Multiple OB Subwoofers -- where to put them?

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tnargs

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Multiple OB Subwoofers -- where to put them?
« on: 22 Feb 2020, 11:23 pm »
I'm thinking about building 4 OB subwoofers in their separate H-frames. The idea being to have some freedom in placement and get them to interact beneficially. I'm a bit concerned about where I would place them in a typical rectangular room like mine.

Has anyone done a proper model to analyse this? Or made measurements?

With the usual goal in mind, i.e. smoothest response across the listening area before EQ. Not trying to maximize SPL.

The issue that keeps haunting me is what happens if they are placed along the side walls -- should they be opposing polarity to their "side wall partner", to prevent the back wave from one cancelling the front wave from the other?

This got me thinking more generally. Scattering them around the room, in the manner often used for monopole subs, seems to invite all sorts of front-wave/back-wave interactions, potentially a disastrous mess.

I would really appreciate hearing from anyone who has 'solved' this.

cheers
Arg

Early B.

Re: Multiple OB Subwoofers -- where to put them?
« Reply #1 on: 22 Feb 2020, 11:58 pm »
We need a lot more info such as room dimensions (a diagram would be most helpful) and limitations (i.e., WAF, furniture, etc.). I have a third OB sub a few inches from the back wall. It's the only place I could reasonably put it and it works great. I wouldn't worry so much about placement.

BTW -- if I could do it all over again, I'd start with putting triples up front, and then add a pair of dual OB subs in the rear later on when my budget recovered. There's also a modular approach, so something to consider, as well.

   

tnargs

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Re: Multiple OB Subwoofers -- where to put them?
« Reply #2 on: 23 Feb 2020, 12:30 am »
We need a lot more info such as room dimensions (a diagram would be most helpful) and limitations (i.e., WAF, furniture, etc.).
It's a simple rectangle 6m x 4.2m x 2.4m and the only limitation is the door in one corner (behind listener's left ear).
Quote
I have a third OB sub a few inches from the back wall. It's the only place I could reasonably put it and it works great. I wouldn't worry so much about placement.
I do. I see potential issues.  cheers

jtcf

Re: Multiple OB Subwoofers -- where to put them?
« Reply #3 on: 23 Feb 2020, 01:06 am »
Here's a link that describes set up of multiple subs.It's looong so scroll way down where set up is described.Multiple subs will not cancel each other out.They will smooth out peaks and nulls throughout the entire frequency in your room.My four subs are actually facing the wall instead of out into the room.
http://jamesromeyn.com/old-pages/home-audio-gear/dsa-1-0-distributed-subwoofer-array-5-pieces-4k-usd/

poseidonsvoice

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Re: Multiple OB Subwoofers -- where to put them?
« Reply #4 on: 23 Feb 2020, 01:40 am »
Here's a link that describes set up of multiple subs.It's looong so scroll way down where set up is described.Multiple subs will not cancel each other out.They will smooth out peaks and nulls throughout the entire frequency in your room.My four subs are actually facing the wall instead of out into the room.
http://jamesromeyn.com/old-pages/home-audio-gear/dsa-1-0-distributed-subwoofer-array-5-pieces-4k-usd/

As much as I agree with you, the OP is looking to implement multiples of Open Baffle subwoofers. So placement close to a wall boundary can be an issue especially if space is a premium.

I’m a bit time constrained this evening but if the OP wants to discuss, I would be happy to via phone/email, just pm me and I’ll reply later.

Best,
Anand.

tnargs

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Re: Multiple OB Subwoofers -- where to put them?
« Reply #5 on: 23 Feb 2020, 04:03 am »
Here's a link that describes set up of multiple subs.It's looong so scroll way down where set up is described.Multiple subs will not cancel each other out.They will smooth out peaks and nulls throughout the entire frequency in your room.My four subs are actually facing the wall instead of out into the room.
http://jamesromeyn.com/old-pages/home-audio-gear/dsa-1-0-distributed-subwoofer-array-5-pieces-4k-usd/
Hi, thanks for your assistance. The link does not work, though. Also, I am reasonably across the ideas behind multiple subwoofers, but want to know more about multiple OB subs.
As much as I agree with you, the OP is looking to implement multiples of Open Baffle subwoofers. So placement close to a wall boundary can be an issue especially if space is a premium.

I’m a bit time constrained this evening but if the OP wants to discuss, I would be happy to via phone/email, just pm me and I’ll reply later.

Best,
Anand.
Quite right Anand, I am asking in what way is OB subwoofer placement unique and different to normal monopole subs.

PM sent. Also quite happy to discuss in the open in this thread.

Regards,
Arg

Tyson

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Re: Multiple OB Subwoofers -- where to put them?
« Reply #6 on: 23 Feb 2020, 04:55 am »
I think using OB subs is at odds with using a swarm approach.  With OB you are trying to minimize room interaction by the null at the sides figure 8 pattern, so OB subs are best in stereo and also best place near the main speakers. 

A swam approach is used to excite the room as much as possible, so box subs are a better choice for that. 

poseidonsvoice

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Re: Multiple OB Subwoofers -- where to put them?
« Reply #7 on: 23 Feb 2020, 02:05 pm »
I think using OB subs is at odds with using a swarm approach.  With OB you are trying to minimize room interaction by the null at the sides figure 8 pattern, so OB subs are best in stereo and also best place near the main speakers. 

A swarm approach is used to excite the room as much as possible, so box subs are a better choice for that.

I have a bit more time this morning and it is better to answer publicly in case the question is asked again.

Tyson is exactly right.

Dr. Geddes specifically did research on this when he was formulating his PhD thesis a long while back. He found that using asymmetrical distribution of monopole LF transducers allowed for dramatically flatter FR’s and that as Tyson stated above, is recommended so as to engage as many LF modes as possible and not avoid them like OB’s do. And yes, he specifically tested multiple OB subs as well.

I have found that using a pair of OB subs are advantageous in a stereo configuration vs a single monopole sub but that advantage is lost when monopole subs are used in multiples. The other thing I have found is that it is easier to setup a pair of OB subs just by ear vs a single or multiple monopole subs (impossible actually). The advantage with OB’s here is in the time domain. There are less lingering tails on the waterfalls and less ringing with stereo OB subs vs a single monopole sub. However, the waterfalls with multiple monopole subs can have less ringing than stereo OB subs if set up correctly. The devil is in the details and execution.

Next, stereo OB subs are advantageous for those users whose listening habits gravitate to classical music. Very few % of recordings have stereo bass which can render spatialization cues and this is is where OB subs have the advantage. With the great majority of other recordings (primarily non-classical), bass is recorded in mono and spatialization isn’t perceived; as such multiple monopole subs are recommended. Multiple monopole subs are also recommended for home theater installations.

Can you do both? Yes. You may get the best of both worlds but in room measurements are absolutely necessary. No free lunch. An example is (2) OB stereo subs and 1-2 extra monopole subs. I have helped set one up like that.

I have played with all the above configurations (specifically with a GR Research setup). My system is listed in my systems page but I personally don’t use any GR Research products anymore.

Best,
Anand.



tnargs

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Re: Multiple OB Subwoofers -- where to put them?
« Reply #9 on: 23 Feb 2020, 10:45 pm »
I have a bit more time this morning and it is better to answer publicly in case the question is asked again.

Tyson is exactly right.

Dr. Geddes specifically did research on this when he was formulating his PhD thesis a long while back. He found that using asymmetrical distribution of monopole LF transducers allowed for dramatically flatter FR’s and that as Tyson stated above, is recommended so as to engage as many LF modes as possible and not avoid them like OB’s do. And yes, he specifically tested multiple OB subs as well.

I have found that using a pair of OB subs are advantageous in a stereo configuration vs a single monopole sub but that advantage is lost when monopole subs are used in multiples. The other thing I have found is that it is easier to setup a pair of OB subs just by ear vs a single or multiple monopole subs (impossible actually). The advantage with OB’s here is in the time domain. There are less lingering tails on the waterfalls and less ringing with stereo OB subs vs a single monopole sub. However, the waterfalls with multiple monopole subs can have less ringing than stereo OB subs if set up correctly. The devil is in the details and execution.

Next, stereo OB subs are advantageous for those users whose listening habits gravitate to classical music. Very few % of recordings have stereo bass which can render spatialization cues and this is is where OB subs have the advantage. With the great majority of other recordings (primarily non-classical), bass is recorded in mono and spatialization isn’t perceived; as such multiple monopole subs are recommended. Multiple monopole subs are also recommended for home theater installations.

Can you do both? Yes. You may get the best of both worlds but in room measurements are absolutely necessary. No free lunch. An example is (2) OB stereo subs and 1-2 extra monopole subs. I have helped set one up like that.

I have played with all the above configurations (specifically with a GR Research setup). My system is listed in my systems page but I personally don’t use any GR Research products anymore.

Best,
Anand.

Thanks to you both for your additional, certainly most interesting, comments.

I have had another look at the Geddes material on bass, "Why Multiple Subs?" and "Optimal Bass Playback in Small Rooms", and I cannot find any reference to dipole (open baffle) subwoofers. It was a rewarding refresher for me, though.

The idea, that monopole subs are best suited to multiple deployment and dipole subs are best suited to stereo deployment, is intriguing.

What I am keen to see, though, is if anyone has done some modelling of dipole subs, so we can see the effect as multiple units are deployed in various locations.

Measurements from someone using dipole subs --multiple dipole subs -- would be fascinating and very helpful too.

I am mainly keen to find the best way to arrange multiple dipole subs. Discussion of which is the better type of subwoofer was not my intention.

thanks again

Early B.

Re: Multiple OB Subwoofers -- where to put them?
« Reply #10 on: 23 Feb 2020, 10:49 pm »
I think using OB subs is at odds with using a swarm approach.  With OB you are trying to minimize room interaction by the null at the sides figure 8 pattern, so OB subs are best in stereo and also best place near the main speakers. 

A swam approach is used to excite the room as much as possible, so box subs are a better choice for that.

Geez. You guys can get awfully technical sometimes. Just keep it simple -- if you believe that OB servo subs sound better than box subs, then buy/build them. End of story. Throw box subs in the mix with OB servo subs and you'll run the risk of screwing up that great OB servo sound, regardless of how it measures.

I get it -- measurements are important and if you have the ability to do them, by all means, go for it. But don't throw the baby out with the bath water. There will always be compromises. You will always get imperfect measurements in your room. However, start with the best sounding subs and make it work, whether it's one, two or ten of them.   

tnargs

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Re: Multiple OB Subwoofers -- where to put them?
« Reply #11 on: 23 Feb 2020, 10:57 pm »
Geez. You guys can get awfully technical sometimes. Just keep it simple -- if you believe that OB servo subs sound better than box subs, then buy/build them. End of story. Throw box subs in the mix with OB servo subs and you'll run the risk of screwing up that great OB servo sound, regardless of how it measures.

I get it -- measurements are important and if you have the ability to do them, by all means, go for it. But don't throw the baby out with the bath water. There will always be compromises. You will always get imperfect measurements in your room. However, start with the best sounding subs and make it work, whether it's one, two or ten of them.   
Hello! Your point, which I am sure is debatable, is one I can sympathize with. I, too, want to make the best of a dipole sub setup.

I don't want ten of them -- life's too short -- but I would like to know what happens when you have more than two of them. Do things actually get worse? (i.e. is two the optimum number, as has been mentioned?) Or can we get better results with up to a maximum of four? If so, where to position them?

cheers

Early B.

Re: Multiple OB Subwoofers -- where to put them?
« Reply #12 on: 23 Feb 2020, 11:19 pm »
but I would like to know what happens when you have more than two of them. Do things actually get worse? (i.e. is two the optimum number, as has been mentioned?) Or can we get better results with up to a maximum of four? If so, where to position them?

Like I said, I have three (can't fit four), and three OB servo subs sound much better than two. I doubt seriously if adding a fourth sub will make it sound worse than two or three.

BTW -- my room size is nearly identical to yours (except my room is measured in feet, not meters  :lol:).

poseidonsvoice

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Re: Multiple OB Subwoofers -- where to put them?
« Reply #13 on: 24 Feb 2020, 02:13 am »
Thanks to you both for your additional, certainly most interesting, comments.

I have had another look at the Geddes material on bass, "Why Multiple Subs?" and "Optimal Bass Playback in Small Rooms", and I cannot find any reference to dipole (open baffle) subwoofers. It was a rewarding refresher for me, though.

The idea, that monopole subs are best suited to multiple deployment and dipole subs are best suited to stereo deployment, is intriguing.

What I am keen to see, though, is if anyone has done some modelling of dipole subs, so we can see the effect as multiple units are deployed in various locations.

Measurements from someone using dipole subs --multiple dipole subs -- would be fascinating and very helpful too.

I am mainly keen to find the best way to arrange multiple dipole subs. Discussion of which is the better type of subwoofer was not my intention.

thanks again

Arg,

My colleague has GR Research NX Otica's along with a pair of GR/Rythmik Triple 12 inch OB subwoofers, placed as recommended here in a stereo setup in a 15 foot wide and over 25 foot deep room with tall ceilings as well as a good number of treatments. We performed NUMEROUS measurements. The FR was choppy below 300Hz to say the least. No amount of changes to the DSP (i.e. EQ, gain, slope filters, etc...) helped to completely address the issue. The addition of (2) monopole sealed subwoofers very much flattened the frequency response curve. This was something he did on his own after he listened to my setup. Sadly I do not have any of those measurements, as I was just assisting.

Prior to my multiple monopole setup I also experimented with a pair of H-frame dual 12 inch OB subwoofers from GR Research that I had picked up used. Of course it sounded good and detailed but the measurements in the frequency response domain was also choppy (though the waterfall measurements were very clean and quick). It was most certainly subjectively better than any SINGLE boxed sub I had used. Although I thought of adding additional GR Research/Rythmik OB subs I went through the same question/answer session that you did. That was when I had discovered some of the reasons for why OB was sounding cleaner. They are directional and as such try to engage less modes, and this was evident in the waterfall measurements with their quicker decay times (less than 450msec in the region from 40Hz to 300Hz). I also found that it became inefficient to be using MORE OB subwoofers than just a stereo pair because at that point you just entered the multisub paradigm. Boxed subs have 360 degree radiation patterns which when used in multiples will engage MORE of the room modes and as long as they are not colocated (they should be distributed around the room), they will render a flatter response along with better/quicker waterfalls as well - you don't have that advantage with OB subs due to their directional radiation patterns. This was why I didn't add additional OB subwoofers. The other advantage I found was that multiple monopole subs were more dynamic at higher SPL's and sounded even cleaner. So as to not show favoritism, I stuck with 12 inch Rythmik drivers in sealed boxes for all my experiments.

The research that Geddes had done with OB subs is not available online. It was part of his thesis which he may have copies of. So you will have to contact him directly to be honest. He mentions it here and there in some whitepapers and on forums but you will have to dig for that information I suspect.

BTW, my previous post is credited to my readings of articles and comments (it wasn't to sound interesting as you said!) published by Earl Geddes, Floyd Toole, Sean Olive, Matthew Poes, David Griesinger,  etc...

https://www.audioholics.com/room-acoustics/stereo-bass

I think what you will find is that most people haven't tried multiple OB subs primarily because it is 1) Expensive since you can't just use 1 driver in each OB sub, the EQ requirements are too high, you must have at least 2 drivers per OB 'sub' module or the driver itself has to have a large piston area and large Xmax or both, and 2) There are space constraints with each OB sub, i.e. they must be "X" feet away from a wall boundary, so suddenly you have the OB subs sitting on your lap (!) and 3) If you are going to try multiple OB subs, it seems so wasteful when the advantages in engaging more room modes in an efficient manner to render a cleaner and flatter response may not be there due to narrower radiation patterns.

But if you do build multiple OB subs, please report back! And please ask your question on diyaudio specifically to see if anyone there has implemented and measured multiples of OB subs in a room.

Best,
Anand.

richidoo

Re: Multiple OB Subwoofers -- where to put them?
« Reply #14 on: 24 Feb 2020, 02:24 am »
Excellent insights, Anand! Thank you!

tnargs

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Re: Multiple OB Subwoofers -- where to put them?
« Reply #15 on: 24 Feb 2020, 05:43 am »
Like I said, I have three (can't fit four), and three OB servo subs sound much better than two. I doubt seriously if adding a fourth sub will make it sound worse than two or three.

BTW -- my room size is nearly identical to yours (except my room is measured in feet, not meters  :lol:).
OK, very interesting. And where have you positioned your three? Was that by necessity, or did you try some other positions that didn't work so well?

Early B.

Re: Multiple OB Subwoofers -- where to put them?
« Reply #16 on: 24 Feb 2020, 06:14 am »
OK, very interesting. And where have you positioned your three? Was that by necessity, or did you try some other positions that didn't work so well?

Mostly by necessity, practicality and common sense. I don't have a dedicated room. Oh, and there's the wife...

I'd love to measure my room, but would likely be very limited in ameliorating the issues. Can't do treatment, for example, and placement is what it is. I'm sure lots of audiophiles are in the same boat. You work with the hand you're dealt. During critical listening sessions, I move the furniture around for better sound.   

pankon

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Re: Multiple OB Subwoofers -- where to put them?
« Reply #17 on: 23 Apr 2020, 04:15 am »
OK, very interesting. And where have you positioned your three? Was that by necessity, or did you try some other positions that didn't work so well?

Apologies if I may seem to be diverging from the main question of the OP, but may I ask what's better, i.e. cleaner and faster: a) a single closed box sub or b) a single OB servo sub with two woofers?  Both may be placed anywhere in a room. Thank you and apologies again.

Tyson

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Re: Multiple OB Subwoofers -- where to put them?
« Reply #18 on: 23 Apr 2020, 04:28 am »
An OB sub placed between the speakers will be your cleanest/fastest option.

pankon

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Re: Multiple OB Subwoofers -- where to put them?
« Reply #19 on: 23 Apr 2020, 10:15 am »
An OB sub placed between the speakers will be your cleanest/fastest option.

After consulting with Danny, I will proceed with a single dual 12"-woofer subwoofer in an H cabinet, placed horizontally on the floor between the main speakers (Falcon LS3/5a), which are positioned on stands in nearfield, and far away from the back wall. I have two questions:

a) should both woofers be front-facing or one front and one back?
b) does it make any difference if the woofers are 8-Ohm or 16-Ohm?

Thanks