AudioCircle

Audio/Video Gear and Systems => Open Baffle Speakers => Topic started by: BrunoB on 21 May 2008, 04:17 pm

Title: Neighbor friendly dipole sub
Post by: BrunoB on 21 May 2008, 04:17 pm

I want deep bass but I am living in an apartment with neighbors above me. What to do?

The idea is to focus the bass energy on the listener.

I built a W frame dipole using two 15'' drivers (views with the top removed):
(http://www.audiocircle.com/image.php?id=14584)
(http://www.audiocircle.com/image.php?id=14583)
.

This is the first speaker I built from scratch. This sub was very easy to build, this is a one afternoon project.

The sub is installed very close to the listening position, just behind the listening sofa , at ear height:
(http://www.audiocircle.com/image.php?id=14581)
The red part is a blanket that covers the sofa. I temporally placed two pieces of rockwool between the sub and the back of the sofa in order to decrease reflections from the hard surfaces.

The slot is facing the listener.  The slot acts as an acoustical lens that concentrates bass energy on one small spot. Outside this spot, the bass level decreases very quickly, which gives a neighbor friendly dipole sub.

Another advantage of this set up is that there is zero room interaction for the lowest frequencies. Pure bass!

This is the frequency response measured at the listening position:
(http://www.audiocircle.com/image.php?id=14470)

Boosting of low frequency and low pass filtering are applied.

My next post will provide more measurements and technical details.

Bruno
Title: Re: Neighbor friendly dipole sub
Post by: mcgsxr on 21 May 2008, 08:08 pm
Very interesting, I had not thought of that type of install, for that type of implementation.

I look forward both to the objective and subjective details!

What are the drivers?
Title: Re: Neighbor friendly dipole sub
Post by: iON on 21 May 2008, 08:11 pm
Nice curve! I haven't seen that before, no walls on the side?

/Jon
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 21 May 2008, 09:29 pm
Drivers are a pair a PA Audio WN-15R:
http://www.intertechnik.de/index.html/JTI2bmF2aWQlM0QxNzY4JTI2bGFuZyUzRGRlJTI2c2lkJTNEbjQ4MWRmMjAxOTdjYzMlMjZiJTNE.html?detail=45955

I choose this driver because it has a relatively low moving mass (66 g) and  a good BL/Mms ratio (about 0.24). This ratio is my main criterion for choosing a driver for this project. It is like a car power to weight ratio, which determines the acceleration capabilities of a car. The BL represents the force that moves the moving parts whereas Mms is the moving mass.  With a ratio of 0.24, the PA Audio WN-15R (15'' woofer) has a BL/Mms ratio twice as higher than most 12'' woofers. The magnet looks small because it is a neodymium magnet.

The amplifier is a Panasonic SAXR58 digital amplifier that provides 2 x 100 W. These digital amplifiers have very good control on the woofer. I choose the speaker cables as thick and as short as possible (R ~= 0.01 Ohms). The Panasonic works nicely for this application because it is very quiet (no hum or hiss, which is important for a speaker that is placed very close to the listening position).

The bass module is a Reckhorn B1. This module contains a subsonic filter that, unfortunately, cannot be bypassed. The subsonic filter is set to 20 Hz (minimum). Boost level is set to +12 db and boost frequency is somewhere above 20 Hz (knob set at 9). The low pass filter of the B1 is very bad (< 6db /octave). I am not using it. Presently I am using the sub output of a Sharp digital receiver, which gives a 80 Hz low pass filter of 24 db per octave. A good low pass filter is very important because of the 200 Hz resonance of the sub (more on this in one of my next posts).


Thanks to the W frame, the two drivers move in opposite directions, consequently the sub frame does not vibrate at all. This type of dipole is well described (Linkwitz and/or Ripole). The difference between my sub and Linkwitz/ripole is that I don't use side walls.

Bruno


Title: Re: Neighbor friendly dipole sub
Post by: TRADERXFAN on 21 May 2008, 09:50 pm
very clever Bruno. Great thinking. :thumb:

How well does it integrate with the mains though? Do you have phase control?
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 22 May 2008, 07:43 am
very clever Bruno. Great thinking. :thumb:

How well does it integrate with the mains though? Do you have phase control?
Thanks for the nice comments.

I don't have phase control but I can set up a delay for the subwoofer. I choose the sub delay by measuring the low frequency response of the subwoofer and main speakers playing together. I guess that the delay was correct when I had the least cancellation between main speakers and the sub. When the setup is right, the deep bass seems to come from the main speakers only. It is always tempting to push the sub level higher. That sounds very nice at first, but after a while, I found that an excess of very tight deep bass becomes tiring, especially with music. Furthermore, when the sub level is set too high, the integration with the main speakers is not as good - bass seems to come from my back. I am still playing with the level, boost frequency, delay to get the bass I like the most (which is not necessarily the most accurate).


Bruno
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 22 May 2008, 10:37 am
Measurements
The mic is an uncalibrated ECM-8000. THe audio sound card is a M-Audio Duo. Software is SoundEasy v 10.0.

Impedance of the sub only  (no filter/boosting/eq):
(http://www.audiocircle.com/image.php?id=14471)
FS is 26-27 Hz. FS of driver alone:  about 34 Hz. Strong resonance around 200 Hz.



FR from 20 to 20K at the listening position:
(http://www.audiocircle.com/image.php?id=14473)
The black line shows the FR at the listening position when the slot of the W frame is directed towards the microphone, as shown in the pictures above. The blue line shows the FR when the sub is rotate 180 deg, the larger openings are facing the microphone, the slot is facing the back wall. No LF boost , no EQ and no filtering performed.
One can see that the 200 Hz resonance is relatively much stronger  when the sub is rotated 180 deg.






To decrease the 200 Hz resonance, I added pieces of memory  foam inside the sides:
(http://www.audiocircle.com/image.php?id=14582)



Waterfall plot with memory foam measured at the listening position:
(http://www.audiocircle.com/image.php?id=14472)
The foam makes a visible difference in the water fall plot around 200 Hz.


FR from 10 to 500 plus phase (green line) at the listening position (memory foam present):
(http://www.audiocircle.com/image.php?id=14541)
No filter boosting or eq.




Bruno
Title: Re: Neighbor friendly dipole sub
Post by: Graham Maynard on 26 May 2008, 09:12 am
Hi Bruno,

This is a nicely presented project - far better than anything I could ever do.

Were some measurements taken with the sides removed, or were the photos taken at a different time ?

Have you run it without the sides, and if yes how does it compare/sound ?

I notice the 50Hz blip in the impedance plot which is not noticeable on other responses.  It might equate to a room dimension, but is very sharp and there are not any others similar.  Any known reason for it ?

Cheers ............ Graham.
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 26 May 2008, 11:18 am
Hi Bruno,

This is a nicely presented project - far better than anything I could ever do.

Were some measurements taken with the sides removed, or were the photos taken at a different time ?


Have you run it without the sides, and if yes how does it compare/sound ?


Hi Graham,

You have probably noticed slight differences between the FR's. I used two different amplifiers and probably slightly different mic positions . I also used foam for the second set of measurements.  I liked the sound better without the sides. I will redo FR measurements with and without the sides.

Quote
I notice the 50Hz blip in the impedance plot which is not noticeable on other responses.  It might equate to a room dimension, but is very sharp and there are not any others similar.  Any known reason for it ?

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

The blib is due to the 50Hz AC from the power supply of my external sound card.


Bruno
Title: Re: Neighbor friendly dipole sub
Post by: Graham Maynard on 26 May 2008, 02:51 pm
Hi Bruno,

So the drivers facing each other still reduces the resonant frequency, but it sounds better without the rearward facing resonant chambers.

Interesting.

Cheers ....... Graham.
Title: Re: Neighbor friendly dipole sub
Post by: tubamark on 27 May 2008, 04:20 am
Bruno,

Good stuff - 'appreciate the measurements!  I've pondered a similar notion, but haven't tried anything serious yet, as I'm moving my listening room soon.
A couple questions, If you can share:
1)  I understand the neighbor/SPL objective drove the placement to be right by yer head.
Have you tried with the frame on the floor just for kicks? :hyper: like a foot or so behind the seat.  Basically I'm wondering about sofa coverage rather than single-seat as you've described.   Also because SAF goes up when the box goes down (outta sight)  :oops: . . .
2)  How far is the frame and/or your listening position from the rear wall?  'Apologies if this was mentioned and I missed it.  Maybe not a big factor at the super-nearfield listening distance you are using, but I'm still curious.


This could prove to be an awesome alternative to IB bass!  Please keep us posted on any new discoveries or variations you try!

Envious and curious, grateful for your sharing,
-- Mark
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 27 May 2008, 04:49 pm
For those who can read German,
I 'd like to recommend this issue of Hobby-Hifi:

http://www.hobby-hifi.de/Archiv/05/02_05/02_05.html (http://www.hobby-hifi.de/Archiv/05/02_05/02_05.html)
(http://www.hobby-hifi.de/Archiv/05/02_05/hh52_titel_mi.jpg)

There is one article about bass dipole with different frames (H,U,I,A, ripole). The effect of room positioning, freq of resonance, impedance plots plus also comparison with bass reflex , ... are presented with measurements.



Here is the issue that inspires me for doing this project:
http://www.hobby-hifi.de/Archiv/07/04_07/04_07.html (http://www.hobby-hifi.de/Archiv/07/04_07/04_07.html)
(http://www.hobby-hifi.de/Archiv/07/04_07/hh74_titel_mi.jpg)
(look at the bottom left picture)

They compared four different drivers (12") for the dipole sub. All gave very similar FR's but sounded slightly different.

Bruno
Title: Re: Neighbor friendly dipole sub
Post by: Graham Maynard on 28 May 2008, 04:49 pm
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.
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 28 May 2008, 06:53 pm

Here is an impedance plot measured on a single woofer:
(http://www.audiocircle.com/image.php?id=14684)

I first thought  that my dipole sub was transformed into a bass-reflex because of the two peaks :scratch:.

It seems that the two drivers really see each other although they are not placed on a air tight enclosure.

Bruno


Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 28 May 2008, 07:30 pm
Bruno,

Good stuff - 'appreciate the measurements!  I've pondered a similar notion, but haven't tried anything serious yet, as I'm moving my listening room soon.
A couple questions, If you can share:
1)  I understand the neighbor/SPL objective drove the placement to be right by yer head.
Have you tried with the frame on the floor just for kicks? :hyper: like a foot or so behind the seat.  Basically I'm wondering about sofa coverage rather than single-seat as you've described.   Also because SAF goes up when the box goes down (outta sight)  :oops: . . .


I havent' tried with the sub on the floor. On way to increase sofa coverage is to rotate the sub 180 deg, then the slot is facing the back wall. In this case, the amplifier volume must be increased and the low pass filter must be steeper because of the relatively stronger 200 Hz resonance.

Quote
2)  How far is the frame and/or your listening position from the rear wall?  'Apologies if this was mentioned and I missed it.  Maybe not a big factor at the super-nearfield listening distance you are using, but I'm still curious.



the listening position is 1.5 m far from the back wall and the on the sub is 0.5 m deep. I have a small listening room. I would not placed the sub on the floor between the sofa and the back wall because it would increase cancellation of the dipole. A better placement would be the middle of the room, far away from walls and corners. I don't know when I will try another position for the sub.


Bruno


Title: Re: Neighbor friendly dipole sub
Post by: Michael V on 30 May 2008, 01:16 pm
Bruno-

Would you mind sharing the dimensions?  I have a pair of Goldwood 15 inchers lying around that I could try in your design.  Definitely an afternoon project!

Any thoughts on the suitability of these?

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=290-384

Regards,
Mike
Title: Re: Neighbor friendly dipole sub
Post by: mcgsxr on 30 May 2008, 04:46 pm
I have considered the Goldwoods you mention, as their QTS, FS are attractive - what remains to be seen is how they handle excursion, and if they make nasty noises as they bottom etc - or whisle or make other noises.

Lots of swept area, that is for sure!
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 31 May 2008, 03:27 pm
Bruno-

Would you mind sharing the dimensions? 
(http://www.audiocircle.com/gallery/albums/userpics/10910/disub15%2Bmeasures.JPG)

Unit is millimeter. I used a MDF  thickness of 18 mm.

Bruno
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 1 Jun 2008, 05:38 pm
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.


Hi Graham,

I remeasured the impedance plots with and without sides. The two drivers are connected in parallel.

First, without side wall.
(http://www.audiocircle.com/image.php?id=14745)


Second with the side walls. Note that my side walls cover only 50% of the surface of the sides. Unfortunately, I don't have full size walls to try.
(http://www.audiocircle.com/image.php?id=14740)

We can see now two resonance peaks, one at about 180 and another stronger at about 240 Hz. Also, the main FS decreases slightly in intensity (41.5 Ohms) and frequency (24 Hz)



Finally, without the sides walls but with plenty of memory foam attached to the walls (I posted a pict earlier in this thread)
(http://www.audiocircle.com/image.php?id=14745)
.
The intensity of the 200 Hz resonance peak is lower. The FS decreases in intensity (40.5 Ohms) and frequency (24 Hz) .


And now yet another strange plot. The setup is the same as the previous plot: memory foam and no sides. But this time I connected the two drivers out of phase!
(http://www.audiocircle.com/image.php?id=14745)

There is no more 200 Hz resonance and I don't understand why. :scratch:

The FS is about 34 Hz and 45 Ohms. This  looks like a free air measurement.
There is a new resonance at 850 Hz.

Bruno
Title: Re: Neighbor friendly dipole sub
Post by: Davey on 2 Jun 2008, 01:19 am
"There is no more 200 Hz resonance and I don't understand why."

Because the cavity is not pressurized now.  More of a free-air result measurement is what you'd expect, and that's what you have.

Dave.
Title: Re: Neighbor friendly dipole sub
Post by: Graham Maynard on 2 Jun 2008, 08:01 am
Hi Bruno,

Thats a nice group of investigation curves.

I must agree with Dave - the front cavity is radiating the main upper resonance, as can H frames, and (through the driver cone) U frames too.  Damping can help but affects output.

That is why I suggested making a toroid out of carpet and fitting it inside the cabinet around the driver apertures like a 100mm thick ring, though squashed to the outer edges at the front for maximum vent opening.
This should extend from the outer wood to between the cone edges but still be clear of them, and the carpet should deform resistively in a manner which will de'Q' the peak and minimise its recognisable reproduction characteristic.

The problem with this kind of peak is that although AF drive can be notched at this frequency, it is a resonant mode which can still be energised by large amplitude waveforms of lower frequency within the operating passband.

I am afraid that if I recognised a resonant peak like that I would choose to listen through LSs which would not oblige me to tolerate it.

Do you find it audible when compared to say listening to a flat mounted OB alternative, or a well damped boxed LS ?

Cheers ......... Graham.
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 3 Jun 2008, 02:50 am
Hi Bruno,

Thats a nice group of investigation curves.

I must agree with Dave - the front cavity is radiating the main upper resonance, as can H frames, and (through the driver cone) U frames too.  Damping can help but affects output.

Hi Dave and Graham,

if the front cavity is radiating the 200 Hz resonance, how do you explain the following?

1)  I measured much less resonance from the front cavity than from the sides
(http://www.audiocircle.com/image.php?id=14473)
the black line line is the FR at the listening position when the front cavity faces the listening position whereas the blue line is the FR when the side cavities are facing the listening position.

2) adding foam in the side cavities decreases resonance.


Quote
That is why I suggested making a toroid out of carpet and fitting it inside the cabinet around the driver apertures like a 100mm thick ring, though squashed to the outer edges at the front for maximum vent opening.
This should extend from the outer wood to between the cone edges but still be clear of them, and the carpet should deform resistively in a manner which will de'Q' the peak and minimise its recognisable reproduction characteristic.
I tried two times to place some foam inside the slot. Each time I ended removing it because the bass was slower. Therefore, I would not add any sound adsorbing material inside the front cavity. If I would add a ring inside the slot as you suggested, I would use wood or another non adsorbing material.

Quote
The problem with this kind of peak is that although AF drive can be notched at this frequency, it is a resonant mode which can still be energised by large amplitude waveforms of lower frequency within the operating passband.

I am afraid that if I recognised a resonant peak like that I would choose to listen through LSs which would not oblige me to tolerate it.

Do you find it audible when compared to say listening to a flat mounted OB alternative, or a well damped boxed LS ?

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

I don't plan to try a flat OB alternative in the near future. The sub sounds pretty good thanks to the steep 80Hz low pass filter (200 Hz is 27 db lower than 80 Hz at the listening position).

Bruno
Title: Re: Neighbor friendly dipole sub
Post by: Davey on 3 Jun 2008, 04:15 am
My comment was only regarding your out-of-phase impedance measurement.  That's obviously not a mode you would use so it shouldn't be of concern.  In that case the two woofers are always moving in the same direction so there is no pressure created in the cavity and thus you aren't "exciting" it.

I think you might try taking some close-up measurements to better define the radiation pattern.  I'm not sure it's as directional as you think it is.

Cheers,

Dave.
Title: Re: Neighbor friendly dipole sub
Post by: Graham Maynard on 3 Jun 2008, 06:45 am
Hi Bruno,

You say that the bass sounded 'slower' when any front slot damping was inserted.  Clearly the characteristics of the bass reproduction were changed in some way, thus the impedance plot must have been changed too.
Did you try an impedance plot with the front cavity damped ?

Where impedance is not flat due to the development of any resonant peak, ( the Ripole has 2 ! ) and yet the SPL plot does not show that resonance, then it is the dynamic ( not steady sine ) reproduction which becomes affected.  Some enclosured subs can measure flat and sound impressive, yet where there is resonance within the listening passband their dynamic ( drum ) reproduction qualities are not entirely natural sounding;  ie. electrical phase changes lead to energy storage modes and modified sound reproduction.  I can't describe the differences I might well hear here, and recognition of those differences is not easy in isolation when there is not a better reference to listen to ( even headphones ).
I am not however saying that Ripole bass is not acceptable.

My thoughts also follow Dave's.  A radiation pattern made by rotating the cabinet would be interesting, at say 200Hz where that upper resonant mode arises.

Cheers ...... Graham.
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 8 Jun 2008, 05:47 pm
I have the best bass I have ever heard. I made two modifications to the sub:
1) fill the small cavity with incompressible material while still allowing air flow
2) Using full length side walls

During  listening, I had to decrease the 20 Hz bass boost level.

I watched two times the same movie this weekend (Day after tomorrow, on Blu ray with soundtrack encoded in DTS-HDMA). The first time for the movie itself. The second time just to enjoy the new bass quality. In chapter 25, around 1:30, when the space station flies over the earth, some strong  drums can be heard. Theses are very fast, clear,  deep and ... scary!

I'll post picts and measurements next weekend (If I don't (re)watch too many movies  :D).

Bruno
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 17 Jun 2008, 03:50 am

I built a stand for the sub.
(http://www.audiocircle.com/image.php?id=14908)

This is a small table with wheels. A shelve holds the electronics.


Bruno

Title: Filling the small cavity
Post by: BrunoB on 17 Jun 2008, 03:58 am

Here is how I filled the small cavity with incompressible material while still allowing air flow.


I built a U shaped piece of wood
(http://www.audiocircle.com/image.php?id=14905)
(http://www.audiocircle.com/image.php?id=14905)

I inserted the U inside the small cavity
(http://www.audiocircle.com/image.php?id=14906)

(http://www.audiocircle.com/image.php?id=14906)


Bruno
Title: Re: Neighbor friendly dipole sub
Post by: Michael V on 17 Jun 2008, 12:36 pm
Great pics, thanks for sharing.  With the addition of the side walls, how did that affect placement of the sub?  Do you still have it firing directly behind your listening position?

PS I built one a few weekends ago but haven't even hooked it up yet (embarrassing!).
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 17 Jun 2008, 05:29 pm
Great pics, thanks for sharing.  With the addition of the side walls, how did that affect placement of the sub?  Do you still have it firing directly behind your listening position?


I still have the sub just behind the sofa. The full side walls seem to enlarge the bass sweet spot.

The main reason for using sidewalls is that the dipole resonance frequency moves higher (> 200 Hz). I will follow up on this with a more detailed post.

I made another modification that shifts the frequency of resonance even higher (about 300 Hz). I also have rotated my sub by 90 deg such that the front cavity is horizontal. I am still doing a lot of experimenting. This is why I haven't posted much lately.

Quote
PS I built one a few weekends ago but haven't even hooked it up yet (embarrassing!).

I hope you will hook up your sub soon and will try a similar set up. The bass is really that good.


Bruno







 
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 18 Jun 2008, 04:45 pm

I built a stand for the sub.
(http://www.audiocircle.com/image.php?id=14908)

This is a small table with wheels. A shelve holds the electronics.


Bruno



This little table with wheels is very convenient. Unfortunately, it is not as stable as the chair I had before. I noticed that bass was not as good:  slower. The solution I  tried yesterday is to place a heavy stone on the top of the sub. Works.

Bruno
Title: Re: Neighbor friendly dipole sub
Post by: Rudolf on 18 Jun 2008, 05:42 pm
You could even integrate the stone into the sub:

(http://rudolffinke.homepage.t-online.de/audio/Dipol/AD%2015308/H%20Frame%20Parts%205.jpg)
Title: Re: Neighbor friendly dipole sub
Post by: scorpion on 18 Jun 2008, 10:15 pm
Please Rudolf, remember this is a friendly forum, you shouldn't get stoned or perhaps more people should ! :D

/Erling
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 22 Jun 2008, 06:13 pm
...

The problem with this kind of peak is that although AF drive can be notched at this frequency, it is a resonant mode which can still be energised by large amplitude waveforms of lower frequency within the operating passband.

I am afraid that if I recognised a resonant peak like that I would choose to listen through LSs which would not oblige me to tolerate it.

Do you find it audible when compared to say listening to a flat mounted OB alternative, or a well damped boxed LS ?

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

Hi Graham,

you suggested two times to try a flat mounted OB alternative and to compare the sound to the ripole. It is a good suggestion but I haven't had the time to do so. What I did, is to measure the waterfall plots of the driver alone and mounted on the ripole. Here are the results:

1) The driver is placed on a small speaker stand and the microphone is placed very close to the membrane. The idea is to simulate the results one would obtain if the driver would be placed on a flat mounted OB.
(http://www.audiocircle.com/image.php?id=14944)

2) Two drivers are mounted on the ripole and the mic is placed in front of the small opening. The small cavity is filled with the U (see my post above) and full length side walls are used.
(http://www.audiocircle.com/image.php?id=14943)



The second plot is certainly noisier than the first plot. The ripole shows longer decays even at lower frequencies.
Note that I am not completely confident in these measurements. I have read elsewhere that WF plots are not reliable for low frequencies.

What surprises me is that the main resonances (34 Hz for open air driver and 22 Hz for the ripole) are barely visible.



Bruno
Title: Side walls and U
Post by: BrunoB on 22 Jun 2008, 06:31 pm
The plot below shows the effect of the sidewalls and the "U" on the FR of my sub.

(http://www.audiocircle.com/image.php?id=14945)

The mic is placed just in front of the small cavity.

The red line:  no side walls, no U.
The green line: + full length side walls.
The blue line: + full length side walls  + U

Adding the "U" increases the 20 Hz level by 4 db.

Bruno
Title: Re: Neighbor friendly dipole sub
Post by: Graham Maynard on 23 Jun 2008, 07:37 am
Hi Bruno,

I cannot comment on the waterfall 'ripples' because I do not know the how and why of their origins.  However a 4dB relative increase clearly shows at 20Hz wrt 100Hz for the Ripole mic compared to single driver mic measurement.

Resonant development requires 'Q' and a steady sine drive waveform continuing for more than one full cycle. 
With low Qes LS drivers and SS drive the 'one-note bass' resonance cannot develop.
Insert series R or use a SET amplifier and it will though !

So the front 'U' insert improves LF output and gets rid of the notch at about 420Hz.
Wonder what rear 'U's would do ? 
Or rear aperture damping - maybe reduce the new 270Hz SPL peak ?
Rear damping might reduce some of the Ripole waterfall 'noise' too ?

Cheers .......... Graham.
Title: Linkwitz configuration
Post by: BrunoB on 24 Jun 2008, 07:21 pm

I also tried a Linkwitz configuration of the two drivers http://www.linkwitzlab.com/woofer.htm (http://www.linkwitzlab.com/woofer.htm).

(http://www.audiocircle.com/image.php?id=15015).

More details later.


Bruno
Title: Neighbor friendly dipole sub Linkwitz configuration
Post by: BrunoB on 28 Jun 2008, 11:27 am
Here are the measurements of the sub with a Linkwitz configuration.
Frequency response:
(http://www.audiocircle.com/image.php?id=15055)
The red line:  no side walls, no U.
The blue line: + full length side walls  + U
The black line: + full length side walls  + U + Linkwitz configuration
The black line shows clearly that the sound level in a Linkwitz configuration is decreased. However, it is actually not as strong as shown on the plot.
I made a mistake when mounting the driver in the Linkwitz configuration. The driver hole was slightly too small and there was an air leak. I measured afterwards (after fixing the leak) that this leak accounts for a loss of about 2 db at 20Hz and 1 db at 100 Hz. Still, even taking the effect of the leak into account, there is still a slight decrease of the output level.



This is the impedance plot of the sub described above (see my post above):
(http://www.audiocircle.com/image.php?id=15054)

The secondary resonance moved to a higher frequency, almost 300 Hz.

The waterfall plot (not shown) looks slightly better in the region < 150 Hz.

I don't know yet which configuration sounds better.

Bruno
Title: Re: Neighbor friendly dipole sub
Post by: Graham Maynard on 1 Jul 2008, 06:57 am
Hi Bruno,

Clearly running drivers face to face with your centre 'U' section improves output and reduces cavity resonances.

I am tempted to ask what it would be like with 'U' sections at the rear as well, but both the impedance and SPL plots already look pretty clean.

Cheers ........ Graham.
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 1 Jul 2008, 05:28 pm
Hi Bruno,

I cannot comment on the waterfall 'ripples' because I do not know the how and why of their origins.  However a 4dB relative increase clearly shows at 20Hz wrt 100Hz for the Ripole mic compared to single driver mic measurement.

Resonant development requires 'Q' and a steady sine drive waveform continuing for more than one full cycle. 
With low Qes LS drivers and SS drive the 'one-note bass' resonance cannot develop.
Insert series R or use a SET amplifier and it will though !

Hi Graham,

This is why I am using a digital amp and very short and  thick cables.


So the front 'U' insert improves LF output and gets rid of the notch at about 420Hz.
Wonder what rear 'U's would do ? 
Or rear aperture damping - maybe reduce the new 270Hz SPL peak ?
Rear damping might reduce some of the Ripole waterfall 'noise' too ?

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

I have prepared two "U"'s made of relatively rigid foam for the sides. I haven't had the time to install them yet.


I'd like to share another finding. I moved the side walls closer to the driver such that the volume of the two side cavities decreases slightly. I measured the impedance plot and found that 1)  the secondary frequency of resonance increases slightly (>= 300 Hz), 2) the main resonance decreases slightly in frequency (-1 Hz) and intensity (-2 Ohms).



Bruno
Title: Re: Neighbor friendly dipole sub
Post by: iON on 10 Jul 2008, 01:19 am
Thanks for sharing your experimentation Bruno. 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 :wink:). It looks puzzeling that sensitivity on that particular measurement is lower though...
Title: Re: Neighbor friendly dipole sub
Post by: Rudolf on 10 Jul 2008, 07:43 am
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 :wink:).
Sorry, where do you see a cancellation of non-linearities?

Quote
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?
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 17 Jul 2008, 02:26 am

 

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

I had forgotten to save the plot. I did remeasure it:
(http://www.audiocircle.com/image.php?id=15203)

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

Bruno
Title: Re: Neighbor friendly dipole sub
Post by: Graham Maynard on 3 Aug 2008, 08:12 am
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.
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 5 Aug 2008, 04:36 pm
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 (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 donĀ“t have time to try it at the moment (I am on vacation :-)).


Bruno
Title: Re: Neighbor friendly dipole sub
Post by: panomaniac on 6 Aug 2008, 08:59 pm
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!
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 20 Aug 2008, 05:21 pm
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.

Quote
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.

Quote
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.


Quote
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.

Quote
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
Title: Re: Neighbor friendly dipole sub
Post by: panomaniac on 3 Sep 2008, 03:21 am
Thanks Bruno for all the precise answers. =)

Looking forward to reading more about your experiments.
Title: Re: Neighbor friendly dipole sub
Post by: Telstar on 18 May 2009, 07:26 pm
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?
Title: Re: Neighbor friendly dipole sub
Post by: dvenardos on 3 Jun 2009, 06:27 pm
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
Title: Re: Neighbor friendly dipole sub
Post by: Graham Maynard on 4 Jun 2009, 08:52 am
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.
Title: Re: Neighbor friendly dipole sub
Post by: dvenardos on 4 Jun 2009, 05:55 pm
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.
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 14 Sep 2009, 04:39 pm
I have decreased the inner volume of the small cavity. Here is how the sub looks from the listening position:

(http://www.audiocircle.com/image.php?id=22026)

Here is what I built. I started from the "U" that I described in a previous post:
(http://www.audiocircle.com/image.php?id=14907)

I added several layers of wood and two plates:
(http://www.audiocircle.com/image.php?id=19598)

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

Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 14 Sep 2009, 04:49 pm

Here is the impedance plot:
(http://www.audiocircle.com/image.php?id=21945)

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
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 14 Sep 2009, 05:06 pm
Measures made with the mic placed inside the small cavity

Frequency response:
(http://www.audiocircle.com/image.php?id=21941)


Waterfall plot:
(http://www.audiocircle.com/image.php?id=21943)

Title: Re: Neighbor friendly dipole sub
Post by: Rudolf on 14 Sep 2009, 05:07 pm
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?
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 14 Sep 2009, 05:26 pm
Measures made with the mic outside a few inches in front of  the small cavity (more or less the listening position)

Frequency response:
(http://www.audiocircle.com/image.php?id=21942)



Waterfall plot:
(http://www.audiocircle.com/image.php?id=21944)

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
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 14 Sep 2009, 06:02 pm
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:

(http://www.audiocircle.com/image.php?id=14909)

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
Title: Re: Neighbor friendly dipole sub
Post by: Rudolf on 14 Sep 2009, 08:32 pm
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?
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 15 Sep 2009, 04:19 pm
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
Title: Re: Neighbor friendly dipole sub
Post by: Rclark on 14 Aug 2010, 12:19 am
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.
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 14 Aug 2010, 08:16 am
Any updates to this topic forthcoming?
None on my side. I am very happy with the bass of my OB sub.

I am using now a Hypex DS 8 digital amp. The transition frequency between main and sub is 40-50 Hz.

I plan to decrease the dead volume in the small cavity even further.

Quote


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.

I would try the plain OB first: it is much simpler and it does not suffer from a secondary resonance. See Graham Maynard's post above.

Interesting reading: http://www.humblehomemadehifi.com/Serious-Sub.html

Bruno
Title: Re: Neighbor friendly dipole sub
Post by: Rclark on 15 Aug 2010, 01:22 am
Thank you for that, will definitely read. :)

Say, I'm still at a somewhat early build stage with my system, I'm just now putting together my monitors, and have yet to order preamp, amp, and some other items. They will also be diy items and may take me some time.

 Literally at this moment about to tear into the flatpack for my Statement Monitors and start gluing.

Could I possibly talk to you in PM at date in the near future regarding my sub application? 
Title: Re: Neighbor friendly dipole sub
Post by: face on 30 Dec 2012, 11:48 pm
Any updates?
Title: Re: Neighbor friendly dipole sub
Post by: Bob in St. Louis on 6 Jan 2013, 01:02 am
Neat thread, and a very cool design.
Looks like a combination of a Nelson Pass Slot Load and a RiPole.
Updates would be great!  :D

Bob
Title: Re: Neighbor friendly dipole sub
Post by: BrunoB on 7 Apr 2013, 08:04 pm
Two years and half later ...

I am still enjoying the my subwoofer. A year or more ago, I added a digital sub-harmonic synthesizer Behringer EX1200 which I modified according to:

http://www.cowanaudio.com/more.html

but using different values for the replaced capacitors (smaller if I remember correctly).


For a nearfied subwoofer, the most useful part of the Behringer EX1200 is the automatic bass level limiter. It allows to push the  bass level up, which is useful for shy recordings and movies.

The  Behringer EX1200 is connected to the Hypex DS8 with a XLR cable.

I talked to my neighbors a few months ago: they did not know and never noticed that there was a home theater below ...

Bruno