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Old 28th January 2014, 12:02 AM   #21
xrk971 is online now xrk971  United States
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Tux,
I love my miniDSP - they are very slick and I can't imagine going back to passive crossovers. The ability to reconfigure on the fly or to test out 1st, 2nd, 4th order filters is amazingly easy. I am with you, I think I will need a second one.

I got lucky with that woofer as I picked it mostly for price but liked it for the high Qts, the 88dB sensitivity, the 3.5mm xmax, and the 4 ohms. It appears to be the same driver Dayton uses in their B652 bookshelf speakers. Regarding transient response of a smaller woofer vs a bigger one: certainly the lighter mass of the cone will allow the smaller driver to accelerate faster on a step response. Even though the XO is at 300 Hz, that is not saying that the fastest rise time is 3.33 ms. The rise time is dictated by the motor strength (Bl), the cone mass, and the suspension stiffness and damping. Even with a 30 Hz low pass, a cone can still have sub ms rise times if it is light. For woofers with really heavy cones their fs may be low but that comes at the expense of possible phase delay between the drive voltage and the actual woofer response. I think this is why tweeters are sometimes given delays for time alignment with woofer even on a flat baffle. Sometimes done by leaning baffle backwards?

I don't have a 15 in woofer to test against but I think transients will sound more authentic and crisp with a bunch of smaller drivers as long as they push similar displacements. I also think that spreading the work over smaller woofers also reduces distortion.

I plan on aligning the 6 drivers vertically just like the picture in the Nelson Pass article. It would be even better to put the basket of one side in the slot and wire out of phase so that motor nonlinearities are cancelled out.
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Old 28th January 2014, 04:04 PM   #22
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What you're describing is different from impulse response. And there are all kinds of opinions on woofer speed

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Originally Posted by xrk971 View Post
I think this is why tweeters are sometimes given delays for time alignment with woofer even on a flat baffle. Sometimes done by leaning baffle backwards?
This is because the acoustic center of the woofer is physically further back than the tweeter's acoustic center. Not because the tweeter is faster.
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Old 28th January 2014, 04:14 PM   #23
xrk971 is online now xrk971  United States
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Impulse response as we can get from sweeps is inverse fast Fourier transform of the frequency response. It is an approximation of a true time domain measurement with a microphone and an oscilloscope. Rise time of the cone ultimately what I am talking about.
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Old 28th January 2014, 04:38 PM   #24
xrk971 is online now xrk971  United States
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I took my own advice and reconfigured the XO at 210 Hz to avoid having to EQ out the bump at 270 Hz. It worked! Here is the in-room response at listening position with some miniDSP REW magic applied. You will have to interpolate the 5dB grid with your eyes as it is 10dB. My mini netbook screen is too small and at 5dB the image gets clipped. Anyhow, this speaker sounds quite nice - only had a chance to test out some vocals and jazz so far but liked what I hear.
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Old 28th January 2014, 04:51 PM   #25
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I'm not sure I'm understanding what you're saying. Are you saying, the impulse response is a measurement of the rise time of the cone? Or is STEP reponse the rise time of the cone? Or they're the same?

Here are three tweeter measurements I made:

Click the image to open in full size.

Can you tell me which one is the fastest? Sorry, the IR window is fairly small.
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Old 28th January 2014, 05:03 PM   #26
xrk971 is online now xrk971  United States
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They are related. A driver/speaker with poor (non-smooth) frequency response will not be able to produce a good IR - as it shows up as a smaller bandwidth and bumpy or irregular FR plot. Every little bump in a FR (freq domain) shows up as a ripple in the IR (time domain) through the inverse FFT. The close to ideal FR is flat plateau with gently sloping low freq roll off, and gently sloping high freq roll off. The only perfect FR is an infinitely wide bandwidth FR to produce an infinitely narrow IR. Smooth and wide FR give clean and tight IR. Based on this I would say that red FR from your tweeter will give best IR as it is the best compromise of wide and smooth (flat and not leaning) - but it is so close to the green that it is a wash.
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Old 28th January 2014, 07:01 PM   #27
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So then you agree that IR has nothing to do with speed? So the smaller woofers won't necessarily provide a better IR, perhaps the larger one will because it'll give a wider bandwidth.

BTW, they're all three the same tweeter with different high pass filters applied. So all the same "speed".
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Old 28th January 2014, 07:54 PM   #28
xrk971 is online now xrk971  United States
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I think there may be a difference in terms we are using. "Speed" is a silly term to use to describe driver performance. I am saying a low mass cone will accelerate faster than a heavier cone (F=ma). This affects the rise time of a pressure pulse that can be generated. A filter or cross over changes the range of freq that the driver can act, but its native ability to accelerate given a step voltage function is a function of its mass and motor strength. For two drivers with the same motor and suspension, the lower mass cone will produce a pressure pulse with a faster rise time.

I know that you used the same tweeter and within the ability of the inverse FFT to recreate the time domain from the measured frequency domain - you see that the IR is all about the same. Look at the rise time - it is the same - the decay is affected by the filters you add.

If you want to argue that a 15 in woofer has the same impulse rise time in the time domain as a 3 in full range or tweeter, you should use that as tweeter.

Last edited by xrk971; 28th January 2014 at 08:01 PM.
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Old 28th January 2014, 07:58 PM   #29
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this is getting interesting
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Old 29th January 2014, 08:11 AM   #30
Rudolf is offline Rudolf  Germany
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I mounted the TC9FD18 in two open test baffles and compared the polar response from 0.5-5 kHz:

OB4_OB3.jpg
Left baffle is 50x45 cm, right baffle is 14x21 cm.

This is the 0-90 response of the large baffle:
OB4 pur polar.gif

And this for the small baffle:
Silent1 polar norm 0 grad.gif

I choose 0.5-5 kHz because that's where the imaging happens according to Toole.

Just to make you guys aware that there is more than the 0 response .

If I normalise the large baffle response to constant spl at 0 too, it looks like this :
OB4 pur polar norm 0 grad.gif

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