Sealed smaller subs better for music?

[sigbergaudio]

Well, you certainly could have found a better way to handle downfiring woofers than me.

(..)

I agree with you that placing sealed subs close to room boundaries is effective, and respectfully disagree that aiming the sub's woofer at the floor is effective as IME it can lead to issues with most frame construction floors. Possibly you are using a stone decoupling plinth or absorption material under the down-firing woofer to resolve this?

I don't think you will typically excite the floor much by the sound pressure of the driver alone, so it's due to transfer from the sub enclosure. With a downfiring subwoofer you will (of course) not have sideways movement, but up and down. We have a sub that can be placed both vertically (driver towards the wall) or horizontally (driver towards the floor). The cabinet is very rigid, even at 100dB@1m it just vibrates gently, no problem having things placed on top of it. Note that this is a pretty compact subwoofer, if you had a 200l 18" sub the result may be different.

And yes we are using absorbing silicone feet, and spent quite some time finding the right stiffness to minimize transfer to the floor, in part because it also supports wall mounting, so decoupling was important. I have a second story wooden floor myself, and it works just fine there. I'm sure there are less stable floor structures out there than mine, but overall I doubt it would cause more vibration than a standard front firing subwoofer.

 

[nerdoldnerdith]

Group delay might not be the main culrlprit that makes ported subs sound "slow." Ported subs also suffer from port compression that hinders their output around the tuning frequency.

Notice how much output sags when you push output around the port tuning.

Sealed subs will eventually compress when they run out of excursion in the low end, but this usually happens at a much higher level. Most ported subs will start to compress at low levels because their ports are too small to allow enough air to move. You can design a ported sub with more compression-free output but the port has to be enormous.

 

[OWC]

haha...good try

??? Clarify yourself

If it's true that the subs create some mechanical disturbances somewhere else, this can only be created by the reaction force of the woofer going through the floors etc. So when we remove the coupling between the two, there can't be any mechanical energy introduced anymore.

 

[gnarly]

Group delay might not be the main culrlprit that makes ported subs sound "slow." Ported subs also suffer from port compression that hinders their output around the tuning frequency.

View attachment 206820

Notice how much output sags when you push output around the port tuning.

Sealed subs will eventually compress when they run out of excursion in the low end, but this usually happens at a much higher level. Most ported subs will start to compress at low levels because their ports are too small to allow enough air to move. You can design a ported sub with more compression-free output but the port has to be enormous.

Is it fair to generalize how ported subs work, or don't work, based on one (not so so great) example?

Ports don't have to compress...when they do it's almost always because the designer was chasing the lowest frequency possible (for specs sake) , instead of a balance between lowest freq and usable SPL.

 

[gnarly]

With a dsp , you can easily implement a HP filter just below the tuning point in a ported subwoofer . If the tuning freq is 28 Hz for the port, a HP filter ( third order or more ) at 20 Hz protects the driver excursion below the tuning freq.

This way the distortion in a good ported box can be lower for the same SPL than a closed box - but with worse group delay.
I have tried this with my DIY subs and the bass gets a bit better, at the cost of extension.

Yes, good points.

There's a way with DSP to take it to a higher level still. A ported sub can be free or any electrical highpass filter until overexcursion becomes an issue. It takes frequency and level dependent sideband actuated limiting. It's starting to appear in prosound ported subs.

I built such in q-sys for DIY 18"s using Faital 18FH500's.
here's the family of level dependent response curves. Excursion protection was also needed around 55Hz as drive levels increased to max.
Allows the same bottom end rolloff order as sealed ...green trace...until big SPL is needed.

 

[antennaguru]

I don't think you will typically excite the floor much by the sound pressure of the driver alone, so it's due to transfer from the sub enclosure. With a downfiring subwoofer you will (of course) not have sideways movement, but up and down. We have a sub that can be placed both vertically (driver towards the wall) or horizontally (driver towards the floor). The cabinet is very rigid, even at 100dB@1m it just vibrates gently, no problem having things placed on top of it. Note that this is a pretty compact subwoofer, if you had a 200l 18" sub the result may be different.

And yes we are using absorbing silicone feet, and spent quite some time finding the right stiffness to minimize transfer to the floor, in part because it also supports wall mounting, so decoupling was important. I have a second story wooden floor myself, and it works just fine there. I'm sure there are less stable floor structures out there than mine, but overall I doubt it would cause more vibration than a standard front firing subwoofer.

Yes, I too had initially placed decoupling pads/feet under the large down-firing subs hard feet, but still had too much floor interaction. The large woofers were overexciting the frame floors by sound pressure even with the compliant decoupling pads/feet under the down-firing subs eliminating mechanical coupling. This was the case every time I was called in to help optimize a system utilizing down-firing subs. As a result I started also using Sonex foam absorption material under the down-firing subs as well as the compliant pads/feet. In a couple of cases I placed stone/concrete plinths placed under the down-firing subs, instead of Sonex, and that helped as well by decoupling the floor from excessive excitation. I would say that Sonex or Stone/Concrete underneath down-firing subs were equally effective, though in the end neither was fully effective in all cases (with frame floors). My preference was the Sonex because it was lighter to carry around in my vehicle and "easier to pull out of my hat", but nicely finished granite/marble plinths were possibly a better option aesthetically.

The carry-over to today is that I still apply compliant pads/feet under EVERY subwoofer irregardless of which way the woofer faces, and this always helps provide more natural bass. In the case of larger subwoofer systems like my own it also allows the turntables to be completely unaffected by the bass.

The challenge as you mention is finding the correct compliance, rated in durometers, for the weight of the subwoofers. Naturally my own 6 foot tall subwoofer towers with 4 X 12 inch woofers each are quite heavier than most subwoofers and require a higher durometer rating so as to not become over-compressed by sheer mass alone.

 

[gnarly]

??? Clarify yourself

Can't say i feel the need. Twas you who put down the sweeping all-encompassing comment...

If it's true that the subs create some mechanical disturbances somewhere else, this can only be created by the reaction force of the woofer going through the floors etc. So when we remove the coupling between the two, there can't be any mechanical energy introduced anymore.

Sure, and sub's mechanical forces can go down into the floor, or up into boxes on top of them.

hey, here's a way anybody with two subs, a few boards, and some bar clamps can test on their own whether opposed matters.
First, run a sub by itself, no signal to main speaker. Sit on the damn thing and feel its vibration.
(hint: if you can't sit on it, it's probably not big enough to be called a real sub)

Now, place your two subs facing each other, or facing away, doesn't matter.
Use the bar clamps to clamp some boards running from one sub to the other. 1"x4", 2x4's ..whatever can tie the two subs together.
Run the subs at same level as before and sit on one of them.
Even this hokey put together is bound to impart less vibration into the butt.

It's what i did before embarking on my opposed projects...a simple stupid proof of concept test.
Ended up with dual18" bass-reflex in opposed mounting.

Here's raw (green) and processed (blue) response...

Now, the good part....admittedly a shift from simply taking about motor force cancellation,
but here is THD at a little over 125dB @1 meter.
How much of that low distortion is due to opposed motor force cancellation? No clue...
But no matter, it rocks....and the dual opposed has sooo much less physical vibration that two of the exact same underlying single 18" bass reflex subs stacked together.

 

[OWC]

Is it fair to generalize how ported subs work, or don't work, based on one (not so so great) example?

Ports don't have to compress...when they do it's almost always because the designer was chasing the lowest frequency possible (for specs sake) , instead of a balance between lowest freq and usable SPL.

Well if it is or can be a fundamental part of the system, yes.

That's also the whole issue with asking super general questions to begin with.
Because you can never say anything else except; it depends.
I personally don't even understand why keep thinking in terms of "better".
"Better" on itself without context is a totally meaningless word.

That's like saying a 500HP car is better, without knowing were you need it for.
A 500HP car with crappy tires on a slippery hill is extremely useless.
In fact a person on a mountain-bike (0.3-0.5HP) will probably be faster.
Although not as comfortable and warm.

 

[OWC]

Can't say i feel the need. Twas you who put down the sweeping all-encompassing comment...


Sure, and sub's mechanical forces can go down into the floor, or up into boxes on top of them.

hey, here's a way anybody with two subs, a few boards, and some bar clamps can test on their own whether opposed matters.
First, run a sub by itself, no signal to main speaker. Sit on the damn thing and feel its vibration.
(hint: if you can't sit on it, it's probably not big enough to be called a real sub)

How much of that low distortion is due to opposed motor force cancellation? No clue...
But no matter, it rocks....and the dual opposed has sooo much less physical vibration that two of the exact same underlying single 18" bass reflex subs stacked together.

I would like to keep my methods objectively and being able to quantify things.
If not, use deductive logic and reasoning plus my 10-15 years of experience as a professional as a close 2nd.

Don't really see how sitting on a sub proves anything except what we literally already expect from the good old theory from standard physics and/or other from books like Acoustics from mister Beranek.
From that knowledge we also know that there are ways to decouple it (or couple when the structure itself is very heavy and big).
(Often I very much wonder how many people actually read these kind of things)

How much it is, it the most important question of it all, otherwise we can literally quantify every single little bit as equally important.
Which is obviously not true at all.

I am happy and the first one changing thoughts about certain things when people can provide new data and experiments that are different from the current literature and knowledge. Although I probably will see those results quicker at the AES library and updates.
Anecdotal home experiments with just sitting on subs is cute, but definitely not one of them.

 

[gnarly]

I would like to keep my methods objectively and being able to quantify things.
If not, use deductive logic and reasoning plus my 10-15 years of experience as a professional as a close 2nd.

Strongly agree.
Afaict, the only regular-type guys i see posting that make more speaker measurements than me, are Amir and Erin.
( if you include into regular-type guys those who are working towards some kind of an eventual paying scenario)

I am 100% measurement based in terms of trying to mentally understand how things work ..(.and 100% hearing based in terms of trying to ultimately decide what i like, which in itself isn't easy.)

Don't really see how sitting on a sub proves anything except what we literally already expect from the good old theory from standard physics and/or other from books like Acoustics from mister Beranek.

Sometimes, the most basic things are thrown out for the intellectual/egoic desire of more exotic concepts.

I am happy and the first one changing thoughts about certain things when people can provide new data and experiments that are different from the current literature and knowledge. Although I probably will see those results quicker at the AES library and updates.
Anecdotal home experiments with just sitting on subs is cute, but definitely not one of them.

I cram alot of AES papers into my mellon too.
You do realize how political AES has often shown itself to be, right?
Honestly, i do trust AES, but i trust my butt vibrations more

 

[nerdoldnerdith]

Is it fair to generalize how ported subs work, or don't work, based on one (not so so great) example?

Ports don't have to compress...when they do it's almost always because the designer was chasing the lowest frequency possible (for specs sake) , instead of a balance between lowest freq and usable SPL.

Based on my experience modeling ported subs, yes. Ported subs will enter audible compression (more than 1dB) when particle velocity exceeds about 15m/s. It is common practice to set 30m/s as a limit for max output. Designing a ported sub that can play at high levels at the port tuning while maintaining relatively low particle velocity is difficult. The best examples are pro subs with a high port tuning and very large ports.

The problem is that to get the port tuning lower, the port has to be longer. This means that subs designed for home theater with low port tunings at or below 20Hz have to compromise port area, which leads to compression.

 

[Jon AA]

Group delay might not be the main culrlprit that makes ported subs sound "slow." Ported subs also suffer from port compression that hinders their output around the tuning frequency.

OK, but as compared with what?

Sealed subs will eventually compress when they run out of excursion in the low end, but this usually happens at a much higher level. Most ported subs will start to compress at low levels because their ports are too small to allow enough air to move. You can design a ported sub with more compression-free output but the port has to be enormous.

A comparable sealed sub? No, this is where you go wrong. If the above was true, there would be no reason for ported subs to exist at all--sealed subs would basically do everything better, all the time. Clearly that's not true.

Even "generally speaking," in general the opposite of that statement is true. Given a half-way decent design, when port compression becomes an issue it is generally at a higher output level than a similar/equivalent sealed sub is capable of producing in the first place. For an example, let's continue the one you started--the Rythmic FV18 and compare it to it's price/quality/driver size equivalent--the F18. Same brand, same price class, same sized driver, tested by the same guy (Josh Ricci) with the same methodology. Let's look at the output of the FV18:

Given that and the chart you posted above, especially knowing this sub comes with a more aggressive HPF setting to limit output below 18 Hz if desired, I think we can call the 110 dB sweep the limit of this sub's clean, worry free output. At that level, it outputs a solid 110 dB from 20 Hz on up.

Now let's compare that with it's sealed equivalent--the F18. Same sized driver, price range, brand, etc:

Here you can see significant compression up to nearly 30 Hz on the 110 dB sweep, so call the 105 dB sweep the max clean, safe output level. As you can see, at 20 Hz this sub is done at 101 dB, a solid 9 dB below the ported version's capability at that frequency. 9 dB at 20 Hz is a HUGE difference in capability--and it maintains an advantage to over 40 Hz. Anybody concerned about port compression limiting output is obviously looking for as much output as he can get down at those frequencies--and for that person, the ported sub is the clear winner. Other people may choose the sealed for other reasons, but lack of output of the ported version close to the tuning frequency compared with a similar sealed sub is not one of them.

To take the comparison further, how does distortion compare? To keep things simple, a quick look at THD:

Ported (you're looking for the green line for the above determined output levels):

It stays below 9% to well below 20 Hz.

Sealed (you're looking for the black line):

It goes up to about 18% at 20 Hz, so certainly no advantage there.

Group delay?

It's really only different enough to make any difference (if such a thing exists ) below 30 Hz, so lack of group delay isn't going to make one better than the other for music that has no content that low anyway.

Now obviously that's just one comparison, but when comparing apples to apples subs (similar cost/quality/driver size) that's pretty much how most turn out (of somewhat decent subs, I haven't paid attention to really cheap/crappy subs where their crappiness likely precludes any generalizations from holding true) or ported subs wouldn't exist--why would anybody choose a bigger, more expensive sub if there was no advantage at all? When writing that up James Larson's recent review of the Arendal Sound 1961 1S and 1V Subwoofers came to mind as it is about as apples to apples as it gets, and the results are very much the same. https://www.audioholics.com/subwoofer-reviews/arendal-1961-1s-1v

 

[Kvalsvoll]

Group delay might not be the main culrlprit that makes ported subs sound "slow." Ported subs also suffer from port compression that hinders their output around the tuning frequency.

View attachment 206820

Notice how much output sags when you push output around the port tuning.

Sealed subs will eventually compress when they run out of excursion in the low end, but this usually happens at a much higher level. Most ported subs will start to compress at low levels because their ports are too small to allow enough air to move. You can design a ported sub with more compression-free output but the port has to be enormous.

It is true that port compression limits performance, to the extent that a very small ported subwoofer is physically impossible to make. But in this case, it sure looks like there are other issues that limits the output. Looks like the amplifier clips, is is also possible that nonlinearities in the driver motor affects the output.

From the name this may be a 18" driver, and then the box is likely not very small, so the port also is likely to be large enough to be able to work well at significant output levels. Judging from this graph alone, it seems likely that usable output will drop significantly if the port is closed, and thus it is not correct to say that the port does not work, even if it starts to compress a little and introduces nonlinearities when approaching the subwoofers output capacity limit.

 

[Kvalsvoll]

OK, but as compared with what?

A comparable sealed sub? No, this is where you go wrong. If the above was true, there would be no reason for ported subs to exist at all--sealed subs would basically do everything better, all the time. Clearly that's not true.

Even "generally speaking," in general the opposite of that statement is true. Given a half-way decent design, when port compression becomes an issue it is generally at a higher output level than a similar/equivalent sealed sub is capable of producing in the first place. For an example, let's continue the one you started--the Rythmic FV18 and compare it to it's price/quality/driver size equivalent--the F18. Same brand, same price class, same sized driver, tested by the same guy (Josh Ricci) with the same methodology. Let's look at the output of the FV18:

View attachment 206915

Given that and the chart you posted above, especially knowing this sub comes with a more aggressive HPF setting to limit output below 18 Hz if desired, I think we can call the 110 dB sweep the limit of this sub's clean, worry free output. At that level, it outputs a solid 110 dB from 20 Hz on up.

Now let's compare that with it's sealed equivalent--the F18. Same sized driver, price range, brand, etc:

View attachment 206916

Here you can see significant compression up to nearly 30 Hz on the 110 dB sweep, so call the 105 dB sweep the max clean, safe output level. As you can see, at 20 Hz this sub is done at 101 dB, a solid 9 dB below the ported version's capability at that frequency. 9 dB at 20 Hz is a HUGE difference in capability--and it maintains an advantage to over 40 Hz. Anybody concerned about port compression limiting output is obviously looking for as much output as he can get down at those frequencies--and for that person, the ported sub is the clear winner. Other people may choose the sealed for other reasons, but lack of output of the ported version close to the tuning frequency compared with a similar sealed sub is not one of them.

To take the comparison further, how does distortion compare? To keep things simple, a quick look at THD:

Ported (you're looking for the green line for the above determined output levels):

View attachment 206937

It stays below 9% to well below 20 Hz.

Sealed (you're looking for the black line):

View attachment 206938

It goes up to about 18% at 20 Hz, so certainly no advantage there.

Group delay?

View attachment 206939

View attachment 206940

It's really only different enough to make any difference (if such a thing exists ) below 30 Hz, so lack of group delay isn't going to make one better than the other for music that has no content that low anyway.

Now obviously that's just one comparison, but when comparing apples to apples subs (similar cost/quality/driver size) that's pretty much how most turn out (of somewhat decent subs, I haven't paid attention to really cheap/crappy subs where their crappiness likely precludes any generalizations from holding true) or ported subs wouldn't exist--why would anybody choose a bigger, more expensive sub if there was no advantage at all? When writing that up James Larson's recent review of the Arendal Sound 1961 1S and 1V Subwoofers came to mind as it is about as apples to apples as it gets, and the results are very much the same. https://www.audioholics.com/subwoofer-reviews/arendal-1961-1s-1v

Exactly. The port in this subeweoofer is large enough to be usable at low frequencies, and this is confirmed by the measurements. Usable output is significantly higher for the ported version.