Originally Posted by unretarded
We be building a cabinet here...a big UN,a few actually, just want to understand as much as possible.
I think I have the basic concepts down, since the information has run dry......google search after google search turns up little now.
Such as how apparent amp load VA effects the design....what does it do, why does it do it, what is desirable, where do you want it to peak and why...........how that translates into driver coil temp or how much heat the amp will put out, long term output durability. Which sounds better and does it matter where and when it occurs.
Or phase signature....what does the ideal phase signature look like, can we achieve it, does it matter and in what situations does it not matter .
Impeadance/ resistance ohms.........what is the ideal shape, can we skew that shape.....how does that translate into amp load, can we change it, should we change it and how does it effect performance if we skew it one way or the other on the chart.
Group delay...less sounds tighter, more sounds sloppier........20ms at 20hz is tossed out as a number to stay at or below.
Best I can do is approx. 11-12 ms at 20hz for group delay....is that horrible, is that standard.......that can be skewed up or down a little while keeping the same basic cabinet output....which is more desirable and at what point does the secondary consideration become more important than skewing a couple ms off the group delay.
I remember going down this road with engine design/building......
Amplifier load is dependent on box size, tuning and woofer parameters. If you look closely at the graphs, the lowest power use is at high impedance. At an impedance peak, you may require high voltage from the amplifier, but the amount of amperage flowing through the coil is low. Total power is low, coil heating is low.
Ohm's law calculators here: http://www.the12volt.com/ohm/ohmslawcalculators.asp
For example, 40 volts into 4 ohms is 400 watts, but the same 40 volts into a 65 ohm impedance spike is 24.6153 watts.
Where do you want to put your impedance peaks? Depends on the content and intended usage of your subwoofer. For loud music / pro sound you might want to have a large peak ( or multiple peaks from a different design, say a tapped horn ) in the 60+ hz range where the 'meat' of the bass is.
Phase: in a vented box, around tuning, you will get a radical shift in phase, there is not much you can do to change it. You will get additional phase rotation from crossovers applied and any eq. Also, you will have additional phase rotation at the listening position due to reflections inside the room.
Tip for using WinISD: put your cursor in a box and use your up and down arrow keys to watch what happens in real time as you adjust a value.
Group delay is acceptable if below 1-1.5 cycles, as you go lower in frequency, higher GD is still OK, based on the longer period to complete a cycle. Filters ( eq, high pass, and low pass ) will also affect group delay, try it in simulation and you will see.
Read this post, you may just re-think about wanting maximum SPL at 10 hz:
There is a lot of data on system measurements at DataBass, especially under other tabs where impedance is shown, the compression ( thermal and mechanical ) can be eye-opening.
We don't listen to single tones, rather complex signals with multiple bass frequencies simultaneously. What matters is keeping the excursion relatively low, this reduces many different types of motor and suspension distortions and non-linearities.
Two enclosures could produce the same SPL, but the one with larger radiation area ( cone area ) will sound cleaner, less frequency modulation distortion.
There is additional reading at the Klippel website on motor distortions.
As far as ports go, the larger the better, but they eat up precious enclosure volume. ( you must subtract the port volume from your finished internal volume to get your 'net' volume, as well as any bracing and the displacement of the driver [s] )