfs of the cabinet appear to be independant.

Thanks for the input though, I was reading about passive radiators as an alternative to port tuning (specifically on subs) a few months ago, but I'm pretty sure this is not passive.
 
Re: ...I'm prety sure it's not passive

With the complex XO in the B&W you might well be best off with a passive bi-amp. This, although not usually as beneficial as using an active XO is simple & will allow you all the benefits of any FR tailoring done in the built-in XO.

For this you need 2 identical stereo amps (or 4 monoblocs). Disconnect the biwire jumpers and connect a separate amp channel to each set of binding posts.

Doing an active XO would require pulling the passive XO, tracing its circuit, figuring out what it does, and then duplicating this with a custom active XO -- this is where John Pomann's Active XO Xperimenters Kit is very useful. You play with the active XO till you get it right, then you freeze it.

dave
 
I don't know about your particular speakers, but the B&W 803 used the similar principle for woofer and midbase drivers. The crossover was rather simple. If you wan't to bi amp you could do it at 4k removing passive filtering for tweeter and ULF driver (but I might be wrong on that), leaving the series coil for LLF driver in place. This should work fine providing you use the same slopes in active crossover. I would start with obtaining crossover schematic from B&W first or figuring it out yourself.
 

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HPotter said:
If you wan't to bi amp you could do it at 4k removing passive filtering for tweeter and ULF driver (but I might be wrong on that), leaving the series coil for LLF driver in place.

You would get better use of 2 amplifiers by driving ULF & HF with one amp thru the passive XO and LLF with the other amp with a simple 1st order PPLOXO. This could be built right into the bass amp.

Best of course would be to tri-amp them. Tweeter protection would come in the form of a big cap that has its XO well below the active XO.

dave
 
MRehorst said:
In a speaker with a passive raditor, the passive radiator does little for the upper bass and works primarily at low bass frequencies, which sounds a lot like the description of "2.5 way" operation.

There really is very little new stuff around, especially in loudspeaker boxes. The designs were thought of many years ago and maybe a few wouldn't work with drivers made when they were first thought of, but modern materials have now made them possible. But whether they have any truly new stuff or not, the marketing department wants to sell "New, improved!" stuff every year, so guess what? They come up with some new way to describe something old and voila! the money rolls in.

I'm not saying that that is the case here- it will take someone opening up the speaker and looking at the wiring to know for sure, but B&W is a business like any other, subject to the same pressure as everyone else to keep coming up with new stuff. Don't be surprised if a "2.5 way" speaker is really just a 2 way plus passive radiator.

My 9th grade science teacher, Ralph Vena, taught me the most valuable lesson of my life- "a good student is eternally skeptical".
I can't even remember any of my other teacher's names. I want them to engrave "here lies a good student" on my tombstone.

MR

Found this old thread while searching for some info ...

I have 2.5 way speakers, and there is no secret as to what it means. It's simply a 2 way speaker to which a second identical driver has been added with a lowpass filter. Hence the second midbass driver effectively provides BSC. Mine has first order LP at 200 Hz. It is not a simple 2 way and it's not a 3 way as there is deliberate overlap instead of BSC.