New listening room

The glass will reflect high frequencies so I'd expect a need for room treatment at the listener's position. OTOH, glass will transmit low frequencies and could be beneficial to bass response. You'll never know how much until you get the gear into the room and listen. Hopefully you can be flexible with the speaker and listening position to find the best sites for both. Floor covering will be a big factor. Carpet best in such a room, tile or hardwood sonic pitfalls with the glass.

Go active before you go NDS

You'll only really find out by actually measuring the room using a sweep generator, microphone and a FFT frequency analyser.

Glass will give you shreeky (nails on a blackboard) sound. It's best to cover with acoustic curtains, this will sort high frequency. But low frequency you need bass traps in corners. On ceiling and first reflective points absorption panels. Then and only then get yourself a minidsp processor stick that in between your pre/power amp and run Dirac Live. You'll be in sonic heaven! Download REW and get a minidsp UMK1 mic either calibrated version or uncalibrated. Measure your room from seated position at every stage.

I think anyone who invests in quality Hi-Fi, the above is a must. To get the best out your system. Majority don't bother and they have wasted their money on a system which they are only getting 30% of the potential of their system. Room acoustics plays an exceptional amount to the end sound. Invest time & money in it to gain the benefits of your hard earned spent cash!

I think the above is the cheapest option unless you start demolishing walls and re-building. Plus getting in a professional acoustic consultant, who would charge you an arm and leg. Majority of what the consultant is going to tell you, you can find out yourself.

If the above tickles your fancy then there is a interesting read by Floyd Toole.

Given the sonic nasties predicted by the Forum here wouldn't it be easier to move house rather than extend. Just remember to check back here before exchanging contracts to ensure your new listening room dimensions meet with the members approval.

I think other people have told you what you already thought - that big expanse of glass is very likely to alter the sound quite a lot - make it brighter and harsher. Whether it does it to the point that you dislike the changes you won't know until you try it.

We rebuilt our house five years ago and the listening room went from 26'x14', fairly typical amount of windows, carpet to 26' x 22', lots of glass and hardwood floor. The sonic changes were significant - bigger than any change in electronics or speaker I had made before. Some of my favourite music became hard to listen to while other stuff might even have been enhanced - depends on the recording. Such is life. Curtains, a rug, bigger sofa all helped a bit.

I hadn't spent money on hifi for several years but addressing the issues set me down a path that led to me changing everything. Of course the key step was a speaker change. Matching speakers to your room seems to me to be a huge part of getting the sound you want. My system wasn't and isn't anything like as good as yours and your ears are your ears but personally I'd suggest not making any changes until the work is done but prepare yourself to audition new speakers.

FWIW I went from CD3.5/Hicap/NAC 102/Hicap/Napsc/NAP 180/ Monitor Audio Studio 20SE (quite a forward speaker)

First step was to switch speakers to Linn Majik Isobariks (gently rolled treble plus much more and punchier bass offset the brighter room) but subsequently have got to SU/NAP 250 biamp with all CDs ripped to NAS (I find steaming a tad sweeter than CD too). 

We have bifold in doors with lots of glass, and it does impact sound quality. We installed electric blinds from Luxaflex which work a treat in dampening town the round when they are closed. The louvres can be tilted to allow some view of the garden while playing music.

As others have indicated, lots of hard surfaces in general are detrimental to replay sound due primarily to high frequency flutter echoes and/or near reflections. Ensuring that the wall opposite the glass expanse has plenty of HF absorbance would be very likely to help with flutter echo (eg sound absorbent panels), ditto the floor (carpet a good area of rugs).

Also, if you have the ability to amend the design, it can help to avoid having parallell walls, and if ceiling is not parallel to floor. That is what I would aim to do if I had the freedom to design a listening room. Relatively small angle changes can significantly change flutter echo,  while larger angles can also help reduce standing waves at the bass end.

You will be spending a considerable amount of money in such a project so you want to get it right. I thing it would be worthwhile to employ the services of an acoustic engineer/architect at the design stage. You have the advantage of a new build. Most of us have to put up with an existing room and make it work as best as possible. The room interface between it and the louspeakers is the hardest one to get right.

I have a theory that at Hi-Fi Shows with indifferent hotel rooms, the easiest demo source is often a female singer with a small jazz group. This is least likely to "drive" the room with upper bass not drawing attention to itself.

If you have watched the "how its made" TV clip on the Linn LP12 the voice over refers to that nice "boomy" bass. Ouch!

lotus

If you play music at a decent volume in a predominantly glass room it will drive the neighbours mad and they'll be on the phone to Environmental Health before you can say 'ooh, feel that bass'. I certainly wouldn't want to live next to it. Maybe you live miles from anyone else, but if you have close neighbours I suggest you reconsider. 

HH has a good point there, distance and high mass are just about the best forms of acoustic isolation!

Triple glazing, which should be the standard insulation for any living room these days, does provide a modeeate degree of sound attenuation, though the bigger the gaps the better - but the room needs to be fully sealed, none of those silly over-window vents beloved of Building Control, so other arrangements are necessary for ventilation - e.g whole house, with heat recovery for winter, with silencers are necessary in ducts from/to living rooms where there are noise sources (and bedrooms for discretion). When I play rock music at 'live' levels in a lounge with big windows that are triple glazed (without vents direct to outside), with full range speakers, even when there is powerful bass it is not loud outside: it is audible up to a few tens of feet away, but not very intrusive, and not as loud as when the neighbours sometimes play the radio indoors with a window open. (Note to self - measure some time)

A room that is too lively with lots of reflections and a long reverb time is quite a stressful acoustic environment. Have you ever sat in a noisy café and been unable to follow a conversation?  That's typically the result of an underdamped, highly reflective room.

Its no different in a hi-fi room. Lots of reflections, slap and flutter echoes and too long a reverb time make for a very uncomfortable listening environment and difficulty following the music. Certainly not the relaxing experience the hi-fi enthusiast is looking for

Most hi-fi equipment is designed for an averagely damped listening room with an ST of between 0.2 and 0.6 seconds (RT is the time it takes for frequencies to decay by 60dB) 

I would guess that the room you are considering would make an extremely poor listening environment due to the extensive use of glass, a material that reflects almost everything and absorbs almost nothing.  But what do I know?  Here's a calculator to help you work out the RT that your combination of materials is likely to have

http://www.csgnetwork.com/acou...reverbdelaycalc.html

Having built my own dedicated listening room last year , there can be a lot of planning involved.

Firstly its not clear , is this room going to be a listening room or a general purpose room with the hifi aspect added on. It makes a lot of difference on what you can do.