Modular Active Crossover Boards in development

[charlielaub]

Hey All,

I am currently developing modular active crossover PCBs that have baffle step, fully parametric EQ, and make it possible to create a wide variety of crossover functionalities/topologies. Basically, it's all the goodies that you need to construct a serious crossover for your 2-way, 3-way, 4-way speaker or subwoofer system!

I have designed the circuit boards and sent them out for prototyping. Hopefully I will have everything tested and checked out by the end of JAN. Once all the kinks are worked out, I plan to offer these as kits of PCBs plus parts. Some assembly required.

For now, click on the link below to get an overview of how they work, and what they can do.

-Charlie


Click Here to view the Attachment: MODULAR CROSSOVER OVERVIEW.pdf


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[charlielaub]

FYI - I updated the OVERVIEW PDF and added more content related to designing the stages, comparing response types, etc.

Use the link in the first post in this thread to down load it.

-Charlie

[philiparcario]

Hey All,
...
I have designed the circuit boards and sent them out for prototyping. Hopefully I will have everything tested and checked out by the end of JAN. Once all the kinks are worked out, I plan to offer these as kits of PCBs plus parts. Some assembly required...


-Charlie




.

Charlie will it be solder assembly or nice easy assembly like the sure amps pe are selling. My eyes are old even after the cataract surgery. I see middle and far nice but close is bad. the sure amp assembly would be best for a guy like me mostly set screws and mounting in a case. I would be interested in some x-overs if I don't have to solder. phil

[charlielaub]

Charlie will it be solder assembly or nice easy assembly like the sure amps pe are selling. My eyes are old even after the cataract surgery. I see middle and far nice but close is bad. the sure amp assembly would be best for a guy like me mostly set screws and mounting in a case. I would be interested in some x-overs if I don't have to solder. phil

Hi Phil,

I suggest getting a couple of these very handy helpers:
http://www.parts-express.com/pe/show...number=360-670
I have several of them! You can hold parts with one, and the circuit board with another. They are currently on sale, too!

These will be initially sold as a parts kit - everything must be soldered on to the board. But it's all thru-hole components THERE ARE NO SURFACE MOUNT DEVICES! Op amps are in DIP packages. Connections are made via terminal blocks. Nothing the average guy with a basic soldering iron can't handle.

-Charlie

[Deward Hastings]

I suggest getting a couple of these very handy helpers:

I use the PanaVise version, which I believe is a lot sturdier, and a fluorescent ring light with a 5" magnifier in the middle (a Luxo knockoff). Amazon has a LED version that looks nice, but is a lot more pricey than what I've got:

http://www.amazon.com/Ultra-Efficien...pr_product_top

Key is the quality of the magnifier lens . . .

I can generally do SMD under what I've got, but sometimes I take the board to the stereoscope for a better look . . .

The flip-down magnifying visors help a lot too, and can be had in various focal lengths from the better vendors. Again, it's all in the quality of the lens(es).

[charlielaub]

WAIT, THERE'S MORE!

I'm currently finalizing the design of a continuously adjustable active delay circuit. The design concept is similar to what I used for the modular crossovers - with emphasis on being extremely flexible and adaptable - so that they are suited for use with many kinds of loudspeaker systems.

The current design provides a maximum delay of approximately 450micro seconds, which corresponds to the delay resulting from driver offset of around 6 inches (or 16 cm). It's intended for use to delay the tweeter output. The delay, as a function of frequency, is constant, within a few uS up to about 10k Hz. As a result, even with high tweeter crossover points, there will still be constant delay throughout the crossover region.

Using the same circuit design but modifying a few component values, the delay time may be increased to as much as 8-10 milliseconds, while the frequency above which the delay is no longer constant falls to around 500 Hz. For reference, 2.9ms is about 1m distance. Several ms of delay would be useful for delaying the woofer output, not because of delay arising from the physical offset, but because of crossover-generated phase difference. Points on the curve in between these extremes are possible as well, so that one could trade off the frequency and delay characteristics to suit crossovers in any frequency range.

Offset-generated phase mismatch is often most problematic (and obvious) in the crossover to the tweeter, however any significant phase difference between drivers within their crossover region can produce undesired peaks and nulls in the response.

I think that this should round out the full set of capabilities that are needed to produce high performance active crossovers, with the exception of a Linkwitz-Transform board perhaps... Thanks to everyone for their input on these projects.


-Charlie

[lasse]

Hello,

The last post on a unit for time delay made the picture complete for me. I have been searching for a "hard-wired" active XO for my main speakers, that now is fed by a DCX2496. I have read all the posts on improvements to the DCX and think that a better way would be to get a dedicated XO with top-of-the-line components, after developing the XO-parameters, including delay, with the DCX.

Your product, Charlie, can be a commercial success, I think. (I will at least buy a couple, if I may)

Regards//lasse

[Deward Hastings]

that this should round out the full set of capabilities that are needed to produce high performance active crossovers, with the exception of a Linkwitz-Transform board perhaps...

Linkwitz transform capability is invaluable these days, as we push woofers to mate with subs, and tweeters down into their roll-off. It can often be fudged, especially with tweeters where there is usually "extra" sensitivity that allows an inverse filter to flatten the low frequency response curve, but with woofers . . . well . . . being able to put in a LT to force the LF curve to B2 *at the desired crossover frequency* is one of the stronger arguments *for* active crossover. For the M/T crossover you must have delay, and for the W/SW crossover you must have LT. If the SW is not going to be co-located with the mains delay capability is needed there, too, but that's more difficult to implement in analog . . .

[mzisserson]

WOW the first active x-over I may actually concider! What a great concept/idea. If you are going active you may as well just get it all in there. Thanks!

[Deward Hastings]

WOW the first active x-over I may actually concider!

Well, if you want analog there were the "bob ellis group buy" boards a couple years ago which host the same functions (but a bit crowded sometimes) . . . there may still be some of those floating around . . . and the Linkwitz boards, which are a lot bigger and have everything on them (and are easy to work with as a result), but look kind of odd "underpopulated" for a two-way. They're $50 ea. as I recall . . .

And there are the new "plug and play" digital boards that come in (fully populated and ready to go) at about $150. It looks like the active crossover is finally becoming cheap-and-easy enough (along with low-cost high quality Class D amps) to see significant adoption . . . a good thing for "quality" audio . . .

[charlielaub]

Well, if you want analog there were the "bob ellis group buy" boards a couple years ago which host the same functions (but a bit crowded sometimes) . . . there may still be some of those floating around . . . and the Linkwitz boards, which are a lot bigger and have everything on them (and are easy to work with as a result), but look kind of odd "underpopulated" for a two-way. They're $50 ea. as I recall . . .

And there are the new "plug and play" digital boards that come in (fully populated and ready to go) at about $150. It looks like the active crossover is finally becoming cheap-and-easy enough (along with low-cost high quality Class D amps) to see significant adoption . . . a good thing for "quality" audio . . .

Actually, not only can my crossover boards do more than the Bob Ellis PCBs, they are a lot more flexible, too. Once you build up a set of my boards, you can adjust them over and over without replacing any components. Bob's boards need to have some components unsoldered and new ones soldered in, I believe. I am not sure that he has any more to sell, either, but you can contact him over at DIY AUDIO and ask. Since I will be supplying all the components along with the boards, you are sure that you will get everything you need to build them up - it's one stop shopping.

I think that the competition is the MiniDSP boards. These sell at about $110 for one board and one software package for it. If you want to install one in each speaker cabinet you need to buy TWO. A stereo pair of my main board and filter board should come in below the cost of ONE of the MiniDSP boards.

-Charlie

[Deward Hastings]

I think that the competition is the MiniDSP boards. These sell at about $110 for one board and one software package for it.

There's also (currently, anyway) $44 for shipping (for the miniDSP). I suspect that there will be a lot of people who are hesitant about another ADA conversion device, and would prefer a (relatively) simple all-analog crossover. Still, the miniDSP does seem to have replace the DCX2496 as the one to which everything else will be compared . . . even though there are very few of them in service at this point . . .

[DoubleTap]

I'd be interested in trying these out ... definately keep us updated!

[charlielaub]

Linkwitz transform capability is invaluable these days, as we push woofers to mate with subs, and tweeters down into their roll-off. It can often be fudged, especially with tweeters where there is usually "extra" sensitivity that allows an inverse filter to flatten the low frequency response curve, but with woofers . . . well . . . being able to put in a LT to force the LF curve to B2 *at the desired crossover frequency* is one of the stronger arguments *for* active crossover. For the M/T crossover you must have delay, and for the W/SW crossover you must have LT. If the SW is not going to be co-located with the mains delay capability is needed there, too, but that's more difficult to implement in analog . . .

Deward, you brought up a very good point which I think is often overlooked regarding the Linkwitz Transform. The LT has gotten a reputation for "boosting" the low end output of a sealed subwoofer driver in a small box, but this is only one of its uses (as you correctly point out).

The LT is extremely useful when paired with active crossovers. That's because a driver in a sealed box forms a second order HP filter. This has a Q and corner frequency just like an electrical stage, and so you can use the driver response as part of the overall crossover function. The problem arises when the Q and/or corner frequency of your driver-in-box have different values from what is required as part of the desired overall crossover. This is where the LT comes in - you can change both the phase and amplitude of the driver-in-box using the LT so that the Q adn corner frequency take on the values you want! This can done by lowering the corner frequency, like one does in a sub application (which requires additional power/lift), or it can increase the corner frequency (which does not require additional power/lift compared to the passband). You can just dial it in to the Q,Fc values that are needed. It's more than just contouring the frequency response like and EQ because it also changes the phase response. The combination of the LT electrical circuit plus the in-box driver response creates a new response shape, characterized by a new Q and corner frequency, e.g. the response is "transformed" to a new one.

Anyway, I am currently working on an LT circuit design that is fully adjustable, e.g. once you build it you can tweak some pots (five of them, actually) to change the behavior without having to replace any components or do any additional soldering. The circuit is based on a special implementation that is not widely known, but should permit fully independent adjustment of the parameters.

The LT is just a biquadratic filter, and for some background reading, check out the following links:
Biquadratic Filter Transfer Function (caution: poles and zeros discussed!)
SL's LT implementation using a single op-amp (but NOT adjustable!) - See the figure of the "s-plane" (5th figure) that shows the biquadratic filter transfer function (middle term in the equation H(s) = ... )
LT circuit by Marchand Electronics (component values limit it to subwoofer EQ only)


-Charlie

[charlielaub]

There's also (currently, anyway) $44 for shipping (for the miniDSP). I suspect that there will be a lot of people who are hesitant about another ADA conversion device, and would prefer a (relatively) simple all-analog crossover. Still, the miniDSP does seem to have replace the DCX2496 as the one to which everything else will be compared . . . even though there are very few of them in service at this point . . .

The MiniDSP does seems like a new roll-your-own DBX2496. It's a very interesting product, really. But if you want to build a basic 2-way speaker, it is really overkill.

-Charlie

[Deward Hastings]

But if you want to build a basic 2-way speaker, it is really overkill.

Yes . . . and at some price point it devolves back to "passive" and just using the amps in the HT receiver. Where the "transitions" occur is continuously evolving, what with "active" crossovers and excellent amplifiers becoming ever less expensive . . .

[jpomann]

These sell at about $110 for one board and one software package for it. If you want to install one in each speaker cabinet you need to buy TWO. A stereo pair of my main board and filter board should come in below the cost of ONE of the MiniDSP boards.

-Charlie

What do you estimate the the total cost would be for your kit, for a 2-ch 3-way system, including boards, components, and all pots? (minus power supply, connectors, chassis, etc.)?

JP

[Æ]

I'm definitely curious and probably interested. I'll be watching. Thanks

[penngray]

The MiniDSP does seems like a new roll-your-own DBX2496. It's a very interesting product, really. But if you want to build a basic 2-way speaker, it is really overkill.

-Charlie

The miniDSP, DCX are only overkill if you enjoy building passive XOs.


btw, Great thread its great to read about new active crossover options. If your price point is true then you can put me down as a buyer too

[mzisserson]

. It looks like the active crossover is finally becoming cheap-and-easy enough (along with low-cost high quality Class D amps) to see significant adoption . . . a good thing for "quality" audio . . .

That is the key. I am as geeky as the next guy, but from what I have seen of active x-overs, they take WAY too long to tune in properly, then if you move your speaker 1" you are screwed.

This is a great concept, affordable (I assume) and fun for a DIY-er, not convinced a consumer will prefer over plug & play, but I would love to get one, build a passive x-over, and A/B.