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Old 19th May 2012, 11:32 PM   #1531
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Quote:
Originally Posted by Djim View Post
Click the image to open in full size.

Keep in mind the original SS15 40Hz measured response (in light blue) [c/o jbell]
Attached Images
File Type: jpg ss15 vs stadium spl.jpg (189.7 KB, 444 views)

Last edited by CRESCENDO; 19th May 2012 at 11:36 PM. Reason: Djim's pic
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Old 19th May 2012, 11:35 PM   #1532
r23d is offline r23d  Australia
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Quote:
Originally Posted by r23d View Post
We have almost finished the other pair, so soon will have plots of a matched set each side...

Richard
next to each other that is.
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Old 20th May 2012, 06:30 AM   #1533
Djim is offline Djim  Netherlands
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Horn extensions:

Each time you extend a 1/4WL horn or tapped horn by: 0.6 x diameter the mouth, the new mouth area of the extension needs to be doubled. For the SS15 that is easy since the total front of the SS15 is very close to twice the area of its mouth:

The mouth area on the SS15 = 2168cm^2
The total front of an original Jbell SS15 is 4267 cm^2

The mouth is 2168 cm^2. If you calculate that to a circle you get a diameter of 53 cm.
53 x 0.6 = 31.8 cm

Therefore the extension for the SS15 can be made max. +/- 30 cm long (if the extender follows the outlines of the SS15 like my example in post#1525)

Smuggling:

In practice you sometimes can extend the front a little longer, depending on the driver's response. In my previous example of post#1525 we smuggled a little by using bracing to prevent internal resonances within the extension. The horizontal braces, covering the last 10cm of the extension, were used to prevent internal standing waves (A similar approach was used in the Stage Accompany XL-bins for instance). The vertical brace was mainly used to enforce the structure, to support the braces and had cut out sections (not visible in the example).


Building a 1/4WL horn or tapped horn from rectangular sections:

If you want to build a 1/4wl horn or tapped horn and use it to maximal its full wavelength you can build it from 6 rectangular sections. If you want to use it up till 1.5 its full wavelength you can build it from 9 rectangular sections…and so on.

The total pathlength of an original JBell SS15 is 227.54cm.
In case of r23d, he extends it with 60cm

227.54 + 60 = 287.54 cm
The new full wavelength is therefore 119.5Hz

If you want to use it up till 119.5Hz you can build it from 6 equal rectangular sections. 287.54 cm : 6 = 47.92cm

Therefore in r23d’s case, the extension of 60cm is way too long to be made from one rectangular section.

(Edit: See Jbell! It's 8:46 am here and way too late so I hope I didn't make to many mistakes in my calculations )

Last edited by Djim; 20th May 2012 at 06:47 AM.
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Old 20th May 2012, 05:39 PM   #1534
jbell is offline jbell  United States
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Djim:
Remember your comments about my 1:00am designing??

Got a smile from your post.....
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Old 20th May 2012, 07:15 PM   #1535
tb46 is offline tb46  United States
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Hi jbell,

Post #1526: "...H and E are about 1" apart"

That sound a little tight. Could you (or anybody who has a 3015LF on hand) take a look at the attached drawing of a 3015LF, and make whatever corrections to the dimensions? I don't have a 3015LF, and thus have to go from pictures, and by Eminence's data sheet specs.

Regards,
Attached Files
File Type: pdf 3015LF_preliminary_notes.pdf (14.8 KB, 47 views)
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Last edited by tb46; 20th May 2012 at 07:18 PM.
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Old 20th May 2012, 09:40 PM   #1536
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Quote:
Originally Posted by r23d View Post
Yes Art, we did try using the full frontal area to start the extension from, and against my wishful thinking, the results weren't quite so good. Not as smooth, and not as much output, though I'm sorry I don't have any figures right now.
Richard
Richard,

Thanks for the reply.

Proximity to walls and houses etc. still has a large impact on outdoor LF testing.
Were both the extender measurements and the dual cabinet only measurements taken in the same exact place and orientation?

Was the mic the same distance in front of the extender as ist was from the front of the cabinet?

Art
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Old 21st May 2012, 12:50 AM   #1537
r23d is offline r23d  Australia
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Originally Posted by weltersys View Post
Richard,

Thanks for the reply.

Proximity to walls and houses etc. still has a large impact on outdoor LF testing.
Were both the extender measurements and the dual cabinet only measurements taken in the same exact place and orientation?

Was the mic the same distance in front of the extender as ist was from the front of the cabinet?

Art
Good point Art - the measurements were all taken without moving subs or the measurement mic, so this means the speakers were closer to the mic by about 600mm with the extensions on. That would be 2m away with two subs, 1.4m away with the extender added.

If this means the speakers were closer by a factor of 2/1.4=1.43, then should they be 1.43*1.43=about 2 times louder, or about 3db anyway?

This puts my gains in a more conservative light.

Once I have all four working, I'll be heading out to a more open area for more testing at bigger distances and let you know ho I go.

cheers,

Richard
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Old 21st May 2012, 05:18 PM   #1538
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Quote:
Originally Posted by r23d View Post
Good point Art - the measurements were all taken without moving subs or the measurement mic, so this means the speakers were closer to the mic by about 600mm with the extensions on. That would be 2m away with two subs, 1.4m away with the extender added.

If this means the speakers were closer by a factor of 2/1.4=1.43, then should they be 1.43*1.43=about 2 times louder, or about 3db anyway?

This puts my gains in a more conservative light.

Richard
Richard,

Once the measurement distance is within about the diameter of the radiating surface of an enclosure, the inverse distance law (6.02 dB loss per doubling distance) will not apply exactly, the so called “horn bubble” makes for different levels in the very near feild.
If I understand your mic placement, 1.3 dB at minimum would need to be deducted from the closer extender measurement .

As large as your horn extender is, 2 meters from the front of the extender, and the same distance from the front of the cabinets would be the minimum distance to get a decent comparison. If you can find a large enough area with any wall or building at least two wavelenghts of the lowest frequency of concern (around 56 feet for 40 Hz) tests at a greater distance than 2 meters will give more accurate comparative results.

A 3 dB difference is the equivalent of doubling power, assuming no power compression. Sounds like your extender probably does about that, still a good deal.

To sound twice as loud at 1000 Hz requires a 10 dB difference, at 20 Hz a 5 dB difference, at 50 Hz roughly a 6 dB difference.

Art
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Old 21st May 2012, 11:20 PM   #1539
Phil B is offline Phil B  Australia
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Hi

Phil here...R23d`s partner in crime making the SS15`s with barn doors.

I have had a dig around my laptop and I think I have found the measurements for barn doors off the horn and off the end of the box.

Click the image to open in full size.

So green is off the end of the box and red is off the horn. This was done in a large warehouse with a concrete floor. Measurement mic on floor. I still don`t believe Holm at the low end, it just doesn`t seem to relate to real life? Would like to try this all in Smaart when I get a) the time and b) my work measurement setup !!

Top respect to Mr R23d ( neighbours and family) as he did a few days continuous measurements in his garden of these SS15`s and the Unity horns we`re building!

Phil B
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Old 22nd May 2012, 10:47 AM   #1540
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Quote:
Originally Posted by Phil B View Post
Hi

Phil here...R23d`s partner in crime making the SS15`s with barn doors.

I have had a dig around my laptop and I think I have found the measurements for barn doors off the horn and off the end of the box.

Click the image to open in full size.

So green is off the end of the box and red is off the horn. This was done in a large warehouse with a concrete floor. Measurement mic on floor. I still don`t believe Holm at the low end, it just doesn`t seem to relate to real life? Would like to try this all in Smaart when I get a) the time and b) my work measurement setup !!

Top respect to Mr R23d ( neighbours and family) as he did a few days continuous measurements in his garden of these SS15`s and the Unity horns we`re building!

Phil B
Something really looks a bit off there. Did you do an impedance response test on your SS15 to see if it was a good match for the HornResp model?
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