Sealed vs Ported Cabs

[Al Krow]

Sealed or Ported. Something that is often mentioned in connection with cabs but not a topic that I could claim any degree of knowledge on.

I found this helpful article on the net earlier and thought I'd share it, in case it's of interest / use to any other fellow BCers who, like me, aren't expert in all matters to do with cab design.

For the cab design experts amongst us - please feel free to jump in with a more succinct summary of the topic and what you're looking out for in well designed cabs.

Sealed vs Ported Cabs.pdf

[Lozz196]

I`m certainly no techy expert, but the majority of the cabs I`ve liked the sound of have been sealed. And I far prefer my Ashdown ABM410 now it`s sealed. 

[Bill Fitzmaurice]

A few notes:
Sealed enclosures have better transient response

Transient response is a primarily a factor in the higher frequencies, where the cabinet alignment has no effect. A very poorly designed ported enclosure can have poor transient response in the mid bass, but being very poorly designed it will have other problems as well. A well designed ported enclosure will not have any transient response issues.

This is one reason why they sound punchier and more accurate.

In blind testing with the systems EQ'd for identical response listeners are unable to identify ported versus sealed cabs. There is no difference in accuracy so long as the speakers are not played at a high enough level for there to be high level harmonic distortion.  'Punch', by and large is the term applied to the sound of a speaker being pushed past its linear excursion limits, resulting in high level harmonic distortion. High THD isn't more accurate, it's less accurate, and it's far easier to realize with a sealed cab than ported. It's also neither inherently good nor bad where amplified instruments are concerned, being a matter of taste. If you have a ported cab and want to get it to sound like sealed that's easy enough, turn the bass EQ down. If you have a sealed cab and want it to sound like ported turn the bass EQ up. The ported cab with lower bass EQ still won't have the THD of sealed, and the sealed cab with bass EQ boosted still won't have the low end output capability of ported, but that's why you can still buy both types.

There are some disadvantages to ported enclosures. Transient response is poor compared to a sealed
enclosure. The result is decreased accuracy.

If ported enclosures had less accuracy than sealed then the vast majority of high end speakers, as in over $10K each, would be sealed. They're not. For that matter the vast majority of speakers are ported, irrespective of the price range.

A poorly designed ported enclosure can cause all sorts of problems.

That's true, but since the advent of speaker modeling software back in the 1990s there's no excuse for a ported enclosure to be poorly designed, other than the designers lack of knowledge. 

There is one instance where by and large a sealed enclosure is preferable to ported, that being a mid bass speaker specifically intended for use with a subwoofer. When a speaker isn't going to be used below 80 to 100Hz in most cases sealed will work just as well as ported, so there's no good reason to incur the added design complexity, cost and physical size of a ported enclosure.

 

 

 

 

Edited October 28, 2018 by Bill Fitzmaurice

[dave_bass5]

Cool thread topic. I was going to start one about the design of my new TCE RS212 cab.

I was surprised they put two ports, next to each other on it. Im sure there is a reason and its all worked out in software frist, but i was wondering why two, why next to each other, and why these cabs are not the norm when it comes to design.

[chris_b]

I would imagine more and smaller ports maintain the integrity, the rigidity, of the panel.

[itu]

With two ports it is easier to put them to a smaller front panel along with the driver. A bigger one needs more space. Simple as that.

If people think that some design principle is better than another, I suggest them to do some blind tests. If the listener sees the equipment, they give funny comments on system's performance. One of the best tests was a speaker test that had just one pair of speakers. This pair was dressed with three different coloured fabrics, one at a time: white, brown and black. With brown cloth the sound of the pair was told to be somewhat muddy (no wonder), with white the speakers had a bit too clean, nearly metallic sound, and with black the sound was articulated. Same music, same pair, different colour. And you were thinking that music is not visual?

There is no such thing as The Superior Design. Otherwise everybody would use that and that only. Ever seen such a design? Me neither.

Another thing is that PA (i.e. bass) amplification is everything but linear/flat. The frequency response is not that important and that is why there are very different sounds coming from different systems.

[Chienmortbb]

13 hours ago, itu said:

With two ports it is easier to put them to a smaller front panel along with the driver. A bigger one needs more space. Simple as that.

If people think that some design principle is better than another, I suggest them to do some blind tests. If the listener sees the equipment, they give funny comments on system's performance. One of the best tests was a speaker test that had just one pair of speakers. This pair was dressed with three different coloured fabrics, one at a time: white, brown and black. With brown cloth the sound of the pair was told to be somewhat muddy (no wonder), with white the speakers had a bit too clean, nearly metallic sound, and with black the sound was articulated. Same music, same pair, different colour. And you were thinking that music is not visual?

There is no such thing as The Superior Design. Otherwise everybody would use that and that only. Ever seen such a design? Me neither.

Another thing is that PA (i.e. bass) amplification is everything but linear/flat. The frequency response is not that important and that is why there are very different sounds coming from different systems.

We did some testing on the Basschat 1x12 design. One large port versus four small ones. There was no contest, the four port design was making noises way before  the single large port.I  believe that there is less friction on the larger port and that makes for less turbulence.

Real estate is a problem though as a 5" port takes up a lot of the area of a front panel. One of the reasons people rear port.  Other ports are chosen to aid cabinet strength. Corner/triangular or slot ports port also act as bracing and are efficient users of space when paired with circular drivers. However they (triangular)  are the worst in terms of friction. One large round driver has less surface area than any other design.

Every speaker design is a compromise. It is like squeezing a balloon. A gain in one area raises problems elsewhere.

 

[Bill Fitzmaurice]

1 hour ago, Chienmortbb said:

We did some testing on the Basschat 1x12 design. One large port versus four small ones. There was no contest, the four port design was making noises way before  the single large port.I  believe that there is less friction on the larger port and that makes for less turbulence.

Assuming the total area of the four ports was the same as the area of one port that result is to be expected. There is an area of high friction close to a port wall. That can cause chuffing noise with multiple small ports or narrow slot ports, which put the center of the port closer to port walls. It's easy enough to cure, by making the port area larger when those configurations are used.

 

[fleabag]

I dont get chuffing with my 4 ports. Maybe because they're 100mm diameter each in a large-ish  1x15 cab ??

[Bill Fitzmaurice]

That's correct. A single 12cm diameter round port is usually sufficient for a 15 inch driver. Split into four 6cm ports you might get some chuffing. The added area of four 10cm ports prevents it.

[fleabag]

Result. 

Cheers William

[stevie]

On 31/10/2018 at 12:03, Bill Fitzmaurice said:

Assuming the total area of the four ports was the same as the area of one port that result is to be expected. There is an area of high friction close to a port wall. That can cause chuffing noise with multiple small ports or narrow slot ports, which put the center of the port closer to port walls. It's easy enough to cure, by making the port area larger when those configurations are used.

 

No. That's not how to fix the problem at all. Particularly with small, high power cabinets, you can't just increase the port area willy-nilly because you soon run into problems with port length. The best solution is to reduce the wall area of the ports. That means, ideally, a single round port.

The only bass guitar cab designer who seems to understand the importance of this is David Nordschow.

Edited November 1, 2018 by stevie

[Kevin Dean]

what I love about my Ashdown Cl310 DH   is that the two bottom 10" speakers are ported & the top one is sealed , I get a great clear tone while standing right next to it on tight stages but a full bass sound is hitting the dance floor area .

[Bill Fitzmaurice]

That's a logical arrangement if the upper driver is high passed and is a driver with specs optimized for a sealed enclosure, perhaps a guitar driver. But there are two other issues with that cab design that make me hesitant to assume how well it's engineered. The port area is too small for a pair of tens, while the horizontally placed tweeters should be splayed inward in a cross-firing arrangement, not splayed outward. That's not to say that it doesn't sound good, but it could probably be better.

[msb]

I have used sealed and ported cabs over the years , today all but one cab are ported.
So I guess I prefer ported cabs.

Mine are modern cabs , best sounding cabs I’ve ever owned , lightweight too. Bergantinos.