Honest Experience on Effects of Subwoofer Please

@ryder, Subwoofers will always make an improvement more or less depending on what type of speakers you are using but there are rules that have to be followed to match the subwoofer correctly with the rest of the system. Trying to do it on the cheap can certainly be worse than doing it at all. My own experience with subwoofers goes back to 1978 when I bought my first pair. It was a love hate relationship. 

To make it brief, never start with just one subwoofer. Two is the minimum, the larger the better. You need a full two way digital crossover with delay capability. There are inexpensive ones out there now. The low pass filters that come with most subwoofers are a cheap and dirty way of messing up your system. You want to cross over as high as you can, 80 to 100 Hz anyway. I have heard systems operating at 125 Hz sound wonderful. Doing this lowers the distortion of everything else produce by your main system's woofers. Subs should always be placed right against a wall (1/4" off) or in a corner. They are more efficient this way and you cancel out a few early reflections. This is why delay capability is so important. You have to be able to match the subwoofer's phase and time with the main speakers or you just get mud in the crossover region. 

Done correctly subwoofers not only add low bass but a sense of power and effortlessness. The midrange becomes cleaner, more detailed and a system's headroom can improve up to 10 dB. That is twice as loud. There are very few systems that could not benefit from subwoofers. You can not get the feeling of a live performance without them.

I suppose REL subs implement the high pass crossover or filter.

No. REL's design philosophy is not use a high pass crossover with their subwoofers.

The way I look at it (YMMV) is if you can swing a quality set of speakers that plays into the 20hz region you are way ahead of the game. A speaker that has good material and integrates well will run you near $20k new (YMMV). At this point you have two boxes with excellent bass down to say 24-30hz. From here you can use a sub to cover the rest. I would never want to play a sub to 35 or 50hz. 

You will get lots of opinions and mine is free and you get what you pay for. 

From personal experience, deeper bass rarely loads seamlessly in the same plain as the mid/highs, and will likely interfere with them due to the greater vibration that they create

Some 10 years ago I bought SVS subs as they were inexpensive compared to audio dedicated subs. I finally sold them last year as I could not get them to blend  as their plate amp choices volume control was too sensitive, meaning even barrel cracking it, the bass would overpower the room. So, it seems high quality subs are essential, and SVS may well make them now, but not then.

hth 

I admit I did not read everyone else's answer, so apologize if I am repeating something.

First, what are your main speakers?  Some main speakers need a sub more than others.

A really good sub will be better at the lowest octave than pretty much any speaker.  This is not subtle, it is very, very obvious.

It's a matter of personal taste whether the sub is integrated well enough with your other speakers for your liking.

Benefits to the midbass are real IF main speakers are being CROSSED OVER at a higher frequency, that is to say if BASS frequencies are being diverted from the main speakers - they will be moving with smaller excursion so that should give a cleaner midrange, greater power handling.

If main speakers are still playing the whole range then benefits to mids would not be as obvious. Maybe could still occur somewhat if your need to turn the volume knob up changes with the introduction of a Sub.

"There is no replacement for displacement" (zero fidelity?)   If you need loud music in a large room, played with authority and accuracy, you need large woofers.   A more modern possibilty would be the use of small woofers combined with a ton of power and digital processing as some of the modern subwoofers just coming out recently.

There is a YouTube channel called Nemo Propaganda Reviews.  This dude knows more about subwoofers than anyone on earth!