robbie010

Active / DSP / EQ / WTF?

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Super Wammer

I don’t get it...... help!?

I keep seeing these words and reading threads where people have “active” speakers or have “gone” active. 

Then there are those that have used “DSP” or Mini DSP or those that have EQ’d room modes etc etc.....

Do you have to buy active speakers?....... how do you turn passive speakers in to active speakers?....... is it always going to be an improvement when changing passive to active?

So many questions.........

Would it be worthwhile setting up a sticky thread that explains these things in layman's terms to help the uninitiated?

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Super Wammer

It's late maybe tomorrow :D

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In this context 'active' means powered (almost always from the mains). 'Passive' means not powered. The thing that is either powered or not powered is the speaker crossover which divides the whole frequency range into different levels. This is needed because the drivers in any given speaker are designed to handle a specific frequency (large drivers handle bass, tiny drivers handle upper frequencies etc) and would sound bad or blow up if fed with an inappropriate signal. In addition crossovers can be skewed at certain frequencies to handle anomalies in the cabinets to provide (a goal) a 'flat frequency response'. A flat frequency response is merely an even representation of the original recording without any undue emphasis.

Active crossovers can be enclosed in the cabinet itself or, for DIY speakers, can be purchased in a separate box with dials to adjust the frequencies for each driver and the volume for each level. Typically in a DIY (often horns but not necessarily) system amps and drivers will come from different manufacturers and need 'matching' to achieve that 'even' sound and same volume from each driver - that is the goal. The crossover sees the whole signal and divides it up, sending the different bits to the appropriate amp. Its source > crossover > amp > driver (speaker).

We could stop there. But I choose to highlight related issues..read on if you like..

Analogue and digital active crossovers: this is more advanced and where it gets more 'theoretical'. Basically they have the same job description as above but digital converts the signal to better manipulate it - they are able to fix anomalies in the speakers in a more comprehensive way (correct time delays between drivers say). Analogue devotees, (who have turntables rather than CD, or streaming devices (which are already in the digital format))' regard the changing from analogue to digital and back again to proceed through the system, as illogical and harmful to the sound.

Broadly speaking supporters of digital crossovers (who will use the term DSP = digital signal processing) will also recommend other digital devices to measure and correct room anomalies. As a clan these 'Measurists', as I call them, would favour instruments  and their measurements to assess and evaluate hifi kit over actual listening. As a generalisation, to support their allegiance Measurists downplay the ability of listeners and their senses (ears) to accurately assess replay systems appealing to various psychology tests and concepts to back their views up (e.g., so-called 'confirmation bias') and instruments to do their listening for them. They are reliable. Humans arent.

Opponents of the measurement school, simply think that they can hear any differences in equipment, drawing on experience, and with the use of simple scientific methodolgy of changing one thing at a time and trusting their senses to spot not only differences but improvements (and disappointments). Often verification is provided by having a second opinion on hand.

A middle ground is where the theory and measurement is backed up by listening tests. This is what the HiFi World magazine editorial staff recommend (led by Noel Keywood) - they have some of the most advanced equipment available and keen experienced ears to match.

Are they biased towards their advertisers or otherwise swayed? Hard to say.. But one internet hifi review site that I like is TNT Audio, which has a good deal of Italian input run by Geoff Husband, who delight in their independence, guaranteed by excluding all advertising and engaging enthusiastic amateurs to do their reviewing.

Ive strayed a bit from the remit, but I was on a roll..haha...

Jack NSM

Edited by Non-Smoking Man
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Super Wammer

Jack has explained things very well but as usual I have to add in my little bit of cobbled together ideas .

Fully Active Speakers - To me this means that the crossovers either digital or analogue have to be before the Amplifier . The amplifier is then connected directly with each individual driver and has the filtered signal for that driver only . In this case you will need one amplifier for each driver so 4 amplifiers (2 Stereo Amplifiers or 4 Mono) for a Two Way then Six for a Three Way and so on .

Equalisation - This is where often measurements are taken of the loudspeakers with crossover applied using a calibrated microphone and stand at a set distance from the speaker or speakers . Then using software on a computer like REW it reviews the results and generates a set of filter designs which will smooth the performance of the speakers to closer match a flat response . There are probably huge numbers of software that can offer this both free and paid .

DSP - This is Digital Signal Processing and can be applied in lots of different ways but in this area it is again a system that uses a calibrated microphone and in the case of the DSP I use DIRAC Live a set number of points in a pattern that you need to move the mic to and perform a sound sweep that is picked up and stored . Once all of the measurements are completed (from 9 - 15) then the software has a good sonic digital idea of how the speakers in your room are performing and again against a known reference they produce a set of digital filters that are fed to your amplifiers to match the reference sound . There are lots of different ways to complete this Linn use a system were they ask for the accurate measurements of the room and the type of material it is made of plus the identity of the speaker then they use stored calibrations of that speaker and what the room is doing to it to again generate a set of filters to apply . DSP works for me but does not for many so it is only an additional add on not something you have to have .

Active Speakers - Active Speakers can be bought ready made as active units with Amplification / DAC / DSP already installed without either a DAC or DSP or just one depends on the mfg.

DIY Active - This is what some on here do as they have the knowledge and the technical skill to complete . They often buy drivers and match them in to a Two Way / Three Way or even more . They then design and build the cabinets , fit the drivers and then test them with methods like above and then often use their ears to fine tune the sound to what they want . This is the cutting edge of active and way beyond me .

Passive Speaker Conversion - Now this is where my journey started and stopped . What i did was find a pair of passive speakers complete with passive crossovers that I liked the sound of . I then proceeded to remove the crossovers from the speakers in my case add additional binding posts so that I had connections for the bass and the treble . I then used a MiniDSP unit (DDRC 24 ) which when plugged in to your computer lets you set the individual crossover points for each driver (these crossover points in my case came from the KEF archive for each driver so are very accurate) . So then from a digital signal in the DDRC24 adds the crossover points and lets that signal be routed to four analogue out channels one connected to each drivers amplifier which is filtered to give that driver only its individual signal. After this basic work I then apply a full DIRAC Live(within the same DDRC 24) to the signal and again this applies the filters in the digital domain and sends them to the four analogue outputs for each amplifier / driver pair .

All of the above is much harder to write down and explain that it is to do . In my system the MiniDSP DDRC 24 acts as my Digital Crossover / DAC / DSP / Digital volume control so custs out a few additional stages and boxes for me. I have done two conversions to date and i am going to try a third very soon . In each case the sound of the active unit compared to passive is greatly improved by being made active . In my current set up they have original timbre and general appeal of the original passives but they are now much better at imaging have lots more bass and then that thing that only seems to happen with actives , speed notes stop and start faster rhythms are just more precise and make your feet want to dance . For me there is no going back active is what pleases me .

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I’ve had a foot in the latter two camps Andrew described for the past 4 years, encouraged by Serge amongst others no longer active on here.  Converting std passive speakers to active is an easy route to start out your active journey on as I did but using a Behringer DCX unit as opposed to the mini DSP units Andrew uses. Andrew described this process really well and it’s nit dissimilar using Behringer kit apart from you can’t use the DIRAC Live system.

Ived moved on to the full audio nervosa level of custom building my own bass and monitor speakers fed by multiple amps in a 5 way system .....would I go back to one amp and passive speakers - noooooooo.

It would be interesting to see/hear how your klipsh build responded to a dsp setup....I’m sure you have a spare amp you could use etc .....and I’ve a Behringer DCX unit due back with me soon that you borrow to explore the active world.

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Andrew has covered the basics very well in his post.

My experience of active to date started off with "conversion" - actually using a DSpeaker Antimode unit as a means of integrating a sub with a pair of Lowther single drive unit back-loaded horn speakers. This gave me enough of a flavour of what DSP can achieve to encourage me to do a from-scratch DIY project - initially a 2-way, then a second 2-way, and currently a 3-way, all using the same miniDSP family of DSP units that Andrew is using. As both Keith and Andrew have said, once you've dipped your toe in the active water there is no going back - especially if you are of the DIY mentality - the possibilities for building something that sounds fantastic and costs relatively little are pretty much limitless. I would definitely be interested in hearing what active tech could do for your Klipsch build - I suspect you would be very pleasantly surprised.

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Super Wammer

Not really alot to add this, I first built some Ls35a clones that I liked and they garnered some praise from those that heard them. I decided to build another  2 way,  but this time a bigger cabinet using an 8 inch  driver for deeper bass, after building I struggled to get it to sound right with passive crossovers. Serge was always singing the praises of actives, so a few conversations with him, and I bit the bullet, and added another set of binding posts, removed the passive crossover, and added a Behringer DCX 2496, like Keith, which is no surprise as Serge told us they were fit for purpose, and adequate 9_9. I set the crossover points as suggested by Kef for the drivers in use, and straight away there was an improvement , more speed, deeper bass and a wide soundstage. But after longer listening I found the bass a bit overblown and the treble a bit fatiguing. More conversations with Serge, and I decided to try the DSP capabilities of the Behringer. I tried by ear, but in my honest opinion I found it fools errand, forever chasing your tail so to speak. So a calibrated mic 🎤 was bought, REW learned and then some measurements taken, parametric eg settings entered and hey presto it all came together, no more Boom & Tizz. 

In lockdown this year I built 2 more boxes so as I could go 3 way. I added 5 inch mid drivers to these,and they have been placed on top of the 2 way set up. To save having 3 stereo power amps, I bought a 6 channel power amp from KJF Audio, so I only have one power amp now. 

Edited by greybeard
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Super Wammer
35 minutes ago, MF 1000 said:

It would be interesting to see/hear how your klipsh build responded to a dsp setup....I’m sure you have a spare amp you could use etc .....and I’ve a Behringer DCX unit due back with me soon that you borrow to explore the active world.

I think the La Scala may benefit greatly from the level of control that this setup seems to allow. Because the crossovers use autotransformers there is some small control over the levels (db) but its more rule of thumb than anything else.

Thank you for the loan offer, thats very kind. I may take you up on that  

After reading the replies above, I now have a better understand of the chain of connections i.e. source - crossover - amplification - driver/speaker. This makes sense with the explanation that the source signal is split before being amplified and then fed to the driver. With that in mind, for the Klipsch, am I right in thinking I would need 3 matching stereo amps or 6 matching mono amps, is that correct?

If so, what kind of amplification are you using?

I have a couple of amps hanging around but not matching. Amp / driver matching is mentioned above, do some of you use the same amp for each driver, or do you pick different amps to match the driver i.e. higher wattage amps for large woofers etc. and are we talking branded “hifi” amps or more commercial type amps?

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Super Wammer
1 hour ago, robbie010 said:

After reading the replies above, I now have a better understand of the chain of connections i.e. source - crossover - amplification - driver/speaker. This makes sense with the explanation that the source signal is split before being amplified and then fed to the driver. With that in mind, for the Klipsch, am I right in thinking I would need 3 matching stereo amps or 6 matching mono amps, is that correct?

Yes you would need 3 stereo power amps or 6 mono amps. The more power for the bass the better in my experience, I use Hypex ncore modules in the 6 channel power amp 500 wpc for bass 250wpc for mids 125wpc highs that is into 4 ohms.

The other thing I forgot to mention is the ability also to use delay, so the sound from the individual drivers reach you at the same time.

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The chain is source - preamp- dsp- amps- speakers 

I use pa amps for bass duties and more subtle amps  for midrange etc ....but initially try it with those you can beg/steal/borrow etc

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Super Wammer

Thanks all. The Behringer unit has really piqued my interest, I think I may have to accept Keiths kind offer and have a play first. 

I Will definitely need to do some research in to the right kind of amps to use. 

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I’ve a pair of Behringer A500s that would give you 300 wpc for bass duties too 

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3 minutes ago, robbie010 said:

Thanks all. The Behringer unit has really piqued my interest, I think I may have to accept Keiths kind offer and have a play first. 

I Will definitely need to do some research in to the right kind of amps to use. 

Keith PM me your address and I'll post the Behringer back along with the serial to usb cable, so you can send to Robbie

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Super Wammer
14 minutes ago, MF 1000 said:

I’ve a pair of Behringer A500s that would give you 300 wpc for bass duties too 

Another very kind offer, Keith. I’m not sure I could accommodate so many boxes at the moment, I was initially looking at picking up a cheap 6 channel amp, maybe something like this Rotel:

https://www.ebay.co.uk/itm/254718681186

I will definitely drop you a line RE the DCX. It seems you’re only an hour from me so I can collect, if thats acceptable. 

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Super Wammer
11 minutes ago, robbie010 said:

Another very kind offer, Keith. I’m not sure I could accommodate so many boxes at the moment, I was initially looking at picking up a cheap 6 channel amp, maybe something like this Rotel:

https://www.ebay.co.uk/itm/254718681186

I will definitely drop you a line RE the DCX. It seems you’re only an hour from me so I can collect, if thats acceptable. 

Just in case you are not aware Simon, The DCX has xlr inputs/outputs .

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