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Vas vs Box Volume

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  • Chris Roemer
    replied
    Yeah. If you want to keep "Q" as low as possible, don't start out w/a driver w/a raw Q of 0.93. In a closed box, Q can never be forced lower, it can only go up.
    In 2.4cf (sealed and stuffed), that driver only extends down to around 50Hz. At 50Hz, it'll breach Xmax at 6 watts.

    A good book to help you learn about all this stuff (in an organized manner) is "Speakerbuilding 201" by Ray Alden (sorry Craig).

    Leave a comment:


  • fpitas
    replied
    If Xmax is that small, your best choice is probably ported to reduce excursion. It's often the situation that Xmax is the limit on low frequency output.

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  • sujat
    replied
    Hello!

    My question pertains to power handling that is limited by driver excursion around Fs when mounted in a large sealed box, say Vb = 4*Vas.

    Regarding - https://www.parts-express.com/grs-8p...oofer--292-408

    I want to keep the sealed box Qtc as low as possible, for which WinISD says a minimum 68 litres box would be necessary. I can accommodate this size which is not a concern.

    The concern though is how many watts it will take until it reaches it Xmax of 3mm in such a lightly loaded environment. WinISD shows 4 watts! Is it a reliable figure? In fact, i simulated a range of enclosure sizes, and until I go as small as 12 litres (Qtc > 1.5!) the excursion limited power handling around box resonance remains below 20 watts!

    A very similar case emerges with the Goldwood 8" driver, with the minimum box size being 51 litres for the desired Qtc, and the excursion limited power handling still being a measly 4 watts.

    * I don't understand the point in having its long term thermal power handling at 100 watts but really useable being not more than 8-10 watts in a real life situation. It seems frustrating.

    Could you please help me with these findings through your views or guidance, about the excursion limited power handling in a sealed box with Vb=68 litres for a Qtc < 1.1?

    Thanks in anticipation,
    Sujat (an enthusiastic student looking for guidance)

    Leave a comment:


  • weinstro
    replied
    Re: Vas vs Box Volume

    Originally posted by hotrod View Post
    Thanks for the quick responses..... I tried downloading those programs.... the fisr one didn't seem to respond to the specs I entered.... there was a certain driver already in the graph and when I entered my driver's specs, the box volume info didn't change?? The second program was more confusing for me and I got constant error message as I entered my driver's specs.... If there is a simple (generel rule of thumb so to speak) formula for Vas to Vb formula, that would probably work.... it's just for a sub to go in my garage.... I was looking at this particular sub because PE has it on asle for $14.... thanks...
    Try Unibox. You can input the speaker parameters, enter the box design, and get a response simulation, ignoring things like room gain and baffle step. If you provide a desired Qtc, it will optimize the box size for you. It will simulate sealed, vented, passive radiator, and bandpass enclosures.

    Regards,

    Rob

    Leave a comment:


  • nbuk
    replied
    Re: Vas vs Box Volume

    If you tune a little lower I think you will find 25 to 27 Hz tuning will give you a little better excursion , mind, if you already built it I would,nt bother.

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  • Chris Roemer
    replied
    Re: Vas vs Box Volume

    Originally posted by hotrod View Post
    I ordered the Dayton $78 300-802 -100 W @ 8 Ohms SA 100 sub amp and the Dayton $14 299-106- 10" sub.... While waiting on the order to arrive, I built the above mentioned 2.75 Cu Ft box and planned on using it as a sealed application..... When the order arrived, there was only an amp in the box.... The invoice said that the sub was "out of stock and discontinued"..... I called and reordered a Dayton $20 295-485- 10" sub..... this sub required a smaller box than the sub I originally ordered so I used a Port Size Calculator I found on the net I installed a 3" X 5.5" port.... supposedly tuned to 33 Hz.... Sounds really good, especially for less than $100.....

    Actually, a 3"d x 5.5" long vent tunes a 2.75 cf box to 30 Hz, which is almost exactly perfect for your situation.

    That SD sub series was a good one. While I never tried the 10", I DID use the 8" in about 1.5 cf with the 70w amp, and the 12" in 3 cf with your 100w amp.

    Have fun.

    Leave a comment:


  • hotrod
    replied
    Re: Vas vs Box Volume

    I ordered the Dayton $78 300-802 -100 W @ 8 Ohms SA 100 sub amp and the Dayton $14 299-106- 10" sub.... While waiting on the order to arrive, I built the above mentioned 2.75 Cu Ft box and planned on using it as a sealed application..... When the order arrived, there was only an amp in the box.... The invoice said that the sub was "out of stock and discontinued"..... I called and reordered a Dayton $20 295-485- 10" sub..... this sub required a smaller box than the sub I originally ordered so I used a Port Size Calculator I found on the net I installed a 3" X 5.5" port.... supposedly tuned to 33 Hz.... Sounds really good, especially for less than $100.....

    Leave a comment:


  • Blooze
    replied
    Re: Vas vs Box Volume

    Originally posted by hotrod View Post
    Thanks for all of the help and responses... I think I'll go with 2.75 cu ft..... this should be a good trade-off in freq resp and power handling?
    Let us know how it works out. I purchased a pair of the 10" buyouts to add a couple of subs to my 2 way rig. I'm not looking for pounding bass, just something to fill in and smooth out the bottom end. I think I'm going to build a pair of 4 ft^3 boxes, so if I don't like these drivers I can upgrade to some of the LAB12's ported by just switching the front baffles.

    Leave a comment:


  • hotrod
    replied
    Re: Vas vs Box Volume

    Thanks for all of the help and responses... I think I'll go with 2.75 cu ft..... this should be a good trade-off in freq resp and power handling?

    Leave a comment:


  • daver
    replied
    Re: Vas vs Box Volume

    For that small of a box,

    Vb = 1.25 ft^3 (35.4 liter)
    Qtc = 1.14
    Fc = 50.7 Hz
    F3 = 33.3 Hz
    F10 = 21.9 Hz

    Also, this higher Qtc creates a boomy peak of over +2 dB above sensitivity between about 50 and 80 Hz. (+2.5 dB centered at 60 Hz).

    Might be alright, if that's what you're looking for. Usually most prefer to have smoother bass response for home audio. Always tradeoffs between size, deep bass, and loudness.

    Leave a comment:


  • Chris Roemer
    replied
    Re: Vas vs Box Volume

    Originally posted by hotrod View Post
    Seems like this 10" needs a rather large box? I'm much more familiar with car audio subs where average 10" sub can work well with a .65-1.25 cu ft sealed box....

    In a (small, closed) car, the bottom end gets boosted by +12dB due to "cabin gain". You won't have that "in home". You CAN put this sub in a 1 cf box, but it won't reach flat down low if you due that.

    Not only THAT, but Vas, Fs, and Qts ultimately determine box size and extension.

    Leave a comment:


  • hotrod
    replied
    Re: Vas vs Box Volume

    Seems like this 10" needs a rather large box? I'm much more familiar with car audio subs where average 10" sub can work well with a .65-1.25 cu ft sealed box....

    Leave a comment:


  • hotrod
    replied
    Re: Vas vs Box Volume

    I was planning on using amp part # 300-784 from PE.... it is rated 70W @ 4 ohms..... I was going to wire the sub's 2 8-ohm coils parallel for 4 ohms....

    Thanks for the help....
    Last edited by hotrod; 11-18-2010, 07:30 PM.

    Leave a comment:


  • duanebro
    replied
    Re: Vas vs Box Volume

    When I model this sub in a 3cf box I see it hitting xmax at 20 watts. Does this match what you've seen? (I used winISD alpha)

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  • killersoundz
    replied
    Re: Vas vs Box Volume

    Originally posted by Chris Roemer View Post
    WinISD Pro (alpha) shows that it will reach 33 Hz in a 3 cf stuffed/sealed box, but at 33 Hz, it can bottom out with 15 watts at 109 dB.
    Mechanical power handling is just as important as anything else. It's a balancing act.

    Leave a comment:

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