Deciphering UniBox graphs

[MCFuryNZ]

I was modeling multiple subs and vented enclosures and the max spl at max cone excursion (red) line was well into the response line (on the first graph on the Vented tab). I was even putting in models of subs that people had built and was seeing this happen. Either I'm doing something wrong, interpreting it poorly, or most people ignore that since those power and spl levels are rarely reached. Am I far off base here?

Also, can I just grab a cheap sub (Mach5 MAW-12?), 20" Sono, ~300w rms, a proper port, and hope for the best? I know I want about 20hz tuning or so, say 60/40 music/ht, so I can calculate port length and Sono height accordingly. Is there any other science to this (besides just experimentation for fun, which is exactly what i'm doing)? I have been playing with the modeling software often and besides the excursion issue I think I know what i'm doing.


Thanks guys,
Max

[ThomasW]

Without seeing your sims much comment is pretty difficult.

This thread is one I whipped up to be a Unibox tutorial.

You can upload your screen shots as attachments too...

http://www.htguide.com/forum/showthread.php4?t=23273&highlight=Unibox+tutorial

[---k---]

You're probably modeling it correctly, but post the graph for us to take a look at to make sure.

It is near impossible to not have the cone exceed the xmax below the tuning point. This is just the nature of the beast with a vented sub. It is also why a high-pass filter is highly recommended for a ported sub. A high pass will filter out and roll the signal off to protect the sub from exceeding it's excursion limits. However, the rub is that there aren't any good diy high pass filters out there. (YET, Thomas and Chuck are going to have one very soon.- reportedly)

Many of us are willing to risk our drivers and go without the highpass filters. We do this out of the belief that we have soooo much sub, and that the tuning point is so low, that there just isn't going to be much signal in that range. It may get riskier as more movies have that low freq. rumble. You just really have to pay attention to the limits of the sub. Its a gamble that I'm taking, but I can afford to replace my drivers.

As far as if there is a science, yes. But unibox makes it pretty easy. You want to have enough volume to get a nice flat response, but maybe with a little gentle roll off to allow room gain to fill in. then you need to check your port velocity and resonance. make sure you port doesn't exceed say 25 - 35m/s, and make sure the first port resonance is above say 200hz. And you're good. You'll find it can be quite the balancing act sometimes. These aren't hard limits, but good guidelines.

Again, use the export feature to save your graphs and then attach them. We'll let you know.

[MCFuryNZ]

Without seeing your sims much comment is pretty difficult.

This thread is one I whipped up to be a Unibox tutorial.

You can upload your screen shots as attachments too...
http://www.htguide.com/forum/showthr...nibox+tutorial

Your post, #24, that thread, that diagonal red line. "SPL produced by driver at peak excursion". That part has me worried... as I said before, are we just trying to stay below those SPL levels? Or am I interpreting wrong?


Thanks again

[ThomasW]

Are you talking about this?



Yes in theory we want to keep the black driver output line below the red line. That said you need to remember these are anechoic sims, not how things are going to happen in-room once room-gain is taken into account

[JonMarsh]

Are you talking about this?



Yes in theory we want to keep the black driver output line below the red line. That said you need to remember these are anechoic sims, not how things are going to happen in-room once room-gain is taken into account

One other point... the redline is the driver output vs frequency, for just the driver. The black line just below it that dips at the box tuning frequency is the driver excursion for that power level of drive- at the Fb, the box/port combination reduces the driver excursion substantially. There are several versions of Unibox, and you won't always see the same data in the combined plots.

Let's look at this one, done in Unibox 3 for an Aurasound NS12 woofer in a 75 liter box.



The Legend describes the outputs for each colored trace. The dark blue is the anchoic SPL output for the combined port and speaker with 100W drive. In the room, this is modified by near by boundary placement, and in the lower frequencies may reach a level 6 dB or more higher. This is why this system is designed and tuned with a drop off toward lower frequencies, with lower Q, so that the transient response is tighter and the in room balance with proper placement will be perceived as relatively flat, not as bass heavy.

The Red line is the maximum SPL that can be produced directly by the driver with 10 mm peak excursion.

The thin black line with the dip at box tuning is the SPL produced by the driver in this box with 100W drive. At the box tuning, most of the output is coming from the port- one reason why you DON'T want to cheese out on the port diameter and impair the clean output capability.

The upper light blue plot trace is the SPL produced by the port. The lower green-blue trace is the estimated output due to leaks.

The light gray trace is the maximum SPL that can be produced (anehoic) by this cabinet, driver and port combination when driven to 10 mm excursion. This is not a frequency response versus input per se, but a maximum output capability of the speaker and cabinet combination at maximum Xmax.

~Jon