1x fi spf4 18" on a 4500 watt crescendo amp. SUBWOOFER BOX QUESTIONS

[Kyblack76]

Ahmed and tree thanks for your replies. I will go as big as i can with ported. I may try a sealed to start just to hear what it sounds like and post my experience for everyone. Regard to your other question ahmed.

What exactly am i sending this amp and can u explain why my sub if wired to 1 ohm and the amp is 4500 rms at 1 ohm and i have constant no loss of power. Why it wouldnt be 4500?

I need to kow these things haha

That is a nominal load........not reactive. Then, electrical comes into play, and many many other things.

[Triticum Agricolam]

The reason you won't see 4500 watts is amps don't put out watts, amps put out volts. The impedance of your sub determines how much amperage flows and thus how many watts that are put out.

Watts aren't whats really important anyway. Volts do the work.

[ShadeTreeMechanic]

What he said. And the impedance is all over the place because it is dependent on the frequency so the power is up and down.

[Mack187Murder]

Very good thanks for all the info guys. I got the amp with dual 1/0 gauge power and ground inputs. And im hoping the 370 mechman and the 2/0 gauge copper power and ground wire i have throughout the truck keep my voltage strong and constant and my power good. Shouldnt be a problem with only one alt hey? Im only.running one other amp whoch is the hertz hdcp 1000 watt 4 channel

[Mack187Murder]

Think im bought 8 or 10 gauge to wire the sub as well

[Triticum Agricolam]

I think your idea of using the SP4-18 sealed should work out just fine. It won't have the low end output a ported box would, but I'm sure it will sound good and above 50 Hz you won't really have any less output than a ported box. The SP4 is pretty well suited for sealed box usage.

As far as box specs go, larger sealed boxes will have better low frequency performance than smaller ones do, but they also have higher cone excursion, so you have to reach a balance. FI recommends 4-6 cu ft, you are going to be putting a pretty healthy amount of power, so to keep cone excursion reasonable I probably wouldn't suggest using more than 5 cu ft. Setting your subsonic filter at 24 hz probably wouldn't be a bad idea either. Usually ported boxes don't need a subsonic filter, but with the amount of power you are running I'd use one.

Your talk about using 1.5" MDF makes my back hurt. I've used 1" MDF and those sheets were really difficult to maneuver by myself. I don't know if 1.5" sheet would be possible for one person to handle. If you want 1.5" thick walls, just double up 3/4" material. Without a port getting in the way its really easy to brace the tar out of a sealed box, so if it were me I'd just make the walls 3/4" thick and brace it well. To give you some ideas, here is the bracing I did for a sealed 18" home theater sub.

[Mack187Murder]

I think your idea of using the SP4-18 sealed should work out just fine. It won't have the low end output a ported box would, but I'm sure it will sound good and above 50 Hz you won't really have any less output than a ported box. The SP4 is pretty well suited for sealed box usage.

As far as box specs go, larger sealed boxes will have better low frequency performance than smaller ones do, but they also have higher cone excursion, so you have to reach a balance. FI recommends 4-6 cu ft, you are going to be putting a pretty healthy amount of power, so to keep cone excursion reasonable I probably wouldn't suggest using more than 5 cu ft. Setting your subsonic filter at 24 hz probably wouldn't be a bad idea either. Usually ported boxes don't need a subsonic filter, but with the amount of power you are running I'd use one.

Your talk about using 1.5" MDF makes my back hurt. I've used 1" MDF and those sheets were really difficult to maneuver by myself. I don't know if 1.5" sheet would be possible for one person to handle. If you want 1.5" thick walls, just double up 3/4" material. Without a port getting in the way its really easy to brace the tar out of a sealed box, so if it were me I'd just make the walls 3/4" thick and brace it well. To give you some ideas, here is the bracing I did for a sealed 18" home theater sub.

Always really appreciated your input Trit*

Question tho dont ported need subsonic cuz it has less negativy pressure? and sealed dont need the filture. And if it was a type your suggesting i run a subsonic in a sealed just in case? This wont hurt sub or amp?

[Triticum Agricolam]

Ported boxes actually have greater internal pressure (both positive and negative) than sealed boxes do. The reason a ported box needs a subsonic filter is because below tuning the port unloads and the sub begins to perform like its in free air. Without the subsonic filter you can pretty quickly exceed the mechanical excursion limits of your sub.

The reason most sealed boxes don't need a subsonic filter is because there is no port to unload so the air inside the box usually provides enough resistance to keep cone excursion at safe levels. The larger you make a sealed box, the less resistance to cone movement it produces. Making a sealed box smaller helps protect the sub but it also limits low frequency output. Unlike ported boxes, with sealed boxes (and infinite baffles) low frequency output is directly related to cone displacement (cone area X excursion) so anything that limits cone excursion limits output as well. The balancing act is making the box small enough to protect the sub without negatively affecting low frequency output any more than you have to. In your case your could make the box smaller than 5 cu ft and then you wouldn't need a subsonic filter (4 cu ft would do it). However a 4 cu ft box is going to have slightly less output on pretty much everything below 40 hz compared to a 5 cu ft box. So by making the box 5 cu ft and setting the subsonic filter to 24 hz (actually you could probably get away with setting it to 22 Hz), you still protect your sub and you have slightly better performance from about 27 - 35 Hz.

If you don't want to screw with setting a subsonic filter, you could just make the box 4 cu ft and not worry about it, especially if you want to save some space in your vehicle. The difference in performance is pretty small.

[Mack187Murder]

Your unreal brother. Like a fucking professor. Thank you for the taking the time to answer my questions. I will follow your advice on the sealed. And when it comes to the vented box can i pay u to design me one and ill build it.

[Guest]

I have the same sub (15") and amp goodluck with a sealed box