Timn8ter said:
FWIW, I've had good results calcing the minimum distance this way:
I use the reasoning that the minimum 'slot' area between the perimeter of the baffle/floor be ~the driver's useable Vd ((2*Xsus)*Sd) to ensure free flow up to this point, with some acoustic loading above it to help protect it if pushed harder. I normally use Xsus = 1.5*Xmax since it isn't usually readily available.
I haven't done any elaborate testing, but haven't measured any obvious impedance increases until the driver's pushed, nor heard any 'vent' noise.
For example: estimated Xsus for the JX92S = ~0.35"*1.5 = ~0.525" and Sd = ~12.19"^2, so Vd = (~12.19"^2*(2*~0.525")) = ~12.8"^3.
If the vent is flush with the bottom, then the perimeter of the bottom would be ~(6.97+4.31+1.5)*2 = ~25.56"
~12.8"^3/25.56" = ~0.5" min..
If the vent is stuck out away from the bottom and assuming a 2" i.d. pipe is 2.25" o.d, then 12.8/(2.25*pi) = ~1.81" min. between the baffle/floor, though if carpeted and only using legs I would make this to the top of the pile.
I'm not a fan of just legs though, much preferring a relatively massive base such as dense wood, marble, slate, concrete, etc., to attach the sub's legs to.
wingman said:
Not sure what design you decided on, but FWIW here's a T/S max flat I posted earlier, then vanished for whatever reason:
L = 45.25"
CSA (w x d) = 91.304"^2
density = 0.2lbs/ft^3
eta = 0.3754 (17")
rp = 1.5"
Lp = 4.5"
This is for one driver. For two, double the CSA and use two vents, three drivers, triple the CSA/three vents, etc.. WRT best matching the sim when using multiple drivers on the front, put their summed acoustic center at the eta point, i.e. for two this would be the midpoint between the two, for three - the center of the middle one, etc..
GM
Hey GM,
I've heard this a few times, that for two drivers you double the CSA, however, when I run sims I find that it's not quite double, although close. Any thoughts?
Also, running your calcs on floor clearance for a down firing vent I come up with something very small, under 0.5 in. If using a three sided stand with a slanted baffle, you're suggesting that the minimum clearance between the vent and the baffle be the number derived from the equations? This is different than saying the stand/baffle combo be 1/2" from the floor right?
I've heard this a few times, that for two drivers you double the CSA, however, when I run sims I find that it's not quite double, although close. Any thoughts?
Also, running your calcs on floor clearance for a down firing vent I come up with something very small, under 0.5 in. If using a three sided stand with a slanted baffle, you're suggesting that the minimum clearance between the vent and the baffle be the number derived from the equations? This is different than saying the stand/baffle combo be 1/2" from the floor right?
Greets!
Don't know why you're getting a discrepency since both the theoretical and real world measurements are in agreement. Got an example set of WSs you can email me to review?
OK, but understand that the acoustic vent area is the slot formed between the bottom of the speaker and the floor x 0.707 (due to 'mirror' imaging if the surfaces are perpendicular), a substantially larger CSA. As the speaker's base gets smaller and/or the excursion increases, the height must increase to compensate.
Hmm, if I understand you, correct, firing a vent off a sloping baffle is much more mathmatically complex (well beyond my skills anyway), but since the BW of interest is normally narrow band LF, using my calcs will work fine, though you might be able to SWAG a reasonably accurate response using MJK's 'sections' WSs.
In this scenario, the slope angle/length is more important since it sets the gain/BW of the acoustic 'elbow', so I visualize it in terms of a very short, one fold, 'fast' flare rate floor coupled compression horn. This means the shorter the pathlength, the higher its HF cutoff, ergo a steeper, longer sloped baffle will improve vent damping (allowing the vent to be shorter for a given Fb)/attenuate unwanted spurious HF output somewhat.
GM
altec210-at-yahoo-dot-com
Timn8ter said:
Don't know why you're getting a discrepency since both the theoretical and real world measurements are in agreement. Got an example set of WSs you can email me to review?
OK, but understand that the acoustic vent area is the slot formed between the bottom of the speaker and the floor x 0.707 (due to 'mirror' imaging if the surfaces are perpendicular), a substantially larger CSA. As the speaker's base gets smaller and/or the excursion increases, the height must increase to compensate.
Hmm, if I understand you, correct, firing a vent off a sloping baffle is much more mathmatically complex (well beyond my skills anyway), but since the BW of interest is normally narrow band LF, using my calcs will work fine, though you might be able to SWAG a reasonably accurate response using MJK's 'sections' WSs.
In this scenario, the slope angle/length is more important since it sets the gain/BW of the acoustic 'elbow', so I visualize it in terms of a very short, one fold, 'fast' flare rate floor coupled compression horn. This means the shorter the pathlength, the higher its HF cutoff, ergo a steeper, longer sloped baffle will improve vent damping (allowing the vent to be shorter for a given Fb)/attenuate unwanted spurious HF output somewhat.
GM
altec210-at-yahoo-dot-com
wingman said:
At an average SPL that pushes the driver to its max ratings (and especially, beyond) on LF fundamental/transients, mine will probably audibly outperform it, but at more moderate levels I imagine it will be ~same-same once the stuffing is 'dialed in'.
One thing about mine though is that the driver is low enough to 'force' a longer cab that has a cavity that can be filled with kitty litter, sterilized sand, or similar to mass load the cab. Combined with a heavy object on top, such as a marble or slate cap or heavy potted plant (good SAF), the LF/midbass/lower mids audibly 'tightens' up, increasing the critical upper BW's clarity.
GM
This idea has a great deal of merit in my mind. It addresses some issues with straight TLs; driver placement (which I think should be lower as in GMs model), port placement and driver height vs. ear height along with the benefits of a much more stable enclosure.
(oh yeah, don't forget the doily
)
Take a look at this example of a TL. There is a picture taken from the bottom of the cabinet showing a couple of small dowels holding up the stuffing.
http://www.quarter-wave.com/Project05/Project05.html
http://www.quarter-wave.com/Project05/Project05.html
wingman said:
Oops! These are fields you fill in on MJK's Mathcad worksheets to plot a sim. I just assumed that you were using Mathcad, or at least the demo version available at his website, to 'see' the predicted response various folks are suggesting. I see Tim has explained them. FYI, 'eta', the little symbol MJK started using on his later WSs is the Greek symbol for the letter 'h', which translates to the letter 'e' in English. I do not have a clue why it is used to describe a point along a line. I assume it has something to do with the Greek's early plane geometry notations.
WRT containing stuffing, attaching a net made from bug screen cloth or similar open weave material across the cab at the desired point works well. Do not stretch it tight though or it can 'hum' loud enough that the stuffing does not damp it down enough.
Tim,
Did you send the WSs?
GM
Hi GM,
Actually, it is a symbol used in finite element theory that describes a dimensionless dimension (a ratio). A lot of times finite element derivations describe the element's dimensions in terms of eta (and a few other greek symbols) with it being -1 < eta < 1, no matter how physically big or small the element size. I guess my day job is creeping into my hobby job.
Actually, it is a symbol used in finite element theory that describes a dimensionless dimension (a ratio). A lot of times finite element derivations describe the element's dimensions in terms of eta (and a few other greek symbols) with it being -1 < eta < 1, no matter how physically big or small the element size. I guess my day job is creeping into my hobby job.
Greets!
Not sure I grasp the concept, but thanks for the explanation anyway.
BTW, do you mind if I send you some sims to review? I've mentioned before that I don't always get a good correlation between different WSs and have figured out why in most cases, but you posted one recently that not only is contrary to what I expect based on experience nor can I come even close to duplicating yours with any of the WSs I have.
GM
Not sure I grasp the concept, but thanks for the explanation anyway.
BTW, do you mind if I send you some sims to review? I've mentioned before that I don't always get a good correlation between different WSs and have figured out why in most cases, but you posted one recently that not only is contrary to what I expect based on experience nor can I come even close to duplicating yours with any of the WSs I have.
GM
Hi GM,
I would be happy to look at your sims. Are you talking about the one I posted the other day for the JBL? I already got questioned on that result and I am still trying to figure out how I got there. I used a worksheet that is not released so I need to go back and look a little closer tonight when I get home and the kids are in bed.
I would be happy to look at your sims. Are you talking about the one I posted the other day for the JBL? I already got questioned on that result and I am still trying to figure out how I got there. I used a worksheet that is not released so I need to go back and look a little closer tonight when I get home and the kids are in bed.
Yep, based on my experience it's pure fantasy. Model it in an older release of your WS for a much more realistic sim. Anyway, thanks for the offer, but since you're already aware of it, no need to waste mine/your's time with my sims.
Since this thread's already totally highjacked, for whatever reason you haven't responded to several of my private emails to you in the past, or ~recently, so I'll ask here:
I only browsed your new horn docs awhile back since I can't follow the math, but you posed what I assumed at the time were rhetorical Q's, or are they actually Qs you want feedback on, and if so, have you gotten what you wanted already?
GM
Since this thread's already totally highjacked, for whatever reason you haven't responded to several of my private emails to you in the past, or ~recently, so I'll ask here:
I only browsed your new horn docs awhile back since I can't follow the math, but you posed what I assumed at the time were rhetorical Q's, or are they actually Qs you want feedback on, and if so, have you gotten what you wanted already?
GM
Hi GM,
I have not received any of your e-mails, I don't know why. I make it a point to try and respond to every e-mail I get within 24 hrs. I think that I am about 99% within this time frame on most e-mails. GM, I would never stiff you on a response. Your insights are always appreciated.
I have not received any feedback on my newer horn articles. Nothing, no reaction at all (Klipsch.com has accessed them 197 times in the past two weeks). I continue to work on the horn theory and am almost done with sims of floor and wall reinforcement. As always, any feedback from any reader is most helpful and appreciated. I would not have advanced this far this quickly on TL's if it were not for the comments and suggestions I received from the Internet DIY community.
I'll post my findings on the resolution of the JBL sim in that thread tonight or maybe tommorow as time permits. Could be I was trying to do too many things at once again and made a mistake, the sim might be correct and a logical answer is right in front of me, or it might be I just wanted to poke at Bill Fitzmaurice one more time.
I have not received any of your e-mails, I don't know why. I make it a point to try and respond to every e-mail I get within 24 hrs. I think that I am about 99% within this time frame on most e-mails. GM, I would never stiff you on a response. Your insights are always appreciated.
I have not received any feedback on my newer horn articles. Nothing, no reaction at all (Klipsch.com has accessed them 197 times in the past two weeks). I continue to work on the horn theory and am almost done with sims of floor and wall reinforcement. As always, any feedback from any reader is most helpful and appreciated. I would not have advanced this far this quickly on TL's if it were not for the comments and suggestions I received from the Internet DIY community.
I'll post my findings on the resolution of the JBL sim in that thread tonight or maybe tommorow as time permits. Could be I was trying to do too many things at once again and made a mistake, the sim might be correct and a logical answer is right in front of me, or it might be I just wanted to poke at Bill Fitzmaurice one more time.
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