His problem is that he wanted to find out the alignment AFTER BUILDING the speaker. We know this is not very sensefull, but he asked why his DATS measuring device could not tell him.
I think by now he has understood that he should measure the drivers TSP and make a simulation instead. If it matches his measured impedance curve, he can estimate what he build.
I think by now he has understood that he should measure the drivers TSP and make a simulation instead. If it matches his measured impedance curve, he can estimate what he build.
Neville Thiele (yes, that Thiele) offered instructions for that here: http://www.hornlautsprecher.net/Dokumente/Grundlagen/Tiele-Smal-LSPRMTRS604.htm
It's a difficult read, so I summarized it all in Appendix A of the paper mentioned in my post #12, above. Anyone can PM me and I'll send a copy. Just ask for the Linkwitz Transform paper.
Yes, DATS can do it.
Of course it can. Or one valuable tool in a very simple process anyway. It doesn't tell you the alignment itself because it measures impedance, not FR. But all you need to do is to use it to find the system Fb, establish Vb within a reasonable limit (a tape measure & eyeball work well), then pop the driver & use DATS to measure the free-air T/S values. You then have everything you need to establish the alignment, to as-near-as level, with Hornresp, VituixCAD,, WinISD, BassBox Pro, Basta, Woofer Box or any of the many [many] freeform lumped element vented box modelling tools available (assuming you didn't for some reason want to do it by hand on graph paper). Total work: about 5 minutes. Job-jibbed.
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I am not entirely convinced that adding high levels of boost (e.g., +10dB) below the tuning frequency of a bass reflex system is a good idea. Wouldn't boosting that frequency region produce a lot of driver cone excursion?
If you place the same driver in a much larger enclosure, the room doesn't care. The only thing that is of interest, is the amount of air that is moved. Which, to some extend, is dependent on the cone movement. So as long as there is x-max to use, you can "transform" any woofer.
Some DSP's, for example the ones build into the i-Nuke / NX Behringer amps with a "D" at the end, have a smart, frequency dependent limiter. They allow the woofer only that much excursion = voltage as it can take. So at some point, excursion in the low end doesn't rise, while the upper range still increases in level. Something, a decade later, is found in some active HIFI speakers too. That is some kind of "cheating", but enables a small speaker to reach surprisingly high SP-levels. I thing "Buchard" uses this trick. Many HIFI people are simple souls with too much money and fall for such tricks. If you call it a trick...
Some DSP's, for example the ones build into the i-Nuke / NX Behringer amps with a "D" at the end, have a smart, frequency dependent limiter. They allow the woofer only that much excursion = voltage as it can take. So at some point, excursion in the low end doesn't rise, while the upper range still increases in level. Something, a decade later, is found in some active HIFI speakers too. That is some kind of "cheating", but enables a small speaker to reach surprisingly high SP-levels. I thing "Buchard" uses this trick. Many HIFI people are simple souls with too much money and fall for such tricks. If you call it a trick...
If you want to "Linkwitz" transform (just to give it a name) a vented cabinet, you got to understand how it works. There is this point where the cone hardly moves at all and the vent is moving all the air allone. Now, if you play with a simulation, you can see how the cone excursion changes.
Basically to do it right, you tune a vented system too low, so the response falls, but doesn't directly drop like a stone with 18dB/oct. Best is to make the volume a little larger than theoretically optimal. Then lift the low end up again, combined with a steep high pass filter, to prevent the cone from flapping around under the usefull frequency. May sound more complicated than it is. There are driver that allow for such a tune with reasonable small vented volumes.
Anyway, size= volume in DIYS is often less a concern than with commercial subs. Once we grow up, we should understand that a "neat, small" sub is not a miraculous product, but an expensive way of doing things wrong. This often heard "oh, it's so cute and still does so much bass" is always a first impression and wears of quite fast. So don't try to build subs too small, just because you think it may be cool.
Basically to do it right, you tune a vented system too low, so the response falls, but doesn't directly drop like a stone with 18dB/oct. Best is to make the volume a little larger than theoretically optimal. Then lift the low end up again, combined with a steep high pass filter, to prevent the cone from flapping around under the usefull frequency. May sound more complicated than it is. There are driver that allow for such a tune with reasonable small vented volumes.
Anyway, size= volume in DIYS is often less a concern than with commercial subs. Once we grow up, we should understand that a "neat, small" sub is not a miraculous product, but an expensive way of doing things wrong. This often heard "oh, it's so cute and still does so much bass" is always a first impression and wears of quite fast. So don't try to build subs too small, just because you think it may be cool.