Why do bigger subwoofers sound different?

[dannut]

Doesn't that have an impact on the wave plane (excuse my english if it's not the right term).

There is a difference. A larger source has a sound intensity (I) velocity component (v) (in addition to sound pressure) that is different in the near-field vs far field.
Fwiw, there are anecdotal testimonies that large sound source in a near-field has more 'punch'.

All else being equal, outdoor concerts with 'slam' have a massive (massive is an understatement. 18dB, up to 30dB is not uncommon!) eq shelf in the 50-100Hz region.

 

[ozzy9832001]

Well, it's actually different systems. There is my system, which has four 12" subs which has been DSP'ed to an inch of it's life. Then there's my friend's system, who has two 18" subs. The rooms are roughly the same size. Even at the same SPL, the impact of those subs is something else. So I am not sure I can post a recording, or even a sweep. I can post my own sweep, but not the other system.

Sounds like the room is having a bigger effect on the sound.

If your room is more porous, for lack of a better term, and his is more like a bunker, then I could see the difference. Also an 18" woofer would be higher off the ground and heavier. Placement could be another factor where whatever frequency is causing the chest thump or slam or whatever term is used to describe it, is modal and it's a peak and they never bothered to EQ it down...or just like the sound of it. Maybe that same frequency is a null in your room.

Lots of different explanations.

 

[ozzy9832001]

Is using 10" driver really a subwoofer? Way too small to output enough, can seldom take much power, and there's high modulation distortion. Two don't equal a quality 18" either.

Plus small commercial subwoofers like that are generally poorly designed.

Honestly, I don't think that sort of elitist attitude is necessary or helpful. Not everyone needs or wants a subwoofer that goes into the teens with its frequency response and not everyone needs concert levels of volume. A quality 10" is fine for most people's applications. Mocking them or their purchase isn't helpful...at all.

 

[Music1969]

That seems rather apples vs oranges then, not really "10in vs 18in"

^^ this

 

[Bjorn]

In cone area, two 10" is less than one 15". And two 12" is less than one 18".

 

[574stereo]

First post on ASR, hi all.

My belief that this is due to inherently higher group delay in smaller subs. A larger cone is going to inherently have a lower resonant frequency due to the increased diaphragm mass + generally stronger/bigger motor assembly to compensate. The larger box is also equally part of the equation as the overall system roll-off is based on how the driver + enclosure interact.

Small drivers in smaller boxes will inherently tend to have much higher roll-off frequencies. You can correct for the frequency response issues with DSP of course, but you're still stacking on phase shift/group delay as 'correcting' the low frequency roll-off of a speaker system isn't minimum phase. The more correction is needed, the more group delay/phase shift in a non-minimum-phase system.

It's all to do with the basic physics of what causes a speaker driver in a box to start to roll-off in the low frequencies.

Just my 2c.

 

[thewas]

Small drivers in smaller boxes will inherently tend to have much higher roll-off frequencies. You can correct for the frequency response issues with DSP of course, but you're still stacking on phase shift/group delay as 'correcting' the low frequency roll-off of a speaker system isn't minimum phase. The more correction is needed, the more group delay/phase shift in a non-minimum-phase system.

This statement is not generally correct. A small closed baffle subwoofer + correctly implemented DSP correction has an identical group delay if the frequency response is identical to the larger subwoofer.
When using PEQ, the GD is often higher at very low frequencies (due to the "bell curve" of the filter). However, when using shelving LP and Linkwitz transform, the GD is identical to the large sub with the same FR.

 

[Chrispy]

I am sure that this has been discussed before in ASR, but I did a search and could not find it. Mods please feel free to merge the thread if this topic has come up before.

Basically I have noticed that even if two subs (say) with a 10" driver and an 18" driver produce 40Hz at 80dB, the bigger sub sounds different. I can't get my head around this, after all if they are both outputting the same frequency at the same volume, at those super long wavelengths surely they must sound the same? What am I missing here?

On this post alone a lot is missing. Define "sounds different" and with what particular actual comparison and methodology (let alone the different system/room thing you mention later). Generally good subs aren't going to be all that audibly different as your ability to differentiate in that range is quite limited, particularly if proper comparison is setup.

 

[audio2920]

However, when using shelving LP and Linkwitz transform, the GD is identical to the large sub with the same FR.

Interesting! So any sealed sub with the same FR (so long as it's not achieved through PEQ or other methods that affect GD) will have the same GD? I guess that makes sense to me really, but I imagine it doesn't hold true of ported (etc.) designs?

I'm a sound engineer rather than a speaker guy, so this is a outside my expertise really, but I do observe that in my home studio I have 3x 12" and 2x 18" subs and while they sound radically different natively, post Dirac, shelves & filters, I'd likely be unable to tell you which was which. When soloing them, they all sound a touch different (even amongst the same type) due to positioning, but I can't say the bigger or smaller of them have any audible characteristics that I could use to tell you which was which, unsighted. They only really differ in my usage in terms of SPL capability in the bottom octave.

 

[Blockader]

Well, it's actually different systems. There is my system, which has four 12" subs which has been DSP'ed to an inch of it's life. Then there's my friend's system, who has two 18" subs. The rooms are roughly the same size. Even at the same SPL, the impact of those subs is something else. So I am not sure I can post a recording, or even a sweep. I can post my own sweep, but not the other system.

It's not only about the size, it's more about the dimensions of the room. The only difference between a large and a small subwoofer at the same SPL is that the larger one has more directional sound dispersion than the smaller one, meaning the spread is narrower, not wider. Depending on its size and the dimensions of the room, the larger subwoofer interacts with the walls around it less, theoretically providing a cleaner sound.

When comparing subwoofers, it’s important to position them at precisely the same location before testing. The center of their cones should be horizontally at the same place/aligned. This requires marking the position of the first subwoofer's cone center, removing the subwoofer from that location, and then placing the second subwoofer so its cone center aligns with the mark. Failing to do so can result in perceptible differences in sound.

Edit: Additionally, the transition from near-field to far-field listening is approximately at a distance equal to four times the size of the driver. With larger subwoofers, there's a higher likelihood of being within the near-field range.

 

[thewas]

Interesting! So any sealed sub with the same FR (so long as it's not achieved through PEQ or other methods that affect GD) will have the same GD? I guess that makes sense to me really, but I imagine it doesn't hold true of ported (etc.) designs?

Even with the normal PEQ it will have the same GD as long as its tuned to the exactly same FR as both a CB driver as well as such filters are minimal phase.
Unfortunately it doesn't hold true for BR, TL etc as those can be seen as additional drivers/resonators (same like with a multiway crossover) which add an excess phase component.

 

[Bob from Florida]

Could the explanation be a bit simpler? The 18 inch sub's low frequency roll off is going to be lower - well into "feel it rather than hear it" frequencies. Having the sensation of "feeling it and hearing it too" could account for at least some of the perceived difference.

 

[Blockader]

Could the explanation be a bit simpler? The 18 inch sub's low frequency roll off is going to be lower - well into "feel it rather than hear it" frequencies. Having the sensation of "feeling it and hearing it too" could account for at least some of the perceived difference.

The sub-bass extension of a driver is determined by its resonance frequency, not by its size. Assuming equal excursion capabilities between a larger and a smaller driver, the larger one should always produce a higher sound pressure level above a certain frequency. However, the point at which it begins to roll off is dependent on its resonance frequency, not its size. It is possible for a small driver to maintain a flat extension down to 14-15Hz, but distortion will become excessively high at anything above low listening levels.

The resonance frequency of a driver is influenced by its stiffness and weight. A driver that is very heavy and made from a soft material may have better extension capabilities.

Below you can see the free field response of B&C 21 IPAL, one of the loudest 21 drivers ever designed, if not the loudest:

as you can see its response starts dropping below 100hz. Of course it is possible to tune it lower with different enclosure design methods.

Here's SB Acoustics 10'' driver, SW26DBAC76-8BLK 10":

Rolls of very smoothly and slowly down to 15hz.

One is a 10'' driver, other one is 21''.

This is of course against human intuition. How can something larger can produce lower sound levels than something smaller in low frequencies? The reason is, the efficiency of moving a light-weight/stiff driver in low frequencies become so low that, the power required to make it push enough air becomes extremely high. Resonance frequency is where a driver can be moved most efficiently and outside of that frequency, the drivers tend to become less efficient.

 

[charlielaub]

The answer is pretty simple: you are only considering or comparing one small part of the output of ANY driver by comparing the SPL at one frequency. What about the HD and IMD distortion products? What about cone breakup or other resonances due to the driver itself? What about the radiation from the enclosure walls, e.g. panel resonances? What about port resonances or port noise?

Each driver size, each model driver, and enclosure type/shape/design will have different amounts of each of these "additional" sources of acoustic output. And this is why no two speakers will "sound' alike, and that is the same not only for subwoofers but also for e.g. N different variations on the theme of a small monitor speaker built using a 6.5" woofer and a 1" dome tweeter.

 

[Bob from Florida]

The sub-bass extension of a driver is determined by its resonance frequency, not by its size. Assuming equal excursion capabilities between a larger and a smaller driver, the larger one should always produce a higher sound pressure level above a certain frequency. However, the point at which it begins to roll off is dependent on its resonance frequency, not its size. It is possible for a small driver to maintain a flat extension down to 14-15Hz, but distortion will become excessively high at anything above low listening levels.

The resonance frequency of a driver is influenced by its stiffness and weight. A driver that is very heavy and made from a soft material may have better extension capabilities.

Below you can see the free field response of B&C 21 IPAL, one of the loudest 21 drivers ever designed, if not the loudest:

View attachment 356821

as you can see its response starts dropping below 100hz. Of course it is possible to tune it lower with different enclosure design methods.

Here's SB Acoustics 10'' driver, SW26DBAC76-8BLK 10":

View attachment 356822
Rolls of very smoothly and slowly down to 15hz.

One is a 10'' driver, other one is 21''.

This is of course against human intuition. How can something larger can produce lower sound levels than something smaller in low frequencies? The reason is, the efficiency of moving a light-weight/stiff driver in low frequencies become so low that, the power required to make it push enough air becomes extremely high. Resonance frequency is where a driver can be moved most efficiently and outside of that frequency, the drivers tend to become less efficient.

Momentarily lost my mind with my earlier post - I forgot that nothing is ever "simple" on this forum. LOL

Perhaps the sub experienced by the OP had lower tuning than your example. I have 2 SVS 3000 Micro's that have 2 - 8 inch drivers in a sealed box. They roll off pretty steeply from 23 Hertz, I don't have room for bigger subs - but they do what I need.

 

[abdo123]

Couldn't it be that the two systems have slightly different settings for the lows? What I mean is for example the bass boost, low shelves, etc. are set up differently?
Even a slight difference in how the low end is boosted can result in totally audible differences, the point in frequency where the boost starts, the amount of boost and the Q value of the boost all contribute to it

I totally agree with this.

 

[574stereo]

This statement is not generally correct. A small closed baffle subwoofer + correctly implemented DSP correction has an identical group delay if the frequency response is identical to the larger subwoofer.
When using PEQ, the GD is often higher at very low frequencies (due to the "bell curve" of the filter). However, when using shelving LP and Linkwitz transform, the GD is identical to the large sub with the same FR.

Don't forget you also have a HPF implemented in all of these designs which screws up the entire minimum phase aspect. It's not out of the ordinary to find +20dB gain at 20 Hz or lower being applied, so a (usually very steep) high pass filter is always needed in EQ reliant designs.

 

[sigbergaudio]

Don't forget you also have a HPF implemented in all of these designs which screws up the entire minimum phase aspect. It's not out of the ordinary to find +20dB gain at 20 Hz or lower being applied, so a (usually very steep) high pass filter is always needed in EQ reliant designs.

I think you will find +20dB at 20hz to be out of the ordinary.

GD in small sealed subwoofers can be kept at inaudible levels even with a HPF.

 

[thewas]

Don't forget you also have a HPF implemented in all of these designs which screws up the entire minimum phase aspect. It's not out of the ordinary to find +20dB gain at 20 Hz or lower being applied, so a (usually very steep) high pass filter is always needed in EQ reliant designs.

But again if the FR it tuned to be indentical to a larger woofer their GD will be the same.

 

[574stereo]

But again if the FR it tuned to be indentical to a larger woofer their GD will be the same.

No this is incorrect, sorry! Go build and measure some subwoofers and you'll see this to be the case. Corrective EQ to extend FR at the low end is not minimum phase...