A sphere doesn't help to get away with the reflection but with the diffraction. A tweeter mounted on a baffle will face more amount diffraction than a sphere would. Sphere simply reduces the amount diffraction that occurs compared to baffle. Tweeters installed on A-pillers are prone to have more reflection than having them on sail panel / doors / kick panel. But diffraction on the A-piller is less than what would happen on doors or sail panels. With reduced diffraction and placing them 90 deg off-axis on the it makes up some what against the reflection coming off the windscreen. But, most importantly it's the nature of the tweeter that also matters here. Some tweeters by nature deliver bright sound, some are warm, some sound laid back when played them in free air. At times, reflection caused by the windscreen is good in case of some tweeters where it aids in wider dispersion. For instance Morel's dome tweeters, they sound very detailed irrespective of whether you play them on or off-axis. But, what makes a difference in on-axis is the amount of space it adds to the sound, vocals have more depth and it stays cleaner even on high volume. For now, mine are installed A-piller with 90 deg off-axis. But, here's what I have done for the time being. I cut the tennis ball in 2 equal halves and placed them behind the tweeter magnet, it acts as an enclosure to the tweeters. Result, well instantly I realised that the tweeters were sounding more lively, it adds like a reverb effect, more detailed and added more space to it. Had to cut down to -3 db on them.
Determining what size of sphere enclosure is needed for one, depends on what freq. you would limit them to. With reduced diffraction the result will be less amount peaks and deeps in freq response resulting in much smoother response. Peaks and dips in freq. range adds to the way tweeter behaves when played with higher volume. With more amount of peaks and dips caused by diffraction, tweeter may land up sounding harsh when being pushed to the limit. Diffraction is a matter of concern with freq. above 1khz. It can make the music sound harsh on higher volume even when playing the best tweeter available in the market.
Cure to diffraction is not just about adding the sphere enclosure to the tweeter. But, it's also about the placement and where the tweeter is pointing. Not all like the sound coming from it. We are so accustomed to the traditional way of installation and the way it sounds that at times some really don't see any sense going for it and prefer the traditional way. But, for me, it sounds in away where it gives me a feeling that all the highs coming just from one place or off the center and not from left or right corners.
The plan is to use the sphere, mount it on custom fabricated stand that I am making which would be 4" off the dashboard, 4" away from the windscreen, 2-3" away from the A-piller, pointing / facing both the tweeter towards the rear view mirror. Stand is already under fabrication, once it's done will be under going for powder coating. And finally mount the Sphere enclosure on it. I have already tested this position. The result were much better. Could hear every detail in vocals. It added a lot more space / presence to the overall sound. As of now they are running under passive, but soon will be going active with these with 100 RMS on each. Apart from this, it's always better to play around with the phase. You will be surprised as to the difference it could make. Greenh0rn: A sphere has no edges and usually the diffraction occurs on the edges as the music from the tweeter starts dispersing. Once it reaches the edge of the baffle, there are peaks and dips that occur in the freq. response. This could make one believe that the tweeter are brighter or they lack detail. Note the tweeter quality and characteristics also plays the role here. Some tweeters when played on-axis tend to sound much brighter and harsh, that is because one it's the characteristics, two there is both diffraction and reflection making the sound for the person to conclude that indeed the tweeter is bright by nature. But, in some case if the tweeter is of higher quality it can make them sound detailed. In other words reflection cannot be controlled in car environment but diffraction can, it can be reduced to some extent where reflection doesn't play the spoilsport and muddies the sound, in a way some reduced reflection result.
This can also reduce the much need of the individual EQ required to make it sound balanced. GILL: Dyn's are power hungry and also slightly less efficient. I would say if you really want Dyn's to sing, play them in Active with loads of power. There will be day and night difference as to the way they will sing. |