[Rudolf]

It's is interesting to note that the cancellation of non-linearities in the push-pull mount is so clearly visible! (seems to work then ).

Sorry, where do you see a cancellation of non-linearities?

It looks puzzeling that sensitivity on that particular measurement is lower though...

The efficiency of a W-baffle or ripole depends on the air volume trapped in the center "U" section. Less volume => less efficiency. With one driver basket protruding into that section the volume is reduced significantly.
On the other hand: less volume should lower Fr of the driver.

Bruno, have you got an impedance plot of the ripole configuration for comparison?

[BrunoB]

 

Bruno, have you got an impedance plot of the ripole configuration for comparison?

I had forgotten to save the plot. I did remeasure it:


So this is impedance plot of  the sub with full sides, the "U" installed and the two drivers facing each other.

Bruno

[Graham Maynard]

Hi Bruno,

I now have my own 2x 15" OB here, and whilst I have achieved excellent bass reproduction, the most notable aspect is the 'neighbour friendly' way in which bass does not leave the listening room when compared to conventionally enclosured drivers.

I wonder if this is the reason for your thread title.  Did you have enclosured drivers before, and then notice the reduction in pressurised boom and thud beyond the listening room - like as soon as you walk out of the door ?

Looking back on your last response characteristics, the sidewalls plus 'U' provided a most creditable output.

I was wondering if further improvement might be possible by optimising the area of back opening with a separate panel across the top of the full cabinet rear. 
It might be that a panel across the top back could optimise the response, and that this could be established with a family of curves taken with a board across the top which is added and then moved down in steps of 5cms after each measurement.


Cheers ......... Graham.

[BrunoB]

Hi Bruno,

I now have my own 2x 15" OB here, and whilst I have achieved excellent bass reproduction, the most notable aspect is the 'neighbour friendly' way in which bass does not leave the listening room when compared to conventionally enclosured drivers.

I wonder if this is the reason for your thread title.  Did you have enclosured drivers before, and then notice the reduction in pressurised boom and thud beyond the listening room - like as soon as you walk out of the door ?

Hi Graham,

the first time I tried my sub, the bass was strong at the listening position, but  2 meters away I could barely hear the sub ( the sub had no sidewalls). I thought this was cool because I though the neighbors would not hear it. BTW, my neighbors never complained. My mains are also open baffle.

I attributed the neighbor friendliness of my sub to two factors:

- open baffle cancellation
- very nearfield


Recently, I came across the subwoofer page of Humble Homemade Hifi: http://www.humblehomemadehifi.com/Serious-Sub.html.
The author describes that his open baffle sub has a sweet spot.

At this point I was thinking that most OB subs could be neighbor friendly as well. I mean here that near field might not be necessary. Your post somehow confirms my thought.

Looking back on your last response characteristics, the sidewalls plus 'U' provided a most creditable output.

I was wondering if further improvement might be possible by optimising the area of back opening with a separate panel across the top of the full cabinet rear. 
It might be that a panel across the top back could optimise the response, and that this could be established with a family of curves taken with a board across the top which is added and then moved down in steps of 5cms after each measurement.


Cheers ......... Graham.

Interesting suggestion for an experiment. Unfortunately, I don´t have time to try it at the moment (I am on vacation ).


Bruno

[panomaniac]

I had not read this thread until today - wow!  Sorry I missed it.  Cool work, Bruno.

Of course it raises some questions:

1) Would a smaller driver do as well?  Since this is so very nearfield, maybe a pair of 8s or 10s could be "good enough."
2) Would a monopole sub do as well?  In the very nearfield, the level should be low enough not to bother the neighbors, right?
3) Up to what frequency might this work?  How high could the sub work without giving away its position? (Delayed, of course)

4) In your latest version, where is the open part?  Just in the back?  Top bottom and sides are all closed?

Thanks for posting this and all your hard work.  A great idea!

[BrunoB]

I had not read this thread until today - wow!  Sorry I missed it.  Cool work, Bruno.

Of course it raises some questions:

1) Would a smaller driver do as well?  Since this is so very nearfield, maybe a pair of 8s or 10s could be "good enough."

In theory yes. But I haven't tried it. What about using two pairs of 8s or 10s? The more power, the better.

2) Would a monopole sub do as well?  In the very nearfield, the level should be low enough not to bother the neighbors, right?

In theory yes. But I haven't tried it.

3) Up to what frequency might this work?  How high could the sub work without giving away its position? (Delayed, of course)

I just installed a new AV receiver (Sony DA7100ES) two days ago. This receiver is very flexible. I set the sub XO frequency at 60 Hz. Previously it was at 80 Hz with my older receiver (80 was the lowest possible frequency). With the new receiver at 60 Hz, it is more difficult to localize the sub. This a preliminary result. When pushing the sub, I can feel some wind and the sofa is vibrating slightly.

4) In your latest version, where is the open part?  Just in the back?  Top bottom and sides are all closed?

Facing my neck, I have the slot with the U lined horizontally (I rotated the sub 90 deg). The other side of the sub is still open and faces the back wall. Yes, top, bottom and sides are all closed.

Thanks for posting this and all your hard work.  A great idea!

Thanks.


Now I am going to repeat my self: the sub must be as stable as possible. May be it is because the air is moving in and out faster than a normal sub.


Bruno

[panomaniac]

Thanks Bruno for all the precise answers. =)

Looking forward to reading more about your experiments.

[Telstar]

Hi Bruno,

I know you filter out the Ripole peak around 200Hz, and this must be related to the cabinet rather than a driver dimension.

Does taking the sides away help in that regard ?

It also occurs to me that if a Ripole was shrunk in size - as for say 8" drivers - then that 200Hz resonance might be shifted away from bass frequencies - to around 400Hz - and thus further away from the wanted LF working range.  Of course more 8" drivers would then become necessary to match the 2x 15" cone area, though with a potential to be more efficient too.

Cheers ....... Graham.

This is my plan, using a single 12" driver, I need to have the resonance above 200hz, because i need to cross around that point.
So, the smaller cabinet the higher the resonance point?

[dvenardos]

I have never seen an OB with a port like an IB, very interesting.
Any other experiences with the neighbor friendliness of OB subs?
I am having a problem vibrating my neighbors walls and am looking for a neighbor friendly alternative to my boxed/ported sub, but have limited placement options for an OB sub, although, I have been dying to do one.

More detail on my issue:
http://www.audiocircle.com/index.php?topic=68547.0

[Graham Maynard]

Vibrating a neighbour's walls is often down to LF pressurisation, generally from a monopole.

OB sub radiation sums to zero beyond the confines of the room, so as Bruno says - you have neighbour friendly bass - as long as you don't open doors and windows !

Or it could be down to your ceilings and floors vibrating, then their's also - sympathetically.  OB bass can vibrate your walls and ceilings too, though not nearly as much as monopoles do.

[dvenardos]

OB sub radiation sums to zero beyond the confines of the room, so as Bruno says - you have neighbour friendly bass - as long as you don't open doors and windows !

Wow, that's perfect.
So how does the physics of that work?

Or it could be down to your ceilings and floors vibrating, then their's also - sympathetically.  OB bass can vibrate your walls and ceilings too, though not nearly as much as monopoles do.

My walls don't vibrate at the spl that I listen at, so it sounds like I would be in good shape.

Thanks, not trying to thread jack but this is just what I was looking for.

[BrunoB]

I have decreased the inner volume of the small cavity. Here is how the sub looks from the listening position:



Here is what I built. I started from the "U" that I described in a previous post:


I added several layers of wood and two plates:


Then placed the new "U" back  inside the small cavity
The idea is to decreased the volume while still allowing air flow.

I will show the measurements in the next posts.

Bruno

[BrunoB]

Here is the impedance plot:


The main frequency of resonance is lower than before (about 22 Hz).
The troublesome dipole resonance has shifted to higher frequency: about 350 Hz. That's 150 Hz higher than my first version of the sub that did not have a "U" inside.

More measurements are coming.

Bruno

[BrunoB]

Measures made with the mic placed inside the small cavity

Frequency response:



Waterfall plot:

[Rudolf]

Bruno,
I am not sure about that new baffle in the middle of the front cavity. Do I see both drivers bolted clamshell-like to that baffle? And where is the air flowing to now? Can you explain?

[BrunoB]

Measures made with the mic outside a few inches in front of  the small cavity (more or less the listening position)

Frequency response:




Waterfall plot:


30 Hz is at about -5 db from 100 Hz without any boost.

The  resonance at 350 Hz is mush stronger when measured outside than inside the small cavity for a reason I don't understand.


Bruno

[BrunoB]

Bruno,
I am not sure about that new baffle in the middle of the front cavity. Do I see both drivers bolted clamshell-like to that baffle? And where is the air flowing to now? Can you explain?

Hi Rudolf,

I will try to make it clearer (I should have taken more pictures while I built it).

Let's start with a view from the sub with the "U" installed:



The point of view is similar to the one I used for the picture (sub covered with felt)  I presented three or four posts before this post.

Now , in the middle I glued vertically a white board that hermetically divides the internal cavity into two identical parts. The two drivers are still placed at the same position: they face each other but do not see each other because of the white board.

The next step is to fill some of the empty space in front of each driver with a kind of cone made of wood and a plate (does not look very nice I admit). These cones are glued to the white board. They face the black driver cones. A few centimeters of free space is left between the cones I made and the driver cones.

Hope this is clearer.

Bruno

[Rudolf]

Thanks a lot Bruno,
now I DO understand. So it is becoming some sort of compression driver.

Have the last measurements been done with the cones in place already?

[BrunoB]

Thanks a lot Bruno,
now I DO understand. So it is becoming some sort of compression driver.

Have the last measurements been done with the cones in place already?

yes

[Rclark]

Any updates to this topic forthcoming?

As the last phase of my system build, I have a pair of Adire Brahma 15's that I wish to use as OB subs, and for the same reason, neighbor friendliness. However, I've never heard OB before and was wondering if perhaps this elaborate setup is uneccessary and a regular set of OB panel mounts would achieve same result (in terms of neighbor friendliness). The Brahma's are particulary nice looking as well and I'd prefer to see the cones out front.

However, if this configuration would keep me from being evicted (is superior to plain OB) then I would do it.