[js1955]

Please view these 2 pics, I think they say it all.....

12' wide wall of glass, RIGHT side:




from behind RT spkr, open layout beyond LEFT speaker:




-  Very tall ceiling, slopes from RIGHT to LEFT, 9 to 15 ft.
-  Speaker spread is 7.5 ft
-  Speaker baffle to LP is 9 ft
-  Front baffle to front wall is 5.5 ft
-  Back wall to ears is 2 ft  (unfortunate, but unavoidable)
-  65" TV between spkrs is against front wall, and covered with comforter + tapestry
-  Left Speaker:  open layout to the left,  front wall ends at left edge of speaker cabinet

Bass is not a problem, so I'm not thinking bass traps.  Slap echo is creating serious discord in the sound and very rapid listener fatigue,
to the point of unlistenable.  So I'm focusing on just general across the spectrum frequency absorption.
100% sure problem is the room, as I had the identical gear in my previous house and it sounded GREAT!

For starters, I plan to:

*  build and cover the RIGHT glass wall with 4 acoustic panels, 2' x 4' x 2 inches thick.

*  build 3 - 5 panels (same size) for front and back walls.

I will use either Owens Corning 703 (or 705), or one of the Rockwool / Roxul variants.   I plan to fabric wrap the front and
rear in the traditional way.

I know it's best to put a 2 inch or so air gap between panel and wall.   But for the panels over the glass, I'm not sure what to do.
So I have these questions:

(1)  Should I put panels flush on the glass?

(2)  Should I put some bumpers behind the panels to create an air gap between panel and glass?

(3)  Should I install some hardboard on the rear of the panel, and use bumpers between it and the acoustic material to create an air gap?

I'm not sure, but I think (1) and (2)  will result in sound waves going thru the panel and still bouncing off the glass?

Under scenario (3)  I figure:  (a) the hardboard effectively replaces sheetrock that is normally present, (b) the desired air gap is present,
and (c) the glass is taken out of play......so it is probably the best option?

Is my layman's logic and intuition correct?   Should I be doing something else?

Thanks in advance for all input and advise, it is most welcome!

~ John

[WGH]

Are those Klipsch speaker? If so they are notorious for sounding terrible in large echoey spaces. I hope you are not in love with them. The money spent on room treatments would be better spent on different speakers, either open baffle that work best in large open spaces (Magnapan) or a speaker with a more focused presentation. Speakers with a RAAL tweeter don't have as much a wide dispersion as a dome tweeter. The big, flabby, phat, slow passive radiator on the back of the speaker isn't doing you any favors either.

You have enough rugs and furniture in the room that room treatment is not needed with the right speakers.

[js1955]

Are those Klipsch speaker? If so they are notorious for sounding terrible in large echoey spaces. I hope you are not in love with them. The money spent on room treatments would be better spent on different speakers, either open baffle that work best in large open spaces (Magnapan) or a speaker with a more focused presentation. Speakers with a RAAL tweeter don't have as much a wide dispersion as a dome tweeter. The big, flabby, phat, slow passive radiator on the back of the speaker isn't doing you any favors either.

Thanks for the input!   

Yes they are Forte IVs, and yes I do know of their energetic / tipped-up reputation, and no I'm not in love with them.   

They are a recent purchase that I had for only a short while in my previous place.  Never really got them zeroed in, moved shortly after the purchase, and I'm not in my current place very long.  Just wanted to play around with low power tubes.

My main speakers for over 10 yrs are Sunny H2W10.  They have sounded great over that period in 2 different previous houses.  Sound like crap in here.  If you look closely they are in pics, against front wall, gloss maple.

And the slap echo is very real in here.  I can hear it even when speaking.  In addition to the glass,  the tall ceiling and wide walls results in lots of sq footage of hard blank wall space.  So I am convinced that absorption and dampening are required.

[Early B.]

I recently dealt with a similar issue, although in a smaller room with large windows covering three sides, a sloped ceiling, and a stone tile floor. I did two things to eliminate the echo -- I purchased sound barrier curtains and got a rug to cover nearly the entire floor.     

https://www.amazon.com/gp/product/B08V8JBDZ1/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

You can spend thousands experimenting with acoustic treatment. At the end of the day, you've got a tough room to tame and it may sound lousy no matter what you try to do, so spend your money wisely. I agree with WGH about acquiring a set of open baffle speakers. This purchase will solve 58% of your problems.   

[WGH]

And the slap echo is very real in here.  I can hear it even when speaking.  In addition to the glass,  the tall ceiling and wide walls results in lots of sq footage of hard blank wall space.  So I am convinced that absorption and dampening are required.

I don't think those Klipsch can be tamed, there is a limit to the amount of panels a partner will tolerate. Are you single? Put in too many panels and you will never make it to the second date.

It's both the highs and bass bouncing around. I'm thinking Fritz Carbon 7 speakers, they are not as detailed as his Carrerra's, the highs are very well controlled and won't drive you out of the room. I have a pair of Carbon 7s on long term loan, so far our audio club has heard them in four rooms and they have sounded excellent every time, we love them. The Carbon 7s can be driven by a 2.5w amp too.

Bass in your room has to start and stop on a dime to control room reflections. The Klipsch woofers are still making noise long after the note has stopped. A pair of REL woofers will be super fast plus they can be located where they sound the best. Don't get the biggest, the lowest notes will overwhelm your room. A pair of T/9x with the 10" driver would work.

Once you have the speakers and sub decided on, then you can work on room corrections. Until then you have no point of reference. Right now adding a lot of absorption would like be trying to make a pair of chain saws sound great.

[js1955]

I recently dealt with a similar issue, although in a smaller room with large windows covering three sides, a sloped ceiling, and a stone tile floor. I did two things to eliminate the echo -- I purchased sound barrier curtains and got a rug to cover nearly the entire floor.     

https://www.amazon.com/gp/product/B08V8JBDZ1/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

You can spend thousands experimenting with acoustic treatment. At the end of the day, you've got a tough room to tame and it may sound lousy no matter what you try to do, so spend your money wisely. I agree with WGH about acquiring a set of open baffle speakers. This purchase will solve 58% of your problems.

Thanks man!   I hear ya and agree with ya.  Been at this game since 1995, owned many speakers, in 4 different houses, in several rooms in each house, and have done lots of reading and research.,

I did consider covering that entire window wall with "acoustic curtains",  but my research reveals that they must come from actual pro companies that build them for pro situations like sound studios, theatres, auditoriums, etc.   The ones from Amazon etc. typically just have the label "acoustic" or "soundproof" hung on them, but they are just hyped-up ineffective junk.  Like lots of stuff in this hobby.

Something like this might work:

https://vocalboothtogo.com/product-category/acoustic-sound-blankets-sound-absorption-panels-producers-choice/

But those pro ones are ugly as sin.  Panels will be more attractive since the glass part is exactly 2' wide, the panel will cover it, but the nice white molding and trim will show between each panel.  Also, the panels add a nice splash of color with the fabric covers.   And my plan was to maybe hang the panels with french cleats, so they are easily removed for light and views.   Hard to do with the ugly black curtains that look like moving blankets.

And the big unknown to me:   which one is actually more effective?

In an effort to reduce room effects, I have moved the speakers closer to LP, toed them in, and put lots of air around them.   Try to up the ratio of direct sound.  And what you say about OBs having less room interactions conforms with my readings.   

Save the pennies....one day......

[toocool4]

Rather than guessing and wasting your money contact experts that will take measurements and design something to address your issue.

They may well suggest as part of the solution, to have panels you can slide in front of your windows when you want to do some serious listening or even use heavy curtains to help tame the high frequencies as curtains will do nothing to help with the low end.
Rockwool is not designed for music, it’s an insulation. It may work a bit, but it works badly so why bother with it.

Try Acoustic fields for a bespoke solution, everything else is just guessing. www.acousticfields.com

Once I get my new place, I will not be guessing like I have done in my current place.

[WGH]

In 1991, I bought a new pair of Klipsch Quartet speakers for $844.50 each and put them in my open floorplan, 14' high metal ceiling, echoey woodshop. The Klipsch were perfect for a woodshop, I could hear the music over almost every power tool. The Quartet's were driven to outrageous levels with an Adcom GTP400 preamp and GFA 535 amp combo, my neighbor said he really liked my music.

Whenever I upgraded my home electronics the old stuff went into the woodshop, which was when I noticed the Klipsch magic disappearing even though the 'new' electronics was more precise with more power. The new electronics were revealing the flaws in the Klipsch crossover hidden by the sweet sounding Adcom GFA 535.

My old JBL L100 speakers I bought new in 1972 replaced the Klipsch. They are a much better speaker for a woodshop and still rock.

[js1955]

I don't think those Klipsch can be tamed, there is a limit to the amount of panels a partner will tolerate. Are you single? Put in too many panels and you will never make it to the second date.

It's both the highs and bass bouncing around. I'm thinking Fritz Carbon 7 speakers, they are not as detailed as his Carrerra's, the highs are very well controlled and won't drive you out of the room. I have a pair of Carbon 7s on long term loan, so far our audio club has heard them in four rooms and they have sounded excellent every time, we love them. The Carbon 7s can be driven by a 2.5w amp too.

Bass in your room has to start and stop on a dime to control room reflections. The Klipsch woofers are still making noise long after the note has stopped. A pair of REL woofers will be super fast plus they can be located where they sound the best. Don't get the biggest, the lowest notes will overwhelm your room. A pair of T/9x with the 10" driver would work.

Once you have the speakers and sub decided on, then you can work on room corrections. Until then you have no point of reference. Right now adding a lot of absorption would like be trying to make a pair of chain saws sound great.

Thanks WGH.

Don't be deceived by the pics, I'm not trying to improve things with the Klipsch.   They are not my goto speaker.  Was just playing around with them. 

My Sunny H2W10 actually errs on the side of smooth, warm and soft.   Because that's my preference.   Can't stand shrill and bright.   It's also why I prefer tubes and vinyl.  Sunnys can be very dimensional and full, and quite musical.  But they possess none of that good stuff in here.  And they had it all in spades in my previous rooms.  So I know for a fact from living with them since 2009, with many different amps, in several different rooms, that they are not the problem.  They don't possess any of that negative stuff you are tagging the Klipsch with.   So please let's not focus on the Fortes and blame them for my problems.  I'm convinced the room is the problem.   IMO very few speakers will be able to overcome it as is.   So I need to focus on taming the room.  Like I say, I can hear slap echo with normal conversation.   No speaker will overcome that.

Thanks for all the input.  Food for thought.  Keep it coming.   

[js1955]

As far as your suggestion re: the Fritz monitors.....

I just don't believe ANY monitor can give a full and impactful and satisfying musical experience in here.   The room is large open layout,  30' x 17', with 15 ft ceilings, and hallways leading to other areas.   My 2 pair of floorstanders (with 10 and 12 inch woofs) sound "small" in here.  And I use a pair of subs!

No matter how good the monitor, law of physics.

[Tyson]

I’d spend money on thick carpet, heavy drapes and room treatments instead of new speakers.  The problem is the room.

[js1955]

I’d spend money on thick carpet, heavy drapes and room treatments instead of new speakers.  The problem is the room.

Thank you, Tyson!   

I've had four pair of speakers in here that I know very well in other rooms.....
and I don't recognize them.   It's the room!

PS:   thick area rug is done.   It's 8 x 10, 100% wool, 1/2" thick w/ 1/4" thick pad

I guess wall-to-wall carpet would work better, but I hate that stuff.  Not doing it.

[js1955]

Rockwool is not designed for music, it’s an insulation. It may work a bit, but it works badly so why bother with it.

Surprised to hear this.

Both Rockwool / Roxul and Owens Corning are commonly used by many reputable panel mfrs  (ie:  GIK, ATS, Acoustimac), and all the specs I've seen online, including this one,  say the NRC (noise reduction coefficient) across the mids and highs is comparable on both products,  in the 1.0 range. 

https://www.atsacoustics.com/page--Selecting-the-Right-Acoustic-Material--ac.html

I could be wrong, but I don't think any absorptive material exists that gives an NRC much better than this over the range.   When using 2 or 3 inch thickness, not as effective in the LF.   For that you need 4 or 6 inches of the same material.

[studiotech]

Tyson is entirely correct. Chasing a speaker to tame the room is a mistake.  Get the room sorted out first and you'll be amazed.  And YOU are entirely correct that Rockwool is and excellent acoustic absorber.  Rigid fiberglass and bonded logic recycled denim are also excellent and readily available.

Thin wall hangings and thin carpets are only minimally effective.  They might tame the top couple of octaves, but do nothing at midrange frequencies.  Start at the window wall.  Purchase heavy velvet or sound absorbing curtains.  I personally do two sets back to back. I've got a wall of windows to my right side as well. A triple slider.  Try the windows first and see how much improvement you get. Walk into the room, close your eyes and ask yourself if you can still easily hear the sound of the room.  You want to get yourself to a point that it sounds neutral.  Like you can't tell how big the room is, but not so far that it sounds muffled and dead.

If that's not enough, maybe go for the back wall since your couch is up against that wall. Again, a thin carpet or tapestry is not good enough. Minimal 2" thick material back there.   I used a thick wool rug screwed to a wood frame holding 2" bonded logic. 

Greg 

You could also call GIK for recommendations if the diy route is not your thing.

[js1955]

Tyson is entirely correct. Chasing a speaker to tame the room is a mistake.  Get the room sorted out first and you'll be amazed.  And YOU are entirely correct that Rockwool is and excellent acoustic absorber.  Rigid fiberglass and bonded logic recycled denim are also excellent and readily available.

Thin wall hangings and thin carpets are only minimally effective.  They might tame the top couple of octaves, but do nothing at midrange frequencies.  Start at the window wall.  Purchase heavy velvet or sound absorbing curtains.  I personally do two sets back to back. I've got a wall of windows to my right side as well. A triple slider.  Try the windows first and see how much improvement you get. Walk into the room, close your eyes and ask yourself if you can still easily hear the sound of the room.  You want to get yourself to a point that it sounds neutral.  Like you can't tell how big the room is, but not so far that it sounds muffled and dead.

If that's not enough, maybe go for the back wall since your couch is up against that wall. Again, a thin carpet or tapestry is not good enough. Minimal 2" thick material back there.   I used a thick wool rug screwed to a wood frame holding 2" bonded logic. 

Greg 

You could also call GIK for recommendations if the diy route is not your thing.

Thanks so much Greg, all excellent points.

The wall hangings you see in my pics are not an attempt to control anything.   I know they do nothing.  Just trying to warm up the space a bit with color and texture.

Can you recommend sound absorbing curtains that actually work?   Links would be great.

The rigid fiberglass and recycled denim you mention -- are you able to provide links on the products, and who the sells them locally?  Are you referring to Owens Corning 705?

Ideally I'd like to build panels with OC 705, as it's rigid enough such that frames are not required.  Appeals to me since they are lighter and easier to mount over the glass (maybe using heavy duty Command strips?) and remove when light / views are desired.  But it's impossible to source locally.  I checked the local HD and Lowes, and their websites, and 3 local building supply companies.  The latter could not even special order it.  Only available online from GIK, BuyInsulation, Acoustimac and ATS. 

Materials for framed panels are easily obtainable at local box stores.  Shipping charges make the all-in cost of unframed panels a bit pricier than framed ones, but they are more attractive to me for:  the labor / time savings, lightness, and ease of mounting / removing without mucking up the walls.

Excellent video on the approach here:

https://www.youtube.com/watch?v=5jY8yaYob_w&t=756s

Thanks again for all the input/advise!

[WGH]

AV RoomService has tested Frequency Response Panels designed to control room modes, first order reflections, reverberation times and flutter echo.
Their site has plenty of well written acoustic articles too, start with "Measurement Beyond The Atomic Level"

https://avroomservice.com/frp/

[Rocket_Ronny]

I will use either Owens Corning 703 (or 705), or one of the Rockwool / Roxul variants.   I plan to fabric wrap the front and
rear in the traditional way.

I think you would be far better off skipping the fiberglass or Rockwool insulation and consider the panels at acoustic fields.com.

You might want to watch, or consult with, Acoustic Fields.com, they are on YouTube.

Their solution might not be so waf friendly though.

I am in the same boat. Will use window coverings and live with it.

Rocket Ronny

[Tyson]

I think you would be far better off skipping the fiberglass or Rockwool insulation and consider the panels at acoustic fields.com.

You might want to watch, or consult with, Acoustic Fields.com, they are on YouTube.

Their solution might not be so waf friendly though.

I am in the same boat. Will use window coverings and live with it.

Rocket Ronny

Of course, they are trying to sell you something.  However their claim about absorbing better below 500hz is dubious.  Regular acoustic panels can do this too, they just need to be thicker.  I use 4 inch thick panels and it absorbs below 500hz quite well. 

If you build out acoustic panels big enough and thick enough, you end up with corner traps that absorb all the way down to the bass.  No need for 'special foam' at all.

[CherylJosie]

12' wide wall of glass, RIGHT side:
-  Very tall ceiling, slopes from RIGHT to LEFT, 9 to 15 ft.
-  Back wall to ears is 2 ft  (unfortunate, but unavoidable)
-  Left Speaker:  open layout to the left,  front wall ends at left edge of speaker cabinet

Slap echo is creating serious discord in the sound and very rapid listener fatigue,
to the point of unlistenable.

I will use either Owens Corning 703 (or 705), or one of the Rockwool / Roxul variants.   I plan to fabric wrap the front and
rear in the traditional way.

You are on the right track but you are failing to identify the biggest bang for the buck.

Let's sort out the facts from the myths so you apply your effort where you will get the biggest bang for the buck.

Slap echo happens between two closely spaced walls. It sounds like a pinging ring because when you clap your hands you hear the same wavefront ricocheting back and forth between two high gain/low loss surfaces.

Your problem is that huge front wall in front of you, and that huge rear wall behind you. It is especially problematic for listening because the slap echo bouncing off that nearby rear wall behind you is contaminating everything you hear in that room, even more so than it would if you were closer to the center of the room.

But there's more. To get the best modal reinforcement of bass, you need to be somewhere between the 1/3 and 2/5 point between parallel surfaces, where modal bass is strongest.

I've taken the liberty of downloading a Harman modal analysis spreadsheet and put your room dimensions into it. I've assumed that your underestimated the length of that glass wall by not including the portion that is not glass, so I opened it up to 14'.

Since your ceiling is sloped and its modal behavior is quite complex, I've put a guess for a halfway point at 12' just to fill something in that is somewhat realistic. You also didn't specify the left-right dimension so I estimated 25', but again this is immaterial to the meat of this analysis which is that rear wall 2' behind your head.

Sorry, can't find the original Harman link, but I found the calculator archived here. Use at your own risk:

https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/Harman_Int'l/Calculators/Room%20Mode%20Calculator.xls

So here is your room:





The place you need to put your ears is about 4.5' off that rear wall.

That will attenuate the reflection off that rear wall and reduce the amplitude of the slap echo you hear relative to the direct sound.

It will also improve your sense of ambience in the entire space by rebalancing the relative contributions of ambient sound from all directions.

It will also preserve your modal bass response on that front-rear dimension, particularly regarding the muddy bass you are currently hearing from sitting too close to the rear boundary where modal pressure is building up. Moving away from the wall while not moving into a modal null should help rebalance the tone.

You don't want your ears 3.5' off that rear wall either. That is where you'll be in a modal null at 80Hz. If you are using a subwoofer (even if you aren't using a subwoofer) listening from that null may seriously disrupt your bass.

Here's how nearby boundaries work. You don't want any nearby boundaries close to your seating. They amplify the bass and the ambient reflections while drowning out the critical direct sound for voice/midrange intelligibility. Don't do this, or you will never be satisfied with the sound of your system.

It's bad enough that you've got the floor 36" from your ears. Don't put any other boundaries near your ears, or you might as will downsize to a sound bar because you'll have gobs of muddy bass reinforcement and your main speakers will sound distant and ambient no matter what else you do, unless you put them right in front of you.

Except...there's one thing I've done in the past that helped a lot with a nearby rear wall when I had no other options.

I filled 11"x14" crates with pillow stuffing and stacked them behind my sofa. I put two rows of empty crates at floor level, and another three rows of stuffed crates above them to cover ear level. I made the wall of stuffed crates about 7' wide so that it covered all the seating positions on the sofa.

Wow, what a difference! You can try this out for very little money. It's about $15 per absorber, $5 for empty crate. You can completely tame that rear wall for about 6x3x15+6x2x5=$330. That's about what you'd pay for a single 4x3 membrane absorber, and when you're done you still have some spare crates and pillows to experiment with elsewhere.

Very thick fluffy absorption will tame bass down to about 200Hz (11" crate dimension) or 100Hz (14" crate dimension) and that's great for people sitting next to a rear wall. It will help as much as spreading bass traps all around the room because it will damp out the very strong front-rear modal bass you are hearing off that rear wall while also removing the slap echo plus all the other nearby ambient reflections off that rear wall to improve intelligibility of the direct sound markedly.

Something else you could try that looks better and takes less room is very high quality wide bandwidth membrane absorbers (about 4" thick) with a lot better appearance. More cost and complexity, but the cosmetics aren't in the same universe let alone the same galaxy. You can cover them with attractive fabric if need be.

If you still have too much slap echo in the room once you have treated that rear wall, try putting some more absorption on the front wall, but don't worry too much about the thickness because you don't need to tame muddy bass on that wall. You aren't sitting close enough to it to make that much of a difference in the bass you hear from that front wall.

That front wall is where your narrow bandwidth rigid panel absorption belongs.

You can try hanging any old thick thing like carpet, tapestry, comforter, whatever you have on that wall to test out this solution.

For best effect, place it opposite spaces where your rear wall absorber isn't. Best practice if you are taming ambient reflection problems is to stagger your absorption between walls so that you get the most bang for the buck on your slap echo. Try placing it to the left and right sides, just in alignment with the outer edges of your rear absorber.

The beauty of this acoustics treatments stuff is that you don't have to invest in expensive absorbers to try it out. You can buy cheap crates and pillows from department stores to prove to yourself whether I'm telling you the truth about your rear wall, and you can borrow your bedding to prove to yourself whether I'm telling you the truth about your front wall too.

Regarding the windows to your right, the primary problem is that they aren't in balance with the nonexistent boundary to your open left side. That's tough to deal with because it's not so much the presence of strong reflections there at play as it is the absence of strong late (delayed) ambient reflections you are getting on the left side. You don't want to completely damp out the ambient reflections from that glass, or the imbalance will only get worse. However, you can partially rebalance the ambient reflections by only blocking the very early focal (specular) reflections from the reflected imaging of your speakers.

You can address that best by only placing absorption in front of the windows that are causing very early reflections at your seating position. You can tell which windows they are (after you finalize your seating position) by sitting in your main listening position and looking in the glass for the reflection of your speakers. It's best to do this at night with the lights on inside the room and off outside the room. Once you've blocked the focused early reflections from your speakers that are coming off that glass, you should be just about done with your room treatments, and you won't have to block all the natural light from your room to do it. You can probably get away with hanging long drapery rods and bunching up your drapes right in front of the problem spot(s) to effectively add some thickness and create effective high frequency absorption that blots out that strong early reflection. When you aren't doing critical listening, you can push the curtains back into a more normal appearance. If you do this right, maybe you can put curtain rods only over the windows that are causing the problem.

Another possibility is to place a movable panel such as are typically used in recording studios. You can set it out of the way against a wall when you don't need it as part of the acoustic solution on the sofa, maybe even using it to address another acoustic problem that's only an issue when you are not sitting in that main listening position.

The rest of your room probably doesn't need any treatment at all, but you can apply these same principles to identify other problem areas. You've already handled the early reflection off the floor with that carpet. That's also a big problem for intelligibility.

Something else you could do is rotate your layout by 90 degrees, but that puts your TV in front of all that glass and puts your sofa right in the middle of your walkway too. I'd call that a non-starter for cosmetic and functional reasons, even though it might be the best solution regarding viewing and hearing, especially if you block all the windows with opaque drapery so that the incoming light doesn't shut down your pupils too much.

You can also invest in a UMIK-1 and do some Room EQ measurements, but it will take you months to years to master it and all it will do is confirm what I've already shared. Or, if you really want to tune your system like a pro, REW will dramatically help you place your subwoofers and main speakers for best bass. Modal response and speaker-boundary interference can be tricky to deal with unless you take measurements.

Good luck and be sure to update us on how it comes out.

[studiotech]

Acoustic Fields products are overpriced and likely underperform plain old fiberglass or Bonded Logic or Rockwool.  They have no real measurements that I can find on their website, and the only comparison they offer to other products is low freq. performance versus standard acoustic foam, which is almost worthless.  Their  panels are $300 each for a chunk of foam.  You can purchase an entire pallet of Bonded Logic for $700 from Home Depot.  Or you can purchase 6 rigid fiberglass panels or 6 pieces if something like Bonded Logic of the same size for around $100.

https://www.acoustimac.com/acoustic-insulation-materials/acoustic-insulation

If you want premade, Acousticmac has those too.  All for VERY fair prices and with proven performance.