Speakers 101

[purecarsound]

Speakers.

Speakers are the key to getting the music from the electronics to your ears, yet so often they are not given the same amount of importance as the rest of the equipment in the chain.

Let’s take a quick run through the various types of speakers that are likely to be installed in a vehicle and the Pro’s and Con’s of each.

The first type of speaker is the Coaxial. This is a single chassis speaker where the tweeter is mounted in the centre of the woofer. It in theory offers the best possible imagine as all the sound will be coming from one place. However as the car is not the ideal environment for audio often this advantage is more than wiped out by the fact it usually is hard to aim the tweeter where it is needed although more expensive Coaxial speakers may allow a certain amount of movement in the tweeter mounts – something which is very useful as you can then get good results from them.

The other thing that tends to limit coaxial speakers is they usually do not come with a proper crossover. What happens is you are left with a simple “bass blocker” on the tweeter to prevent it from blowing up, however the midrange part of the speaker is left completely unfiltered, often causing excessive harshness in the upper midrange. However, as the coaxial is normally a more budget option it is not as often a problem.

Moving up into component speaker’s gains the owner several key advantages over coaxial\'s. First and foremost is the ability to place the tweeter wherever he/she likes. A general rule of thumb is that if you enjoy a relaxing listen and normally travel alone then the tweeters in the foot wells is normally the best place for them – they are nearest the mids, and the path length between left and right is nearly equal giving the most “hi – fi” sound.

If you prefer a more detailed sound then often the tweeters on the “A” pillars about a third of the way across pointing at the middle of the screen (NOT towards you – it would sound harsh) is often a good place to start. I have found that when up there the slightest of movements is going to be very noticeable to the listener.

For loud listening silk tweeters are the way to go, with the smoother lower resolution sound they give. If you like a brighter treble, or are prepared to listen at lower volumes, but want a higher resolution sound then aluminum or titanium may be a better material to use (I personally use silk always over metal.) Again style of music, as well of style and preference of listening come into it.

Moving onto Subwoofers there are 3 common sizes, 10, 12 and 15.

The style of music and what you want to achieve come into the choices here once more. A 10 would be my choice for a rock driven system. Always sealed. For general use a 12” sealed is a great all round solution, and a ported 12 is also excellent for general street bumping. If you want more output then a ported 15 is an awesome provider of loud heavy bass and is the volume king.

General AVERAGE box sizes are as follows (in cubic feet…)
Sealed 10 -- 0.5 cubic feet.
Sealed 12 – 1.25 cubic feet.
Ported 12 – 2 cubic feet.
Ported 15 – 4.5 cubic feet.

Remember that on ported boxes the port has to be taken into account – and for modern low tuning high power enclosures this can easily account for up to another 50% of the box on a 12, or 25% on a 15. Also those are INTERNAL measurements – using common ¾ inch MDF 1 cubic foot is 13.5” x 13.5” x 13.5” externally.

Porting a box effectively doubles the output, meaning that you can actually get at least as much volume with one sub as you could with 2 sealed drivers. Also ported has a lot more aggression and “balls” down low. Often people say ported subwoofers don’t drop – that is a fallacy which is a result of cheap speakers and badly designed systems (and yes, some of the big makers are quite capable of selling you shoddy products of this nature) If you can get a ported box in your boot and want ground shaking bass then it is the way to go without any doubt.

Also porting a box is not something that can be guessed – it takes either designing to maker’s specs, or better still finding someone with the requisite computer software to design one to your needs. I am happy to design people boxes to their specs if required. Throughout the summer people should start seeing me at the cruise more often.

After considering which enclosure suits you best the next thing to do is to find the ideal driver to suit your needs. Things to consider are the power handling of the subwoofer, voice coil configuration, and sometimes some of the Thiele Small parameters (such as Vas, BL and XMAX) which will tell you of the speakers needs.

Generally speaking most speakers nowadays will work well in a sealed box as it is the smallest enclosure allowing you to fit more in the vehicle, so the makers often have that as a goal, as a car with 2 subs in not one is twice as profitable.

The voice coil configuration of your subwoofer is critical. With “DVC” (Dual Voice Coil) woofers it has also become easier to end up with a mismatched combo. Generally speaking too low impedance will cook your amplifier and also drain your battery power and too high the amp will not produce all its power.

NOTE – If a STEREO amp is “2 ohm stable” as 90% are, then it is 4 ohm stable when BRIDGED. Monoblocks are not bridgeable and therefore their stability is easier to work out.

If you have a 4 ohm “SVC” (single voice coil) woofer then it has a nominal 4 ohm impedance.

If you have a 4 ohm “DVC” woofer then you have either an 8 ohm or 2 ohm nominal impedance. Parallel wiring gives 2 ohms, Series 8.

If you have 2 4 ohm “DVC” woofers then you have either a 16 ohm, 4 ohm or 1 ohm SYSTEM nominal impedance. Parallel wiring gives 1 ohm, Series 16 and “Series Parallel” (Either Sub in series then in parallel with other sub, or Sub in parallel series\'d into other sub) wiring gives 4 ohms.

I wouldn’t worry too much about this – most reputable woofers come with good instructions nowadays. The point is that there are various system options and you need to choose accordingly.

As far as power handling goes, match the speaker to the amp +/- 20% and you should be fine.

Written by Dave Wilkins