Help! My friend bought a cube

Friend of mine bought this house and this is the ONLY room available to set up as his listening room.

Not exactly a cube but room measures 17'4" x 18'3" with a 9' ceiling. Everyone knows a square room is terrible, but I've quickly learned that a square room where the ceiling height is a multiple is super extra terrible bad.

Initial setup was listening position 38% off back wall, JBL 4435's about 3' from each sidewall which put them almost right up against the main wall when doing an equal lateral triangle. There's no bass, tried multiple speakers with the exact same listening position, JBL L-300, Infinity Quantum 2's, Polk SDA 2.3 TL's, and many more, all speakers that should be able to knock a listener back in this room. Multiple amp's and preamps. The room has no bass, its like there's a crossover at 125hz or so, just nothing below that.

So my friend and I are on a wonderful journey together learning about room nodes! Yay!

My question to you all, if anyone here has any insight, can this be trapped/treated or DSPed out?

DSP would be an adventure, I'm going to try and teach him how to use a UMIK and REW soon, but I'm not great at it myself.

Another friend says lowering the ceiling by a foot and heavy corner and reflection point treatments are the only answer. The owner really doesn't want to have to lower the ceiling, and definitely isn't moving any walls.

Can it be fixed without changing the dimensions of the room?
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As i read your post my thots immediately went the same place as Allen’s.

Overspecced/priced for the job, we are seeing the multi-woofer DSP EQ solutions more from the R&D realm into the commercial kit. They likely are employing Idiot Savants (aka AI) to assist in getting amplitudes, phase, and time all right, then adding gentle EQ to smooth out any left over rough edges.

Trinnov has demoed a system woth a dozen woofers for home theatre.

May they be inpriation for the diy community.

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The crossovers in his 4435's can be bypassed he's got a DBX and a six channel Parasound amp, maybe I'll suggest that be his next step. He's also got a 18" Velodyne out in the garage, one of those giant old-school down firing coffee table looking beasts. I'm going to try and get him to focus up on getting one set of speakers and one amp, preamp combo sounding good. He's a vintage audio collector and likes to swap things around often which can make things difficult when it comes to getting the sound that he likes, loud and bass heavy.
One question, as you walk the room is there bass anywhere?

It seems there must be something beyond room modes if not. Is this room on a soft floor over a crawl space or basement? I have a friend whose living room is where bass goes to die. He has never figured it out, now the basement has become the audio room. I think the floor acts as a wide band diaphragmatic wide and absorber.

Since all speakers sound bass thin is there any possibility that there is a polarity inversion somewhere in one channel?

Does it sound better, worse or the same, bass wise with only one speaker playing?

Room modes I have measured are very narrow, only several Hz wide and using a mode calculator your friends room has a few multi dimensional mode stack ups but that shouldn’t absorb all the bass in the room.

I am curious to know what you find. I have 4435’s in my office and powered by a solid amp they are certainly capable of filling a room that size with very good bass.

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Whereas most rooms have problems with boomy bass, yours is a literal bass killer :confused:
There's indeed a great loss of anything below 120-125Hz.
Front wall treatment will bring MASSIVE improvements.
I've attached pictures of REW room sims below. I assume that your speakers can reach 50Hz.
Moving them around has little effect. The only way is to do heavy room treatments, and follow the advices of other users, who I have no doubt, are far wiser than I am :)
#1: No front wall treatment.
Bass killer 1.png

#2: With 0.5 front surface absorption. Still huge dips, but further treatment in other areas will help (P/s: further experimentation tells me they're probably the front/back wall, left wall and floor :))
Bass killer 2.png
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Just a quick update. Currently waiting on some cooler weather!

We're in the process of building 6 x 8' tall, 30" wide, 5" deep 703 panels to straddle the corners and to use on the ceiling. Another 6 or 8 4' tall panels on stands for reflection points. After straddling the corners we're likely going to back fill with either pink fluffy in some sort of mesh bags with supports to keep it from compressing, one of the denim based products or stacks of safe n sound. We have a good friend who owns a commercial HVAC business and is willing to get us materials at cost. The floor is finished concrete, he has a circle rug down now but it leaves quite a bit of concrete exposed directly in front of the speakers. He's bought a few small area rugs to cover this area and if testing and measurements show that this is a critical step to getting good sound he'll reevaluate the rug situation.

After doing all this we're going to get his 4435's setup with a DBX unit and his big ol' 6 channel Parasound amp to at least get something setup that measures well and to use as a type of reference system. Then we're going to focus on getting either the L300's, or Quantum 2's sounding good, as both sets of speakers have been recently rebuilt and are in guaranteed good working order.

I'll try and remember to post some updates on here as things move along, and take plenty of pictures and measurements as things progress. Thanks a ton to all those who have provided some advice!
@rayma if it were my room I would’ve installed carpet, or found a rug that’s as close to wall to wall as I could get. Or even better I would have probably installed, at a minimum, 2x4” insulated subfloor on top of the concrete slab with some heavy carpeting.

Unfortunately my buddy can be a bit hardheaded, not trusting of things on the internet and prone to conspiracy theories and such.

I hope he’s not lurking but he knows it’s true. Things typically have to be proven in real time A/B examples before he agrees to jump on board with certain changes.
17-18 feet is about 60-65Hz, 9 foot ceilings is an octave up. Don’t get a ground loop! The men in black will show up. But seriously, I like room furnishings rather than massive absorbers and death star defusers because the room doesn’t look like a laboratory, it looks like a room. I would put in a bookshelf (full of paper books), some cabinets (full of bourbon), carpet, rugs, a big yellow dog, drapes, and furniture. Then give it a listen (the stereo, not the dog). You can reduce a wall length by two feet if you add cabinets, and you create storage for all the hify stuff you aren’t listening to. Your room changes to 15x18 and two of the corner cabinets can be purpose built as bass traps. Next I would try multitudes of subwoofers, not because I think it would work but because it would be cool to have subwoofers of various sizes all over the room. Curious young lady: What’s that? You: A subwoofer. And that? That’s a subwoofer too. That? That’s my dog.