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Cubo Sub - Measured with three different drivers

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HyggeJJ View Drop Down
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    Posted: 19 June 2018 at 2:22pm
Hi All,

I have build one Cubo Sub, for test purposes with a number of different drivers.

All drivers are 18" PA bass drivers from SB Acoustics Pro division, with supposedly suitable parameters. I can share the T/S-parameters if wanted.

Attached are the measured responses.

Do my measurements look similar to other frequency response curves on the Cubo Sub, or..?

I find it very hard to find any documented measurements on the Cubo Sub, and I have used quite a lot of time googling for measurements to have an idea of what to expect.

The graph has 6 curves in groups of 3.

Lowest set of curves are measured with the microphone centered in the horn opening, and in plane with the opening.

Upper set of curves are measured at 3m distance with app. 150W RMS input.

All measurements where done outside, as seen on the photo (though on the photo the mic is at 1m distance from the Cubo Sub).

Measurement:
https://www.dropbox.com/s/1atsab4j3b7clku/Three_drivers.jpg?dl=0

Test Setup:
https://www.dropbox.com/s/j2djdc72js4hu19/Meas_Setup.jpeg?dl=0

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HyggeJJ View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote HyggeJJ Quote  Post ReplyReply Direct Link To This Post Posted: 21 June 2018 at 9:54pm
Wow.. 95 views, but not a single reply..

Is the Cubo Sub not a well known construction on this forum, or what is the reason for everyone being quiet..?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mobiele eenheid Quote  Post ReplyReply Direct Link To This Post Posted: 21 June 2018 at 10:20pm
Well, you asked for documented measurements, I've designed Cubo Sub and even I have trouble finding well documented measurements. I know to find some on freespeakerplans but that site has been down for a couple days now.

Now that you got me talking ;) What made you choose for that specific measurement set up? I mean the cabinet up side down and the measurement mic so far from the ground, also off-axis? To my knowledge that enhances the higher frequencies around 100 - 120 Hz. My own measurements (indoors) started to drop quickly at 90 Hz and up.

Also are those drivers new?

Best regards Johan/ Cubo


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 21 June 2018 at 10:22pm
It might have helped if you'd embedded the pics into the post and put this in the 'general forum' or 'advanced discussion'..and shared some of the details that would help people make sense of the data. Which line is which driver? Model number/manufacturer's spec sheet links, etc.

Very interesting results at any rate - the red line driver really seems to excel in this design.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 22 June 2018 at 3:48am
Measuring in the mouth is somewhat useful but your measurement setup doesn’t give comparable results to other boxes really.

I would flip the cabinet over so the opening is on the floor and you should have the mic on the floor to avoid reflections on the response as well. And then measure 10m away and scale back to get a 1m response, as people are rarely in 1m distance of a sub.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote HyggeJJ Quote  Post ReplyReply Direct Link To This Post Posted: 22 June 2018 at 8:08am
Hi Johan

Originally posted by mobiele eenheid mobiele eenheid wrote:

Well, you asked for documented measurements, I've designed Cubo Sub and even I have trouble finding well documented measurements. I know to find some on freespeakerplans but that site has been down for a couple days now.

I actually tried to find some on freespeakerplans, but all I found was subjective opinions on the sound and a lot of photos of the enclosure. Perhaps I did not look hard enough.

Originally posted by mobiele eenheid mobiele eenheid wrote:

Now that you got me talking ;) What made you choose for that specific measurement set up? I mean the cabinet up side down and the measurement mic so far from the ground, also off-axis? To my knowledge that enhances the higher frequencies around 100 - 120 Hz. My own measurements (indoors) started to drop quickly at 90 Hz and up.

Also are those drivers new?

Cabinet upside down is purely for convenience. It is a lot easier to exchange the driver and it also allows me to easily see the cone movement during measurements.
The measurement mic was on-axis for all measurements, even though the photo may suggest otherwise.
For frequencies below 100Hz, I would not expect having the cabinet upside down and the mic 55cm off the ground, would have a significant impact on the frequency response, but I could be mistaken. I can, when the weather permits, make a new set of measurements with the horn opening at ground level.

The drivers are new, yes. I did not pre-condition them in free air before putting them in the cabinet. Hmm... I could perhaps do that this weekend, and measure how much it lowers Fs of the driver, before I re-measure the response.


Edited by HyggeJJ - 22 June 2018 at 4:46pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote HyggeJJ Quote  Post ReplyReply Direct Link To This Post Posted: 22 June 2018 at 8:13am
Originally posted by Hemisphere Hemisphere wrote:

It might have helped if you'd embedded the pics into the post and put this in the 'general forum' or 'advanced discussion'..and shared some of the details that would help people make sense of the data. Which line is which driver? Model number/manufacturer's spec sheet links, etc.

Very interesting results at any rate - the red line driver really seems to excel in this design.


I found it a little difficult to figure out in which sub-forum I should post, but if it fits better in a different sub-forum a moderator should feel free to move it.

Agreed, the "red line" driver is by far the best in this particular construction.

All drivers are from SB Acoustics Pro division.
Driver 1 (Black line in top curves)
Fs = 37 Hz
Re = 5.2 Ohm
Qts = 0.34
Qes = 0.35
Qms = 9.20
Mms = 235.8 g
Cms = 0.09 mm/N
Bl = 27.1 Tm
Vas = 208.4 Liters
Sd = 1256.6 cm^2
Xmax = 13 mm
Voice coil diameter = 113 mm

Driver 2 (Red line in top curves)
Fs = 35 Hz
Re = 5.2 Ohm
Qts = 0.3
Qes = 0.31
Qms = 10.37
Mms = 286 g
Cms = 0.07 mm/N
Bl = 31.5 Tm
Vas = 162.3 Liters
Sd = 1256.6 cm^2
Xmax = 11.6 mm
Voice coil diameter = 127 mm

Driver 3 (Purple line in top curves)
Fs = 34 Hz
Re = 5.2 Ohm
Qts = 0.37
Qes = 0.39
Qms = 8.74
Mms = 204 g
Cms = 0.11 mm/N
Bl = 23.9 Tm
Vas = 244.9 Liters
Sd = 1256.6 cm^2
Xmax = 8.7 mm
Voice coil diameter = 113 mm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote HyggeJJ Quote  Post ReplyReply Direct Link To This Post Posted: 22 June 2018 at 8:19am
Originally posted by toastyghost toastyghost wrote:

Measuring in the mouth is somewhat useful but your measurement setup doesn’t give comparable results to other boxes really.

I would flip the cabinet over so the opening is on the floor and you should have the mic on the floor to avoid reflections on the response as well. And then measure 10m away and scale back to get a 1m response, as people are rarely in 1m distance of a sub.


Yes, well.. For my particular use case, most people will be 3-5m away from a sub.

I can measure at 10m, but what would the added distance give me compared to the 3m measurement?

It is interesting, I think, that the measurements in the mouth are extremely similar to those at 3 meter distance.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 22 June 2018 at 8:43am
Low Vas, high BL, low Qts, Looks great for the job - you can probably find better but not much better (higher xmax is something you could find in high end drivers with similar qualities from other manufacturers). If you've built it well then your results will be near enough to optimal. You could do a lot worse than to stick with that driver.

All the plots look near enough to what you'd expect from a Cubo design. What are you worried could be wrong exactly?


Edited by Hemisphere - 22 June 2018 at 8:47am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote HyggeJJ Quote  Post ReplyReply Direct Link To This Post Posted: 22 June 2018 at 1:21pm
Originally posted by Hemisphere Hemisphere wrote:

Low Vas, high BL, low Qts, Looks great for the job - you can probably find better but not much better (higher xmax is something you could find in high end drivers with similar qualities from other manufacturers). If you've built it well then your results will be near enough to optimal. You could do a lot worse than to stick with that driver.

All the plots look near enough to what you'd expect from a Cubo design. What are you worried could be wrong exactly?

I am not worried as such, but I always aim to verify what I build. That is easy enough on ported boxes, with simulations, and I have lots of experience with ported boxes (and sealed for that matter).

This is my first hybrid (I have zero experience with horns) and since I could not simulate the box+driver, and all I found was subjective evaluations on the Cubo Sub, I had no way of knowing what real life performance to expect.

The Cubo Sub should be able to give decent output down to 30Hz, from what I can read. This is more or less obtainable with one of the drivers I have tested, but it is borderline, in my opinion.

Therefore I am seeking information as to what results others have measured with the Cubo Sub.

I might actually have an easier time getting a bit more low frequency extension in a much smaller ported box, at the cost of some efficiency above 60Hz, but I wanted to try something that was new for me. And, I like the fact that the driver is exposed to a lot of air which should help it stay cool.


Edited by HyggeJJ - 24 June 2018 at 5:44pm
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