Front or Rear Port...Room treatment quandary?

[Dapper Dan]

When considering a Bass Reflex design speaker cabinet for a home theatre, and for that matter, a two channel system, won’t the room treatment affect the port location? (assuming using LEDE treatment)

Assume that a Bass reflex speaker cabinet of a volume say, 30 to 40 litres is used. From my understanding, the port could either be on the front baffle or the rear. (I guess for that matter, it could really be on any side of the cabinet, but the front and rear seem to be the most sensible). The rear port is obviously the preferred position in most of today’s designs as it cosmetically does not affect the front baffle appearance (read symmetry).

If we treat the area behind the speaker, to reduce the reflections/resonances, would that not also adversely affect the sound from the port equally? That is to say, if the rear port was being used to reinforce the bass by using the room wall, then treating it in such a way would cause a loss in the bass that was desired? (Not considering a Sub in this example)

Rear ports have a recommended minimum distance from the rear wall and moving them closer affects the sound reproduction, with rear wall treatment, I would guess doubly so in some instances. Also using bungs in the port only add to the dilemma.

If bookshelf speakers are to be used, they also suffer from being rear ported if indeed they where to be placed near a wall on a shelf. (Heavens fordid a bookshelf, anyone remember JBL L100 Century bookshelf speakers…must have been big books!)

What about Surrounds that are ported, does this have the same effect on Bi/Di poles?

So would that then suggest a front port on the speaker is a better option?

Most Studio Monitors I have seen have front ports (JBL, Tannoy et. al), but they are usually near field, or mid field monitors so that room acoustics treatment are of little consequence in the listening position (not suggesting that studios are not treated, just they have different requirements than most household rooms). A home theatre is a different story in this case.

Any ideas?

Designers, engineers, manufactures and hobbyist who have actually experimented with and tried the LEDE concept with relation to the port design, I would like your empirical input.

Cheers,

Dapper Dan…

 

[bpape]

The only times I would worry about a rear port are:

1. You're already too close to the wall behind

2. You're trying to build the speaker into a column or cabinet of some sort.

The bass from the port will radiate in a spherical pattern. Think of it this way. If it were a front port, you'd be moving throughout the space first, then hit the absorbant, then back in space, then the absorbant, etc.

With the port in the back you just start in the opposite direction - absorbant, out in space, absorbant, out in space.

 

[Dapper Dan]

The only times I would worry about a rear port are:

1. You're already too close to the wall behind

Well that’s exactly the problem....small room, so putting speakers about 2~3 feet away from the wall is not really viable.

2. You're trying to build the speaker into a column or cabinet of some sort.

To avoid standing waves and to prevent nodes from developing, I was thinking about insetting the speakers into the column. (Location previously calculated) That’s why dipoles would be a preference, to disperse the sound rather than "focus" it in one direction. The columns would also assist in cosmetically hiding the speaker in that location

The bass from the port will radiate in a spherical pattern. Think of it this way. If it were a front port, you'd be moving throughout the space first, then hit the absorbant, then back in space, then the absorbant, etc.

With the port in the back you just start in the opposite direction - absorbant, out in space, absorbant, out in space.

Thanks for the info...Whilst I am only learning about the subject of room treatment, I may have opened a Pandora's Box. I would like to make corrections/decisions before installation so the best results can be achieved without too much unnecessary increase in room preperation work load.