First time DIY Subwoofer AV12 Tube - Help!

Discussion in 'Home Theater Projects' started by Scott Heaton, Jun 10, 2003.

  1. Scott Heaton

    Scott Heaton Auditioning

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    I am planning on making 2 SVS type subwoofers (Sonotube with driver on one side and ports on the other) using Strike's TC Sounds AV12 driver. I plan to lay the subs on their sides behind the couch and drive them with a Sampson S1000 amp.

    My goal is to be able to produce sound at near referance levels all the way down to at least 20 Hz.

    I am looking at a 125 L volume tuned to 19 Hz.

    I have enough 15.5" ID cardboard tube at work and a nearly unlimited supply of free 3 7/8 ID X 4 3/8 OD cardboard tubes that I will use as ports. I am figuring using free ends on the port, although, I may try to later put a bit of a flange into one end.

    I calculate using ported.xls that I should use 2 of the ports about 37" long. This gives me a tube length of 48 1/8" long. I get about 5" of clearance from the back of the driver to the ends of the ports.

    Questions:
    1. Does it look like I am doing this right?
    2. Are the ports too long? It seems like I would get chuffing if I used one shorter one.
    3. Could someone check my calculations for me on a better program? I check mine on WinISD beta and got about the same numbers.

    I guess I am just nervous that I am missing something or doing something wrong because this is my first attempt at DIY speakers and I am just going by everything I have learned on these threads.

    I hope I am in bounds asking these questions in an advanced forum. I tried to read up as much as I could about this before posted so I didn't ask a "dumb" question.

    Thanks for your help....

    AV12
    Fs: 21Hz
    Qms: 4.41
    Qes: .399
    Qts: .366
    Vas: 88 L
    Re: 2.97 ohm
    Z: 4 ohm
    BL: 15 Tm
    Cms: .25 mm/N
    Mms: 228 g
    Pe: 500W
    1W/1m: 85.5dB
    2.83V: 89.5dB
    Xmax: 23 mm
    Xsus: 30 mm
    Sd: 498 sq cm
    Vd: 2.33 L
     
  2. TimForman

    TimForman Supporting Actor

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    Try modeling it using a 6 inch port. You'll get low mach with a slightly shorter tube. Your other numbers seem to look ok at first glance. Have you tried a little more volume say 135 L?
     
  3. Scott Heaton

    Scott Heaton Auditioning

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    Actually, I get a longer tube with 6 inches. 2 ports 3.875 inches in diameter have less volume than one 6 inch tube so the 6 inch one would need to be longer, right?

    Anyway, I have the 3.875 sitting here for free so there would need to be a good reason not to use it. I was hoping that it would not resonate as much being thick cardboard rather than PVC.
     
  4. TimForman

    TimForman Supporting Actor

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    Well, unless WinISD is lying I get a slightly shorter length with one 6" tube vs. two 4" tubes, however, the mach is lower with the two tubes. Since they're free who can argue. Just throwing some stuff out there.
     
  5. Rob Formica

    Rob Formica Stunt Coordinator

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    "Actually, I get a longer tube with 6 inches. 2 ports 3.875 inches in diameter have less volume than one 6 inch tube so the 6 inch one would need to be longer, right?"

    The cross-sectional area of your 2 3.875" tubes is about the same as the single 6" (about 5.5" internal diameter)... so they should be very similar, but you are correct in assuming normally that a larger tube x-section requires a longer length.


    Are the Stryke AV series manufactured by TC Sounds? just curious... i seem to remeber seeing it posted somewhere else, but now i'm no longer sure... [​IMG]
     
  6. Bryan Michael

    Bryan Michael Supporting Actor

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    did you order yet? i have dual av15 with the samson and it is awsome to put it modestley. they are not that much more a piece and are just so awsome.

    bigger the box the shorter the tube. the bigger the box you can tune lower and go lower.



    but 2 av12 will rock the house.

    i have a frend with a single av12 and he is very happy and olny has 250 wats going to it.
     
  7. Scott Heaton

    Scott Heaton Auditioning

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    Yes, They are made by TC Sounds.

    I didn't know that a 6" tube had a 5.5 inch ID. Now they come out as similar lengths.

    I have the AV12s on the preorder so I have at least a month to wait for them and build my tubes. I have all of the endcaps cut. And am thinking about cutting the tubes and ports to length and putting them together.

    This is a pretty big tube right now. Looks like I will cut the tube at about 48" long and with the caps they will be 49.5" long. I did think about going longer and getting shorter ports but I would always end up designing it with a lower tuning frequency instead. I think that 50" is all I will be able to get away with.

    Does it look like it will work well for me? I shouldn't get much port noise? What about port resonance?
     
  8. Greg Monfort

    Greg Monfort Supporting Actor

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    Using the published driver specs and your sonotube/venting diameter limitations, 125L is too much of an underdamped alignment IMO, so going larger just makes it worse. Unless it's an extreme EBS I've found it best to limit oversizing the cab to ~1.414x the max flat alignment's Vb, or ~92L in this case. Tuned to ~18Hz looks good even when VC heating is factored in, maintaining good impulse/transient response. A couple of these in a corner should 'rock you'. [​IMG]

    WRT vents, according to MK's pipe simulator, two 3.875" i.d. need to be 48" long (much longer than I would like to see), but if 80Hz/4th is used it may be OK. Vent mach is low, but if their upper harmonics are audible then shortening to ~36" and mass loading to make them aperiodic should damp them right out and lower Fb back to where you want it to best blend to the room's gain.

    GM
     
  9. Scott Heaton

    Scott Heaton Auditioning

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    Greg,

    Thank you very much for taking the time to look at this. I would love to go with a 92L tube that is tuned to 18Hz, however, the ports always needed to be too long to fit in the tube. It seems that I would need to use PRs to go that small (in my newbie thinking).

    When I calculate port length of 125L @ 19 Hz, I get 37 inches long. Why do you get 48" long with your calculations? I am not saying that you are wrong, I am just trying to figure out if I need to be doing this differently.

    As far as the crossover, I will use the crossover on the Pioneer 45tx and I think it will end up being around 80Hz but it must be a 12 dB / octave.

    I never thought of making the ports aperiodic with fabric over the port. Does that work well?
     
  10. Greg Monfort

    Greg Monfort Supporting Actor

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    >Thank you very much for taking the time to look at this. I would love to go with a 92L tube that is tuned to 18Hz, however, the ports always needed to be too long to fit in the tube. It seems that I would need to use PRs to go that small (in my newbie thinking).
    ====
    You're welcome! Yes, PRs would be preferred. As for the other, I don't let asthetics get in the way of high performance, so having vents sticking up above the main body isn't a big deal to me. That said, why not make the main tube as tall as need be, put a baffle in at ~92L and fill the cavity with polyfil or foam? With 48" long vents, supporting them at both ends is a good idea anyway. Also, you don't want the vent's entrance near the driver as it will overload them and won't get the predicted response/good performance.
    ====
    >When I calculate port length of 125L @ 19 Hz, I get 37 inches long. Why do you get 48" long with your calculations? I am not saying that you are wrong, I am just trying to figure out if I need to be doing this differently.
    ====
    That's about right for a golden ratio reflex, where the Helmholtz formula is used/applicable, but they would be shorter for a pipe with the driver at one end and the vent at the other like yours is. My calcs are for 92L/18Hz, which probably are considerably longer than 48" if calc'd with a standard box program since it doesn't take the 1/4WL standing waves of the cab into account like MK's program does.
    ====
    >As far as the crossover, I will use the crossover on the Pioneer 45tx and I think it will end up being around 80Hz but it must be a 12 dB / octave.
    ====
    Then the long vents may very well cause some audible distortion if the sub is pushed to high SPLs around Fb, such as sustained 16Hz organ pipe notes or I never thought of making the ports aperiodic with fabric over the port. Does that work well?
    ====
    Extremely. Blow through a few layers of double knit material stretched across your mouth. Indeed, it's easy to overdamp a system this way as many folks figure if some is good then a bunch more must be just right. Coffee filters are popular, as is fabric softener sheets which gives the room a shot of scent when strongly energized. [​IMG]

    GM
     
  11. Scott Heaton

    Scott Heaton Auditioning

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    Thanks again! This is great! You are right, who cares what they look like as long as they sound great. I will just convince my wife that funny tubes always stick out of the good subwoofers.

    I calculate that I can reduce the 92L tube (15.5" ID) to around 34.75" long with 24" of the port inside and 24" of the port outside the tube. I am going to use 3/4" MDF plug and cap with the driver sunk through the cap and attached to the plug. If I get low frequency distortion I can try shorter tubes with grill material over the opening. Does this sound like a good plan to you?

    My program says 92L at 18Hz should have 2X 58" long ports and at 20Hz it is 2X 46" ports. It is not a tube program so it does not change anything based on my standing waves. I really have no idea how that works but I will take your suggestion at 48" and do some searches for info on standing waves in tubes.

    Also, am I correct that I should not add any fill to a ported tube?

    Thanks again for all of your help.
     
  12. Greg Monfort

    Greg Monfort Supporting Actor

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    >Thanks again! This is great! You are right, who cares what they look like as long as they sound great. I will just convince my wife that funny tubes always stick out of the good subwoofers.

    >I calculate that I can reduce the 92L tube (15.5" ID) to around 34.75" long with 24" of the port inside and 24" of the port outside the tube.
    ====
    I wouldn't put them that close to the driver. Modeling programs assume that the entire vent is outside the cab and one reason why they never measure exactly as predicted, so it's best to limit their intrusion as much as practical.
    ====
    >I am going to use 3/4" MDF plug and cap with the driver sunk through the cap and attached to the plug. If I get low frequency distortion I can try shorter tubes with grill material over the opening. Does this sound like a good plan to you?
    ====
    LF distortion shouldn't be an issue, it's the vent's harmonics that may cause trouble. If you can view MS Word docs I can send you a pic of the sim. A pic is worth a thousand words. [​IMG]
    ====
    >My program says 92L at 18Hz should have 2X 58" long ports and at 20Hz it is 2X 46" ports. It is not a tube program so it does not change anything based on my standing waves. I really have no idea how that works but I will take your suggestion at 48" and do some searches for info on standing waves in tubes.
    ====
    Good luck, there's lots of bad info out there, including the AES. MK's been researching it for years and has finally hit on the 'truth' IMO and developed some spreadsheets to design with. They're not particularly user friendly since he designed them for his own use, but well worth the effort if you plan to design speakers as a hobby/whatever. I have built/measured enough tower designs and horns to be satisfied that they're the 'real deal'. http://www.quarter-wave.com/
    ====
    >Also, am I correct that I should not add any fill to a ported tube?
    ====
    Hmm, no fill to the vent unless you have a net to retain or catch it. [​IMG] Adding fill to the VB will lower the vent harmonics without affecting the useful BW much so it's certainly a tuning tweak to try, just make sure it doesn't impede the driver at all.

    GM
     
  13. Scott Heaton

    Scott Heaton Auditioning

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    I will have to see if I have the space for 2X 32" tubes with 48" ports sticking out of them. It didn't seem right before having the port come close to the back of the driver.

    I can open word files. Thanks in advance for sending the graph.

    I tried reading some of MK's stuff last night, however, it is pretty complicated and deals mostly with tower speakers rather than a simple subwoofer. I will keep reading, but I bet I won't quite get it till I build the sub and tinker with it and MK's spreadsheets.

    So, you would reccomend a poly type fill to reduce the possiblilty of harmonics in the long ports as long as I keep it away from the ports and the driver. Does a poly type fill work well?
     
  14. Greg Yeatts

    Greg Yeatts Second Unit

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    The 6" port I used actually had an i.d. of 5 7/8". I found it at Lowes. This is the only sized pvc sewer pipe that I could find that would work with the 6" Aeroport.
     

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