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Discussion Starter · #1 ·
Vehicle: 2012 VW Passat CC
Location in the vehicle: trunk, firing through seats
Space available (Length x Width x Height): plenty
Subwoofer make and model: Hertz HX250D
Subwoofer Size: 10"
Number of Subwoofers: 1
Type of Port (Kerfed, Slot, Aero, etc.): Sealed
What type of music do you like?: Acoustic, rock, blues
Is your goal SPL or Everyday Music?: Everyday Music
Volume: 100dB or below.
Amplifier: Audison AP1; [email protected]

Question: I am looking at the Hertz literature on sealed-box size. They specify using "FONOFORM" in the box. I can't figure out what this is, where to get ti, or if I really need it. If I skip the foam, can I just make a larger box? Hertz spec sheet: http://www.hertzaudiovideo.com/wp-content/uploads/2014/05/Hertz_HiEnergy_hx250d.pdf

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Fonoform is just another form of box stuffing. If you can't find any, then polyfil will work. Being in the UK, not sure what you have available there.

Be careful with trying to increase box size. If anything I'd stick with manufacturer recommendations for the larger 16 liter sealed for the shallower rolloff after F3. Haven't modeled the 250d, but as with most subs in sealed, it takes a greater size change to see definite difference in response. However excursion will change quite a bit for the power applied.
 

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Discussion Starter · #3 ·
Fonoform is just another form of box stuffing. If you can't find any, then polyfil will work. Being in the UK, not sure what you have available there.

Be careful with trying to increase box size. If anything I'd stick with manufacturer recommendations for the larger 16 liter sealed for the shallower rolloff after F3. Haven't modeled the 250d, but as with most subs in sealed, it takes a greater size change to see definite difference in response. However excursion will change quite a bit for the power applied.
I was using an online tool to find my box volume (Vb): Car Audio - Sealed Subwoofer Box Design Calculator

This gave me a Vb of .273 cu ft, at Qtc of .707. Am I dong something wrong? Vas is 20.54 liters, or .725 cu ft; Qts is .37; Fs is 34 Hz; all this according to the sheet I attached earlier.

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Your calculations are correct, but it's much easier to just roll with the recommendations if you trust all else from the manufacturer. Qtc of the sub/box outside of the vehicle will play differently once in a vehicle. Everything must be calculated with the acoustics of the car if you really want to see what it will do. Your modeled box is .707, the medium .388 cube box is Qtc of .6, and the largest .56 cube box is Qtc of .55.

The rolloff point between all boxes including yours is quite neglible, but the slope gets shallower as size increases. Excursion with the same power input also increases. I'd stick with the manufacturer suggestions for better low end performance.
 

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Bayboy's number are all about dead on.

I've built many enclosures for those Hi-Energy woofers. Excellent drivers all the way around. For the 10's, anywhere between 0.4-0.7 cubic foot sealed works really well. So long as you have plenty of power on tap, you'll be good to go. As the enclosure size increases, you will get slightly more low end, but it's not a massive difference. I've gone as high as a full cubic foot for them, but the sound gets very thin at that volume.

They also work well in a smallish vented enclosure. Somewhere around 1 cube if I remember correctly. Can't recall vent specs off the top of my head.
 
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