Skrivet av Troelsgravesen :
”Now to the good question of what we can get away with! Should we make a 2-way from an 8" and a dome tweeter? Well, it all depends.
It depends on the actual 8" driver and we have to listen to different drivers because they're not equally bad despite same cone diameter and - on paper - same dispersion pattern. I launched a small study some years ago on two-ways from an 8" + dome tweeter. One of the drivers actually did quite well and the other didn't and I couldn't pin it down to a specific feature of one of the drivers over the other. My feeling is that that polyprop cone due to an usually smooth response and roll-off profile made the best match.
The thing is that mating the right 8" and finding a tweeter going down to 1.5 kHz may be possible, but in the end it still sounds like an 8+1 speaker! It has a distinct character due to the large driver having to handle everything up to 1.5 kHz. The dispersion pattern may look exactly as good as a 3-way, but the sound is very, very different. At higher frequencies the 8" driver cone also acts as a waveguide and this may count for some of the distinct sound.
Crossing over at 1.5 kHz is challenge and few dome tweeter like this - and some even require a steep 4th order filter to save it from voice coil burning. Most dome tweeters start having serious distortion when we get down below 1.5 kHz. My own solution to this in the TQWT and DTQWT constructions is to use a large dome fitted with a waveguide, a soft-cone 8" driver and a shallow slope crossover around 2 kHz. This way the dome helps the 8" in upper-mid and provides adequate dispersion in this critical range. For most domes we need 4th order filters so they don't "help" the 8" in its upper frequency band.
One way or the other, an 8" + dome is a compromise - as any other loudspeaker construction. Previously we saw numerous brands taking advantage of the 8+1, like Snell. But Snell used a very benign coated soft-cone Vifa driver. It had its strengths and weaknesses, but provided at lot of good sound for a modest price.
As you may know, I love the classic 3-way and so far, 4 constructions have been made. Adding a small 3-5 inch midrange solves the issue of dispersion in upper-mid and it doesn't cost much. End of story.”
Hela artikeln om beaming:
http://www.troelsgravesen.dk/Beaming.htm
