Beginners question about speakers

kcsun

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I know that when setting up the ideal sitting position in a HT setup the left and right speakers should each be set at 30 degrees from the centre line

Is there a calculation based on the size of the left, centre and right speakers in relation to the distance between them and the ideal listening position?

What I am suggesting is that for example you bought a pair of B&W 805's as left and right with only one midrange driver of 6.5 inches Is there a limit on the distance to the listener that they will work to, whereas if you bought B&W 803 speakers with one 6 inch and three 7 inch cones, the amount of air the B&W 803's would displace would be lots more than the B&W 805's therefore throwing the sound further. I assume the quality of the sound at a further distance would be better

I realise budget and "I want those big speakers because I can" plays a part in the final decision but what is the point of putting 803's in a 10 foot depth room or 805's in a 30 foot room?

Also is there an agreed volume the listener in a HT should listen to music or films at (measured with an spl meter)?

I am trying to use this info to find out why we have trouble with speech in films not being clear. Why do my existing B&W 9NTs have three midrange cones and my B&W cnt centre only has one smaller midrange cone and yet it works alot harder than the left and right when watching a film?
Sorry to bang on about B&W but I just luv em! but I would think the questions seem to apply to all speaker brands

kc
 
How far apart your speakers are depends mostly on how far away from the speakers you are, and of course the configuration and layout of the room somewhat dictate and limit the possibilities.

With stereo system, it is generally said that you should be from equal to the distance between the speaker up to double that distance. For example, if the speaker are 8 feet apart, then you should sit from 8 feet to 16 feet from the center-line between the speakers.

The size of the drivers does not dictate the distance the listen must be from the speakers. Though that is within reason. To some extent, it doesn't work to put giant speakers in a tiny room, nor tiny speakers in a giant room. But in between with reasonable sized rooms and reasonable sized speakers, there aren't any restriction. I have two tower speakers with twin 8" woofer, PLUS two 3-way speakers with 12" bass drivers, all in a room 16 feet x 17 feet, though it is something of an open floor plan. The speakers work fine.

So, common sense more than strict numbers is the guide here.

As to the B&W 800 series, I would say all but the top largest two would work in any normal room.

As to the amount of air moved by any speaker, and comparing these woofer sizes to those woofer sizes, simply calculate the area of a circle the size of the speaker.

A = (PI) R²

Area = PI time the Radius Squared

You can take the rated size of the speaker, or to be more accurate, you can take the diameter of the driver from the center of the surround to the center of the surround suspension on the opposite side. That is usually the rated speaker size minus 1.5 inches. So the true diameter of a 6.5" speaker would be about 5 inches, and so on.

I already have a chart of relative driver sizes. I set a 4.5" speaker to a value of 1, and all other speaker are rated relative to that.

4.5" - 1
5.0 - 1.3
6.5 - 2.6
8.0 - 4.3
10 - 6.8
12 - 9.9
15 - 16.0

So, a 15" speaker is 16 times larger than a 4.5" speaker, and an 8" speaker is 4.3 times larger than a 4.5" speaker. But you can use this to determine relative size.

For example, two 8" speakers is 4.3 x 2 = 8.6

A 12" speakers is 9.9 and two 8" speakers are 8.6", so 9.9 / 8.6 = 1.15, which in turn means a 12" speaker is 15% larger than two 8" speakers.

Three 6.5" speakers is 2.6 x 3 = 7.8. So to compare two 8" to three 6.5" we divide 8.6 for the two 8" speakers by 7.8 for three 6.5" speakers and -

8.6 / 7.8 = 1.10

Which tells us that two 8" are 10% larger than three 6.5" drivers.

Again, the size of the driver has nothing to do with the distance from the speaker or the distance the speakers are from each other. The room and the prime seating position dictate those factors to a reasonable degree.

As to your particular problem with your front and center speakers, again, I'm more inclined to suspect the room rather than the speakers. Typically Center speakers are design for convenience rather than function. There is limited space to place them and that means a limited size, shape, and configuration for the Center speaker. Also, how close to the wall, and other general placement factors come into play.

You must absolutely and positively verify that all speaker are wired properly, that in every case the RED(+) of the amp goes to the RED(+) of the speaker.

Next, run setup on the AV amp and verify that the results it gives make sense.

Further, much of the dialog is directed toward the center speaker, it might help to bump the volume setting on just the Center.

The configuration, best guess of the B&W 9NT is tweeter, midrange, mid-bass, low-bass. I'm not sure what the model number is on the matching Center, but it is most likely mid-bass, tweeter, mid-bass.

Google-UK - Image Search - B&W 9NT

Wait, I found the Center model number -

Google-UK - Image Search - B&W CNT

These look like something near the current CM series or the older 700 series. These should be very good speakers, and I would expect them to preform very well. If that does not match your results, than I am more inclined to suspect setup and room acoustics.

For what it is worth.

Steve/bluewizard
 
Hi Steve
thanks for replying, as you say my room is not very good accoustically and I am at the moment fiddling with mats etc (tiled floor) to try and improve things rather than the "open chequebook" approach.
I am also experimenting by swopping the centre speaker with one of the L&R ones (your photos are correct) and by putting a 9NT in the centre has improved/altered the sound. There now seems to be more of a roundness to the centre although I think I now need to tweak the treble a bit to "crisp" the voices up a bit.
If that is the case I may try to find a 2nd hand pair of 9NT's and replace the centre with one of them.

kc
 
Yep I have tried turning up the centre channel but it did not cure the problem, however I have now been using one of my 9NT's as a centre for three days and both my wife and I have found a large improvement in speech quality. Two programmes that we know were giving us problems before the switch have improved 10 fold listening with the larger speaker as centre. we are going to continue with this setup till friday and then switch the speakers back - hopefully the dialogue will be noticeably worse and prove the cause and remedy of my problem
KC
 

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