Untuned ports

[ficelles]

Untuned ports i.e. just a hole... anyone in favour / not in favour? Any rule of thumb for size?

ficelles

[alexclaber]

They're all tuned in the sense of having a resonant frequency, the port length is just determined by the port shape and baffle thickness and thus the wodge of air that thus resonates on the air spring of the enclosure - same as the soundhole on a classical guitar. Only work well when Vd is low, Vb is high and Fb is meant to be high.

[stevie]

[quote name='ficelles' post='1320497' date='Jul 29 2011, 02:46 PM']Any rule of thumb for size?[/quote]
Doesn't it depend on the EBP and Qtc?

[Bill Fitzmaurice]

[quote name='ficelles' post='1320497' date='Jul 29 2011, 09:46 AM']Untuned ports i.e. just a hole... anyone in favour / not in favour? Any rule of thumb for size?

ficelles[/quote]
All ports result in a tuning frequency (Fb), which can be determined with any speaker modeling software. The duct length is the thickness of the panel.

[Dekker]

If you just want to add a hole (or two or more) just for aesthetic purposes, consider just having it lead to a false cavity in your cabinet. Maintain the required internal volume for the main cabinet by making it bigger by the amount of space the false cavity takes up.

If you want it functional, the above are correct: the baffle thickness "is" your port. The purpose of any port is to (generally) increase the bass output, and it can only do this if the port is the correct diameter and length for the drivers in your cabinet. As BF mentioned, consult any number of speaker modeling software to determine these parameters. Having the incorrect parameters can (and probably will) result in time smearing, and an overall "muddy" sound.

[fatback]

there should be a competition for the greatest number of acronyms (or whatever they are) in a BC thread.

Vd, Vb, Fb, EBP, QTC ????

Edited July 29, 2011 by fatback

[alexclaber]

Venereal disease, Very bad, eFfing big, Evil *astard Ports, Quite Techy Considerations. HTH.

[ficelles]

[quote name='Dekker' post='1320607' date='Jul 29 2011, 04:19 PM']Having the incorrect parameters can (and probably will) result in time smearing, and an overall "muddy" sound.[/quote]

For front porting don't you get that to some degree anyway? The backwave is inverted but one wave out at the resonant frequency...

ficelles

[Bill Fitzmaurice]

[quote name='fatback' post='1320641' date='Jul 29 2011, 11:53 AM']there should be a competition for the greatest number of acronyms (or whatever they are) in a BC thread.

Vd, Vb, Fb, EBP, QTC ????[/quote]
[url="http://www.eminence.com/support/understanding-loudspeaker-data/"]http://www.eminence.com/support/understand...udspeaker-data/[/url]
[quote]For front porting don't you get that to some degree anyway? The backwave is inverted but one wave out at the resonant frequency...[/quote]The port radiation is only out of phase below the tuning frequency, and in a properly designed cab it's moot as that lies primarily below the speaker operating bandwidth.

[fatback]

[quote name='alexclaber' post='1320646' date='Jul 29 2011, 04:56 PM']Venereal disease, Very bad, eFfing big, Evil *astard Ports, Quite Techy Considerations. HTH. [/quote]

wtf

[Blademan_98]

I was going to get involved in this discussion but realised that I haven't got a clue.......

I know ports are supposed to be worked out mathematically but they all just look like holes to me

I'll get me coat............

[xgsjx]

Sorry Bill, Alex's definitions win.

[ficelles]

[quote name='Bill Fitzmaurice' post='1320736' date='Jul 29 2011, 07:03 PM']The port radiation is only out of phase below the tuning frequency, and in a properly designed cab it's moot as that lies primarily below the speaker operating bandwidth.[/quote]

Indeed, but isn't it in phase but a wave behind at and above the resonant frequency? I.e. the backwave phase is inverted by the port so in phase with the frontwave but with a single wave time lag?

ficelles

[LawrenceH]

[quote name='ficelles' post='1321881' date='Jul 31 2011, 12:36 AM']Indeed, but isn't it in phase but a wave behind at and above the resonant frequency? I.e. the backwave phase is inverted by the port so in phase with the frontwave but with a single wave time lag?

ficelles[/quote]

Hello my fellow Devonian. At the port's resonant frequency nearly all the output will be from the port rather than the speaker. The threshold of audibility of group delay (frequency-dependent delay) is a bit of a controversial topic. It's important to remember that even a non-ported speaker exhibits group delay in the low register. I suspect that audibility thresholds show considerable individual variability and can change with practice, but I don't know if this latter point has ever been tested properly.

[Bill Fitzmaurice]

[quote name='LawrenceH' post='1322000' date='Jul 31 2011, 05:51 AM']The threshold of audibility of group delay (frequency-dependent delay) is a bit of a controversial topic.[/quote]Not within the community of acoustical engineers, who are well aware that group delay below 100 Hz is moot. It does bother the heck out of those who see a group delay of, say, 10ms at 50 Hz on a chart, but it doesn't bother those who know that you can't hear 10ms at 50 Hz.

[Balcro]

[quote name='ficelles' post='1320497' date='Jul 29 2011, 02:46 PM']Untuned ports i.e. just a hole... anyone in favour / not in favour? Any rule of thumb for size?

ficelles[/quote]

What for you is the purpose an untuned port?

Balcro.

[ficelles]

[quote name='Balcro' post='1322631' date='Jul 31 2011, 11:18 PM']What for you is the purpose an untuned port?

Balcro.[/quote]

Lets the air out.

ficelles

[Balcro]

[quote name='ficelles' post='1322644' date='Jul 31 2011, 11:41 PM']Lets the air out.

ficelles[/quote]

Rule of thumb for size: sized so you can fit a 100mm plastic drain pipe in the hole. That way if
you don't like the first result (just a hole in the baffle) you can try fitting a length of pipe for an alternative tuning.

If you really want to look cool try one or two of these -

[url="http://www.madisoundspeakerstore.com/flares/ports/vents/scan-speak-aperiodic-vent/"]http://www.madisoundspeakerstore.com/flare...aperiodic-vent/[/url]

Balcro.

[LawrenceH]

[quote name='Bill Fitzmaurice' post='1322181' date='Jul 31 2011, 03:10 PM']Not within the community of acoustical engineers, who are well aware that group delay below 100 Hz is moot. It does bother the heck out of those who see a group delay of, say, 10ms at 50 Hz on a chart, but it doesn't bother those who know that you can't hear 10ms at 50 Hz.[/quote]

Bill, you seem a bit fond of putting words into other people's mouths and then gleefully contradicting them as a self-appointed "engineers' representative". I said absolutely nothing about 10ms. To take an extreme case, clearly a group delay of, say, half a second, is extremely audible well below 100Hz. But the exact cut-off is reported differently in different studies - that is the area of controversy.
From a neuroscientific perspective it would be very surprising if there wasn't a degree of individual variation in the threshold.

[Bill Fitzmaurice]

[quote name='LawrenceH' post='1322704' date='Jul 31 2011, 08:41 PM']Bill, you seem a bit fond of putting words into other people's mouths and then gleefully contradicting them as a self-appointed "engineers' representative". I said absolutely nothing about 10ms. To take an extreme case, clearly a group delay of, say, half a second, is extremely audible well below 100Hz. But the exact cut-off is reported differently in different studies - that is the area of controversy.
From a neuroscientific perspective it would be very surprising if there wasn't a degree of individual variation in the threshold.[/quote]
If you somehow managed to obtain an electric bass cab with 50ms of group delay, let alone 500ms, the speaker would have to be so completely AFU that the group delay would be the least of its problems. As to being an 'engineers representative', it's what I do for a living. Deal with it.

Edited August 1, 2011 by Bill Fitzmaurice

[alexclaber]

[quote name='ficelles' post='1322644' date='Jul 31 2011, 11:41 PM']Lets the air out.[/quote]

And why would you want that to happen? Just curious about the thinking - I think I might write an article about ports soon...

[Mr. Foxen]

[url="http://www.hometheaterhifi.com/volume_5_2/cmilleressayporting.html"]This article[/url] has some pendulum anigifs that make visualising how ports work easier (if they are right).

[Higgie]

Fb?? I thought that was E!



Sorry, I'll get my coat

[Bill Fitzmaurice]

[quote name='alexclaber' post='1322743' date='Aug 1 2011, 03:13 AM']And why would you want that to happen? Just curious about the thinking - I think I might write an article about ports soon...[/quote]
He's not really off track. When I opened up my first bass cab in '66 the thought occurred that there was compression inside that was restricting the movement of the cones and that they might move more freely if I cut a hole in the cab. What I knew about how speakers worked at that point was precisely nothing, but as it turned out my hypothesis was correct, all that I lacked was the knowledge of how to properly carry it out. I did cut a hole in the baffle, and it seemed to work a bit better. I know it didn't work any worse.

[LawrenceH]

[quote name='Bill Fitzmaurice' post='1322712' date='Aug 1 2011, 02:49 AM']If you somehow managed to obtain an electric bass cab with 50ms of group delay, let alone 500ms, the speaker would have to be so completely AFU that the group delay would be the least of its problems. As to being an 'engineers representative', it's what I do for a living. Deal with it.[/quote]

Tough guy. There are plenty of subwoofer configurations out there that have audible group delay, 30ms or more - not great designs (though to call them bad really depends what you are trying to achieve, you can't defy physics) but they are commercially available so LF group delay is a real world issue.
You have taken a comment I made, that group delay exists and the audibility threshold is disputed, and managed to pointlessly manufacture an argument out of it by putting words into my mouth and atttributing me a stance that I haven't taken. Nice. Fortunately for me, I am a research scientist and know perfectly well without your 'help' how to read AES papers, design and evaluate experiments, and assess evidence (and see through BS). Oh yes, and understand basic, not even undergraduate-level physics. Because that is what I do for a living. Incidentally, as part of that living I've attended seminars at the MRC Institute for Hearing Research and dealt directly with their scientists. But apparently a so-called acoustic engineer knows better than my scientific colleagues at the cutting edge of hearing research, how the ears and brain work.