FS or BS for 200 ft room size ?

Hi
How does one decide on BS or FS for a room which is around 200 sq ft. Do you always go with FS ? Wouldn't BS be better here.
Is the below understanding on room acoustics correct ?

- The wall behind the speakers is important dissipator of sound waves.
- The side walls too should not absorb too much sound.
- The behind walls should absorb sound.
- The ceiling also reflects.
- It helps to fill the room with sound if walls reflect well.
- Having a FS is small room will cause boomy effect of low freq has longer wavelength required to reflect from sound.

My room is a bit funny for acoustics. I have a curved wall behind speakers made of open brick finishing. The distance between two corners of this wall is 13 ft.
Then one side wall has french windows which opens into dining area also. The other side wall also opens up to another room and has brick layered here too.
The length of this room is 17 ft has the end wall with another opening to stairs. The ceiling is the best part, half of the room is 20ft height above the speakers and rest is 10ft high, near the listening area. The listening distance is 8 ft.

I do feel that with the listening distance of 8 ft, a bookshelf would do wonders. Is a BS only for a 1000 cubic ft room ?

Thanks,
Ashok

Ashok:

There is no hard and fast rule about room size and speaker size. The main difference between the BS and FS is the capacity to handle low frequencies. In the mid and high frequencies, many times, BS are better as they have to deal with lesser cabinet resonance.

The sub woofers have also changed the landscape quite a lot. Since they have to deal with just low frequencies, they do the job quite well. Most FS cannot compete with a sub for low frequencies as they have to deal with low, mid, and high frequencies, and there will be some compromise.

The advantage FS provide over BS is volume and sound staging. This becomes very important depending upon the original recording location. For example, if you listen to a Orchestral number recorded in a large auditorium, a FS will always be able to render the sound stage better.

Wall reflecting sound can be good and bad. The good is small reflections add to spaciousness of the sound. This is particularly true if the time between reflected sound and original sound is very small. Dolby uses this concept by adding a 15 to 20 milliseconds delay between front and surround speakers to add dimension to the sound. The bad news is what as called 'standing waves'. If the walls are very near each other and reflect sound well, the sound waves keep bouncing from one wall to another creating a distortion. This is particularly there for frequencies of 33Hz and below.

Play some music with a lot of bass, like pipe organ music or reggae, and walk around your room, listening at different spots: the middle of the room, near the walls, and in the corners. If you hear stronger bass near the corners and near the walls, your room is resonating and creating distortions. These can be corrected using sound absorbers on the walls, and bass traps on the corners.

By 'dissipate', I assume you are referring to 'diffusion'. There is a subtle difference - dissipate means 'to spend or use wastefully or extravagantly; squander; deplete'. Diffuse, on the other hand, means to 'spread or scatter'. In acoustics we usually use the term 'diffusion'.

A wall by itself will either reflect or absorb sound. Special materials are required for diffusion. One common item that diffuses sound very well is a shelf full of books. Special materials include wall mounts that have producing cone shapes in large numbers that spread the music in all directions. Generally this is done on the side walls and never on the wall behind the speakers. These walls have to reflect, particularly for speaker that have rear bass reflex.


Side walls, particularly in small rooms, should NEVER reflect sound. Some absorption is all right. Please refer to my above notes on reflected sound.

By this I assume you are referring to the wall behind the listener. In surround sound, the wall to the rear of the listener should DIFFUSE sound. That will help in enhancing the spaciousness of the sound.

Yes, it does.

The best is a 'dead' room. That is why cinema halls are built that way. But to fill such rooms with sound, you need very large amplifiers and a large number of speakers. Very high end home theater room deaden the room completely, and have speaker even on the ceiling. But, since this is an expensive affair, we allow the room to be a little reflective, thus filling the room with sound.

See if you can cover the French window with heavy drapes. Open brick is actually better than those covered with plaster and painted. The room should not have any openings. Either use heavy drapes or (preferably) install a door.

Your ceiling with two different heights may create issues. See if you can install a simple false ceiling using Armstrong or similar ceiling tiles. Very high ceilings could create an echo and a boominess that may be unpleasant.

Keep the following points in mind.

• A smaller room will color bass response more.
• A sloped ceiling tends to scatter ceiling mode effects.
• Drywall (one that is not painted) will absorb a significant amount to bass under 125Hz. In that sense they are better than painted walls.
• Sitting a little further away from your speaker, will help you get out of the standing wave hot spot.
• Standing waves are always stronger closer to the walls. Never sit too close to the walls
• High ceilings tend to create more standing waves near the corners, Bass traps help eliminate this.

Cheers

Thanks Venkat. This is amazing information. Thanks again for taking the time to explain.

regards
Ashok

One small correction.

The Line, 'This is particularly there for frequencies of 33Hz and below.' should read 'This is particularly there for frequencies of 300Hz and below'. Sorry for the typing error.

Cheers

Can this be corrected without room treatment?

Yes I believe so. There is something called parametric equalizers like the Behringer feedback destroyer that compensates this. There are number of thread on the forum. Pleas search for them. One of the threads I found is the following:

http://www.hifivision.com/speakers/1...ls-15-a-2.html

Cheers

Wow - Venkat - that's a lot of very useful information.

Ashkok: I recently switched from FS to BS for my room which is 13X20X8.5 feet. I am very happy with the sound, the speakers are 5 feet away from the rear wall, but I don't feel any lack of bass what so ever.

I switched from Monitor Audio RS6 FS to Usher BE-718 BS speakers and it's been a huge improvement.

Ah! Surrealistix. That was just the response needed. Thanks a lot.
However, you have an advantage in a good speaker like an Usher BE 718(based on reviews which I read). Would Usher S-520 also give the same performance in such a room, especially with increased ceiling height of 10+ ft. My listening distance would be 8ft though.

Thanks
Ashok

Another person who jumped from floorstanders to bookshelves. Had Jamo E855 earlier and shifted to Usher Be-718. There's simply no comparison between the two. The Usher is way way better in everything. Also I have a fairly large listening room(read living room) which measures 26ftx15ftx10ft.

My suggestion would be don't discount speakers just by size. Listen to every speaker and choose one based upon sonic merit, not based upon how large it is or how many drivers it has.

Hi
The Be-718 is one of the rare bookshelves which can give the kind of bass and allround peformance. The S-520 are entry level speakers from Usher. They are very very good for the price but from the mid-bass upwards. You could add any good sub I suppose but by itself they roll off under 50 Hz. If you are looking for something in between the Usher X-718 (similar to Be-718 but without Beryllium tweeter) may fit what you are looking at, however, it will help to get an idea about budget.

cheers
sridhar@arnsystems.com