Questions about sub designs, drivers?

Discussion in 'Archived Threads 2001-2004' started by Greg P, Jul 23, 2001.

  1. Greg P

    Greg P Stunt Coordinator

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    Im thinking of starting my first DIY sub. I currently have an SVS 25-31. But I want more output and a more percussive bass. From experience sealed subs have this characteristic and and inert (nonresinate) cabinates also do. I can attest about inert cabinate made of stone (ceramic, marble) as I own nOrhs, the inert cabinates have more bass (with the same driver!), are more percussive, and are faster. A sealed enclosure wont bring the output or depth I want. So the plan for my cabinate is to be of either granite, sandstone, synthetic marble, or cement. What do you think? Ive heard from some people that I cold get left over granite for free possibly and would just have to pay to get it cut!
    So the design Im looking at will either be a passive radiator or a ported design tuning it to around 23, 24hz. What are the advantages, disadvantes of a Passive Radiator vs. a Ported design? Which would you do? Size is not an issue.
    Third decision is the driver. Right now the front runner is the Adire Tempest. Others in consideration are the Lambda drviers (Stryke makes some also). A third one but not high in the running is the massive HE 15 from TC put out by Stryke. Know any other drivers? I want this to be good for music as well as home theater.
    Im learning some specs and trying to get things drawn out if I got the Tempest. I went towww.diysubwoofers.com and am learning a lot the last few days. Know any other good sites?
    Thanks guys for all your input
    Greg
     
  2. David Giesbrecht

    David Giesbrecht Second Unit

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    Ported boxes have better transient response than PR's if you decide to go with Tempest Tune it much lower like around 18 hz or even 16. A tuning of 23 or 24 hz would probably sound pretty boomy.
     
  3. ThomasW

    ThomasW Cinematographer

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  4. Jack Gilvey

    Jack Gilvey Producer

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  5. Brian Bunge

    Brian Bunge Producer

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    Thomas, Jack, etc.,
    Isn't the main goal of a subwoofer enclosure to make it rigid enough to raise it's resonant frequency well above the BW of the sub will be operating in? That's my understanding from what GM and others have posted here. I don't quite get this whole "inert material" discussion anyway.
    Just for all our benefit could you give us some reasoning why that statement is false? I'm not doubting you at all, I'd just be interested in your explanation. One thing that comes to mind is the possibility that internal cabinet dampening may suffer, but that may be a falsehood as well.
    Thanks,
    Brian
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  6. Jack Gilvey

    Jack Gilvey Producer

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    Thomas and Greg know infinitely more about materials than I do, I just thought that his final statement, not applied specifically to Norh, should be read carefully by many of the "contributors" to this forum.
     
  7. ThomasW

    ThomasW Cinematographer

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    Brian
    Ok here we go, but understand this is going to be just a bit condensed so as to deal with the major issues
    High density/mass/stiffness cabinets are a good way to go. But the density/mass/stiffness of the enclosure has nothing to do with the making the actual driver "faster". The Qts of the driver gives accurate info as the "speed" of a driver. The cabinet materials don't change the Qts of the driver, they can effect the Qtc to some degree
    One of the most nonsensical things on the nOrh site is their statement about small drivers = fast bass. This completely fails to take driver design into consideration.
    Here's an example of why they are wrong. Take 2 cars, one a lightweight sports car with a small but powerful motor. The other a muscle car twice as heavy but with a big block motor. Now if both cars can go from 0 to 100mph then back to 0 in 12sec, which one is faster? [​IMG] This analogy is the same for two different sized drivers that have the same T/S parameters. So a properly designed 12" driver can be just as "fast" as an 8" one.
    Box design can take one of two directions. But they both end up trying to achieve the same goal. You are correct about having the resonant frequency out of the operational frequencies of the driver. Using an extremely high density material like marble/granite/concrete does a good job of this, but so does making a high strength box. GM's favorite material being laminated Baltic/apple/marine plywood. These are two approaches that address the same issue, but from different directions.
    Now regarding the "sealed" box statement. The best box subs from a pure sonic standpoint are sealed designs that have a Qtc .5. That is considered critically damped. So it's fairly illogical to say that sealed boxes are sonically inferior.
    Finally the statement attributing the sonic characteristic of "depth" to a sealed subwoofer indicates a lack of understanding as to how a soundstage is created. Now it may be that the statement is regarding how low a sealed box can play, that too would be inaccurate
    [Edited last by ThomasW on July 24, 2001 at 12:15 PM]
     
  8. Brian Bunge

    Brian Bunge Producer

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    Thomas,
    This makes sense. Qts of the driver is totally independent to cabinet materials. I also understand that how the cabinet is constructed can affect Qtc.
    Also, I remember the two different cars analogy. And I also understand different Q alignments for sealed enclosures. So you basically stated what I already knew, but it's nice to have some reassurance! Plus I think you put it into words better than I could have.
    Thanks again!
    Brian
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  9. Greg Monfort

    Greg Monfort Supporting Actor

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    >Box design can take one of two directions. But they both end up trying to achieve the same goal. You are correct about having the resonant frequency out of the operational frequencies of the driver. Using an extremely high density material like marble/granite/concrete does a good job of this, but so does making a high strength box. GM's favorite material being laminated Baltic/apple/marine plywood. These are two approaches that address the same issue, but from different directions.
    ====
    Yep, there's more than one way to 'skin a cat'. Being lazy and having a bad back, I go the lighter route of raising the cab resonance, but you can go the other way and lower it below the BW. With infrasonic subs though, this means a really inert cab, like a concrete bunker. [​IMG]
    The best sub I ever heard before the CB was in an architect's basement listening room where a concrete septic tank was mounted next to one of the poured concrete walls and coupled with concrete pipes for the drivers to use the tank as the IB cab.
    The house is long gone now due to 'progress', but it sure would have been interesting to try these new high output sub drivers in it.
    GM
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    Loud is beautiful, if it's clean
     
  10. Greg P

    Greg P Stunt Coordinator

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    Thomas,
    I asked for some help on building a subwoofer not to get riduculed and bash my main speaker of chose. I used the analogy of experience of wood vs. inert cabinates. Why do you say they are not more percussive? Have you ever compared exactly the same componants of a speaker in a wood vs. inert cabinate?
    Sealed boxes can bring the depth and output of a ported enclosure, (note Im talking about the same driver, I could probobly build a sealed enclosure that would go low and have high output but it would require many woofers and a huge box, correct) ya right.
    When I am stating all these comments Thomas I am not stating this is true to ALL sealed, IB, PR, etc. I was just stating what very good things I myself have attested from inert cabinates. As far as main speakers go woods with even better drivers, wiring etc have a hard time keeping up with the speakers in inert cabinates.
     
  11. ThomasW

    ThomasW Cinematographer

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    Greg
    The idea is to not post generalizations based on false conclusions, for example.
    quote: As far as main speakers go woods with even better drivers, wiring etc have a hard time keeping up with the speakers in inert cabinates.[/quote]
    This simply isn't true. And the fact that you continue to post it indicates your lack of understanding as to fundamental design principles, construction methods and operational principles of loudspeakers
    quote: Why do you say they are not more percussive?[/quote]
    Ahh, I suppose it's because they aren't.......
    quote: Have you ever compared exactly the same componants of a speaker in a wood vs. inert cabinate?[/quote]
    Well as a matter of fact I have. [​IMG] I've been designing and building speakers for 40 years, so I do speak with a reasonable amount of knowledge. And there is no fundamental inherent advantage to high mass/high density cabinets when compared to properly designed and constructed wood ones. So for example if you hear a difference between a wooden nOrh speaker and a marble one containing otherwise identical components; this indicates a problem with the construction techniques or design of the wooden speaker, not the inherent the superiority of the marble one
    Perhaps you could obtain a copies of "The Loudspeaker Design Cookbook" by Lance Dickason and "The Master Handbook of Acoustics" by F. Alton Everest. Reading these would at least give you a basis for some comprehension of what's being discussed here.
    Kindly understand I don't have an axe to grind, but what you're posting is stereotypic of the classic statement made by Abraham Lincoln.......
    Regards
    Thomas
    [Edited last by ThomasW on July 24, 2001 at 11:04 PM]
     
  12. Mark Seaton

    Mark Seaton Supporting Actor

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    Greg P.
    I'll give you the benefit of the doubt since you already made a decent decision on schools [​IMG].
    Take the criticism here for what is being offered, and don't worry about the frustration of those giving it. Most people react similarly after addressing the same misconceptions 100 times over. Thomas is pretty much right on track with his statements though. You happened to use that garrish term "fast" in association with bass, and while the term gets used to describe perceptions quite often, it's also one of the most misleading descriptors in the audiophile vocabulary.
    As for the issue of intert cabinets, if you design a cabinet that does not resonate or flex under the range of operation, the results will be positive no matter what materials you use to get there. Wether it be a few inches of concrete, or layer upon layer of MDF, both can yeild great results. So don't confuse the goals in achieving a proper cabinet with the matierals used to do so.
    When the cabinet is "inert" you will have less losses in the driver/box system, and the cabinet walls won't be making spurious sounds of their own, so indeed the results should sound cleaner.
    Now, let's try and actually get at the main questions you asked.
    Since you already have the SVS subwoofer, I would suggest you shoot to go a bit further with the design than what you have now. My first suggestion would be to start with your intended tuning frequency at or below 20Hz. By the statements you have made above, I get the feeling you are looking for what is percieved as that "tighter" sounding bass, which generally is had with a more gradual roll-off to the bottom end, rather than maximizing the anechoic flat response of your sub.
    As for the "more precussive" desire, it's hard to figure where your system is really lacking without more information about how you have the sub and mains integrated. I would definitely consider something like one of the Lambda 15" drivers since you already said that size is not much of an issue. What you really need to determine is what you are looking for out of your system, and what you would consider using to get there? What about power for such a subwoofer, and more importantly, where/how will you mate it to your mains?
    Mark Seaton
     
  13. Greg P

    Greg P Stunt Coordinator

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    Thanks for the advice Mark,
    Heres my goals of my DIY subwoofer:
    1. Tight, percussive bass
    2. High output (in room 115db - 120db)medium sized
    room My SVS can do close to 115 now so I want
    at least that output
    3. Flat extension to 25hz at least (slight roll off
    after is exceptible)
    4. I will probobly cross the sub over at 50hz or
    60hz
    I know this is a hefty order to fill, but Im gonna spend $800 so I think I can acheive pretty much what I want.
    Thomas, Mark, I understand what you are saying about MDF vs. the stone cabinates Im contemplating. But there is possible that meausurements cant explain the difference in sound Ive heard. Ive never heard an MDF cabinate sound like a ceramic. Is it also possible that neither cabinate is resonating but the MDF is "absorbing" sound energy in the cabinate where the rock (granite, marble etc. ) is not?
     
  14. ThomasW

    ThomasW Cinematographer

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    quote: Ive never heard an MDF cabinate sound like a ceramic.[/quote]
    The ceramic cabinets I've heard "ring", this is a bad thing. The only good ceramic cabinets I've heard were made from an advanced ceramic composites,(space age stuff), and they weren't available to the public
     

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