Tempest Excursion Confusion

Discussion in 'Home Theater Projects' started by Greg Conti, Sep 4, 2004.

  1. Greg Conti

    Greg Conti Stunt Coordinator

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    I've read quite a few times that you really can't put much more than about 250 watts into a tempest before you reach its excursion limits. Since I have an 800 watt amp, I would like a driver that can take alot more power. However, when I model a 120L vented enclosure tuned to 25Hz using UniBox404, at 600 watts, the Tempest doesn't reach its Xmax at anything above 20Hz which is all I care about. Is the 250 watt limit only apply to sealed boxes? Am I doing something wrong? Is UniBox correct?

    [​IMG]
     
  2. Greg Conti

    Greg Conti Stunt Coordinator

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    Hmmm...Everything else being equal, WinISD pro gives an excursion of twice that of UniBox404. Is one of these programs calculating one way and the other peak to peak? Adire Audio lists the Tempest as having a Xmax of 16.4mm one way. Does that mean its peak to peak is 32.8mm?

    [​IMG]
     
  3. Janne Ahonen

    Janne Ahonen Extra

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    Janne Ahonen
    WinISD pro 0.50a6 and below uses peak-to-peak excursion plots. With still upcoming 0.50a7 version you can actually choose how you want to show excursion and port velocities.

    One way value is multiplied by two when expressed as peak-to-peak. So 16.4 mm one-way means 32.8 mm peak-to-peak.

    Regards,
    Janne
     
  4. Joe L.

    Joe L. Stunt Coordinator

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    Greg,

    I think you are modeling the driver correctly, the problem is that many of the DVDs we play in out home theaters have content way below 20 Hz. If you are playing music only, you will be fine.

    I have an Adire Tempest in a 260L sonotube enclosure. I'm pretty sure I can reach its excursion limits at 12 Hz with very little power, way less than the 250 watts I am using to power it. I know I've had to turn down the volume on some movies because I was fearful of hurting it.

    If you have a good rumble filter that will sharply cut off at 20 Hz, then you can use the 600 Watt amplifier and not worry about the driver. (You can start worrying about the neighbors, pictures on the walls, the plates and glasses in the china cabinet instead, cause they will all be rattling at that point and power level)

    Here is my unequalized in-room response
    [​IMG]

    If you are planning the Tempest for movies, you will want to limit the very low frequencies sent to the sub by using an amplifier with a built in rumble filter. I plan on putting a BFD equalizer in line with my sub to tame the peak at 65 Hz, but other than that, it has a pretty nice house curve shape to it. Oh yes, it is awesome to listen to really deep bass.

    [​IMG]

    Joe L.
     
  5. Greg Conti

    Greg Conti Stunt Coordinator

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    Thanks for the replies. 12Hz. Wow. I guess with the kind of extension you have, it wouldn't take much to overdrive a Tempest or two. I currently have an 18"JBL 2242H in a 8 cu ft box which gives me tons of output to 22 Hz. I have a subsonic filter so I don't get much output below that. However, I'm beginning to tire of the huge box in my living room. I can conceal a 120L box fairly easily. While the Tempest doesn't match the JBL from 22Hz up in terms of max spl, it does come close. My concern was that something was wrong with my modeling and that the Tempest wouldn't come close to the JBLs output
     
  6. Joe L.

    Joe L. Stunt Coordinator

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    Greg,

    8 cubic feet is just a tiny little bit smaller than my Sonosub's 9.2 cubic feet. Surely you can hide the cabinet in the room somewhere [​IMG]

    I've been told I should have painted my sub white and then applied big yellow labels describing "Efficiency" all over it. It would then "blend" in with the water heater in my basement and nobody would notice.

    Seriously, I'm using a Parts Express plate amplifier to drive it and although it is advertised as having a rumble filter it does not seem to kick in till it gets to about 16 Hz. As you can see from the graph, I'm only about 4 dB down at 12.5 Hz. I'm guessing the roll-off is mostly from the rumble filter.

    I did my frequency response measurement at a level well below the max output of the Tempest and it was very interesting. I used a tone generator program and found that I had to silence many rattles in the room as I adjusted the frequency downward. At 17 Hz the closet door at the far end of the room was visibly vibrating about a half an inch and rattling against its door frame. (resonance is a strange beast, isn't it)

    Usually, a sealed enclosure can take more power than a ported one because the trapped air acts as a spring helping to limit driver excursion. Unfortunately, it also makes the sub less efficient. Hey... you might just be able to use your 800 watt amplifier after all (with a good rumble filter).
     
  7. RodN

    RodN Stunt Coordinator

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    Greg,

    Dunno why you would want to go that close to the tempest excursion limits. Isn't the question flat response to around 20Hz without reaching that limit? Your graph would suggest you are achieving this.

    Joe L,
    Are you sure there's any rumble filter in that amp? I'm using the 250W amp from Adire with my 120L sealed tempest and it cuts off quite sharply.
    PS: Get a BFD, you could make an already very nice response nearly perfectly flat, will improve the harmonics of your whole system.
     
  8. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Most people use a much larger box and tune it much lower when they're using a Tempest. This makes a big difference in the amount of power the woofer can take above the tuning point. Try modelling some of the Adire recommended alignments and you'll see they reach max excursion with only 250 - 350 watts. You've picked a very different alignment.
     
  9. Joe L.

    Joe L. Stunt Coordinator

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    RodN,

    Edit: I've since learned that LSPCad was using double the power I entered since it was being applied to two voice coils in parallel. See the explanation a few posts further on in this thread. In the interim, the power levels in this post actually represent the power to each voice coil... the total power is double.

    PartsExpress says my amplifier has a Rumble filter... Link to PE page In fact the first paragraph boasts of how it helps.

    I feel certain that Greg will need a sharp cutoff if he has 800 watts of power available.

    I used LSPCad (downloaded from the Adire Web-site) to model the Tempest in a 120L ported enclosure and it showed with 600 watts he would be over 32mm excursion between 55 Hz and 29.7 Hz with a p-p excursion of 47.3mm at 38.5 Hz. I'm not sure a rumble filter will help there. (800 watts is even worse with over 32mm p-p excursion predicted between 60 Hz and 28.4 Hz)

    At 250 watts, the highest p-p in the audible range is 30.5 mm at roughly 32.8 Hz. In the near-subaudible range, it is over 32mm at 19.8 Hz.

    At a mere 25 watts, it predicts over 32mm p-p excursion at 12.4 Hz. Ouch... Now you can see why a good sharp rumble filter is almost mandatory.

    It does not take a whole lot of power to get into trouble in a ported enclosure below the tuning frequency with just about any driver.

    120L, 25Hz tuned, ported enclosure excursion plot for Tempest Driver with 800 watts applied
    [​IMG]

    Joe L.
    PS.
    I do have a BFD, I just have not had time to put it in line and configure it. (been watching too many movies)
     
  10. Greg Conti

    Greg Conti Stunt Coordinator

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    Joe L.
    Firstly, your unequalized room response is amazing compared to mine. I'm very jealous.

    When I model with LspCad I get the same thing as you if "Sep. sources" is checked under dual voice coil. If I select "series" I get excursions that agree with WinISD and Unibox. The TS parameters for the Tempest in LspCad look to be for a single voice coil so I would assume "series" should be checked if running them in series?

    BTW, I definitly will be using a subsonic filter. Always do with ported boxes.

    This is for the Tempest, 120L, 25Hz, 800 watts
    [​IMG]
     
  11. Joe L.

    Joe L. Stunt Coordinator

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    Greg,

    I had checked off "Parallel" since most folks parallel the two 8 ohm voice-coil windings to get a 4 ohm load to the amplifier.

    If you put the Tempest windings in series, it will be a 16 ohm load and your 800 watt amplifier will deliver way less power than you might expect. (probably about one quarter of its 4 ohm spec.) If that is the case, you might find it is perfect at about 200 watts output [​IMG]

    I did a quick search to find out the volume of air displaced of your current 18 inch driver at max p-p excursion but did not find that spec. I saw the max excursion distance was about 1/2 so I expect the volume of air moved by a 15 inch Tempest driver traveling about twice the p-p distance would result in close to the same SPL. (Your original observation)

    And thanks for the compliment on the frequency plot. I think I got lucky in that my wife is OK with it being several feet from the corner of the room. I think that helped even out the in-room response when measured at my favorite seat in the theater (Just in front of and under the projector) As I said, I did pick up a BFD equalizer but have not yet put it in line since we've been so busy with other things. (in addition to watching movies)

    Joe L.
     
  12. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Joe, you're entering the power information incorrectly. If you select "Sep. Sources" for your DVC connection then under "General Settings" enter 600watts into 8 ohms then LspCAD will simulate 600 watts into each of 2 voice coils. I don't think thats what we're after here.

    Similarly, if you select "Parallel" connection for the DVC and enter 600 watts into 8 ohms then LspCAD will simulate 1200 watts into the 4 ohm load that the Tempest presents when wired with coils in parallel. This is because LspCAD goes calculates the amplifier's voltage rails based on its power output at 8 ohms and then it calculates the actual power available to the woofer based on that rail voltage.

    So, assuming Greg is talking about 600 watts TOTAL, then we'd want to enter 300 watts into LspCAD when specifying either "Sep sources" or "parallel" and then we will get cone excursion plots that agree with WinISD pro and Unibox.

    Once you've done this you'll see that the sim indicates that the Tempest can almost handle 600 watts in this alignment - it hits around 34mm peak-to-peak at 38Hz.
     
  13. Joe L.

    Joe L. Stunt Coordinator

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    Ryan,

    Wow... Thanks... that makes a lot of sense, but it never occurred to me that LSPCad was trying to interpret what I was entering in that way.

    Greg,
    Go for it. Now we at least know why the other two simulation programs were so different from LSPCad in their p-p excursion predictions. I'm sorry if I confused the issue.

    I did take a few minutes to model the Tempest in a 260L tuned to 16.9Hz box and it seems to be a perfect match to a 250 watt amplifier (I entered 125 watts as the amplifier power as I just learned) It hit 33 mm p-p at 25 Hz. It still needs a sharp rumble filter as it easily can exceed xmax below 14 Hz.

    Modeling the smaller 120L enclosure tuned to 25 Hz results in a less efficient sub so it would be able to handle much more power. It is interesting how it all interacts.

    Joe L.
     
  14. MichaelAngelo

    MichaelAngelo Stunt Coordinator

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    Greg Conti wrote:

    I currently have an 18"JBL 2242H in a 8 cu ft box which gives me tons of output to 22 Hz. I have a subsonic filter so I don't get much output below that. However, I'm beginning to tire of the huge box in my living room. I can conceal a 120L box fairly easily. While the Tempest doesn't match the JBL from 22Hz up in terms of max spl, it does come close.
    ================================================== ======
    Greg, may I suggest something a lil different? You say you're tired of the big enclosure for the JBL, and that 120L is OK. You also want a little more lower extension right? And you already have a large (800watt right?) amplifier. I suggest isobaric Tempests. Many people on this forum are using 250L boxes with this sub, with a port to tune to ~16hz. To halve this enclosure size, one way is with an isobaric alignment. These are usually done "face-to-face", or clamshell mounted, with one driver wired opposite the other, so that when driven by the amp, the cones move in the same direction (otherwise cancellation would occur.) This effectively halves the necessary box size for fb.


    more good info here :

    This would result in a 120L enclosure, and the 2 drivers would suit your amp better. Also, you get the lower extension over the JBL.
    HTH
     
  15. Jeff::Hunt

    Jeff::Hunt Auditioning

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    Hi, I am a newbie when it comes to home theater and I am building my own subwoofer. After reading reviews of the Adire speakers, I have decided that I am going to go with the tempest and am building the 214L cabinet on Adire's website. My question, however, is about amps. I want a relatively cheap amp (I'm in college and have a budget), but I also want to be able to have the protection of the rumble filter. I have narrowed it down between the Parts Express 250W amp and the Adire 250W amp. Is one better quality than the other? Does one have a better rumble filter? The PE one is cheaper which is better, but if necessary I can go the extra dollar to get a better one if its necessary. Thanks for the help!!!

    ~Jeff
     
  16. Jack Keck

    Jack Keck Second Unit

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    Hey, Joe.

    That's one nice looking sub you got there. Any chance of posting the plans or posting a link to where your plans are?
     
  17. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Jeff, they are virtually the same amp. The adire amp has just a tiny bit of boost above the rumble filter - about 1dB IIRC - where the PE is flat to the rumble filter. You might also consider the new PE 200 watt amp. It performed at 240 watts into 4 ohms under test and if you read the details you'll see that it has some other advantages like the soft-clip circuitry.
     
  18. Cam McFarland

    Cam McFarland Supporting Actor

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    Hey Joe,

    Yep, that is mighty flat! Are those uncorrected numbers?
    MY Tempest is all over the place....
    At 20Hz (uncorrected), our output is identical, but mine
    hits 105db at 25Hz, jumps as high as 113db at 30Hz & then we are back equal again at 40Hz.
     

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