Based on what I've read online, some sort of diffuser on top of the fireplace mantelpiece behind my television may be a good place to start? Would anyone be able to recommend something that I could possibly put together myself using my own tools and materials (to save on cost)? Other recommendations would also be greatly appreciated. Thanks in advance.
Hello Alexander, and Welcome to AudioCircle!
The flavor of the front wall reflections (diffused or direct) is further down the list of your room acoustics priorities, imo.
Wow, that's a terrible place for a stereo. Please try to move it to another wall, or another room in the house. Or just do it anyway, perfect the setup, then sell it later.
Problems with current location are numerous and serious. Fireplace hole is reflection cauldron. Lots of reflective bass support on left, none on right. Short sidewall reflection delay on left, long delay on right. You only need one sub, not two, to match SPL of small main speakers. You are sitting too far back. Reflex ports on mains prevent accurate phase integration with subs.
If you think you have absolutely no other option, or not willing to charge up the hill with your audiophile battle flag, then I suggest you build 2 temporary movable walls to improve the space you have been allotted. Materials and tools probably <$500. They would about 5-8 feet tall, connected together temporarily at a right angle to extend the front wall to the right, and form a small right side wall to restore balanced sidewall reflections and redirect some bass energy. Taller is better for bass, but 1-2 feet taller than the main speakers would be the minimum. Put a shelf board and painted trim along the top, paint to match house, hang pictures and plants, etc. The right stub wall should be 2-3 feet further out from the front than the front of speaker, so 3-4 feet. The front wall extension should be wide enough to allow your listening position to be comfortable, slightly elongated equilateral triangle. Ideal listening distance from 5-6" woofer is probably 6-8 feet.
Then:
Fill fireplace with FG pink insulation, cover with wood panel or fabric curtain for appearance.
Seal reflex ports on mains
Move left speaker into left corner as far as possible, almost touching front and side walls.
Move listening seat closer to front, and as far right as possible, considering it must be centered between right and left speakers.
Push left speaker far into corner as it will go. Place right speaker to form equilateral triangle with ears and left speaker.
Put a single sub in center, up on white shelf, so sub woofer is same distance to your ears as main speaker woofers.
Use only one sub.
If there is no temporary walls surrounding the right speaker, then you will have huge SPL discrepancy between the right and left main speakers. Cure this with balance control on your preamp/receiver so the image of vocalists are centered on your listening axis.
Adjust the sub plate amp controls to integrate with the sealed main speakers, or use receiver DSP settings to integrate sub.
Start a new thread if you want details on manual sub integration if your sub has adjustment controls.
If your tube electronics have no balance control, you can make a DIY interconnect with balance control pot added.
Good luck!!
