Hybrid H-Frame, OB and nude driver

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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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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.
 
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?

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:
586721d1482173077-pass-baffle-help-ob-spkr-gif


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.
 
@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
 
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.
 
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.

Yes probably, I'm referring to edge diffraction having the same effect as a very early reflection and blurring the image.
 
Still about floor reflections...

Dipole response will be substantially lower only at 60 deg or more off-axis. Here sims with listening distance of 3 meters and rough estimate of angles when radiator is at 40 or 80 cm height. Tilting of the mid is a way ot enhance reflection minimization - Jorma Salmi was a smart guy!

I usually measure around 3-4db down at 45 degrees or so and 6-7db down around 60 degrees. I've not liked the result of tilting the mid when I've tried it in the past, with regard to phase and imaging, but perhaps I should fiddle with crossover points and try it again.

Appreciate the info Juhazi.
 
Regarding this system:



Tilting the exposed woofer back has two effects:

1. It positions the projections of the 90 degree null outwards and more towards the place on the floor where the "floor bounce" reflection would be found if the listener is at a distance from the speaker.

2. It allows the tweeter to be located above the woofer and next to the driver mounting flange AND be more or less aligned with the acoustic center, which is between the mounting flange and the dustcap. It's taking advantage of the geometry of these things.

On the other hand:

1. Tilting the woofer back changes the acoustic center placement and position of the dipole lobe as viewed from the rear. This will make what is happening at the rear much different than what is happening in front of the system, e.g. it will change the axis where drivers sum, etc. because it is tiling the woofer's output.

2. By tilting the woofer "up" as viewed from the front, the bass cabinet below the nude woofer is placed more in the null in the front of the speaker, but less so to the rear. The output from the rear of the cone is seeing/reflecting off of the bass cabinet more with the driver in this position compared to if the driver axis was parallel to the floor. This will impact the rear output.

Not trying to make a comment on the system. Perhaps it's a brilliant design. Seems to do many things right. I never saw/heard one. But there seems to be some tradeoffs, as usual.
 
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How critical is the acoustic center between the 18" woofer and the lower midrange 15" when place perpendicular to each other?

That would depend on the crossover point between the two drivers!

The bottom line is that you do not want the acoustic center offset to impact the phase at the crossover point to much because that would impact how the two drivers sum together. So it is a matter of how long a wavelength of sound is at the crossover frequency compared to the offset distance, and of course keeping in mind there are 360 degrees phase rotation for each wavelength.

IF you know that you do not want the phase to be influenced more than X degrees then you can calculate how much offset that is for a given frequency.

The physical offset imparts a "tilt" onto some new "on axis" axis where the offset becomes zero. Sometimes this is used to the designer's advantage but more often the crossover filter delay time the speed of sound is greater than the physical offsets.

Getting back to your question, with crossover points like 80Hz or 100Hz, where the wavelength is around 4.3m and 3.4m, you can have an offset of several centimeters and it will be OK. For example, 36 degrees equates to 40cm at 80Hz, and 34cm at 100Hz.
 
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