You know, in chapter one we see a hypothetical but also very typical circumstance. The first car stereo purchase by a person of average intelligence and equipped with average knowledge about car stereo. I know the story to be accurate because I was that person once, and remember my first experiences. I have since that time also been the other person, the salesman. I specialized in car audio sales for several years and watched thousands of people go though the same experience. I am still learning new things about audio almost every week, and I own a loudspeaker company where we design and manufacture high end home speakers and high performance sub woofer enclosures for car audio. If after all these years of experience I can admit that there's more to learn, you should feel more comfortable doing the same. First of all, to finish our story in chapter one, a sequence of events takes place which is all too common for the average car audio consumer. Lets call our character in chapter one Fred. After about 3 weeks, Fred becomes somewhat displacement about his stereo. He has taken several critical listens to everyone else's stereos, and while better than 2 he heard, his system just doesn't measure up. The biggest problem is the bass and distortion. Not enough of one and too much of the other. Had Fred purchased his stereo from the stereo store he went to instead of Wally World (or whatever), it is probable that he would have received a better system for around the same money. However probable is not to say always, it could have been the same and in some instances worse. It really depends on the credibility of the store you deal with and the expertise and experience of their staff. Trust me, it is better to pay more money for something if it comes with a knowledgeable human to help you use it, and to fix it if it breaks. Saving 15 or 20 dollars on a car stereo component is usually the same thing as spending twice that if it means being on you own vs. having a store with people you can depend on to help you. If money is a concern but not a serious deal, then my advise would be to find a small to medium size specialty shop that carries a good reputation with custom work. If they don't do custom work, find another shop. Find a sales person you are comfortable with and give him a very GENERAL idea of what you want, let him know you trust him, and tell him to do whatever he wants. Give him a reasonable spending limit, between 1500 and 5000 dollars, and have them call you when they are done. In a specialty shop with a competent reputation, their personal pride will guarantee you get more than your moneys worth, and the system will sound good. For some of however, it's the hands on that makes car audio so exciting. There is a great feeling in listening to a system that you've worked on and as a result of, increased your education in audio by leaps and bounds. For others it's just being in charge of deciding what goes in and where it goes. This book will explain some fundamental truths about audio and cars, truths which are not always parallel with everything you read and see in the stereo shops. Marketing and its necessity for "Buzzwords" does not always display information in an accurate light. Back to Fred. Fred's problem is that the bass only sounds good at low levels. When he turns up the volume everything sounds crappie. Since Fred likes to party, Fred on several occasions has elected to ignore the fact that it sounds crappie and play it as loud as he could. Fred simply wants to enjoy his stereo. The last time Fred did this, one of his speakers blew up. Fred can't understand how a speaker rated at 150 watts could get blown up by an amp that only puts out 100 watts! Fred knows he can probably get the speaker replaced but is so frustrated that he now has the urge to go back to the stereo shop and complain about his situation. Unfortunately the sales people at the stereo shop couldn't find much sympathy for Fred since he took an hour of their time and then bought his stereo somewhere else. "Fred" was my stereotype customer who was sent over hearing that I was sort of a Maverick in the local audio industry. I spent hundreds of hours talking to hundreds of Fred's. In each case it took a crash course in car audio, an injection of knowledge before I could really help them. Sometimes the injections were too big and I lost a few, and sometimes the injections had no effect at all. But for those with a strong common sense, the reward was great, they got their stereo sounding great and did it without being sucked into the marketing hype and spending more money than they should have. Lets just bring Fred over and see what we can do for him. There is a knock on the door. Guess who it is? Yup, its Fred. "Hello, are you Steve?" he asks. We walk out to his car. It's a 1979 Chevy Nova with a little rust on the drivers door. The first thing I do is ask him to open the trunk. He wants me to listen to it first. I tell him to turn it on and proceed to listen to it. The first thing I do is turn all of the adjustments on the cassette deck to flat. Set the balance to the center position, and do the same with the Fader. I felt sorry for him right away. The sound was thin, there were no highs, bass was barely there and when you turned it up the sub woofer got muddy. Fred exclaims that you have to turn the bass up to make it sound bad. Knowing full well what he meant I asked him why he would want to make it sound bad! He returns with a dumfounded look and says "Yea but there is no bass." OK, go ahead and show me I said as he turned the bass up and demonstrated the distortion. Fred also mentions that this is a lot better than it was before because some guy put the dash speakers on their own amplifier. Before he did that they were hooked up to the cassette deck and distorted real bad when you turned the bass up. I asked Fred what kind of amp did he buy for the dash speakers, and he took me back to the now open trunk and showed me. It was a little tiny thing that used a 5 AMP fuse. On the case was written 40 x 2 max. power. He boasted "Yea, and it was only 39.00!" Fred's system consists of the following: Cassette deck - valued at 219.00 with RCA outputs for rear out. 5.25 Coaxial Door speakers located in the doors. Value 79.00. A band pass box using 2 10" woofers. Value 179.00. An amplifier claiming 200 x 2 max. power Value 179.00. An amplifier claiming 40 x 2 max. power Value 29.00. An 2 way electronic crossover Value 59.00. Fred, I said, come in here for a minute and sit down. We need to talk... Fred followed me inside and sat down. He made himself comfortable and we proceeded to talk. First of all you don't have anywhere near enough bass, right? His eyes lit up, and he nods his head while scooting to the edge of his seat. Amazing how bass effects people isn't it? Your system is letting you down. Think of it like a car that only goes 56 miles an hour. Everyone wants to pass it on the highway, and since you have to floor it to go 56 miles an hour your car is always breaking. I'll bet you've blown a speaker haven't you. Fred sits up and admits that its happened twice. He continued that someone told him he needed a crossover so that the dash speakers wouldn't pop and crackle with every bass note. He then added that he also had to buy a little amp which he did. So you bought an active crossover and a second little amp to run your dash speakers right? He nodded. Fred stops me and insists "What is wrong with it anyway?" Well, I said, your sub woofer is a little under powered, your power cable running from the battery to the amp is barely big enough to service the sub amp. Adding the second amplifier increased this problem. The second amplifier isn't any good at all. The door speakers are crossed over a little high, and could be re-installed to sound twice as good in the same door. The frequency response on the tape head in your cassette deck only goes down to 50 cycles. Your box is tuned at 40 Hz and in an effort to hear base you're increasing the gain at 80hz with the bass control which makes the 50hz notes play half as loud which means you really can barely hear them. The small amplifier has poorer specs than the amplifier in your cassette deck, and about the same power. The gain control on the small amp is set too high, and the gain on the sub amp is also set too high. The efficiency of the front speakers are 91db at 1 watt, and the sub woofer has an efficiency of 87db (typical in cheaper sub woofer packages). That means to play at the same loudness the sub woofer needs over twice the power. The smaller amp has a total of about 30 watts clean, and the bigger amp is only about 90 watts clean. So you see they play at the same volume. What you want is for the sub woofer to play at a level 3 to 9 dB louder than the front speakers. To do that you could double the power of your sub amp 3 times, or get a better sub woofer. I recommend the later. The simplified secret to good audio is balance. You want to hear each note in the music without coloration. If your system exhibits real peaky frequency response that is coloration. In Fig. 1 we show a graph of each frequency our ears can hear. The lowest note is 20 cycles per second. If take the speed of sound and divide it by 20 you will see that the sound wave travels over 40 feet before the next wave follows it. So a 20 cycle note would be 20 waves spaced around 40 feet apart in one second. The highest note we can hear is 20,000 cycles. Most music does not exceed 16,000 cycles. Some people can't hear past 12,000 cycles, and if for example you were to continue to listen to your car stereo when it is distorting for another year your will be one of them. Fred has now taken the poise of a tree stump, motionless on the couch and in some sort of a daze. The bomb has been dropped. Poor Fred, all he ever did is try to buy a car stereo.
FIG. 1 If you examine fig 1 again, you see a solid line and a dashed line. At the far left the graph represents 20 cycles. At the far right the graph represents 20,000 cycles. The solid line lays fairly flat. That means all the notes will play at the same volume. This way you can hear all of the notes. If you look at the dashed line you will see it is very peaky. The peaks represent notes that are way too loud. The dips are notes that are way to soft. When dips and peaks are close together you cannot hear any of the notes in the dips. In Fred's case, his bass response sounds like it only goes down to about 75 cycles, in other words no bass, when in fact it can reproduce 50 cycles. Fred created a large peak at 80 cycles with his bass control, and then another one at 120 cycles. The dashed line is an accurate representation of the average frequency response found in cars. Cars have very different acoustics than houses. Cars are different than living rooms in two ways where stereo is concerned. The first is that the noise floor (noise around you) is bass heavy and fairly high, around 80db. A living room can reach a noise floor as low as 40 dB in the evenings. This means car stereos must have more power than home stereos just to sound like home stereos. The second is that rooms effect dramatically how the frequency response will balance out. A car is so small that we're not sure if we should treat it like a room or another box. When you put a box inside of another larger box, an interesting thing happens. The low bass is amplified. This is referred to as "cabin gain". So it should be easier to get bass in a car then in a living room you ask? If you consider only the two different types of rooms, yes. To make a long story short Fred, what you need to do is leave me your car, and come back outside so I can show you some things about your sub woofer box. Fred, now carrying the weight of the world on his shoulders slumps a little and then pops up to his feet. He follows as we go back outside. At the trunk, we look at his box. It is about 4 feet wide and 13" tall. It is crammed as close to the back seat as possible. The trunk is full of rattles, and the box itself is so thin that it too is creating a very annoying peak at around 400 cycles. Fred given your two options of doubling your amplifier power 3 times or getting a new sub woofer, I would recommend getting a new sub woofer. Fred thinks for a minute and asks how much power would that be. I pointed out that at a rating of 200 x 2 max. power he should get one that is 3200 watts. Fred hits his head on the trunk lid and starts to turn a little white. Then he realizes they don't make an amplifier that big. If they did, and if Fred could afford it, the cheap sub woofer wouldn't handle the power anyway. I think its time to let Fred off the hook, before he melts. But not until we bring him back up with a little tease. I unhook his box and take it into the shop. In there I have 20 or so different sub woofers on a switcher for demonstration and testing reasons. I hooked up his box to switch one. His box has two tens, with an efficiency of 87db. I demonstrated his box on a good flat CD source on an amplifier similar to his own. His eyes got big when for the first time he heard 50 cycle notes from his box. He starts to speak... I hold up my hand and tell him to hold on, and let me finish. This I said is what your box should sound like. This is as good as your box can sound. If you buy an indash CD player you can achieve this sound, if you only listen to your box in this show room. Fred, your box is a little large for your trunk. In fact it is so large that it obstructs the air flow in your trunk and does not breath properly. Fred is amazed. I then hook up a properly and professionally built box, also a band pass, about 1/2 the size using only one 10 inch woofer. I let Fred hold the button and tell him to wait till the music plays and then flip the switch. I explained that what will happen is that the smaller sub woofer will start playing instead of his, all without changing the signal going to the box. Fred lets the music play for a bit. I choose Mariah Carey, because there is a rich harmonic bass line centered around 35 Hz. Fred's box begins to roll off at 45hz, and at 35hz is playing only half as loud. The smaller sub woofer has a reference efficiency of 91db and is ported to achieve 12 dB of gain centered at 38hz. That makes it well over twice as loud as Fred's box on 35hz frequencies. Fred flips the switch, and a bass note straight from hell rips through our pant legs. Fred almost knocked over a speaker setting on the bench just behind him. Fred was flabbergasted. It took about 15 minutes for Fred to wind back down and he realized the story about his grandma's bird bath which he was somehow in the middle of telling... oh well. Twice as loud with half as much. This is the difference between a good box and a bad box. What makes a good box good is design and craftsman ship, and the proper materials. Just for kicks, and since he asked, I decided to let Fred hear the 28 cubic foot folded horn over in the corner. He walked over to it and stood directly in front of the horn throat. I suggested he get over here across the room with me where its safe. He laughed, and then realized I might actually not be kidding and came over. "OK," I said, "Now your going to hear all the notes we've been talking about for the past hour." I reached around behind me and flipped on my vacuum tube frequency generator and let it warm up. I switched the signal back to Fred's box, and adjusted the dial for 100 cycles. I turned it up until the box started to hack, and backed it off a little. "This is 100 cycles," I said. I then slowly rolled the dial down until the bass reached 45 cycles. The box was starting to get quieter fast. I continued to turn the dial until I reached 30 cycles. Now the box was just making a soft puffing sound. I continued to turn the dial until I reached 20 cycles and either of us heard anything at all. A short discussion followed, and then without adjusting the volume, I returned the dial to 100 cycles. I pointed to the switch and Fred knew what to do. Pow! On came the Imperial which was using one 12" woofer at the time. It was about 15 dB louder than Fred's box. We had to turn it down. Arriving at the same level that we heard on Fred's box, I continued. As I turned the dial down the bass kept increasing until at 50 cycles we had to turn it down again. Finally I finished at 12 cycles and you could feel the concrete floor resonate, and when we talked our voices went up and down. It was a unique twist on the Doppler effect. The folded horn had a sweet spot at 28.5 cycles in this particular room so I turned the volume down and adjusted the dial to that frequency. I then turned to Fred to see if he was ready. Grinning with anticipation, I turned the volume up to one quarter. The bass was so deep and so strong that the cabinet doors on the wall started to open. I increased the volume to one half and the experience started resembling an elephant sitting on your chest 28 times a second. I held it there until a multitude of things started falling off the shelves, and then backed it off, and shut it down. Fred was no longer carrying the weight of the world on his shoulders. If bass were like drugs, and it is, Fred just about had an overdose! On the way back out to his car Fred asked me if I could make him a box, and he would sell the one he has. I told him to sell the small amplifier as well, and come back with two tweeters, and some better power wire. An hour latter Fred returned with two tweeters and some of the fat red power wire, and a noise filter. Pretty soon we are going to take Fred's car stereo and re- install it but before we do that, we need to go over some of the basic facts about car stereo components. One of the most miss- understood things is BASS and how to achieve it efficiently. The next chapter will clue you in on how bass works and the most common problem found in car stereo systems, cancellation. If BASS is Superman, then Cancellation is Kryptonite