Hi,

As a hobby, I am currently spending some time to understand the physic behind speakers design (most of my readings are on this forum, diyaudio + F Toole book). There is one subject which is often discussed and is still not clear for me: drivers spacing on front baffle in particular between mid and tweeter).

Until now, I was on line with the simple theory: the closest the better (ideally within 0.5 wavelength of the XO) in order to avoid vertical off axis nulls around crossover frequency. It is easy to simulate with xdir software.

But then I read the following post of kimmosto (creator of vituixcad simulator) which clearly has a huge expertise in the subject i quote:

"As close as possible' could be 'the worst possible' for directivity index i.e. either on axis (~listening window) or power response or both should be compromised to get balanced sound.

Of course if minimal vertical lobing is priority #1 then you should locate as close as possible. Coaxial driver wins that game always, but otherwise not necessarily...probably.

With simplified theory c-c = 1/2 wave length is the worst case for power response with equal DIs, and c-c = wave length at XO is the best case. Simply because sum with difference of 1/2 wave length is null and vertical +/-90 deg have the biggest weight in power calculation (due to dual orbit data to spherical intensity conversion). Early vertical reflections have significance too and DI of different radiators are not always equal => the smoothest DI and ERDI is found when c-c = 1.0-1.4 x wave length. This means that possibility of the worst DI is when c-c = 0.5-0.7 x wave length."

If my understanding is correct, the power response of a speaker is more important than vertical off axis. Hence, in order to obtain the best drivers position on front baffle, one should measure each driver on and off axis and use a software (vituixcad for instance) to calculate the power response with respect to frequence to find the best driver spacing. The off axis dispersion is then something we deal with, not that important as long as the listener is within speaker axis.

Is my understanding correct ? If yes, do you agree with the statement ? Sorry if I missed a similar thread.

I suppose the next step for me is to download vituixcad and start playing with it.

Edit : I post on the wrong place... I dont find how to move my post to "Room Acoustics and General Speaker Discussion", if a someone could help or move it ?. Thx !

As a hobby, I am currently spending some time to understand the physic behind speakers design (most of my readings are on this forum, diyaudio + F Toole book). There is one subject which is often discussed and is still not clear for me: drivers spacing on front baffle in particular between mid and tweeter).

Until now, I was on line with the simple theory: the closest the better (ideally within 0.5 wavelength of the XO) in order to avoid vertical off axis nulls around crossover frequency. It is easy to simulate with xdir software.

But then I read the following post of kimmosto (creator of vituixcad simulator) which clearly has a huge expertise in the subject i quote:

"As close as possible' could be 'the worst possible' for directivity index i.e. either on axis (~listening window) or power response or both should be compromised to get balanced sound.

Of course if minimal vertical lobing is priority #1 then you should locate as close as possible. Coaxial driver wins that game always, but otherwise not necessarily...probably.

With simplified theory c-c = 1/2 wave length is the worst case for power response with equal DIs, and c-c = wave length at XO is the best case. Simply because sum with difference of 1/2 wave length is null and vertical +/-90 deg have the biggest weight in power calculation (due to dual orbit data to spherical intensity conversion). Early vertical reflections have significance too and DI of different radiators are not always equal => the smoothest DI and ERDI is found when c-c = 1.0-1.4 x wave length. This means that possibility of the worst DI is when c-c = 0.5-0.7 x wave length."

If my understanding is correct, the power response of a speaker is more important than vertical off axis. Hence, in order to obtain the best drivers position on front baffle, one should measure each driver on and off axis and use a software (vituixcad for instance) to calculate the power response with respect to frequence to find the best driver spacing. The off axis dispersion is then something we deal with, not that important as long as the listener is within speaker axis.

Is my understanding correct ? If yes, do you agree with the statement ? Sorry if I missed a similar thread.

I suppose the next step for me is to download vituixcad and start playing with it.

Edit : I post on the wrong place... I dont find how to move my post to "Room Acoustics and General Speaker Discussion", if a someone could help or move it ?. Thx !

Last edited: