SB acoustics SB12MNRX25-4 "full range" Build thread - Page 10 - diyAudio
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Old 2nd February 2014, 10:33 AM   #91
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OK so I had an 11uF Axon, a 1uF axon and an 8.2 ohm 10W resistor sitting around.
I took a quick and dirty measurement of the speaker in the study sitting on the daybed. Distance about 50cm and only about 5cm off the surface of the bed. Sort of like a mini ground plane measurement

I then put the RLC in series with the speaker and measured again. It is pretty much working as expected from the sim.

Pics attached of the test setup, and the comparison in holm with and without the notch. Finally I loaded the new measurement into speaker workshop and compared the simulated result (using the new measurement) with the actual measurement of the realised notch. I changed the values in SW to match what I now had.

Pretty good correlation, and I think shows the worth of speakerworkshop in prototyping notch filters. Interestingly if I leave the original values in SW (ie 22uH instead of 23uH and 7 ohms instead of 8.2 ohms) it is almost an exact match for the actual measurement...

1st pic, the (dodgy) measurement setup.
2nd pic, SW showing green actual no notch measurement, blue actual measurement with notch filter, black simulated response.
3rd pic the measurement in holm with and without the notch filter.
4th pic same as 2nd execpt with original vals of 22uH and 7 ohms in the sim.

Tony.
Attached Images
File Type: jpg measurement_setup.jpg (169.8 KB, 186 views)
File Type: png actual_vs_sim.png (29.2 KB, 185 views)
File Type: png sb_4in_notch_test.png (52.4 KB, 181 views)
File Type: png sim_compare_orig_vals.png (28.3 KB, 175 views)
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Last edited by wintermute; 2nd February 2014 at 10:41 AM. Reason: added 4th pic
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Old 2nd February 2014, 08:15 PM   #92
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Tony, what do they look like off-axis? (as in on-axis measures are only really useful in the conrext of off-axis)

dave
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Old 3rd February 2014, 01:35 AM   #93
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Good question Dave. I can't remember if I did any off axis measurement yet, I know I thought about it, but I suspect that I decided I'd do it next time (as my "gauge" for my speaker test stand had gone missing). It would be revealing to do a set with and without the notch filter.

I probably should wait till I've done something about the baffle step first though. edit2: BTW the dodgy measurements above are shown with 1/16th octave smoothing.

Tony.
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Last edited by wintermute; 3rd February 2014 at 01:39 AM. Reason: add comment about baffle step.
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Old 4th March 2014, 05:19 PM   #94
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Tony,

Looks like a great liitle speaker, I was checking out the driver wrt use in a 3 way, you mentioned you wanted to ***** its viability for use in a 3 way at the begining of the thread... can you share your thoughts following your experiences so far with the drive unit?
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Old 4th March 2014, 08:26 PM   #95
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Hi Nannoo, I think that they would make an excellent mid driver in a three way (though not a high efficiency one as they are only 88.5db efficiency).

The tonality and clarity of them is very good. The main problem is going to be sensitivity, and baffle step I think. With only 88.5 db to start with if you drop say another 3db for baffle step compensation it is starting to get pretty low in the efficiency stakes. With a narrow baffle like here they start to drop off below about 1Khz. Obviously in the wider baffle of a three way that will be lower so it *may* not be too much of an issue.

I'll have to do some off axis measurements as well as Dave suggested. That will help with showing how high you could cross to the tweeter as well

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Old 4th March 2014, 10:15 PM   #96
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Quote:
Originally Posted by wintermute View Post
The main problem is going to be sensitivity, and baffle step I think. With only 88.5 db to start with if you drop say another 3db for baffle step compensation it is starting to get pretty low in the efficiency stakes.
Best to deal with BS by XOing at or just below the BS frequency to more sensitive woofer(s) so that the full sensitivity of the mid can be used.

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