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Old 19th October 2020, 09:25 PM   #61
impuls60 is offline impuls60  Norway
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Thx for that link! Seems like they had problems with recreating the HRTF curve with passive mods. Seems to me that it could work with some effort and DSP.
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Old 20th October 2020, 07:47 AM   #62
ErikdeBest is offline ErikdeBest  Switzerland
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Default measurements on SLIM 8

Yesterday I received 4 SLIM8 units, and I made some rough initial measurements with a (calibrated) UMIK and REW.

Drivers were suspended by wire, no baffle was used. Mic a 1m distance, only did on-axis measurements (for the moment). Signal ran through a MiniDSP 2x4 which was used to put a low shelving filter with 10dB gain at 400Hz, as well as a 48dB LR also at 400Hz. Furthermore I put 80uF of capacitance in series with the drivers (protection). Same volume settings for all units (but I did not measure actual voltage applied to drivers). Gating set in REW with 7ms in left window, 0 ms window ref time and 9ms right window.

The first picture shows the response and distortion for a single unit. The second and third picture are the overlay of respecitvely the FR and distortion of all 4 units.

I was hoping to be able to make a line array to be used from 400Hz onwards, but I do not think this is a wise idea...
Attached Images
File Type: jpg 1xSLIM.jpg (507.7 KB, 1072 views)
File Type: jpg 4xSLIM8.jpg (384.3 KB, 1065 views)
File Type: jpg 4xSLIM8_distortion.jpg (322.4 KB, 964 views)
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Old 20th October 2020, 12:18 PM   #63
diyiggy is offline diyiggy
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Thank you very much for the measurments...so not asgood as the Neo10 that was usable from something 400 hz...
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Old 20th October 2020, 12:42 PM   #64
ErikdeBest is offline ErikdeBest  Switzerland
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You are welcome.

The NEO10 and Slim8 are very different, not only pricewise. The NEO10 is twice as wide, that gives it an advantage in the low extension (dipole peak of NEO10 is at half frequency of Slim 8) while worse in the HF. I did not do off axis measurements on the SLIM 8 yet, but I expect that this driver will not need an additional tweeter (the NEO10 does). So I would not say "it is not as good", because it is a different driver with a different operation range

My wish for 400Hz operation was probably more wishful thinking. The idea is that the large number of drivers in the line array would lower the required SPL (and therefore distortion) per driver, but I think that even that is not possible.

I will do more measurements know they are there
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Old 20th October 2020, 02:25 PM   #65
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by ErikdeBest View Post
I did not do off axis measurements on the SLIM 8 yet, but I expect that this driver will not need an additional tweeter (the NEO10 does).
If I am reading your plot correctly, the frequency response is dropping like a rock above 12kHz. This makes it a tweeter only for the hearing impaired... Off axis will likely be worse than that (more attenuation, and starting lower in frequency) because of beaming.
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Old 20th October 2020, 04:07 PM   #66
ErikdeBest is offline ErikdeBest  Switzerland
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Hi Charlie,
I see your point and I do agree that it may not be good as tweeter based on these curves. A pity that another driver would have to be added for about half an octave.

To obtain the above curves I did the shelving low pass with MiniDSP. Looking at these curves I would say this driver could be used from about 800Hz upwards. Currently I have a gain of about 10dB at 800Hz due to dipole cancelation, so instead of positive gain at the low end I thought about attenuating the HF up to about 12k. Ie, cut off everything above the red line.

If that is doable and how it sounds I have to find out.
Erik
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File Type: png slim8.png (256.8 KB, 918 views)
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Old 20th October 2020, 04:26 PM   #67
RogerGustavsson is offline RogerGustavsson  Sweden
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There seems to be a problem at about 4.3 kHz, a peak in the distorsion.
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Old 20th October 2020, 04:37 PM   #68
CharlieLaub is offline CharlieLaub  United States
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Originally Posted by ErikdeBest View Post
Hi Charlie,
I see your point and I do agree that it may not be good as tweeter based on these curves. A pity that another driver would have to be added for about half an octave.

To obtain the above curves I did the shelving low pass with MiniDSP. Looking at these curves I would say this driver could be used from about 800Hz upwards. Currently I have a gain of about 10dB at 800Hz due to dipole cancelation, so instead of positive gain at the low end I thought about attenuating the HF up to about 12k. Ie, cut off everything above the red line.

If that is doable and how it sounds I have to find out.
Erik
Although it depends on the input sensitivity of your amps and the output voltage drive capability of the miniDSP, from what I recall it is better to EQ using attenuation than to boost so that you do not overdrive the DAC stage. That might happen with a 10dB boost, for example. You can add back a bit of gain using flat gain later to balance out the gain between channels.
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Old 20th October 2020, 04:44 PM   #69
mattstat is offline mattstat  United States
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Quote:
Originally Posted by RogerGustavsson View Post
There seems to be a problem at about 4.3 kHz, a peak in the distorsion.
Which harmonic is the red trace? Problem may be higher in frequency.
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Old 20th October 2020, 04:49 PM   #70
ErikdeBest is offline ErikdeBest  Switzerland
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Quote:
Originally Posted by RogerGustavsson View Post
There seems to be a problem at about 4.3 kHz, a peak in the distorsion.
Yes, at the low SPL levels shown here only my unit 1 has this. Unit 4 was tested at higher SPL levels, and it looks like in the attachment. Again, the distortion peak at almost 5k.

As written in the previous post, I will probably attenuate the HF anyway, so this distortion will be lowered.

There is quite some tinkering regarding this
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File Type: png slim8_distortion.png (259.5 KB, 971 views)
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