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Making multiple sub-woofers work in practise

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Every now and then I get the urge to try multiple sub-woofers (as per Geddes, Welti et. al.) in an effort to smooth in-room bass response across a few seats which, shortly thereafter, is replaced with a tinge of disappointment. My main issue is that the need to avoid localisation of sub-woofers results in a steep low-pass around 80Hz so whilst the <80-100Hz region is addressed the 100 to 200-300Hz region remains problematic. Perhaps the answer is to further reduce the volume of the sub-woofers whilst increasing the low-pass x/o frequency but I’m not sure. I’ve read a few sites on the topic but it’d be good to hear from anyone who has got this type of set-up working.   

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Noted system set-up man Jim smith has (more than a few) a few comments on multiple sub-woofers in a music system..  One is if you cannot have two subs don't bother until you can afford two.  Another is, if the listening position and the main speakers are not positioned for the smoothest bass response then sub-woofers will never integrate properly..

Jim Smith is writing a series on sub-woofers on the PS Audio site, go to :  http://www.psaudio.com/copper-magazine/    and start reading from issue 14.  Also go to Jim's site : www.getbettersound.com

Pt3:Finding the anchor for the best Dynamics, Presence & Tone

Pt4: Why a RTA is useful, even if you are not technical – and how to get   a good one nearly free

Pt5: Sub set-up info you probably haven’t seen (but you should)

Pt6: X-over freq. vs. level; location, location, location

Pt7: The role of EQ and room correction when working with subs

Pt8: A true story with a good outcome and lots of documentation

Another good resource is Paul Spencer articles on bass and sub-woofers

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Thanks - I'll take a look. My thinking has always been that stereo subs co-located would be excellent if one has the luxury of a dedicated room with a single listening position. The thought being that this setup would allow for optimal integration between the speakers and subs. If, though, these constraints aren't met then I'd guess that best alternative would be to address the various issues via smoothing via multiple subwoofers

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On 10/21/2016 at 10:11 PM, zydeco said:

Every now and then I get the urge to try multiple sub-woofers (as per Geddes, Welti et. al.) in an effort to smooth in-room bass response across a few seats which, shortly thereafter, is replaced with a tinge of disappointment. My main issue is that the need to avoid localisation of sub-woofers results in a steep low-pass around 80Hz so whilst the <80-100Hz region is addressed the 100 to 200-300Hz region remains problematic. Perhaps the answer is to further reduce the volume of the sub-woofers whilst increasing the low-pass x/o frequency but I’m not sure. I’ve read a few sites on the topic but it’d be good to hear from anyone who has got this type of set-up working.

 

I got your PM.  I guess it makes the most sense to reply here.  As you're aware, the "classic" multi-sub approach of Geddes and of Welti and Devantier requires that the subs be in mono mode.  In general, the subs can be located in just about any practical position, which may be quite distant from the main speakers.  Both of theses properties work against using the multi-sub approach much above, say, 80-100 Hz as you've mentioned.  One might push this a bit by using 8th-order Linkwitz-Riley LPFs on the subs.

 

Above that, the only workable solution I'm aware of (and I have not tried it) is to use some variant of the mid-bass module (MBM) idea.  For two-channel, these would be in stereo mode, with each one located close to its corresponding main speaker.  One concern is the Allison effect, where the perpendicular distance from a forward firing woofer, back to the wall is 1/4 wavelength.  My main speakers are placed so that the center of the front baffle is about 27" from the wall behind them.  To find the Allison effect frequency of this setup, look at:

 

c = 1126 * 12 inches/sec

L = 27 inches

lambda / 4 = c / 4f

27 = 1126 * 12 / 4f

f = 1126 * 12 / (4 * 27) = 125 Hz

 

I do get a measured dip in the frequency response of about 10 dB right at this frequency.  One solution I've seen is to use the MBM as a speaker stand, and have it facing backwards towards the wall, such that its distance to the wall is much less than that of the main speaker's woofer.  This can be done so that its Allison effect frequency is greater than the maximum frequency at which the MBM operates, eliminating the Allison effect dip of the MBM.  The MBM and the main speaker would be sharing output in the 80 Hz - 300 Hz range.  The distance difference from the seating position means that each main speaker must be delayed relative to its MBM.  Also, the integration of the main speakers and MBM as a function of frequency is not obvious, since they are sharing output over this frequency range.

 

I wrote an article on MBM integration which describes a design for a shelving filter intended for main speakers that's meant to work together with a 4th-order Linkwitz-Riley LPF on the MBM to integrate a main speaker and MBM.  I don't think this would work with, say, mixing sealed and vented.  I suspect that the more similar the MBM and main speaker woofer are, the better for integration.

 

Multi-Sub Optimizer (MSO) has this shelving filter available.  It's called a "fourth-order Linkwitz-Riley shelf".  One could use the software by defining a configuration that consists of, say, only the left speaker and left MBM.  It could be used to determine the optimum delay of main speaker relative to MBM.  A quirk is that delays aren't allowed for main speakers, but that can be worked around using negative delay for the MBM.  There's no real way to optimize the combined response of MBM and main speaker at multiple listening positions with this approach though, as there aren't enough degrees of freedom to do it.  A second configuration might be used to integrate right main speaker with MBM.  Once integration of each main speaker and MBM is accomplished, the system would be re-measured with the MBMs, and MSO could be used to integrate the multiple subs with the main speaker / MBM combination below about 100 Hz.

 

I've never tried this though.  It's just something I thought of as a possible answer to your question.

Edited by andyc56

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9 minutes ago, andyc56 said:

 

I got your PM.  I guess it makes the most sense to reply here.  As you're aware, the "classic" multi-sub approach of Geddes and of Welti and Devantier requires that the subs be in mono mode.  In general, the subs can be located in just about any practical position, which may be quite distant from the main speakers.  Both of theses properties work against using the multi-sub approach much above, say, 80-100 Hz as you've mentioned.  One might push this a bit by using 8th-order Linkwitz-Riley LPFs on the subs.

 

Above that, the only workable solution I'm aware of (and I have not tried it) is to use some variant of the mid-bass module (MBM) idea.  For two-channel, these would be in stereo mode, with each one located close to its corresponding main speaker.  One concern is the Allison effect, where the perpendicular distance from a forward firing woofer, back to the wall is 1/4 wavelength.  My main speakers are placed so that the center of the front baffle is about 27" from the back wall.  To find the Allison effect frequency of this setup, look at:

 

c = 1126 * 12 inches/sec

L = 27 inches

lambda / 4 = c / 4f

27 = 1126 * 12 / 4f

f = 1126 * 12 / (4 * 27) = 125 Hz

 

I do get a measured dip in the frequency response of about 10 dB right at this frequency.  One solution I've seen is to use the MBM as a speaker stand, and have it facing backwards towards the wall, such that its distance to the wall is much less than that of the main speaker's woofer.  This can be done so that its Allison effect frequency is greater than the maximum frequency at which the MBM operates, eliminating the Allison effect dip of the MBM.  The MBM and the main speaker would be sharing output in the 80 Hz - 300 Hz range.  The distance difference from the seating position means that each main speaker must be delayed relative to its MBM.  Also, the integration of the main speakers and MBM as a function of frequency is not obvious, since they are sharing output over this frequency range.

 

I wrote an article on MBM integration which describes a design for a shelving filter intended for main speakers that's meant to work together with a 4th-order Linkwitz-Riley LPF on the MBM to integrate a main speaker and MBM.  I don't think this would work with, say, mixing sealed and vented.  I suspect that the more similar the MBM and main speaker woofer are, the better for integration.

 

Multi-Sub Optimizer (MSO) has this shelving filter available.  It's called a "fourth-order Linkwitz-Riley shelf".  One could use the software by defining a configuration that consists of, say, only the left speaker and left MBM.  It could be used to determine the optimum delay of main speaker relative to MBM.  A quirk is that delays aren't allowed for main speakers, but that can be worked around using negative delay for the MBM.  There's no real way to optimize the combined response of MBM and main speaker at multiple listening positions with this approach though, as there aren't enough degrees of freedom to do it.  A second configuration might be used to integrate right main speaker with MBM.  Once integration of each main speaker and MBM is accomplished, the system would be re-measured with the MBMs, and MSO could be used to integrate the multiple subs with the main speaker / MBM combination below about 100 Hz.

 

I've never tried this though.  It's just something I thought of as a possible answer to your question.

 

Thanks for the comprehensive response! I'll take a look at the document but, basically, the mid-bass module is a second mid-bass unit that is located between the main speakers and front wall such that it has a much higher cancellation frequency. And the shelving filter you mention is designed to ensure that the combined response sums to flat. Is this the concept?

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18 minutes ago, zydeco said:

Thanks for the comprehensive response! I'll take a look at the document but, basically, the mid-bass module is a second mid-bass unit that is located between the main speakers and front wall such that it has a much higher cancellation frequency. And the shelving filter you mention is designed to ensure that the combined response sums to flat. Is this the concept?

 

Yes, that's exactly right.  The summation of the filter outputs is shown in Figure 1 of the linked article.

 

In the Linkwitz-Riley LPF/HPF combination, the LPF and HPF have exactly the same phase shift vs frequency if their cutoff frequencies are the same.  The same is true with the shelving filter and corresponding LPF in Figure 1.

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On 10/22/2016 at 2:11 PM, zydeco said:

My main issue is that the need to avoid localisation of sub-woofers results in a steep low-pass around 80Hz so whilst the <80-100Hz region is addressed the 100 to 200-300Hz region remains problematic. 

 

You could increase absorption in the 100 Hz to 300 Hz frequency range to improve the performance of the mains.

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3 hours ago, svenr said:

 

You could increase absorption in the 100 Hz to 300 Hz frequency range to improve the performance of the mains.

 

Yes. Or, potentially, move the speakers close to the back wall to increase the cancellation frequency (but I'd guess that this will impact the imaging). The main point, for me at least, is that the multi-sub approach represents a big investment in funds & time to address issues over a relatively small frequency range (40-80Hz) when at least some of the issues might be addressed via DSP. 

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On 10/26/2016 at 5:00 PM, zydeco said:

 

Yes. Or, potentially, move the speakers close to the back wall to increase the cancellation frequency (but I'd guess that this will impact the imaging).  

That depends on whether there's any treatment behind/beside the speakers and the radiation pattern of your mains...

...my recollection is you have Unity Horns??

If you apply the heavy toe in approach (eg Geddes), imaging shouldn't be affected (even with "normal" toe-in, the Unity's should be fine).

 

On 10/26/2016 at 1:52 PM, svenr said:

 

You could increase absorption in the 100 Hz to 300 Hz frequency range to improve the performance of the mains.

I would do this regardless of moving the speakers closer to the back/side walls.

IME some absorption in this range cleans up the mid bass significantly, and EQ in this freq range is too position dependant.

 

On 10/26/2016 at 5:00 PM, zydeco said:

The main point, for me at least, is that the multi-sub approach represents a big investment in funds & time to address issues over a relatively small frequency range (40-80Hz) when at least some of the issues might be addressed via DSP. 

I'm a self confessed bass nut, so 40Hz doesn't cut it for me.

20Hz - 80Hz is 2 octaves - your range of 40 - 80Hz is still an octave - that's not a "relatively small" frequency range.

I'd be happy to compromise 10kHz - 20kHz before I'd compromise 40Hz - 80Hz - they're both a single octave.

 

Issues between 40-80Hz do lend themselves to addressing with EQ, as absorption at these frequencies gets too large. But cleaning up the 100Hz-300Hz freq range with some treatment first will make a big difference.

If your room is lightly constructed, you may not have any acoustic issues 40-80Hz that need EQ.

 

Being a bass nut, I regard a sub as essential in any system. Good integration is part of the process.

Adding a 2nd sub does complicate the integration, but once achieved will provide smoother bass across multiple seats in typical rooms. If good bass at only 1 listening position is required, then a single sub is fine.

 

IMO, DSP makes sub integration so much easier that it basically becomes essential (I wouldn't know where to start trying to integrate a sub and especially multiple subs, without DSP) - and a measurement rig.

 

Again IMO, for the best integration, the DSP needs to extend to your mains, as almost always you will need to delay your mains to allow the sub or subs to "catchup", because the sub low pass filters create more delay than the mains high pass filters (unless all subs are much closer to the LP than the mains - unlikely).

Having multiple subs adds complexity, as you have to time align your mains with the "slowest" (or most delay) sub, and apply appropriate delay to the other subs according to how far from the listening position they are.

 

With a measurement rig and free software like REW or Holm Impulse, this is not difficult - but it is time consuming.

You take individual sub and mains measurements at the listening position and compare impulse responses, and adjust delay as required on each (based on time aligning the peak on the impulse) - obviously more complicated the more subs you have.

 

Following time alignment, level adjustment between mains and sub or subs is the next step...no-one said great integration was easy...

 

My current setup only has a single sub, and I've spent many hours (days) getting it right.

I'm about to build a 2nd sub - just to experiment - my setup provides enough DSP flexibility for the extra sub, but I'm sure it will take days/weeks of tweaking to get it right.

 

cheers

Mike

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So, re-reading this thread, it seems as if there are wide range of suggested methods:

 

  1. Jim Smith - Stereo subwoofers, typically located behind the main speakers as per mid-bass module, with focus on getting the listening position right (close to back wall)
  2. Geddes - (Quasi-) randomly located subwoofers with gain and phase varied to get an overall smooth response. Option for overall EQ once variation is reduced.
  3. @andyc56 (Geddes V2)  - Algorithm run that does PEQ on the individual subwoofers with objective function being to have an overall flat response
  4. Variant of 3 - PEQ applied on individual subwoofers to get flat response at listening position with, then, overall EQ applied to the combined set of sources.
  5. Strategic Placement - Place subwoofers at specific locations to deal with specific issues; e.g., MBM or axial mode

 

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With regard to method 3, I have been experimenting with AndyC's MSO with good results.

 

My room is far from ideal, being non symmetrical, open at one end, glass wall the other and we sit across the room with the couch on the rear wall (about 300mm away).

 

I am using three subs, two are SVS PC13's, one with a Bash amp the other is a Sledge amp, thus they are not identical.  The third sub is a 4 x 12" driver couch kicker which sits behind couch. 

 

Whilst this is still a work in progress, I am very happy with the results to date -from a listening perspective, not just measurements.

 

MSO has a bit of a learning curve, however I found that the following link helped simply some if it (obviously some of the steps should be disregarded if an 88A is not being used).

58fc144ddd2b1_IndsubsatMLP.jpg.b9f17c3359ad452d4eb1247a67f0a165.jpg58fc145a57564_3couchseatspreMRO.jpg.c1e2ef0bea471e4737712ff585f2949b.jpg58fc146241d48_3couchseatspostMRO.jpg.781e849b18fdd5e67b1b731d404a43b3.jpg

 

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On 22/10/2016 at 3:25 PM, zydeco said:

Thanks - I'll take a look. My thinking has always been that stereo subs co-located would be excellent if one has the luxury of a dedicated room with a single listening position. The thought being that this setup would allow for optimal integration between the speakers and subs. If, though, these constraints aren't met then I'd guess that best alternative would be to address the various issues via smoothing via multiple subwoofers

 

zydeco, with just one main listening position as I have, id be surprised if suggestions from welti's wouldn't  hit the spot. i.e. 

 

https://www.harman.com/sites/default/files/white-paper/12/11/2015 - 06%3A12/files/multsubs.pdf

 

one sub in front centre with eq. or two subs one main up front mid room, one secondary at the back mid room.

 

is there reason to run xover so high ? for localisation that wouldn't help around 100hz though quality of sub and other anomalies can also impact localistion. I run 40hz and below as my mains have plenty have output down to their anyways. one sub mid front wall with eq(minimal - little to none required) back to main listening position is quite sufficient i have found for pretty smooth response 

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6 hours ago, mcb said:

With regard to method 3, I have been experimenting with AndyC's MSO with good results.

 

My room is far from ideal, being non symmetrical, open at one end, glass wall the other and we sit across the room with the couch on the rear wall (about 300mm away).

 

I am using three subs, two are SVS PC13's, one with a Bash amp the other is a Sledge amp, thus they are not identical.  The third sub is a 4 x 12" driver couch kicker which sits behind couch. 

 

Whilst this is still a work in progress, I am very happy with the results to date -from a listening perspective, not just measurements.

 

MSO has a bit of a learning curve, however I found that the following link helped simply some if it (obviously some of the steps should be disregarded if an 88A is not being used).

58fc144ddd2b1_IndsubsatMLP.jpg.b9f17c3359ad452d4eb1247a67f0a165.jpg58fc145a57564_3couchseatspreMRO.jpg.c1e2ef0bea471e4737712ff585f2949b.jpg58fc146241d48_3couchseatspostMRO.jpg.781e849b18fdd5e67b1b731d404a43b3.jpg

 

that's a great result - well done!

 

Mike

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I am also using a pair of subs. One front centre, one rear centre. 

Initially setup as a source/sink config. Ie rear out of phase and delayed.

I then used MSO to improve the response, and it has successfully reduced the length room mode.

This setup is much better than the stereo front or mid wall subs setup

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17 hours ago, almikel said:

that's a great result - well done!

 

Mike

 

Thanks Mike.

 

A couple of other points for anyone considering using MSO

 

i) I used 5 locations, the three couch positions and also the two mid-points

ii) MSO contains options for subs only, or subs and mains.  I have used the subs only option.

iii) At Optimisation Options, I used the Best match of MLP to other listening position option, as final correction will be done at the AVR or 88A.

iv) Experiment with differ target levles and also which position is to be used as the MLP, as changing these can can result in different solutions and some look better than others.

v) run MSO for a considerable period of time ( I use 90 mins), as the default is 0.5min and the results after a longer period are normally quite different to the 0.5min result.

 

Edited by mcb
Added point iii)

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On ?23?/?04?/?2017 at 10:51 AM, mcb said:

With regard to method 3, I have been experimenting with AndyC's MSO with good results.

 

My room is far from ideal, being non symmetrical, open at one end, glass wall the other and we sit across the room with the couch on the rear wall (about 300mm away).

 

I am using three subs, two are SVS PC13's, one with a Bash amp the other is a Sledge amp, thus they are not identical.  The third sub is a 4 x 12" driver couch kicker which sits behind couch. 

 

Whilst this is still a work in progress, I am very happy with the results to date -from a listening perspective, not just measurements.

 

MSO has a bit of a learning curve, however I found that the following link helped simply some if it (obviously some of the steps should be disregarded if an 88A is not being used).

58fc144ddd2b1_IndsubsatMLP.jpg.b9f17c3359ad452d4eb1247a67f0a165.jpg58fc145a57564_3couchseatspreMRO.jpg.c1e2ef0bea471e4737712ff585f2949b.jpg58fc146241d48_3couchseatspostMRO.jpg.781e849b18fdd5e67b1b731d404a43b3.jpg

 

 

 

Murray

 

Thanks. That's a great result and I'm inspired to give it a go when time permits. My take on all this is that we should be thinking about 20 to 100Hz and 100 to 300Hz differently. The former might be best dealt with via multiple subwoofers whereas the latter is best dealt with via a combination of speaker / listening position and acoustic treatment.

 

Regards

Andrew

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On 4/23/2017 at 10:29 AM, zydeco said:

So, re-reading this thread, it seems as if there are wide range of suggested methods

 

They're all basically the same method .... but each one just takes a slightly different view of what is the best possible practical compromise.

 

(The method)

 

Determine the bandwidth requirements of the subwoofers, and number of desired subwoofers

Place the subwoofer(s) in the room in an optimised position

EQ the response of the subwoofer(s) to the desired target response

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Yes, another question on bass. I've noticed that a far few people are advocating high-pass to the mains at ~80Hz with a fleet of (identical) subwoofers

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Yes, another question on bass. I've noticed that a far few people are advocating high-pass to the mains at ~80Hz with a fleet of (identical) subwoofers. This seems to be the standard in HT even with bass capable main speakers. I'm guessing that the rationale is that it just simplifies integration (i.e., avoid different stereo signal and phase / delay from main speakers) but don't know. What do the bass experts say?

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MSO easily compensates for dissimilar subs. You can limit the gain for the smaller subs. Delay between subs and mains calculated. Not sure it has been mentioned, but MSO is superb at evening the bass response across different listening positions.

 

Much more difficult to adjust gains, delays without MSO. Evening bass response takes patience and lots of trying different sub placements.  Hence, people suggest using same subs to make things easier.

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if you have the DSP tools to individually manage multiple subs (gain/delay/EQ) I see no reason to use identical subs.

@Paul Spencer suggests a "heavy lifter" sub + other "fill in" but less capable subs.

Geddes proposes multiple dissimilar subs.

Toole discusses "bass management" of multiple subs with variable delay using a mono signal to drive them all.

@Paul Spencer also suggests using your mains (where they are capable) to add additional bass sources (ie not Crossing your mains to your subs, but allowing the mains (assuming they're capable) to go lower than the low pass on the subs)

 

This all adds to integration complexity, but achievable with flexible DSP and a measurement rig.

 

cheers

Mike

 

 

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the risk with two identical subs especially with say front back harman arrangement is they neutralise either other. end up with a sucky result. its why in this arrangement too it is recommended you go one big ba@stard up front as master and the one down back is really a smaller capability sub acting as slave to fill in gaps. 

 

its also not as clear cut as things such as rooms can have quite a few variables, there are no text book or even similar rooms and two subs can be double trouble i.e. twice as much in peaks and twice the depth in nulls from just running one if not careful. so positioning is key with dual subs, you can just expect eq / dsp to be the magic pudding with subs just where you think they should be.

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Ideally you should keep in mind that many things change, once you know the specific acoustic characteristics of your room. As an example, you may have read it's beneficial to overlap the mains and the subs. If you have just one sub, that means you are now combining 3 sources, which can smooth the response in the overlap region. The benefit of doing so is quite specific. That means it's only a good idea in the precise instance where it provides the intended benefit. Otherwise, there is no benefit and at the same time, you have added a bottleneck in terms of headroom.

Another example is the Harman configuration. It works well based on the chosen assumptions involved in the original study. They were looking for the greatest consistency over means seats in a multi-row rectangular room. However, when I work with clients and ask about their seating arrangements, quite often they want to focus on one or two prime seats. If they can get a good result with one or two subs in practical locations, they are often happy with that. With this in mind, actual tests in the room often lead to other sub positions working better than front and back midwall positions. It's not a problem with the Harman paper but rather the reality involved in applying one configuration to a specific room with different priorities and conditions.

Typically you won't run the subs higher than 80 Hz, so the benefits of multiple subs are confined to two octaves. The actual experience is greater than this implies. If the bass is right, everything else improves.

The low midrange region, from say 80 - 500 Hz is a separate consideration. Quite often studios have this region better under control, with a nearfield setup, some consideration given to boundary interference and treatment that is effective here. When I measure studios, the response is usually much flatter than you ever see in a listening room. Often things in a room, whether dedicated acoustic panels or furnishings, aren't very effective in this range.

 

Here, you aren't as free with placement as with subs. Maintaining a good relationship with the midrange along with a coherent stereo image is key. This will usually be the highest priority. It's a good idea to trial some different positions. See how they measure. See how this impacts the sound stage. It's a trial and error process. Once you've found the compromise you like best, it's then a matter of looking at treatment and calibration.

 

When you have a horn system with dramatic dynamic range capability, if you get these things wrong, it can fail in a big way. When you get to have a listening session and turn it up, a not quite right calibration can stick out and get ugly! But when you get it right and it all comes together, the experience goes to another level ... and you can get carried away, flying high as a kit in your own little musical experience ... then you hear a banging sound. It strikes you as startlingly realistic and life-like. For good reason - it's the police at the door!

 

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Ideally you should keep in mind that many things change, once you know the specific acoustic characteristics of your room. As an example, you may have read it's beneficial to overlap the mains and the subs. If you have just one sub, that means you are now combining 3 sources, which can smooth the response in the overlap region. The benefit of doing so is quite specific. That means it's only a good idea in the precise instance where it provides the intended benefit. Otherwise, there is no benefit and at the same time, you have added a bottleneck in terms of headroom.

Another example is the Harman configuration. It works well based on the chosen assumptions involved in the original study. They were looking for the greatest consistency over means seats in a multi-row rectangular room. However, when I work with clients and ask about their seating arrangements, quite often they want to focus on one or two prime seats. If they can get a good result with one or two subs in practical locations, they are often happy with that. With this in mind, actual tests in the room often lead to other sub positions working better than front and back midwall positions. It's not a problem with the Harman paper but rather the reality involved in applying one configuration to a specific room with different priorities and conditions.

Typically you won't run the subs higher than 80 Hz, so the benefits of multiple subs are confined to two octaves. The actual experience is greater than this implies. If the bass is right, everything else improves.

The low midrange region, from say 80 - 500 Hz is a separate consideration. Quite often studios have this region better under control, with a nearfield setup, some consideration given to boundary interference and treatment that is effective here. When I measure studios, the response is usually much flatter than you ever see in a listening room. Often things in a room, whether dedicated acoustic panels or furnishings, aren't very effective in this range.
 
Here, you aren't as free with placement as with subs. Maintaining a good relationship with the midrange along with a coherent stereo image is key. This will usually be the highest priority. It's a good idea to trial some different positions. See how they measure. See how this impacts the sound stage. It's a trial and error process. Once you've found the compromise you like best, it's then a matter of looking at treatment and calibration.
 
When you have a horn system with dramatic dynamic range capability, if you get these things wrong, it can fail in a big way. When you get to have a listening session and turn it up, a not quite right calibration can stick out and get ugly! But when you get it right and it all comes together, the experience goes to another level ... and you can get carried away, flying high as a kit in your own little musical experience ... then you hear a banging sound. It strikes you as startlingly realistic and life-like. For good reason - it's the police at the door!

 

Thanks. My situation is that like some others you mentioned I'm most interested in one or two adjacent seats. The other objective is to alleviate the main speakers of main bass for more headroom and less distortion etc. So, to paraphrase you're response, in this situation one (or perhaps two) sub with good EQ might solve the problem. And, consider a high pass on the mains because this will provide more headroom and might simplify integration. The caveat being of course to measure, measure, measure. Is this right?


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On 8/19/2017 at 7:02 AM, zydeco said:


Thanks. My situation is that like some others you mentioned I'm most interested in one or two adjacent seats. The other objective is to alleviate the main speakers of main bass for more headroom and less distortion etc. So, to paraphrase you're response, in this situation one (or perhaps two) sub with good EQ might solve the problem. And, consider a high pass on the mains because this will provide more headroom and might simplify integration. The caveat being of course to measure, measure, measure. Is this right?


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You are starting with an ideal situation here, in terms of getting the ideal bass performance. You have a pair of large 18" woofers that could easily cover 30 Hz with some EQ. Once you start taking measurements, you can see if they will help with a smoother midbass response. This might not be on the table, since you might do just as well with a pair of subs in that range. Then it's a simple decision and a simpler set up.

Another factor is the EQ requirements to achieve extension. Room gain and room modes are factors here. How low can your woofers go without boost? Or, how low can you go with a modest amount of boost that still retains enough headroom?

 

The real key here is to use the data to help you find the best solution.

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