Don't stress over the fact that you can't get the last millimeter of bandwidth out of your CD player, when there are many other far more serious obstacles to sound quality. One is intermodulation distortion, which to a human is a much more objectionable artifact than a slightly truncated top end. Even more important is smooth frequency response, and since you have an FFT, you've no excuse for not getting that one nearly perfect!
That leads us into the topic of equalization and its effect on frequency response, and phase with its effect on imaging and staging. Equalization is pretty important, but I think that many enthusiasts who begin the quest for sound quality focus on the wrong approach. For instance, they will throw in equalization as an automatic fix for any acoustic or installation problem, which isn't going to work. The goal should be to build the system so that it sounds decent the first time you turn it on and set a few crossover points. Equalization is then used to "trim up" the system to as close to perfection as you can get. Once the frequency response is smooth (not to confuse with "flat"), the musical spectrum will sound good.
It won't, however, sound cohesive. You can have a fabulous sounding sonic character without ever having the instruments in the correct locations. This is where serious professionals tend to differ in their approach to "imaging and staging," which is about how phase affects the perceived location and placement of instruments on an imaginary stage in front of you. With carefully thought-out construction, a pro-built SQ vehicle will intentionally have speaker path length problems addressed to achieve naturally good imaging and staging. This is an easy concept that's very difficult to accomplish in the actual build. But when it all works out, it's amazing, and that's what pro installers are all about.
The other option to achieve staging and imaging is to use digital time correction to electrically delay signals to nearby speakers so that the information arrives at the non-central listening position in proper time alignment. This serves two purposes: It makes it easy to correct for speaker positions in general purpose systems where you aren't allowed to make serious changes to the vehicle just to accommodate the speaker positions. The other purpose is for when you're building a car that just won't allow you to place speakers in the optimum locations - digital time correction can be a really good alternative to an ideally installed system.
If your system is showing a dropout at the very top end, you might want to tweak a little bit of equalization to fool the meter. Remember more points are awarded for sound quality than for a perfect RTA reading. You need to decide where to focus your technology and energy.
Q: Hello! Hope you are all doing well. I've been a subscriber off and on for around 12 years now and have a couple of questions. I am NOT an installer so my questions are very, very simple, yet very, very confusing for me. First, what is the formula for figuring out impedances? Second, I have six 18" Hifonics Zeus subs that are still brand new in the box that I've had for 9 years now. They are 4-ohm subs and I'm most likely only going to use four of them. How do I get a 1-ohm impedance out of four 4-ohm subs? Do I parallel two and two, then parallel that? What if I used all six subs? What impedance could I get out of six 4-ohm subs? The reason I'm asking is because I hope to be able to get by with only one large sub amp - like the Rockford Fosgate 4,000-watt amp.
Next, I have two USD Waveguide A-700 horns that are 8 ohms. I'm planning on using a 4-channel Fosgate amp that's 100 x 4, but 200 x 4 at 2 ohms. So how can I get a 2-ohm load on the amp using the horns with midrange speakers? In other words, what impedance of mids could I use with the 8-ohm horns to get a 2-ohm load so I can get the most power out of the amp?
As you can see, most of my questions center around figuring impedance. I'm not going to compete this time around - I'm "old school" and 45 years old. I just want to put together a system that will hit at least 155dB and sound great with rock 'n' roll like AC/DC, Van Halen, Metallica, etc. I'd greatly appreciate your help on this - all the stereo shops I've called either give me wrong information or act like Ohm's law is a big secret!
One last thing. The Zeus 18" subs are rated at 400-watts continuous. I want to get the most out of them and I'm considering putting 600 watts on each sub. Since I'm most likely only going to use four of the six subs, I'll have two extra in case I blow a couple. How much power do you think I can safely put on the subs to get the most out of them? I'd greatly appreciate your help with this.
Sincerely,
Dave W. Thomas
Unadilla, GA
A: Thanks for being a longtime reader!
First, we don't really calculate impedances at the installation level, but we do calculate basic nominal impedances. For that you don't need a formula, but just a simple method of calculation. Providing all speakers are identical, if you connect all speakers in parallel, you just divide the nominal impedance of one speaker by the total number of speakers. For example, if you used all six subs and they were all 4 ohms each, then four divided by six equals 0.67 ohms when rounded off. So to get 1 ohm, use four subs all connected in parallel: four divided by four equals 1 ohm. As to the wiring, you simply connect all the positive speaker terminals together on the positive terminal on the amp, and all the negative speaker terminals to the negative terminal on the amp.
Since these speakers are 9 years old, I'd test them by running power through them in a basic cabinet before I committed to build the real enclosure you intend to use. You may find that the speakers have degraded and might just begin to come apart under power.