![]() For this reason, to be an effective full range speaker, these drivers usually need special cabinet construction designed to enhance the bass output, such as a rear-loaded horn. Some (like Lowther) have very high efficiency, low excursion, and a frequency response graph that shows lowered sound pressure levels at medium to low bass (below 400 Hz). Driver units have quite different characteristics depending on the design and manufacturer. The whizzer cone type has two cones, a large cone (as in normal cone speakers) and a smaller whizzer cone inside the large cone. ![]() The center cap type looks like your normal cone speaker with a dome center cap. For example if you cross over the OB bass driver at 800Hz, it will be -6dB relative to the boxed driver at 400Hz, -12dB at 200Hz and -18db at 100Hz.Full-range (or wide-range) drivers come in two general types: the center cap and the whizzer cone. Look to others for the exact figures but if the OB has an 6dB/oct drop off compared to a box system, if you start with a 102dB/w driver rather than an 84dB/w driver you have 18dB of drop off (3 octaves?) before the bass output falls to that of the less efficient driver. Also the PA speaker will give you the extra efficiency that gets thrown away by not having a cabinet. It is the big panels of a box that are driven by bass drivers that move at lot more than treble units that cause the problem. The typically 6" car speaker would give you such small amounts of bass you miss out on the main benefit to me of OB- the lack of cabinet talk at lower frequencies. (the clue is how many cars could deal with a 15" speaker in the door?). Start with a PA speaker rather than a car audio one. The BMR covers the critical midband in its own so you have no crossover in that area. The BMR idea I mentioned did also include a crossover for the real bass end via something like a 12 or 15" driver. * Use a closed box low frequency driver, and only use full range driver in frequency range where baffle response is flat. Martin King has some designs like this see * Use extra driver of larger output, and fix in the crossover. ![]() ![]() * Electronic (active) boost to compensate There are several approaches to handling the bass rolloff: At higher frequencies, where the baffle is many wavelengths across, you more or less get the ordinary response and polar pattern of the driver. At lower frequencies (longer wavelengths) the air from the back of the driver runs round and partly cancels with the front, giving a fall in output of 6dB an octave, relative the same driver in an enclosure. ![]() The density of slate is of secondary help, but the damping is nice.įor a very good introduction to open baffle speakers, look at Ĭutting to the chase, when the baffle width is about a wavelength, you get peak output. ![]()
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