damping the room and treating first reflections should be the first place you start. I have purchased wicker baskets with lids before and stuffed them full of insulation and placed them in the corners. This, of course, will help absorb some of low end. Second, you can buy a curtain to cover the glass but be careful not to kill the room. If it gets over-damped, you are doing as much damage as if you didn't treat the room at all.
My advise would be to add one pair of treatments at time. Make sure you are keep everything symmetrical-if you can. Since you are familiar with the sound those speaker give you in your home, you will know when you have your office treated just right!
Bass will be reinforced with movement back towards rear wall or to side wall but imaging could suffer.if you have hard room then adding drapes could help and carpet on floor but actually a diffuser of thick carpet behind speaker can have dramatic affect.You can also treat side walls with sonex or other absorbing material in a very narrow area on side walls where music hits side wall to stop "smearing" with standing waves.Aldo triangles in ceiling corners.This can help in a soft room but even more in a "hard" sounding room without furniture etc.The Stereophile book to High End is worth getting as it covers much of this.
As you noted, thick curtains would help reduce high frequency reflections. The curtains, however, will not help with mid and low frequencies. It may be that the high frequency reflections are what you notice the most now, but when the high frequency reflections get reduced, you may discover that you have other issues going on in the low and mid frequencies. I suspect that you do in a room like that.
One thought is to consider broadband absorption panels, like the GIK Acoustics 244. The idea of broadband absorption is that it is absorping a very large range of frequencies, with the idea of smoothing out the frequency range in the room. Any room has peaks and dips at certain frequencies just based on physics and room dimensions (and it sounds like you have lots of extra reflections going on). The 244s can be hung on the wall, but they also make stands to place them on which may make more sense if three of the walls are sliding doors (that is, so you can move them when you need to).
I was amazed out how much the GIK 244s did for the sound in my room -- for example, I realized I was not hearing all the notes (bass notes, as well as higher frequency notes), voice became much clearer and focused, and everything sounded more natural.
The folks at GIK Acoustics are very helpful and you can email them room dimensions and pictures and get a free recommendation. There are other companies that sell similar products, but I mention GIK because I had a very good experience with them, their prices are very reasonable, and I received very good service.
Depending on how the sliding doors work, you may also consider broadband absorption/bass trapping in the corners. The post above mentions triangles in the corner. You can also do something like a GIK Tri-Trap. Also, if you like the idea of do it yourself, the Gearslutz forcum (under bass trapping, room acoustics) has lots of info on DIY corner traps and other DIY room treatments.
I found that Ready Acoustics were very helpful and had good prices. If you will send them a photo of your room they will make suggestions. Totally transformed my room.
Thanks Holenneck, Chazzbo, Edge22, Stanwall
"One set of treatments at a time" is great advice.
the first thing I've done so far is to get some test wave files to play various frequencies in steps from about 16Hz to 18kHz to find out what is happening over the spectrum. I found certain spots where all the bass is trapped behind the speakers, others that rattle the plexiglass sliding doors, and even some that I can hear loudly with my ears pointing one way and almost not at all in another.
I'm going to replay these wave files, along with very familiar music over a wide range of styles, between each "set of treatments," on your advice.
Three of the entire "walls" are just plexiglass sliding doors in light wooden frames. Its a modern-ish room built-on to an ancient Japanese house. Thus, the Yamahas are not near any walls at all. there is a good eight feet to a cement wall behind them, across a hallway behind plexiglass. The only solid wall in this room is where the desk, computer, and Quads are. That can't be changed.
I am looking for "thick carpet"-like objects to try behind the Yamahas as my first big room tweak. I'll start with woolish blankets and move progressively thicker up to some old futons (real Japanese futons are like 2-inch thick blankets, sort of, not like what they call futons in North America).
I wish I had time to read a whole book on the subject, as you recommend, but I'm a super-busy guy most of the year.
I'll try blankets over the plexiglass on the sides first to simulate curtains and see how it sounds, after first trying the above stuff to sort out the bass.
As I'm in Japan, and on a budget (Thus the Yamahas rather than JM Utopias or SF Stradi Homage or something...), so pro service or materials would be logistically impossible and economically beyond my means. I'll look into your and Holenneck's suggestions about corner treatment, a la DYO.
Thanks for the tip, but as above I'm not in North America right now.
Meantime, there are some movable bookshelves and some big storage boxes in this small room to try moving around, too. No other space to put them in, can only shift them inside here somehow...
If anybody out there thinks of some other tips, I'm all ears!
Thanks again, all. This is a fun and interesting challenge.
Before experimenting with room treatment I recommend you restore your speaker's tonal balance by removing the brass cones, granite slabs, cement blocks and blue tack.
It is a good idea to research what cables were popular when your speaker was manufactured. Sometimes the newer cables do not work well with older equipment.
Try tilting the speaker back with it resting on the floor. Very small changes in the tilt angle can make a big difference in the sound.
Rrog - Thanks! That sounds like rational advice. I was just about to start moving stuff around. I'll try taking them off the blocks, etc, first. As for cables, I have another set of these speakers in another room, where they sound great. I'll try switching cables with the ones in that room, to see if that makes an improvement.
I know this is stupid, guys, but I solved my problem. I just moved my Luxman amp and CD player in from the other room, and wa-la! It sounds absolutely superb. The bass in my office is even better from the new Yammies on cement blocks than in my listening room on thin stone slabs.
The problem wasn't in room reflections or bad acoustics, though there is certainly room for improvement there.
I had been assuming all along that the iDecco had to sound great with the Yammies, because it sounds so good with the Quads. WRONG!!...
This was perhaps my first expensive, involved lesson in component compatibility.
iDecco + Quad bookshelves = Good
Luxman + Yamahas = bliss
Couples that can't be intermixed.
Thanks for all your help. I'm still going to try some of the tweaks you all suggested, and see just how good it can get...
Go out and land yourself a copy of Dr Floyd Toole's latest book.
In it you'll learn why treating 1st reflection points is NOT a good idea; where your room's transition frequency lies and how the treatment strategy below this frequency differs from the strategy above it; how various bass absorption methods work and which may be best for your room size; why mid/high frequencies should be reflected or diffused rather than absorbed; where diffusion should be placed and whether it should be 1D or 2D kind of diffusion and what available brands/models are which; how thick absorption should be and how far out from the wall the air space behind it should be . . . and many more very important nuggets.
In the end you are listening to direct (from the speakers) and indirect sound (reflections of room boundaries) and ideally you wish to remove the room from the equation, or at least minimize its negative effects on the sound and enjoy its positive effects on the sound. But knowing which parts of the room will harm the sound and which will be beneficial is of untmost importance. Otherwise you'll spend (waste?) much time trying many itterative variations of speaker, listening position placement options.
Dr Toole is not affiliated with any acoustical treatment manufacturers so he calls a spade a spade. He wrote the book after he retired so again he is unbiased and a world renown expert.
(I have never met the man, nor am I related in any way.)
"treating 1st reflection points is NOT a good idea"
I think you're distorting what Toole says.
On page 116 of Sound Reproduction he suggests "add sound absorbing material to front wall."
On page 119 he suggests "for stereo listening, leave side walls reflective at reflection points."
There's a lot of discussion of how side wall reflections increase a sense of spaciousness.
I find a mix of absoprtion and diffusion works best. You really have to experiment to achieve the right mix and the effect you desire. Diffusion would decrease and spread out specular reflection and make the room sound bigger.
With mostly absorption, the sound in my room was very focused but I was always aware of the side boundaries. The diffusors along the side and front wall increased the perceived width and depth of the soundstage and relieved a lot of combfiltering problems at mid and high frequencies. The traps or absorption was not as effective as the diffusors at the upper frequencies.
When I had too much diffusion along the frontwall, the soundstage was too far away and individual instrument lost focus. It is really up to you to decide whether you want a large hall sound vs small Jazz venue. Good luck.
Glai - I agree with what you've said and experienced.
I'd add that I find a mix of LOW FREQ absoprtion and MID/HIGH FREQ diffusion works best. Broadband absorption for low-to-high frequencies tends to narrow the soundstage and create more defined sound images in space when placed on side walls, whereas diffusion achieves the opposite effect - personal preferences prevail of course. I found that absorption on the front wall center deepened the apparent sound stage depth.
The diffusors along the side wall should be 1D and diffuse horizontally to increase apparent sounrce width if bare wall reflections are not being used. I used diffusion (hemi-cylindrical) to eliminate flutter echo between two paralel side walls. If your absorption traps were not as effective as diffusors at upper frequencies may be due to the density of the fiberglass and angle of incidence: Higher fibreglass densities will tend to reduce higher frequency absorption as will small angles of incidence.
One conclusion Toole arrived at was that 1st reflection point absorption was a GOOD thing IF you were a musician mixing your music or a stereo component reviewer, otherwise 1st reflections were a positive things that increased listener envelopment and apparent source width, which my humble unscientific tests have concurred with.