There's no reason not to rotate the manifold 90 degrees though.
Flipping the enclosure every so often is a fine solution though if you're dedicated to the upfiring layout. Every one of those tapped horns, if it's used that way for 12 months, will have measureable suspension sag by the end of that time. I like to build in such a way that even if I keep the same setup for years, there will be minimal upkeep. When you're 60, flipping a dual driver subwoofer might not be as appealing as when you're 40, if you wind up really enjoying the project and keeping it long-term.
Flipping the enclosure every so often is a fine solution though if you're dedicated to the upfiring layout. Every one of those tapped horns, if it's used that way for 12 months, will have measureable suspension sag by the end of that time. I like to build in such a way that even if I keep the same setup for years, there will be minimal upkeep. When you're 60, flipping a dual driver subwoofer might not be as appealing as when you're 40, if you wind up really enjoying the project and keeping it long-term.
Tapped horns are a relatively recent invention, and it seems many younger folks are unaware of cone sag.
Many TH users have burnt up or torn up their drivers before cone sag would have been an issue.
Consideration of cone sag was partially responsible for my upright Keystone TH layout.
I have a lightweight down firing 8" woofer in my kitchen.
Just checked on it, and it appears the cone has sagged around 2mm.
The design won't allow me to flip the cone, but I don't do much loud or critical listening in the kitchen, so no big deal.
Of course, if I were so concerned about second order harmonic distortion as to consider a PP design, I'd also be concerned about cone sag 😉.
Art
OK, After some reading up on the subject some particular themes seem to arise. Do cones 'sag'? It appears that some do......but there are particular circumstances common to this affliction. By and large it seems to be large heavy coned industrial gear. The common theme goes like this" My EVs I got in '77' seem to sag...they've been in my stage monitors & I used them when I was playing gigs in the Eighties & the sag got so bad the voice-coils rub now"
The common theme seems to be THEY ARE WORN OUT. 36 years old, unknown thousands of hours of use, unknown volume levels, unknown physical 'G' loads applied to the cabinetry etc.
There seems to be a corellation of lower Fs being more prone to 'sag' vs. a driver with a higher Fs. Also the surround types seems to have an effect (half-roll and pleated).
With a new build like the OP is contemplating, it is doubtful he will be using a vintage driver......with the obligitory thousands of hours running time.
Tell ya what I'm gonna do, an experiment. I have two identical drivers. One has been stored in its' original box, unused, oriented vertically. The other was used in an experimental sub-woofer enclosure built in 2003. While the second "used" driver only had some 50 Hrs on it..........it has been stored horizontally, kicked around from place to place....surprised it hasn't had its cone ripped accidentally, dusty, dirty and has always been "set down", magnet side down. Do you think the one set horizontally will have any sag relative to the NIB one? I'll find out for you.
________________________________________________Rick..........
The common theme seems to be THEY ARE WORN OUT. 36 years old, unknown thousands of hours of use, unknown volume levels, unknown physical 'G' loads applied to the cabinetry etc.
There seems to be a corellation of lower Fs being more prone to 'sag' vs. a driver with a higher Fs. Also the surround types seems to have an effect (half-roll and pleated).
With a new build like the OP is contemplating, it is doubtful he will be using a vintage driver......with the obligitory thousands of hours running time.
Tell ya what I'm gonna do, an experiment. I have two identical drivers. One has been stored in its' original box, unused, oriented vertically. The other was used in an experimental sub-woofer enclosure built in 2003. While the second "used" driver only had some 50 Hrs on it..........it has been stored horizontally, kicked around from place to place....surprised it hasn't had its cone ripped accidentally, dusty, dirty and has always been "set down", magnet side down. Do you think the one set horizontally will have any sag relative to the NIB one? I'll find out for you.
________________________________________________Rick..........
😀
unused and stored vertically....wow, that's unusual
I thought most were stored horisontally 😛
Vertically v horizontally- Easier to say "cone up" or "cone forward"
Note that the process is slower with an unused driver. Run some watts and thus heat and motion through it and you'll be surprised what you can achieve in terms of deforming the suspension.
The OPs polk 10s probably have 80g+ MMs, similar to pro 12/15"s, and a softer suspension to boot, and would be prime cone-sag candidates.
I don't understand why anyone would wish to disregard a legitimate concern.... that is readily addressed in the design phase. MANY have experienced this deformation- sometimes it can be corrected for. Here are some subs presumably similar to the polk 12"s that had this issue. (bottom of article)
http://www.enjoythemusic.com/diy/0512/kaboominator.htm
Note that the process is slower with an unused driver. Run some watts and thus heat and motion through it and you'll be surprised what you can achieve in terms of deforming the suspension.
The OPs polk 10s probably have 80g+ MMs, similar to pro 12/15"s, and a softer suspension to boot, and would be prime cone-sag candidates.
I don't understand why anyone would wish to disregard a legitimate concern.... that is readily addressed in the design phase. MANY have experienced this deformation- sometimes it can be corrected for. Here are some subs presumably similar to the polk 12"s that had this issue. (bottom of article)
http://www.enjoythemusic.com/diy/0512/kaboominator.htm
Last edited:
Rick,
Sagging cones do not have to be worn out, many dealers with old NIB have found their cones to have sagged without any use at all.
The good thing is the sag can be reversed, the bad thing is that takes a similar time period..
Will be interesting to hear how much your magnet side down driver has sagged compared to the NIB vertically stored unit, and what type suspension they use.
I actually was a little surprised that the lightweight poly cone foam surround 8" kitchen woofer had sagged 2mm in around 10 years.
Or was it 15 years...
Art
There is a reason, and that is rotating the manifold 90 degrees will result in a much wider enclosure than having the drivers in a facing up/down configuration. I have some WAF issues I have to deal with and having a significantly wider enclosure could be a problem.
This particular enclosure is just kinda a cheap experiment for me since I have all the hardware already and if it doesn't work out for some reason its no big deal. In future designs I will definitely take cone sag into consideration and try to avoid it if at all possible.
Unless you put the manifold on the side! This is to be a 100hz sub right? No reason you can't use the manifold on the side and the vent front or rear firing- the slot won't care unless you're running up above normal sub range- in fact, having the manifold face away from you is a good thing for sub frequencies- some vent or mechanical noise, or distortion components, will be further attenuated as they're higher frequencies, while the bass wraps around the enclosure without loss.
Hmm, yeah, I never thought of that. Thanks for the suggestion. This is why I ask these kinds of questions here, I always get solutions that I wouldn't have otherwise. Unfortunately I've already 3/4 complete with the enclosure and I can't change it now but I'll keep this idea in mind for next time, and there will be a next time.
I agree having the slot face away is a good idea. Also, to minimize resonances within the slot itself, maybe put chamfers in the back corners instead of just having a square. Or even make the slot progressive, opening up in a kind of a V.
Do cones sag? Of COURSE they do, even when brand spanking new! It's called GRAVITY, people😛
How much the cone sags depends on the suspension stiffness and the cone mass. But each cone face-up or face-down will absolutely sag a bit as Mother Earth pulls on it, and over time this will get worse due to suspension softening and suspension creep. Note: when the Moon passes overhead, it pulls upward, and the suspension will not sag quite as much, but we can write a program to digitally compensate for that using an astronautical database from the Meade Telescope Company. 😉
Seriously, though, I wouldn't mount cones face-up or face-down without some really compelling reason.
Even mounted normally, there is still some sag from gravity but much smaller as suspensions are typically quite stiff in the radial direction (spiders in particular). It wouldn't hurt to rotate periodically even in this orientation though.
Also glad you could redo the port without that bend at the end. JBL research found that at very high volumes, the air just "jets" in and out...which won't happen very well with any kind of bend. (And they also found radiusing doesn't matter at high SPL because the air jets in and out too fast, although the radiusing helped lower distortion at lower flow speeds). Other researchers favor a gentle taper, but I've never found any researcher who likes bent ports.
Do cones sag? Of COURSE they do, even when brand spanking new! It's called GRAVITY, people😛
How much the cone sags depends on the suspension stiffness and the cone mass. But each cone face-up or face-down will absolutely sag a bit as Mother Earth pulls on it, and over time this will get worse due to suspension softening and suspension creep. Note: when the Moon passes overhead, it pulls upward, and the suspension will not sag quite as much, but we can write a program to digitally compensate for that using an astronautical database from the Meade Telescope Company. 😉
Seriously, though, I wouldn't mount cones face-up or face-down without some really compelling reason.
Even mounted normally, there is still some sag from gravity but much smaller as suspensions are typically quite stiff in the radial direction (spiders in particular). It wouldn't hurt to rotate periodically even in this orientation though.
Also glad you could redo the port without that bend at the end. JBL research found that at very high volumes, the air just "jets" in and out...which won't happen very well with any kind of bend. (And they also found radiusing doesn't matter at high SPL because the air jets in and out too fast, although the radiusing helped lower distortion at lower flow speeds). Other researchers favor a gentle taper, but I've never found any researcher who likes bent ports.
bending the port helps minimize high frequency content too, and most of the time, the lower low-level distortion is going to be a bigger benefit. I'd leave it in. It's a mild way of making a "scoop" cabinet.
On driver sag, I'm surprised there's actually this much back and forth about it, there's actually a formula to determine if it's going to be an issue for your driver or not.
It depends purely on mechanical compliance and element weight.
Obey gravity, it's the law.
It depends purely on mechanical compliance and element weight.
Obey gravity, it's the law.
parts-express.com said:
That's two different things. Flaring of the port ends was found by the JBL guys to reduce distortion at lower levels. Some newer papers (albeit by more theoretical non-PA folks, and I have not read them yet) seem to advocate gentle tapers through the whole length.
But I've never seen any tout the benefits of bending a port. Intuitively, it makes airflow harder. Yes, with a lot of "scoop" maybe not too harmful, but also harder to get the port to the right frequency. But even the newer paper's abstract talk about symmetry, which stands to reason. For low distortion, you want the airflow out to be the same as the airflow in-that also helps avoid rectification effects of air pressure within the enclosure. So sorry, I just don't like bent ports, I prefer vertical shelf ports on the cabinet back or whatever as an alternative.
As for the blocking high frequencies, the scoop might allow MORE high frequencies to escape. Or not. I think this just depends way more on specifics of the entire geometry, and we cannot really predict at all. Have to be modeled in Akabak or such.
hi dyna- that formula is fine short-term- but what happens after you heat it up and vibrate it (as in, use it)? The suspension deformation isn't a one time pull, it's a creep.
Of course- but there's a similarity enough to make the comparison. In any case, I suspect he'll be fine.
@ DrDyna
That's very useful info, so Thanks for posting 🙂
Interestingly, in WinISD Pro's Help File is this
That's very useful info, so Thanks for posting 🙂
Interestingly, in WinISD Pro's Help File is this
This is true too. I'd still guess though that the lower the sag % is to begin with (and the higher the quality of the driver is), the longer it'd probably last oriented up or down...I dunno though.
SAG CONFIRMATION, DOCUMENTATION
OK, Apologies to all, I just had to confirm an affliction of driver sag for myself.
The driver in question is a Radio Shack DVC sub-woofer 40-1350A
Published Specs(coils in parallel)
Qes .42
Qms 4.4
Qts .38
Fs 21
EBP 47.7
RE 3.5
Sd .0532 SQ M
Vas 13.3 Cu Ft
Xmax .46 "
SPL 95 Db
PE 60
Measuring as best I can, I came up with a value of 15-16mm on the "old" horizontally stored driver, open to the elements indoors
Measured values of the vertically stored NIB driver gets me 13mmm....a sag value of 2 to 2.5mm.
Mind you, the "used" driver had very little hours of usage, the only variable was the horizontal orientation & the exposure to indoor elements.
Wow..........I guess I will have to flip over the "old" driver, cone down & let it sit for another ten years or so.....if I want to use it.
( I have a bunch of pictures as documentation here, I just can't get them all to load, I'll try later)
___________________________________________________Rick.........
OK, Apologies to all, I just had to confirm an affliction of driver sag for myself.
The driver in question is a Radio Shack DVC sub-woofer 40-1350A
Published Specs(coils in parallel)
Qes .42
Qms 4.4
Qts .38
Fs 21
EBP 47.7
RE 3.5
Sd .0532 SQ M
Vas 13.3 Cu Ft
Xmax .46 "
SPL 95 Db
PE 60
Measuring as best I can, I came up with a value of 15-16mm on the "old" horizontally stored driver, open to the elements indoors
Measured values of the vertically stored NIB driver gets me 13mmm....a sag value of 2 to 2.5mm.
Mind you, the "used" driver had very little hours of usage, the only variable was the horizontal orientation & the exposure to indoor elements.
Wow..........I guess I will have to flip over the "old" driver, cone down & let it sit for another ten years or so.....if I want to use it.
( I have a bunch of pictures as documentation here, I just can't get them all to load, I'll try later)
___________________________________________________Rick.........
Hi Y'all,
While it has probably nothing to do with this proposed design, I find the discussion of cone sag very interesting, and the formula posted by DrDyna in Post #32 could be quite helpful; but, it may be more important to take a closer look at the model for the enclosure. I doubt that the simple Hornresp bass reflex simulation (Post #3) represents what this enclosure would do. I think it might take AkAbak to even get close.
Regards,
While it has probably nothing to do with this proposed design, I find the discussion of cone sag very interesting, and the formula posted by DrDyna in Post #32 could be quite helpful; but, it may be more important to take a closer look at the model for the enclosure. I doubt that the simple Hornresp bass reflex simulation (Post #3) represents what this enclosure would do. I think it might take AkAbak to even get close.
Regards,
tb you're right. It would simplify the enclosure behavior to have 2 tuned chambers. Simply add a second vent at the top, retune the one on the bottom, and add a divider behind the manifold. (easier said than done depending on phase of project)
- Status
- Not open for further replies.