Round Port Vs Slot Port For Spl
One of the more common questions on the Audioholics forums is the matter of which is superior: sealed or ported subwoofers. Unfortunately, there are a lot of popular misconceptions out there: you might hear some folks say that ported subwoofers are no good for music, and are only useful for delivering big sound effects, or conversely that sealed subwoofers are “musical”, but lack the depth to deliver the bass called for in today’s blockbusters. While some subwoofers may certainly fit these stereotypes, the truth is considerably more complex. Ultimately, sound quality is far more a function of good engineering and choosing the right tool for the job rather than a question of sealed vs ported. Nonetheless, each alignment does come with specific strengths and weaknesses, the balance of which may make one type more suitable to your situation than the other.
- In this video I answer a few questions you guys have had about ports. I give examples of the most common types of ports and all the different ways to channel.
- I am trying to open port 3000 on Ubuntu 12.04, cause I have a web server listening there. I'm a bit out of my confort zone here, and spent many hours trying to solve the problem without success. Port seems to be open in the firewall.
- Square and Round ports are the best you can use, the further off your ratio of a Rectangular port, the more likely for port noise, and the more the tuning is going to be off from what the port calculators calculate (considering there is more square inches of port wall given a set amount of port area in a rectangular with a ratio of 1:9 than a.
Round Port Vs Slot Port For Splash
Sealed vs Ported Subwoofers YouTube Discussion
Sealed Subwoofers
For example, Apple's newest MacBook Pro models feature several Thunderbolt 3 USB-C ports. But the standard MacBook's single USB-C port lacks Thunderbolt 3 support. Because of all this, USB-C is a bit confusing. The port can either be a basic USB port similar to the ones above, or it can be a multi-purpose jack. This depends on the device. That's really how more port area (such as in a slot port) helps you, by decreasing air velocity through the port. So if your port velocity is 13 m/s with a 100 sq. Inch slot port and 13 m/s with 60 sq. Inches of aero port, there should be no difference.
The simplest type of subwoofer to design and construct, sealed subwoofers consist of a driver, an enclosure, and an amplifier; the driver is responsible for 100% of the system’s output.
The SVS SB13-Ultra, a compact yet powerful sealed subwoofer.
Overall system performance is a function of the driver’s Thiele/Small parameters and enclosure volume, which together will determine system Q and the system’s resonant frequency. Below the resonant frequency, sealed subwoofers typically feature a shallow roll-off of 12dB/octave, which also corresponds with relatively low levels of group delay and ringing in the deep bass.
Frequency response of driver X modeled in boxes with a Qtc (system Q) of 0.5 (critically damped), 0.707 (optimally flat), and 1.0 (moderately underdamped).
As you can see in the graphs above, it’s possible to get a wide variety of response profiles from sealed subwoofers. The simulations above were achieved by simply varying box volume, with a Qtc of 1.0 being achieved in a small 54L box, 0.707 in a medium sized 136L box, and 0.5 in a very large 525L enclosure. Subjectively speaking, lower Q boxes (0.707 and lower) tend to be characterized as relatively tight, while high Q enclosures can be a bit boomy without equalization due to their response hump in the mid-bass range. On the other hand, one benefit of higher Q enclosures is that they offer a greater degree of protection for the driver against high-energy, low-frequency transients.
Excursion of driver X modeled in boxes with a Qtc of 0.5, 0.707, and 1.0, with 200W of power applied. Note that while a Qtc of 0.5 corresponds with a relatively extended response, there is a price to pay as this requires tremendous amounts of excursion at low frequencies.
Bottom Line
While not all sealed subwoofers are created equal, properly done the alignment has a lot to offer. Size is typically manageable; the earlier pictured SB13-Ultra is effectively a 17.5” cube, giving it a lot of flexibility in placement as well as a high SAF (spouse acceptance factor). While small size tends to come at the expense of extension, sealed subwoofers generally have a shallow low-end roll-off profile, which corresponds with good performance in the time domain (i.e. group delay / ringing). Last but not least, sealed subwoofers offer some degree of protection against bottoming out the driver, though it is still possible with sufficient power and the right content.
Ported Subwoofers
Round Port Vs Slot Port For Split
Where sealed subwoofers are relatively simple devices, ported subwoofers add a bit of complication to the mixture, i.e. the port. On the upside, porting augments system output at the vent’s resonant frequency, which extends the subwoofer’s response and allows for substantially more output capability at the tuning point relative to a comparable sealed subwoofer.
The SVS PB13-Ultra is a deep-bass monster, but is substantially larger than its sealed brother.
However, below the tuning frequency, the driver is no longer loaded by the enclosure, and acts as if it is in free air. This results in a much steeper roll off rate of 24dB/octave relative to the 12dB/octave slope typical of sealed subwoofers; as a consequence, group delay is typically higher in ported models. In addition, below the tuning frequency, the woofer is in danger of over-excursion without appropriate filters for protection, which can further exacerbate problems related to group delay. Of course, like sealed subwoofers, many different response profiles are possible by varying enclosure size as well as port length vs diameter (larger enclosures and longer ports result in lower tuning points). It should also be noted that ported enclosures are typically much larger than their sealed counterparts.
Frequency response of driver X modelled in a maximally flat ported alignment and a BB4 ported alignment. Relative to the maximally flat alignment, the BB4 utilizes a smaller enclosure (221L vs 305L) but longer port, and achieves a broader “knee” at the low end.
Some folks may also be familiar with variable tune subwoofers, made popular by brands such as SVS and Hsu Research. In such cases, you have a subwoofer with multiple ports, one or more of which can be plugged to lower the system’s resonant frequency. This in turn changes the system’s frequency response profile, and adds a bit more work for the woofer. In addition, with one port open versus two, port air speed increases dramatically, increasing the possibility of chuffing.
Frequency response for driver X when modeled with two ports open resulting in a maximally flat alignment, and one port open offering an extended response.
Excursion of driver X in maximally flat two-port mode vs one-port mode with 200W of input power. In one-port mode, the woofer must dig deeper before the port begins contributing, increasing its excursion requirements. Note in both cases below tuning, excursion goes off the charts quickly.
Bottom Line
Relative to their sealed cousins, ported subwoofers typically offer better low-end extension as well as greater output around their tuning point. However, there is no free lunch; deeply-tuned ported subwoofers tend to be quite large, making them less décor friendly as well as reducing placement options. Further, while ported subwoofers have a big output advantage down to their tuning point, below tune, frequency response drops off steeply while driver excursion goes off the charts. While most commercial subwoofers employ filters to protect the driver from over-excursion, this usually results in an even steeper low end roll off, and consequently problems with group delay and ringing.