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toymachine2628 10+ year member
Junior Member
- Thread Starter
- #31
Thank you so much! I am starting to understand.Actually a speaker can and does move both fast and slow at the same time. The best speakers do it quite well and they are the ones that give good midbass response. There is no hard and fast rule as to the exact frequency cutoff where sound is easily placeable as to its source. As such you try to get the front speakers going as low as possible to remove any chance of a random bass note suddenly placing itself as coming from the sub behind you.
Yes, the full spectrum of frequencies should be balanced and that is why getting good midbass is important. The resonance nodes of the typical car along with the typical speaker placement causes a cancellation node right in the middle of the midbass range and most car installs horribly lack midbass. This leads many to turn up the low pass freq on the subs which then drags the midbass range to being localized as coming from the subs. Totally wrecks the soundstage when it sounds like the band is in front of you except for the bass player and the drum kit is spread all over the place.
As driver diameter increases it also tends to cause an effect called beaming. The freq at which a driver beams is inversly proportional to its diameter. So a large diameter driver beams at a lower freq than a smaller one. A driver that is playing above its beam freq displays a very focused dispersion pattern and the response off axis gets pretty ragged. This is one of the reasons that tweets are small. The other problem associated with driver size is breakup. As a large diaphram tries to reproduce a high freq, the cone begins to flex and ad harmonic content that colors the sound. Smaller drivers can be made stiffer than larger ones for a given mass. High stiffness to mass ratios become important because of voicecoil inductance. To move a heavy cone you need a large voicecoil. A large voicecoil will have a higher inductance which will limit the upper range of the driver's response. High freq drivers need to have a very low inductance and thus need a small coil.
The end result of all of this is that the ideal setup would be a driver able to play from below 20Hz to above 20kHz by itself. This isn't possible so the next best thing is to have a single driver cover as much of the audible spectrum as possible. To this end most DIY guys try to find a tweeter that will play as low as possible allowing them to pair them with a larger midrange. The larger cone area of the midrange allows it to play down low with some authority and limiting it on the top end keeps it from beaming and/or breaking up at higher freqs. The other way that this is handled is to run a 3-way front stage where the midrange plays well up into the freq normally handled by the tweeter in a 2-way setup leaving a dedicated midbass driver and the tweet to fill in the rest. Either method can yield excellent results depending on the specific goals of the system.
Notice I didnt' even mention the subs. If the front stage is done right, the subs are almost an afterthought. They will only cover the bottom octave and a half at most.