Pro Audio Subwoofer special DSP filtering

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   I was always wondering what kind of processing or "magic" is in pro audio subwoofers that make them (often, not always) sound very good.To be more precise I'm taking about ported or bassreflex enclosures
and probably impulse response or let's say "tight and controlled" sound.

I know there are many factors that have influence on the overall sound of a subwoofer.

First there is the driver, the enclosure (material, volume, bracing, damping), port(s) (size, position and gemometry), then the amplifier, cables, temperature and humidity environment and so on probably aswell.

On the other side, and that's what I'm thinkin of, there is eq, crossover (frequency and slope), delay and phase in relation to the tops / line array / whatever,
maybe an excursion limiter, peak (clip) burst and or rms limiter, voltage, current or true power (powersoft).

Does anybody know what else could be there?

One thing that comes into my mind for example the Powersoft IPAL mod has a pressure sensor that feeds the dsp with information so it corrects the cone movement to lower distortion and "after ringing" (right term?) and it works actually quite well.

Is it possible (or is this already implemented in modern pro audio sound systems ) to use this correction even without a pressure sensor by measuring the behaviour of a subwoofer and calculating the correction function?

Edited by airbell - 22 May 2023 at 6:29pm

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airbell Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 11 June 2009 Location: Berlin, Germany Status: Offline Points: 284	Post Options Post Reply Quote airbell Report Post Thanks(0) Quote Reply Topic: Pro Audio Subwoofer special DSP filtering Posted: 22 May 2023 at 9:03am
	I was always wondering what kind of processing or "magic" is in pro audio subwoofers that make them (often, not always) sound very good. To be more precise I'm taking about ported or bassreflex enclosures and probably impulse response or let's say "tight and controlled" sound. I know there are many factors that have influence on the overall sound of a subwoofer. First there is the driver, the enclosure (material, volume, bracing, damping), port(s) (size, position and gemometry), then the amplifier, cables, temperature and humidity environment and so on probably aswell. On the other side, and that's what I'm thinkin of, there is eq, crossover (frequency and slope), delay and phase in relation to the tops / line array / whatever, maybe an excursion limiter, peak (clip) burst and or rms limiter, voltage, current or true power (powersoft). Does anybody know what else could be there? One thing that comes into my mind for example the Powersoft IPAL mod has a pressure sensor that feeds the dsp with information so it corrects the cone movement to lower distortion and "after ringing" (right term?) and it works actually quite well. Is it possible (or is this already implemented in modern pro audio sound systems ) to use this correction even without a pressure sensor by measuring the behaviour of a subwoofer and calculating the correction function? Edited by airbell - 22 May 2023 at 6:29pm

VECTORDJ Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 11 June 2006 Location: United States Status: Offline Points: 489	Post Options Post Reply Quote VECTORDJ Report Post Thanks(0) Quote Reply Posted: 22 May 2023 at 7:40pm
	Looking at EAW I see a 10 dB boost at 35-40 Hz in the Active Crossover....This may allow a smaller box but sure EATS up Watts....................

Elliot Thompson Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 02 April 2004 Location: United States Status: Offline Points: 5086	Post Options Post Reply Quote Elliot Thompson Report Post Thanks(0) Quote Reply Posted: 22 May 2023 at 8:45pm
	When designed correctly, Reflex Cabinets do not need a lot of processing. There are no major dips and valleys in the response curve like horn-loaded cabinets that require a lot of processing, in order to attain a smooth response. Best Regards,
	Elliot Thompson

smitske96 Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 16 February 2016 Location: The Netherlands Status: Offline Points: 1006	Post Options Post Reply Quote smitske96 Report Post Thanks(0) Quote Reply Posted: 23 May 2023 at 9:32am
	Most manufacturers don't use any special processing. Almost all subwoofers in pro audio have a rising response down low. Most use a relative small cabinet, add EQ around tuning and apply good limiting to prevent the driver from burning up. Because excursion is lowest at tuning, you will not be limited by excursion. You can add quite a lot of EQ if the music material allows it. Coda audio use an excursion sensor like MFB but more refined. If I am correct besides Ipal, there are no others in pro audio.

airbell Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 11 June 2009 Location: Berlin, Germany Status: Offline Points: 284	Post Options Post Reply Quote airbell Report Post Thanks(0) Quote Reply Posted: 23 May 2023 at 1:17pm
	@ Elliot: I agree with what you said, but I was thinking more about time domain, group delay and ringing. @ Smitske96: Agree with that, and I think the reason for this is actually if they would build huge enclosures with so much output at tuning that they wouldnt need some lowend eq, the subwoofer would sound very boomy and not precise at all anymore because of too much group delay and after ringing. But its also a question about the music that is played and demand for low end. About that the pro audio companies dont have that special filters/whatever, does somebody know that for sure? I mean has anybody here taken a d&b j sub, j infra, sl gsub, l acoustics ks28, nexo sth/rs18 or even meyer 1100 with an external/ other brand amplifier and not the manufactures' and tried to make it sound exactly the same as with the system amp and actually compared it side by side? Edited by airbell - 23 May 2023 at 1:18pm

airbell Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 11 June 2009 Location: Berlin, Germany Status: Offline Points: 284	Post Options Post Reply Quote airbell Report Post Thanks(0) Quote Reply Posted: 23 May 2023 at 1:29pm
	And what about dynamic processors? For example at some rock radio station here they put some mastering stuff that the bass of each track sounds more punchy than at the original record. I compared it. But actually it colours the sound so its not original anymore, but in most cases better. Or damn, even my sony wh-1000xm3 have a bass boost that is not only an eq but also some dynamic stuff. I can imagine that at least in some speakers/subwoofers manufacurer put something like this, so at 95% of the music it sounds improved. But this is only an assumption. Edited by airbell - 23 May 2023 at 1:31pm

smitske96 Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 16 February 2016 Location: The Netherlands Status: Offline Points: 1006	Post Options Post Reply Quote smitske96 Report Post Thanks(0) Quote Reply Posted: 23 May 2023 at 2:04pm
	What would be a special filter in you eyes then? If you have the knowledge and tools you can quite easilty measure the output of any amplifier and remake the whole slope. You can even do it at several power levels to see if any dynamic EQ is applied (which I doubt for most). Its mostly in the limiting found in most high end products. You can buy the same linea amps that Martin or EAW, Danley etc uses. Same goes for Lab PLM, Powersoft etc. You can btw find several extended KS28 measurements on the net, with LA12X. Its a nice subwoofer, but definately not magic.

airbell Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 11 June 2009 Location: Berlin, Germany Status: Offline Points: 284	Post Options Post Reply Quote airbell Report Post Thanks(0) Quote Reply Posted: 23 May 2023 at 3:00pm
	Well the (in my opinion) good sound of the KS28 comes mainly from the oem driver, I know it because I tested and compared it. In this case i can imagine it is without any other "special" filters If you load the ks28 preset with lab plm series you realise there is a frequency dependent limiter, besides the fact that several users wrote with the lake load library you have only "similar performance" but not the same processing as in the original amps, maybe more related to the tops / line arrays. From the production partner measurements online you can read a lot but surely not everything. For example the time constant of the limiting at full level, because they used 180ms fixed bursts, and again, the after ringing / burst decay is not visible. You wouldn't see from the measurement if its a really fast sounding hard hitting, or a warm sounding, "air filling" but soft and boomy subwoofer. Anyway, the question is if you can really see everything in Arta? You can see the magnitude and phase response but this is always just an average/part of a peridoic signal at a certain level. And you can look at things just seperated. You can look at burst decay to see after ringing, but dont see the dispersion in the air of it. That are just thoughts, maybe there is no "special filter" in pro audio subs, just wanted to share thoughts and knowledge. I dont have the resources to rent all that speakers and test/measure it by myself, thats why I asked. What about frequency depentent delay? If i remember correctly d&b audio said once they use it in their speakers. Would it be possible for example to have a delay parametric peak filter the same as for parametric eq without changing the magnitude? I thought this is only possible with fir filters and that they have too much delay for sub Application. Or did they only talk about the phase shift towards the xover to meet the phase of the tops better that you can even find in behringer dcx2496? Best regards Edited by airbell - 23 May 2023 at 3:35pm

Elliot Thompson Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 02 April 2004 Location: United States Status: Offline Points: 5086	Post Options Post Reply Quote Elliot Thompson Report Post Thanks(0) Quote Reply Posted: 23 May 2023 at 3:06pm
	Subwoofer Shootouts held in the States revealed the true frequency response of the cabinet(s) as, there is no influence of the manufactures processing coming into play. Usually, the smaller companies sound better than the larger companies as, they are not under some means of corporate guide lines touring manufactures must abide. Enclosure sizes are based on how tightly packed you can fit an ample amount in a truck when marketed for the touring industry. In addition to size restrictions, customized TS Parameters for the (OEM) driver(s) in the enclosure plays a tremendous factor on the end result. Such sacrifices (having a box that does not go extremely low) are something the majority of end users are willing to accept and, add minor equalization to make up the loss. There was a time (Predating the Internet era) when many would build cabinets based on their requirements. Nowadays, the majority would rather copy cabinets from “Insert Manufacture Here” using off the shelf drivers, that are the most popular at the moment. Audio processing pre-electronic-crossover-network has always been implemented in the States for decades. Nowadays, many process audio files (for Car Competition, Spotify, Itunes, etc.) according to what they are playing the audio files through. Having a “Purists” mentality with no audio processing is something not even Classical Music offers these days. Best Regards, Edited by Elliot Thompson - 23 May 2023 at 5:18pm
	Elliot Thompson

smitske96 Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 16 February 2016 Location: The Netherlands Status: Offline Points: 1006	Post Options Post Reply Quote smitske96 Report Post Thanks(0) Quote Reply Posted: 23 May 2023 at 6:06pm
	Well, DSP is not necessarily a bad thing. Its just another tool to get to the desired outcome. You can get away with certain EQ at a certain point. B6 allignment is purely based on this. Its one way to get a smaller cabinte with still enough extension. Eventually in the pro audio world, getting as much sound out of the least volume is one of the key pillars. A balance between both will get you the best result most of the times. Its the same thing with the newer high BL drivers that definately require enough voltageswing + EQ to get to the desired response. This has nothing to do with purist etc.

Elliot Thompson Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 02 April 2004 Location: United States Status: Offline Points: 5086	Post Options Post Reply Quote Elliot Thompson Report Post Thanks(0) Quote Reply Posted: 23 May 2023 at 8:12pm
	As with anything, there is always a limit. Some will emphasize on one thing and sacrifice another. Providing the end result is to the users liking, that's all that matters. It is always good to listen to the sound system in its entirety. Focusing on one piece out of the chain, does not mean extracting that one piece would offer the same results when used outside of it's designated chain. Best Regards,
	Elliot Thompson

Jo bg Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 08 March 2017 Status: Offline Points: 551	Post Options Post Reply Quote Jo bg Report Post Thanks(0) Quote Reply Posted: 26 May 2023 at 8:57am
	All pass filters are basically the frequency dependant delays you are asking for, and are common IIR filters not FIR. Yes lots of delay at bass frequencies, with fir or iir it's the same .