Active Crossover with DSP for dummies

[bencat]

Hi after hearing the efforts of Colin and Tony at shows (Harrogate , Kegworth) I would like to be able to at least try to get to grips with doing something along similar lines . However I have a number of severe draw backs in that my woodworking skills are pretty non exisitent , I have no workshop or other space I can use and my electrical circuit skills are pretty weak.

My inital thought was just abandon any thought of this but part of me still says stop being a wimp and at least make an attempt to see what can be done .

So given my lack of speaker building ability I would be looking to make changes to a current ready built speaker that I like now and remove the passive crossover and replace it with an active unit that would include some DSP control . I would also look to using exisiting ready built amplifiers rather than the kit units around (perhaps with advice and assitance I could look at using pre made kit amps class D or otherwise but not sure if this is possible or advisable.) .

What I want to ask of those of you who have already tried this type of work is it possible without too much soldering / Woodworking ability ? I know that this will place limitations but at this time I just want to give it a try without investing too much in learning new skills and hopefully not spending too much money .

Any thoughts ?

 

[insider9]

I've done this to two pairs of speakers last year. It's not that difficult but will depend on speakers you choose. No woodworking, nor soldering, the way I did it. But amplification was external. Some speakers will respond better to being "activated" than others. 

What's you plan for amplification? How serious do you want to go with this and what are you looking to spend? 

 

[insider9]

Also what speakers are you likely to use 2-way, 3-way or more?

 

[greybeard]

Andrew, like Luke has said, it should be fairly straight forward if you are using existing speakers. You will need to either remove, or at the least, disconnect the wires from the drive units and xover and from the speaker binding posts and xover. If the speaker you are using only has one set of binding posts you will need to add 1 or 2 more sets depending on whether you are using a 2way or 3way, you will need one set per driver. These will then need to be connected to 1 driver each.

 

[insider9]

Here's what I've used at my first go:

- Minidsp OpenDRC DA-8; $385 delivered, it was around £320 from memory after import related costs and exchange rates

- 2 of Sony STR DB-930 (seriously good sounding av amp for music, handles difficult loads and lots of power) ~ £80 for both 

- Dali 104 ~ £80 delivered

- Cables and connectors ~ £50 (used cheap garden variety, highly recommended)

- REL Quake subwoofer ~ £100

Total circa £600



Here are the results. Frequecy response of +/- 1dB 20Hz - 20 kHz. 1/6th octave smoothing (left axis by 1dB) and house curve applied.

 

[Tony_J]

Hi Andrew

Simplest approach soldering-wise would be to choose a pair of commercial speakers that are wired for bi- (or tri-) wiring, and bypass the passive crossover components (i.e., rip them out and wire the drivers direct to the binding posts) - that way, you already have the right number of binding posts & don't have to drill more holes in the cabs. 

The systems Ed & I showed at Harrogate and Kegworth used commercial amps - for a while I have just been using a couple of spare tranny amps I had lying around, but borrowed Ed's Behringer amps for Kegworth, which are good for the job and inexpensive. The MiniDSP 2X4 HD unit that I am using is good for building a 2-way system, but if you have aspirations to go 3-way eventually then the Behringer DSP unit that Colin used would be a simpler way to go as it gives you 6 outputs, otherwise you would need 2 MiniDSPs, one for each  (stereo) channel. Of course, with 2 MiniDSPs you could go 4-way... :dunno:

I am now working on amplification that I can build into the speaker cabinets, based on 2-channel class D plate amps plus much messing with a soldering iron, but I wouldn't advise that route if you are weak on electrical skills. 

Best starting point would be to play with a pair of inexpensive 2-way speakers to get your toe in the water and get a feel for what the tools can do for you. It is perfectly possible to take a good pair of passives and DSP them to the point where they sound bloody awful; on the other hand, when you get it right, the results can be stunning. Needless to say, you are embarking on a path that can absorb many, many hours of tweaking!

Of course, feel free to ask for help.

 

[bencat]

Okay I need as you always do to get the best help to specify what I am looking to do sorry for forgetting the basics when asking for help .

Right I am going for this as a first trial to stick to a two way speaker . I am also going to try and stick to a  a sealed / infiinite baffle unit as these tend to be the speaker loading that produces the sound I find best to listen too .

Amplifiers are going to be certainly solid state intergrated units of general good quality . I will look to getting two identical units as this makes the most sense. Purchase will be second hand and idea is two identical stereo power amplifiers unless I get really luckly and find four identical mono units (no I know it is not likely but for me that would be ideal )

My ideal Speaker to go for would be the original 70's KEF 103 Reference which is a speaker I know very well and use in my current system . Ideal in that it has an easily removed crossover plus I have full circuit diagram from KEF as a starting point and it is a sealed unit  . Drawbacks are that it is a single wire unit so I am going to have to drill to get a second set of inputs.

I am open to any suggestions for other speakers to look at but I do really want to keep with my Sealed /Infitine Baffle loading .

 

[insider9]

Sounds good. With this in mind I'd go with Minidsp 2x4 HD that will be ideal for this scenario. Lovely sounding unit. I've used this before OpenDRC DA-8.

Alternatively maybe look at EB Acoustics EB2 or what they are now called Arcaydis Acoustics EB2s. If you can find a pair this is.

 

[MF 1000]

You can always pop over to Wrexham Andrew to listen to my behringer active xover setup, have a brew and chat about what your trying to do etc 

 

[TheFlash]

I’ve only heard a couple of active setups and both have impressed me hugely.

A dumb question. I have always assumed that a speaker is “active” only when the amplification, whatever it is and however configured, is inside the cabinets. I can’t see how, for example, the large Sony’s could do this... so it appears some of you might be working to a different definition. Could you enlighten me?

 

[bencat]

Hi MF 1000

Thats a very good offer and will certainly look to take you up on that as my knowledge of how to do this is very sketchy . I know the equipment and understand what it is doing but have to admit to not really understanding how to decide on what filter to use as a starting point .

Nigel

My understanding of an active speaker is that it is one where there is a single amplifier for each drive unit connected by an active crossover before the Power Amplification and with no passive crossover after the amplification . It does not seem to matter if these amplifiers are built in , or outside the enclosure it is the position in the chain of the crossover which makes them active. Then again what I just said may be wrong as well .

 

[greybeard]

Yes Andrew, the active xover goes between the pre amp and the power amps, and as you correctly say, an amplifier driving each driver, that can be 4 monoblocs or 2 stereo power amps for a 2 way design. There are then no passive components, between the power amps, and the speakers. The Behringer does a good job for the money, and if you decide to go 3 way, it can do that too. I would also recommend that you get a u-mik 1, and REW software, so that you take the guesswork out of the calibrations. 

 

[TheFlash]

Thanks both. This also anticipates my subsequent musings about why setting up a bi-amped config - one amp dedicated to each channel not one amp per tweeter/woofer - or multi-amped (say 4 monoblocks) config to passive speakers would not also count as "active'. It wouldn't simply because of the positioning of the crossover in the chain. Old dog+new tricks=still breathing.

 

[Tony_J]

Thanks both. This also anticipates my subsequent musings about why setting up a bi-amped config - one amp dedicated to each channel not one amp per tweeter/woofer - or multi-amped (say 4 monoblocks) config to passive speakers would not also count as "active'. It wouldn't simply because of the positioning of the crossover in the chain. Old dog+new tricks=still breathing.

Exactly so - it is only active if you remove the passive crossovers and insert an active crossover between the source and the amps. Just bi-amping (or bi-wiring) a pair of passive speakers makes naff all difference.

 

[Tony_J]

I’ve only heard a couple of active setups and both have impressed me hugely.

A dumb question. I have always assumed that a speaker is “active” only when the amplification, whatever it is and however configured, is inside the cabinets. I can’t see how, for example, the large Sony’s could do this... so it appears some of you might be working to a different definition. Could you enlighten me?

It isn't the physical placement of the amps (inside or outside the cabinets) that matters - what matters is where the crossover sits in the electrical chain. Passives have a (passive) crossover that sits between the power amp and the speakers, actives place the crossover between the source and the input to the power amp. The idea of building the whole lot into the speaker cabs is merely a cosmetic optimization - means fewer cables and boxes on show.

 

[TheFlash]

Get all that now. My superficial view is what you get if you google “active loudspeaker”... until a few hours ago I thought the main advantages of actives were (a) the close matching of the amplifier to the drivers by the manufacturer, ensuring each was optimised for the other and ruling out any messing about by the end consumer and (b) the short cable runs from power amps to drivers. The positioning of the crossover makes much more sense.

 

[Tony_J]

Get all that now. My superficial view is what you get if you google “active loudspeaker”... until a few hours ago I thought the main advantages of actives were (a) the close matching of the amplifier to the drivers by the manufacturer, ensuring each was optimised for the other and ruling out any messing about by the end consumer and (b) the short cable runs from power amps to drivers. The positioning of the crossover makes much more sense.

Your (a) and (b) are very much second order advantages; the much more important one is the placing of the crossovers (and what you can do with the crossovers if you have DSP), which has a much greater effect on the resultant sound. 

In the case of the actives I am fiddling with at the moment, I am currently using a pair of class D "plate amps" that could be screwed onto the back of the cabs eventually, and they each have 2 channels rated at 125W. The bass drivers are relatively insensitive, so they will need all of the 125W to drive them well, but I am having to turn down the gain on the Lowthers that I am using for mid/highs by about 24DB to get a good balance with the bottom end. So I could get away with a very much less powerful amplifier for the high frequencies. In fact, I am seriously considering dusting off an old, yet to be completed project to build a pair of 10W Class A monoblocks (to the original Lindsay Hood design) and use them for the top end - they should be well capable of doing the job. However, I don't expect that a change of that kind would have any real effect on the overall sound (and will have a bad effect on power consumption!) - but in a commercial environment, it could lead to a cheaper manufacturing cost. Ruling out the messing about by the end consumer of course helps greatly with predictability - what you are selling will broadly be what the end consumer ends up hearing - but it also takes some of the fun out of the experience for those that like to box swap. 

Apart from general tidiness, I'm not convinced that shortening the power amp to speaker cables is a great advantage; obviously, they are taking the largest signal in the system, and the trade-off is that the source-to-preamp cables get longer, and they are carrying the smallest signals. So there is more opportunity for introducing noise - unless, of course, you go for balanced or optical inputs to the preamps.

 

[insider9]

There's many reason why active approach is better. Or should we say, why passive design is a huge compromise. Looking at active. 

From system perspective, fewer losses of gain with crossover other side of an amp. You only amplify what's needed. From amp perspective, less complex load and better control over driver with more headroom. From speaker perspective, improved coherence and timing due to far better time alignment which is often hard or impossible to do using passive xo.

The one thing active doesn't do, yet is mostly associated with is flat (as a frequency response). That misconception is mostly because active speakers are often seen in studio environment. But that's all to do with speaker voicing and not the fact they are active. Also often powered speakers are incorrectly labelled active. But as mentioned above active speakers don't have to have built in amplification. 

Generally speaking with the right speaker "activated" you can expect gains in coherence, timing, dynamics, micro detail, making it feel as if it breathes more effortlessly. For many these gains might be not worth the effort. And won't sound significantly better with some speaker designs. For others it's a night and day difference. 

 

[Tony_J]

There's many reason why active approach is better. Or should we say, why passive design is a huge compromise. Looking at active. 

From system perspective, fewer losses of gain with crossover other side of an amp. You only amplify what's needed. From amp perspective, less complex load and better control over driver with more headroom. From speaker perspective, improved coherence and timing due to far better time alignment which is often hard or impossible to do using passive xo.

The one thing active doesn't do, yet is mostly associated with is flat (as a frequency response). That misconception is mostly because active speakers are often seen in studio environment. But that's all to do with speaker voicing and not the fact they are active. Also often powered speakers are incorrectly labelled active. But as mentioned above active speakers don't have to have built in amplification. 

Generally speaking with the right speaker "activated" you can expect gains in coherence, timing, dynamics, micro detail, making it feel as if it breathes more effortlessly. For many these gains might be not worth the effort. And won't sound significantly better with some speaker designs. For others it's a night and day difference. 

You're right that active doesn't imply flat frequency response; if you go the simplest route, you use an analogue crossover that has no other function than to introduce a matched pair of low pass and high pass filters that operate at the crossover frequency, so any non-linearities in the frequency response of the drivers is still there, as it would have been in a passive system. However, you have more options for achieving an overall flat response (along with the improvements in coherence and timing that you mention) - you can add further (analogue) filtering to the active crossover to shape the output response, or much easier, go the DSP route where all of the filtering is performed digitally. To me, that is where the real gains can be made. In the case of the system I am playing with at the moment, there is no way I could realistically achieve the result I have now without using a DSP-based approach. Having said that, what I have ended up with is a combination of analogue and digital filtering; I am using an analogue active crossover, adjusted to give me appropriate levels to balance the drive into the bass and the mid/high amps, and I feed a DSP-processed signal into the crossover to clean up the overall FR.