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The first step in choosing a good subwoofer is determining your ideal crossover point. Usually, the lower you can cross over, the better. A 10-inch or 12-inch full-range box will not be able to be crossed over as low as a 15-inch full range box. Below 80-100 Hz, cone excursion and power requirement in full range boxes starts to rise tremendously. The more you can keep 80-100 Hz and lower out of your "top boxes," the better they will sound at high power.
To really know the importance of a good crossover point, you need to understand an important phenomenon called source localization . Source localization is how you perceive where a sound is coming from. Ideally, you want to perceive the sound coming out of your subwoofer full-range combination as a single source, not a dual source. You do not want to hear the subwoofer functioning as a separate unit. This becomes more pronounced as the distance between the subwoofer and mid-high speaker increase. For a good starting point, calculate the distance between the two components (in feet) and then divide that distance into 1130 (the average distance sound travels in one second.) This will give you the highest frequency you can cross over at. The equation looks like this:
Maximum Crossover Frequency Equation:
Maximum crossover freq. = [distance between components) / 1130
If this Fmax equation results in a frequency higher than 100 to 120 Hz, try to cross as low as your system output will handle at the sound pressure level you feel would represent the maximum output you will need. In other words, try to cross over as low as possible keeping in mind that both components need to be capable of the same acoustic output at that crossover point. If you need to cross over higher than 120 Hz, it's best for the speakers to be as close together as physically possible.
Next, make sure that your sub and mid-high speaker can obtain the same output at the crossover point. If for example, you choose 80 Hz, make sure your mid-high speaker can keep up with the subwoofer's output at 80 Hz. Usually, the larger the mid-bass component you use, the lower it can go. This also works the other way. An 18 inch speaker may not sound as clean and tight as a 15 inch speaker if you are trying to use a higher crossover point. We at Ramsdell Pro Audio always shoot for an 80 Hz crossover point if we can get it, but a lot of our customers like slightly higher ones in the 100 to 120 Hz area.
If you need to move lots of air in the 30 - 40 Hz region you will want to consider larger units like 18 or 21 inch subs. If your low frequency needs don't go lower than the 45 Hz region, consider a good 15 inch sub. When compared, the 15 inch subwoofer is usually tighter and cleaner, while the 18 inch sub moves more air in the lowest octaves.
- Choosing the Right Crossover Point
- General Rules to Follow to Get the Most Out of Your Subwoofer Investment
- What Type of Subwoofer Design Would be Best
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