Small Tempest Sonosub - Vented?

Discussion in 'Home Theater Projects' started by Sven_DP, Apr 23, 2003.

  1. Sven_DP

    Sven_DP Agent

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    Well, lets start saying that most of the sonosubs I have seen here are huge. I want to try to sneak something a little bit smaller into our living room. Lawyers have been contacted... ;-)

    So for a 60m2 irregularly shaped room, half of which is the actual sitting corner , I have settled on a vented Tempest sonosub design of 4" diameter x 48" height. Usage will be 70/30 music/movies.

    I have been playing around extensively with Unibox, WinISD and LspCAD after having read hundreds of threads and web pages.

    I would really appreciate some of the 'sub' humans looking into this design I am aiming at for the moment.

    - 4"x48" = 200L - driver,port,amp and plates gives me 175L available.
    - Tempest
    - DT300 plate amp
    - Minimal fill : Qa = 80
    - Minimal leaks : Ql = 15
    - Two flared port ends : Qp = 140
    - Fb = 19Hz
    - F3 = 23,13Hz (I'm not able to get this down)
    - 4" port, 12.89" length
    - At 20Hz air speed reaches 25m/s, at 15Hz max at 33m/s

    I have allways understood that heavy stuffing is the thing to do when you have size constraints, but adding heavy filling (Qa=20)moves the F3 to somewhere around 33Hz.

    So what do you think? Am I missing something or is this reasonable? Or should I move to a Shiva? Or to a sealed sonotube maybe? Has anyone ever built this?

    Thanks for all comments!
     
  2. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    First, I'm pretty sure that a 4" diameter x 48" long sonotube will not give you 200 liters. You meant 18" diameter, right?

    Using WinISD pro I get a 12.2 inch vent for that alignment. Add 1 inch for the effect of the flares and you get 13.2 inches. The 12.89 inch length gives me a 19.2Hz tuning point. That's pretty good agreement from one simulator to another.

    The alignment has a very nice rolloff. Group delay stays under 20ms almost all the way down to 20Hz. Plenty of extension and it'll handle about 400 watts above tuning. The port air speeds get a little high, but with 300 watts its only about 25% higher than the air speeds I'm seeing in my DVC12 sonosub that uses the same flared port. I never hear any chuffing so you may be fine there. If you do hear chuffing you'll know you're probably near the woofer's limit anyway. I'd rather have some sort of warning than go straight to the "clack, clack, clack" of a driver beating itself to pieces.

    All in all, I like it.
     
  3. Sven_DP

    Sven_DP Agent

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    Oops! Yes indeed, thanks Ryan, I meant 48" x 18"!! I hate these small scrolling forum typing windows. ;-)

    What about taking lowering the vent speed by taking a larger port diameter? Problem is that F3 goes up.

    Do you (or anyone else?) have any ideas about the stuffing? I read Tom Noussaine's 1995 article, so I don't quite understand my results. Stuffing should give me an average 25% gain in volume, which means a sub still going lower, yes?

    Well, at least I (think) I will stay with the Tempest.

    Thanks. Sven
     
  4. AjayM

    AjayM Screenwriter

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    If you're looking mostly for music and some movies why not go sealed? I have a sealed tempest powered by a 250w PE plate amp (boost removed) sitting in a 170l cabinet and I get flat response down to 20Hz in room (before BFD). I may not have the absolute volume that the ported enclosures do, but I have more than enough to shake stuff off the walls and piss off the neighbor. And I have enough volume that even when playing a quick demo for somebody I've never stressed the thing to the point of bottoming out or anything drastic.

    And you could drop the height of your tube a little bit as well, a 4ft tube sitting on 4-5" legs may not sound very big, but in your room it's gonna be big.

    Just my 2 dinar's worth.

    Andrew
     
  5. Sven_DP

    Sven_DP Agent

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    Thanks Andrew. I just have been playing around with LspCAD and Unixbox for a sealed Tempest sub. I never really looked at it, and I must say it gives me strange results without the possibility to tune the thing. I'll try some more calculations but at first view it seems that below 40-50Hz there isn't much going on (at least not on the graph), or am I missing something? Do I really need a BFD and/or an equalizer? The DT300 amp from Adire, well its German in fact, has some basic equalizing on board I believe.

    At 170L which is around 6 cu ft, you get 20Hz flat in room, but I fear that I won't gain much in my room which is very irregular and open to the left and which has a LOT of large windows. What do you think?

    On the other hand my wife will be delighted with 3-4 cu ft instead of 7...I think...because everything above 50L is huge in her mind. [​IMG]

    Something else I tried out is the Stryke AV15 and the good old Shiva. All things more or less the same I get an F3 and Fb which is 2,5Hz lower than with the Tempest. The LSP curves are equal. The Shiva allows me to get a F3= 18 and Fb=18 with a little SPL 'bump' at around 220Hz, but I don't think that matters anyway.

    And again thanks for all advice. [​IMG]
     
  6. AjayM

    AjayM Screenwriter

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    I didn't think I'd get much room gain either in that room I was in either. The room had a 20ft ceiling, was around 20ft wide, 40-50ft long and was t-shaped. It was very alive with a tile floor, two HUGE windows (one was a sliding door), and a few smaller windows. The whole a/v system sat on one side of the T of the room, so it was basically open all around, and the sub in the corner. I would have never believed that I got that kind of response if I hadn't measured it (about 3 times to make sure I wasn't doing something wrong).

    Anyways, most of the software programs told me in 170l I would have an anechoic F3 in the low/mid 30hz range (32-35Hz), and an F10 usually just around 20Hz. In the room my 3db down point is 18Hz and I didn't bother to measure the -10db point. I believe Dan Wiggins uses a 122l Tempest in his system and he's measured a -3db point of 20hz in his room, so I don't think it's that much of a stretch. So if you're getting grossly different results than that you may want to see why.

    As to needing a BFD or some type of EQ, I would say no you don't need one, but it certainly helps. In the above mentioned room I had a few holes and a few spikes that I was able to work out, at least to around +/- 3db for almost the whole range (still one small hole I couldn't get in that range).

    Another point to consider, no matter what room you are in you will get some room gain, so if you design a flat response in one of the programs you won't have a flat response in your room, it will rise starting at the bottom (how much it will rise is the mystery), along with all the other problems a room gives.

    If you listen to music 70% of the time, I'd seriously look at some sealed options. You can get a .7Q out of 122l with a Tempest which is just plain out tiny compared to some designs out there (your 18" tube would be around 26 or 28" tall as a rough gross volume estimate). And you still have a strong possibility of "flat" response to 20Hz in your room for watching movies (but again you give up some SPL capability).

    Andrew
     
  7. Sven_DP

    Sven_DP Agent

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    So sealed sub performance in real life seems like a question of hope based on more or less room gain? Is this room gain as important with a vented design? Would an anechoic F3 of let's say 23Hz give me a in room F3 of maybe 14Hz? (in your case from 35Hz to 20Hz)

    If I understand well sealed will give me lower SPL's in the ultralow bass and 'tighter' (read : lower groep delay?) bass in the 30-60Hz region?

    Would it be a good idea to start with a vented sonosub and seal and stuff the port to be able to hear and feel the difference? If sealed sounds better, I could always make the tube smaller,yes?
     
  8. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Room gain is going to affect every subwoofer. Sealed sub designs do tend to rely on it a bit. My sealed DVC 12 sub just didn't cut it for me, in my very large, open-floorplan living room. The Tempest with its lower resonant frequency and higher displacement would certainly fare better. But I don't know how much better.

    When designing ported subs its actually smart to design in a little bit of rolloff in the bottom end to keep the low end from sounding exaggerated. You'll see this in the EBS alignments and Adire alignments in the Shiva and Tempest vented application white papers. The sims of your design look decidedly similar to the Adire alignment. We're talking about a low-Q vented alignment that is about as close as you can get to the transient performance of a sealed sub without giving up the port. And because of the low-Q design you don't get quite as much of the deep, deep, sub-20Hz bass as an EBS alignment. But you do get a naturally lower group delay.

    The EBS alignment is actually a high-Q vented alignment where the tuning frequency is pushed so low that the group delay doesn't peak until you get down into the low-low frequencies (20Hz and below) that most people can only feel. The idea is its unlikely that your butt will register the higher group delay of the vibrations in your couch. So the EBS and the Adire alignments shoot for the same goals - low end extension and good transient response - but in very different ways. In my opinion, the the Adire alignment is really the best compromise you'll find between the typical ported sub and a sealed sub. In other words, if there is a halfway point ... this is it. If you can't decide between sealed and vented - try a low-Q vented.
     
  9. Michael Hartwig

    Michael Hartwig Stunt Coordinator

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    Have you gone to the Adire site? They give extensive info on various types of possibilities for the Tempest. I built mine sealed in an octagon shape at about 145L; about 21" in diameter and 36" tall, outside measurements (including feet). As for the bass output I'm impressed. I'm using the Adire AV250 sub amp.
    I was listening to Patricia Barber 'Modern Cool' in SACD and the Tempest does very well with the phemonenal bass of this disk. For music I think the sealed is the way to go. The sealed configuration is far more forgiving than implementing a ported design.
     
  10. Sven_DP

    Sven_DP Agent

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    Oh yes, I have gone to the Adire website! It's nr 1 on my favorites lately.[​IMG]

    I didn't really look at the sealed enclosures until now, but the vented apps all look to large for me. Dan Wiggins gave a 3rd 175L alignment for the Tempest some time ago on this forum and by mail, but I don't seem to be able to duplicate his results.

    - 175L net
    - Fb = 17,5 Hz
    - 10,2 cm port dia(4")
    - 43,2 cm port length
    - 150W - parallel connected
    - Stuff 100% (20gr. / liter)
    - F3 = 22 Hz anechoic

    Depending on fill (Qa) and leaking (Ql) I'm getting an F3 between 24,8 and 30 Hz, so not even close to 22Hz.

    After heaving read Tom Noussaine's article on stuffing I was under the impression that 100% stuffing should be avoided because it makes things worse. So why 100%?

    Going up to Fb = 19 gives me an F3 = 23,13 Hz which was my design at the beginning of the thread. Still I would like to be able to simulate Dan's design as close as possible.

    Has anyone tried Dan's 'non-official' design yet?

    Btw. Replacing the Tempest by a Shiva lowers Fb and F3 easily to 17-18Hz. Would this be better for my usage?
     
  11. Ryan T

    Ryan T Second Unit

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    Sven

    I have a 230L sealed Tempest and let me tall you it rocks! I have it in my basement right now. The basement is about 30' by 25'. The sub goes louder than I care to play it with all the low bass scenes in movies yet it has incredible accuracy from being sealed. And keep in mind i'm using a stereo receiver which has about 60 watts RMS to power my Tempest. If you get some real power behind it you will improve the bass output and clarity considerably. If size is a limiting factor I would suggest looking into a 15" Dayton DVC. It's pretty much the same thing as a Tempest but works better in smaller boxes. I hope this helps.




    Ryan
     
  12. Jonathan_D

    Jonathan_D Stunt Coordinator

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    I have a 122L sealed Tempest and ran some quick and dirty measurements with my RS meter and True Audio's TrueRTA software generating sine waves through my system. My room really peaks in the 50hz range and dips somewhere between 27 and 24 hz but then right at 22hz and 21hz it was back dead on. Then it drops swiftly from 20hz down. I was actually getting a little queasy from the signals - not loud, but low! (I'm on a waiting list for a BFD - got get the "boominess" out.)

    My point is, the 122L sealed will hit 20hz, no problem.
     
  13. Sven_DP

    Sven_DP Agent

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    Thanks people for all the input so far. As I had a very hard time finding my 18"x48" piece of sonotube, I will start with the 175L allignment. (I can always make it smaller later on...) I will go for a vented design and at the same time providing a way to close the port to enable sealed/vented comparing in my living room. A sealed design just seams to uncertain to go for straight away. This way I can postpone the final decision until after sub construction.

    The problem with other drivers like Stryke and so, is that I didn't find any European resellers. Importing myself is just to expensive, otherwise I would have gone for an SVS a long time ago. [​IMG] I could go for a European driver, but then again Sonotubes are like UFO's in Europe, so not much real-life exemples to follow...

    Still nobody who actually calculated and made Dan Wiggin's 175L Tempest design? Maybe I should start a thread with this question? [​IMG]
     
  14. Sven_DP

    Sven_DP Agent

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    And up...

    Nobody's done the 175L vented Tempest design? [​IMG]
     

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