Front vs. Rear Port

I went from front to rear port in one of my designs.

It's not at all uncommon for some midrange energy to emerge from the port. If the woofer is active up to frequencies where the port is 1/4 wavelength long, you stand a good chance of getting midrange port resonances (imagine talking through a cardboard tube). If that happens, better to aim it backwards than forwards.

As you correctly suspect, proximity to room boundaries will reinforce a rear-firing port's output. This is usually detrimental, and can be a cause of "boominess". On the other hand if the enclosure were tuned with the expectation of boundary reinforcement of the port's output, the net result would likely be deeper than normal bass extension. Audio Note uses this technique with their rear-ported AN/E, which is intended to be placed in a corner. I borrowed the idea and incorporate a variable-length port system in my rear ported designs.

Now if a rear-facing port is close enough to the back wall, the wall will increase the effective port length enough to change the box tuning. This may or may not be beneficial in a given situation. Keeping the port two or more port diameters distance away from the wall reduces this effect to negligible (which again may or may not be beneficial).

As long as the path length around the box from the rear-facing port to the front-firing woofer is less than 1/4 wavelength at the port's tuning frequency, there should be negligible loss of bass impact from the path length difference. In fact, placing the port in a different plane from the woofer would help to spread out their room interaction effects by giving them different path lengths to the room boundaries. In theory this would smooth the bass a little bit.

All that being said, port location is probably unlikely to be a major factor in the overall sound quality of a loudspeaker system.

Duke

Aktchi, I showed two speakers of my own design at the Rocky Mountain Audio Fest in Denver a few weeks ago, using "AudioKinesis" as my brand name. I don't sell through a dealer network - just peddle 'em myself.

Don't want to hi-jack Raduray's thread, so will just mention that you can read about 'em on my website, www.audiokinesis.com.

Johnk, I also like down-firing ports, though at the moment I'm not using a down-firing port in any of my designs. But I'll concede that down-firing is probably the ideal. Do you find that the floor surface underneath a down-firing port is a significant consideration? I mean, like whether it's a hard surface or carpeted?

Cheers,

Duke

JohnK, thanks for sharing your experiences. I built a large Snell Acoustics Type A-inspired system with downfiring woofer and port nearly twenty years ago, but I only used it in one room, which had a hardwood floor.

Raduray, there's more to a speaker working well in a corner than just the porting issue. You see, the walls that intersect right behind the speaker will act sort of like a giant horn and redirect energy that normally would have spread out to the sides, sending it towards the listening area. The result can be coloration if the speaker is putting a lot of energy off to the sides at some frequencies but not at others.

Loudspeaker radiation pattern is sort of my hobby within a hobby. I'll e-mail you offline about something that might work in your situation, as it addresses the port tuning issue and the radiation pattern control issue.

If you have any questions that might be of general interest, post 'em here and I'll offer my $.02 worth.

Duke