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Subwoofer Selection Criteria

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Some excellent points raised by folks here. To recap/pile on:

1. Match the size of the sub to the room. Too much sub in too small a space will sound terrible.

2. When you think you've found the right sub, buy two of them. It's not about adding bass/power, it's about placing two subs asymmetrically in a room to even out nodes.

3. Room correction software can be overwhelmed. It has much better odds of finding the sweet spot if you first do all of the old school stuff (graph and calculate cut-offs, do a sub crawl, and match levels) before employing it.

4. Subs shouldn't be heard or even felt. A sub is meant to cover, but not accentuate, the low frequencies that all bookshelf and most floor standing speakers cannot reproduce without dropping off SPL.
1. Well yes and no imo. A small space is sometimes all you have but in that case Dirac is your friend. It's better with a real bass trap but with only two great subs and Dirac you can do some magic even in small spaces. But it also depends on what kind of walls you have etc. If it's a small concrete room than yeah don't waste your time but there are usually options.

2. Rules of thumb are really dangerous route to take in acoustics.

4. Not sure what you mean here but I hope you mean that the subs should be so well blended into the front speakers that it sounds like it's just them playing but when the low notes hit then it's just all around you. I don't agree with that you should not feel the low notes. Not sure what you mean there? The stuff under 18Hz or so should only be felt - if you can hear it you have distortion. And if you don't feel it then you don't have the output capacity. Very few systems can reproduce the low notes loud enough for them to be felt. I requires a lot of cone area and room gain.
 
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pozz

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This is my goal for sure! With my current setup there is more of this as suppose to having all the subs up front and having an acoustically treated room with a giant bass trap. If you have any links to his advice I'd gladly read it as I haven't ever heard of this person.
His website is http://www.davidgriesinger.com/ It's mostly text and not easy to navigate, though.

The first attached paper, "Speaker placement, externalization, and envelopment in home listening rooms," is the one I was thinking of. The other two are for reference, if you're interested.
 

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pozz

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I think Geddes argues along these lines. In a «statistical» sense, where should you put your subwoofers to have them contributong to overall sound as independently as possible?
His research is really interesting. The guide on sub setup and paper on the effects of multiple subs are here: http://www.gedlee.com/Papers/papers.aspx I like that the principle is very simple.

Short version:
  1. Use three subwoofers.
  2. Place one sub along the front wall, one sub along the back wall and one sub at either side.
  3. One sub should be in a corner.
  4. One sub should be close to the main speakers.
  5. Do not place subs symmetrically (e.g., two in the front corners, or in the middle of opposing walls facing each other) since this will excite the same modes.
  6. Ideal placement can be played but it isn't crucial to be very precise.
 

GrimSurfer

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1. Well yes and no imo. A space is sometimes all you have but in that case Dirac is your friend. It's better with a real bass trap but with only two great subs and Dirac you can do some magic even in small spaces. But it also depends on what kind of walls you have etc. If it's a small concrete room than yeah don't waste your time but there are usually options.
Room correction software can mitigate nodes and nulls in certain parts of the room but they cannot eliminate them. My point, however, is that room correction should be applied after good speaker/sub placement (ie. bass crawl, room node calculations etc.).

What Dirac does isn't magic. Rather it uses frequency and time to help/help counter room effects. Those room effects don't change unless the room does, which is why acoustic treatments work so well.

QUOTE="audioBliss, post: 183457, member: 7592"]2. Rules of thumb are really dangerous route to take in acoustics.[/QUOTE]

Agree. And it works both ways. Run room mode calculations, do a sub crawl.

4. Not sure what you mean here but I hope you mean that the subs should be so well blended into the front speakers that it sounds like it's just them playing but when the low notes hit then it's just all around you. I don't agree with that you should not feel the low notes. Not sure what you mean there? The stuff under 18Hz or so should only be felt - if you can hear it you have distortion. And if you don't feel it then you don't have the output capacity. Very few systems can reproduce the low notes loud enough for them to be felt. I requires a lot of cone area and room gain.
That's exactly what I mean.

I don't see much relevance in seeking sub-sonic bliss. If you want that, buy a bone shaker. It's more efficient than trying to use energy travelling from one medium (air) to another (tissue) to achieve an effect.

The truth of the matter is that 99% of musical instruments have primary frequencies above 20 Hz. So, for my money, the sub with the best performance at this frequency and above is the winner.

Granted, certain (though not all) pipe organs can get down to 16 Hz. So anybody really into compositions featuring pipe organs operating in the sub sonic range might want a sub they can feel. Doing so, however, requires one of two things:

- a massive amount of power or
- coupling of the sub to its surroundings, which will almost certainly lead to rattles and buzzing at higher frequencies.
 

pozz

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Granted, certain (though not all) pipe organs can get down to 16 Hz. So anybody really into compositions featuring pipe organs operating in the sub sonic range might want a sub they can feel.
On top of that, there aren't many releases with sunstantial subsonic energy. No idea which mastering studio and which engineers can handle those kinds of lows, either. Anyone have any info on this?

And for subsonics, has anyone ever experimented with rotary subs?
 

blueone

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On top of that, there aren't many releases with sunstantial subsonic energy. No idea which mastering studio and which engineers can handle those kinds of lows, either. Anyone have any info on this?
The interest in sub-20Hz output seems to come entirely from the home theater crowd, in action/fantasy/science fiction movies. Movie foley is oftentimes synthesized or augmented through various means, so sub-20Hz sounds are probably easy. I'm not a fan of these genres myself, but I know a few folks in my neighborhood who have spent lavishly to feel the air shudder.
 
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andreasmaaan

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I admit I skipped directly to the section entitled “Dual Subwoofer Placement”, but I didn’t find any arguments or evidence in favour of asymmetrical sub placement there.

FWIW, my view is that - all else equal and assuming the subs are not flown - centred on opposing walls is the optimum location for dual subwoofers (which is ofc symmetrical).

This is based on harman’s research, which to my knowledge is the only approach that combines theory, modelling, and experimentation.

Geddes’ view is intellectually elegant but his research is limited compared to Harman’s. In other words, his an interesting approach that is nevertheless shown to be suboptimal by Harman’s research.

I would love to see a controlled study investigating Griesinger’s assertion that asymmetrical placement can lead to greater envelopmemt, but in the absence of this I don’t think we can treat what he says as more than speculation. He also acknowledges himself IIRC that asymmetrical placement is sub-optimal insofar as smoothness of response is concerned.
 

GrimSurfer

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I admit I skipped directly to the section entitled “Dual Subwoofer Placement”, but I didn’t find any arguments or evidence in favour of asymmetrical sub placement there.

FWIW, my view is that - all else equal and assuming the subs are not flown - centred on opposing walls is the optimum location for dual subwoofers (which is ofc symmetrical).

This is based on harman’s research, which to my knowledge is the only approach that combines theory, modelling, and experimentation.

Geddes’ view is intellectually elegant but his research is limited compared to Harman’s. In other words, his an interesting approach that is nevertheless shown to be suboptimal by Harman’s research.

I would love to see a controlled study investigating Griesinger’s assertion that asymmetrical placement can lead to greater envelopmemt, but in the absence of this I don’t think we can treat what he says as more than speculation. He also acknowledges himself IIRC that asymmetrical placement is sub-optimal insofar as smoothness of response is concerned.
The link was intended more as a basis for discussion on nodes, from which one could asset that certain symmetric layouts will be particularly troublesome.

Harman certainly has the facilities and budget. I'm concerned about how results from such a tightly controlled environment might apply to the very messy spaces in which we live (hodgepodge of refracting, reflecting and absorbing surfaces).

Geddes is an academic... and academia usually deigns to elegance. It would be interesting to see what Winer might say... he's not a loudspeaker guy but seems to have an excellent grasp on practical room acoustics.

Griesinger's approach raises the cost of smoothness of response. This is a fair cost but not as bad as what one would hear in a setting in which strong nodes and nulls exist. It might not be fair, however, to dismiss his views as unfounded then to take his acknowledgement of the smoothness issue as gospel.
 
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On top of that, there aren't many releases with sunstantial subsonic energy. No idea which mastering studio and which engineers can handle those kinds of lows, either. Anyone have any info on this?

And for subsonics, has anyone ever experimented with rotary subs?
https://www.kvalsvoll.com/blog/2018/04/15/dypbass-del-2-dypbass-i-musikk-og-film/

Spectrum plots from all kinds of music, and movies. Text is in Norwegian, a great language, may be difficult to understand for some, but the graphs shows everything.
 

GrimSurfer

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https://www.kvalsvoll.com/blog/2018/04/15/dypbass-del-2-dypbass-i-musikk-og-film/

Spectrum plots from all kinds of music, and movies. Text is in Norwegian, a great language, may be difficult to understand for some, but the graphs shows everything.
Looks like a great resource.

There's no doubt that the low frequency effects applied to movies are more expansive than occurs in music. The dynamic range is greater too.

Being a music guy, I put much greater effort into 2ch because the fidelity of music tends to be better. In my opinion anyway...
 

andreasmaaan

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Harman certainly has the facilities and budget. I'm concerned about how results from such a tightly controlled environment might apply to the very messy spaces in which we live (hodgepodge of refracting, reflecting and absorbing surfaces).
Fair point. I think it's fair to say that the study was restricted to rectangular rooms with no major openings (IIRC there was just a single door in the test room), and that the experimental verification of the modelled predictions could have been more robust.

OTOH, I don't see how the messier reality of most domestic living rooms would tend to favour asymmetrical approaches, as the primary modes are unlikely to be significantly affected by furnishings etc. Large doorways, openings, and sloped/curved walls/ceilings are probably another story, though...

It would be interesting to see what Winer might say... he's not a loudspeaker guy but seems to have an excellent grasp on practical room acoustics.
I agree :)

Griesinger's approach raises the cost of smoothness of response. This is a fair cost but not as bad as what one would hear in a setting in which strong nodes and nulls exist. It might not be fair, however, to dismiss his views as unfounded then to take his acknowledgement of the smoothness issue as gospel.
Ok, but I'm not basing my view on smoothness on what Griesenger says about it, but rather on the Harman research, which shows that symmetrical placements are most optimal for smoothness of response. I noted Griesenger's own statements on smoothness only to point out (1) that he himself acknowledged what Harman demonstrated and (2) that his approach is indeed not aimed at smoothness of response, but rather at creating a sense of envelopment.

Also, I didn't intend to dismiss Griesinger's views as unfounded (there clearly is a theoretical foundation), but rather to point out that they are (to my knowledge) experimentally unverified. Interestingly, even if Griesinger's approach turns out to be subjectively effective, this would in fact put the goals of smoothness and envelopment in conflict with each other.
 

watchnerd

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You really want to offload the rest of your speakers to lower distortion from them or else there is no point.
Doesn't REL disagree and advocate running the speakers full range with subs?

I don't have an absolutist position (it depends), but it would seem not all sub manufacturers agree.
 

watchnerd

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3 months after starting this thread, I finally ordered some new subs.

Aside from being busy with work, my wife is out of town for 2 weeks, so it's the perfect time for me to do crazy stuff with microphones and sweep tones in the living room that would normally cause eye-rolling.

Ordered 2 x Martin Logan Dynamo 1100X (12", 650 watts, built in Anthem Room Correction and smart phone app).

They should arrive on July 3 (fingers crossed) which means I can spend my 4th of July holiday playing with subs.
 

FrantzM

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Looking forward for your results Watchnerd.

I am a fan of Geddes and remain convinced that what happen in the low bass below 80 Hz is a steady state phenomenon. I am not familiar with Griesinger researches but he is respected in the small room acoustics field.
While REL the company, should have no place or mention in such a serious discussion ... they run parallel to Geddes views. Running the Mains Full Range add more low frequency generator in the room which allows to smooth out the peaks and valleys.. Geddes own speakers however don't do much below 60 Hz leaving the lows to subs ...

Now when it come to subsonics it is interesting how a full range speaker system brings an enhanced of realism to even pieces music that on paper don't have much bass.. Western Classical Chamber music for example. The difference is rather pronounced when the same piece is heard on a bass-limited monitor and a real serious full range speaker system one that can do 20 Hz to 20 KHz... I understand this is anecdotal and will try some time to do a Ray Dunzl-like analysis of a Chamber Music piece to see its spectrum

Fascinating stuff !
 
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3 months after starting this thread, I finally ordered some new subs.

Aside from being busy with work, my wife is out of town for 2 weeks, so it's the perfect time for me to do crazy stuff with microphones and sweep tones in the living room that would normally cause eye-rolling.

Ordered 2 x Martin Logan Dynamo 1100X (12", 650 watts, built in Anthem Room Correction and smart phone app).

They should arrive on July 3 (fingers crossed) which means I can spend my 4th of July holiday playing with subs.
Nice! I've been singing the new Dynamo's praises for months now, glad to hear someone else took the plunge. My two ML Dynamo 800x(s) are fantastic, and compliment my Ascend Acoustics Sierra 2 bookshelves amazingly well. BTW, the Anthem room correction setup only takes a few minutes each and is done entirely with the smartphone sitting in the main listening position.

Feel free to reach out if you have any questions about setup. I contacted Martin Logan about integrating 2 subs to make sure I wasn't missing anything. Both subs can be controlled by the apps, but adjusted separately (I named mine Martin and Logan in the app to keep them straight). You run the room correction separately and can adjust the levels independently. The app is responsive enough to where it's not really an issue.
 

watchnerd

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Did you get these setup? Curious to hear impressions...
Okay, started off with them between the two mains, at first in 'manual' (without the app), which defaults to a x-over way too high for my use case (120 Hz).

This, perhaps needless to say, was an over-powering amount of bass and didn't blend at all. But it definitely pressurized the room very tactically.

Switched to same location, but with app control. Ran ARC. Dialed the crossover down to the recommended starting point (per the manual) of 28 Hz (.7 of F3). 3rd-over crossover, -6 dB.

Definitely closer, but now not enough bass. Move the crossover up to 55 Hz...which was better than 28 Hz and 120 Hz. But imaging was suffering.

Move the subs to the two front corners. Ran ARC again. MUCH better.....imaging was restored, but there was still some blending issues, particularly on acoustic bass (which I play, so pick up on weirdness easily).

Switched to 50 Hz, -4 dB on right side, -3 dB on left side, and 4th order crossover.

I'd say I'm about 80% of the way there.

Choices left to examine:

1. Yeah, I need to run REW at some point.

2. Do I high pass the mains? This is actually hard to do without ruining my headphone set up.

3. Keep the mains ported? Or put in the plug to seal them up?
 

andreasmaaan

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1. Yeah, I need to run REW at some point.
Yeh :)

2. Do I high pass the mains? This is actually hard to do without ruining my headphone set up.
I would generally advise it. Especially if you're not going to HP filter them, and especially if your XO point will be as low as 50Hz, which is probably getting very close to the port tuning frequency.

But please remind me what your mains are?

3. Keep the mains ported? Or put in the plug to seal them up?
Will definitely be easier if they're plugged. In the absence of measurements, I'd say it would be almost the only way to do it.
 

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