Where to put the port: Front or back?

[JonW]

I was wondering about where a good port placement is- the front of the speaker or the rear? Most speakers use the rear. Some the front. A few the bottom.

Against front placement might be that having the port on the front baffle could make baffle diffraction effects a little crazy. And if the port is in the rear, you don’t have to look at it.

But my guess is that front placement might be best in terms of having the sound from the port come from the same general location as the drivers. If the port is in the rear, the port output comes from, say, a foot away from the bass driver and is firing into the opposite direction. Then all your bass would sound could be smeared out because it’s coming from different places and hitting your ears at such different times. So put the port on the front, up close to the woofer.

People don’t seem to do that very often. So I’m probably missing something.

I’d also guess there’s no need to offset the port from the center of the (front or rear) baffle because the frequencies coming out of a port won’t really be influenced by baffle diffraction.

I ask because I’m wondering where I should be putting the port for my ongoing MT design. Thanks.

-Jon

[ThomasW]

I think you need to form a research committee to investigate this ....

Or

Put it on the front below the woofer if there's room, otherwise put it on the back...

[Jed]

I People don’t seem to do that very often. So I’m probably missing something.



-Jon

I measured some noise coming out of the front firing port once. Then, with a bit of dampening material (acousta stuff) in strategic locations it took care of it. Lately I like having the port near the floor boundary to get some added slam.

[JonW]

I think you need to form a research committee to investigate this ....

It’s all the rage with the kids, these days, I hear. :

Put it on the front below the woofer if there's room, otherwise put it on the back...

You’re being very practical. Maybe I’m thinking about it too much.

I measured some noise coming out of the front firing port once. Then, with a bit of dampening material (acousta stuff) in strategic locations it took care of it. Lately I like having the port near the floor boundary to get some added slam.

More slam close to the floor. Interesting. Was your noise from air flowing too quickly through the port? I’ll try to use wide (and Precision) ports to try and avoid that.

[Jed]

I think it was a standing wave of some sort or too much midrange not getting absorbed and coming out of the port.

[cjd]

Big ports put a resonance ripple in the response. You can't win, you know.

Seriously, consider a nice ML-TL and a front "port".

C

[thadman]

Rear placement would probably be fine, the wavelengths the port will be expected to deal with are very, very long. The wavelengths for frequencies below 100hz exceed 10'...much larger than the distance from front to rear (box depth). Side firing woofers and seperate module subwoofer/woofer cabinets are not on the listening axis but are perfectly acceptable and are used much higher in frequency than your port, apply that knowledge to your situation. You should be good to go :B

This is all just a postulation on my part, someone more educated than I may feel free to correct any and all misinformation

[Bent]

Aw come on - who puts their ports on the front?

[JonW]

Big ports put a resonance ripple in the response. You can't win, you know.

Seriously, consider a nice ML-TL and a front "port".

C

Yeah, everything about speaker design seems to be picking your compromises.

What do you mean by ML-TL? And you like a front port?

aw come on - who puts their ports on the front?

Personally, I was considering a port narrower than one capable of ingesting a small child. :P

[cjd]

Mass Loaded Transmission Line Martin King is your friend when it comes to way more info than you ever wanted. I'm not partial to any specific port location, but front porting tends to limit the boundary loading more likely with a rear port (or a down-firing port). So it's still a game of compromises either way. You could buck the trend and side port...

C

[Bent]

Personally, I was considering a port narrower than one capable of ingesting a small child.

The little fella is bigger (safer) now.

[JonW]

Mass Loaded Transmission Line Martin King is your friend when it comes to way more info than you ever wanted. I'm not partial to any specific port location, but front porting tends to limit the boundary loading more likely with a rear port (or a down-firing port). So it's still a game of compromises either way. You could buck the trend and side port...

C

I just had a quick read on ML-TL's. Interesting. I've got a few "standard" box speaker designs in mind to play with (MT's, 3-ways, etc). Maybe I'll branch out some day to OB, TL, or something different. Need more experience first.

Idunno about the port placement, even after what I read. I'm still thinking front and close to the woofer might be best. If the space is available. (It will be on my MT's.)

The little fella is bigger (safer) now.

Good to know that he outgrew the sub. And that he's not stuck in there, with you having to feed him through the port.

[69Stingray]

You missed one option, firing down.

• Given the wavelength, I don’t think it technically matters, the port should be able to blend with the woofer that is rolling off. The "delay" from a rear firing port (from port to wall back to front firing speaker) is probably of little impact (I am guessing).
• Biggest plus/minus is that a rear or down firing port will probably have some boundary gain from the floor or rear wall. Also, a rear firing port may help hide some of the midrange "leakage". If used in the three-way for bass duties the "ported" woofer is crossed over to the midrange before the "midrange leakage" freq. then a low (for floor gain if needed) front firing will probably be fine.

[cinema bob]

Wilson puts the "port" for the alexandria on the front... thats good enough for me

[MarcE]

If using a down firing port, is there a minimum distance between the port exit and the ground that is recommended? Any comments on what effects various flooring surfaces have on down firing ports?

[ThomasW]

The space between the driver and the floor should be no less than the Vd of the driver.

Thick carpet with heavy pad will absorb some output

[MarcE]

The space between the driver and the floor should be no less than the Vd of the driver.

Thick carpet with heavy pad will absorb some output

oh this is nice to know! Thanks! However, I was wondering about the distance from the floor to the port, or the distance from the floor to the bottom of the speaker, assuming the port is flush mounted :B

[ThomasW]

! However, I was wondering about the distance from the floor to the port, or the distance from the floor to the bottom of the speaker, assuming the port is flush mounted

Read the first sentence in my previous post.

[MarcE]

The space between the driver and the floor should be no less than the Vd of the driver.

Sorry, your post is not clear. If the driver is forward firing, with a port on the bottom of the enclosure, how could one measure "the space between the driver and the floor"?

[Jed]

oh this is nice to know! Thanks! However, I was wondering about the distance from the floor to the port, or the distance from the floor to the bottom of the speaker, assuming the port is flush mounted :B

For a 2" port, 2" from the floor should do it. For a 3" port, figure around 3" from the floor.

[Paul H]

The space between the driver and the floor should be no less than the Vd of the driver.

...

????

[kevmurray]

Vd is volume displaced by the driver (in one direction I believe). Seems to me this follows conventional wisdom since the diaphram would hit the floor otherwise. Someone correct me if I'm seeing this wrong.
As far as port distance, I have always read that any obstacles should be at least the port diameter away (like what JED said).

[MarcE]

As far as port distance, I have always read that any obstacles should be at least the port diameter away (like what JED said).

I've always wondered how that worked with double flared ports. I'm assuming you use the nominal diameter of the port. But is the minimum distance to the floor from where the flare begins, or the bottom of the box (assuming the port is flush mounted). Similarly for the inside of the box. Can the edge of the flare be less than one port diameter from the walls? :??

I know these are all guidelines, but seems like things may change with the double flared ports.

[Geoff Gunnell]

Jon, if you are never going to wall, shelf, or cabinet mount your speakers, (ie if you are only going to stand mount them with at least 30" from the back wall), rear porting is reported best to ease airflow away from the back of the woofer.

If you might want to wall, shelf, or cabinet mount the speakers use a front ported configuration.

A couple of smaller diameter ports will reduce midrange leakage compared to one larger port. An ideal location is one smaller port near each bottom corner below the woofer.

With floorstanders, port placement near the floor allows the pressure wave to flow out along the floor with the least disruption. With an eye on subsequent posts, this is not as much a port-to-room impedance issue as it is a fluid flow / wave propagation phenomenum.

[Q45]

If using a down firing port, is there a minimum distance between the port exit and the ground that is recommended? Any comments on what effects various flooring surfaces have on down firing ports?

I actually used a down firing port on a tower project that used (1) 10" & (1) 8" woofer in the lower compartment that was very large. The cabinet was up on legs with 3" of clear air space.

I did that project when I lived in a house that had wood floors and was raised, ie.. did not have a slab.

The bass was awesome!

Then I moved to a house that had a concrete floor slab and the living room was all stone tile. The bass was completely lost and just bounced all over the room.

Definitely consider your house and surroundings.

[ThomasW]

I've always wondered how that worked with double flared ports. I'm assuming you use the nominal diameter of the port. But is the minimum distance to the floor from where the flare begins, or the bottom of the box (assuming the port is flush mounted). Similarly for the inside of the box. Can the edge of the flare be less than one port diameter from the walls? :??

I know these are all guidelines, but seems like things may change with the double flared ports.

With this kind of 'paralysis through analysis', I'm amazed you're able to make breakfast in the morning....

Varying the distance to the floor increases or decreases the resistive load on the port. That of course changes the tuning....

and that's why this forum is dedicated to DIY

[MarcE]

and that's why this forum is dedicated to DIY

sorry, your post isn't clear. Do you mean Do-It-Yourself, or Design-It-Yourself



I'm more of a "nanos gigantium humeris insidentes" man myself than a true DIY person.

Thanks everyone!

[---k---]

"nanos gigantium humeris insidentes"

English Translation:
standing on the shoulders of giants (Latin:nanos gigantium humeris insidentes)

http://en.wikipedia.org/wiki/Standing_on_the_shoulders_of_giants

[kevmurray]

Ot

Off topic but I couldn't help it:

If I have seen farther than others, it is because I have stood on the shoulders of giants.
--Isaac Newton

If I have not seen as far as others, it is because there were giants standing on my shoulders.
--Hal Abelson, Professor of Computer Science and Engineering
(Refering to management and accounting.)

[Kevin Haskins]

I've always wanted to build either a sub or a loudspeaker with a bunch of small flared ports sticking out the top like a carb. A V-8 configuration with eight smaller ports. It would look cool.

[chasw98]

I've always wanted to build either a sub or a loudspeaker with a bunch of small flared ports sticking out the top like a carb. A V-8 configuration with eight smaller ports. It would look cool.

You mean like this? A la Cobra :T

[Kevin Haskins]

You mean like this? A la Cobra :T

Yeah Baby! I may even put an intake manifold and valve covers on the top. That would be REALLY cool.

[Dennis H]

Yeah, buy some Webers for your ports! Should only cost about $2K.

[Kevin Haskins]

Yeah, buy some Webers for your ports! Should only cost about $2K.

I'm too cheap... I'd just use plastic ones. Maybe paint them with that Walmart Chrome paint.

[MJKing]

Martin King is your friend when it comes to way more info than you ever wanted.

Hmmmmmmmm ......

My opinion is as follows. Port on the front, near the floor, and use lightly packed fiber fill inside the box to control standing waves and potential mid-range leakage from the port.

[Dennis H]

I'm too cheap... I'd just use plastic ones. Maybe paint them with that Walmart Chrome paint.

Yeah but if you used real Webers you could have a throttle pedal by your chair to change it from sealed to ported.

[MarcE]

Hmmmmmmmm ......

My opinion is as follows. Port on the front, near the floor, and use lightly packed fiber fill inside the box to control standing waves and potential mid-range leakage from the port.

I'm coming to the conclusion (incidentally after I bought the 4" ports on sale the other day at PE, figures...) that a slot port is the way to go. I think TacoD was the one that originally suggested it to me! :^x

Maybe a slotted port with a bunch of straws stuck in it ...... definitely one to try!

[kevmurray]

Yes back to the subject of this thread... strombergs... or was it triple deuces? Ok OK my vote is for down or rear firing if the tuning frequency is below 40 Hz. I know some people have had success "hiding" port noise with a rear exit. I also know some people who claim that a rear port behind the woofer(s) helps to provide cooling air to the motor. Others find it channels motor/suspension noise into the room. Application specific as always...

[cjd]

Yeah... if you're having problems with motor heating... you're pushing your system too hard and need something bigger! Putting it behind the driver means you get output beyond just the low end augmentation (see the Statements for a design that does this intentionally in the midrange).

Port noise won't go away, it may just get smeared to the point you can't discern the cause of distortion.

And Straws? Doesn't that become an aperiodic system at that point?

C

[Astroguy]

With a downfiring port is there a notable difference between firing directly to the floor versus firing to a base pedestal? I see downfiring subwoofers use both configurations, and I'm trying to figure out the way to go for the subwoofer I'm building.