Help fixing massive 20dB peak!!

I can see that NicolasB can't be pursuded to change his mind and like him I will just be repeating what I've already said. He is wrong and when he relaxes his grip on peices of string he might get somewhere.

I will just point people again to the Harman White Papers on speaker positioning and standing waves and in particular NicolasB to the bottom 2 pictures on page 11 of the Loudspeakers&roomPt3.pdf. The papers are produced by one of the largest audio companies in the world and by Dr. Floyd E. Toole a world leader in acoustic science. Ignoring any technical arguments the positioning advice in the paper is the same as I recommend not as NicolasB recommends.

For anyone interested in understanding their room acoustics I also recommend buying or borrowing the 'Master Handbook of Acoustics' about £20 from online bookstores.
 
wow thanks alot guys.

I haven't the time to read it all now (i will later promise)

Just like to add, with the use of the graph i've managed to record a new curve from about 20Hz - 160Hz which is +/-9dB, a big change from >20dB peaks i'm sure you'll all agree!

1 more question, my front door is inline with my seating position, does this mean the standing waves across the width will be weak at the seating position as energy is lost through the wooden door? in effect the room ceases to be 13ft as there is no brick wall on one side.

Much apreciated

Dom.
 
these highly technical explanations are fantastic
I'm actually slightly miffed that you should regard them as "highly technical" - they're designed for someone who doesn't have much grasp of physics, hence all the analogies about strings and springs.

This isn't exactly degree-level. In my day it was in the Physics O-Level syllabus. I would imagine it's still in the GCSE syllabus now.
 
Dom I'm glad all this has improved your sound.

Good one with the door. The door will have an effect due to it's differing acoustic properties. Calculating it would be complex I think and it's surface area in relation to the brick wall will be small. So it won't throw out the calculations too much. Changes in air pressure/temperature between days will have more effect on the calculations as sound travels at different speeds depending on the air pressure.

Incidentaly opening the front door would act as a perfect bass trap as any sound wave hitting the opening can't reflect and will dissappear outside. It would be cold in winter :D
 
Ahhhh.... I see what the problem is: you're talking about variations in pressure, where I'm talking about the movement of air. (Not surprising I couldn't figure out what you were talking about with all that gibberish about "polarity" and vacuums).

Yes: areas of high pressure variation correspond to areas of low oscillation of air molecules, and vice versa. So, in air movement terms the wall is a node - the air is stationary at that point. (It has to be because the molecules can't flow backwards and forwards through the wall). But in pressure variation terms it's an anti-node.

What a subwoofer does is to cause air to move to and fro. To cause it to excite as little standing wave as possible, you need to put it where the air is moving the most - at an air-movement anti-node. (As I've already explained at some length). But in pressure variation terms that's a node.

Either way, you're actually talking about the same point! As far as the first harmonic is concerned, the centre of the room is a pressure node and a movement antinode, so, whichever way you choose to describe it, putting the subwoofer in the middle of the room is the best possible place to minimise the first harmonic.

And the rest of what has been said previously also applies: the centre of the room is the optimum position for reducing odd-numbered harmonics, but it's the worst possible position for the even-numbered harmonica, so there are going to be trade-offs....
 
Originally posted by NicolasB
This is called a "longitudinal" or "compression" wave. It behaves much the same way as a "transverse" (side to side) wave, and can be described in the same way. The distance between regions of maxmimum compression is the wavelength. How much closer together or farther apart the coils are is the "amplitude" of the wave - analogous to the "height" of a transverse wave.

Riiiight! Just the sort of talk I use down the pub or might have heard in the playground while at school.

I'm not much younger than you are Nic AND passed A-level physics - however I was refering to these sort of posts as highly technical in COMPARISON with others here such as those that quote well-known "hifi magazine speak", such as "keep it away from walls & corners" without backing them up with technical data. This forum is the better for both kinds too IMO.

:)
 
What! Ack, my brain is about to explode! Surely if the pressure increases in a given area, it means air molecules have moved into that area, and vice versa... So when pressure is changing between high and low, it means air molecules are rushing in and out of it... So how can you have an area of high pressure variation that isn't also an area of great air movement??

I'm so confused.......

Dunc
 
Personally speaking I'm as thick as the FA's hearing list and all this physics means nothing to me yet I have a freq response from 10-75Hz that is +1/-1db..................something to be said for enthusiasm over knowledge IMO.
 
Originally posted by NicolasB
Ahhhh.... I see what the problem is: you're talking about variations in pressure, where I'm talking about the movement of air. (Not surprising I couldn't figure out what you were talking about with all that gibberish about "polarity" and vacuums).

For the Gibberish comment I will have to point out that I used pressure several times in my replys.

Next time we will have to agree on the standards before hand.
 
just to add i've got it down to around +/-3dB with 1 peak of about 9dB. Sounds silky smooth, the bass blends in seamlessly
 
Great, it is not as difficult as it looks, if you know the principles... ;)
 

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