So,
Bass reflex ports facing the rear are not so room friendly (depends)
Front facing ports are from what I know are also not ideal...
I have a port of 110mm width and 550cm length. Is there disadvantages to a port facing upward?
Yes the kids will throw some stuff inside the speaker, and it is a bit weird looking... something I am missing?
Bass reflex ports facing the rear are not so room friendly (depends)
Front facing ports are from what I know are also not ideal...
I have a port of 110mm width and 550cm length. Is there disadvantages to a port facing upward?
Yes the kids will throw some stuff inside the speaker, and it is a bit weird looking... something I am missing?
Dunno, never tried it, personally found 'best' to be floor loaded if practical and use gap to fine tune, otherwise (preferably pair of) PR(s).
Hello Noam
I guess the dust thing will just mean a little bit of additional work now and then. But I am not so much a fan of cloth over reflex ports.
Timmermans of "Hobby HiFi" is a fan of ports on the side.
Regards
Charles
I guess the dust thing will just mean a little bit of additional work now and then. But I am not so much a fan of cloth over reflex ports.
Timmermans of "Hobby HiFi" is a fan of ports on the side.
Regards
Charles
Thank you Charles for your response. A side port will probably be the right solution. still wondering if I ever saw an upward firing port on commercial speakers, I don't think so...
FWIW, the KEF 201/2 had an up firing port, worked well. It has a small bit of grille cloth built in flush to stop items/dust being deposited down it.
KEF 201/2 by Robert Seymour, on Flickr
Shown below in the cutaway
KEF 201/2 by Robert Seymour, on Flickr
Shown below in the cutaway
Also looks very nice to have this flat matte disk instead of a flared port hole.
It's a good idea to keep the port length no more than three times its diameter.
How I love those open speaker photosFWIW, the KEF 201/2 had an up firing port, worked well. It has a small bit of grille cloth built in flush to stop items/dust being deposited down it.
KEF 201/2 by Robert Seymour, on Flickr
Shown below in the cutaway
Not really, I've done up-firing ducts before now & there have been commercial types too like the KEF above; in the latter case it's mostly a question of space / configuration. It couples slightly differently to nearby boundaries & is usually less efficient in that sense than near-floor types as GM refers to. Otherwise, as far as the internal loading goes, the same rules apply to it as they do to any other external positioning: it's the location of the internal throat relative to the driver & the box dimensions that counts.
A 550cm / 5.5m long vent might be a touch excessive though. 😉
Attachments
Funny, I've just been doing this as part of some port design study. I have to fit a port inside a small enclosure so I started by making a front exit L shaped port with a smooth curve. The idea being the extra length from the L shape allows a larger cross-section than a standard front (or rear) port to minimise turbulence.
However my conclusion was that making even a very slight and smooth curve in the port brings additional 'closed-ended pipe resonance' that are unwanted. They are at about half the frequency of the typical open-ended port resonances but still high in amplitude. In my port the open-ended main resonance was around 950Hz but the curve added another at 450Hz.
I have now opted for a top firing flared port without any bends. It is still longer with more cross-section than a front or rear port could be and it lacks the additional unwanted resonances the curve introduced. If the port were to exit on the bottom it would need to take another turn / bend to exit under the cabinet and I'm quite sure that will cause additional unwanted resonances due to the impedance mismatch and reflection from the boundary, exactly like my L shaped port. Unless you can float the speakers high enough in the air (I guess like 5 inches or more) or have a special open stand.
Covering the port with cloth or open-cell (reticulated) foam will also bring unwanted turbulence. I'll be trying a fine mesh like fly screen but didn't test any yet.
Quite a lot of info there I hope I explained it clearly enough.
However my conclusion was that making even a very slight and smooth curve in the port brings additional 'closed-ended pipe resonance' that are unwanted. They are at about half the frequency of the typical open-ended port resonances but still high in amplitude. In my port the open-ended main resonance was around 950Hz but the curve added another at 450Hz.
I have now opted for a top firing flared port without any bends. It is still longer with more cross-section than a front or rear port could be and it lacks the additional unwanted resonances the curve introduced. If the port were to exit on the bottom it would need to take another turn / bend to exit under the cabinet and I'm quite sure that will cause additional unwanted resonances due to the impedance mismatch and reflection from the boundary, exactly like my L shaped port. Unless you can float the speakers high enough in the air (I guess like 5 inches or more) or have a special open stand.
Covering the port with cloth or open-cell (reticulated) foam will also bring unwanted turbulence. I'll be trying a fine mesh like fly screen but didn't test any yet.
Quite a lot of info there I hope I explained it clearly enough.
To be fair, although rear facing ports seem to show less colouration than front facing in anechoic measurements, this is largely due to the anechoic conditions (and the increased distance from the mic at 1m or less). In most real rooms there will be a hard reflective boundary a short distance from the rear of the speaker that reflects the port resonances in to the room. Same with a bottom firing port if the boundary below the speaker is hard and reflective.
Yes, the eternal juggling act with acoustically small vented boxes: reduce duct CSA to keep axial length down & ensure the 1/2 wave modes are sufficiently high in frequency they're unlikely to cause issues at the price of a higher air velocity in the duct, or use a larger CSA to drop velocity at the price of a longer duct and self-resonances lower down the range, where they're more likely to get triggered / cause issues.
Personally I won't go beyond a duct length of 6in / 150mm [nearly] for most regular vented enclosures as this generally ensures the 1/2 wave fundamental is at or > 1KHz. If that means a slightly higher air velocity -most of the time that can be negated by positioning on the rear baffle & if it is audible, chances are the design itself is marginal for the task. If it's near a boundary, then the overall alignment comes into play -flat or peaking are usually problems, well-damped much less so / often non-issue providing the speaker isn't rammed right up against a wall or stuffed into a cavity. Minor damping for ducts if necessary usually solve more audible issues in my experience than they cause though (assuming they cause any audible issues at all in many cases).
Personally I won't go beyond a duct length of 6in / 150mm [nearly] for most regular vented enclosures as this generally ensures the 1/2 wave fundamental is at or > 1KHz. If that means a slightly higher air velocity -most of the time that can be negated by positioning on the rear baffle & if it is audible, chances are the design itself is marginal for the task. If it's near a boundary, then the overall alignment comes into play -flat or peaking are usually problems, well-damped much less so / often non-issue providing the speaker isn't rammed right up against a wall or stuffed into a cavity. Minor damping for ducts if necessary usually solve more audible issues in my experience than they cause though (assuming they cause any audible issues at all in many cases).
When I finish my study I'll share a couple of effective ways to deal with the unwanted resonances that don't f*ck the turbulence. 👍
Plenty of those that can be (sometimes are) lifted from exhaust / muffler design -I've done a few myself. TBH though, I very rarely bother since I've never found any audible issues with turbulance, so I suspect the audiblity or otherwise is something that will vary with design & implementation. Always good to have more data points though, so will look forward to reading. 🙂