Propagation vs Speaker Resistance

Julian Croft · 2nd July 2011

Morning all

I have been wondering how speaker resistance affects propagation. How does having a higher resistance in the speakers affect the where the amp puts the power, I know its not heat as the drivers are not getting hot so where is the power going? The potential volume is less but it sounds more solid at 16 ohms than it does at 8 ohms.

What's happening?

Paul Spencer · 3rd July 2011

Julian,

This might sound nit picky, but this is about impedance rather than resistance. Resistance only applies to DC, audio is AC.

Speaker impedance affects the power output of an amplifier - an amp will put out more power into a lower impedance. Lets say you get 160w into 8 ohms, 4 ohms more like 230w. 16 ohms will mean less power yet again.

The damping factor is also affected. The higher the impedance, the higher the damping factor. In practice whether this translates into an audible improvement is another matter.

A speaker driver will probably not get hot. The critical part is the voice coil and you are likely to destroy the driver before the whole driver becomes hot.

I can't comment on why it sounds more solid at 16 ohms because what is causing the difference may not be related to the impedance directly. Do you have two speakers which differ in no other way than their impedance? There are so many ways in which a comparison can be misleading and lead to a wrong conclusion.

Julian Croft · 3rd July 2011

Hi Paul

The problem is this. I have been asked to consult on acoustics for a hi fi shop and they are topical installing B&W 800 series for the clients I will be working with but much varies in the system to system as far as bi wiring and bi amping with as you know uses two amp channels at 16 ohms one to drive the mid highs and the other yo drive the low driver rather than one amp at at 8 ohms for both.
The problem is the bi amp setup the sound travels a lot further into the surrounding neighbourhoods at a similar sound pressure level. I'm just not sure why.

How would the damping factor affect how the sound travel through the air at the same SPL and travel further?

they are favoring the bi amp setup as it has a remarkable improvement on sound quality.

Thanks

Dange · 4th July 2011

How sure are you on your statement "The problem is the bi amp setup the sound travels a lot further into the surrounding neighbourhoods at a similar sound pressure level"?

Generally SPL is SPL, however you could have the same SPL average across all frequencies, but with different spectual content. E.g. you have more bass less mid and it measures, 90dB at one metre. You could also have less bass and more mid and it still measures an average 90dB at one metre.

Once the soundwave has left the speaker, in broad terms the speaker has no further effect on the propagation. (An exception would be in the near field at high frequency, sound leaving one side of the loudspeaker meets sound from the other side of the loudspeaker an causes destructive intereference. This is related to the diameter of the cone though and measurement distance).

Julian Croft · 4th July 2011

so if I have it right it is a frequency power issue rather than a propagation issue, as SPL is SPL no matter where it came from. I should deal with it on a power frequency aspect as overall it is more power to the speaker as we are using 2 amps putting out 1/3 less power and it may sound better perhaps because the damping factor is higher.

I use RplusD for FFT but my laptop and external sound card was stolen so I still need to replace it before I can get different measurements.

2nd July 2011	#1
Julian Croft Gear Head Joined: Jun 2011 Posts: 41 Thread Starter	Propagation vs Speaker Resistance Morning all I have been wondering how speaker resistance affects propagation. How does having a higher resistance in the speakers affect the where the amp puts the power, I know its not heat as the drivers are not getting hot so where is the power going? The potential volume is less but it sounds more solid at 16 ohms than it does at 8 ohms. What's happening?

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3rd July 2011	#2
Paul Spencer Gear interested Joined: Oct 2010 Posts: 12	Julian, This might sound nit picky, but this is about impedance rather than resistance. Resistance only applies to DC, audio is AC. Speaker impedance affects the power output of an amplifier - an amp will put out more power into a lower impedance. Lets say you get 160w into 8 ohms, 4 ohms more like 230w. 16 ohms will mean less power yet again. The damping factor is also affected. The higher the impedance, the higher the damping factor. In practice whether this translates into an audible improvement is another matter. A speaker driver will probably not get hot. The critical part is the voice coil and you are likely to destroy the driver before the whole driver becomes hot. I can't comment on why it sounds more solid at 16 ohms because what is causing the difference may not be related to the impedance directly. Do you have two speakers which differ in no other way than their impedance? There are so many ways in which a comparison can be misleading and lead to a wrong conclusion.

4th July 2011	#4
Dange Lives for gear Joined: Feb 2008 Location: London, UK Posts: 857	How sure are you on your statement "The problem is the bi amp setup the sound travels a lot further into the surrounding neighbourhoods at a similar sound pressure level"? Generally SPL is SPL, however you could have the same SPL average across all frequencies, but with different spectual content. E.g. you have more bass less mid and it measures, 90dB at one metre. You could also have less bass and more mid and it still measures an average 90dB at one metre. Once the soundwave has left the speaker, in broad terms the speaker has no further effect on the propagation. (An exception would be in the near field at high frequency, sound leaving one side of the loudspeaker meets sound from the other side of the loudspeaker an causes destructive intereference. This is related to the diameter of the cone though and measurement distance).