Electronic bandwidth limiting for bassreflex speakers?

[Heinrich]

Bass reflex loudspeakers have the characteristic that the diaphragm movement increases drastically below the tuning frequency. This not only produces harmonic distortion, but also intermodulation. In extreme cases, a loudspeaker can destroy itself. Also the ineffective pumping of air back and forth through the port also produces clearly perceptible wind noise.

In passing, I have seen that modern content quite often has components of relevance below 40Hz. These are mostly exceptions, such as thumping noises, but now also regularly recurring 'musical' parts.

Speakers are getting smaller these days, are mostly vented but then show tuning frequencies well above 40Hz. The consequential distortions create a certain “drama” that replaces the boom from the lowest frequencies to a certain extent, but it would be cleaner to switch off the distortion machine.

What are the simplest means of limiting the signal bandwidth downwards?

Tuning at 50Hz, output @-10dB in that register, though, still 5%HD (86db median):

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Tuning at 70Hz (!), on the verge of unusable at least for EDM:

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Tuning at 60Hz, output @-15dB (!) in that register, 100%HD (!) at 40Hz (86db median):

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[ppataki]

What are the simplest means of limiting the signal bandwidth downwards?

Simply use a high-pass filter, preferably a steep one (24dB/oct. for example). It will protect the driver and will tame distortion too

 

[Heinrich]

Simply use a high-pass filter, preferably a steep one (24dB/oct. for example). It will protect the driver and will tame distortion too

Sure, but how?

 

[ppataki]

Sure, but how?

I use Jriver's DSP Studio + various VST plugins to apply filters like this

You can also use hardware, like miniDSP and various other DSP solutions

You can also apply it with a passive circuit but I will let others comment on that, I am not familiar with that domain

 

[Heinrich]

I use ...

Thanks! Can you share any personal impressions of how much it helps or not?

 

[ppataki]

Thanks! Can you share any personal impressions of how much it helps or not?

I use a linear phase 24dB/oct. high-pass filter on my main front speakers (in case of all these projects) at 80Hz where I to cross them to my subs (currently I use Fabfilter Pro-Q 4)
And I also use the same filter but at 40Hz with my rear speakers to simply take the burden off of them
It definitely helps and it makes a big difference, especially if you turn up the volume - cone excursion will be limited by the filter so you get more control and less distortion

 

[Oddball]

Ideally you wound also want to understand in-room response of the speakers by measuring them (REW+Umic 1). That would give you a more precise idea where to apply the filter and what roll-off to use. Since you will be cutting the signal (and not crossing over to subs) probably best to cut only what is necessary.

 

[ZolaIII]

Sure, but how?

Right under the port tuning and higher order if need be.