• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

mini/micro subwoofer thread

Victoria

Member
Joined
Jul 26, 2019
Messages
86
Likes
269
But wouldn't two 6.5" drivers be the same as one 13" driver?

Nope, you truncated the most important part of my statement which is (in bold): “two 6.5” drivers would be somewhat equivalent to a single 9” driver in terms of the total surface area there is to push air around.”

Also you don’t really need to be good at maths for this, trust me, my maths is horrendously bad (it was bad way back in school and it’s even worse now after many good years out of school haha). The good thing for us however is that there’s tons of online resources around and there’s many diameter/circumference to area quick reference charts too which can come in handy for many other purposes too.
 
OP
carewser

carewser

Senior Member
Joined
Sep 30, 2020
Messages
310
Likes
284
Location
Victoria, BC
^I omitted that part of your post because I didn't understand what you were talking about. Rather simplistically, I thought that 6.5+6.5=13 but with speakers that math obviously doesn't work
 

Sancus

Major Contributor
Forum Donor
Joined
Nov 30, 2018
Messages
2,923
Likes
7,616
Location
Canada
I can't remember which online reviewer tested it but they said it "only" goes down to 15hz (which is still crazy deep) considering the only sound that goes that low is a pipe organ which KEF's little sub can reproduce accurately.

Well the key part is what output you can expect at those frequencies. The best info we have so far until someone completes a CEA2010 is this chart @napilopez linked from their white paper. I'll note it doesn't seem to say anywhere whether those measurements are 2m RMS or 1m Peak or what... but either way they don't look high enough to me to compete with even a(good) basic 12" sub like the Arendal 1961.

So it doesn't seem like there's any physics-destroying miracles happening here. That said, adequate for music listening at low-medium levels? Quite possibly yeah, especially if you buy 2 or 3.... although the price tag is very discouraging there. The 3000 Micro seems to be less than half the cost which is a pretty strong point in its favor.

^I omitted that part of your post because I didn't understand what you were talking about. Rather simplistically, I thought that 6.5+6.5=13 but with speakers that math obviously doesn't work

If a speaker driver is a circle(oversimplified), then you'd need to calculate the area. Same reason a 14" pizza is double the size of a 10" pizza.
 

mkawa

Addicted to Fun and Learning
Joined
Sep 17, 2019
Messages
788
Likes
695
The 3000 micro was quite adequate at medium levels up to moderately loud at near field. My 12” beats it handily though
 
OP
carewser

carewser

Senior Member
Joined
Sep 30, 2020
Messages
310
Likes
284
Location
Victoria, BC
^What is "BL product"?
Well the key part is what output you can expect at those frequencies. The best info we have so far until someone completes a CEA2010 is this chart @napilopez linked from their white paper. I'll note it doesn't seem to say anywhere whether those measurements are 2m RMS or 1m Peak or what... but either way they don't look high enough to me to compete with even a(good) basic 12" sub like the Arendal 1961.

So it doesn't seem like there's any physics-destroying miracles happening here. That said,? Quite possibly yeah, especially if you buy 2 or 3.... although the price tag is very discouraging there. The 3000 Micro seems to be less than half the cost which is a pretty strong point in its favor.

If a speaker driver is a circle(oversimplified), then you'd need to calculate the area. Same reason a 14" pizza is double the size of a 10" pizza.

The problem with your suggestion of that Arendal sub is that i've never heard of Arendal so I have no idea where/how to hear/buy their speakers although $800 is obviously much cheaper than $2G for KEF's little sub but KEF is everywhere. You said the KEF KC 62 is "adequate for music listening at low-medium levels"? You can't be serious. You know that little sub has a 1000 watt RMS amp, right? To put that in perspective my 8" Audioengine sub goes down to 27hz and has a 125 watt RMS amp (neither spec is even close to the KEF's nor should it be since it's 1/4 the price) but my Audioengine sub can make the windows rattle on the floor above me (my neighbors complained once). I'll bet that little KEF sub could make the windows rattle on the floor above that

As for explaining speaker diameter to me, thanks for that, I was woefully ignorant. It shouldn't come as a shock that I really struggled with math in school
 
Last edited:

MrPeabody

Addicted to Fun and Learning
Joined
Dec 19, 2020
Messages
657
Likes
942
Location
USA
Scaling laws come in handy even in cases this simple. If the question is how large two smaller drivers would need to be, to have the same effective area as a single larger driver, the answer is found by multiplying .707 by the diameter of the larger driver. How do I know? Since area scales as the square of linear dimension, the answer has to be the square root of two or else its reciprocal, and since the answer is obviously not 1.414, it is obviously .707. Just saying ...

I had to do this because the only other option was to dredge up that stupid old joke about pie not being square.
 

MrPeabody

Addicted to Fun and Learning
Joined
Dec 19, 2020
Messages
657
Likes
942
Location
USA
P.S. Before doing these comparisons it is important to take into account the part of the diameter taken up by the driver flange. This varies a bit from driver to driver, so it is a little precarious to apply a rule of thumb.

Also, what matters is total volumetric displacement. Two smaller drivers having combined area the same area as a single larger driver will typically not have the same volumetric displacement, because as a general rule, smaller drivers have smaller linear excursion. And there is no good rule of thumb here because of the substantial variation in linear excursion for drivers of any given size.

Owing to these two reasons, it isn't particularly useful to simply compare the diameters of drivers. You have to subtract for the part of the diameter taken up by the flange, and you have to multiply by the linear excursion to obtain the useful volumetric displacement.
 

Chrispy

Master Contributor
Forum Donor
Joined
Feb 7, 2020
Messages
7,757
Likes
5,918
Location
PNW
Generally you mention a bunch of poor examples of "subs" more ineffectual bass modules perhaps. Audiophiles are weird when it comes to proper subwoofage ( or speakers for that matter thinking subs aren't necessary).
 

617

Major Contributor
Forum Donor
Joined
Mar 18, 2019
Messages
2,404
Likes
5,296
Location
Somerville, MA
I am very, very skeptical of the quoted KEF figures. 15hz is really low. Like, if you want 15hz to be audible it needs to be 15-20db higher in level than the rest of the music. Normally people use 15-18" woofers to get significant output below 20hz, and that's generally in ported or PR enclosures.

The KEF whitepaper shows some really clever engineering in making this unit; in particular getting two voice coils with different diameters to fit into one magnet structure and still have the same BL curve. Very cool stuff. I'm sure this is a very good small subwoofer, but high output at 11hz? Doubtful. I'm not even sure that's desirable for a product like this.

Having said that, I agree that this is an exciting segment, and just getting some beef in the 25-50hz range would do a lot to improve a lot of popular small speakers, especially if the subwoofer can provide a high pass filter for them.

I have some CSS SDX10 subwoofers, and I put them in oversized sealed boxes, but they can essentially be put in a cube about 11" a side. The output that one provides blows away the bass of most small or medium floorstanding speakers, and any bookshelf speaker. The technology exists to make small subs, and it's cool to see some refined offerings from big names.
 

Sancus

Major Contributor
Forum Donor
Joined
Nov 30, 2018
Messages
2,923
Likes
7,616
Location
Canada
The problem with your suggestion of that Arendal sub is that i've never heard of Arendal so I have no idea where/how to hear/buy their speakers although $800 is obviously much cheaper than $2G for KEF's little sub but KEF is everywhere. You said the KEF KC 62 is "adequate for music listening at low-medium levels"? You can't be serious. You know that little sub has a 1000 watt RMS amp, right? To put that in perspective my 8" Audioengine sub goes down to 27hz and has a 125 watt RMS amp (neither spec is even close to the KEF's nor should it be since it's 1/4 the price) but my Audioengine sub can make the windows rattle on the floor above me (my neighbors complained once). I'll bet that little KEF sub could make the windows rattle on the floor above that

You misunderstand, it was just an example. Any good 12" sealed sub will have similar performance, within a few db. Rythmik F12, SVS SB-2000 Pro, etc. "Making things rattle" isn't a metric for performance lol. The Kef doesn't even get to 100dB at 30hz WITH Kef's(generous, most likely) assumptions of room gain, pushed to the max. That's not enough for high-level listening(say 83dBC reference) with a dynamic range of +/- 20dB. And even if it was, you don't really want to be pushing your sub to the max. It's also not even CLOSE to enough for -10dB on tv/film, which requires as much as 113dB. Sealed 8" subs don't normally have enough 20-30Hz output to even reach 80dB peak. So whatever resonant frequencies are making things rattle for you are probably much higher than that. It's a bit silly to even call them subs, they're more like midbass woofers.

Again, not saying it isn't adequate for music listening, just that no miracles are being performed here. It looks like a great product for people who are happy with the kind of bass you get from an 8" sub. I just wish it was a bit cheaper, at its price it seems really cost ineffective to buy multiple. The size is perfect for having 2-3 subs even in a small apartment. And I say that as somebody who never really had trouble finding space for a 12" sub in a 500-600sqft apartment.

I am very, very skeptical of the quoted KEF figures. 15hz is really low. Like, if you want 15hz to be audible it needs to be 15-20db higher in level than the rest of the music. Normally people use 15-18" woofers to get significant output below 20hz, and that's generally in ported or PR enclosures.

Well 100dB at 20hz is 40 Phons, and this won't even do that with room gain. So yeah, you're not going to produce meaningfully audible 15hz with this thing lol. Measurable, sure. I kind of doubt anyone looking at a KC62 cares about infrasonics, though.
 

617

Major Contributor
Forum Donor
Joined
Mar 18, 2019
Messages
2,404
Likes
5,296
Location
Somerville, MA
You misunderstand, it was just an example. Any good 12" sealed sub will have similar performance, within a few db. Rythmik F12, SVS SB-2000 Pro, etc. "Making things rattle" isn't a metric for performance lol. The Kef doesn't even get to 100dB at 30hz WITH Kef's(generous, most likely) assumptions of room gain, pushed to the max. That's not enough for high-level listening(say 83dBC reference) with a dynamic range of +/- 20dB. And even if it was, you don't really want to be pushing your sub to the max. It's also not even CLOSE to enough for -10dB on tv/film, which requires as much as 113dB. Sealed 8" subs don't normally have enough 20-30Hz output to even reach 80dB peak. So whatever resonant frequencies are making things rattle for you are probably much higher than that. It's a bit silly to even call them subs, they're more like midbass woofers.

Again, not saying it isn't adequate for music listening, just that no miracles are being performed here. It looks like a great product for people who are happy with the kind of bass you get from an 8" sub. I just wish it was a bit cheaper, at its price it seems really cost ineffective to buy multiple. The size is perfect for having 2-3 subs even in a small apartment. And I say that as somebody who never really had trouble finding space for a 12" sub in a 500-600sqft apartment.



Well 100dB at 20hz is 40 Phons, and this won't even do that with room gain. So yeah, you're not going to produce meaningfully audible 15hz with this thing lol. Measurable, sure. I kind of doubt anyone looking at a KC62 cares about infrasonics, though.

I find it odd how commonly the term 'room gain' is. The room doesn't add energy to the bass. Buildings are far too leaky for pressurization gain to be a factor. This is a discussion for another time perhaps.
 

Sancus

Major Contributor
Forum Donor
Joined
Nov 30, 2018
Messages
2,923
Likes
7,616
Location
Canada
I find it odd how commonly the term 'room gain' is. The room doesn't add energy to the bass. Buildings are far too leaky for pressurization gain to be a factor. This is a discussion for another time perhaps.

Ya you're right, the majority of the difference is between testing done in free space or half space and real-world quarter or eighth space, but whatever you want to call it you usually get about 8-12dB more than CEA2010 in the real world. Kef looks to be assuming maybe 12-15dB which is certainly generous and may not be reality in many rooms.
 

jonfitch

Senior Member
Joined
Sep 2, 2019
Messages
479
Likes
532
Despite its overall volume, a slim profile sub like the KEF T2 seems like it would take a lot of less functional space because you can push it right against a wall. I haven't seen anyone measure them yet, which is a shame. KEF also seems to have another slim sub, the HTB2, for those who like a more curved shape.
 

KSTR

Major Contributor
Joined
Sep 6, 2018
Messages
2,690
Likes
6,013
Location
Berlin, Germany
I find it odd how commonly the term 'room gain' is. The room doesn't add energy to the bass. Buildings are far too leaky for pressurization gain to be a factor. This is a discussion for another time perhaps.
Depends on where you live. In Europe, we tend to have houses with brick or concrete walls and floors/ceiling and we also tend to have very strong and airtight windows and doors, compared to US standards. Traditional Japanese houses with paper walls won't have any room gain...
 

richard12511

Major Contributor
Forum Donor
Joined
Jan 23, 2020
Messages
4,335
Likes
6,700
I find it odd how commonly the term 'room gain' is. The room doesn't add energy to the bass. Buildings are far too leaky for pressurization gain to be a factor. This is a discussion for another time perhaps.

Would you mind expanding on this a bit? I think it's relevant for this thread, as such 'room gain' is what KEF is relying on to push their 11hZ figure.

I can't (and don't pretend) to understand the physics of room gain, so I'm genuinely curious. I do know that I get volumes at low frequencies in my main room that the CEA-2010 figures of my subs suggest should be impossible. If that's not 'room gain', what would it be?
 

617

Major Contributor
Forum Donor
Joined
Mar 18, 2019
Messages
2,404
Likes
5,296
Location
Somerville, MA
Would you mind expanding on this a bit? I think it's relevant for this thread, as such 'room gain' is what KEF is relying on to push their 11hZ figure.

I can't (and don't pretend) to understand the physics of room gain, so I'm genuinely curious. I do know that I get volumes at low frequencies in my main room that the CEA-2010 figures of my subs suggest should be impossible. If that's not 'room gain', what would it be?

Room gain is an imprecise term which KEF ought not to be using. On a semantic level, it's not accurate because as I said, the room isn't adding energy, so it shouldn't really be called 'gain' to begin with.

'Room gain' as far as I can tell is a term which people use to describe the phenomena of an acoustic source becoming louder when it is put in a room, but the causes are attributed to different mechanisms, which another reason why the term shouldn't be used.

There are a few real and imagined mechanisms by which so called 'room gain' occurs. First there is pressurization gain, where the air displacement of your subwoofer actually raises the air pressure in the room. In theory this is dependent on the volume of the room irrespective of shape. In reality, only cars show measured pressurization gain afaik, buildings are far too leaky and big and have doors and so on, so you're not likely to see this kind of gain in a typical installation. I work in architecture and I can tell you that unless you specifically design a room for air tightness, it's going to be very leaky, and this is a good thing for reasons having nothing to do with acoustics.

Another supposed mechanism is the idea that if a subwoofer is measured in a free field or on a flat plane, it will get louder when it radiates into a more restricted space (like a floor against a wall) or even louder if the space is more restricted (like in a corner, where a wall, the floor, and another wall meet.) But is this 'gain'? When KEF shows 'room gain' they don't show all frequencies getting louder, they show the low bass getting (conveniently) extended, but in reality moving from a less to more restricted space boosts all frequencies (this is what a horn does, in essence.)

As a practical matter, the term room gain is at best misleading and at worst intentionally so. What actually happens with LF sources in rooms is that they create a complex sound field in the room of cancellation and augmentation that is spatially and frequency dependent. If you look at any measurement of a LF source like a speaker or sub in a room you will see the same thing - huge SPL variations below a certain frequency. Yes, at some points in space it will look like a big boost, but at others it will be a huge null. Simply stating the sub you designed which has a simulated f3 of 30hz will actually do 20hz in a real room is not honest.
 

voodooless

Grand Contributor
Forum Donor
Joined
Jun 16, 2020
Messages
10,229
Likes
17,811
Location
Netherlands
It’s not just the small woofers, it’s also the air volume in those boxes limiting output, especially at the lowest end.
 
Top Bottom