Ported Enclosure Design w/o Driver Theil-Small Parameters

[misterbobman]

I need advice on ported enclosure volume and port dimensions for drivers that I have no Theil-Small parameters on.
The drivers are Infinity auto separates, model RS400, from a decade ago. I want to build a small ported enclosure to be used for a small table top system (maybe incorporating a Bose-esque mini-sub at a later time).
Specs:
Woofer: 4", polypro, foam surround, very large/heavy magnet, 125 watts max;
Tweeter: .75" Polycell soft dome in mini-flangeless enclosure;
X-over: 3.5 kHz hi-pass 2nd order Butterworth;
System: 89 dB - 2.83 V @ 1 meter, 4 Ohms, 60 watts max.
I was guesstimating a 1.25 liter enclosure volume with a 1 sq-in port opening.
Any suggestions?

 

[Nappylady]

Without T/S parameters, there is no way to know how to tune your BR enclosure properly. Your best bet is probably to make a sealed, stuffed box for it, guessing at the volume, and adjust the amount of stuffing to make it sound better. A vented enclosure will be nearly impossible to get right unless you can get the T/S parameters.

 

[rjon17469]

I don't know what tools you have, but you could consider trying to measure the T/S parameters.

Reece

 

[Paradise_Ice]

These driver are designed for Free air use so there Vas will be very large indeed, a small sealed box will not work nor will a small vented box, but out of the 2 the vented box would be best dare i say it.

 

[rjon17469]

out of the 2 the vented box would be best dare i say it.

Interesting. Can I ask, any particular reasons you say that?

Without the T/S parameters, it's hard to calculate the vent requirements. Without knowing those, you run the risk of making a pretty bad sounding speaker.

With a sealed enclosure, all you risk is a higher rolloff and higher Q.

Reece

 

[Paradise_Ice]

The assumption is because they are designed for car audio, they are for free air use & so are not designed for a sealed box type applications, unless a very large sealed box is used to simulate the drivers vas i would say experimenting with a vented box, this would be smaller and closes to a ok bass alingment when a sealed box would give a very steep bass roll off, unless there is a dedicated subwoofer, a vented system could give a better low FQ response, this is just an opinion and they only way to know for sure is to have a listen to the drivers.

 

[rjon17469]

In this case, a ported enclosure has the possibility of having a better low frequency response. Yes. However, it also has the possibility of having a much worse frequency response. Since it's in-car, your risk of an even uglier response exists.

If you do want to go the ported route, I would recommend you get your port diameter (according to your woofer size and general capabilities) and make it as long as possible to start. Test it out, and if you need to, cut it down, and listen again.

I would recommend however that you just go with a decent-sized sealed, as it'll be much easier to get a good response.

My $.02

Reece