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| By: Ash on Fri, 3 Oct 12:43:50 -0500
| | This is a very important topic that is often overlooked, yet can be very vital when selectively thought out.
Midbass is simply the description of frequencies that occur between sub and mid frequencies. It is the range that gives sub bass definition and midrange realness. To further describe this, let's break down approximately what range this covers.
Subsonic to low bass frequencies mostly cover from 10 to about 80 hertz. Of course, this is where subwoofers lay. Mid frequencies actually spread from around 400 to 2000 Hertz. Around 2000 hertz and up, of course will be your high frequencies which are in the tweeter range. The realm of midbass lies between the sub and mid around 75 to 300 hertz.
Not a hard one to swallow, yet we may ask ourselves.... why do most upgraded car speaker systems consist just of a subwoofer and coaxials/or 2-way component set if it is so important? This is where you have to realize where the "market" dominates. Space and cost rule! So there is a compromise of usually of an overly expensive component set that can do it all or a mediocre lower cost one that can leave quite a bit of music out. Of course it would be nice to have just a simple speaker cover a broad range, if not all of the spectrum. Only problem, this is barely physically possible if reproduction is to be real and as close to the original recording as possible. Just like a job, everyone has a specific task that they do that adds to each other to produce a given product. If one person were to cover all the tasks, then there would be a large of amount of deficiency and possibly a lack of quality. Likewise in drivers, this can prove to be true as well. Thus you see the basics: sub, midrange, tweet. There is a downside to this as well, we will get to in a minute.
Now that you have, if you already haven't, grasped the basics of what ranges there are, we can talk about the dilemma of simplicity.
Of course it could be debated that a simple three speaker setup (sub, mid, tweeter) should cover everything. In fact, I would love to see it where it only consisted of two (bass/mid and tweet as in home audio). However, in a high SPL or pure SQL (car audio), each range must be covered accurately and efficiently as possible in order to squeeze the most potential of the signal that is available. Don't forget that they are playing in a harsh environment (noisy with intrusive frequency bumps and dips)! This means that each range (or task) should have it's own driver (worker) or one that is highly multifunctional (costly). This is where a potent midbass comes to play...
With a sole midbass driver(s), subs can be crossed over lower and just concentrate output into the range where they perform best, where music is felt. Likewise, midranges on the mainstay of music, where voices and instruments are the most intelligible. For neither one can do a exceptional job when they have to play out of their range to help cover another's . At lower volumes it may not be a problem but, when starting to reach their peak is when stress from overworking can occur. This is surely audible and can ruin even the most elaborate of "simple" setups. Bass will tend to get muddy or too snappy without depth. The definition in midrange can tend to breakup early as well. This can even preclude driver burnout if sustained at high volumes for long periods. It's either that or cross them at the proper point and lose some of the qualities that is supposed to be there. It's just not a good situation, especially after the money spent.
Not to say that all systems suffer from it, but a good solution that is most overlooked is to add or design from the begining separate driver(s) to further alleviate the other's task. This way bass can be played much deeper and midrange more clearer. The proper setup will add definition to low notes to help discern when they start and where they originate from (kicks, toms, low synths, etc). It also helps to add realism to voices (chestiness) and instruments in that range by giving them depth and impact. And most of all it helps to add to imaging by keeping the bass of the total system forward of the listener, helping to make "appear" that all sound is up front.
There is a downside to this as mentioned before. Because of the added drivers, crossover points, and placement, a 4-way setup (sub, midbass, midrange, tweeter) can introduce phase problems. Mainly with crossover points and placement. However, there is a way around this or in the least a way to minimize the problem. The simplest way is to use all active crossovers, unless you have access to a plethora of test equipment and time.
Next will be driver options as I attempt to touch on that subject. Remember what was stated earlier about "cost & space"? The majority of vehicles present only a simple infiinite baffle in which to accomodate drivers. There are some that have simple to complex enclosures built into the vehicle cavities, but not many. These are considered "premium" systems so I won't touch on that subject. However, since the infinite baffle is most common, a driver for that purpose can be chosen to maximize the install. I must stress, this cannot be done from the already put together component systems unless the manufacturer specifies so. You could easily assume that all are IB types, but "cost" can rule otherwise at times. To be sure of what you have, T/S parameters (Qts, Fs, Vas, Qes, Bl, etc) must be known.
A good overlooked source for these type of drivers are DIY companies like: Partsexpress, Madisound, Zalytron, David Levy Company, just a few to name. The first three are known for giving full driver specs including frequency plots. Another advantage: quality verses price is staggering considering what you will pay for normal car audio.
IB is simply a sealed box where the volume is up to 4 x the specific driver's Vas. In this event the drivers suspension is soley responsible for cone control. Output is also controlled by the Qts and Fs. If you modeled in a program the largest sealed box for a given woofer it, notice how it will never go below the driver's Qts. This can give an idea of what to look for in a IB compatible driver. Although, there are some drivers designed to play in the IB realm whose specs state otherwise, other parameters have been adjusted for such purpose. Here, we are concentrating on a simple and quick door location upgrade since kickpanels have become so popular.
For a start, look for drivers with a Qts from .38 on up to 1.2. A fairly low Fs around 30 to 60hz. Large Xmax is always a plus- 2.5mm minimum for a 5.25". For a 6.5"- 3 to 5mm is ideal. The lower Q speakers will tend to sound a little dry, but with a bit more midrange detail, these will also require the most xmax. As you move up the Qts chain, sound will become warmer to almost too tight and snappy at the high end of the Qts. Still all this will depend on the auto as well as the Fs. You will want as large a xmax that is available for the products you target to keep them from bottoming out as you crank them. Another factor that is important, but not wholly reliable is frequency response. Of course you will want one that presents the smoothest plot, but again realize that it can change drastically once installed in the vehicle.
A surprising aspect of this all is the vast array of high quality/ low cost 8 ohm drivers that is available. Yes, I said 8 ohms! Since, sensitivity is not rated the same as 4 ohm, more output than assumed can be attained with less amp strain. There are a plethora of these currently being used with great reviews ( check out Dayton's Reference series). On a bad note some extended depth will be required to use some of these drivers. Yet, if the space can be attained, good results can be had as well. Be sure to choose one that can withstand the auto environment or you may have to provide some extra protection.
Well this again is a quick, but not so quick brush up on what it is and what to look for. Creativity and some thorough research can go a long way in building a better stereo for it is just as much an art as it is a science.
This all makes for a simple upgrade especially if smaller kickpanel comps are used, for they can add the extra oomph for the comps and help fill in the gap between sub and mid.
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