Alpha15a distortion measurements log

[MJK]

I made more measurements in other locations, and feel confident that there is a steady/smooth 6dB/octave roll off in the bass at listening distances.

I ran my MathCad H frame worksheet and got calculated SPL curves that are very similar to your outdoor measurements at the various distances. But I would never use the H frame design without an appropriate crossover, when I add a 2nd order filter at 125 Hz the combined response is flat from about 30 Hz to 300 Hz at all distances. It would be really interesting to see you repeat the measurements with a crossover in place, or post-process the data adding a 2nd order filter to see the anticipated SPL curves.

 

[cuibono]

Okay, here we go - I built an active, line level XO, 125Hz, 2nd order. Here is the transfer function:

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Here are outdoor measurements:

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Here is a close up, clean take at 6 feet distance:

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Here are the indoor measurements:

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Firstly, hats of to MJK for knowing what he is talking about - the measurement at 6' looks pretty good. I guess the only caveat is that the -3dB point is closer to 38 than 28Hz.

The in room measurements look pretty dismal at 6' and 9' feet...

Anyway, sometime soon I'll do the same for another cheap woofer, with low Qts. I'm interested in seeing what happens in lieu of the 45Hz knee, and if that area drops off at the same rate between the two drivers.

 

[ScottG]

The in room measurements look pretty dismal at 6' and 9' feet...

That should tell you something right there.

Consider a Goldwood 18" based dipole SUBWOOFER - NEAR FIELD. (..behind your listening position with appropriate phase adjustment via a plate amp.)

This is something I learned via trial and error quite some time ago.

Conclusion (for me):

Dipole on your "mains" really shouldn't extend to more than about 60 Hz. You *also* need to factor in gain via impedance with reactive amplifiers (i.e. those with high out-put impedance and low input impedance.) So the low-pass isn't necessarily "pat" either.

 

[MJK]

Firstly, hats of to MJK for knowing what he is talking about - the measurement at 6' looks pretty good. I guess the only caveat is that the -3dB point is closer to 38 than 28Hz.

I am a little surprised by the closer measurements, were you measuring on the axis of the driver? When I simulated the response at the different distances, I assume the H frame was on the ground and the mic was 32" above the ground to simulate a seated position, then all the simulations looked the same except for the SPL magnitude.

The in room measurements look pretty dismal at 6' and 9' feet...

Anyway, sometime soon I'll do the same for another cheap woofer, with low Qts. I'm interested in seeing what happens in lieu of the 45Hz knee, and if that area drops off at the same rate between the two drivers.

Lets be honest, almost any in room measurement is going to contain many peaks and dips. This is true for dipole and boxed speakers. Take a look at the unsmoothed raw SPL data if you want to see something really ugly.

 

[shrub0]

"I've been very happy with them, but as 'progress' marches on, I've been examining other drivers, enclosures, etc."

Can we revisit the original purpose of this thread? Have you found a driver or enclosure that works better?

Any thoughts about how the AE IB15, Goldwood 18" or dayton ib385 would compare?