Subwoofer Selection Criteria

[Biblob]

Do you mean high pass the monitor at 80 Hz and low pass the sub at 80 Hz?

I mean the former, yes.
Would it be problematic because of the porting?

 

[DonH56]

The manual of my B&W PV1d sub suggests to choose a crossover frequency at the -6dB point of the main speakers and choose a 12dB 2nd order slope for sealed main speakers (and 180 degree phase) and 24 dB 4th order slope (and 0 degree phase) for ported main speakers. This is what I did , and it worked out exactly right, both with my Quad 2805s (with a 4th order slope on the stats to have them least affected by the dynamic sub) and in an experiment with my Harbeth P3ESRs. This is, of course, with the main speakers playing full range without any high pass filtering.

That assumes the sub provides enough energy to "fill in" the -6 dB "hole" and that depends upon placement of the mains, sub(s), listener, and characteristics of the room. Phase also depends upon placement and the phase characteristics of your speakers. I usually measure and dial in my system's response using step (time) and frequency response. But I have already stated my experience is better sound is achieved without the mains running full-range. Some like that, but it is harder to dial in, and places undue burden on the mains -- again, my experience, my measurements, my preferences, so need not apply to anyone else. But do be aware B&W's guidance is fairly generally, and so if you change things like speaker or listener positions (or get new sub or speakers), you may find different optimum settings.

A steeper slope is often recommended for ported speakers as the woofer becomes "unloaded" at and below the port frequency. Below that, speaker distortion usually rises rapidly and output drops, so it makes no sense to be driving them harder. Overdriving down low leads to things like port noise and "chuffing". Sealed speakers roll off more gradually and do not "unload" the driver below their -3 dB (or whatever) frequency.

 

[watchnerd]

Just by the spec sheet, as was the B&W suggestion. The result was 33 Hz for the Quad 2805s and 45 Hz for the P3ESRs. In short, as per REL theory, only filling in the very lowest frequencies.
In addtion, the sub's manual writes: 'If the specification of your speakers only quotes a –3dB frequency, multiply this by 0.6 for closed-box systems and by 0.7 for vented-box (reflex) systems to get a close enough approximation to the –6dB frequency.'

Here is what Martin Logan says in the Dynamo X-series manual:

"As a general rule, the Low-Pass Filter should be set at a value approximately equal to (or below) 70% of your main speaker’s lowest
frequency response. For example, your speaker’s frequency response goes down to 43Hz. 70% of 43Hz equals 30.1, so you should set the subwoofer’s low pass filter to 30Hz."

It doesn't explicitly say if that 70% of F3 is based on running full range or after high passing the mains.

70% of F3 is probably pretty close to -6 dB in many cases.

 

[DonH56]

I'll just leave it at I disagree. But no harm in trying and seeing if that works best for you.

 

[watchnerd]

I'll just leave it at I disagree. But no harm in trying and seeing if that works best for you.

I could simply be expediency:

It might be much easier for a sub manufacturer to explain to a user how to add bass to his existing sound, when compared to telling him how to calculate a high pass in such a way that doesn't ruin things.

In other words, it may not be optimal, but it's probably easier for many to do reasonably right.

 

[andreasmaaan]

I could simply be expediency:

It might be much easier for a sub manufacturer to explain to a user how to add bass to his existing sound, when compared to telling him how to calculate a high pass in such a way that doesn't ruin things.

In other words, it may not be optimal, but it's probably easier for many to do reasonably right.

I considered this too, but then I thought how many factors would have to come together for this to work:

1. Manufacturer correctly specifies the F3
2. 70% of F3 is the -6dB point
3. Speaker roll-off closely resembles the filter slope used by the sub’s LPF
4. Etc...

Just can’t imagine that it’s more likely for all these factors to miraculously combine successfully, than for a HPF one octave or more above the speaker’s F3 with the same slope as the sub’s LPF at the same frequency to integrate reasonably well.

 

[watchnerd]

I considered this too, but then I thought how many factors would have to come together for this to work:

1. Manufacturer correctly specifies the F3
2. 70% of F3 is the -6dB point
3. Speaker roll-off closely resembles the filter slope used by the sub’s LPF
4. Etc...

Just can’t imagine that it’s more likely for all these factors to miraculously combine successfully, than for a HPF one octave or more above the speaker’s F3 with the same slope as the sub’s LPF at the same frequency to integrate reasonably well.

Oh, it may not actually lead to better outcomes.

But the decision tree is simpler:

"Hey my speakers sound like they always do, but now with too much bass / not enough bass / just right bass."

vs.

"Hey my speakers don't sound like they used to....and the bass is different, too..what to do?"

 

[andreasmaaan]

Oh, it may not actually lead to better outcomes.

But the decision tree is simpler:

"Hey my speakers sound like they always do, but now with too much bass / not enough bass / just right bass."

vs.

"Hey my speakers don't sound like they used to....and the bass is different, too..what to do?"

Fair point

 

[watchnerd]

So given the following situation, which do you think would be better:

Listening room: 22' x 17', 10-15' sloping ceiling. Room is semi-open, as there are 3 permanent openings: 2 on left wall, one on back. Listening position is 17-18' from front monitor speakers (Dynaudio Contour 20).

Would it be better to go with:

2 x 10" subwoofers, which will fit concealed behind my LP storage, about 1/3 into the room on each side, *between* the mains

or

2 x 12" subwoofers, in the left and right corners, *outside* the mains

Cost isn't really the deciding factor...it's more about what I can WAF-blend where. The smaller 10" subs are easier to hide between the speakers, while the 12" are too big for that and would have to go in the front corners.

Thoughts?

 

[Willem]

Since your main speakers already go pretty low, adding very small subs may not add that much. As for location, I discussed this with the engineers of my Antimode 8033 and their advice was to push the sub(s) well into the corner(s) of the room, for maximum corner reinforcement and shallowest dips. Peaks would be bad, but the Antimode would cure those.

 

[watchnerd]

Since your main speakers already go pretty low, adding very small subs may not add that much. As for location, I discussed this with the engineers of my Antimode 8033 and their advice was to push the sub(s) well into the corner(s) of the room, for maximum corner reinforcement and shallowest dips. Peaks would be bad, but the Antimode would cure those.

This true...in port-open mode 39 Hz, in sealed-port mode, 53 Hz.

Would it be better then to go 2 x 15"?

 

[Willem]

The size of the drive units is not the only thing that matters, of course. Cabinet size, amplifier power and internal electronic equalization make a big difference as well. All subs have such internal equalization to boost the lowest frequencies. The danger here is increased distortion, so driver design matters, as does fancy electronics to keep that distortion in check at higher volume levels. My B&W PV1d (with opposing 10 inch drive units) can reach very low (7 Hz), but only at quite low volume. Play it louder, and the electronics start cutting the lowest frequencies to limit distortion. So the answer also depends on desired volume, type of music (is there a lot of loud and deep bass), and room size. Hence, it will not do nuclear explosions and the like, but with most music it does what needs to be done in a fairly large room (40 sq m sitting room and open plan layout with 20 sq m dining room and 15 sq m study. US rooms, of course, are often rather larger. I chose this model because of its small size and good looks in a modern interior, and because its design with dual opposed drive units favours clean sound over very deep bass. That at least is the theory. Auditioning subs at a dealer is even less informative than auditioning main speakers in a room that is not yours. My only planned upgrade is for a second one. It is a bit overpriced so I am on the lookout for a discounted one. When I spotted one it was gone before I could snap it up. In the US SVS offers a money back guarantee so you can audition at home and at your leisure.

 

[FrantzM]

Hi

The literature is abundant: Science-based peer reviewed, provable, repeatable: Multiple subs, in most rooms, provide smoother and more linear bass than one. This is beyond simple anecdote. A few "el cheapo subwoofers will provide more accurate and powerful bass than a single more expensive one. I am willing to go on a limb and advance that 4 cheap around $250, sealed subwoofers + an appropriate controller, say a mini DSP 2x4 @<=U$D 125.00 + A UMik at U$D100, for a grand total of $1500 cables included, shall provide better results, in quality, smoothness and linearity than a single sub with any DSP and do-dad you want to add to it at $2000 and over ... Since this is my mind experience, , I'll bring the price to $5000 for the single sub, I dare not say what a $10,000 single sub will do but physics (a branch of Science ) are against the lone sub whatever its price in most rooms the normal or even the well heeled audiophiles are likely to have. For the record a 20 x 15 X 10 meters room fall in the realm of "Small-Rooms Acoustics"... thus everyone (Save for the hidden castle of the King, he won't let us know ) on this board has a room that falls under the "Small Room Acoustics" realm.
Of course , truism-alert!!!, there is not free-lunch. This not automatic. You don't just drop the subs and Voila! linear bass! Nope . You read a lot, you learn, you learn to measure with REW and UMik, you fail, you learn more, you learn to interpret the results and you learn how to use the not so great interface and get to the results. The miniDSP 2 x 4 + UMik + REW combo is not the only way to get there but it is one of the cheapest IMO. I don't see how you can get to great bass without measurements... so REW (Free) and (at least) UMik $100 are a requirement. Now way around it

I'll try a formula: If Bsub is the budget for the greatest single subwoofer you can afford with the specs you dream of in your room then the price for each of the 3 lesser subs would be:

LesserSubPrice= (Bsub-225)/3
Example: you budgeted $3000 for the one sub with the great specs , rather go for 3 lesser subs @ $925 each ... Guaranteed better results

 

[watchnerd]

Hi

The literature is abundant: Science-based peer reviewed, provable, repeatable, that multiple subs in most rooms provide smoother and more linear bass than one. This is beyond simple anecdote. A few "el cheapo subwoofers will provide more accurate and powerful bass than a single more expensive one. I am willing to go on a limb and advance that 4 cheap around $250, sealed subwoofers + an appropriate controller, say a mini DSP 2x4 @<=U$D 125.00 + A UMik at U$D100, for a grand total of $1500 cables included, shall provide better results, in quality, smoothness and linearity than a single sub with any DSP and do-dad you want to add to it at $2000 and over ... Since this is my mind experience, , I'll bring the price to $5000 for the single sub, I dare not say what a $10,000 single sub will do but physics (a branch of Science ) are against the lone sub whatever its price in most rooms the normal or even the well heeled audiophiles are likely to have. For the record a 20 x 15 X 10 meters room fall in the realm of "Small-Rooms Acoustics"... thus everyone (Save for the hidden castle of the King, he won't let us know ) on this board has a room that falls under the "Small Room Acoustics" realm.
Of course , truism-alert!!!, there is not free-lunch. This not automatic. You don't just drop the subs and Voila! linear bass! Nope . You read a lot, you learn, you learn to measure with REW and UMik, you fail, you learn more, you learn to interpret the results and you learn how to use the not so great interface and get to the results. The miniDSP 2 x 4 + UMik + REW combo is not the only way to get there but it is one of the cheapest IMO. I don't see how you can get to great bass without measurements... so REW (Free) and (at least) UMik $100 are a requirement. Now way around it

I'll try a formula: If Bsub is the budget for the greatest single subwoofer you can afford with the specs you dream of in your room then the price for each of the 3 lesser subs would be:

LesserSubPrice= (Bsub-225)/3
Example: you budgeted $3000 for the one sub with the great specs , rather go for 3 lesser subs @ $925 each ... Guaranteed better results

I think there is the agreement than 2+ subs are better.

But, in your example, how confident are you that 3 is the right denominator?

That Bsub/3 is better than Bsub/2? Or Bsub/4?

 

[andreasmaaan]

3 subs is very likely to perform worse than 2 or 4 subs. You need an even number of well-placed subs to correctly cancel room modes. This is not possible with an odd number.

@watchnerd if I were you I'd probably go for bigger subs placed in corners over smaller subs placed between the speakers. According to Harman's subwoofer placement paper, both configurations give fairly similar results in terms of smoothness of response and sound power, which means that the greater surface area of the larger subs should probably be the decisive factor.

See again the graph that Amir posted in the other thread. The relevant configurations for your purposes are #3 (sub or subs directly between speakers) and #4 (1 sub in each corner on the wall behind the speakers):

 

[FrantzM]

3 subs following Geddes are better than 2. 4 is the threshold of diminishing returns for Welti et Devantier. Geddes approach favors a quasi random positioning of the (at least 3) subs. Geddes almost advocates different sealed or passband subs.

 

[andreasmaaan]

3 subs following Geddes are better than 2. 4 is the threshold of diminishing returns for Welti et Devantier. Geddes approach favors a quasi random positioning of the (at least 3) subs. Geddes almost advocates different sealed or passband subs.

I appreciate that Geddes believes more is always better. I don’t agree with him on this, though. Harman’s paper on this is the most cogently thought-out tying together of theory, modelling and measurements IMHO.

 

[FrantzM]

Not exactly: he prefers 3. Rarely if ever suggests 4.

 

[suttondesign]

i second rythmik. very clean and effective, great value. made in my hometown. attend to ground loop issues, however.

 

[andreasmaaan]

Not exactly: he prefers 3. Rarely if ever suggests 4.

My reading of Geddes was that he believes 3 is the minimum number for good performance. I've never read him as saying that 3 is better than 4. Perhaps you have a link or can recall what he said?