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Can you help me understand.....


FantasticBass

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So I attached a PDF of the Transfer Function Magnitude from WinISD Pro for the box I'm designing for my two Sundown Audio SA-15D4's. 

So I know that a lot of people will use this program to see how the box will "sound". So by looking at this graph, how do I know how it will sound? 

And in explaining the theory of it to me, how will this design actually do with my two SA-15's? What I can understand from the graph is that it will be a low end monster. Again no clue what I'm truly looking at so, just guessing really off of what information I've found through researching on the internet via google. 

So what am I looking at basically? Does F0.5 at 30hz mean it's going to be louder than say if it was at F-3? Also on this box 55.81hz is something crazy like F6.5, so what does that mean?

transferfunctionmagnitude for two sa-15 @ 1500w.pdf

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It looks like peak output will be between 50hz and 55hz. The lowest frequency usable output is considered to be the 3db down point and appears to be around 35hz. Will it play lower? Sure but won't do so loudly and at the risk of unloading the sub. What are the specs of the box and port?

91 C350 Centurion conversion ( Four Door One Ton Bronco)

250A Alternator (Second Alternator Coming Soon)

G65 AGM Up Front  / Two G31 AGM in Back

Pioneer 80PRS

CT Sounds AT125.2 / CT Sounds 6.5 Strato Pro component Front Stage

CT Sounds AT125.2 / Lanzar Pro 8" coax w/compression horn tweeter Rear Fill

FSD 5000D 1/2 ohm (SoundQubed 7k Coming Soon)

Two HDS315 Four Qubes Each 34hz (Two HDC3.118 and New Box Coming Soon)

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31 minutes ago, ShadeTreeMechanic said:

It looks like peak output will be between 50hz and 55hz. The lowest frequency usable output is considered to be the 3db down point and appears to be around 35hz. Will it play lower? Sure but won't do so loudly and at the risk of unloading the sub. What are the specs of the box and port?

ShadeTreeMechanic, Box is 9.18 cu ft after all displacement with two SA 15" DVC 2 ohms with the SAE1500 wired to 1 ohm to deliver the full 750 watts rms per sub. I'm using 2 6" aeroports at 13.5" long for a final tuning of 29.89hz. Now from what I read though F -3 (negative three) is the cut off point where it won't play loudly and run the risk of unloading. and that's at 23hz on this graph. At 35hz I'm actually close to F1.5, so is it F0 where you won't hear the bass anymore and the sub will unload?

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Everything relative, when one sound is 3db down from another it would only be half as loud. The peak being so much louder than everything else means that this would be the highest output. Sure it will play the lows, it will just play the upper bass louder.  Two 6" ports sounds small for two 15s. I don't know your subs that well, but maybe someone else will chime in.

91 C350 Centurion conversion ( Four Door One Ton Bronco)

250A Alternator (Second Alternator Coming Soon)

G65 AGM Up Front  / Two G31 AGM in Back

Pioneer 80PRS

CT Sounds AT125.2 / CT Sounds 6.5 Strato Pro component Front Stage

CT Sounds AT125.2 / Lanzar Pro 8" coax w/compression horn tweeter Rear Fill

FSD 5000D 1/2 ohm (SoundQubed 7k Coming Soon)

Two HDS315 Four Qubes Each 34hz (Two HDC3.118 and New Box Coming Soon)

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3 minutes ago, ShadeTreeMechanic said:

Everything relative, when one sound is 3db down from another it would only be half as loud. The peak being so much louder than everything else means that this would be the highest output. Sure it will play the lows, it will just play the upper bass louder.  Two 6" ports sounds small for two 15s. I don't know your subs that well, but maybe someone else will chime in.

They're not beastly subs lol. They're nice though. I'm only at 8% port velocity at 23hz, which I won't be playing anyways by 30 hz i've dropped down to 6.5% port velocity. I know you want 5% port velocity but I've plugged in box recommendations from manufacturer box designs and they've been upwards of 10-15% in the port velocity print out

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