New system has fatiguing, harsh high frequency sounds. How to fix?

I just purchased my first audio and home theater system (other than a bluetooth speaker or computer speaker system). I use it for listening to music as well as watching movies. It is a tremendous upgrade and I’m enjoying it. It has clarity and detail that I have never heard before. However, I notice a harshness in the high frequency sounds when listening to music.

I would like my treble to be smooth, sweet, soft, silky and gentle. Right now it is the opposite of that. It is annoying, screechy, metallic and harsh.

I am seeking a solution to that issue. From the little I have been able to find on this subject, it seems that room acoustics might be a big part of my solution. Is that true? If not, what is my next step? An equalizer? I can’t see many options for big changes in speaker placement. At most I can move them a few inches or change the angles.

My listening room is about 11.5 feet by 11.5 feet and square except for the doorway in the back corner which protrudes into the room 18 inches x 44 inches. In the room are a bookcase, couch, end table, media center stand (holding TV, center speaker, receiver, disc player and Roku), computer & computer monitor, my speakers (and rear speaker stands), a ceiling fan and that’s about it... I’m describing the room on the assumption that the room (or its contents) are relevant to the treble problem I’m describing. (However, throwing some thick blankets over my TV and computer monitor, as a test, did not change the issue.)

Here are my home theater components:

  • Computer monitor: WASABI MANGO UHD400 40" 3840X2160
  • TV: LG OLED65C7P 65"
  • Receiver: Sony STRDN1080
  • Disc Player: LG UP875 4K BLU-RAY PLAYER BestBuy SKU 5979504
  • Streaming Box: Roku Ultra streaming player (model 4660)
I mention the monitors (and their size) in case they play a role in reflecting sounds.

  • Front 1: Polk Audio RTi A7 floorstanding speakers
  • Front 2: Polk Audio RTi A5 floorstanding speakers
  • Center Speaker: Klipsch RP-250C Center Channel Speaker
  • Subwoofer 1: Polk Audio PSW125 Subwoofer
  • Subwoofer 2: Klipsch R-112SW Subwoofer 
  • Rear/Surround: Polk Audio RTI A3
Speaker Layout: 5.1 layout with two pair of front speakers and two subwoofers.

The front speakers are on either side of the LG TV on the front wall (and near the room corners. The front speakers are angled in. Minimum distance to wall is 10", but measuring straight/parallel from back of speaker to wall is at least 18". From side of speaker to wall is at least a foot (one side of room has 30 inches). There is only 3" between each RTi A5 and RTi A7 speaker.

The rear speakers are behind the couch at each corner and against the back wall.

One subwoofer is in the back corner. The other is midway on the other wall and angled toward listening area.

For music, I usually prefer listening in 2-channel stereo. The dual pairs of front speakers are awesome. (I initially started out with a 7.1 layout but I prefer this layout now.) The high frequency problem exists even in 2-channel stereo. It also exists if I use only 1 pair of front speakers.

All speakers are bi-wired, except the center (and subwoofers), which don’t support it. (Not bi-amp’d, just bi-wired*.)

Speaker wire: Mediabridge 12AWG 4-Conductor Speaker Wire (100 Feet, White) - 99.9% Oxygen Free Copper - ETL Listed & CL2 Rated for In-Wall Use


Banana Plugs:
  • Mediabridge Banana Plugs - Corrosion-Resistant 24K Gold-Plated Connectors - 12 Pair/24 Banana Plugs (Part# SPC-BP2-12 )
  • Sewell Silverback , 24k Gold Dual Screw Lock Speaker Connector
  • Ocelot Banana Plugs, 24k Gold Plated Connectors, Open Screw Type
BTW, my prior speakers were the Edifier e25 Luna Eclipse. I thought they sounded good and I did not remember them having these harsh high frequency sounds. After listening to my new system for a week, I went back to those for a test and they sounded horrible in comparison. The harsh high frequency sounds are much worse, and every other aspect is worse as well. (That shouldn’t be a surprise given the price ranges being compared, but my incorrect memory had been that they didn’t have this issue.)
Some good suggestions here. 
I would follow Johnny at Audio Connection suggestions as close as possible. He gave me some advice after I had played with my system for about 3 years. After I followed his suggestion I let him know how it turned out as he asked, then he suggested something else and no more issue after that. 
My opinion on your system. My first pair was RTI10 and the 505 sub with B&K components. These are bright to start with. Get them away from the wall about 18 inches so they can breathe. Get rid of the silver anything with those speakers,you need good solid copper with gold power cables and speaker cables. You can maybe throw in some silver interconnects to see how thin they sound or bright. Your Sony is also bright right out of the box. I would suggest Audience PC, they will smooth out your sound and tame the brightness down a bit. The others are also correct about the burn in time,although I don`t think Polk needs a lot of time for that. I had a Mark Levinson system that was bright. I bought some Audience Powerchords for all of my AC connections. I also have some interconnects and Powerchords left over from that system if you would like to try different things. The PC have a lifetime warranty and the best bang for the buck in my opinion with what you have going on here. Congrats on the new system. Let me know if I can help.
To address the elephant in the room, you're using Polk, Sony, LG and Klipsch equipment.  Mid-fi at best, and all known for over-emphasizing upper frequencies in a bid to sound "detailed" and "airy".  Your best bet is to turn the treble down on the receiver and move on.
There are a lot of good suggestions here, I’ll just give my .02:

- agreed this is way too much gear for a room of this size. Big speakers will do movies well but for music, smaller monitor speakers will likely do a better job.
- agreed the combo of Sony + Polk could be contributing. Break in of the electronics will help smooth out the highs but it will take a very long time, 400+ hours.
- Marantz leans a lot warmer and smoother and should help. I have a NR1403 and while I would never call it audiophile it’s quite pleasant and agreeable with music.
- I disagree the brightness is a lost cause in this room. The right gear will be a lot less harsh sounding and make it more livable even with all the reflections. Speakers are likely the biggest culprit here so if changing the receiver alone doesnt help enough, that’s probably your next step.
- wire can make a big difference. For something smoother and more mellow I’d try Anticables.
Ridiculously expensive power cords are of questionable value in a very high end system.  On a Sony they are an absolute waste of money.  On a similar note, while expensive interconnects and speaker cables may have more validity, their effects would be mostly inaudible in this system.  And don't let someone talk you into $150 fuses, either.  Back off on the speakers, you only need two - four tops, lose the subwoofers and stop trying to blow yourself away.