subwoofer driver

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  • Dr. Spec
    Dr. Spec Posts: 3,780
    edited February 2003
    I am not familiar with the 5X rule of thumb. Can you explain why?

    I do know if you use flared on both ends (which I recommend), the port length needs to be a bit longer to achieve the same tune point. I calc'd it out with flared ends (k=.850) and I'm getting about 23" for two 3" ports and a Fb of 18 Hz.

    What are you coming up with?

    My SVS is around 5.8 (edit: ft3 - duh) internal volume and I'm thinking the ports have gotta be around 28 inches long......
    "What we do in life echoes in eternity"

    Ed Mullen (emullen@svsound.com)
    Director - Technology and Customer Service
    SVS
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  • burdette
    burdette Posts: 1,194
    edited February 2003
    I read the 5x rule in several places on the net. Can't say exactly where - I've read just about every page I've found and there are a LOT of DIY subwoofer pages... which is nice. No, I can't say why specifically, I think port noise was the general reason.

    I'm getting about 21 inches for two 3" ports on WinISD, and I think it calculates assuming no flaring, so I suppose 23" sounds about right to be "a little longer."

    I assume you mean ft3 and not liters... I'm coming up with about 5.4ft3 overall... I've got a spreadsheet that adds in driver volume and port volume to the volume calculated for the cabinet (roughly).

    I should know tomorrow which driver I'm getting.. either Stryke sends it out or I'll get the Shiva. Then I can finally finalize some of this rather than just play around. It has been fun playing on WinISD with the EBS designs. I'll get much more benefit from lower extension than I will ability to play loud... so it is a good choice. Thanks, again, for the reminder/suggestion. I'm not sure I totally understood the concept of EBS when I abandoned it earlier.
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  • Dr. Spec
    Dr. Spec Posts: 3,780
    edited February 2003
    Yeah, that would be ft3 - I fixed it. It was late, what can I say?

    It's easier to cut a port than to stretch it. :-) Go with 23" inches and see what happens.

    If you can find a reason for the 5X rule, I'm all ears. I know one thing for sure - Tom V at SVS is a DIY legend, and if he uses 3" ports that are longer than 15", it must be completely OK.

    As long as you keep the velocity out of the red zone, I see no reason against it. I'm not an expert though and would still like to see the physics engineering logic behind this supposed rule of thumb.

    I like the EBS concept and I'm glad you revisited it. Taking advantage of room gain to fill in that slight sag in the FR before the tune point makes a lot of real world sense. I'd be interested in seeing your FR sweep after you are done. Ron-P built a sonosub - get with him for details on build or visit the tons of DIY sono-tube sites.
    "What we do in life echoes in eternity"

    Ed Mullen (emullen@svsound.com)
    Director - Technology and Customer Service
    SVS
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  • goingganzo
    goingganzo Posts: 2,793
    edited February 2003
    i thing the 5x rule aplys to rediance. just stuff some extra polly fill around the ports. and you will be fine. if you want to save some cash buy the flaired ports ends and some pvc and make your own.
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  • Dr. Spec
    Dr. Spec Posts: 3,780
    edited February 2003
    Originally posted by goingganzo
    i thing the 5x rule aplys to rediance. just stuff some extra polly fill around the ports. and you will be fine. if you want to save some cash buy the flaired ports ends and some pvc and make your own.

    What does "rediance" mean?

    I agree - custom port length is very easy with thin wall PVC and purchased flared ports - good call.
    "What we do in life echoes in eternity"

    Ed Mullen (emullen@svsound.com)
    Director - Technology and Customer Service
    SVS
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  • goingganzo
    goingganzo Posts: 2,793
    edited February 2003
    sorry about that it is resonance. aka you get the port resonance near the tume resonance and you have problems. that is what i think. inseead of spending alot for the aero ports. i baught a 4x4in flaired port end and mated it with some thinwall pvc and used culpings to do it. then you paint the port and pvc when you paint the front of the box. or you just paint the port and pvc if you laminate the box.
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  • Dr. Spec
    Dr. Spec Posts: 3,780
    edited February 2003
    Ahh...I get it. All tubes have a natural resonance frequency.

    You don't want the tube's natural resonance frequency to be anywhere within the bandpass of the sub. High or lower is fine, though.

    I guess the question to be asked is this: How do we calculate the natural resonance frequency of a given length of tube?

    Have either of you received shipping tracking numbers yet?
    "What we do in life echoes in eternity"

    Ed Mullen (emullen@svsound.com)
    Director - Technology and Customer Service
    SVS
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  • burdette
    burdette Posts: 1,194
    edited February 2003
    No tracking number yet.. he told me last week he'd get it to me this afternoon or evening. I'm on faith now... I really want that driver and hope it all works out, but I'm already acclimated to the expectation that it ain't gonna happen and that I'll be ordering a Shiva this week. I can only go UP from here.

    I've been planning on PVC tubes the entire time. Stryke told me he uses them and simply flares the wood itself with a 3/4 roundover bit. Always looking for a reason to buy another carbide router bit. Parts Express has some flared ends that could be mated to longer tubes.. I'm trying to find out how good the fit is.

    Right now, I think I'm sold on two 3" ports, each around 21 inches long.. or the 23" if flared. Dickason's book says go with the largest diameter you can, but a single 6" port is supposed to be 42" long.. I don't think I want to do that.

    I agree that if SVS violates the 5x rule, perhaps there isn't much to it, especially considering they also use drivers that move a lot of air. There are a ton of resources on Shiva, but not that much to look at for DIY applications of the AV12.

    Doc.. do you have an opinion on just how much I should worry about flared ends? If I use two 3" pvc pipes and flare the wood...?? Also, opinions on having both ports upward firing? I want to use 16" sonotube, and don't want to try to squeeze a port on that baffle. 4" wouldn't fit, anyway.

    Thanks.
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  • Dr. Spec
    Dr. Spec Posts: 3,780
    edited February 2003
    Definitely use commercial flares - they increase the effective port area more than simply rounding the edges of the wood will.

    I also recommend having both ports fire upwards - opposite the direction of the woofer.

    See Ron-P's "There's A New Subwoofer In Town" in Off-Topic for some nice photos of what to expect.

    Also go here for how to jam three 3" ports into an 18" tube endcap if you really want to flow some air.

    http://www.svsubwoofers.com/subs_pcplus_features.htm

    It's interesting - the AV12 looks EXACTLY like the SVS ISD with the cone from the dB12. Check out both drivers and tell me what you think!
    "What we do in life echoes in eternity"

    Ed Mullen (emullen@svsound.com)
    Director - Technology and Customer Service
    SVS
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  • goingganzo
    goingganzo Posts: 2,793
    edited February 2003
    win isd pro will give you the resonance. i think it is a lenth thing the longer the port the lower the resonance fr. i have read by adding extra fill around the port you can reduce this efect.
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  • goingganzo
    goingganzo Posts: 2,793
    edited February 2003
    did you get your av12 shiped? he just got in the av15 and shiped 1/2 of them today. i dident get mine but he will ship them tomarrow he sent out 36 out of the 60
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  • burdette
    burdette Posts: 1,194
    edited February 2003
    My AV12 should be here tomorrow. I just ordered the 250watt amp from PE, the no-bass-boost model.. on special and no shipping, so I got it to my door for $120.
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  • Dr. Spec
    Dr. Spec Posts: 3,780
    edited February 2003
    Originally posted by burdette
    My AV12 should be here tomorrow. I just ordered the 250watt amp from PE, the no-bass-boost model.. on special and no shipping, so I got it to my door for $120.

    Excellent news guys! Looking forward to progress reports from both of you.

    Gonzo will be first out of the gate, I think. All he has to do is wire up the drivers and button them up in the enclosure. The rest is already done.

    Make sure to get out the SPL meter Bryan - I've got a fin on 130 at one meter.
    "What we do in life echoes in eternity"

    Ed Mullen (emullen@svsound.com)
    Director - Technology and Customer Service
    SVS
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  • burdette
    burdette Posts: 1,194
    edited February 2003
    Got a port question for you, Doc. I know I've sortof asked around this before, but the port dilemma is my final hurdle.

    WinISD is telling me that if I go 142 liters for an EBS alignment, and tune to 18 Hz, I need two 4" ports, each 38" long. If I go two 3" ports, they have to be 21" long. A single 6" port is too long.

    I can find commercial double-flared port kits that max out at 17". If I change my tuning to 19.5Hz, I could use the commerical 3" kits. Drop off is quick... changing that tuning changes the -3dB frequency from 17.3 Hz to about 18Hz.

    EDIT: Stryke's website shows an F3 of 16Hz for the same EBS tuned to 18Hz... I'm not getting that at all with WinISD... mine shows -5dB at 16 Hz with an 18Hz tune.??? end of edit

    I can find 4" flared ends, but I'd have to connect them to PVC pipe and I can't find references on whether they'll fit (I asked PE, no reply yet). I know gonzo did this, but I don't know if the ends he found are the same ones I've found (PE and Madisound and a few other places on the net).

    I know you strongly suggested commercial flared ends. So, what is the solution to all this? Frankly, at this point, I'm tempted to just buy 4" PVC pipe and save the money on kits or ends, round the wood some, and (most likely, I'm assuming), be just fine because I certainly will NOT be after the high SPLs. Those kits are $13 a pop and I have to change my tuning to use them. It seems like two 4" ports could move a lot of air, and I'm really wondering if I need to be so concerned about flaring right now given my usage...? WinISD gives me a mach number of 0.04 for two 4" ports, 38" long.

    I really don't have to decide this right now as far as construction schedule, but I need to place another order with PE and I'd like to get everything at once. $8.50 shipping is too much for some port ends that run a buck each.
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  • Dr. Spec
    Dr. Spec Posts: 3,780
    edited February 2003
    You are overlooking the obvious - if you are stuck with a 17" port, simply alter the enclosure size to accomodate for the shorter ports. A 6 ft3 enclosure should do the trick if you are using twin 3" ports x 17" long.

    With sonotube, it's as easy as pie - just add some height! Go with an 18" tube diameter to keep the height reasonable - around 42" should do it.

    Also, bear in mind SVS uses a single 4" flared port for its CS and PCi subs and the T/S parameters for the AV12 are probably VERY close the SVS ISD. A single 4" port of 17" will get you very close to a 18 Hz tune with your original 5 liter enclosure.

    The Parts Express kits are very nice, BTW and should serve you well either way.

    Hope this helps!
    "What we do in life echoes in eternity"

    Ed Mullen (emullen@svsound.com)
    Director - Technology and Customer Service
    SVS
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  • goingganzo
    goingganzo Posts: 2,793
    edited February 2003
    if you go with the 4x4 flaired ends and make your own it mates op nice. you just have to make sure you sit the flair and the pvc all the way down on the culping.
    6 cf gives you a 31 in vent for dual 4 in and dont you forget to add a in to the 31 for the flairs.
    5.5cf gives 34in

    actuley i went out and got some wire and some more bana conectors.
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  • burdette
    burdette Posts: 1,194
    edited February 2003
    Originally posted by Dr. Spec
    You are overlooking the obvious - if you are stuck with a 17" port, simply alter the enclosure size to accomodate for the shorter ports. A 6 ft3 enclosure should do the trick if you are using twin 3" ports x 17" long.

    Also, bear in mind SVS uses a single 4" flared port for its CS and PCi subs and the T/S parameters for the AV12 are probably VERY close the SVS ISD. A single 4" port of 17" will get you very close to a 18 Hz tune with your original 5 liter enclosure.

    The Parts Express kits are very nice, BTW and should serve you well either way.

    Hope this helps!

    It does help.. I very much like having my thoughts confirmed by those with more experience. I like to take risks SOMEtimes, but sometimes not.

    True enough, a single 17" port will work ... the reason I started looking at multiple ports was due to the mach number I'm getting from WinISD. The single port shows a mach of 0.15, and the number turns red at 0.16 (I think).

    If that mach number isn't a concern, then I suppose my question is answered. Increasing size to accomodate two 3" ports only 17" long isn't what I want, so I think I'll go with the single 4".

    Thanks, Doc and gonzo.

    I'm waiting to hear the FedEx guy come into the office.. he should have a big, 25lb box for me! Got word that my amp shipped yesterday as well, should be here Friday.
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  • goingganzo
    goingganzo Posts: 2,793
    edited February 2003
    also i was told to play a 10hz sogonal throgh the subs to break them in. it will move them throgh most of their range and is not audible.
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  • burdette
    burdette Posts: 1,194
    edited February 2003
    Two things.. first.. my AV12 did indeed arrive today.. in an unassuming plain white box. Opened the box, looked in, and thought "wow" and "cool." Took out the packing and took out the woofer and thought "Holy ****." In fact, I do believe I actually said "holy ****" out loud.

    This thing is a beast... a monster... I am absolutely impressed with the look, feel, build quality... holy ****. Not since I was the first on my block to get a Dolby C cassette deck have I felt this puffed up about a piece of my gear. Anyway.. wanted to pass that along. I can't even imagine being in the imposing presence of gonzo's two fifteen-inchers (I think there might be a good title to a sci-fi **** flick in there somewhere).

    Second.. christ I can be such a **** woman sometimes with worrying. It usually serves me well in that I rarely have buyers' remorse or think "oh I should have...." about a project. But geez.. these ports. I went to Lowe's this evening and they have SUCH a selection of pipe and connectors.. I'm definitely ordering the flared port ends from PE for $1.09 each (in fact I got 3 in case I mess one up) and picking up the rest from Lowe's. I should have less than ten bucks in the port and can make it any length I choose. Thank you for not **** slapping me during that, my one and only subwoofer project-related panicky moment. I'm feeling much better now.
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  • goingganzo
    goingganzo Posts: 2,793
    edited February 2003
    when you cut your pvc make sure it is seated all the way ti the botom if the culping or the lenth will be off. but that wont afect you very much unless you have 2 or more ports. i hope i get my subs someday.
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  • Frank Z
    Frank Z Posts: 5,860
    edited February 2003
    Originally posted by burdette
    I can't even imagine being in the imposing presence of gonzo's two fifteen-inchers (I think there might be a good title to a sci-fi **** flick in there somewhere).

    THAT is a mental image I did not need..THANKS A LOT!!
    9/11 - WE WILL NEVER FORGET!! (<---<<click)
    2005-06 Club Polk Football Pool Champion!! :D
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  • goingganzo
    goingganzo Posts: 2,793
    edited February 2003
    just got my tracking # today and it should arive today. good thing i have most of the day off. i will post some pics as soon as they arive. and if i can find the digital camera.
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  • Dr. Spec
    Dr. Spec Posts: 3,780
    edited February 2003
    Gonzo:

    Have you actually assembled your ports yet? The last I saw you just had the flares in the box.
    "What we do in life echoes in eternity"

    Ed Mullen (emullen@svsound.com)
    Director - Technology and Customer Service
    SVS
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  • goingganzo
    goingganzo Posts: 2,793
    edited February 2003
    it is all done and i got my subs today happy day. did you check out the suround on the thing it is like an inch high. these are massave the 2 subs weigh as much as my old velo did with box. they are so sweet looking too. i dont have a digital camera at hand so i will have to wait till monday to take pics. just amagine my box with 2 sweet subs in it. the ports are easy to do you take you cleaner and put it on bith the flair and culping then add the glew.push in till seated then 1/4 twist. repet steps for thinwall pvc pipe. but it is harder to seat so use extra force. then cut hole in endcap put other flair in then join togher. after you have i side thrigh hole for port.

    on my first atempt when i was makeing the ports for my sono tube i got 1 longet than the other caues i didnot seat them very well.
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