The Subwoofer DIY Page - Projects
Retrofitting a subwoofer.
 26 October 2018
My INF10 subwoofer has almost always performed to my satisfaction.  Almost.  It had one particular problem that could be quite annoying at times.  Whenever it was called upon to reproduce a fairly large low-frequency signal, the driver would respond with a loud cracking noise (caused most likely by the voice coil former slamming into the back plate).  This might have something to do with the driver being theoretically capable of handling only 60W in this particular alignment and I was driving it with a 270W amplifier!

For some time I've been looking for a replacement driver that will work well in the box  I built for the INF10 (2.5 cu.ft. tuned to 21 Hz), but most of the 10" drivers I came across either had too high an Fs, too low a Vas or Xmax, or were simply to expensive (>US$100) to consider as a suitable replacement.

My luck changed a few months ago when ACI announced a sale on their subwoofer drivers. I've always been interested in their SV10 10" driver (with a rated Xmax of 16mm!), but the price was just a little to expensive.  However, the sale brought the price down to $99, so...

Physically, the SV10 is a beast - it makes the INF10 look very wimpy in comparison.  Specs-wise, the drivers' published parameters compare as follows:

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 Madisound INF10 ACI SV10
Vas 109 litres 84 litres
Qts 0.34 0.36
Fs 22 Hz 18.5 Hz
Re 6.3 Ohms 2.72 Ohms
Xmax 8 mm 16 mm
Sd 0.0330 M^2 0.0314 M^2
Pe 100 Watts 250 Watts

Some points about the specifications that might be of interest:

1. The lower Vas, Fs and Qts of the SV10 result in a driver that is just over 4 dB less efficient than the INF10.  However, as the SV10's impedance is less than that of the SV10, the difference in sensitivity works out to considerably less - just about 0.3 dB.
2. The SV10's Xmax is twice that of the INF10, and its Vd works out to be roughly that as well.
3. Because of the greater Vd, the SV10 driver can absorb considerably more power (225 W compared to 50 W) before reaching its theoretical excursion limits in a 2.5 cu.ft. box tuned to 21 Hz. As its sensitivity is almost identical to that of the INF10, the SV10 will produce approximately 3dB and more linear SPL at all frequencies, as the graph below suggests.
4. The SV10 will produce a response that's 3dB at 20.5 Hz in the given alignment. This suggests that low frequencies may be exaggerated (as compared to the INF10 in the same alignment) when "room gain" is taken into effect.  But this of course depends on how much the "room gain" of my living room actually adds to the subwoofer's response at low frequencies.

Shown below is the predicted frequency response of both systems up to their theoretical peak SPL limits (note: I have not included an adjustment for room gain, so the "modified response" plot is the same as the theoretical plot without room gain):

SV10vsINF10.gif (7978 bytes)

Uh-oh....
I initially thought that "upgrading" my subwoofer would be a simple issue of matter of removing the INF10 and inserting the SV10 in its place.   After all, they're both 10" drivers, right?  Wrong! While they are both rated as 10" drivers, the SV10 requires a larger mounting hole than that of the INF10. Not too much of a problem - I simply made a mounting template for the SV10, marked out the required hole diameter on the box and enlarged the hole accordingly using my jigsaw.  A router would've probably produced better results, but I don't have access to one at the moment.

Shown below is a picture of the box with the SV10 installed. Constructing a proper protective grill for the front of the speaker has always been on my "To Do" list, but I've never gotten around to it :-).

sv10box.jpg (26133 bytes)

Observations
The theoretical response of the INF10 and the SV10 in this alignment is fairly close down to about 40 Hz. However a simple before/after listening test suggests to me that the SV10 produces a more "solid" sound than that of the INF10.  And it's power handling at higher SPL levels is certainly better than that of the INF10 - the SV10 is apparently able to handle the peak output from my subwoofer amplifier, all the way down to the alignment's Fb.  At lower frequencies, the SV10 exhibited greatly increased excursion (a characteristic of all vented systems), but did not exhibit any of the harsh cracking noises that characterized the INF10's response to such frequencies at those levels. Great!

Conclusion
Overall I'm very satisfied with the upgrade, which leaves one question..

What to do with the INF10 driver?
As mentioned previously, the INF10 will produce loud cracking noises if driven beyond its limits, but sounds quite clean up to that point. Evidently what is required is an alignment that ensures that the potential for over-excursion is reduced.   This suggests a small sealed box will probably work best. Or perhaps a 4th order bandpass box tuned for higher SPL.  In fact, that's exactly what I tried - you can read about that project at the following link: http://www.diysubwoofers.org/projects/inf10bp