Article: Dutch & Dutch 8c Loudspeaker Review

[dc655321]

Nice review, @mitchco.

I'd like to hear your thoughts on the acoustic/electric design of the rear-facing subs of the 8c, as it's unclear to me if the subs are designed to also produce or contribute to the controlled (cardioid?) radiation pattern. From the video clip you shared, it appears to my eyes that the subs are out of phase with each other. I could be deceived about this though given that only a small piece of the bottom driver is visible.

 

Given the recommended proximity to the front-wall, the subs will pick up some boundary gain. They will also radiate half of their power around the enclosure (less so if significant radiation-shaping is in play). Do the enclosed back-waves also contribute here? Add to this recipe the blending of the subs with the mid-range speaker and the result is that I'm both super-impressed and super-confused ?

 

A little help, please?

[dc655321]

30 minutes ago, mensink said:

 

Hi @dc655321!

 

The 8c conceptually is quite unlike conventional loudspeakers. In the midrange (100 - 1250 hz) the radiation pattern is more or less cardioid. The waveguided tweeter has directivity that matches with the cardioid quite well. Below 100 hz I initially considered going cardioid as well, but you sacrifice a lot of headroom in order to do it and the benefits of a cardioid in the modal range (the frequency range where standing waves dominate what you hear, not the loudspeaker itself) a questionable. Then I remembered the work of the late Roy Allison. He came up with the idea of coupling a speaker and the wall, in order to deal with the early wall reflection. In the 8c a very welcome additional benefit of boudary-coupling is that the wall increases the directivity in the bass, for a better directivity match with the cardioid midrange. 

 

The two woofers in the back only do bass below 100 hz, they get the exact same signal. The visual effect you describe is probably the effect of aliasing. The woofers in the back don't work together with the midrange driver or the slots in the sides to create the cardioid pattern. In the midrange the directivity pattern of the 8c is strictly the result of the acoustic cardioid that is formed by the midrange driver frontwave and its filtered backwave, through the vents in the sides. 

 

What I as the designer personally think is really cool about the acoustic cardioid, is that it kills two birds with one stone: you get the very welcome cardioid radiation pattern, but you also deal with the backwave of the midrange driver, but putting it to use instead of having to go to great lengths to keep it contained inside the cabinet and turn it into heat. 

 

Thanks for addressing my question(s), Martijn. Your time and expertise are much appreciated!

Again, fantastic design you've achieved here. Very elegant engineering.