I noticed this in the FINEBox PDF underneath "Figure 7: FINEBox Acoustic Loadings"
I was wondering if anyone here has tried it, & what with, & what were the results ?
I was wondering if anyone here has tried it, & what with, & what were the results ?
Hi there Zd: Dickason staes "Thiel's analysis... result in the following changes in normal vented box operation: increases F3, decreases efficiency, increases excursion near cutoff, lowers Qts", however, given these limitations, "why bother". No I have not tried to stuff/modify a vent. If you can compare your tests of open vent vers your experimental vent modifications, why not try it? Also Dickason (page 81 & 82) recommends stuffing vents with bundle plastic straws to effect resistive loading. ...regards, Michael
First of all, why do you readily assume you want a flat response (just because your model gives you no choice in the matter anyway)? I'd say for most real-world systems, you want a rising response at the bottom.
Stuffing the port sounds like a good idea to me. Converts a resonant box into something more like my favourite, a leaky sealed box.
Ben
Stuffing the port sounds like a good idea to me. Converts a resonant box into something more like my favourite, a leaky sealed box.
Ben
This is the way to 'critically damp' a simple reflex [baffle thickness] port to remove any 'hangover'/'boom' typical of them and to a lesser extent a ducted port's inherently better damping to fine tune the speaker's roll off slope in room. Way back when, a consumer speaker's grill cloth's density/weave was chosen to accomplish this, while prosound relied on the bug/rodent protective screen to do it.
Historically, DIYers use a DP/DT switch powered by a 1.5 V battery with a series resistor to account for the amp's output impedance + the speaker wiring's resistance, then continuing adding some form of damping till you only hear the switch's sharp 'snap'. Anymore and you're just rolling off the bass.
A similar [once] popular tweak was to stuff a ducted port with soda straws.
GM
Historically, DIYers use a DP/DT switch powered by a 1.5 V battery with a series resistor to account for the amp's output impedance + the speaker wiring's resistance, then continuing adding some form of damping till you only hear the switch's sharp 'snap'. Anymore and you're just rolling off the bass.
A similar [once] popular tweak was to stuff a ducted port with soda straws.
GM
What GM posts is a reliable account of matters as shared by many. But I think we can rush to the heart of the matter by examining the term "critical damping". True, that is the conventional term, but wouldn't it be more accurate to call it "optimal damping" because there is nothing particularly "critical" about it?
(Need I point out, folks on this forum are more inclined to "maximize" rather than to "optimize"...... eh. So, "optimal damping" may not be such a great target after all.)
Likewise, I ask readers of this thread to think whether it is better to say, "just rolling off the bass" or to describe that effect as "just reducing obnoxious and multiply harmful resonance"?
Some may find my remarks on this topic novel (or as in the current cliche, "disruptive"). But I hope modelers will give it some thought.
Ben
Any stuffing or damping material in or near a port aggressively attacks output down near tuning. Any stuffing or damping well away from the port (like the opposite side of the box) works well on damping out higher resonances without harming the output down near tuning too much. You can see this with real world measurements or just play around with a simulator a bit.
Output down near tuning is fairly precious, it's gained only by box size. If you didn't want so much output at tuning your box size could be considerably smaller. For that reason I'm not a fan of damping ports, I'd rather have a smaller box size. The ONLY way I'd ever stuff a port is if I already had an oversized box and needed to calm it down, otherwise the problem is best addressed at the design stage. The smaller box will give the response curve shape you want AND higher power handling without having to damp the port.
BTW, your link just goes to the home page, not a pdf so I have no idea what the article says.
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Your absolute loathing of simulation software is well documented, although it seems you know very little about this thing you love to hate. Why do you assume your model gives no choice in response curve shape? Every simulator I've ever seen is almost infinitely variable, you can change the variables to give almost any response curve shape you want.
Also your comments are almost perfectly completely contradictory. A leaky sealed box will absolutely not ever give a rising response on the bottom unless the driver q (and therefore resulting box q) is ridiculously, obscenely high.
Just a couple of days ago you were arguing that q should be as low as possible, now you are saying a rising response on the low end (which is exactly the opposite of low q) is desirable.
When a large amount of your posts completely contradict each other it's hard to tell if you are trying to be humorous or if you don't understand the most basic terms and concepts that you are trying to discuss.
A rising response on the bottom is ONLY ever a good thing if it compliments your natural room gain curve or if you have a preference for response that is not flat.
I suspect your preference for leaky sealed boxes is mainly due to the fact that you've had terrible luck with any other type of box because of your inability to simulate or even guess what might work well due to your insistence of clinging on to old world rules of thumb.
Critical damping has a definition and we don't need to go changing things because you are uncomfortable with established terminology.
Your absolute loathing of any type of resonance in enclosure output is as well documented as your dislike of simulators (and rather odd given your choice of one of the world's most resonantly peaky and unflat undersized antique horns in your system) but resonance is NOT harmful when used properly.
In your previous post you were arguing for a rising response on the low end and now arguing that this "harmful resonance" should be damped out. Which is it, Ben? How else can you get a rising response (high q response curve) without a resonance? Even with a leaky sealed box the only way to do it is with a high q driver, which is by definition a driver with a very high resonance and will in turn lead to a very high system q which you argue against.
In a blind test I am confident that you could not pick out a leaky sealed box from a properly designed ported box, horn or tapped horn if they were all eq'ed to the same level and response curve. This would prove very effectively that resonances are not in fact the problem you think and can in fact be very useful.
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Hi guys & thanx for the inputs.
How about ONLY lining the port/s with for eg, 1/4 inch felt/carpet etc ?
Here's the FINEBox Tutorial PDF link Downloads Others on there too, plus downloadable presentations etc etc 🙂
The software appears to very comprehensive, but i expect it's very expensive too !
How about ONLY lining the port/s with for eg, 1/4 inch felt/carpet etc ?
Here's the FINEBox Tutorial PDF link Downloads Others on there too, plus downloadable presentations etc etc 🙂
The software appears to very comprehensive, but i expect it's very expensive too !
Same effect but not as much. Kinda like drinking a small glass of water is the same as a big glass but not as much. That's probably a really bad analogy but you get the point. Maybe.
You can quickly and easily see the effect if you have MJK's worksheets, Hornresp, Akabak or TL.app. All four allow you to place stuffing wherever you like and vary the density.
if you line a reflex vent with anything that does not have a smooth surface you will generate turbulence and negatively impact vent performance. Keeping air flow smooth and laminate is very important so that the air in the vent is able to behave as it it were a solid weight plug on a spring that why you will sometimes see small thin wall tubes filling a vent so the air is forced to flow smoothly. I guess this is all determined with fluid mechanics that why you will see flared vent tubes and an assortment of other shapes all to keep the air flow smooth.
As Moray implied, this will create friction losses that are hard to predict and may over-damp ['kill'] too much of the port's output, so you're better off overall to either do the stretched fabric/whatever porous material over the port's terminus tweak I mentioned or stuff it with a porous material, with open cell foam being popular with some manufacturers.
GM
Agreed, but the pioneers had their own 'jargon' as you know, so at this late date it would probably cause more confusion than not.
Indeed, when I learned the term, it meant that the response was maximally flat with no audible 'ringing', then T/S came along and a maximally flat response became a 0.707 Qt, which has minor 'ringing' and somewhere along the line it became the term for a 0.5 Qt 'transient perfect' response [big difference!].
GM
The damping tweaks I mentioned are for reducing the port's pipe harmonics with minimal impact on output near/at Fb, so reducing box size for a given Fb, power handling would actually increase them due to needing a larger, longer vent, hence more damping.
Better over all then to 'globally' damp the speaker by loosely covering the driver
GM
GM - thanks for your helpful and clearly written posts. Agreed.
"Critical" doesn't mean critical and it doesn't even mean "optimal" in all ways. All it means is Thiele likes it (and it is computationally tractable). Can anyone link to a text that says Q=.7 sounds best?
Sort of the same reason scientists use "standard deviations" even though SDs have no particular value as a descriptive or heuristic metric... but only because of their computational simplicity in doing probabilies*.
Other posts seem to show that (1) you can start by modeling but then (2) you need to tweak for your listening objectives (AKA your house curve). That's all I am saying too. For example, you can trade-off some bass extension for some cone control; I think floppy cones (or Doppler distortion) in BR boxes is not sound design. Or, if you don't mind me saying it again, you might really dislike resonances and want to tame them by any means available and not have any kind of rigid adherence to Q====.7.
Ben
*I've generally described my data with inter-quartile ranges which make more sense to most readers.
"Critical" doesn't mean critical and it doesn't even mean "optimal" in all ways. All it means is Thiele likes it (and it is computationally tractable). Can anyone link to a text that says Q=.7 sounds best?
Sort of the same reason scientists use "standard deviations" even though SDs have no particular value as a descriptive or heuristic metric... but only because of their computational simplicity in doing probabilies*.
Other posts seem to show that (1) you can start by modeling but then (2) you need to tweak for your listening objectives (AKA your house curve). That's all I am saying too. For example, you can trade-off some bass extension for some cone control; I think floppy cones (or Doppler distortion) in BR boxes is not sound design. Or, if you don't mind me saying it again, you might really dislike resonances and want to tame them by any means available and not have any kind of rigid adherence to Q====.7.
Ben
*I've generally described my data with inter-quartile ranges which make more sense to most readers.
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You're welcome!
Not me! Except for prosound and the occasional 'bookcase' speaker apps, I can't recall ever winding up with a maximally flat alignment in room and why I always recommend a probably too large a cab and vent or driver damping to allow an adequate amount of in room fine tuning.
GM
Not me! Except for prosound and the occasional 'bookcase' speaker apps, I can't recall ever winding up with a maximally flat alignment in room and why I always recommend a probably too large a cab and vent or driver damping to allow an adequate amount of in room fine tuning.
GM
Hi GM and others! Does anyone have a link or more info about protective screens in reflex ports? I got small kids who most probably put toys through the large port of my next project. We also have some spiders happily living in the house. I'm thinking some kind of protection is necessary. Can't find tips or examples by Googling. I could just experiment, but any info beforehand reduces the work 🙂
ps. I found this thread when searching how to reduce resonances in a port. Here is a patent to reduce port resonance, kind of related to this thread so might as well post it US6275597B1 - Loudspeaker system having a bass-reflex port
- Google Patents .
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Greets! Nowadays I recommend pet screen tightly stretched over it as it's beyond tough!
Hopefully it or something close is available in Finland: World's Leading Outdoor Mesh Screens | Super Screen™
GM
Hopefully it or something close is available in Finland: World's Leading Outdoor Mesh Screens | Super Screen™
GM
Thanks GM!
No Super Screen available it seems but similar bug screens in plastic, fiberglass and multiple different metal variety are available. I'll get some tougher if my stock plastic mesh blows out at mach 1 🙂
No Super Screen available it seems but similar bug screens in plastic, fiberglass and multiple different metal variety are available. I'll get some tougher if my stock plastic mesh blows out at mach 1 🙂
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You're welcome! OK, in that case I previously used fiberglass pet screen, which installed on a glass sliding patio door screen withstood a ~25 lb tomcat climbing/clinging to it without stretching/tearing it, though ultimately he buckled the flimsy alum. channel frame to the point I had to replace it and 'bulletproof' it to withstand the abuse.
GM
GM
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