Using high Q shelving to gain 10 Hz in the bass without severe drawbacks

[sams99]

This is a trick thats often used in studios to make the soundmix more fuller and more impressive - the use of high Q shelving function to high pass the signal . This can also be implemented in a ported speaker . And as very few streamers on the market, the WiiM can do this.

This can be done with any ported loudspeaker , using the advantage of the back pressure from the tube at the tuning frequency , making the driver cone stand still and the tube makes all the sound . At the tuning frequency the sound spl advantage are about 10 dB compared to a closed box speaker .

If using a highpass high Q shelving filter with a Kef ls50 meta, centered 10-11 Hz below the tuning frequency of the speaker , you get a boost at the tuning frequency at 51 Hz making the loudspeaker sound much more potent in the bass area. The high Q filter gives you an overshoot right before the bass drops below the tuning frequency .

Simulation example with a WiiM pro and Kef ls 50 meta :

Using PEQ in the WiiM :

LS
Frequency = 40 Hz
Q = 3
Gain = - 9 dB

The Kef ls50 meta has a tuning frequency of 51 Hz . You will get a boost at that frequency about 5 dB and you will have a sharp falloff below the tuning frequency . More bass without overloading the xmax of the driver .

Ls50 meta original without shelving :

View attachment 7052
After high Q shelving it will be :

View attachment 7053


Read the whole article by Perry Marshall about high Q shelving filter here :

https://audioxpress.com/files/attachment/2721

If you have a WiiM streamer and a ported speaker - try it , this will bring better bass in most cases.

I have Q Accoustic 3030i. I did a room correction, that's the EQ I'm using.
So I should add a 46Hz q=3 gain=-9.
How does a negative gain at that frequency improve bass?

 

[alpha_zulu]

I have Q Accoustic 3030i. I did a room correction, that's the EQ I'm using.
So I should add a 46Hz q=3 gain=-9.
How does a negative gain at that frequency improve bass?

Please read the first posts in this thread to understand that "boost".

 

[harkpabst]

I have Q Accoustic 3030i. I did a room correction, that's the EQ I'm using.
So I should add a 46Hz q=3 gain=-9.
How does a negative gain at that frequency improve bass?

No, you shouldn't.

To use this method, you need to know the tuning frequency of your speakers. You cannot just look at the lower boundary of a "frequency response" (lacking any information how it was measured).

The only published impedance plot I found for the 3030i can be seen here:

Q Acoustics 3030i: Seite 4 - i-fidelity.net

www.i-fidelity.net

Unfortunately, it's a low resolution measurement and the tuning frequency can basically anything from 42 Hz to 48 Hz. So, 46 Hz might not even be all wrong, but at these low frequencies +/- 3 Hz is quite a high deviation already. Ideally you should be able to take your own measurements of your very own speakers.

A general limitation of this method is that it can't take room acoustics into account. While the theory is all valid, its practical execution can only hint you to a starting point for further experiments, which are hard to do without measuring equipment. The above link also contains a typical (we might hope) in-room response of these speakers. Look at the graph, extending below 30 Hz! Does this curve look like it needs a further boost at 46 Hz?

Finally, make sure you understand what you're doing, first. The boost comes from the overshoot of a high Q (where high means Q >> 0.7) shelving filter, even with negative gain. It's all shown on the first page in this thread, including the external link. The negative gain (potentially) relieves the speakers from very low frequencies they cannot handle anyway. The center frequency must be located somewhere below the desired boost frequency. fboost = fcenter * 1.27 is just a rough rule of thumb.

All in all, there are three parameters that need to be optimised. You can simply try what happens following the rule of thumb approach, of course. Just don't expect it to be magically right without fine tuning.

Also note that the WiiM PEQ won't even show the overshoot at high Q values, so you're shooting in the dark here, too, unless you can measure for yourself.

 

[sams99]

No, you shouldn't.

To use this method, you need to know the tuning frequency of your speakers. You cannot just look at the lower boundary of a "frequency response" (lacking any information how it was measured).

The only published impedance plot I found for the 3030i can be seen here:

Q Acoustics 3030i: Seite 4 - i-fidelity.net

www.i-fidelity.net

Unfortunately, it's a low resolution measurement and the tuning frequency can basically anything from 42 Hz to 48 Hz. So, 46 Hz might not even be all wrong, but at these low frequencies +/- 3 Hz is quite a high deviation already. Ideally you should be able to take your own measurements of your very own speakers.

A general limitation of this method is that it can't take room acoustics into account. While the theory is all valid, its practical execution can only hint you to a starting point for further experiments, which are hard to do without measuring equipment. The above link also contains a typical (we might hope) in-room response of these speakers. Look at the graph, extending below 30 Hz! Does this curve look like it needs a further boost at 46 Hz?

Finally, make sure you understand what you're doing, first. The boost comes from the overshoot of a high Q (where high means Q >> 0.7) shelving filter, even with negative gain. It's all shown on the first page if this thread, including the external link. The negative gain (potentially) relieves the speakers from very low frequencies they cannot handle anyway. The center frequency must be located somewhere below the desired boost frequency. fboost = fcenter * 1.27 is just a tough rule of thumb.

All in all, there are three parameters that need to be optimised. You can simply try what happens following the rule of thumb approach, of course. Just don't expect it to be magically right without fine tuning.

Also note that the WiiM PEQ won't even show the overshoot at high Q values, so you're shooting in the dark here, too, unless you can measure for yourself.

Thank you very much for your very detailed response.
I shall go back and read it all in more detail. Unfortunately I don't have proper measuring equipment at hand.
But in my experimenting I might stumble across a setting I like.

 

[harkpabst]

But in my experimenting I might stumble across a setting I like.

There's nothing wrong with trying out, of course.