Can active DSP speakers play louder when they are high-passed?

[617]

Normally I'd be the person answering this question, but I'm stumped.

Traditionally if you take your passive speakers and filter out the bass, you can then let them play much louder than they would otherwise. You can accomplish this filtering using any number of methods from DSP to a sock, but they all work.

However, for contemporary monitors from say Genelec or Kali, will sending them a high pass signal enable them to play any louder? My understanding is that these speakers have limiters implemented in the digital processing, so sending any loud signal will trigger the limiter.

Am I mistaken? If I use a high passed monitor will it actually be able to achieve a high spl? I ask because in theory some of these speakers should be able to provide significant output, but I don't know if the limiters prevent this or if they are smart enough to know that no bass is present.

 

[Rednaxela]

Traditionally if you take your passive speakers and filter out the bass, you can then let them play much louder than they would otherwise.

…if you have the extra watts needed to do so available right?

 

[Berwhale]

This is purely subjective, but i'm sure that my iLoud MTMs play louder after high passing them. I have both the HPF on my Sub8 and LF Extension on the MTMs set to 80Hz.

My theory is that the DSP profile for the 80Hz LF Extension has less -ve pre-amp applied because the lower frequencies no longer need to be boosted or corrected.

 

[DVDdoug]

Yes. Lower frequencies require more power and our ears are most-sensitive at mid frequencies (Equal Loudness Curves). DSP or not, if all of the energy goes to the mid-frequencies it will be louder.

 

[Rednaxela]

…if you have the extra watts needed to do so available right?

Never mind. They may be freed up by engaging the HP filter.

 

[Old Listener]

It depends on the content of the music.

Yes, if there is a lot of energy below the high pass freq.

No, if not.

 

[Berwhale]

My understanding is that these speakers have limiters implemented in the digital processing, so sending any loud signal will trigger the limiter.

I don't think the limiter is based purely on input signal level...

Features and benefits of the protection circuit:

- Decreases the signal level when needed (for example, when the temperature of the sound coil of the element reaches the safety limit), which significantly improves the reliability of the speaker.

- The appropriate protection circuit design for each speaker and subwoofer allows the system sound level to be maximized.

From: https://support.genelec.com/hc/en-u...oad-protection-circuitry-do-how-does-it-work-

 

[gnarly]

Normally I'd be the person answering this question, but I'm stumped.

Traditionally if you take your passive speakers and filter out the bass, you can then let them play much louder than they would otherwise. You can accomplish this filtering using any number of methods from DSP to a sock, but they all work.

However, for contemporary monitors from say Genelec or Kali, will sending them a high pass signal enable them to play any louder? My understanding is that these speakers have limiters implemented in the digital processing, so sending any loud signal will trigger the limiter.

Am I mistaken? If I use a high passed monitor will it actually be able to achieve a high spl? I ask because in theory some of these speakers should be able to provide significant output, but I don't know if the limiters prevent this or if they are smart enough to know that no bass is present.

For any specific active speaker, you would have to know the details of what limits each of the passbands in the speaker.
By passband, I mean each separate amp & driver channel.

For instance, if the HF section limits first...that sets the max SPL.
I realize this is probably obvious, but helps to build on the idea each section must be understood. Cause which one limits first can override.

That said, i think it's at least 90% probable the low frequency section it what limits first.

Almost invariably, high-passing an active speaker above the low corner it has in it's specs, and adding a sub, will raise the system max SPL (if the high section has the headroom)

Reason being, just like it takes 4x the displacement of a piston to maintain equal SPL for each octave decrease, it also takes 4X the power for each octave decrease to move that 4X displacement increase.
So lightening the low end load, on both the low freq driver and amp, almost always increases its available SPL higher up.. Just like with passives as you mentioned.

I have a few prosound active boxes that I routinely high-pass, considerably higher than their f-3.
But really, I probably do it more to increase sound quality than to gain SPL. Cleans up the low drivers mid-range contribution, adds some clarity. IMD reduction I guess.

 

[MAB]

Power and temperature are often DSP controlled now.
For a high-passed system with this type of protection, likely zero impact on tweeter/midrange power and thermal headroom.
But, it will definitely reduce the power fed to the woofers, so that will give you more headroom there.
The content you feed and the EQ you use will obviously have an impact on what is limiting the output, so if you have gobs of headroom in your midrange and tweeters, the system will play louder. If you don't have all of these protection features, you may end up driving your midrange and tweeters harder because you got all that extra bass headroom, which I could imagine leading to issues with the midrange/tweeters if not careful!

 

[gnarly]

Power and temperature are often DSP controlled now.
For a high-passed system with this type of protection, likely zero impact on tweeter/midrange power and thermal headroom.
But, it will definitely reduce the power fed to the woofers, so that will give you more headroom there.
The content you feed and the EQ you use will obviously have an impact on what is limiting the output, so if you have gobs of headroom in your midrange and tweeters, the system will play louder. If you don't have all of these protection features, you may end up driving your midrange and tweeters harder because you got all that extra bass headroom, which I could imagine leading to issues with the midrange/tweeters if not careful!

Completely agree...good synopsis.
I think a high-passed system of that type has to have a near zero effect on tweeter/midrange, as they are already high-passed (being multi-way active)

Although i do wonder how many home/studio actives would have any thermal monitoring. My bet is the highest level of sophistication for that market is both rms and peak voltage limiters per band. That's about all i see even in live-sound actives, until into big dog line arrays etc.

When I look at the size of the woofers on Genelecs or Kalis or such, relative to the specified max SPL and f-3, I can't help but believe they could play louder relieved of some low end duty.
But, like we both have said, that's entirely dependent of further headroom availability in the mid/ hf/ vhf.
A very well matched speaker in terms of SPL and headroom across all sections, obviously wouldn't benefit then.

 

[617]

Completely agree...good synopsis.
I think a high-passed system of that type has to have a near zero effect on tweeter/midrange, as they are already high-passed (being multi-way active)

Although i do wonder how many home/studio actives would have any thermal monitoring. My bet is the highest level of sophistication for that market is both rms and peak voltage limiters per band. That's about all i see even in live-sound actives, until into big dog line arrays etc.

When I look at the size of the woofers on Genelecs or Kalis or such, relative to the specified max SPL and f-3, I can't help but believe they could play louder relieved of some low end duty.
But, like we both have said, that's entirely dependent of further headroom availability in the mid/ hf/ vhf.
A very well matched speaker in terms of SPL and headroom across all sections, obviously wouldn't benefit then.

That's a great point. Well designed and optimized speakers will use drivers with similar output capabilities.

It would be interesting to see if thermal sensing is used. The sensor would be on the woofer VC I assume? Or just a sensor on the pcb.

Clearly this isn't clear. I ask because many of these monitors have subwoofers made for them and you would think they would engineer these systems in such a way to allow more output. The Kali subwoofer in particular is not some little toy for low end extension, they advertise it as being suitable for use in a small PA.

 

[KSTR]

It would be interesting to see if thermal sensing is used. The sensor would be on the woofer VC I assume? Or just a sensor on the pcb

Normally, you just model the thermal behavior (after doing the stress-test measurements to obtain the parameters) and work on that, using the amps's output voltage rather than actually sensing the VC temp, much more economical. You need some safety margin anyway and that is usually choosen to account for general long-term heat rise and ambient temperature.
For woofers, there can be excursion modeling as well.
And general clipping sensors on the amps etc.
Sophisticated "transparent" limiting, with the goal of a) fully protecting the drivers/amps/power supply while b) maintaining maximum reasonable output is an engineering challenge and can drive development and production cost quite a bit.

 

[MAB]

Completely agree...good synopsis.
I think a high-passed system of that type has to have a near zero effect on tweeter/midrange, as they are already high-passed (being multi-way active)

Although i do wonder how many home/studio actives would have any thermal monitoring. My bet is the highest level of sophistication for that market is both rms and peak voltage limiters per band. That's about all i see even in live-sound actives, until into big dog line arrays etc.

When I look at the size of the woofers on Genelecs or Kalis or such, relative to the specified max SPL and f-3, I can't help but believe they could play louder relieved of some low end duty.
But, like we both have said, that's entirely dependent of further headroom availability in the mid/ hf/ vhf.
A very well matched speaker in terms of SPL and headroom across all sections, obviously wouldn't benefit then.

I have Genelec high-passed to subwoofers. I initially gave some thought to the potential of overcooking the mid and/or tweeters, but the power and thermal protection on my monitors seems to be so comprehensive. And, for protection/limiting to kick in the system is playing at terrifying and uncomfortable volume, so I am even less worried in my case. But I am not clear on if the thermal driver management that Genelec uses is actually monitoring the voice-coil temperature directly, or if it is integrating the output of the amplifier to estimate the the temperature of the VC relative to some max. It seems the direct VC temperature method might have different results than calculating the thermals from the amp outputs.

On another note, I am also surprised at how subtle the protection sounds. If I was listening repeatedly at the protection limit, I imagine it would be at least partially thermally limited. I'm pretty confident I won't blow the thing up with an accidental twist of the volume knob, but I would be worried if I was always tripping the protection. And the only experience I have with this level of DSP protection is Genelec.

 

[MAB]

Normally, you just model the thermal behavior (after doing the stress-test measurements to obtain the parameters) and work on that, using the amps's output voltage rather than actually sensing the VC temp, much more economical. You need some safety margin anyway and that is usually choosen to account for general long-term heat rise and ambient temperature.

I too was wondering, this totally makes sense.

For woofers, there can be excursion modeling as well.

I was also wondering about this, also makes sense. The same data gets you excursion of each driver.

 

[617]

I'm going to ask Kali, they tend to be pretty responsive.

 

[617]

Interesting update, I contacted Kali which I assume implements the limiters in the most economical way practical, and they said that if high-passed, monitors will exhibit the same peak SPL but may have higher continuous SPL.

So, I interpret that to mean that there are some output gains to be had by filtering bass, but they are probably not as significant as with passive speakers.

I have asked Kali what mechanism is used to make the limiter kick in - I assume it is simply the input signal but it is possible a thermal sensor is used.

 

[Sancus]

This post is confusing to me. Play louder at what frequencies?

If you high-pass an active speaker, lets say the Genelec 8361A, we already know that it has different limits at different frequencies, and that the limits are lower the lower the frequency.

If I have noise from 20-500hz at a level that produces 115dB in-room, and I try to play it through the Genelec 8361A, it will limit immediately. If I high-pass 300hz, it won't limit.

If the suggestion is that high-passing somehow makes the speaker more capable than it was previously at *higher* frequencies, I don't see how that could be the case with passives or actives. It would reduce IMD but that's about it?

Interesting update, I contacted Kali which I assume implements the limiters in the most economical way practical, and they said that if high-passed, monitors will exhibit the same peak SPL but may have higher continuous SPL.

Peak SPL is almost always tested with midrange frequencies, not including bass, to get bigger numbers. So that makes sense.

 

[617]

This post is confusing to me. Play louder at what frequencies?

If you high-pass an active speaker, lets say the Genelec 8361A, we already know that it has different limits at different frequencies, and that the limits are lower the lower the frequency.

If I have noise from 20-500hz at a level that produces 115dB in-room, and I try to play it through the Genelec 8361A, it will limit immediately. If I high-pass 300hz, it won't limit.

If the suggestion is that high-passing somehow makes the speaker more capable than it was previously at *higher* frequencies, I don't see how that could be the case with passives or actives. It would reduce IMD but that's about it?


Peak SPL is almost always tested with midrange frequencies, not including bass, to get bigger numbers. So that makes sense.

I guess the question comes down to, what triggers the limiter and what does the limiter do?

Does the limiter look at different frequencies or does it just look at the total signal? And when it limits, does it limit the whole signal or just the part that's too loud ?

 

[Sancus]

I guess the question comes down to, what triggers the limiter and what does the limiter do?

Does the limiter look at different frequencies or does it just look at the total signal? And when it limits, does it limit the whole signal or just the part that's too loud ?

Yeah it's an interesting question. I guess KSTR posted above you can probably use voltage after modeling the effects on temperature, excursion, etc.

8361A tweeter limiting on a sweep

Spoiler

Looking at what happens with the 8361A tweeter, it seems like it could just be a function of voltage + time, because they know that X voltage for Y time leads to Z temperature on the voice coil and that's the primary factor that needs to be controlled. So you end up with sloping down response with a sweep at constant SPL(assuming the frequency response is flat, when it's not flat then you get the little bump between 20 and 30khz). But you're not limiting by frequency, only reducing the voltage limit gradually over the time that the maximum is exceeded.

But it definitely feels like there could be something more complex going on with the woofer or midrange. Maybe @Ilkka Rissanen would like to teach us how Genelec limiters work?

Certainly I do know for a fact that adding a sub and high-passing an 8351B/8361A will let you play bass-heavy tracks louder without a red light. Multiple people have observed this. The woofer is extra-complicated because we don't actually know the sensitivity of any of the Genelecs! The whole bass range is heavily EQed. It may take quite a lot more voltage to play 100dB @ 40hz vs 100dB @ 100hz, but it's just hidden from us because the internal EQ boosts the FR and therefore voltage for signals containing those frequencies.

 

[617]

Yeah it's an interesting question. I guess KSTR posted above you can probably use voltage after modeling the effects on temperature, excursion, etc.

8361A tweeter limiting on a sweep

Spoiler

Looking at what happens with the 8361A tweeter, it seems like it could just be a function of voltage + time, because they know that X voltage for Y time leads to Z temperature on the voice coil and that's the primary factor that needs to be controlled. So you end up with sloping down response with a sweep at constant SPL(assuming the frequency response is flat, when it's not flat then you get the little bump between 20 and 30khz). But you're not limiting by frequency, only reducing the voltage limit gradually over the time that the maximum is exceeded.

But it definitely feels like there could be something more complex going on with the woofer or midrange. Maybe @Ilkka Rissanen would like to teach us how Genelec limiters work?

Certainly I do know for a fact that adding a sub and high-passing an 8351B/8361A will let you play bass-heavy tracks louder without a red light. Multiple people have observed this. The woofer is extra-complicated because we don't actually know the sensitivity of any of the Genelecs! The whole bass range is heavily EQed. It may take quite a lot more voltage to play 100dB @ 40hz vs 100dB @ 100hz, but it's just hidden from us because the internal EQ boosts the FR and therefore voltage for signals containing those frequencies.

Regarding the bandwidth of the limiter, it seems logical that it would just look at the total level being sent to each driver after the crossover.

In other words the dsp splits the signal in 2 or 3, then monitors total output on these channels after all filters are taken into account. That would explain why the entire tweeter comes down when it limits.

It's interesting that the woofer is often the driver holding back the speaker back. We really do ask a lot of these little high excursion midwoofers.