ports on speakers ?

leftwinger57

This is something I truely do not understand. Looking at my 3 different sets of 2-chl speakers they are all ported differently.The JBL 2060 lower fronts,the Infintys lower rear,and the Bose 601s on the top slant just before the the woofer.So my question is why all the differing designs w/porting and those are just my 3 I'm sure there are others in more positions.Also just remembered the Klipsch sub is rear ported/w the woofer down fireing.I can maybe understand a rear port to blast a wall for reflextion but that's as far as my reasoning will take me.

F1nut

The same reason amps, pre amps, CDP's, cables are all designed differently, the designer thought he had a better idea.

Joe08867

Here is an article that explains how ports work in Sub Enclosures. It works the same way in regular speaker design.
http://forum.blu-ray.com/showthread.php?t=43669

Sealed Enclosure: Originally this design was pioneered by companies like Acoustic Research. It consists of a driver mounted on one side of a sealed box. The air tight enclosure completely isolates the back wave of the driver from the front.
The sealed enclosure system is characterized by excellent transient response, excellent power handling at low frequencies, easy to design and build, smaller box size, and lower sensitivity to misaligned parameters when compared to port enclosure. However, sealed designs have a higher cutoff point and lower sensitivity than ported systems.

Because of excellent transient response (i.e., no boomy sound), when designed and build properly, some audiophiles prefer these type of subwoofers. There are others who completely dispute that sealed boxes have better transient response. They claim that the perception of transient is really a function of perceived sound quality and not the type of enclosure. According to these critics, what does improve transient response (or perceived quality) is usually more headroom, more drivers, larger boxes (depending on the driver), better efficiency, and very low distortion.

Ported Design: Some subwoofer enclosures may add an additional open port (sometimes called duct, vent, or tunnel) which allows the passage of air in and out of the box. At low frequencies, the port contributes up to +3dB to the output and makes the system more efficient and thus increases the bass response. A ported enclosure system consists of a driver mounted on one side of a box that has an open port (duct, vent, tunnel).

The ported subwoofers are characterized by lower distortion and higher power handling in the operating range, and lower cutoff frequency than a sealed enclosure system using the same driver. Distortion rapidly increases below the cutoff frequency however as the driver unloads and loses damping. Due to this, ported enclosures require a low frequency filter. The transient response of a ported enclosure is usually worse than a sealed enclosure system using the same driver. Ported enclosure systems are much more sensitive to misaligned parameters than sealed enclosure systems, which makes their construction more difficult.

Passive Radiator: Another type of subwoofer enclosure may add a passive radiator, instead of a port, to increase the efficiency of the sub. Passive radiators are sometimes drivers with the voice coil and magnet removed, or like a flat diaphragm. The radiator must usually be at least as large (or larger) than the driver in the enclosure.

Advantages of the passive radiator include the absence of port noise, and some audiophiles claim the radiator provides a better sounding bass than a ported enclosure. However, the cutoff (-3dB) frequency is slightly higher than ported design using the same driver.

Other Disadvantages include difficulty in tuning passive radiator designs as they have much higher mass than an equivalent port. In a port, the moving mass is comprised of the air in the port and the driver. The mass of the passive radiator, however, is high because it is the mass of the usually larger moving radiator plus the active driver. It is possible that when the powered subwoofer cone stops, the passive radiator's cone continues to move for a short period of time and may cause the powered driver cone itself to move after the signal has stopped. This so called "ping-pong" effect can cause distortion.

4th Order (Single Reflex) and 6th order (Dual Reflex) Bandpass Design: In a 4th Order Design the driver is completely buried in the enclosure and is mounted in a sealed chamber. It fires into a second ported chamber with the sound emanating from one or more ports.

These designs are very efficient within the operating bandwidth, with superior power handling, but generally can be very difficult to design and build. Companies like KEF helped pioneer this design.



The 6th Order Design was engineered and patented by Bose with their original AM-5 Acoustimass home speaker system.
This design is even more efficient than a single reflex bandpass, but with a compromise. Power handling within its frequency bandwidth is excellent, enabling these enclosures to play very loud. Transient response, however, is relatively poor, making them one of the most difficult enclosures to build and tune.

Now about:http://forum.blu-ray.com/showthread.php?t=43669
Rear Ported vs Front Ported Speakers
Why do some bass-reflex speakers have a port on the rear panel while others have a port on the front baffle where the drivers are? And is the port location important?

Many smaller speakers use a rear port simply because there isn’t room on the front baffle. A designer might specify a woofer that’s comparatively large in relationship to the baffle dimensions. Other speakers use a tweeter with a large mounting plate for rigidity so even if the tweeter itself is small, the physical package it comes in isn’t. Still another reason for not having a front port may be bracing inside the enclosure that mounts exactly where the port would otherwise go.

A rear port solves these problems. There’s generally a lot more room to place the port as the only other element on most rear panels is the speaker wire terminals and they’re comparatively small.

From a performance perspective, there’s virtually no difference whatsoever between a front port and a rear port. The only thing you have to be careful about with a rear-ported speaker is placement. Don’t mount it flush against a wall or other solid surface. That will restrict the air flow in and out of the port and thus restrict bass response. (Without going into details, the woofer cone and port work together to bring you the bass you want.)

The solution is to leave enough room (about 6” will do nicely) between the rear panel of the speaker and the solid object behind it. That’ll allow free air movement through the port so you’ll get all the performance you’ve paid for.

leftwinger57

Joe ,that was fantastic, there had to much more than a design feature as F1 suggested.In all some of the material went right over mind incredibly small mind but I got the jist of it.The point of there is no difference between front and rear ports in sound reproduction surprised me and only the fact that space is an issue.My sub and Infinitys are a good 6'' away from the wall so I'm good there and nothing is blocking any of the front ported speakers.

zane77

Joe, Great response a lot of information in that post. Thanks!

F1nut

there had to much more than a design feature as F1 suggested.

It still boils down to what the designer is trying to accomplish, what he has to work with and the desired price point.

leftwinger57

FI,no argument there. Sure everyone is after the better mouse trap as the old folks say but there is science behind it. I looked at your original response and it really told me nothing,but as you expanded a little I fully understand what your also saying...

cowtrimmer

Great explanation from Joe :cheesygrin:

Face

Port location can make a difference. By placing a port directly behind a woofer in a two way speaker, you will have more midrange leakage, which may or may not be desirable.

Joe08867

F1nut wrote: »

It still boils down to what the designer is trying to accomplish, what he has to work with and the desired price point.

As well as aesthetics. Polk could have placed a larger port in the front of there towers but instead used the power port on the rear and or bottom to keep the look of the group similar across the board.

arny

leftwinger57 wrote: »

This is something I truely do not understand. Looking at my 3 different sets of 2-chl speakers they are all ported differently.The JBL 2060 lower fronts,the Infintys lower rear,and the Bose 601s on the top slant just before the the woofer.So my question is why all the differing designs w/porting and those are just my 3 I'm sure there are others in more positions.Also just remembered the Klipsch sub is rear ported/w the woofer down fireing.I can maybe understand a rear port to blast a wall for reflextion but that's as far as my reasoning will take me.

The most important thing about a speaker's port is where the rest of the speaker is. ;-)

The sound coming out of the port is predominately composed of frequencies near the lower response limit of the speaker system. For most speakers, these are frequencies that have very long wavelengths on the order of dozens of feet, and therefore tend to be very non-directional. If a port emits higher frequencies, this is usually a fault such as excess turbulence due to the port being too small for the rest of the speaker.

Designers therefore have quite a bit of latitude when they position a speaker port as long as it is large enough, not blocked and is properly composed of just low frequencies.