Which Looks better?

[Nathan P]

I've modelled up a couple of enclosures for the DA175 with help from KJP. Which looks to be the better curve? Does the 1.18 cubic foot box come to close to max cone excursion? These will be run full range in a small room at low wattage, probably off of a Sonic T-amp, or if I can swing it a low power HT reciever, and eventually will have a sub to go with them, crossed over around 90ish or so to keep from running out of excursion at higher wattages, but at low wattages the full range seems to work.

Nathan

[Hdale85]

well i believe your over exurting the woofer in both of those with anything under 60hz it looks like? might be wrong but i think thats what that red line means

[Nathan P]

Well, that's the combined SPL, with the port and everything. If you look at the black line, that is the cone SPL, and it doesn't go over until the mid 20s or so.

[Hdale85]

Oh ok. Well i dont know im not so good with this stuff yet getting there.

[Nathan P]

Don't I know it. I had a hard time just figuring out what was good lol.

[ThomasW]

Look where the red line is in relation to the thin black one.

The first plot is fine. The second one runs out of excursion at 40Hz (where the red and black meet).

Don't be concerned where the red crosses the black below the port tuning (big dip in the black plot).

[Nathan P]

Okay! First one it is! It's a little smaller too, so it will sound better if I decide to plug the port when it's being run with the sub, I modelled it up sealed and it looked pretty good, very very gradual roll of below around 100hz with an F3 at 63hz, so crossed over at around 90, it won't even be noticeable. Of course, what would be the advantage of plugging the port when it's aready so flat in the higher regions?

[ThomasW]

Of course, what would be the advantage of plugging the port when it's aready so flat in the higher regions?

Plugging the port will basically double the cone excursion.

[Nathan P]

Say What?

[Nathan P]

Oh I see, the air inside will act like a spring, the cone won't move as freely in the rearward direction, thus increasing extension in the frontward direction?

[KJP]

Oh I see, the air inside will act like a spring, the cone won't move as freely in the rearward direction, thus increasing extension in the frontward direction?

that spring works both ways, rearward and forward.

[BobEllis]

Without the port, the only sound output is from the cone. The cone has to move further to maintain the same output.

[Nathan P]

How does this look?

[Nathan P]

It doesn't cross the excursion limit, but it is awefully close. Is it too close? Max excursion is 4.25mm, this pushes it to just under that at 10W

[ThomasW]

Use the first one you posted. The last one has no margin for error. Remember this is just a computer sim. If the driver or box parameters are slightly off you want a cushion....

[Nathan P]

The first seems to be peaking a bit right before the roll off. Is this bad?

[Nathan P]

Okay, this looks to be the best, it doesn't get as close to Xmax, and is alot flatter than the first.

[cjd]

If that's anywhere near walls, it's going to pick up some output down low. Which could result in a bass "hump". I usually tune for a gentle downward slope on the bottom end.

As far as excursion, as long as I get the SPL I want and it's not too much excursion at that level, I worry less about it. At some point, you have to acknowledgw there is only so much any given driver can do.

C

[Nathan P]

Okay, since it will be within about a foot or two of a wall in my room, I'll try to tune it for that. That should ease the excursion too.

[KJP]

Dont worry so much about the 10 watts your modeling on. You dont have a ten watt amp. You mentioned getting a Sonic Impact T-amp. Those are good for between 9ishwatts @ 4ohm and 5ish @ 8 before the distortion begins to rise.

[Nathan P]

Well, I've modelled up a new one at 8W (A little over what I'll be driving them with, just to be sure) and it looks really good at 1 liter and tuned to 28Hz. Absolutely no port noise, excursion is fine, F3 is 30 Hz, with room reinforcement it will be lower, so just about right.

Oops, 8W

[Nathan P]

So would a little more roll of than even that be desireable in room? I'm new to all this, I'm relying on you guys for guidance

[Nathan P]

So at what frequencies does room reinforcement start to have an effect? Here's another graph with the box tuned to 25Hz.

[cjd]

Shoot for ~27Hz.

Those look pretty good to me (though 25Hz may get a little lean).

C

[KJP]

IMO, If your going to use the 1cube PE boxes, tuning anywhere from 25-30hz looks good.

[Exocer]

I am also modeling for the same driver and am VERY confused. This is what my graph looks like. My f3 is way too low. I am also shooting for around 40hz, even 45hz would be okay. But how do I go about attaining this?

[Exocer]

Wait, i think i figured it out. How does this look?

[Exocer]

BTW,Nathan, what size port are you using?
and what did you use for Sd? Can't find it anywhere ops:

[Nathan P]

I'm using a 2" port, at the low wattages I'm running it is perfectly fine, well below chuffing speed etc. I found Sd on the datasheet that came wiht my driver, it's 127.5 sq. Cm.

[Exocer]

thanks!

[Nathan P]

I was reading in the Modula MTM thread (Very informative, lots of info there!) and it stated that he aimed for a -6db at I think 36 hz so that it would be flat to that point in room. Is this what I should be aiming for? I may go -6 at a little lower point, but still. I don't want my bass to be completely boomy or overpowering.