AB HD15 Enclosure

[bgowdy 5,000+ posts]

Realistically the coil in that can hold 1200W continuous power tops. Even at, say, 20% more power, (1500W) you start building up heat very quickly compared to how fast it can cool. You very well may have some frequency ranges where the sub is seeing over 1000W.
As far as reaching x-max with a single 15 at 40hz that's tough. The port provides plenty of spring/control right @ tuning but unloads outside of that. Obviously as you approach 50 the cone just doesn't need to move as far so it's a non issue.

Try this. Cut up 2 and a half 8 foot 2X4's into blocks the length of one side of your box and screw them in there to take up appx .75 cube (a 2x4 is .29 cubic feet). This will get you closer to the 3.5 cube you think you'll like and also raise tuning for you a bit (best to plug it into some software.... I'm not on a Windows OS now so I can't double check). Ideally if you never play below 32, 40 or 42hz tuning and setting subsonic filter @ 32-34 should let you really wang without running into trouble... tweak subsonic accordingly testing lower frequencies. Between the smaller box and higher tuning it should solve your mechanical issues. You're still stuck with thermal limits of that coil, but with that power you can simply turn it down or play less bass heavy songs if it starts getting stinky until it cools down. You should have a minute or two between smelling it and failure to ease back a bit.

Also bear in mind that you will be going from just fine to hard clip really fast as you're pushing things to the limit which speeds up the heat issues. Consider your amp is making 33V..... (2200W into .5 ohm) and you're chugging along just fine. They give it one more click on the volume knob, you're now asking the amp to make 3100W (likely putting it into a pretty hard clip). That's how fast you can get into trouble!

Anyway, buy a few 2X4's and give that a whirl. Under 10$ and a half an hour to see what 3.5 cube tuned a little higher sounds like.

yes around 40 is were the sound starts go. If i play 37hz down to 30hz and play it kind of hard the subs never makes any odd noises or bottoming out sound at all. Which i figure bottoming it would be eaiser to on low end then at 40-42 hz. I have not really attempted to play 50 or anything.

 

[hispls 5,000+ posts]

yes around 40 is were the sound starts go. If i play 37hz down to 30hz and play it kind of hard the subs never makes any odd noises or bottoming out sound at all. Which i figure bottoming it would be eaiser to on low end then at 40-42 hz. I have not really attempted to play 50 or anything.

A friend of mine has almost the same thing happening with a 15 he built. By the time you get up to 50hz the cone shouldn't be moving that much regardless of tuning.

If you can see the sub while you play you can test at lower power with just playing test tones. Start at 30hz at a safe volume and walk your way up. You'll see cone movement should be high at 30hz and get lower as you approach tuning, then after you pass tuning it'll be more cone movement then it'll be less and less as you increase from there. As you say AT TUNING the port will provide plenty of springiness to the cone to keep it under control.

Also worth mentioning, how close is your port to any hard surfaces? There's good odds you're tuned a good bit lower than you think you are also if a hard surface is acting as an extension of the port.

 

[bgowdy 5,000+ posts]

A friend of mine has almost the same thing happening with a 15 he built. By the time you get up to 50hz the cone shouldn't be moving that much regardless of tuning.
If you can see the sub while you play you can test at lower power with just playing test tones. Start at 30hz at a safe volume and walk your way up. You'll see cone movement should be high at 30hz and get lower as you approach tuning, then after you pass tuning it'll be more cone movement then it'll be less and less as you increase from there. As you say AT TUNING the port will provide plenty of springiness to the cone to keep it under control.

Also worth mentioning, how close is your port to any hard surfaces? There's good odds you're tuned a good bit lower than you think you are also if a hard surface is acting as an extension of the port.

its not close enough to any surface to act as a extension. It moves a decent amount at 30hz when i give it a bit of power but doesnt bottom out even at 36hz where the port/box is tuned the cone still doesnt bottom. But at 40-42 or 43 it does and it gets really peaky from 40-43. I would assume around 50 would also be pretty peaky.

i guess its possible that im tune alittle lower then i think but id still say like 35hz at lowest. When i drew it up it came out as high 36's(like 36.75-.85hz)

 

[hispls 5,000+ posts]

its not close enough to any surface to act as a extension. It moves a decent amount at 30hz when i give it a bit of power but doesnt bottom out even at 36hz where the port/box is tuned the cone still doesnt bottom. But at 40-42 or 43 it does and it gets really peaky from 40-43. I would assume around 50 would also be pretty peaky.
i guess its possible that im tune alittle lower then i think but id still say like 35hz at lowest. When i drew it up it came out as high 36's(like 36.75-.85hz)

When you're up around 50 it shouldn't be moving that far at full power.

I think shrinking that box while leaving the port the same size will help a lot with that cone control issue though.

 

[bgowdy 5,000+ posts]

When you're up around 50 it shouldn't be moving that far at full power.
I think shrinking that box while leaving the port the same size will help a lot with that cone control issue though.

i mean to be technical the port isnt going to change alot. im at 44.16 with 1 aero. But due to depth of the box im going to swtich to a slot port i think to help me make the box less deep. So the port and box i ave drawn up is 53.29 i believe(dont have it with me), so not a huge difference

 

[hispls 5,000+ posts]

i mean to be technical the port isnt going to change alot. im at 44.16 with 1 aero. But due to depth of the box im going to swtich to a slot port i think to help me make the box less deep. So the port and box i ave drawn up is 53.29 i believe(dont have it with me), so not a huge difference

If the inside mouth of the port is too close to the back wall that can give you trouble and the port may not function properly.

 

[bgowdy 5,000+ posts]

If the inside mouth of the port is too close to the back wall that can give you trouble and the port may not function properly.

currently its fine, my port is right at 7" - 8"(can remeber exactly) from the back of the box. The port is 7.5" so its right there on it.

Curious with slot port boxes, for example say my box is 20 inches deep, and my port needs to 23 inches for desired tuning and say the port is 3.5 inches wide. Wouldnt the port length go 15.75 inches back(keeping 3.5" from back wall), then L turn the remaining 7.25 inches?