Big subs vs Small subs

[Urubamba]

I now show how the port output contributes to the total output here:

T6-A/T6 Compact Horn Subwoofer

The T6 has been around for some time now, it is a great way to fix the bass as long as you do not require earthquake levels, and the T6-A provides both dsp …

www.kvalsvoll.com

This is how it works:

View attachment 280907

References to another manufacturers product were mentioned, I found the product page, looking for specifications. It is a small sealed subwoofer, and that is about all that can be retrieved of useful information, as the spec is "105dB" and "11Hz". Which leaves the impression of a nonsense product. But this is also a much simpler design, presumably much less expensive, so not really comparable to the T6. Not meant for the same audience.

It is the acoustic loading that gives the T6 its sound character, it is different, and it is very small. So it is possible to make something that is small, and still has at least some of this exciting sound, BUT it can not play very loud. Because size is directly related to output capacity, it is simply not possible to make a very small subwoofer with high output at low frequencies, regardless of what type it is - sealed or ported or horn.

I'm glad you came to that conclusion. I was beginning to doubt myself.

 

[MattHooper]

I still have the impression and intuition speakers with larger drivers have a more authoritative sound than those using smaller drivers, frequency response remaining the same.

Yet, the more I listen to my current small, slim 2.5 way floor standing speakers (36" high 8.5" wide), with their 5.5" SEAS Excel graphene woofers, I'm blown away by the bass. When JA reviewed the speakers he noted: "When the kickdrum was doubled with synth dropped-bass notes, I was astonished by how much clean, low-frequency energy four 5.5" woofers could pump into my room." And that's what I keep experiencing. I can't believe the scale and grunt these things give even to large orchestral pieces, or the slam of a Depeche Mode industrial synth track. It's floor and seat rumbling.

When I switch the Thiels in to the system with their 8" woofers I'll probably be reminded of the difference, but on their own...these little speakers....wow!

 

[Urubamba]

Well, I feel something similar to all that but quite magnified......
DTQWTII (2) satellites = 2x10 "+ 1 x 8" each , all in double horn
Subwofers (2) = 1x18" BR each - In corners.
I'm too lazy to calculate SD total again, I already forgot it.

 

[Urubamba]

I think this discussion will fall into the realm of:

Vinyl vs. CD
Specialty Speaker Cables Vs. common electricity cables
TT direct transmission vs. belt
etc etc
That is, without resolution, however, you have to give credit to those who say that small cabinets can deliver deep bass, the question is, at what SPL?

" The very slim Totem speakers to the right played really well too! Surprisingly deep bass from so small drivers. Totem makes their own midbass drivers with PP membranes and uses no low-pass filter at all. The tweeter, for good reasons, have some sort of high pass filter but that's all we would know from the exhibitor."

SpeakerTalk

 

[Tom C]

I now show how the port output contributes to the total output here:

T6-A/T6 Compact Horn Subwoofer

The T6 has been around for some time now, it is a great way to fix the bass as long as you do not require earthquake levels, and the T6-A provides both dsp …

www.kvalsvoll.com

This is how it works:

View attachment 280907

References to another manufacturers product were mentioned, I found the product page, looking for specifications. It is a small sealed subwoofer, and that is about all that can be retrieved of useful information, as the spec is "105dB" and "11Hz". Which leaves the impression of a nonsense product. But this is also a much simpler design, presumably much less expensive, so not really comparable to the T6. Not meant for the same audience.

It is the acoustic loading that gives the T6 its sound character, it is different, and it is very small. So it is possible to make something that is small, and still has at least some of this exciting sound, BUT it can not play very loud. Because size is directly related to output capacity, it is simply not possible to make a very small subwoofer with high output at low frequencies, regardless of what type it is - sealed or ported or horn.

It looks to me that below about 33Hz or so, the output of sum is less than the output of the port. And below about 23Hz, the level of sum is below the level of the port and the driver. Is this because of group delay between the driver output and the port output?
But that still wouldn’t explain how the sum can be less than both of its constituents.

 

[Kvalsvoll]

It looks to me that below about 33Hz or so, the output of sum is less than the output of the port. And below about 23Hz, the level of sum is below the level of the port and the driver. Is this because of group delay between the driver output and the port output?
But that still wouldn’t explain how the sum can be less than both of its constituents.

Below tuning the port output and driver cone output is out of phase, so they do no longer sum additionally. The T6 is designed for usable output down to around 30Hz, and rolls off below. There are reasons for this design choice, both required low extension at reduced volume, and physical limits of maximum output form such a small unit are considered. It is better to have usable output to 30Hz, than trying to go lower and then fail to achieve sufficient output to make it usable.

 

[audiofooled]

Yesterday I made an attempt to measure the low frequency transients of my DIY system in the hopes to collect some meaningful data and make some sense of whereabouts of the tactile sensation. I'd like to share this with you guys because to me it turned out to be quite an interesting experience. I'll do my best to describe the process.

I used a free version of the app Physics Toolbox Sensor Suite with my Samsung galaxy tab A8 (my phone turned out to be too lightweight for the purpose). This app collects real time accelerometer sensor data (I chose fastest collection rate of 195 Hz) and converts it to the value of g-force acceleration along X, Y, Z axis, as well total g. The data can be exported as a .csv file.

I placed the tablet right next to me at the MLP (three seat sofa) and recorded the data for 3 tracks I played at fairly high SPL (don't ask how high - the volume pot was at 2 o'clock). The tracks are (in particular order and from now on track 1, 2 and 3):

The tracks were not level matched and were played at the same volume setting:

What you are looking at here are the approx. 600 milliseconds excerpts of the recorded transients (timestamps in the plots are dependent on the amount of data chosen for the plot, but each horizontal field is accounted for about 100 milliseconds of elapsed time in this case). So, again, bass is slow. Note that I did not change anything in the graph representation as the app records it.

What I find interesting is that this app, especially in it's vector mode, gives me a pretty good and accurate representation of the physical sensation I'm getting at my MLP.
The blue graph is x axis (horizontal g's left to right - not much movement over here, but there is some because sofa is soft).
The red graph is Y axis (what I feel in my chest area-but much more detailed), so a single perceived "kick in the gut" apparently contains a much more complex waveform.
The green graph is Z axis (what I feel at my seat - "kick in the butt")
The purple one is total g's which is similar to the Z axis, but slightly different due to a measurement error from the tablet not being able to sit still. With the phone the results were much worse as it is too light and was also "seeing" too much force.
The decimations on the left are approximate decimal values of g's being pulled (also app dependent).

My most interesting observations from the graphs are that the first track (kick drum and toms at about 4:30 ish and on) gives the most force at Y axis (chest thump). It does not excite the floor too much and nothing much at the seat, just a clean and pleasant kick drum. Also note that there are phase differences along X,Y and Z axis which is no surprise because of the differences of wave propagation through air and solids.

Track 2 is equally forceful in the Y axis but presents much more force along Z axis and shakes my entire body, as well as the room. Windows are complaining the most.

Track 3 represents even more force along both Y and Z axis and subjectively it is by far the most "tangible". Transients being a bit more abrupt and shorter in duration, also a bit less different in phase angle and equally forceful on both of the axis...

I know this is very unscientific, moderately accurate and it proves nothing. But to me it was fun, so tell me what you guys think.

 

[jhaider]

I now show how the port output contributes to the total output here:

T6-A/T6 Compact Horn Subwoofer

The T6 has been around for some time now, it is a great way to fix the bass as long as you do not require earthquake levels, and the T6-A provides both dsp …

www.kvalsvoll.com

This is how it works:

View attachment 280907

Am I missing something? This measurement differs wildly from your others of this design. Specifically, this measurement shows the expected massive out-of-band resonances one expects from a 4th order cabinet with a small box and big vent tuned low, and your others do not. It's even worse than intuitively expected if I'm honest - the port resonance is ~6dB louder than passband level at ~270Hz.

References to another manufacturers product were mentioned, I found the product page, looking for specifications. It is a small sealed subwoofer, and that is about all that can be retrieved of useful information, as the spec is "105dB" and "11Hz". Which leaves the impression of a nonsense product. But this is also a much simpler design, presumably much less expensive, so not really comparable to the T6. Not meant for the same audience.

Based on your description of that product and the numbers on your website, I'm guessing pretty similar in price.

Also, I wouldn't say it's "much simpler," but rather that the complexity is elsewhere. Specifically, instead of a Bose style approach of minimum usable driver and maximum cabinet magic, that company designed a novel compound drive unit (not really needed to fit two beefy 6.5" drivers in an 8.6" deep cabinet, but I digress) and creative optimization of a limiter. In my view the big problem with that particular sub is the lack of physical drive-unit protection. I personally don't get it. It makes them more expensive end-to-end because exposed metal "cones" are easy to dent, and dented drivers kill residual values.

it is simply not possible to make a very small subwoofer with high output at low frequencies, regardless of what type it is - sealed or ported or horn.

While that's correct as written, IMO the thought is incomplete. There is a way to get usefully high sound power at low frequencies without large subwoofers: multiple small ones! Subs largely sum coherently below the modal region. For example, here is a measurement (Geddes & Blind "sound power" method spatial average) of two very small subwoofers placed in the "front corners" of a 17' x 14' "room" within an open concept space (roughly 50' x 18' x 8') , left, right, and L+R together (measured, not calculated) at a roughly 10' listening distance. No dedicated acoustic treatments in the room, but typical American drywall-on-wood-studs construction. Note that the modeled F3 of these subs is about 60Hz. There is no EQ applied.

Note that there's little rhyme or reason to the sum above 45 Hz or so, but below that they sum fairly coherently. I can't recall an in-room measurement I've taken where that was not the case. The precise corner frequency moved up or down, but the general behavior was the same. So if each one of these can yield 88dB at 20Hz (modeled SPL at 20Hz at xmax is 92dB, and I think 4dB compression at full tilt is plausible given the 3" voicecoil and decent thermal management) that's still 100dB output at 20Hz anechoic. Not super-sub levels to be sure, but we're talking about under 1 cubic foot of total cabinet volumes and a total floor footprint of well under 2 square feet (each 15" wide x 4.5" deep). Data-bass is down for me right now , but based on Audioholics' Perlisten double 12 review that sub is roughly equivalent in anechoic output but occupies a much larger volume than these four subs. So four 10s (admittedly with ca. 2kW of power total - but power is cheap and readily available today) in roughly 1 cubic foot total cabinet volume can yield similar SPL at 20Hz as a "THX Ultra" labelled single sub. In the real world a little less if you place the single massive sub for maximum room gain, but close enough. And obviously each subwoofer can be scaled up from these super-tiny things, which can lead to higher sound power or reduced amplification demands. Or scaled down, if one doesn't need/want that much sound power.

The caveat is box loading does matter if the goal is maximum ULF sound power in room from minimum subwoofer. Sealed subs without highpass filters work best for this approach, because the relatively slow rolloff means they'll pressurize room modes well below their nominal cutoff,. Many commercial sealed subs, such as most SVS models, incorporate static highpass filters that likely make them more likely to handle user abuse, but to some extent defeats the purpose of a closed box; why not do a PR and win the extra passband efficiency if you're going to cut ULF bandwidth anyway?

 

[Waxx]

Am I missing something? This measurement differs wildly from your others of this design. Specifically, this measurement shows the expected massive out-of-band resonances one expects from a 4th order cabinet with a small box and big vent tuned low, and your others do not. It's even worse than intuitively expected if I'm honest - the port resonance is ~6dB louder than passband level at ~270Hz.


Based on your description of that product and the numbers on your website, I'm guessing pretty similar in price.

Also, I wouldn't say it's "much simpler," but rather that the complexity is elsewhere. Specifically, instead of a Bose style approach of minimum usable driver and maximum cabinet magic, that company designed a novel compound drive unit (not really needed to fit two beefy 6.5" drivers in an 8.6" deep cabinet, but I digress) and creative optimization of a limiter. In my view the big problem with that particular sub is the lack of physical drive-unit protection. I personally don't get it. It makes them more expensive end-to-end because exposed metal "cones" are easy to dent, and dented drivers kill residual values.


While that's correct as written, IMO the thought is incomplete. There is a way to get usefully high sound power at low frequencies without large subwoofers: multiple small ones! Subs largely sum coherently below the modal region. For example, here is a measurement (Geddes & Blind "sound power" method spatial average) of two very small subwoofers placed in the "front corners" of a 17' x 14' "room" within an open concept space (roughly 50' x 18' x 8') , left, right, and L+R together (measured, not calculated) at a roughly 10' listening distance. No dedicated acoustic treatments in the room, but typical American drywall-on-wood-studs construction. Note that the modeled F3 of these subs is about 60Hz. There is no EQ applied.

View attachment 283611

Note that there's little rhyme or reason to the sum above 45 Hz or so, but below that they sum fairly coherently. I can't recall an in-room measurement I've taken where that was not the case. The precise corner frequency moved up or down, but the general behavior was the same. So if each one of these can yield 88dB at 20Hz (modeled SPL at 20Hz at xmax is 92dB, and I think 4dB compression at full tilt is plausible given the 3" voicecoil and decent thermal management) that's still 100dB output at 20Hz anechoic. Not super-sub levels to be sure, but we're talking about under 1 cubic foot of total cabinet volumes and a total floor footprint of well under 2 square feet (each 15" wide x 4.5" deep). Data-bass is down for me right now , but based on Audioholics' Perlisten double 12 review that sub is roughly equivalent in anechoic output but occupies a much larger volume than these four subs. So four 10s (admittedly with ca. 2kW of power total - but power is cheap and readily available today) in roughly 1 cubic foot total cabinet volume can yield similar SPL at 20Hz as a "THX Ultra" labelled single sub. In the real world a little less if you place the single massive sub for maximum room gain, but close enough. And obviously each subwoofer can be scaled up from these super-tiny things, which can lead to higher sound power or reduced amplification demands. Or scaled down, if one doesn't need/want that much sound power.

The caveat is box loading does matter if the goal is maximum ULF sound power in room from minimum subwoofer. Sealed subs without highpass filters work best for this approach, because the relatively slow rolloff means they'll pressurize room modes well below their nominal cutoff,. Many commercial sealed subs, such as most SVS models, incorporate static highpass filters that likely make them more likely to handle user abuse, but to some extent defeats the purpose of a closed box; why not do a PR and win the extra passband efficiency if you're going to cut ULF bandwidth anyway?

I just discussed this with a very experienced pro sound engineer a few days ago, and he said the trick for THX cinema systems with sealed sub (he installed hundreds of them, public and private) is to put a very steep Hpf a decade lower than the fs of the sealed sub. Like that you still protect the driver (if it has shorting rings) against dc leaks and overexcurtion because of bad processed sound) but still keep the sealed sub sound. In THX specified rooms he installed the HPF is at least 48dB/decade at 10Hz (THX Ultra 2 specs need subs that go flat to 20Hz). I'm no specialist in this at all like some here, but it sounded logic when he told me that.

 

[Kvalsvoll]

Am I missing something? This measurement differs wildly from your others of this design. Specifically, this measurement shows the expected massive out-of-band resonances one expects from a 4th order cabinet with a small box and big vent tuned low, and your others do not. It's even worse than intuitively expected if I'm honest - the port resonance is ~6dB louder than passband level at ~270Hz.

The resonances you see are above the intended frequency range, this is also a simulation where there is no bandwidth limitation.

Measured response looks like this:

The signals do not represent each individual output from port and cone correctly, because it is not possible to measure one separately without getting sound from the other that then adds to the measured signal. The sum (blue) will be correct, though.

 

[Kvalsvoll]

Also, I wouldn't say it's "much simpler," but rather that the complexity is elsewhere.

How much simpler can it be, than a sealed box, where all dimensions are << wavelength, it can be modelled as a simple acoustic compliance, stuff it with absorption material, done. Driver can be improved, presumably leading to a more complex driver unit, where improvements can be such as reduced inductance, lower distortion, more usable excursion.

So looking at complexity, the T6 wins. And it is different, acoustically, because of the acoustic loading, and it is primarily this acoustic loading that gives the T6 a different sound character compared to other similar size sealed subwoofers. The purpose of the design is not to achive higher spl from a small driver, it is to achive a sound character closer to the larger units in a small cabinet. BUT, does it matter, is there really a difference. Put them side-by-side, compare. Does it sound different, is one preferable over the other. From a purely technical perspective, there is a difference, but in the end, what matters is if this difference makes it worth the effort to do this complex cabinet.

 

[Kvalsvoll]

While that's correct as written, IMO the thought is incomplete. There is a way to get usefully high sound power at low frequencies without large subwoofers: multiple small ones!

But then they also eventually add up to a large system. So, why. And there are some inherent problems with too small units, when trying to reproduce really low bass. And really low you want, you want decent capacity down to around 15Hz perhaps, and this is problematic in smaller units, either the cone travel gets too large, or acoustic flow velocity gets too high for the dimensions of the aperture.

If you just increase size a little, things get a lot better. And then, you can start stacking multiple of those still reasonably sized units to achieve desired output capacity. +6dB for each doubling of units, if placed close, and even placed at say opposite corners up front, still usually close to +6dB.

 

[jhaider]

The resonances you see are above the intended frequency range, this is also a simulation where there is no bandwidth limitation.

Measured response looks like this:
View attachment 284605
The signals do not represent each individual output from port and cone correctly, because it is not possible to measure one separately without getting sound from the other that then adds to the measured signal. The sum (blue) will be correct, though.

Ah, that explains it - simulation vs. measurement, and low-and-steep low-pass on the measurement. The latter could, IMO, could lead to an integration nightmare with common A/V gear. I always like to see smooth and flattish response out 2 octaves beyond the nominal subwoofer passband. (Another point for simple closed boxes loaded with good woofers!) But with a stereo setup and a manual DSP work with quirky frequency response. Also, assuming it's in DSP you could of course tailor the lowpass to the limitations of the partnering electronics if desired.

How much simpler can it be, than a sealed box, where all dimensions are << wavelength, it can be modelled as a simple acoustic compliance, stuff it with absorption material, done. Driver can be improved, presumably leading to a more complex driver unit, where improvements can be such as reduced inductance, lower distortion, more usable excursion.

Exactly - the box is simpler but that particular sub has one of the most complex drive units yet imagined (for better or worse), with two voicecoils of different diameters working on the same pole against the same magnets.

However, complexity without purpose isn't that exciting, and a small closed box needn't be that complex, even with dual-opposed drivers. The commercial subwoofer on my desktop is ~10% smaller in every dimension than the referenced unit.

With the low cost and high efficiency of modern amplification, and increases in thermal handling and throw in drive-units, it seems to me the better approach for small rooms is a system that can pressurize modes below its cutoff, even if the passband efficiency is lower. There's a reasonable argument to forgo pressurization (which, unless you have a really prominent ULF mode, is not going to amount to much anyway with a small volume displacement system) to gain passband efficiency as well. It's also an interesting engineering challenge to squeeze more bass from less driver.

So looking at complexity, the T6 wins. And it is different, acoustically, because of the acoustic loading, and it is primarily this acoustic loading that gives the T6 a different sound character compared to other similar size sealed subwoofers.

My own experience tells me something different. The "sound character," if any, comes from plebeian factors such as frequency response differences, driver/vent compression, amp clipping, and bandwidth limitations such as top end esonances. That's why I tend to keep subs simple. I also don't at all buy the notion that bigger subs present sound differently from smaller subs, except inasmuch as they differ in FR, driver/vent compression, and top-end bandwidth/resonances.

But then they also eventually add up to a large system. So, why.

Two reasons: it's easier to place multiple small units in many rooms, and you get both the benefits of spatial variance reduction in the modal region and the benefit of largely coherent summing of ULF. Since smoother FR over a wider area is IMO the most important benefit subwoofers confer on an audio system, I would always compromise on individual subwoofer size over subwoofer count, when output potential is roughly similar.

 

[Kvalsvoll]

Ah, that explains it - simulation vs. measurement, and low-and-steep low-pass on the measurement. The latter could, IMO, could lead to an integration nightmare with common A/V gear. I always like to see smooth and flattish response out 2 octaves beyond the nominal subwoofer passband. (Another point for simple closed boxes loaded with good woofers!) But with a stereo setup and a manual DSP work with quirky frequency response. Also, assuming it's in DSP you could of course tailor the lowpass to the limitations of the partnering electronics if desired.


Exactly - the box is simpler but that particular sub has one of the most complex drive units yet imagined (for better or worse), with two voicecoils of different diameters working on the same pole against the same magnets.

However, complexity without purpose isn't that exciting, and a small closed box needn't be that complex, even with dual-opposed drivers. The commercial subwoofer on my desktop is ~10% smaller in every dimension than the referenced unit.

With the low cost and high efficiency of modern amplification, and increases in thermal handling and throw in drive-units, it seems to me the better approach for small rooms is a system that can pressurize modes below its cutoff, even if the passband efficiency is lower. There's a reasonable argument to forgo pressurization (which, unless you have a really prominent ULF mode, is not going to amount to much anyway with a small volume displacement system) to gain passband efficiency as well. It's also an interesting engineering challenge to squeeze more bass from less driver.


My own experience tells me something different. The "sound character," if any, comes from plebeian factors such as frequency response differences, driver/vent compression, amp clipping, and bandwidth limitations such as top end esonances. That's why I tend to keep subs simple. I also don't at all buy the notion that bigger subs present sound differently from smaller subs, except inasmuch as they differ in FR, driver/vent compression, and top-end bandwidth/resonances.


Two reasons: it's easier to place multiple small units in many rooms, and you get both the benefits of spatial variance reduction in the modal region and the benefit of largely coherent summing of ULF. Since smoother FR over a wider area is IMO the most important benefit subwoofers confer on an audio system, I would always compromise on individual subwoofer size over subwoofer count, when output potential is roughly similar.

Just to say I have seen your reply, and your points certainly makes sense. It is my understanding that your view also aligns with how many others with at least some technical knowledge of sound see it.

I need to think through how I can explain how I see it, in a better way than previous attempts, in a way that is possible to understand.