Some thoughts on the ported vs sealed debate

[Steve81]

Well don't! You absolutely do not want a high port velocity. A turbulent noisy port is a distorted output port. You need to keep vent air velocity no higher than 20m/sec. Flaring the ports is fine, but it makes the port significantly longer and the max air velocity still stands.

Just trust me It seems like WinISD really hates this driver. It crashed the latest version, so I installed an older version of the software which wouldn't let me add the thing until I let it auto-calculate Qes (which it reckons is 0.519 based on all other entries). So there's going to be that little caveat to the upcoming design. Also using a 2nd order Butterworth filter at 30Hz to mitigate port velocity and protect the driver below tune (which I'm running at 20Hz tune, with a 40L box, and a 6.35cm (2.5") by 54.57cm (~21.5") port. I'll have charts up in a few, assuming I don't see anything horrid...

 

[Steve81]

Just trust me It seems like WinISD really hates this driver. It crashed the latest version, so I installed an older version of the software which wouldn't let me add the thing until I let it auto-calculate Qes (which it reckons is 0.519 based on all other entries). So there's going to be that little caveat to the upcoming design. Also using a 2nd order Butterworth filter at 30Hz to mitigate port velocity and protect the driver below tune (which I'm running at 20Hz tune, with a 40L box, and a 6.35cm (2.5") by 54.57cm (~21.5") port. I'll have charts up in a few, assuming I don't see anything horrid...

OK, so here's what WinISD came up with (this version doesn't model inductance it looks like, so top end will be a bit inaccurate... close enough.
SPL @ 350W @ 1m

Group Delay doesn't exceed one cycle

Impedance & Impedance Phase; some nasty phase angles, but the Crown ought to be able to cope.

Cone Excursion @ 350W Nominal (with the filter applied). There is a bit of additional room for burst power without exceeding Xmax.

Port Velocity @ 350W Nominal (again, with the filter applied). Don't run full power sine waves around port tune, and you'll be good.

 

[TLS Guy]

Just trust me It seems like WinISD really hates this driver. It crashed the latest version, so I installed an older version of the software which wouldn't let me add the thing until I let it auto-calculate Qes (which it reckons is 0.519 based on all other entries). So there's going to be that little caveat to the upcoming design. Also using a 2nd order Butterworth filter at 30Hz to mitigate port velocity and protect the driver below tune (which I'm running at 20Hz tune, with a 40L box, and a 6.35cm (2.5") by 54.57cm (~21.5") port. I'll have charts up in a few, assuming I don't see anything horrid...

The driver did not crash my program.

The problem is that driver is a car driver designed to be used in small boxes. That makes the design critical. It is hard to port it. It really needs to be an ABR design if you don't want a sealed alignment. If you use that box you should consider a tunnelled port vent.

 

[Steve81]

The driver did not crash my program.

The problem is that driver is a car driver designed to be used in small boxes. That makes the design critical. It is hard to port it. It really needs to be an ABR design if you don't want a sealed alignment. If you use that box you should consider a tunnelled port vent.

I posted up what WinISD gave me right as you posted this; want to double check everything with the posted spec for Qes in BassBox Pro? Everything else is noted in this post (and the quote contains the relevant parameters).

 

[TLS Guy]

I posted up what WinISD gave me right as you posted this; want to double check everything with the posted spec for Qes in BassBox Pro? Everything else is noted in this post (and the quote contains the relevant parameters).

Qes of that driver is definitely 0.48.

The problem with that driver ported is that the box is critically small. That driver was designed as a sealed driver, there is no doubt about that.

I did model a slot vent, which is probably the best bet. A slot vent 1.5" X 5" X 26" does the job. You can wind that round the inside of the the box, along the bottom and up the back. That is probably your best bet. That just gets you in in terms of vent air velocity and group delay.

We have been down this road many times over the years. The plain fact is that car sub drivers are a poor choice for a home DIY sub build. It just gets you off wrong footed before you start.

Lastly that design would be better as an ABR design actually.

 

[caioferrari]

The driver did not crash my program.

The problem is that driver is a car driver designed to be used in small boxes. That makes the design critical. It is hard to port it. It really needs to be an ABR design if you don't want a sealed alignment. If you use that box you should consider a tunnelled port vent.

For a sealed alignment, the driver should have a higher Qts for extend the F3 a little bit. What do you think?

 

[caioferrari]

Qes of that driver is definitely 0.48.

The problem with that driver ported is that the box is critically small. That driver was designed as a sealed driver, there is no doubt about that.

I did model a slot vent, which is probably the best bet. A slot vent 1.5" X 5" X 26" does the job. You can wind that round the inside of the the box, along the bottom and up the back. That is probably your best bet. That just gets you in in terms of vent air velocity and group delay.

We have been down this road many times over the years. The plain fact is that car sub drivers are a poor choice for a home DIY sub build. It just gets you off wrong footed before you start.

Lastly that design would be better as an ABR design actually.

I’m convinced I need to use this driver in sealed mode, besides the fact it gives me a terrible F3 since it’s Qts is a little low for sealed. May be it’s a good idea adding mass to the cone

My main interest right now is: Could I see the driver “slowness” working with my alignment (45 L @ 30 Hz )? Does the group delay show that I was going to get a poor quality bass?
I really want to read those informations before spending money on the enclosure and I want to see where I messed up on the project.

 

[TLS Guy]

I’m convinced I need to use this driver in sealed mode, besides the fact it gives me a terrible F3 since it’s Qts is a little low for sealed. May be it’s a good idea adding mass to the cone

My main interest right now is: Could I see the driver “slowness” working with my alignment (45 L @ 30 Hz )? Does the group delay show that I was going to get a poor quality bass?
I really want to read those informations before spending money on the enclosure and I want to see where I messed up on the project.

Actually I think that it Qts is in a good range. I personally do not favor high Qts drivers. That starts getting into the old, and rightfully discredited, acoustic suspension territory. High Qts drivers tend to produce a sloppy bass. For its intended purpose it is a good driver. Honestly Qts. between 0.3 and O.45 is the sweet spot in my view.

For a sealed alignment you are going to have a high F3. So, as I said if you are going sealed you need a big motor, high linear excursion and lots of power.

I don't know what those drivers cost in Brazil, but your best option would be to buy another driver, double the size of the box and put the drivers on opposing sides. That will get you an extra 6db. That would give a reasonable spl. for a domestic room and use 12db boost per octave below 50 Hz, and high pass it 12db per octave above 25Hz. That I think would do what you want, and be equivalent to a 15" sub.

 

[Steve81]

Qes of that driver is definitely 0.48.

The problem with that driver ported is that the box is critically small. That driver was designed as a sealed driver, there is no doubt about that.

I did model a slot vent, which is probably the best bet. A slot vent 1.5" X 5" X 26" does the job. You can wind that round the inside of the the box, along the bottom and up the back. That is probably your best bet. That just gets you in in terms of vent air velocity and group delay.

We have been down this road many times over the years. The plain fact is that car sub drivers are a poor choice for a home DIY sub build. It just gets you off wrong footed before you start.

Lastly that design would be better as an ABR design actually.

I don’t know, I think either of our builds would do a fair job (with a requisite high pass to protect the driver) of keeping GD and port velocity in check. The output capability and extension in room wouldn’t be awful, though not suitable for floor-rattling organ works. Most anything else, I bet it’d sound passable, especially compared with most entry level gear.

I guess I better pony up for Bass Box Pro here, if just for fun

 

[caioferrari]

Honestly,
if the best solution is build another enclosure with dual driver, I’d buy a comercial subwoofer.
Here in Brazil, these products are very expensive. A SVS SB3000 is around U$5,5k here!
But… I saw a KEF KUBE 12B is U$860 witch is a good buy over here. May be it solves all and gives me the auto on resource that I don’t have with my diy setup.

I have a real interest to know if there is a problem with my alignment that I missed during simulation on WinISD

 

[TLS Guy]

Honestly,
if the best solution is build another enclosure with dual driver, I’d buy a comercial subwoofer.
Here in Brazil, these products are very expensive. A SVS SB3000 is around U$5,5k here!
But… I saw a KEF KUBE 12B is U$860 witch is a good buy over here. May be it solves all and gives me the auto on resource that I don’t have with my diy setup.

I have a real interest to know if there is a problem with my alignment that I missed during simulation on WinISD

That KEF Kube might be a solution. It is a 12" sealed sub with 300 watt amp. F6 is 22 Hz so F3 will be just over 30 Hz. They do not specify the spl. at 22 Hz. I doubt it is potent, as 300 watts is not a lot of power for a sealed sub of that size given the Eq required.

You box is 43lt. which is 1.5 cu.ft. So if you bought an extra driver and made another hole for it, then plugged the port you would have around the optimal box.

I will do a model later, but you probably would be ahead of that Kube. Lets see the spl. is below 30 Hz. I will do a sealed model for two of those driver in your 43 lt. box later. I have a feeling it will be a reasonable performer and best that KEF Kube.

 

[Steve81]

if the best solution is build another enclosure with dual driver, I’d buy a comercial subwoofer.

I have a real interest to know if there is a problem with my alignment that I missed during simulation on WinISD

OK, here's a comparison, all driven at 350W:
1. My build bumped up to 45L with a 3" x 27.65" port and a 2nd order filter @ 30Hz in green
2. Your vented build at 45L with a 3" port and no filter in orange
3. Your sealed build at 45L with a 2nd order filter @ 25Hz (note: WinISD reports this as Qtc 0.642, so Dr. Mark may have erred on that in his sealed report)

SPL: 45L is oversized for a vented 30Hz tune.

Cone Excursion: The sealed is out of steam at 350W; the 30Hz vented needs a HPF to protect against transients below its port tune; mine can bump up to 550W before hitting Xmax at any frequency.

Port Air Velocity: That 45L/30Hz tune needs a lot of port volume to work properly, and is likely compressing & chuffing at high levels

Group Delay: The sealed has no issues; my 20Hz tune never reaches 1 cycle, even with the HPF, and the peak of the delay is in the infrasonic band. The 45L/30Hz tune with no filters is approaching 1 cycle delay around 30Hz, and any filters you add to that will add to the delay.

 

[TLS Guy]

OK, here's a comparison, all driven at 350W:
1. My build bumped up to 45L with a 3" x 27.65" port and a 2nd order filter @ 30Hz in green
2. Your vented build at 45L with a 3" port and no filter in orange
3. Your sealed build at 45L with a 2nd order filter @ 25Hz (note: WinISD reports this as Qtc 0.642, so Dr. Mark may have erred on that in his sealed report)

SPL: 45L is oversized for a vented 30Hz tune.
View attachment 63134
Cone Excursion: The sealed is out of steam at 350W; the 30Hz vented needs a HPF to protect against transients below its port tune; mine can bump up to 550W before hitting Xmax at any frequency.
View attachment 63135
Port Air Velocity: That 45L/30Hz tune needs a lot of port volume to work properly, and is likely compressing & chuffing at high levels
View attachment 63136
Group Delay: The sealed has no issues; my 20Hz tune never reaches 1 cycle, even with the HPF, and the peak of the delay is in the infrasonic band. The 45L/30Hz tune with no filters is approaching 1 cycle delay around 30Hz, and any filters you add to that will add to the delay.
View attachment 63137

I was referring to the Qts of the driver. The model shows Qtc of 0.642.

 

[Steve81]

The model shows Qtc of 0.642.

My model shows Qtc of 0.642 at 45L; you put that in the box properties for the 0.488cu ft build (~14L). The Qes variance (0.519 forced by WinISD vs 0.48 spec) doesn’t appear to be making a material difference one way or the other. WinISD accepted the spec’ed Qts.

 

[caioferrari]

You box is 43lt. which is 1.5 cu.ft. So if you bought an extra driver and made another hole for it, then plugged the port you would have around the optimal box.

I will do a model later, but you probably would be ahead of that Kube. Lets see the spl. is below 30 Hz. I will do a sealed model for two of those driver in your 43 lt. box later. I have a feeling it will be a reasonable performer and best that KEF Kube.

The problem is the enclosure has internal bracing and the panel where the speaker is mounted is triple. The back of enclosure is just a 1” MDF. Put another driver on that box is impossible, I’d make another one from sketch. Aaaand, this driver is discontinued, impossible to find in good conditions.

 

[TLS Guy]

Honestly,
if the best solution is build another enclosure with dual driver, I’d buy a comercial subwoofer.
Here in Brazil, these products are very expensive. A SVS SB3000 is around U$5,5k here!
But… I saw a KEF KUBE 12B is U$860 witch is a good buy over here. May be it solves all and gives me the auto on resource that I don’t have with my diy setup.

I have a real interest to know if there is a problem with my alignment that I missed during simulation on WinISD

Here you go, this looks a lot more promising. You will have good spl. With a boost of 12 db per octave below 55 Hz and high pass between 20 and 25 Hz, you will have a good sub. Two drivers will do the trick. Qtc is 0.547 which is very reasonable. Using two drivers transforms the design.

 

[caioferrari]

OK, here's a comparison, all driven at 350W:
1. My build bumped up to 45L with a 3" x 27.65" port and a 2nd order filter @ 30Hz in green
2. Your vented build at 45L with a 3" port and no filter in orange
3. Your sealed build at 45L with a 2nd order filter @ 25Hz (note: WinISD reports this as Qtc 0.642, so Dr. Mark may have erred on that in his sealed report)

SPL: 45L is oversized for a vented 30Hz tune.

Cone Excursion: The sealed is out of steam at 350W; the 30Hz vented needs a HPF to protect against transients below its port tune; mine can bump up to 550W before hitting Xmax at any frequency.

Port Air Velocity: That 45L/30Hz tune needs a lot of port volume to work properly, and is likely compressing & chuffing at high levels

Group Delay: The sealed has no issues; my 20Hz tune never reaches 1 cycle, even with the HPF, and the peak of the delay is in the infrasonic band. The 45L/30Hz tune with no filters is approaching 1 cycle delay around 30Hz, and any filters you add to that will add to the delay.

I’m ok at cone excursion since I don’t reach the power limit. My room is pretty small and is opened at side. I’ve never reacher excursion limit.

I got a port chuffing during a test only. Pretty annoying.

Since my alignment is reaching 1 cycle and, the crown amp has a HPF at 20 Hz and my receiver is adding a LPF, is pretty possible that I’m above the 1 cycle limit. Soooo, there is a measurable propriety showing my design is f***, am I right?

 

[Steve81]

I’m ok at cone excursion since I don’t reach the power limit. My room is pretty small and is opened at side. I’ve never reacher excursion limit.

I got a port chuffing during a test only. Pretty annoying.

Sin e my alignment is reaching 1 cycle and, the crown amp has a HPF at 20 Hz and my receiver is adding a LPF, is pretty possible that I’m above the 1 cycle limit. Soooo, there is a measurable propriety showing my design is f***, am I right?

Basically A longer port will fix it. Stick it in as deep as the old, have a bend, and run the rest of the port up vertically so it looks like your sub is snorkeling

What kind of HPF at 20Hz, and is it adjustable? I can modify my model as needed.

 

[caioferrari]

Basically A longer port will fix it. Stick it in as deep as the old, have a bend, and run the rest of the port up vertically so it looks like your sub is snorkeling

What kind of HPF at 20Hz, and is it adjustable? I can modify my model as needed.

I will try a longer port. It’s the cheapest shot to try to save the design. If I don’t like the result, I’ll try the sealed or buy I comercial sub anyway.
The HPF is not adjustable and I don’t know what kind it is. Is just a standard filter that digital amps has on input.

I just thought that since I’m not liking my sub, I adjusted the receiver LPF crossover to 40 Hz (before judging me, I don’t reach my system limit!), the group delay of my sub is probably above the roof!!!!

 

[TLS Guy]

I will try a longer port. It’s the cheapest shot to try to save the design. If I don’t like the result, I’ll try the sealed or buy I comercial sub anyway.
The HPF is not adjustable and I don’t know what kind it is. Is just a standard filter that digital amps has on input.

I just thought that since I’m not liking my sub, I adjusted the receiver LPF crossover to 40 Hz (before judging me, I don’t reach my system limit!), the group delay of my sub is probably above the roof!!!!

Unfortunately that sub can not be tuned with a port. It takes a port 4" in diameter and 37 inches long! That would have a horrendous audible port resonance.

If it were me, I would buy another driver and seal the port. That really would make a very acceptable sub, that you would enjoy.