Few weeks ago, a member of CHIP’s forum asked me why do we need a powerful subwoofer (with big magnet, stiff/hard cone, and lots of power) in car audio application?
The question was actually simple, but it took time for me to answer it (since I had forgotten my physic class, anyway I was in social class, not science).
Before answering this, I want to turn back few years ago at my senior high age. At physic class, we all know the equation below:
Speed of sound = Wave Length x Frequency
or
c = λ * f
Let’s say we want to hear the low frequency at 30 Hz.
So, the wavelength is about 11.43 metre (343 divided by 30).The minimum range to hear this 30 Hz is about 1/4 of the wavelength or about 2.8575 metre.Do you have this distance from you subwoofer (at back seat or trunk) to your ears (driver’s ears)? I don’t think so. So, how can you enjoy this low frequency? That’s why most of the car subwoofer is designed with big magnet, stiff cone, weight materials, and big power handling. By doing this way, we all hope that the subwoofer can push the low to the highest limit and make sure that you can enjoy the low frequency (and eliminate shortest distance problem).
Picture above is Earthquake HoLeeS15 15″ Elite Competition Subwoofer.
Over 45 Kgs or 100 lbs, has dual 1 Ohm 4″x8″ voice coils (over 7000 RMS each) and over 4″ long throw excursion! Ready to rumble, eh?
Nothing special (I guess). Some car subwoofer are designed with low impedance (could be as low as 1 Ohm), so you will need a high current amplifier or put them in pararel configuration to achive lower impedance. The rest parameters shouldn’t be special. They all use the same T/S standard. You can input these parameters to your loudspeaker box designer (like WinISD) and design a correct box, even for your home use.I’m not saying that all car subwoofer can be used at home. It’s possible, but it depends on the designer of the subwoofer itself (whether he/she is able to design a correct box with these car drivers). It’s not about the gun, but the man (or woman) behind it.
Nam Nguyen
March 9, 2007 10:48in that paragraph you say to wire speakers in PARALLEL for a higher final resistance…what the hell??
Jimmy Auw
March 9, 2007 21:44My mistake, it should lower the impedance.
Thanks.
Clark Johnson
February 16, 2009 21:14Hi, Jimmy i regularly read posts in your blog and sometimes its a grt help brushing up my knowledge in audio.
I have one question with regards to the above post relating car woofers.
How could 12volt DC car battery provide enough power to such huge woofers???
Whereas we always find that one needs to use 25 to 35 volts of power supply for getting 30-50 watts of RMS power.
Hence how can I design for my home use, to get 30 watts per channel of rms power with just 12 volts 3amp transformer to get audiophile type sound with, lets say, a typical class AB type IC.
Kindly suggest!!
Good regards,
Clark
Jimmy Auw
February 16, 2009 21:30Hi,
Basically, in most car amplifier, we will use switching power supply (most likely, it’s a DC-DC Step Up power supply). So we will create higher voltage, based on 12VDC supplied by car’s battery.
I think you can figure out the rest. We can have higher voltage, so bigger power amplifier wont be any more problem.
And also, most car power amplifier are D-Class Amplifier design which have very high efficiency at minimum cost. So producing at least over 100 RMS wont be a big problem here.
For home usage, you can try to use LM IC (like LM1875, LM3875, etc). But it’s preferable to use symmetrical power transformer, with + and – voltage (switching power supply used at car will cost you the sound quality, so avoid it a home). Such IC above can be used with 15 to 25VDC (+ and – supply voltage).
Thank you.
Clark Johnson
February 17, 2009 20:31Thanks Jimmy, now its very clear to me.
I read earlier abt switching step up transformers but I had no idea that they produce inferior sound.
Now I already have with me, LM 1876 (20+20 watts stereo).
I also have an (18VDC 4 ams) transformer with me from my 14″ old TV set.
1) My question is can i use LM1876 with single supply application circuit as shown in national’s data sheet, with my above transformer??
2) Secondly i also want to build a stereo graphic equalizer with sony’s cxa 1352A ic.
will it be a good idea to pair it with LM 1876??
Also do i need to make any pre amplier with it ??? If yes kindly suggest how to place
the pre amp circuit, i.e. between equilizer circuit and power amp or before equalizer circuit.
Please reply
Thanks.
Jimmy Auw
February 17, 2009 20:58Hi,
Never tried 1876, only 1875. But you can use single supply as shown on the application datasheet.
I dont prefer to use equalizer. It will be better to use preamp than equalizer.
Thanks.
Clark Johnson
February 17, 2009 22:54Thanks Jimmy for your reply.
I shall follow it.
Skye Hussain
August 12, 2010 18:23i always bought Pioneer car amplifiers because they are of very good quality and the price is great too:’~
Auw Jimmy
August 13, 2010 23:28Nice choice bro…
Massage Cushion
October 19, 2010 00:27the best car amplifier that i used is made by ALPINE,*–