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Hybrid H-Frame, OB and nude driver
Hybrid H-Frame, OB and nude driver
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Old 23rd January 2021, 04:26 PM   #101
scottjoplin is offline scottjoplin  Wales
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Edge diffraction is an interesting issue for dipoles. They have twice the level that monopoles do, if my understanding is correct. A nude driver has the advantage (possibly?) of putting it as close as possible to the source?
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Old 23rd January 2021, 04:38 PM   #102
iamvalheru is offline iamvalheru  Canada
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I scaled up Nelson Pass' SLOB, but only the woofer section for use with the Goldwood GW-1858, or any other 18" woofer, and the overall dimensions are 21-1/2" square and no more than 16" high at the back of the magnet (I don't have the woofer with me to verify the actual dimensions).

The over all height can be brought down by reducing the thickness of the base, but I wanted to have it sand filled for added weight, stability, and hopefully lower resonance.

As per threads I've read about the SLOB, the results are similar as using the driver in a flat baffle.

Post #88 shows the design that was tested:
Pass Open Baffle: need help

Post #128 shows measurements of both the SLOB and the baffle mounted woofer:
Pass Open Baffle: need help



Wings could be added around the rear of the driver, thus bringing the overall dimensions close to a H-frame, at which point there are no space savings.

And if we do add wings, then we can extend the front baffle of the SLOB to mount the 15", at which point we are just replicating Nelson's design, but with only the upper midrange and the tweeter being nude.



D
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Old 23rd January 2021, 04:44 PM   #103
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by scottjoplin View Post
Edge diffraction is an interesting issue for dipoles. They have twice the level that monopoles do, if my understanding is correct. A nude driver has the advantage (possibly?) of putting it as close as possible to the source?
A nude driver has the largest size source compared to edge. This has the effect of "smearing" out the diffraction in time and space. Diffraction peaks and dips are absent. Diffraction is still happening, but it has been made as benign as possible.
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Old 23rd January 2021, 04:51 PM   #104
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by scottjoplin View Post
Edge diffraction is an interesting issue for dipoles. They have twice the level that monopoles do, if my understanding is correct. A nude driver has the advantage (possibly?) of putting it as close as possible to the source?
Quote:
Originally Posted by iamvalheru View Post
I scaled up Nelson Pass' SLOB, but only the woofer section for use with the Goldwood GW-1858, or any other 18" woofer, and the overall dimensions are 21-1/2" square and no more than 16" high at the back of the magnet (I don't have the woofer with me to verify the actual dimensions).

The over all height can be brought down by reducing the thickness of the base, but I wanted to have it sand filled for added weight, stability, and hopefully lower resonance.

As per threads I've read about the SLOB, the results are similar as using the driver in a flat baffle.

Post #88 shows the design that was tested:
Pass Open Baffle: need help

Post #128 shows measurements of both the SLOB and the baffle mounted woofer:
Pass Open Baffle: need help



Wings could be added around the rear of the driver, thus bringing the overall dimensions close to a H-frame, at which point there are no space savings.

And if we do add wings, then we can extend the front baffle of the SLOB to mount the 15", at which point we are just replicating Nelson's design, but with only the upper midrange and the tweeter being nude.



D
This is not Nelson's SLOB - it's just the woofer part of his 2-way OB design. They are different animals. Here is his OB design:
Click the image to open in full size.

Nelson's SLOB is described in this PDF document:
https://firstwatt.com/pdf/art_slob.pdf

Your design won't work all that well with the "OB" part, which you omitted in your drawing. In Nelson's OB speaker, the basket side of the driver is behind a sizeable planar baffle. This helps to keep the front to back distance high.

You could close in the basket like a Ripole. That would work much better.
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Old 23rd January 2021, 04:53 PM   #105
iamvalheru is offline iamvalheru  Canada
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Therefore, nude drivers should be the way to go for midrange and above to negate diffraction.
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Old 23rd January 2021, 04:55 PM   #106
iamvalheru is offline iamvalheru  Canada
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I know, this is what I wrote in my post with the screen shot of my CAD, it's only the woofer section of Nelson's SLOB.
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Old 23rd January 2021, 05:01 PM   #107
iamvalheru is offline iamvalheru  Canada
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Instead of converting it into a one driver ripole, and since you mentioned that a 15" can operated efficiently down to 100 Hz, why not just use the 18" woofer in a down firing closed box subwoofer with sand filled walls?

Mind you I have no idea of the box volume needed for this!
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Old 23rd January 2021, 05:03 PM   #108
LewinskiH01 is offline LewinskiH01  Argentina
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Quote:
Originally Posted by iamvalheru View Post
@LewinskiH01

Please start your own thread for your build to keep mine clean.


Regards

Denis
Denis,

I don't think I deserve this message.

My first post (#60) was intended to share with you experience with a dipole tweeter and how it went high enough where people say dipole tweeters need to get (6 or 7kHz). Diypole replied with a great idea for my build and I acknowledged that on my 2nd post and explicitly said I did not intended to derail your thread so posted a link to my thread. Diypole followed up on my thread and it effectively kept your thread "clean".

My 3rd post was asking CharlieLaub about what seemed like a change in his preference for dipole midranges over time, and my 4th was answering him what my reference was, and highlighting an important general takeaway from his post (elevate midbass so dipole null develops and doesn't illuminate the floor).

I won't discuss aspects of my design in your thread, not other's for that matter, but I will continue to post questions on concepts shared by knowledgeable folks. Sharing knowledge is one of the key purposes of forums like this.

Enjoy your journey.

Regards,
Horacio
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Old 23rd January 2021, 05:12 PM   #109
CharlieLaub is offline CharlieLaub  United States
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Quote:
Originally Posted by iamvalheru View Post
Instead of converting it into a one driver ripole, and since you mentioned that a 15" can operated efficiently down to 100 Hz, why not just use the 18" woofer in a down firing closed box subwoofer with sand filled walls?

Mind you I have no idea of the box volume needed for this!
That is what I advocate, actually. In smaller to medium sized rooms where dipole bass doesn't work well, a closed box sub or stereo pair of them, crossed over around 80-100Hz, will like provide a much better bottom end. You will get some benefits from room pressurization.

In a larger room where room pressurization is not as helpful dipole bass works well, and that is where the central H-frame sub can work nicely. It's a matter of choice I guess.

It might be possible to put the 18" driver in a relatively small box (20x20x20) and operate it like the Bag End ELF or with an LT. But a lot of power may be required to get the bass extension you desire.
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Old 23rd January 2021, 05:15 PM   #110
ErikdeBest is offline ErikdeBest  Switzerland
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Originally Posted by iamvalheru View Post
Their only dipole offering, the AMTPRO-4, every free air measurements Iíve seen are meh with a rising response from 1k to 10k, and almost useless performances past 10k, both on and off axis, the vertical dispersion is even worst.
Ok. You wrote about a true dipole ribbon, but you actually talking about one of their AMTs.
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