Port firing downwards?

[markusA]

Just toying with different ideas.
What are the pros/cons/effects of having the port (TL opening, port...) firing downwards the floor?

How do you model this?

I like full range speakers, mine is a ML TQWT.
Most likely my next speaker will be one as well (or TL or something along those lines?).
Getting the most/best bass from these full rangers is always a fun challenge.

I'm thinking one could have some fun with designs if the opening is allowed to fire into the floor.

[edjosh23]

I saw something about this in the subwoofer forum a couple of years ago. Obviously an important issue is the height off the ground. Its worth a search.

Josh

[chrisb]

Since this is posted at the FR forum, I'm thinking that you're not asking about sub woofers.

I'd imagine that the spacing above, and surface material of the floor could have some acoustic affect on the results, but my intuition is that a design that doesn't fire directly (perpendicularly) to the floor might yield smoother coupling to the effective listening area - i.e. less ripple from reflections back through the port/vents.


as to modeling it, there must be someone experienced with that who would care to post?

[Colin]

GM's MLTL for the Jordan 92 has a floor-firing port. In the original design (the 31" version) it has a 45 degree reflector directly below it, built into the stand, to better couple the port to the room. On that basis, I'd imagine a down-firing port should be fine, as long as there's a few inches clearance. Any potential bad effects are likely to be swamped by the room.

[planet10]

All the metronomes have downfiring ports. There is some info in that thread about optimizing the port.

dave

[chrisb]

Originally Posted by planet10

All the metronomes have downfiring ports. There is some info in that thread about optimizing the port.

dave

IINM, many Metronome builders have noted improvements with hard reflecting surfaces (ceramic/granite tiles, etc) under the enclosures if the floor is carpeted

[markusA]

I have started reading the Metronome thread... It's a long one.
Like chrisb says, I'm not thinking subwoofer.
This is a consideration for my next fullrange speaker.

Now for an afterthought or two...
As we are all aware of, one is often forced to use a bsc to fix the bass.
A port firing down should radiate in 2Pi space. (Am I using that term correctly?)
What I mean is the sound from the port is radiating all around the speaker and thus there should be no baffelstep for the port? -> better bass response?

[picowallspeaker]

A port firing down should radiate in 2Pi space. (Am I using that term correctly?)

I guess so . Low frequencies are omnidirectional , beaming starts as frequency raises .
Putting the port below would be useful taking into account where and how the speaker (box) shall be positioned . If it needs space around , but space constraints doesn't permit that , it's a good solution .
Speakers should be positioned far away from the walls ...well , depends on which project...some speakers sounding ugly ,if positioned near a wall (don't matter if and where a reflex port is used)give a correct sound reproduction.

[rjbond3rd]

Actually a downward firing port will radiate into 8pi in a corner, 4pi against a wall. Yes, the low frequencies are omni but the boundary reinforcement still takes place.

It's possible to compensate for baffle step in maybe a dozen ways, including building a "bump" or rise into the desgin at just the right place (whether that bump is built into the cab, or the driver), using a horn design, using the widest possible baffle, EQ, a second rear-firing driver, a 1.5 design etc.

By itself, putting a single-driver cab near/against the wall doesn't by itself totally eliminate it (it just makes the step shallower but maybe so shallow as to make it irrelevant compared to the room factors). Even a BiB has to worry about baffle step. The only cab without baffle step is where you put the driver right into the wall (infinite baffle) in my extremely limited experience.

[markusA]

rjbond3rd> This is my major concearn with the FR speakers.
It's wonderful not having a crossover so I'd rather not add the extra bsc if it can be avoided.

With the cabs I've been toying with the baffel step usually appears around 500Hz +/- 150Hz give or take.
Is it even possible to build a bump that big?
I mean... it's a biggie.
Since we're talking one driver it's kind of unlikely the driver will have such a bump. We're left with the cabinet.

Bi-pole speakers is a solution but arn't you supposed to loose imaging and such? Plus the extra expense...

I'm all ears when it comes to new ideas for solving the baffel step.

Originally Posted by rjbond3rd

Actually a downward firing port will radiate into 8pi in a corner, 4pi against a wall. Yes, the low frequencies are omni but the boundary reinforcement still takes place.

It's possible to compensate for baffle step in maybe a dozen ways, including building a "bump" or rise into the desgin at just the right place (whether that bump is built into the cab, or the driver), using a horn design, using the widest possible baffle, EQ, a second rear-firing driver, a 1.5 design etc.

By itself, putting a single-driver cab near/against the wall doesn't by itself totally eliminate it (it just makes the step shallower but maybe so shallow as to make it irrelevant compared to the room factors). Even a BiB has to worry about baffle step. The only cab without baffle step is where you put the driver right into the wall (infinite baffle) in my extremely limited experience.