Full DSP Pluto Clone

but not specific to the Orion/Pluto platforms. Preamps, VC, cables, etc.

Full DSP Pluto Clone

Postby AndrewW » Tue Jan 24, 2012 7:10 am

Tweeter and woofer impulse responses are captured via swept sine technique:

raw spectra.png
raw spectra.png (28.43 KiB) Viewed 1810 times


Observation at 40Hz and 85Hz reveals resonance of 6”x39” woofer pipe. Gigantic peak at 20kHz reveals that tweeter is a Peerless 2” full range.


Inverse transfer function of impulses is generated with Cool Edit using Aurora pluggin Invert Kirkeby. A FIR filter crossover for 1kHz is generated and applied to the inverse transfer function. Another FIR filter is used to HP the woofer at about 15Hz. A third FIR filter is used to LP the tweeter at about 17kHz:

Woofer and Crossover Filter.png
Woofer and Crossover Filter.png (26.67 KiB) Viewed 1810 times



Tweeter and Crossover.png
Tweeter and Crossover.png (25.95 KiB) Viewed 1810 times


The filters are implemented using Convolver pluggin for Windows Media Player: http://convolver.sourceforge.net. Microphone is placed in front of speaker and a few seconds of drum percussion is recorded. The result is brought into Cool Edit, aligned with the source track, and the two tracks normalized for amplitude. In the following screen shots top track is source and lower track response recording. The first shot is about 100ms and the second shot is about 10ms:

Percussion 94ms.png
Percussion 94ms.png (41.32 KiB) Viewed 1810 times


Percussion zoom 10ms.png
Percussion zoom 10ms.png (39.73 KiB) Viewed 1810 times
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Re: Full DSP Pluto Clone

Postby dewardh » Tue Jan 24, 2012 8:30 pm

AndrewW wrote:peak at 20kHz reveals that tweeter is a Peerless 2” full range.

830983? (I've been playing with that one . . . really nice)

Totally down with using 6" sonotube for the woofer, too . . .

Looking forward to seeing more of your project, and results.
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Re: Full DSP Pluto Clone

Postby ginopalletta » Wed Jan 25, 2012 12:42 am

so those resonances at 40 and 85 are what is left after you stuff the pipe with "sound absorber"?
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Re: Full DSP Pluto Clone

Postby AndrewW » Wed Jan 25, 2012 10:24 am

dewardh,

These are using Peerless 830970. Specs are quite similar. Of course, Aura 2" works quite well too! I milled off flange and glued tweeter into pipe:

IMG_0342 Pluto Clone 320x274.jpg
IMG_0342 Pluto Clone 320x274.jpg (55.31 KiB) Viewed 1712 times


ginopalletta,

Yes, the pipe is very well stuffed. I started with a lot of stuffing with similar outcome, so reduced. In prior post spectrum is with FFT of 65k Blackman-Harris windowing. At sampling rate of 44.1kHz it reveals detail of low frequencies fairly well. Often results are published with too small an FFT, sometimes intentionally because this smooths the result. Here is same result with FFT of 8k:

Woofer fft8k.png
Woofer fft8k.png (18.46 KiB) Viewed 1712 times
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Re: Full DSP Pluto Clone

Postby AndrewW » Thu Jan 26, 2012 10:59 am

Spectrum of system, tweeter, woofer, reverse null, CSD: Microphone is Earthworks OM-1 placed at 9 inches. Results are un-smoothed.

Impulse.png
Impulse.png (24.26 KiB) Viewed 1674 times


Solo impulse.png
Solo impulse.png (28.17 KiB) Viewed 1674 times


Reverse null.png
Reverse null.png (29.92 KiB) Viewed 1674 times


Impulse response ported into ARTA:

CSD impulse2.png
CSD impulse2.png (18.92 KiB) Viewed 1674 times


Microphone moved to 42 inches. A clear view of room mode behavior:

Impulse 42 inch.png
Impulse 42 inch.png (27.17 KiB) Viewed 1674 times


And the above gated to about 3ms. This captures direct sound at expense of low frequency resolution:

Impulse 42 inch gated 3ms.png
Impulse 42 inch gated 3ms.png (25.3 KiB) Viewed 1674 times


And square wave response around 1kHz, 66Hz, and 2kHz:

sq1k.png
sq1k.png (16.22 KiB) Viewed 1674 times


sq 66Hz.png
sq 66Hz.png (18.64 KiB) Viewed 1674 times


sq 2k.png
sq 2k.png (20.35 KiB) Viewed 1674 times
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Re: Full DSP Pluto Clone

Postby SL » Thu Jan 26, 2012 8:03 pm

OK, so how does it measure off-axis at 9 inch?
Do the brickwall xo lowpass and highpass outputs still add ok in the frequency domain or is there pre-ringing in the time domain?
Up to what off-axis angle, horizontally and vertically, does the summation hold?

SL
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Re: Full DSP Pluto Clone

Postby AndrewW » Fri Jan 27, 2012 7:57 am

Hello Mr. Linkwitz:

The system is very stable:

45 degrees off axis horizontal: Gated and un-gated results are shown. Rest of results are all gated.

45 degrees.png
45 degrees.png (43.12 KiB) Viewed 1604 times


90 degrees off axis horizontal:

90 degrees.png
90 degrees.png (39.95 KiB) Viewed 1604 times


30 degrees horizontal and 30 degrees vertical above:

30H 30V degrees.png
30H 30V degrees.png (42.24 KiB) Viewed 1604 times


15 degrees below:

15 degrees below.png
15 degrees below.png (41.79 KiB) Viewed 1604 times
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Re: Full DSP Pluto Clone

Postby AndrewW » Fri Jan 27, 2012 8:06 am

PS to above: Changes in level are due to normalizing amplitude of all results to same peak value.

AW
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Re: Full DSP Pluto Clone

Postby AndrewW » Fri Jan 27, 2012 8:33 am

....and all together.....

All together.png
All together.png (27.67 KiB) Viewed 1598 times



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Re: Full DSP Pluto Clone

Postby SL » Fri Jan 27, 2012 10:14 am

Very nice.
And how does it sound?
Compared to the analog version?

SL
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Re: Full DSP Pluto Clone

Postby AndrewW » Fri Jan 27, 2012 11:36 am

The sound is wonderful. Holographic.

I have gotten very good results with DCX2496, but have not built or heard with ASP.

Currently I am working on integration with sub. Here is link to ground work: http://waveformfidelity.com/arbitrary-s ... nment.html

Andrew
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Re: Full DSP Pluto Clone

Postby SL » Fri Jan 27, 2012 12:29 pm

In your subwoofer tests you are using both a dipole and a monopole cabinet. Are both driven simultaneously, in effect generating a cardioid like source?
Do I understand correctly that you show when the source is equalized to a flat response at the microphone location, then you have almost complete recovery of the modulation envelope and that even serious driver distortion has little effect upon the envelope? That is what I would expect. The loss of modulation depth appears to be a phase response issue, not so much an amplitude response issue of the unequalized response, unless the relative amplitude of the two sidebands changed sufficiently. In any case it is a linear, amplitude independent phenomenon. Is its effect/occurence greater for a monopole than a dipole?

Can you calculate/measure the before/after MTF?

SL
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Re: Full DSP Pluto Clone

Postby AndrewW » Wed Feb 01, 2012 8:32 am

Monopole and Dipole woofer alignments:

An alignment run with separate treatments for monopole and dipole elements:

Log sweep 10 octaves generated from 2Hz to 2205Hz of 1048576 sample length at fs 4410Hz, 1/10th of CD sampling rate. Suitable inverse filter derived using Aurora/Kirkeby inverse plugin. Sweep is just under 240 seconds in length and thus is sweeping 24 seconds/octave. So 24Hz to 48Hz in 24 seconds averages to 1Hz/sec. It’s a very exciting sweep! Re-sampled to fs 44.1kHz for sound card and CD compatibility. Microphone placed about 44” from stack and floor. Sweeps of independent drivers and simultaneous drivers recorded with 26 volts rms drive signal. Very hot and exciting sweeps! After a few goes LP 1kHz applied. The aluminum Dayton 12” HF 4ohm with 26V across it at 1kHz-2kHz is really too loud, even with earplugs in.

Results re-sampled back to fs 4410Hz and each convolved with inverse sweep to recover impulse responses:

Raw Spectrums:

Monopole:

Monopole spectrum.png
Monopole spectrum.png (16.56 KiB) Viewed 1488 times


Dipole:

Dipole spectrum.png
Dipole spectrum.png (16.79 KiB) Viewed 1488 times


Cardioid system as Monopole and Dipole driving together:

Cardioid.png
Cardioid.png (17.1 KiB) Viewed 1488 times


Cardioid as sum of Monopole spectrum and Dipole spectrum, sum is +6db shown result normalized for comparison to Cardioid spectrum above:

Cardioid v Cardiod as sum of Monopole and Dipole.png
Cardioid v Cardiod as sum of Monopole and Dipole.png (18.4 KiB) Viewed 1488 times


Kirkeby engine used to generate inverse function of each IR. Results band-passed 9-175Hz.

Candidate inverses convolved with copies of test sweep, up-sampled to fs 44.1kHz, run, and impulse responses derived as with test sweep:

Spectra with correction filters:

Monopole:

Monopole response spectrum with correction filter.png
Monopole response spectrum with correction filter.png (14.53 KiB) Viewed 1488 times


Dipole:

Dipole spectrum with correction filter.png
Dipole spectrum with correction filter.png (14.45 KiB) Viewed 1488 times


Cardioid system as Monopole and Dipole driving together:

Cardioid system with correction filters.png
Cardioid system with correction filters.png (14.33 KiB) Viewed 1488 times



Raw Impulse responses Monopole top, Dipole bottom:

Monopole top Dipole bottom raw impulses.png
Monopole top Dipole bottom raw impulses.png (22.16 KiB) Viewed 1488 times


Impulse Responses with correction filters: Monopole top, Dipole bottom

Monopole top Dipole bottom impulses.png
Monopole top Dipole bottom impulses.png (30.77 KiB) Viewed 1488 times


Monopole top and Dipole-Monopole bottom:

Monopole top v Dipole-Monopole bottom impulse dif.png
Monopole top v Dipole-Monopole bottom impulse dif.png (28 KiB) Viewed 1488 times


The waveform fidelity performance within passband is similar to the Pluto Clone. The woofer stack and Pluto Clone may be integrated, but a better alignment perhaps would use Monopole <50Hz, Dipole passband 50Hz-100Hz. This would greatly reduce driver demands on the Seas woofer, reducing intermodulation distortion.

The last screen shot was made by subtracting the monopole wave from the dipole wave, and makes clear that the MTF of the monopole and dipole as conditioned must be very similar. I have looked into MTF, and am currently working on a graphical presentation of the complex MTF using Cool Edit.

Andrew
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