I think it's a bit limiting to apply DSP to get to a specific target curve in bass without considering the room. The room is the biggest factor in this equation!
It's better to just measure in-room and DSP from there to the actual target you want. Obviously, you can add measures to limit over-excursion as well, But maybe a limiter is better suited for that task, as it can dynamically limit when actually needed, instead of always incurring a group delay impact.
It's better to just measure in-room and DSP from there to the actual target you want. Obviously, you can add measures to limit over-excursion as well, But maybe a limiter is better suited for that task, as it can dynamically limit when actually needed, instead of always incurring a group delay impact.
I see it this way - one (or two) shelf PEQ will make the box flat and protected from over excursion. The rest can be used for any other purpose. My goal here is to use a certain size box and get as much bass (down to 40 Hz) as possible from it. I already have a sealed 2x12 sub (also EQ'd), this 15" box is going to be a test bass unit for various large horns.
I discovered that Hornresp does have shelf filters as well (with wide range of settings) - and so does my t.racks 4x4 DSPmini - although limited to max Q=3 and min/max gain +- 12 dB. That means I will have to set the DSP by the measurement anyway, since it is showing a bit different filter response than Hornresp.
If this is what I get, then I will be super happy:
If this is what I get, then I will be super happy:
The test box is finished. The kitchen table top board looks better than I expected, I just used a random piece I bought as a discounted leftover piece. I want to do some quick and dirty measurements later today, maybe even some EQ so that it can work instead of the 2x12 sealed box I have there normally.
The WN400 horn prototype is waiting for the return of my DCX464 pair from the factory.
The WN400 horn prototype is waiting for the return of my DCX464 pair from the factory.
So this is the impedance plot. Can one calculate or read the tuning frequency from it? The absolute minimum between the peaks is at 35.9 Hz.
Hornresp calculated 40.8 Hz tuning, but I expected that the vent will be effectively a bit longer and it seems that it is like that. Also the woofer is new from the box, so it needs some burn-in, too. Hornresp predicts the first peak at 16.3 Hz and the second at 83.3 Hz, minimum is at 38.9 Hz.
I tried the shelf filter and listening to a few test tones, 36 Hz can be heard and felt, 30 Hz is already down. So far so good, it seems to be pretty similar to the sealed box subwoofer I had there (also with EQ). I need to find a way how to tune the DSP settings and then add some room correction / house curve to it.
Can the dsp system here do dynamic EQ? It's popular in small systems today to boost more LF when the output level is low (got the headroom) and reduce the LF boost as output level increases. (This also kind of coincides with the loudness curve). You could put a sub-sonic filter on this too.
For a 12" or 15" driver you probably have LOADS of headroom though for domestic use.
For a 12" or 15" driver you probably have LOADS of headroom though for domestic use.
Neither MiniDSP 2x4 HD nor t.racks DSP 4x4 mini can do dynamic EQ. Maybe FreeDSP os similar board usingSigma Studio could do it.
In any case, the parametric EQ correction would have to be applied before that - to gain the extension at the low end and correct the slight bump from undersized box and high Qts woofer.
Using a pro subwoofer like RCF LF15X401 would also work, with a high power amp, insane levels are possible, but I do not think it would work that well for a two way system. Unfortunately, it has 2 mm larger diameter than the 15OB350 and it will not fit the box I built. I should have made the recess so that both would fit
In any case, the parametric EQ correction would have to be applied before that - to gain the extension at the low end and correct the slight bump from undersized box and high Qts woofer.
Using a pro subwoofer like RCF LF15X401 would also work, with a high power amp, insane levels are possible, but I do not think it would work that well for a two way system. Unfortunately, it has 2 mm larger diameter than the 15OB350 and it will not fit the box I built. I should have made the recess so that both would fit
Hey that's a cool idea, PerryMarshall. I haven't tried that, I'll have to give it a listen.
I've got a pair of MarkAudio CHN-50 drivers (small!) in a small BT speaker with DSP. With a high pass and a compressor, it's able to play quite loudly! (by domestic standards) This is especially handy for small drivers that you might wish to port at a higher frequency, since the higher you port the more total energy will exist below your tuning freq.
The idea of choosing a large box is an interesting one also. I had always sorta thought of DSP as a means to compensate for having chosen a small box. But if you can make a big box you'll have an easier time fitting in a large port, which you're going to want if you're setting up to really hammer that design aspect. But if you're avoiding phase shift from a steep HP, maybe you want to keep an eye out for increasing group delay (from a larger box) also?
If you play with reflex alignments on small drivers and try doubling or tripling the size of the box, you'll find you can get, let's say, a +5dB peak at 50Hz (and maybe even have to deal with a dip at 80Hz) and yes you can fix the dip and peak with DSP (at the cost of excursion at 80Hz, where the port is not helping you much).
And yes if you cut it off sharply below resonance it will play fairly loud.
Presumably the reason you're using a small driver in the first place is because it's full range and the small diameter buys you better high end.
Group delay is mostly a function of the tuning frequency and the slope of the DSP subsonic filter, not the size of the box. It's critical that you match the DSP cutoff to the exact tuning frequency of the port (like the article shows) if you want to squeeze every last drop of juice out of the orange.
The article referenced above shows a 1 liter (62 cubic inch) box with a Fountek 3" driver and 4" passive radiator and considering how tiny, they play surprisingly loud and deep.
And yes if you cut it off sharply below resonance it will play fairly loud.
Presumably the reason you're using a small driver in the first place is because it's full range and the small diameter buys you better high end.
Group delay is mostly a function of the tuning frequency and the slope of the DSP subsonic filter, not the size of the box. It's critical that you match the DSP cutoff to the exact tuning frequency of the port (like the article shows) if you want to squeeze every last drop of juice out of the orange.
The article referenced above shows a 1 liter (62 cubic inch) box with a Fountek 3" driver and 4" passive radiator and considering how tiny, they play surprisingly loud and deep.
Really? If I go into my modeling software and 5x the size of the box (driver params and vent freq the same) I see output at the tuning frequency nose up, and group delay curve peaks up also. But maybe if you EQ'd response back the way it was, GD would go back down also?
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I spoke too soon - went on intuition rather than modeling it. I looked and a bigger box does give you a peak in the group delay. This is intrinsic to the shape of a peaked response which naturally comes from a bigger vented box.
All things being equal, if you simply flattened the peak with DSP, it would in turn reduce the group delay. A given response shape no matter how you arrive at it will produce a given group delay. That is a principle of any minimum phase filter.
When you add high pass with DSP it will increase group delay even more. That's why I like using 2nd order shelf filters better than 4th order high pass filters for that purpose.
The bigger box gives you more efficiency from the small driver. You can decide what rolloff shape you want, independently of that, if you have DSP.
All things being equal, if you simply flattened the peak with DSP, it would in turn reduce the group delay. A given response shape no matter how you arrive at it will produce a given group delay. That is a principle of any minimum phase filter.
When you add high pass with DSP it will increase group delay even more. That's why I like using 2nd order shelf filters better than 4th order high pass filters for that purpose.
The bigger box gives you more efficiency from the small driver. You can decide what rolloff shape you want, independently of that, if you have DSP.
@perrymarshall
Most use minidsp boards and elliptic filters to get that desired shelving filter. Anyone tried ACP Workbench and Arylic Plate Amp 2.1?
Most use minidsp boards and elliptic filters to get that desired shelving filter. Anyone tried ACP Workbench and Arylic Plate Amp 2.1?
So I have been listening to this simple BR box for a while and it seems to work pretty well indeed. No hint of "single note bass" - it is as good or better than the dual 12" sealed sub I had there before (that one was definitely not suitable as a bass unit, it will still work fine as the second sub in the room). I am very happy with the result.
I would say that equalized bass reflex using the shelf filter will be sonically better than a similar sealed box, since it needs less boost due to better efficiency of the BR. Please correct me if I am wrong with this.
In any case, this is now my favorite way of building bass enclosures. Maybe before I finally build some proper open baffle bass unit - unfortunately, any kind of OB is not very suitable for my situation, the boxes need to be with their backs on the front wall.
I would say that equalized bass reflex using the shelf filter will be sonically better than a similar sealed box, since it needs less boost due to better efficiency of the BR. Please correct me if I am wrong with this.
In any case, this is now my favorite way of building bass enclosures. Maybe before I finally build some proper open baffle bass unit - unfortunately, any kind of OB is not very suitable for my situation, the boxes need to be with their backs on the front wall.
Then use that to your advantage and design accordingly…….rear firing woofer(s) close coupling to the the front wall.…..run only your mid/woofer fwd facing and down to 120hz or so…..3 way is clearly the best solution in your case
@mayhem13 That may be worth trying. The temporary setup needs to be crossed over at 200 Hz, but I am building two way MEHs which should be good down to 80-90 Hz sealed.
@sheeple I am not sure I understand that fully. The Keele paper mentions a high pass filter, so it would have also over excursion protection built-in. Or do you use only a peak type EQ?
@sheeple I am not sure I understand that fully. The Keele paper mentions a high pass filter, so it would have also over excursion protection built-in. Or do you use only a peak type EQ?