Sealed vs Ported Sub

[voodooless]

Absolutely. IF you'd like to observe the difference in roll-off between a vented-box and closed-box.
Put your microphone 1 inch from the dust cap of the woofer.

But that will not capture the reflex port output. You’ll need to measure that separately and add the two together.

 

[voodooless]

No you don't.
There will be a dip associated with the vent in the direct measurement. (But, that can be just mentally filled in.)
The intent here is to show the general roll-off characteristics of both systems. It will be easily seen if doing a close-mic'd test like this.

Well, most of the extension comes from the port, so omitting that will not give a good picture of that. It should look something like this:

As you can see, the roll off of only the woofer is quite a bit deeper in frequency. Now if you’re only talking about the shape, the yes, they are about the same.

 

[voodooless]

Well, there is no voodoo here. So, if the topic flummoxes you, better read up on the basics and then check back.

Am I missing something blatantly obvious? Where am I wrong? Do tell us…

 

[ZolaIII]

Am I missing something blatantly obvious? Where am I wrong? Do tell us…

Yes a reverberation time (RT60) decay in the room and you are not the only one. Plugging port's with foam or even something more solid won't exactly get you there as real sealed box enclosure but it will improve a bit RT60 and more even uper response for sub or mids with full range speakers and boost it a bit. Waterfall plots with quasi chamber or typical room don't make much sense.

 

[voodooless]

Yes a reverberation time (RT60) decay in the room and you are not the only one. Plugging port's with foam or even something more solid won't exactly get you there as real sealed box enclosure but it will improve a bit RT60 and more even uper response for sub or mids with full range speakers and boost it a bit. Waterfall plots with quasi chamber or typical room don't make much sense.

But what causes this change? The frequency response changes as well obviously. If you make the comparison, you’ll have to correct that first to make it fair.

 

[voodooless]

I have zero interest in getting into an inane discussion on the bottom end roll-off rates of various box speakers.
Sealed systems roll off at an approximate 2nd-order rate.
Vented systems roll off at an approximate 4th-order rate.
This is Loudspeakers 101 and has been characterized and tested for decades.

Nobody disputed that… we were talking about measuring this. That’s a totally different thing. If you want a correct nearfield measurement of a reflex system, you’ll need to measure both sound sources. It’s blatantly obvious.

Read Thiele/Small and myriad other on-line references to educate yourself.

Uhuh…

 

[ZolaIII]

But what causes this change? The frequency response changes as well obviously. If you make the comparison, you’ll have to correct that first to make it fair.

Sealed box doesn't push air out it compresses and bounce back part of energy which give those FR changes. If it doesn't push air out reverberation time will be better (I don't think that really needs to be explained). With closed port it's partial in both ways. If the room is too dead reverberation time will be very low and it will sound pretty much like headphones. So you do need reverberation and under control which is (as usual) hard to do in small room so we either usually tell people to either move speakers out 1 m or more or put them as close to the back wall so that early-to-late arriving sound energy (ISO 3382-1) gets into desired values (again almost impossible to do in small room for bass frequencies) as much as possible to achieve and of course to do as much as they can regarding floar and sealing refractions and without obvious obstacles in between like furniture to listening spot. So it's not all about FR alone (even of course it will show there as well).

 

[Chrispy]

Might like a look here now https://forums.audioholics.com/forums/threads/some-thoughts-on-the-ported-vs-sealed-debate.127738/

 

[voodooless]

Sealed box doesn't push air out it compresses and bounce back part of energy which give those FR changes. If it doesn't push air out reverberation time will be better (I don't think that really needs to be explained). With closed port it's partial in both ways. If the room is too dead reverberation time will be very low and it will sound pretty much like headphones. So you do need reverberation and under control which is (as usual) hard to do in small room so we either usually tell people to either move speakers out 1 m or more or put them as close to the back wall so that early-to-late arriving sound energy (ISO 3382-1) gets into desired values (again almost impossible to do in small room for bass frequencies) as much as possible to achieve and of course to do as much as they can regarding floar and sealing refractions and without obvious obstacles in between like furniture to listening spot. So it's not all about FR alone (even of course it will show there as well).

All the things you describe also affect frequency response. Less output at a certain frequency also lowers decay times.

 

[voodooless]

Yeah, well, I don't think I'll be taking anybody seriously who accused Greg Timbers of "shit engineering."

You mean where they ignore their own compression drivers datasheet and cross it too low, leading to unnecessary distortion products? Yeah, that is shit engineering. I don’t know if Greg Timbers is solely to blame for this… for one, he did not design the compression driver. And he probably had a budget target and the marketing people breathing down his neck. Cuts were made and this was the compromise that was found. Sadly commercial speaker design is not just about engineering.

 

[ZolaIII]

All the things you describe also affect frequency response. Less output at a certain frequency also lowers decay times.

Yes but you can have almost perfect frequency response and it will still sound bad or wrong if those are wrong, that's why EQ isn't cure for all. In the end it's all about entropy but that's way too complex topic for me to discuss even in simplified form of dispersion and transfer even when I am very cheerful and rested. Concept isn't hard to understand but there is much to it. Now I am tired of watching Avatar and playing with HDR processing with my projector (in the way even that's related). At least playing with that makes me happy for now.
Have a nice time and enjoy.

 

[voodooless]

Yes but you can have almost perfect frequency response and it will still sound bad or wrong if those are wrong, that's why EQ isn't cure for all.

Those are quite interesting situations. Obviously it’s really hard to separate these two issues (decay vs frequency response), because they are heavily linked. Same goes for the interaction with the room obviously. The question is: if all else is equal (frequency response), how much of an impact on decay will reflex vs closed really have vs the room itself? Also don’t forget that a 2nd order subsonic filter that you usually add to a closed sub, changes the transient response as well.

Anyway, have fun with your projector

 

[AdamG]

Yeah, well, I don't think I'll be taking anybody seriously who accused Greg Timbers of "shit engineering."
Clearly, you have a lot to learn about speaker system design and execution.

You’re new here and thereby entitled to a little slack. We argue and debate the Science and Engineering here and we don’t do personal insults and slights. Maybe know your audience before declaring “we have a lot to learn about speaker system designs and execution”. I think if you are willing to learn and share openly you will find a depth and breath of Engineering that you may not be accustomed too.

Welcome Aboard @etierevad and please try to keep the conversation civil Sir.

 

[neRok]

The "decay rate" between a sealed box and a vented box is 2nd-order versus 4th-order.

The "decay" you refer to is the SPL slope at the bottom end of the frequency response. That's not what decay actually refers to. Decay is time based (seen on the RT60 plots, Waterfall, Spectrogram, etc, and especially on the aptly named Decay plot) and is a measure of how long a note is heard in the room after it is played by the sub/speaker. This decay is an effect of the room: the shape of the room dictates when certain reflections arrive at the listening position (also it dictates modes, which are time/distance aligned reflections); and the absorption of the room indicates how quickly the note (energy) dissipates in the room.

Another way to look at it - a 30Hz note is 33.3ms long. From the moment the sub begins to play the note until the moment the end of the note's direct wave is heard is at listening position, that is only ~50ms at 33Hz even in a large room. All the time/decay based graphs show the sound that is heard (by reflections) at the listening position in the hundreds of milliseconds that follow. In fact, the way reflections pile up, often the direct wave isn't even the "peak energy" moment, and that moment can be 50-100ms after the direct wave, and that's all the rooms "fault".

Sealed box doesn't push air out it compresses and bounce back part of energy which give those FR changes.

If you are saying that it goes from max-excursion to rest faster, and that makes a difference, then consider that the 1/4 wave time of 30Hz is 8.3ms. All subs are doing their best to "follow the shape" of the sine wave, so even if it wasn't doing a good job at that, then at best you might find a 20%=2ms improvement to get back to ideal (instantly going from max-excursion to 0mm excursion isn't ideal because that's not a "smooth sine wave"). So any difference you describe would have to happen within the length of the note (33.3ms), and at best is an improvement to the 2 "return" slopes of the note.

That's given me a funny thought. If sealed are better at "returning" because of the stored energy, then wouldn't they also be worse at "departing" because the cone has had to work extra hard to store that energy? So by that logic sealed boxes must have slow ramps when the cone moves out, and fast ones in. That doesn't sound good

Am I missing something blatantly obvious? Where am I wrong? Do tell us…

Nope.

 

[Deleted member 48726]

The "decay" you refer to is the SPL slope at the bottom end of the frequency response. That's not what decay actually refers to. Decay is time based (seen on the RT60 plots, Waterfall, Spectrogram, etc, and especially on the aptly named Decay plot) and is a measure of how long a note is heard in the room after it is played by the sub/speaker. This decay is an effect of the room: the shape of the room dictates when certain reflections arrive at the listening position (also it dictates modes, which are time/distance aligned reflections); and the absorption of the room indicates how quickly the note (energy) dissipates in the room.

Another way to look at it - a 30Hz note is 33.3ms long. From the moment the sub begins to play the note until the moment the end of the note's direct wave is heard is at listening position, that is only ~50ms at 33Hz even in a large room. All the time/decay based graphs show the sound that is heard (by reflections) at the listening position in the hundreds of milliseconds that follow. In fact, the way reflections pile up, often the direct wave isn't even the "peak energy" moment, and that moment can be 50-100ms after the direct wave, and that's all the rooms "fault".


If you are saying that it goes from max-excursion to rest faster, and that makes a difference, then consider that the 1/4 wave time of 30Hz is 8.3ms. All subs are doing their best to "follow the shape" of the sine wave, so even if it wasn't doing a good job at that, then at best you might find a 20%=2ms improvement to get back to ideal (instantly going from max-excursion to 0mm excursion isn't ideal because that's not a "smooth sine wave"). So any difference you describe would have to happen within the length of the note (33.3ms), and at best is an improvement to the 2 "return" slopes of the note.

That's given me a funny thought. If sealed are better at "returning" because of the stored energy, then wouldn't they also be worse at "departing" because the cone has had to work extra hard to store that energy? So by that logic sealed boxes must have slow ramps when the cone moves out, and fast ones in. That doesn't sound good


Nope.

There is no "fast" or "slow". Otherwise it's a pretty shit speaker (sub) not able to play all of it's frequencies.

There is also stored energy in a vented box. Until you go below the tuning frequency of the port you "unload" the air volume so the driver no longer see any back-pressure.

 

[ZolaIII]

@neRok where exactly I said it's not time domain related?
A quick illustration starting at 4:40:

And you can hear the difference so it's not mear 2 ms. What I did say is ISO 3382-1 early-to-late arriving sound energy. And also how quasi anechoic chamber isn't quite anechoic chamber or sealed port the same as close enclosure box and especially how in typical room waterfall measurements don't have much sense (if any) and proposed RT60 decay times plots instead.
There is a max Xmas and max linear Xmas. In compression boxes woffer moves little less and faster settle down which help keeping Xmas in the linear limits more than with ported counter part for a same driver and reproduction level. The add harmonics (from port in enclosure) and add oscillations also make a difference (in Xmas) as you don't listen to single note's or tones. Many will argue that today there are subwoofer's with very high Xmas and linear Xmas capabilities thanks to material science advances but such rigid cones will still have higher mass (and cost depending on used material) which will lead to lower SPL efficiency. If for the argument sake difference is 6 dB that requires 4x more power (energy) in W to achieve the same SPL. In case of 200 W and 800 W subwoofer requirement to achieve the same SPL it's quite a bit even today with high output power class D amp's not to mention electric energy bill you will have to pay.
Anyway for me rule of thumb for me is don't make problems (or at least don't make them worser) that you don't have to so you will have to cope less with them.
You do have every right to different opinion but please don't put words into my mouths which I never have spoken.
Best regards and all well.

 

[caioferrari]

I thought that RT60 graph wouldn’t show the alignment differences since it was measured in my room. But… I heard the differences in my room, not on anechoic chamber.

For me, there is a clear difference between the two configuration. I really appreciate why.

I don’t believe that is all about that small difference of 1,5dB…
I don’t hear those differences when I turn the volume up or down of me receiver.

 

[Alegretti]

The port tuning frequency greatly reduces the cone excursion, consequently reducing harmonic distortions. Closing the port will produce distortions that will easily affect around 100Hz, your problem may be distortion. REW has a tool that shows where distortions are landing.

 

[Deleted member 48726]

The port tuning frequency greatly reduces the cone excursion, consequently reducing harmonic distortions. Closing the port will produce distortions that will easily affect around 100Hz, your problem may be distortion. REW has a tool that shows where distortions are landing.

No that doesn't make sense to me.

That would only be around the tuning frequency then because above that the enclosure is still acting as a a closed one.

 

[Alegretti]

The sub is tuned to 30Hz, so when it equalizes so that the sealed sub has the same response as the ported one, it should inject more than 4dBs of power (2.5x) between 20~30Hz. The third harmonic will be at 90Hz, coloring the bass. Just a thought...