Extending bass response with the help of dsp

[ZolaIII]

Ah my favourite mocking bird egg which neither of them finished measurements for not even after update from Erin's side.
Those are more typical for the size, pushed less and with lower woofer Fs and that's why they compress less in the first place. For those ideal is 34 Hz cut off and 120 Hz crossover point to stress them out. I do opposite from you I let them breed and amplifier also and try to remove resonances with it instead of pushing them beyond (and they are all already pushed too much and crossed to high from their designer's in order to pull out as much as possible from them [not a great design rule]).

 

[gberchin]

I recently wrote "Linkwitz Transform Closed Box and Vented Box Tutorial.pdf". The Table of Contents is available here. PM if you want a copy of the whole paper. Feedback is welcome.

 

[Tangband]

I recently wrote "Linkwitz Transform Closed Box and Vented Box Tutorial.pdf". The Table of Contents is available here. PM if you want a copy of the whole paper. Feedback is welcome.

Interesting ! You got PM

 

[Tangband]

With this technique, its possible to extend the bass from a Kef ls50 Meta with 51 Hz ( tuning frequency ) *0.85 = 43,3 Hz . This is, in practice, a big difference.

KEF LS50 Meta loudspeaker Measurements

Sidebar 3: Measurements I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the KEF LS50's frequency response in the farfield, and an Earthworks QTC-40 for the nearfield and spatially averaged room responses. My estimate of the LS50 Meta's voltage sensitivity was...

www.stereophile.com

I have tried more of this now , and with the high pass shelving set exactly at the tuning frequency of 36 Hz of my chn110 speakers, and a Q = 1.5 , gain -12, the bass gets even better and more powerful than without shelving . Using different test tones there are almost no cone movements to be seen below 36 Hz .

The different Q values are important - with a higher Q value than 0.7 you get more bass at the chosen shelving frequency. Q=4 its very evident with much more bass . For me, it sounds best with Q= 1.5 .

Read more here :

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

If I use the shelving filtering exactly at the tuning frequency of the speaker ( not lower in frequency ) - I see no disadvantages with this.

This graph shows what happens using shelving with different Q . Q=5 will overshoot and boost the bass at the chosen shelving frequency . Q=0.7 will have no bass boost.

Parametric Equalizer - JRiverWiki

wiki.jriver.com

 

[Tangband]

Generally speaking you can DSP closed cabinet speakers much better than ported ones
That is due to the fact that the low frequency roll-off of sealed cabinets is more gentle (around 12dB/octave) compared to ported cabinets
So in other words, there is 'material' down there that you can work with
That's the reason why I design and build sealed cabinets only
Having said that, obviously you will sacrifice SPL in exchange for low extension in any case - not to mention that (much) more amp power will be needed too
One shall take all this into account already at the design phase to avoid any unpleasant surprises

I have tried blocking the port on my speakers making them closed, and use PEQ to boost the low bass, but to me it dont sound better than using it with the port. Much better bass with the port. The one note bass we often hear with ported constructions is maybe more common with loudspeaker boxes that are way to small ?

 

[ppataki]

I have tried blocking the port on my speakers making them closed, and use PEQ to boost the low bass, but to me it dont sound better than using it with the port. Much better bass with the port. The one note bass we often hear with ported constructions is maybe more common with loudspeaker boxes that are way to small ?

I am happy to stand corrected but as far as I know stuffing the port will not convert a ported cabinet to a sealed one
You need to actually remove the tube and make sure the hole is sealed airtight (and doublecheck that the cabinet is airtight everywhere)

 

[ZolaIII]

I have tried blocking the port on my speakers making them closed, and use PEQ to boost the low bass, but to me it dont sound better than using it with the port. Much better bass with the port. The one note bass one often hear is maybe more common with loudspeaker boxes that are way to small ?

Closing the port is not the same thing as close enclosure speakers. Fb stays the same and woofer excursion almost the same and it's very, very high and that's why you don't do Linkwitz transform on it, Butterwort high pass (Q) help a bit. In the meantime I read the gberchinis white paper and will do it more thoroughly again in coming days and experiment with my sealed sub's (even I don't need more extension).

 

[Tangband]

I am happy to stand corrected but as far as I know stuffing the port will not convert a ported cabinet to a sealed one
You need to actually remove the tube and make sure the hole is sealed airtight (and doublecheck that the cabinet is airtight everywhere)

Thats true.
Doing the conversion to closed box the right way, I would also have to build new much smaller boxes.
One looses SPL in a closed box compared to an optimal ported box, and the distortion will be lower for the ported. However, a ported speaker with to small box will sound worse than an optimal closed box speaker.

 

[Tangband]

Closing the port is not the same thing as close enclosure speakers. Fb stays the same and woofer excursion almost the same and it's very, very high and that's why you don't do Linkwitz transform on it, Butterwort high pass (Q) help a bit. In the meantime I read the gberchinis white paper and will do it more thoroughly again in coming days and experiment with my sealed sub's (even I don't need more extension).

I will read the very advanced white-paper from gberchin one more time, to

 

[ZolaIII]

Thats true.
Doing the conversion to closed box the right way, I would also have to build new much smaller boxes.
One looses SPL in a closed box compared to an optimal ported box, and the distortion will be lower for the ported. However, a ported speaker with to small box will sound worse than an optimal closed box speaker.

How can anyone even believe that? If at Fb excursion is is far greater at that point for woofer so Is distortion (it's not able to move in linear manner) and it all together produces resonance in the box (which shows both in waterfall and FR). Main idea behind port and ported enclosure is that it extends the bass response beyond what woofer can alone and add to it from port tuned cuff. It gives higher LPS and extension to port tuning frequency of course but it trade in much things to achieve that, from actually needing more power (as not all SPL increase comes for free), higher distortion, resonance, longer decay time... and it stops working at the point of pressure equalisation. Open baffle design again exchange box for the room as after all that's also a box. Advantage is no whatsoever box resonance or refractions but again room dose that instead but far less as it's a much bigger box. Problems are overlap in response from refractions and that you can't get good ratio of back to front refractions not even in a big room and minimum phase also doesn't work. Ideal doesn't exist and in my opinion best to work with (direct to driver response) producing least problems and there for having less to deal with is closed sealed cabinet.

 

[ppataki]

in my opinion best to work with (direct to driver response) producing least problems and there for having less to deal with is closed sealed cabinet.

+1
couldn't agree more!!!

 

[voodooless]

I would not like to see the group delay of that DSPs response curve… it’s not going to be pretty.

Generally, these kind of DSP calculations are nice as theoretical exercise, but as soon as you put the speaker in a room, the room dominates, and getting that straightened out should be a priority. You can extend/shape your bass in the process if you want. There is no magic there, just put the resulting PEQs in the simulation and check if you can keep the woofer within its operating window. If not, compromise.

 

[ZolaIII]

I still didn't figure out multi chamber and multiple ports pressure equalising enclosure it looks promising but it's possible to achieve the same with high pass limiter and Linkwitz transform function or at least very close and that's why I want to experiment and of course to room response so in my case third order Butterwort high pass and Linkwitz transform (even I don't really need it).

 

[Chrispy]

I am happy to stand corrected but as far as I know stuffing the port will not convert a ported cabinet to a sealed one
You need to actually remove the tube and make sure the hole is sealed airtight (and doublecheck that the cabinet is airtight everywhere)

As well as the box volume...

 

[sigbergaudio]

I have tried more of this now , and with the high pass shelving set exactly at the tuning frequency of 36 Hz of my chn110 speakers, and a Q = 1.5 , gain -12, the bass gets even better and more powerful than without shelving . Using different test tones there are almost no cone movements to be seen below 36 Hz .

The different Q values are important - with a higher Q value than 0.7 you get more bass at the chosen shelving frequency. Q=4 its very evident with much more bass . For me, it sounds best with Q= 1.5 .

Read more here :

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

An article stating "DSP Assisted Reflex: The New Way to Design a Loudspeaker" is hard to disagree with for me, since that's exactly what I'm building with the upcoming Sigberg Audio Saranna.

I still however think one needs to be a bit careful doing this with your own speakers. But as long as the main point (from the article) to actually high pass below the port frequency is the main idea you should be fine, and then be careful with any additional bass boost after that.

 

[Tangband]

+1
couldn't agree more!!!

Here is one paper about the pros and cons about sealed and ported speakers :

Sealed vs. Ported Enclosures

Are sealed or ported enclosures better for bass guitar? What are the differences between them? In this article, I will compare the two most common types of bass guitar enclosures and try to highlight the benefits and shortcomings of each. It took me a while to decide what details to cover, and I...

eminence.com

”The port uses the speaker"s rear output to enhance the speaker"s front output, which increases bass output (or SPL) above F3 (see Figure 3 again). This minimizes the movement of the speaker cone, so mechanical power handling at and above the tuning frequency is very good. The port is actually producing most of the output at the tuning frequency and the speaker"s excursion is minimal. Distortion is lower at this point due to less cone movement. There are some disadvantages to ported enclosures. Transient response is poor compared to a sealed enclosure. The result is decreased accuracy. Also, there"s less control below the box tuning, which allows the cone to move more freely. This can result in damage to the speaker mechanically, a phenomenon known as over-excursion.”

 

[Tangband]

I would not like to see the group delay of that DSPs response curve… it’s not going to be pretty.

Generally, these kind of DSP calculations are nice as theoretical exercise, but as soon as you put the speaker in a room, the room dominates, and getting that straightened out should be a priority. You can extend/shape your bass in the process if you want. There is no magic there, just put the resulting PEQs in the simulation and check if you can keep the woofer within its operating window. If not, compromise.

The article explains that using dsp shelving with high Q as a high pass filtering has better group delay behaviour than an ordinary high pass filtering. Its one of the ”good news” for me , I didnt know that before reading the article.

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

 

[ZolaIII]

Distortion is lower at this point due to less cone movement.

No not really. Main thing to understand is that you have to respect physics. If you want to to relax the driver you do high pass filter just above it's Fs frequency and it serves like limiter and again Butterwort With Q of 0.7071 is a good start (18 dB per octave). In ported box if you get potr tuning above it and Fb to it it will give effect of more SPL and slight extension while having less cone excursion but that's not case with home "Hi-Fi" speakers that are already hard pressed with port tuning far below driver Fs. In such cases you either do high pass as limiter just under port tuning hoping it will help prevent over excursion effect under port tuning frequency (it does help but it's not magical and over excursion happens anyway in driver domain when SPL limit for such is reached) or really stress it out making such high pass limiter on driver response and obviously using sub to render what's beneath it.
For example of how it should be done:

https://www.talkbass.com/threads/cone-excursion-in-winisd.1495416/

In this case Butterwort high pass filter at 37 (to Fs of 36.1) and port and box tuning to 40 Hz and you have a happy linear bunny that has terrific SPL but still doesn't go much lower. Keep in mind this whose 15" driver and not best choice of driver to start with. When choosing the woofer for sub main point is as linear response that goes low with as low Fs as possible and in conjunction with as high as possible Xmas and Lmas but keeping it in let's say mid range for SPL per W. This way you can do mentioned proper tuning for ported enclosure much lower and that's about it. That way it will work very good at least until at some SPL level pressure equalisation doesn't start happening and port losses it's function.
I hope you also get a picture why Linkwitz transform is a no go on home small woofer (6.5~8") that's already been violently raped (with port and cabinet tuning far under drivers Fs in order to provide more kick then healthy for it).
I also hope how others now understand how putting healthy high high pass filter on such help there get lower distortion, better dynamic characteristics and/or higher SPL handling. There is no magic to it, just physics.

 

[voodooless]

The article explains that using dsp shelving with high Q as a high pass filtering has better group delay behaviour than an ordinary high pass filtering. Its one of the ”good news” for me , I didnt know that before reading the article.

No, it doesn't exactly do that. It talks about 24dB and higher-order filters.

Traditional 24, 36, and 48 dB per octave filters introduce large group delays, which are plainly audible. More about this in a minute.

It's specifically about steep filters. You do not need those steep filters to keep excursions in check. 12 dB is plenty.

And remember that the group delay you hear, is still dominated by the room. It's rather pointless optimizing this when you have no idea what the room will do. Then again, making sure the bass response doesn't have a too steep falloff, is always a good idea.

 

[Vladetz]

So applying maximum (-12db) negative low shelf (as high pass is not available on wiim pro) with high Q a bit below port tuning frequency is in any case good idea?