Free air modeling

[johnnyrichards]

So I am going to order a pair of those Tang Band 5.25" Neo's... I will be running them in a 2.5 way, active crossover system in my front doors, mated with the Pioneer 5.25" component set.

How do I model a speaker in free air? In WinISD Pro I just start a sealed project, and bump the enclosure size up to about 2.5 cubic feet.

These will be high-passed 4th order at 50 Hz to take care of potential excursion problems. My goal is to get modeled bass down to 70 Hz or so out of these guys.

Is this a valid way of modeling free air response?

[Dirk]

> So I am going to order a pair of those Tang
> Band 5.25" Neo's... I will be running
> them in a 2.5 way, active crossover system
> in my front doors, mated with the Pioneer
> 5.25" component set.

> How do I model a speaker in free air? In
> WinISD Pro I just start a sealed project,
> and bump the enclosure size up to about 2.5
> cubic feet.

> These will be high-passed 4th order at 50 Hz
> to take care of potential excursion
> problems. My goal is to get modeled bass
> down to 70 Hz or so out of these guys.

> Is this a valid way of modeling free air
> response?

Sure. Just use an "infinitely big" sealed box. If it's truely free-air, I'd use a box around 10ft.

[damkor]

> Sure. Just use an "infinitely big"
> sealed box...

...and he is listening inside an approximately 200to 1000 ft3 box. Can he model that? Free air in a car is actually more like the listener being inside a large sealed box.

[Dirk]

> ...and he is listening inside an
> approximately 200to 1000 ft3 box. Can he
> model that? Free air in a car is actually
> more like the listener being inside a large
> sealed box.

No matter your frame of reference, relative to the size of the woofer (and the woofer's Vas), the space is effectively free-air. Pretty much like an infiite baffle subwoofer installation in a home.

[damkor]

It's a much smaller cabin though, so the rise in response starts above 100Hz, rather than much lower. And it's not really sealed, so the back wave of that woofer will rattle. I think he should try it and listen and measure.

[Dirk]

> It's a much smaller cabin though, so the
> rise in response starts above 100Hz, rather
> than much lower. And it's not really sealed,
> so the back wave of that woofer will rattle.
> I think he should try it and listen and
> measure.

We're in agreement, there. However, WinISD isn't going tobe able to predict cabin gain no matter what volume he specifies, so one uber-large box volume is as good as another.

[johnnyrichards]

[jmc]

is that the doors aren't actually large enough to be considered free-air. It is basically a sloppy sealed box of medium size. I find drivers with a healthy x-max, fs around 50-60 and Q of around .4-.6 work nice in doors.

[damkor]

...not get?

[envisionelec]

> is that the doors aren't actually large
> enough to be considered free-air. It is
> basically a sloppy sealed box of medium
> size. I find drivers with a healthy x-max,
> fs around 50-60 and Q of around .4-.6 work
> nice in doors.

It's a lossy vented box. There are multiple tuning frequencies based on how much movement of the door panels increase or decrease enclosure size. Vent tuning is to the outside through the window seal. So, in short - it sucks.

But your parameters are in the ballpark. A small note: use a woofer with a stupidly high Qts (like 1.5 or more) if you lack EQ, power, have badly sealed doors, own a convertible or open top vehicle.

Stupid-high Qts speakers are used in stock speakers which makes them sound markedly better than most aftermarket speakers in the midbass range. Distortion, however, is another matter.