Does port direction matter relative to the sub? - Page 2 - AVS Forum | Home Theater Discussions And Reviews
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post #31 of 66 Old 09-10-2019, 04:34 PM
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Originally Posted by Chris Popovich View Post
Yeah, very small and low is a PITA with ports unless you do some cumbersome folded slot. Go model the tangband w6-1139 for an example of "hard to port". Luckily it's a candidate for multiple drivers giving a touch more wiggle room, but you'll get the idea. Great candidate for a PR.
I just did a quick model with that driver and it seems normal to me.

0.7cf net, 2.5"x2.5" port @ 24.5" long tunes to 30Hz. With the rated 60W it's 99db+ and flat down to 30Hz, staying under xmax and with a peak velo of 17 m/s.

Obviously there are plenty of other options with this driver, but with such a small driver I figured I'd model a nice small sub that would be perfect for music. I went conservative with the port length for ease of build, but there's plenty of room to increase port size, lower tune, shrink the box, really any desired change.

For example, a smaller option would be 0.42cf net, 2.25"x2.25" port @ 20.5" long, tuned to 38Hz. With the same 60W it's 101dB+ and flat down to ~40Hz, again staying under xmax and with a peak velo of 17 m/s.

There are no issues at all fitting those ports in those boxes, as the lengths are very reasonable relative to the possible dimensions of boxes those sizes. I've honestly never run into an issue with port volume eating up too much space, or port length being too long to simply throw along the inside walls of the box as a square or slot. I genuinely would like to see an example, even if for no other reason than I just want to take a shot at it.

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post #32 of 66 Old 09-10-2019, 06:30 PM
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Originally Posted by Aural_Sex View Post
Does port direction matter relative to the sub?
yes, but ONLY if you have a hair piece, with it pointed right at it like Mr. T
Otherwise, "probably not..."
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post #33 of 66 Old 09-10-2019, 07:48 PM
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Originally Posted by aron7awol View Post
I've honestly never run into an issue with port volume eating up too much space, or port length being too long to simply throw along the inside walls of the box as a square or slot. I genuinely would like to see an example, even if for no other reason than I just want to take a shot at it.
Okay, Dayton Audio RSS315HO-4 12", max enclosure size is a 13.5" cube (wife will divorce you if it's bigger than this), port air velocity cannot exceed 17 m/s, 110 dB at 30 Hz, driven to max power. Everything else is fair game. Go. And not to distract from the OP's original question, but now I genuinely want to know.
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post #34 of 66 Old 09-11-2019, 05:59 AM - Thread Starter
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Originally Posted by BassThatHz View Post
yes, but ONLY if you have a hair piece, with it pointed right at it like Mr. T
Otherwise, "probably not..."
You jest, but I had actually considered external ports that came up behind the back of the couch at head level - volume and tuning solved!

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Originally Posted by aktiondan View Post
Okay, Dayton Audio RSS315HO-4 12", max enclosure size is a 13.5" cube (wife will divorce you if it's bigger than this), port air velocity cannot exceed 17 m/s, 110 dB at 30 Hz, driven to max power. Everything else is fair game. Go. And not to distract from the OP's original question, but now I genuinely want to know.
I played with this for a minute and quickly shut it down - this is a case where I'd go sealed for that volume. If you're using 3/4 MDF you've got 1 ft^3 of internal space, .885 ft^3 if you consider the driver. If you throw two 2" ports they're a wrapped 22.3 inches a piece and you cross 17 m/s at 41hz; one 3" port gets you to 17m/s at 35hz with a length of 25.5". I'd build a cube and call it a day.
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post #35 of 66 Old 09-11-2019, 07:41 AM
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Originally Posted by aktiondan View Post
Okay, Dayton Audio RSS315HO-4 12", max enclosure size is a 13.5" cube (wife will divorce you if it's bigger than this), port air velocity cannot exceed 17 m/s, 110 dB at 30 Hz, driven to max power. Everything else is fair game. Go. And not to distract from the OP's original question, but now I genuinely want to know.
Those "requirements" are unreasonable. You can't expect to put that sub in such a tiny box, decide you want an arbitrary 110dB @ 30Hz, and say it has to stay under 17 m/s. Come on, man, be realistic at least.

That being said, here's about the best you can do: 107dB @ 30Hz, 0.75"x12" slot port @ 36" long, 0.68 cf net, 30 m/s velo. That's a damn good compromise given the totally unreasonable constraints.

In any case, this doesn't refute my original point, which is that the volume taken up by the port isn't the issue. I agree with A_S' conclusion on this one. That's just too small to try to port this sub, you're only gaining 3dB for your trouble and just creating issues. Sealed is the way to go with such a small box.

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post #36 of 66 Old 09-11-2019, 06:35 PM
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Originally Posted by aron7awol View Post
I just did a quick model with that driver and it seems normal to me.

0.7cf net, 2.5"x2.5" port @ 24.5" long tunes to 30Hz. With the rated 60W it's 99db+ and flat down to 30Hz, staying under xmax and with a peak velo of 17 m/s.

Obviously there are plenty of other options with this driver, but with such a small driver I figured I'd model a nice small sub that would be perfect for music. I went conservative with the port length for ease of build, but there's plenty of room to increase port size, lower tune, shrink the box, really any desired change.

For example, a smaller option would be 0.42cf net, 2.25"x2.25" port @ 20.5" long, tuned to 38Hz. With the same 60W it's 101dB+ and flat down to ~40Hz, again staying under xmax and with a peak velo of 17 m/s.

There are no issues at all fitting those ports in those boxes, as the lengths are very reasonable relative to the possible dimensions of boxes those sizes. I've honestly never run into an issue with port volume eating up too much space, or port length being too long to simply throw along the inside walls of the box as a square or slot. I genuinely would like to see an example, even if for no other reason than I just want to take a shot at it.
The driver wants .5cuft and about 32 hz tuning, and it also wants more vent area... 2.67x2.67 would work. You're looking at 33.7" length like that, which aint' gonna be easy.

But even if you stick with the sizes you listed, you're either going to have a very strange shaped box, or add significantly to dimensions to get it to work well via slot ports. Can it be done? Yes. Can it be done in a reasonable foot print, relative to what it'd be for a same internal volume sealed box? Nope.

To your point, you can always port anything. But for example, try using standard 4" pvc with this driver and you'll find it's going to be a little off.

Chris
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post #37 of 66 Old 09-11-2019, 06:52 PM
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Originally Posted by Chris Popovich View Post
The driver wants .5cuft and about 32 hz tuning, and it also wants more vent area... 2.67x2.67 would work. You're looking at 33.7" length like that, which aint' gonna be easy.

But even if you stick with the sizes you listed, you're either going to have a very strange shaped box, or add significantly to dimensions to get it to work well via slot ports. Can it be done? Yes. Can it be done in a reasonable foot print, relative to what it'd be for a same internal volume sealed box? Nope.
I'm not sure what you mean by "wants"? The design I mentioned was flat to 30Hz and only had a peak velo of 17 m/s. It easily checks all of the boxes for that kind of application. There's nothing left wanting at all in my mind. One example of possible box dimensions is 13"x13"x12.5" which very easily fits my 24.5" port. I don't consider that a strange shaped box at all.

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post #38 of 66 Old 09-11-2019, 07:35 PM
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Originally Posted by aron7awol View Post
I'm not sure what you mean by "wants"? The design I mentioned was flat to 30Hz and only had a peak velo of 17 m/s. It easily checks all of the boxes for that kind of application. There's nothing left wanting at all in my mind. One example of possible box dimensions is 13"x13"x12.5" which very easily fits my 24.5" port. I don't consider that a strange shaped box at all.
I think it's more semantics. "hard" doesn't mean it's difficult to figure out how to do it. That's always straight forward.

IMO if you drill a hole in the front (side, or rear... lol), plop in your port, and you're there, it's "easy". Add a PVC 90* and go up a bit and it's "not too bad". Have to make it slot loaded, use multiple folds and it's "hard".

None of them are impossible.

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post #39 of 66 Old 09-11-2019, 07:53 PM
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Originally Posted by lknhomeaudio View Post
Not sure why you're laughing lol



Go to your favorite box modelling program, lower the tune, watch airspeed drop, be amazed.



The end!


Not every driver does this but the reason why the airspeed goes down is due to the loss of sensitivity. If you bring match spl levels you will see the port sky rocket.


Sent from my iPhone using Tapatalk
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post #40 of 66 Old 09-11-2019, 10:08 PM
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You're exactly right, it is a compromise! Not a terrible design, given my unrealistic requirements. I wouldn't build it though. My point with the port volume is that when the overall box volume is your constraint, you become very aware of how much volume the port takes up. And the more you attempt to meet an ideal air speed, the longer the port, the more volume it consumes, the bigger the box and so on. But if box volume is not a constraint then you're not likely to notice the extra volume being used up by the port.

I was also sympathizing with the OP in that when it was noted his port was probably too small, his response was exactly what I have also run into, which is if I try and meet the ideal air speed, I have to make the ports bigger and longer which sacrifices internal volume, or I have to make the box bigger to make up for it. So in that case, the compromise is not in accepting some port noise, it's accepting that my sub is going to be bigger than I originally planned it to be. Maybe it's not by much, and will depend a lot on the design, but smaller vented boxes tend to make this situation worse.

As far as my hypothetical proposition, the only way to meet those requirements is not to use a port at all but to use passive radiators. A 13.5 inch cube with a pair of Dayton Audio RSS315-PR 12" passive radiators at 750 grams a piece will do 110 dB at 30 Hz and the port air speed will be 0 m/s. It's no Full Marty, but will get the job done at a very modest footprint. The other option is to go sealed, as you guys already mentioned but with a pair of RSS315HO-4 drivers and active EQ it. That will also do 110 dB at 30 Hz, but requires twice the power to get there. And I know, maybe I cheated a little bit, I knew those requirements wouldn't port worth a darn, but it does drive home that port volume will always cost you enclosure volume when port air speed is truly considered. In which case the better design may be go sealed or PR if total enclosure volume is the constraint. Or you just live with some port noise. I've done all three.
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post #41 of 66 Old 09-12-2019, 06:55 AM
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Originally Posted by aktiondan View Post
I was also sympathizing with the OP in that when it was noted his port was probably too small, his response was exactly what I have also run into, which is if I try and meet the ideal air speed, I have to make the ports bigger and longer which sacrifices internal volume, or I have to make the box bigger to make up for it. So in that case, the compromise is not in accepting some port noise, it's accepting that my sub is going to be bigger than I originally planned it to be. Maybe it's not by much, and will depend a lot on the design, but smaller vented boxes tend to make this situation worse.
I hear ya, it's just that in OP's post you replied to, what he was talking about was ridiculous and not even feasible nor necessary. Literally an almost 15-foot long port:
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Originally Posted by Aural_Sex View Post
Can you expand on that? A single 8" port would need to be 178" inches long and cuts the box volume down to internal 2.25 ft^3 from 6.6 ft^3 - unless I'm missing something obvious (entirely possible).
So I was just saying it's not an issue for OP, has never been an issue in any sub I've ever designed, and I could only see it being an "issue" if trying to design an unreasonably small box. I consider your box to fall squarely in that unreasonably small category, in that it's barely big enough to do sealed.

It's all good, it seems like you have a good handle on how to work around your own issue. Really, the main reason I felt the need to respond is because your post made it seem like it was always an issue with designing ported subs, and a struggle you deal with on every ported design. I didn't want others to get scared off by your post, because ported subs are really very straightforward to design IMO and easy to hit the proper balance of port size and port velocity.

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post #42 of 66 Old 09-12-2019, 07:06 AM
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IMO if you drill a hole in the front (side, or rear... lol), plop in your port, and you're there, it's "easy". Add a PVC 90* and go up a bit and it's "not too bad". Have to make it slot loaded, use multiple folds and it's "hard".
I guess we can agree to disagree that having a slot port simply turn 90 degrees at the inside corner of a box is "hard". I honestly think it's easier than cutting a circular hole. Hundreds of people have done so with Martys and other similar subs. I think slot ports are actually far more common than round ports in DIY sub builds here on AVS.

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post #43 of 66 Old 09-12-2019, 07:47 AM - Thread Starter
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I think you're both right here. My goal is space savings inside the box to eek out as much volume as possible with a desired tune. I'm going round ports not because they are easier or harder but the material volume is smaller - 4" pvc port walls are .25" versus building slots and slot bracing with .75" MDF. Further, it's because I'm lazy - BassBox assumes that you are building a port with two sides and therefore doubles the material volume in the box instead of using the inside wall as the second side; it makes my calculations easier to not have to fight the volume delta in planning.
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post #44 of 66 Old 09-12-2019, 09:00 AM
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Originally Posted by Aural_Sex View Post
I think you're both right here. My goal is space savings inside the box to eek out as much volume as possible with a desired tune. I'm going round ports not because they are easier or harder but the material volume is smaller - 4" pvc port walls are .25" versus building slots and slot bracing with .75" MDF. Further, it's because I'm lazy - BassBox assumes that you are building a port with two sides and therefore doubles the material volume in the box instead of using the inside wall as the second side; it makes my calculations easier to not have to fight the volume delta in planning.
You're getting caught up in something that many of us, myself included, got caught up in when we first started modeling subs: unnecessarily worrying about the volume taken up by port walls and bracing. It's actually insignificant enough that you can ignore it. In this specific case you're mentioning, we're talking about a difference of what, 0.1cf? Model 2 identical subs with the only difference being 0.1 cf of net volume and you'll barely be able to see the two lines on the graph. The difference in the models will be ~0.1dB. The error in the model vs. real life, what you get for room gain, etc is orders of magnitude larger than that insignificant 0.1dB.

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post #45 of 66 Old 09-12-2019, 09:33 AM
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I wanted something extending below 20 Hz. The response was the priority, so when the compromises came up, I compromised in favor of sound quality.

So, 10 ft³ and a 7 inch port later (times two)….

Bass Bliss

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post #46 of 66 Old 09-12-2019, 09:59 AM
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Originally Posted by aron7awol View Post
I guess we can agree to disagree that having a slot port simply turn 90 degrees at the inside corner of a box is "hard". I honestly think it's easier than cutting a circular hole. Hundreds of people have done so with Martys and other similar subs. I think slot ports are actually far more common than round ports in DIY sub builds here on AVS.
It's not so much agreeing to disagree, you asked for an example of what people mean by "hard to port", I gave you some; that's what people mean. If you prefer slot ports anyway then they're all about the same level of difficulty, by that criteria nothing is hard to port, and the term wouldn't really apply to you. No biggie!

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post #47 of 66 Old 09-13-2019, 11:43 AM
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You're hamstringing the design when that's your "method". It's not an efficient alignment. Dropping the tune when the design is already rolling off *DOES* reduce the vent airspeed...
Chris
That's the only statement I ever made. Not sure why people are assuming and arguing lol
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post #48 of 66 Old 09-13-2019, 12:32 PM
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Originally Posted by lknhomeaudio View Post
That's the only statement I ever made. Not sure why people are assuming and arguing lol
I'll try to explain why.

After you said...
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Originally Posted by lknhomeaudio View Post
What?! lol

Tuning lower DECREASES airspeed, which in turn would allow for less port area.
I replied...
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Originally Posted by aron7awol View Post
If you keep box size and port area the same, then lowering tune does appear to decrease airspeed, but if you're doing that, you're not yet striking the proper balance between port resonance and port velocity. If you can simply increase the port area, you don't need to change tune to reduce port velocity. Instead, the issue that normally occurs during design is that you've already maximized port area with the constraint being the lowest port resonance you're comfortable with. If you're not happy with port velocity at that point, the solution is to raise tune and upsize the port to whatever is now possible at that higher tune while holding the same port length constraint. Overall, the port velocity decreases.
The point I tried to make with that reply is that on a properly optimized ported sub design, tuning lower has the opposite effect of what you're claiming; it actually increases airspeed.

Here's a comparison I posted in another thread that illustrates it:

Quote:
Originally Posted by aron7awol View Post
I decided to model a bunch of different options using the different size port tubes @ 48" with a resulting range of tunes of 10-15Hz. This is the same 24" diameter 6' SonnySub, adjusting net volume with port size to model as accurately as possible. I also adjusted the tunes down by 1Hz for a more accurate projected final tune after they are built, which is reflected in the data. They all have 4th-order HPF to keep safe excursion levels.

I really like the yellow option with the 8" port @ 48" as a really nice balance of level and extension.



That comparison is all the same exact size sub externally, same maximized accepted port length (48" in this case), same max excursion, same power, same everything other than tune and resulting maximum port area while holding everything else constant. In other words, each design is fully optimized for the allowable constraints while varying tune.

The trend is hopefully very clear. The lower the tune, the higher the port velocity.

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post #49 of 66 Old 09-13-2019, 04:40 PM
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If your wife is threatening to divorce you because you build something larger than a 13.5 inch cube, you should’ve already divorced her long ago. Unless she pays all the bills and it’s her house I guess
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post #50 of 66 Old 09-13-2019, 10:00 PM
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I stepped into that one I suppose. I was just trying to force a scenario where the overall box size is the constraint to show that port volume can become a factor. There's a probably a myriad of reasons to be constrained to a max enclosure size, I figured the WAF would be the most recognizable. I built a sub a few years ago that had to fit inside the exact space available in my entertainment center. As in inch for inch, that was the largest space I had to work with. The enclosure ended up being about 95 liters, tuned to 22 Hz with a 4" port that was 17" long. The design was a compromise overall, the driver wanted a slightly bigger box and a lower tune, but in the end, achieving ideal port air speed took the biggest hit. I guess when you also constrain the design to nominal PVC port diameters, like 3", 4" or 6" you kind of are left with what you get for length to get to your desired tune. I've never really played around with slotted ports, but I can see one big advantage is you can fine tune the required area with more fidelity. Which means you're not dealing with unnecessarily long ports just because you jumped up one whole standard PVC diameter. I wonder if I had slot-ported that design, could I have come up with something better?
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post #51 of 66 Old 09-14-2019, 02:09 AM
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I was under the impression people don't use round ports because of money. I dropped a couple hundred on flares,connectors, pipe for 4 6" ports. You could always do flares by hand, but more work.
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post #52 of 66 Old 09-14-2019, 06:19 AM - Thread Starter
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Quote:
Originally Posted by Gorilla Killa View Post
I was under the impression people don't use round ports because of money. I dropped a couple hundred on flares,connectors, pipe for 4 6" ports. You could always do flares by hand, but more work.
That's nuts - I don't know how they can justify a flared 6" port for $13 on PE vs a 4" at $2.50. If you were buying from BigAssPorts it gets even worse - $38 for one (though you do get adjustable length and dual flared ends).
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post #53 of 66 Old 09-14-2019, 10:49 AM
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I really like square ports as a best-of-both-worlds sort of compromise. They are really easy (no bracing necessary) and cheap to build as long as desired along an inside corner of the box, and are better than slots with respect to chuffing due to their smallest dimension being larger. A lot of people care about symmetry, and for them I usually recommend a pair of square ports rather than one big one. It's also a good way to minimize front baffle size when desired.

Take the Red Pill (BassEQ) BassEQ Demo Clips
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post #54 of 66 Old 09-14-2019, 10:53 AM
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I think in front, best experience, more air.
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post #55 of 66 Old 09-14-2019, 03:18 PM
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Quote:
Originally Posted by aron7awol View Post
That comparison is all the same exact size sub externally, same maximized accepted port length (48" in this case), same max excursion, same power, same everything other than tune and resulting maximum port area while holding everything else constant. In other words, each design is fully optimized for the allowable constraints while varying tune.

The trend is hopefully very clear. The lower the tune, the higher the port velocity.
Dude! You are INCREASING the port size. lol

Did you expect the port velocity to NOT decrease as you made the port BIGGER?

Do all your experimental modelling again, but keep the port area the same, then sit back and be amazed.



Quote:
Originally Posted by aron7awol View Post

The point I tried to make with that reply is that on a properly optimized ported sub design
Optimized, or not, it doesn't matter. Lower tune on a same size box with the same size port = lower air speed.

Quote:
Originally Posted by aron7awol View Post
If you keep box size and port area the same, then lowering tune does appear to decrease airspeed

It doesn't just "appear to", it DOES! (For the 100th time, if all else is kept the same)
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post #56 of 66 Old 09-14-2019, 03:48 PM
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Quote:
Originally Posted by lknhomeaudio View Post
Dude! You are INCREASING the port size. lol

Did you expect the port velocity to NOT decrease as you made the port BIGGER?

Do all your experimental modelling again, but keep the port area the same, then sit back and be amazed.





Optimized, or not, it doesn't matter. Lower tune on a same size box with the same size port = lower air speed.




It doesn't just "appear to", it DOES! (For the 100th time, if all else is kept the same)
The key part that you're missing/ignoring is that if you keep everything the same and only lower tune, all you've done is made the port longer, right? Well, if you can make the port longer, then you can already make the port area larger and reduce velocity at that current tune. It makes no sense to keep port area the same and lower tune for the sake of trying to reduce port velocity when you haven't even optimized that current tune by making the port as large as possible.

The comparison I posted shows that when comparing optimized designs at different tunes, the lower tune always has higher peak velocity.

Take the Red Pill (BassEQ) BassEQ Demo Clips
Video: Sony 85" X900F @ 80" eyes-to-screen (49.4° viewing angle)
Audio: Denon AVR-X4400H 7.2.4 Atmos
Mains: Fusion-15 LR, Custom Tapered Ported Volt-6 Center, Ported Volt-10 Surrounds, Custom 45°/45° Double-Angled Ported Volt-6 Atmos
Subs: The Two Towers (HT18 32cf 11.5Hz x 2), UM18 4cf x 2, Crowson MAs x 4

Last edited by aron7awol; 09-14-2019 at 03:57 PM.
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post #57 of 66 Old 09-14-2019, 04:49 PM
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The only reason the port velocity goes down is because the sensitivity goes down, thus less excursion. If you add more power the compression goes up quite a bit. You’ll also add power compression by adding more power to match the SPL.


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post #58 of 66 Old 09-14-2019, 05:01 PM
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Quote:
Originally Posted by lknhomeaudio View Post
Optimized, or not, it doesn't matter.
Oh, but it does.
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post #59 of 66 Old 09-14-2019, 07:11 PM
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Quote:
Originally Posted by aron7awol View Post
The key part that you're missing/ignoring is that if you keep everything the same and only lower tune, all you've done is made the port longer, right? Well, if you can make the port longer, then you can already make the port area larger and reduce velocity at that current tune. It makes no sense to keep port area the same and lower tune for the sake of trying to reduce port velocity when you haven't even optimized that current tune by making the port as large as possible.

.
I'm not missing anything. I know the things you mention. I think the key part that you guys are missing/ignoring is the fact that I responded to a simple statement that was just flat out wrong.

I was never trying to optimize anything. And what I said will never be not true.

Will it work? Yes
Would I ever lower my tune to reduce velocity? No.
Do I recommend it? No
Is it the worst way to reduce velocity, regarding overall performance? Probably!

Hell... when you see most of the boxes I build, you could get confused about which hole the sub goes in! 99% of the people on this forum suffer from too little port area. Luckily, the compression isn't noticeable in the typical everyday listening levels..
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post #60 of 66 Old 09-14-2019, 07:18 PM
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Quote:
Originally Posted by Trimlock View Post
The only reason the port velocity goes down is because the sensitivity goes down, thus less excursion. If you add more power the compression goes up quite a bit. You’ll also add power compression by adding more power to match the SPL.

Yeah, no one's arguing that point. And if you're already at the driver's thermal limit, kinda hard to add more power.

All. Things. Kept. The. Same.

I swear, some of y'all can't read... and it shows!

And I'll say it again for the people who keep missing it.... I DO NOT RECOMMEND THIS METHOD!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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