1x Fi SP4 18" v2 & 1x 4500 WRMS CRESCENDO AMP Enclosure advice

[MackMurder]

I'll be running a 18" FI SP4 2ohm DVC sub and 4500 wrms@1 ohm cresendo amp. With 2 XS Power 3300 amp batteries and a MECHMAN 370 bIllet alternator. 2/0 gauge ofc. My cabin space is roughly 60 to 70 cuft ( it's a 2012 denali 1500) and the sub enclosure space I have can be no larger than 9 cuft

 

The v2 sp4 is 3500 wrms. FI recommends a 6-8 cuft vented enclosure.

My enclosure will be aero ported most likely tuned to 27hz and built with a 2" face and the rest of the box 1.5" mdf /w braces inside like fatbox usa does.

This is an everyday driver for me. 

Now since I'm throwing 1000 wrms more at this sub. I'm to understand my sub box should be smaller to handle the excessive power being thrown at it correct? And if so how smaller?  The minimum 6 cubes they recommend?  Or should I drop it down to 5 or 5.5 cubes. Does a half cube make that much difference? 

My next question with a smaller boxof 5 to 6 cubes can I still hit 25 hz with this sub.?

 

Thanks

 

[Kyblack76]

Yoir wired at 1 ohm. You won't see 4500. Maybe 2500. Let it eat. 

[notorious97200]

That amp should be fine !

Follow manufacturer's recommandations for the box. The bigger, the better, for lows, generally...

That 27 Hz tuning is on the low side...you'll have a long aeroport to use   Personally, I like 32Hz. 

Good luck.

[MackMurder]

1 hour ago, Kyblack76 said:

Yoir wired at 1 ohm. You won't see 4500. Maybe 2500. Let it eat. 

Can u explain this. It makes no sense to me.

[MackMurder]

1 hour ago, notorious97200 said:

That 27 Hz tuning is on the low side...you'll have a long aeroport to use   Personally, I like 32Hz. 

I had a jl13w7 at one point tuned to 34 hz. I wasnt impressed with the amount of low notes it couldn't hit. They were non existent. I have hertz mile mids and tweets up front and cdt audio mid bass drivers in the  back doors ( which run 0 to 4000hz) Since my floors, baxk wall, cieling, and doors are dampened and sealed it already sounds like i got subs in there. I want my sub strictly down low 20 to 30hz. If I don't like it I can always change the tune with a different port later 

1 hour ago, notorious97200 said:

 

 

[Triticum Agricolam]

18 minutes ago, MackMurder said:

Can u explain this. It makes no sense to me.

Amps don't output watts, amps output volts.  Your amp makes 4500 watts at 1 ohm, which is about 67 volts.  How much power your sub actually gets is a function of the output voltage of the amp and the impedance of the sub.  When you wire your sub to 1 ohm (which is called the nominal impedance) it doesn't stay at 1 ohm all the time.  Impedance fluctuates all over the place, but roughly as low as it will get is the nominal impedance.  The specs of your enclosure, the environment the sub plays in, just about every pushes the impedance up and thus the watts your sub gets goes down.  There is a lot that goes into it, but you don't really need to worry about it much.  The important thing to know is that your sub pretty much never gets the rated power out of your amp, which is why you can usually put sub on a 50-100% larger RMS amp than what the subs are rated for.  

[Triticum Agricolam]

2 minutes ago, MackMurder said:

I had a jl13w7 at one point tuned to 34 hz. I wasnt impressed with the amount of low notes it couldn't hit. They were non existent. I have hertz mile mids and tweets up front and cdt audio mid bass drivers in the  back doors ( which run 0 to 4000hz) Since my floors, baxk wall, cieling, and doors are dampened and sealed it already sounds like i got subs in there. I want my sub strictly down low 20 to 30hz. If I don't like it I can always change the tune with a different port later 

 

Here is a port area calculator to help you figure out how big of port/s you will need for good performance:

https://goo.gl/STAv4p

[MackMurder]

1 minute ago, Triticum Agricolam said:

Amps don't output watts, amps output volts.  Your amp makes 4500 watts at 1 ohm, which is about 67 volts.  How much power your sub actually gets is a function of the output voltage of the amp and the impedance of the sub.  When you wire your sub to 1 ohm (which is called the nominal impedance) it doesn't stay at 1 ohm all the time.  Impedance fluctuates all over the place, but roughly as low as it will get is the nominal impedance.  The specs of your enclosure, the environment the sub plays in, just about every pushes the impedance up and thus the watts your sub gets goes down.  There is a lot that goes into it, but you don't really need to worry about it much.  The important thing to know is that your sub pretty much never gets the rated power out of your amp, which is why you can usually put sub on a 50-100% larger RMS amp than what the subs are rated for.  

Interesting. And good to know. Thanks. Do you suggest a vent or aero ports triticum. And knowing this that my sub won't see more than 2500 watts can I build my boxthe full 6-8 cubes fi recommends or. .....I have the re audio box builder. Win sid pro alpha ( kinda lost with it tho) and another free box builder fi recommends.  I'm trying to do everything myself but with my first house and a son who's 2 months old I don't have a lot of time to spend fucking up.

[Triticum Agricolam]

Both aero ports and slot port can work equally well if properly implemented.  Both have their advantages and disadvantages.  Just use what you are most comfortable with.  If you think you will want to change tunings at some point aero ports may be easier.  

As far as software goes, WinISD is good, Torres is handy for layout, but I don't like the RE box calculator, it has some problems.  

Don't be afraid to ask any questions about box design or post what your plans are, we are happy to help you.