Quote:
Originally Posted by W9TR
The continuously variable phase control adds variable time delay at the crossover frequency. It%u2019s effectiveness is very dependent on the implementation used by the sub manufacturer. The 0-180 polarity reversal switch does just what it says - it inverts the entire signal, just like reversing the speaker cable + and - terminals.
Why does this matter?
A single cycle at 80 Hz is 12.5 mSec. The speed of sound on air is approximately 1000 ft/sec so 12.5 mSec is approximately 12.5 ft.
Most subs, and any sub with DSP will have a delay of 10 mSec or more. There is no way you can position a sub to be time aligned with your mains - the distances involved are too great. Instead, you find a spot where the sub couples into the room properly and then adjust the polarity and phase Controls so that, at the crossover frequency at least, the output of your sub and mains is the same level and in phase. You will have a result that looks good with REW or other swept measurement system as you will be producing relatively constant acoustic power vs frequency.
What you have not done is time align the system. So while the output of the sub and mains are in phase at the crossover, they may be off by an entire cycle or more in absolute terms.
If you don%u2019t use an outboard crossover, this is where you stop. Your sub and mains may or may not be time aligned. Generally they will NOT be time aligned and the sub output will lag the mains by a cycle or more.
If you have an external crossover with delay adjustment you can time align the system with an appropriate impulse response analyzer like MLSSA.
I have a JL Gotham and Sonus Faber Amati Futuras. In 2 channel mode, the Gotham is not used because I have plenty of bass output. In HT mode, the Gotham handles everything below 80 Hz. Through my pre/pro distance adjustment, the entire setup is perfectly time aligned as measured with my MLSSA analyzer.
A long post, sorry about that, but I thought it would be good to discuss what is really happening when you add a sub to a 2 channel system without compensating for time delay.
Tom
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Appreciate all the useful and interesting, info, Tom.
There is no way for me to control the Timing of the REL's output, as there is no knob/control for timing on the R-305 as there ion the JL subs. So, for my application, this control factor for my DOE is "irrelevant".
Good info, though, and I appreciate knowing more about this.