Help choosing sub

[sqcomp]

...Am I missing something here?

Are you saying that an o-scope won't detect a clipped signal until it's...already clipped or distorting? Are you saying that by the time the scope shows a clipped signal, you've already got a few points of distortion?

A scope will show the wave as it happens. One can follow it (the display of the signal) into clipping if one so wishes by feeding the signal more Voltage.

How about this:

"The real heart of the issue is that every component has a noise floor below which it cannot pass a clean signal. Every component also has a maximum level above which it cannot pass a signal without severe distortion. In operation, it is critical to make sure the signal stays as high above the noise floor as possible without exceeding the maximum undistorted level. This is important no matter what the brand, price, or design the equipment may be. It should be acknowledged that an experienced technician can probably do a quick "tune it by ear" and get most systems pretty close to optimum, but it is just as true that to achieve 100% of a system’s dynamic performance, the use of test signals and at least basic test equipment is needed.

There are really only a couple things that are needed to do a professional job of level setting in an audio system. A good stable low distortion signal is the first thing required. I suggest you use a frequency of somewhere in the 500 Hz to 1 KHz range. A suitable signal would be what we call recorded at “all high bits” (AHB). This means that the signal outputs the highest voltage that would ever be encountered from an undistorted music source. There are numerous test CDs that contain suitable signals or you can burn your own from one of the numerous web sites that contain test signals.

The best way to monitor any electrical signal is to use an oscilloscope...Start with the head unit and while monitoring the output with whatever device you choose to use, advance the volume control until the component just starts to exhibit clipping. Since pure sine waves can sometimes damage speakers, I prefer to turn the power amps off or at least way down just to be safe. After the head unit is set, proceed to the next component in the system and set it right to the verge of clipping. This process is to be continued all the way through the system till you reach the last component that actually feeds the power amps.

There are a couple things that have to be mentioned that can complicate the process thus far described. First is a component that has input and output gain controls. With these components, start with the output control all the way or at least almost all the way down, and adjust the input control first. Then adjust the output only after the input is adjusted.

A second complication is if a previous component seems to be overdriving a downstream component. In such a case it could be necessary to go back to the previous component and reduce its gain enough to accommodate the downstream component.

The third complication is when there are multi-way electronic crossovers in the system. If such is the case make sure that you only monitor the output that is in the pass band that contains the test signal. To set the other bands (usually feeding woofers and tweeters), it is possible to use another test signal or you can set these additional bands to the same gain as the mid-band and you will have things very close, since the maximum voltage of the device will be the same for all outputs since it shares the same internal power supply."

The final adjustment is called Gain overlap. "Gain overlap is an intentional mismatch in the final gain adjustment done right at the power amp. This procedure allows for short term music peaks to be clipped and at the same time allowing the average level of signal to be increased. The net result is a large, noticeable increase in how loud the system will play.

Much testing of skilled listeners has shown that the added distortion of a 10 dB gain overlap is extremely difficult to hear. It just so happens that the real bonus of a 10 dB gain overlap is that the system will play at a level that is perceived by listeners to be fully twice as loud. Of course you can choose the amount of overlap you care to incorporate, but less overlap reduces the usable loudness, and more overlap leads to distortion (that is) audible.

The gain overlap is achieved by doing the very last amp gain adjustment with a test signal that is reduced in level by the amount that you want to have the gain overlapped. As such, a 10 dB overlap would be done by adjusting the amp gains with a test signal that was 10 dB less than the "O" bit signal that is used for the rest of the system components." -- R.C. 2004

Ducky -- Taln has the calculators to help you with the port issues you're asking about. Taln and I are "Geeking" right now about wording on the level matching (see also hijacking your thread)...Sorry bout that.