building active speakers with sub: how to do sub crossover?

[neb001]

I plan on building a set of Zaph's B3S speakers, with integrated amp (exact model TBD, most likely a 41hz.com amp), and a sub consisting of a Tang Band W5-1138SM paired with a Dayton 70W amp. My friend that I plan on giving this to mostly uses their (completely underwhelming) current speakers for their laptop, with occasional ipod use.

My question is what should I do for a sub crossover as this system will not be using a receiver of any sort? From the limited info I was able to find from searching, I'm thinking the simplest way would be to use a y split for the line out, then put a highpass filter before the speakers.

Thanks for the help! (and sorry for the long post)

[BobEllis]

You'll also want a low pass filter on the sub side unless your sub has a suitable filter built in. Many cmmercial subs won't allow you to cross high enough to meet the bottom end of the B3S.

If you want to do more than first order filtering without too much signal level loss, you'll need to go with active filters. Given the B3S's limited low end capacity, active is the way to go.

Marchand has active crossover kits, Rod Elliot (sound.westhost.com) has LR2/4 boards or you could build a crossover on a bit of perfboard if you are careful. I've done the latter several times, but if a PCB is available it is always preferred.

[---k---]

The easiest way would be to use the crossover in the plate amp. If you go from your amp, to the plate amp then to the speakers, you'll be good. You can then set the crossover on the sub anywhere between 60hz and 200hz.

The wiring might be a bit confusing if you put your amps inside the speakers. One cool way to do it might to be to build dual subs and stick a plate amp and the chip amp inside each sub. Then, you'll just have one set of wires to the speakers. A little bit more money, but it would be cleaner.

[JonW]

The easiest way would be to use the crossover in the plate amp.

I'm about to build a smallish sub and I was looking into this recently. I've got the Oaudio plate amp which I think is pretty typical. As I understand it, the crossover in the amp will, indeed, take signal below the crossover point (say, 80 Hz) into the sub. But I think the signal that goes out from the amp and on to the speakers is full range.

In other words, the amp crossover will have the sub play what you want. But the speakers will get signal as if it there is no crossover. So the speakers will not be "protected" from trying to extend down low.

I *think* this is the case with most plate amps. Could be wrong.

[Bent]

Make sure the plate amp offers a slope better than 6 dB/octave,
the B3S has a nasty bump that a 6dB/octave x-over won't hide, but a higher order unit will.

[BobEllis]

...

In other words, the amp crossover will have the sub play what you want. But the speakers will get signal as if it there is no crossover. So the speakers will not be "protected" from trying to extend down low.

I *think* this is the case with most plate amps. Could be wrong.

I haven't seen a plate amp that did any filtering on the high pass side. You'll want to high pass the mains at 150 Hz according to Zaph. Not many plate amps I have seen will go that high on their low pass.

The OP intends to use a separate amp anyway, and 5" TB driver for bass duties. Sorry, I cannot call a 5" driver a sub.

If you're building a chip amp kit already why not add another for the woofer? I've built the chipamp.com kit and it's decent for what it is, not to mention overkill for a B3S. You could also just build three channels point to point and mount on one of Apex Jr's 6"x 8" heat sinks. Small, but given the limited power handling of the drivers, plenty for this application.

You won't need any more power supply than you planned already. You could build the amps and XO into the woofer box, and provide terminals to connect the satellites. One cable to the woofer module and then to the satellites, much like a HTIB.

On a practical note, does the intended recipient actually realize that the laptop speakers sound bad? Would he or she really appreciate the effort?

Those of us into quality sound reproduction often grossly overestimate others' dissatisfaction with their systems. My daughter blasts her car stereo with totally unbearable distortion, but only cares about high volume. A friend with a 100" screen (std def sources only, no video processing?!?) in his HT is satisfied with his knee high towers with 4" drivers placed 6" from the side and rear walls and a $150 "subwoofer" (often with a blown mains fuse) behind his $2,500 seats. He seems to appreciate my system, but he's happy enough with his that he's not interested in upgrading. He spends more time watching a 50" HDTV with B@se sound upstairs, than he does in the HT though. Someday I'll bring a nice set of three ways and a decent sub to show him what he's missing.

[---k---]

I haven't seen a plate amp that did any filtering on the high pass side. You'll want to high pass the mains at 150 Hz according to Zaph. Not many plate amps I have seen will go that high on their low pass.

Really? I wasn't aware of this. I've never used the crossover in a plate amp before, but I always assumed that it would work similar to the crossover in a receiver. I see Zaph has information on his page about this. Ooops, my bad.
You're recommendations are probably on target.

The OP intends to use a separate amp anyway, and 5" TB driver for bass duties. Sorry, I cannot call a 5" driver a sub.

Agree. But considering the use and the price, not much else seems appropriate.

[neb001]

The OP intends to use a separate amp anyway, and 5" TB driver for bass duties. Sorry, I cannot call a 5" driver a sub.

I agree, but I wanted to keep the overall package neat and compact, which is a bit difficult given the speakers themselves....then there's the price point

On a practical note, does the intended recipient actually realize that the laptop speakers sound bad? Would he or she really appreciate the effort?

Yes, I know the amp would complete overkill for for the B3S's At least I plan on going with the low power versions!

I actually believe she would appreciate the effort, though not completely as I would hope. Honestly this project is somewhat of an excuse to build a mostly simple speaker system to use as a stepping stone to a higher difficulty project.

To that end, I've contemplated forgoing the sub completely and simply adding a high pass filter to the speakers, without a sub. That would take care of the evil harmonic distortion, and the end user most likely won't miss the low frequencies too much anyways. Not exactly "HiFi", but I don't think their current speakers play that low anyways

Thank you all for your feedback, it's been helping me think this out!

[BobEllis]

Enjoy your project. I think you were on the right track adding a bit of bass to the B3S. They are OK as computer monitors run full range if you keep the level low. They won't rock you by any means, but may be suitable for small room background music.

[Bent]

Solen and Madisoud bothe sell a 50 watt plus 25w/25w plate amp for a sub/sat set.
The plate amp's crossover affects both.

[BobEllis]

I stand corrected. Sounds like a good idea for this project, too bad it is out of stock at madisound. http://www.madisound.com/catalog/pro...roducts_id=369 Solen shows one in stock http://www.solen.ca/pub/cms_nf_catal...lvbj0yJmZ0PW5m

[Bent]

Bob, I hope my post didn't offend - it wasn't meant to.
It seems the little KG-3100 is a bit of an unknown.

Zaph even approved of it for his B3S's himself.

[BobEllis]

Sorry if my post implied otherwise, no offense taken - it's nice find for projects like this.

[mpotoka]

PE has a Dayton amp that might fit the bill. Not in stock for another month...

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-774

[---k---]

PE has a Dayton amp that might fit the bill. Not in stock for another month...

http://www.parts-express.com/pe/show...number=300-774

If I'm not mistaken, that one is a bit different. That one is for active speakers and has a 3khz crossover in them. JeffB used the MCM version for a design with a pair of RS180 and had to do something weird to lower the crossover point adjust down from 3kzh to something more reasonable (long post on PE board about them). It could be more flexible than I realize though. I haven't looked at the manual or anything.

[benchtester]

another dayton amp

Dayton has a single plate amp that has one sub channel and two satellite channels. So it fits the configuration. It is a class-D amp and I don't have any information about it's sound quality. (It may be nothing like the 41 hz amps which do have a following.)

http://www.parts-express.com/pe/pshowdetl.cfm?&DID=7&Partnumber=300-772&ctab=5#Tabs

A very clean approach would be to add a servo to the 41hz amps to roll off the low end. (Even simplier with a power op amps like a gainclone.) Many people use a 1 hz. high pass to eliminate DC offset without coupling caps. It works well. I also changed the filter values on such a servo to make a tweeter amp with an Fc of 2 khz. and zero coupling caps, sounded great.

Bob Ellis' reference to Rod Elliot's site (sound.westhost.com) would also have information on this.