Front vs. Rear Port

Front Ports generally work better when a speaker is close to the wall. There are some exceptions.

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

Raduray: Yes, conventional wisdom says to use front porting if the speaker is placed close to the back wall.

Duke: Please forgive my ignirance but when you speak of your designs, are these commercially marketed models? What name do they go by?

I port out the bottom or back of cabinet I tried front ports not my cup of tea,best is bottom porting [this is harder and more costly to pull off]next back.Only front ports I now use are slot ports for bass systems only[oris ref]If my customers would let me back port these cabinets I would but they like the look;).

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

Duke spells the truth.
The whole idea of rear port is to isolate woofer resonance.

Hi Duke, I notice little diferance with floor materials but I do include a damping pad if one has a very live room also inc cones or feet if one has deep pile carpets.Problem is spacing of port from floor and designing cabinets to have the free space below for the port this causes extra work for you will need funky bases or arched plinths,more careful tuning of ports, but it sure works. Loads the room with even bass pressure, allows easy of placement, systems so equiped can be placed near walls or far out in room since bass port is using floor for reinforcement I as a designer know distance from floor to port and can design for this with front or rear you dont know distance to walls just floor so loudspeaker with front or rear ports needs more careful room placement.PS if you use a bottom port in one of your designs I want a free T shirt .lol

Interesting about the bottom ports. May be what I need as the only (WAF) acceptable location for my speakers is in the corners of my room. My B&W DM580's are boomy, even with old (clean) socks stuck into the ports - I lost the foam plugs. What are some bottom ported speakers <$3-4K that will give me tight bass in the corners?

Radu

Hope I'm not hijacking here, but a related question on downward firing ports and woofers:

Does a downward firing woofer and port (i.e. all meaningful output below, say 100hz or 150hz) greatly reduce or eliminate the so called "Allison Effect" and make the speaker's in-room response much closer to its anechoic performance? It seems like any speaker (ported or not) using a woofer crossed low enough would benefit from a downward firing scheme. Is this right?

Marty

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