Could Y'all look at this and see if I'm breaking any rules?

[jcardin 2]

Just to start off, I'm building this for the heck of it and recently picked up an inexpensive Memphis audio 15-ms84 to build a box around. This box might be placed in a car just to see what it will do but will stay mostly in the office.

The pictures should give you an idea what I'm trying to do, and should show most of the specs of the box. Basically using an 8.25" x 1" slot port that is 23" in length with a tuning around 38 hz. The box volume is .59 f^3. The response curve seemed to have an nice flat-ish shape that hopefully will make it sound 'full' to the Fs.

If I'm doing something completely wrong, please let me know - Gently please.

Thanks

John

[///M5 2,833]

A few things:

As a rule of thumb your port doesn't have the right profile. I wouldn't exceed a 7 to 1 ratio. I'd also like to see a little more port area, but you don't have to get ridiculous perhaps step it up to 8.25 x 1.25"

For in house 38hz is WAY too high. If you use it at all for movies you need to be below 20hz and if it is just for music I'd still go below 30hz.

I'd also flush mount the driver and double baffle it while you are at it.

[jcardin 2]

ok, gotcha on the port ratio.

But if you don't mind, let me ask that when I make my port larger, (assuming the same Fb) the port is made longer, and if I tune to 30 or lower I get an even longer port. Is there a trick that I'm missing, because I get really really long ports that don't even fit the box. Would I need to make the box larger to accomidate this or should I make my port area smaller or what? (I'm guessing no on the smaller port area) I wouldn't use this for movies, mostly music.

I do appreciate the help.

John

[KU40 173]

38 hz is still real high even for music in-house IMO. 30 is as high as I would go (agreeing with M5). as for the ports, you'll likely have to make the box larger to accommodate the port and keep the internal volume for the sub the same.

[jcardin 2]

So keep my internal volume the same and use some sort of snaking like the pic above?

edit; Ok I model'd up something that I'll post a little later. .6 cf with 29 hz tuning, I was able to get my 54" of port and looking at the graph, I'm kinda excited about this. I've always been a sealed kind of guy but just comparing the response of my sealed id10v3 in winisd against the 8" ported, the 8 looks way better in the 50-20hz range. like 12 db higher at 30 hz.... Sure it's 5 db down at 75hz but who cares!

Edited July 31, 2008 by jcardin

[///M5 2,833]

Beware below the tuning frequency, you can easily harm your sub. If you want 20hz, you better tune even lower.

As an fyi, my Rli8 is in a ported box. It is about a half cubic foot net, but the external size of the box is over 3.5cuft. The port gets really long.

I'd try and snake it the long way so it has the least amount of turns.

[KU40 173]

I'd try and snake it the long way so it has the least amount of turns.

I agree. I don't know if it's just me or what, but the more 180 degree turns I've put into boxes, the more muddy the sound is.

[helotaxi 46]

A tuning lower than the sub really wants will muddy up the response as well. That same low tuning would drive you to have a lot of turns in the port because it would have to be really long for a mid sized box even. Could be the turns, probably the tuning.

[Aaron Clinton 2,372]

Any chance you can go a little larger on displacement to flatten out the response graph?

[BKOLFO4 29]

When I have to turn 180, I route a notch and install pvc to make a smooth curve.