The last few weeks have been amazing. I had the new toy to play with, the amp and ReQ. It took me almost a month to figure out the best settings of the duo and I dont think it is over yet. In the mean time the sub and the speakers also took their own sweet time to run-in. Specially the sub, it's controls had to be continuously reduced in gain and punch (dB boost in Rockford lingo) as it started getting louder by the day. What was a good gain and punch setting during the first week became miserable by the third week.
First the ReQ setting. The front and rear signals were given full voltages. The sub setting was a "band pass" where less than 40Hz were cut off by ReQ's high pass filter and higher than 120 cut off by the low pass filter. Rest of the settings were done on the amp. Here is a diagram of the amp's tuning face, taken from the manual.
As you can see there are separate gain controls for the front and rear. They are kept below 2 and 3 for both to allow the HU and Aux-in stations's volume control to continue it's salaried job. Moreover it eliminates the alternator whine.
Initially I had kept the front and rear filter at "all pass" position. Later I have changed them to High pass at 80Hz position with bass boosted to +6dB. This setting somehow improved the mids. For example without the boost, Aerosmith sounds rather tinny. The spectra of the 80Hz high pass filter and the bass boost are shown in the following figures.
When frequencies starts attenuating below 100Hz for the mid-bass speaker, the bass boost will ensure a sharper cut off as the drop from 100-80 is about 3dB and the boost in the same region is also about 3dB. Without the bass boost, the sound from the mid-woofer lacks power.
The sub is kept at mid gains and the punch control is kept at minimum. The following figure illustrates the sonic spectra of the controls.
Since it is known that bass boost distorts sound, I thought it was better to keep that at a minimum and let the gains do the job. It did. The rumbles and muddy notes from the initial days have disappeared, giving way to cleaner, crisper and deeper thumps. The rumble was totally eliminated by the ReQ subsonic high pass at 40Hz. Apparently no musical instrument produces notes below 40Hz, any recorded sound at those region probably comes from electronic bass. From example when I was playing "Waka waka", the initial sub-sonic rumble was so loud that it was not possible to sit in the car. Now, with these settings, it is much nicer. The subs's high are limited by the amp's low pass filter set at 100 Hz. I had kept it at 80Hz, but the boom was missing.
Crossovers for the twitters are factory set at 4500Hz. Twitters are not the chirpy and bright type like JBLs. Which is fine as there is no deluge of treble at any volumes.
So to summarize, any sound above 4500Hz is going to twitters, frequencies between 100Hz and 4.5k Hz is going to mid-rangers and between 40-100Hz to the subwoofer.
I keep the phone equalizer at default setting, that is flat. Which is fine since sound is reproduced as it was recorded. Most rock and pop numbers sound rather warm and natural in this mode. Bollywood sounds a bit muted as they tend to love highs. Classical sounds very rich, it feels that some one has brought the piano and violin inside the car.
At 50-60% volume, one can hear music outside the car. It is not possible to sit in the car at those levels. I am a guy who does not like too loud music. Normally I keep the phone at full minus one step less volume and use the Aux-in station's volume control to set the sound level. Typically when I am alone driving Scorpo, I keep the volumes at 40-50% levels, depending on the number that is playing. At these levels, one cannot hear outside noise, even the indicator tics. I have not heard any distortion yet. There was a trunk lid number plate rattle. It was solved by three layers of double sided tape on both sides of the plate.
What can improve? At this point I feel that the sound definition can improve. Things like identifying each musical instrument's finer nuances is not clear. For that a better HU and better speakers are needed. Not going to happen as I am done ICEing. However, the experiments with the settings will continue. Hope to give any updates if something changes for the interesting.