Amplifiers… What’s in a Number?

Recently I’ve caught a bit of a car audio bug while working on my sons recently acquired Mustang. We had the JVC KD-SX980 head unit from his wrecked Eclipse and he asked if I could put it in the Mustang. Having taken the time to remove it from Eclipse this had been the general idea. Long story short… The Mustang needed quite a bit of work.

1) No front speakers… Just wires where the speakers had been cut.
2) Only 2 rear 6x9 speakers, mounted in a hacked up rear deck mounts made for 6x8s
3) Factory Amp only had Left side working (which translated to only 1 speaker working in the entire car)

So after much research, blood, sweat and I wasn’t crying I just had something in my eye <sniff>, I managed to get the CD deck in with 4 working speakers of appropriate wattage all working and visually appealing to boot. (Not that it sounds that great but much better that one 6x9 in the rear)

At the same time I realized how woefully ignorant I was about car audio products and the inner workings of such a system. Nor could I build or modify a proper system to get the most from my hard earned money.

So now I am on a kind of self-help mission to better my knowledge of car audio and hopefully improve the current system in my Crossfire with knowledge and confidence. I know there are issues/benefits to integrating a factory amp vs. gutting an entire system and starting from scratch. Those issues are mostly monetary in my case.

A really great article I found as a beginners guide was “The Secrets of Car Audio” by Steve Deckert. This link has 5 free chapters http://www.decware.com/secrets.htm

Reading this really helped me understand why a 3,000 watt amp won’t EVER put out 3000 watts (usually), the importance of each piece of a system, positioning of speakers, enclosures, bass, distortion, etc. At least in a layman’s terms which is exactly what I needed.


So after examining my Crossfire system (which is a stock system, no Nav HU) I have decided a head unit upgrade and a pair of 10” subs w/ Amp would make the most sense with the goal of altering the sound (cleaner more precise bass) and providing enhanced features (MP3, Satellite Radio, HD Radio, etc)

I think I am OK to decide on my own which Head Unit to get as I know what features, brands, and specs are important to me.

Also I am a big fan of DIY. To me there is nothing more rewarding than enjoying the results of a well planned project that you know you worked hard to complete. Also I know if I screw it up I can usually figure out why and how to fix it. And I learn the inner workings of the system so if anything goes wrong later I know where to start looking for faults.

My questions come to integration with the factory amp and integration of an external amp for the subs as well as what type of enclosure would best with the limited amount of space. I am planning on building the sub enclosure(s) myself as well. There are bunches of plans and info online. My first thought was an isobaric enclosure or perhaps 2 “death boxes” as they look easy enough to build.


What would be an economical quality 2 channel amp to drive two 10” subs?
(Looking at specs “Power Acoustik A520-2HP”, “Eclipse XA2000” and “Pioneer GM-5300T” all seem equal, only price differs $80 - $300, I know you get what you pay for but at some point you are paying for a brand name)

What would be the best bang for the buck 10” sub?
(“Kenwood KFC-XW1000F”, “Infinity 1050w Reference”, “Audiobahn AW1051T” again price fluctuates $60-$180 these brands are just examples)

What would the best type of enclosure be to get the most quality in the least amount of space?
(Isobaric vs. 2 sealed vs. ported)

Also what would be the best way of integrating the subs into the factory setup?
(Disable the subs behind the seats? Use the preouts on the HU to the external amp? Use the lines from the rear subs to power the new subs, no external amp?)


I know these questions are not as cut and dry as I may make them sound. I am sure the combination of types of products will make a difference but any tips/hints/suggestions/corrections would be welcome.

Thank You!

 

I like the Infinity Kappa 10 inch sub in a sealed box. One sub is all you will need in the small cabin of a crossfire. I also like Alpine amps. If your going to install an aftermarket head unit then you can use the front speaker outputs to feed the stock amp as it uses speaker level inputs. Then use the sub line level (rca) output if your new deck has one, Or if not use the rear line level to feed the aftermarket amp. Check out crutchfield.com for info.

 

The Kappa 10's are a good speaker, if you can get a good price on them then I say "go for it". Also, I agree, one 10" sub will do the trick.

I'm using one 10" AlumaPro speaker in my RAM. It'll kick the bass out with low distortion. If you decide to use one, buy the dual voice coil version for lower distortion.

I opted to use a 1kW (peak) Nakamichi amp, it has built in features to channel the bass from the left and right channels to one subwoofer. It also provides a few other features that lower distortion. (I'm a BIG fan of low distortion audio).

One of the advantages of using the stock amp in the CF is that it's tied into the speedometer, so the faster the CF goes, the higher the volume. Of course the volume goes back down when the CF slows down.

Here's a little factoid regarding power and speakers. For a one octave decrease in frequency, the power requirement for the same volume is 8X.
Consider midrange speakers generally cut off at 320Hz just due to their physical size. The next lower octave is
Then 160Hz
Then 80Hz
Then 40Hz
Then 20Hz

Now 20Hz is the lower limit of average human hearing (I can't wait for the theory to begin flying regarding this little fact!).

Anyway, that's 8 to the forth, or 4,096 times the same amount of power to reproduce 20Hz at the same volume level as 320Hz. Fortunately, we can hear a mere 10 watts worth of 320Hz easily. So to reproduce 20Hz we need 4,096W. That's ALOT of heat, ergo most music wont go that low (some rap does, and Reba McIntire too).

This is why the dish thumpers like the multi kilowatt systems.

But to reproduce 40Hz only requires 512 watts, much more cool IMHO, and still quite low. The 1kW Nakamichi I'm using provides 2X for headroom (peaks), providing lower distortion. It won't, however, thump any dishes, and it sounds best when the engine is off. I can listen to complete, low distortion bass at low volume levels. Quite pleasant, I might add. I can turn up the volume and listen to bass at higher power levels, but now that I've done that I'm required to drag out one of the AlumPros I have stashed away and replace the one I've managed to burn up over the past several years. I'm also more deaf now than I used to be.

Some of that power will be converted to sound energy, the rest will be converted to heat. And that heat will be dissipated INSIDE the enclosure. So a small, sealed box will literally cook the voice coil if you like to play bass, LOUD, alot.

Besides, to minimize distortion requires the volume of the box to be exact for each specific speaker (Theil/Small parameters), so that the speaker is "critically damped", as us nut cases like to say. I have a speaker design program and can help you out with that if you want to be a nut case too. Just something to consider.

Hope some of this info helps.

 

Good Stuff!

Thanks for the replies.

If one 10” sub will do then my cost has dropped by half. (or the quality has improved by 2x.) Well done!

So phase one of the plan stands. That is to get a new head unit and properly wire the front speaker level outs to the factory amp. That will give me the functions I want, MP3 playback, iPod interface, Sat Radio, HD radio, etc as well as preserving the factory speaker setup. No volume increase, hopefully no decrease in audio quality.

Phase two will be to integrate either a bridged stereo amp or mono amp to power a single 10” enclosed sub via the preouts of the new head unit. I assume some kind of enclosed sub will work best due to the fact the rear cabin of the crossfire does not lend itself to trunk style baffling.

So the details of Phase two are going to be decided / planned in the next 6 months or so once the new HU is in and I learn more about car audio.

So lessons learned thus far are small enclosed space = lots of heat = cooking voice coils. (The first thing that comes to mind would be an enclosed sub that ports outside the cabin… allowing the sub to breath in cooler air expelling heat generated by the electrical exchange. This presents a moisture dust/dirt scenario… But that is another topic)

Also to maximize response one must take into consideration the thiel/small parameters of the specific speaker to the point of the unique specific speaker purchased (as the published parameters are often wrong or slightly off) when designing/purchasing an enclosure with proper volume.

Awesome stuff guys!

PS) Can someone add to the validity of testing the acoustics of a listening area and how you would go about it? I can generate a logarithmic tone sweep from 20Hz – 20KHz CD to play back in the system. How/What would I use to measure performance? I can stick a Mic in the cabin to record the response but wouldn’t that also depend on the quality of the Microphone used? Is there a more precise way to measure?

Thank you!

 

Wow finally a thread that is based in science...

OK so you want to measure the cars response...

You will need a microphone, a well recorded track of uncorrelated pink noise, and a device or computer based RTA.

Now, the question is ...

What resolution is appropriate to measure at 1/3 octave, 1/12, or 1/24?

How are you going to generate the microphone calibration file for the computer or send it out with the RTA to be calibrated (otherwise your readings won't be accurate).

Once you see what is going on, how do you correct the issues? Identify what the issues are, and which ones can't you fix?

Ok, so here are a few tips...

1. Do a search for True RTA and you can download their RTA software (depending on what you want you can go from 1 octave to 1/24th of an octave).

2. Look under microphone calibration and there are some preset files so all you need to do is find one of them at a place like guitar center or other source.

3. Set up the system, (calibrate your sound card ect) and off you go.

4. Only use a CD for the pink noise as a wav file since mp3 sacrifices too much at the top and bottom of the audio range.

5. If using the factory amp set the volume between 20 and 25 that will get you out of the factory volume dependant loudness eq (you are not moving so the speed dependant stuff is not functional) and keep you away form triggering the limiters which begin to come online at 26.

6. Know what you are looking at! Low frequency below 100hz is VERY position dependant and this is where Parametric EQ filtering can be very useful when applied properly, remember you cant fix dips only address the peaks.

7. Above 100hz this issues begin to form around the design of the speaker, destructive interference from surrounding materials, and the interior materials reflective properties. EQ applied higher int he range can generally destroy the quality of the sound so be careful.

8. What is the curve you are trying to get to? There has been years of research to determine the curve that is the best sounding to people, and then there is ruler flat, be sure you know what you want because you will surprise yourself when you get to flat and you seem to have no bass and the top end is too shrill.

9. How are you going to address spatial characteristics? You cant unless you do measurements at multiple points and angles. So since you cant do this with these basic tools don't try, but be wary of the changes you make to the system and the effect it has on the location of sounds across the dash.

10. Never loose sight of the fact that this is your system and you have to be happy with the way it sounds. That means ALWAYS make your product choices based on application, brand does have some influence in performance look for the ones that are still run by their original company (that is very few these days with many going belly up and then bought up for the name). Look for some serious engineering at work on the woofer, is it cosmetic or not... rubber covers, embossed plastics, and chrome do nothing for the sound. If you are looking for SPL one note wonder woofers that don't expect them to be musical. Generally you should stay with the same amp and speaker company as they are now taking a systems approach and thus will make specific recommendation for paring subs and amps based on the application. For example on the Infinity 10" you would look for a Ref 1300 or 1600.

 

If a flat frequency curve is what one is after, then calibrating the system is important. Without specific sound generating equipment that we know is flat, it's not possible to calibrate the microphone.

WinSpeakerz by True Audio is a product that is fairly inexpensive, and will also provide the much needed design help when designing the speaker enclosure using the Theil/Small parameters.

The ECM8000 microphone from Behringer is an excellent microphone. It's inexpensive, and it's response curve is flat, +/- a few dB, until it actually gets to 20Khz, then there's a little 2.5dB bump.

I agree with the concept of adjusting a sound system for listening pleasure. I adjust my systems for a flat response, that way the music I'm listening to is the way the recording engineer intended it. I then use the tone controls on the head unit to tailor it to my own particular taste.

If the sound system is anything other than flat, it's harder to adjust the sound to my own taste, IMO.

 

Ahhh nice to hear their are some of us still left that value the hard work of the artist. We seem to be few unless most of them are too busy listening and spend little time online. :-)