Increasing bass on floor standing speakers


I have some floor standing speakers that were a Visation kit from 30? years ago. 
The treble and mids are amazing but the bass is a little weak. And suggestions on increasing the bass? 
Concrete floor 
Room 3.5 x 11 meters... Speakers on the long wall. 
Rotel ra-01 amp
Project rpm 4 (I think) 
Currently listing to Stevie wonder hotter than july.
Thanks for any suggestions 
speakerboyz
I used a polarity tester and the woofers are on the same phase. The tweeters were giving inconsistent results... One alternated with every pulse, the other was a little more random. I assume I wasn't using the app properly (I played through one phone connected to the amp and received with another. Used different frequencies and the L R fader.)
I'll rewire it with thicker internal wires when I know if I need to change any polarities. 
Speakers on the long wall, I'd guess not much space behind the listening position then? 

Sounds like a perfect case for bass (wave) cancellation. 
If not quite that, figure out about any 'other' unintended bass traps in your listening area. 

I had this issue and only found out once I moved to another location. It can be subtle but annoyingly effective.
I know now. 
Bass problem, in the new location (speakers on short wall), gone like magic. 
Michélle 🇿🇦 
I'm a novice although I purchased my first equipment in the 70s while overseas in the military. I now merely have a Yamaha N803 receiver and Vandersteen 1B speakers that are about 25 years old. I stream Spotify and have it set too the highest quality. I will probably upgrade but for now, I'm pleased that I kept the cost down, and most of my listening is background. I'm considering new speakers, probably from World Wide Stereo in Hatfield, Pa. near my home.  I heard and like their Focals.  Would I be wasting money with such a modest receiver or could I improve my sound considerably with new speakers.  Thanks for any advice.   Doug Hess, Newtown Square, Pa.