http://www.vxm.com/TN-122HO.1.htmI prefer sealed subs to ported for music. But you will be able to have epic dance parties. Here is what I would do:
Overview: Stuff the VR4 ports and stuff the sub port so everything is sealed. Then experiment with the crossover freq, crossover slope phase and volume of the sub to make it as seemless as possible at your listening seat.
Details: You want the sub crossover freq to be as low as possible without leaving a hole in the FR between the sub and VR4. This just depends on how low the VRs will play sealed, probably 80-100Hz for the -6dB crossover freq. You will want the sub's crossover slope to be 12db per octave if there is a Slope control. If you don't seal up the VR4s then use 24db per octave slope setting on the sub crossover, but the port of the VR4s will add mud to the sub's sound so sealed is usually better when going to a sub. Try both if you are curious. Ideally the center of the sub driver is same distance from your ears as the VR woofers, with the sub phase control set to 0 degrees. Within a few inches is fine because you are aligning wavelengths that are several feet long so a few inches is very small variation, but if the boxes are solid and the floor is firm you can hear any misalignment. Bass clarity is all about phase. For hifi music the sub should be placed near the middle between speakers if possible. If you leave the VR4 ports open then sub crossover setting is lower (40Hz) and have more placement flexibility and the phase adjustments are less critical because of all the mud that will ensue. Reflections in the room might mud it up anyway, so basically you have to try things and see what works. If the distances are not equal then the phase control is only a band aid, it can't make the phase match through the whole crossover band, only at one freq. If they are equal distance with phase at 0 then crossover phase should theoretically be better matched through the crossover band, but it's tough. I think this phase mismatching is why people choose full range speakers instead of sat subs for hifi.
Use the right channel from the preamp or amplifier as the input signal for the sub. For rock most bass is in the center so it doesn't matter which channel but for classical bass is often on the right. There will be some records with bass on the left, you can swap channels or get stereo subs.
Don't mix the channels together for sub input or it will sound muddier on most recordings. If you can't place the sub same distance from you as the VR4 woofers then put it no more than 12" farther away. You can put it closer to you, and then use the phase control to delay the sub in time to match the timing of the VR4 bass. Phase control is for delaying only.
Experiment with the height of the sub driver, especially if sealed. You might find it to sound clearer at one height more than another. I have read that placing the sub very close to the listener seat with lower volume level and phase adjusted for the distance can sound clearer due to minimizing room echo effects with the lower volume, and increasing S/N from the sub from the closer distance. WAF Warning!
Some of this Polk sub tuning advice is good, but there is some BS in there...
http://www.polkaudio.com/polk-university/articles/subwoofer-positioning-and-adjustmentRobert Harley's sub phase adjustment trick (use right main speaker only if you use the right input channel:)
"I set the subwoofer phase by reversing the the polarity of the main speakers by connecting the black speaker cable to the red speaker input, and the red speaker cable to the black speaker input. This inverts the polarity of the signal. I then play a test tone at the crossover frequency and while sitting in the listening position, have someone rotate the subwoofer's phase control. I listen for position on the phase adjustment that produces the maximum null (least amount of bass), and know that the phase control is set perfectly. I then return the speaker leads to their normal position.
This technique works because it's easier to hear the maximum null than it is to hear the maximum peak. When the phase control is set perfectly, the main speaker's woofers will move out when the subwoofer cone is moving in, cancelling each other. When the main speaker's correct polarity is restored, the main speakers and the subwoofer are maximally in-phase."
Use freeware Audacity sound editing program to create test tone sinewave at the crossover frequency to adjust the phase, rather than music.
It's not easy to integrate a sub. But occasionally it comes together and sounds good. With speakers as good as yours, you will probably want stereo sealed subs eventually, if you like the extra bottom of the sub. Good luck, keep the libations flowing and remember phase is only relative. If it sounds good to you then it's good.
Rich
