audio amplifier

Thread Starter

Deric

Joined Feb 8, 2010
25
thank you, a good start from someone who knows the ropes is what i need. i want to learn how and why it works, not just build it. so a good start will help, i can ask questions when road blocks come. thank you very much
the sub is a rockford fosgate 8" (p28s8 is the part number,)
for 12v use, rated at 8ohms, 200w rms and 400w max frequency range between 43-250Hz

the tweeters are also car tweeters, rated at 6ohms Power Handling: 20watts RMS / 40watts Max - 87dB
Range: 5,500 - 20,000 Hz

the supply is 12v 20a

i havent chosen the mid yet, but have plenty to choose from
 

R!f@@

Joined Apr 2, 2009
9,918
Are the speakers mounted on a cabinet.

Car speakers or not. Speakers are speakers and shud be handled as such.

I appreciate if u can show pictures.

Few questions
Are u determined to use ur 12V supply?
Are u willing to built another more appropriate amp and supply"
How much are willing to spend?
Will u built or buy ready made amp modules?

Stick with what u decide.
Once u decide, we will progress.
 

Thread Starter

Deric

Joined Feb 8, 2010
25
Thank you. I really want to learn how and why it all works, so a good start is what i need. I dont want to just build it off someones drawing. A good start will help, then i can ask questions when i hit roadblocks. As of now, i just dont know what things to watch out for cause i dont have much experience, yet.

SUB (part# p28s8)-- 8 ohms 200W rms/400W max freq. 43-250Hz

TWEETERS-- 6ohms 20W rms/ 40W max freq. 5500-20,000 Hz

MID-- undecided

Phone out- about 200mV and 10mA (at max volume puts out 196-212mV, spikes at 232mV)

LINKS

sub-- http://www.rockfordfosgate.com/products/product_details.asp?item_id=91803&locale=en_US

tweet-- http://www.emspowered.com/storefront/index.php?main_page=product_info&products_id=355
 

Thread Starter

Deric

Joined Feb 8, 2010
25
Sorry, it didnt show that post went through so i reposted. the sub is in a box fit to specifications. the was going to build a case for the tweeters and power supply and print it on the rapid prototyper. that is not finished. the power supply is already shipped and should be here soon. i want to build the amp myself, so fit the application, although that may be a backwards way of doing it. but yes, i have planned on using 12v just cause they are car speakers, though im sure they can stray from 12v a ways and still be fine. i plan to build the amp, but if its not feasible then ill have to buy.

The reason for this project is not so that i have the finished project, i made up this project to learn the process and how it works. the finished product is just a bonus.
 

R!f@@

Joined Apr 2, 2009
9,918
Hey nice speakers.
Even though they are car speakers, u are not limited to 12V supply.

I have used car speakers woofers, celestion MIds, and JBL tweeters for home stereo.
Built own crossovers and amps.
Nothing commercial came even close to this baby.

I suggest u go for higher supplies. It will be space saving and cooler and efficient.

If u want to use ur 12V supply, u are limited to car amps. And 12V power amp chips with high level of distortion. Bad sound and limited decibels.

I have to decide what is best for ur speakers and will take a few hrs to reply on tht. May be tonight midnight I can do tht. I got to go out.

Try to find a Mid. So can I can comment on the amp to be used.
Try to get higher power than the tweeter. Cone material is very important. range shud cover 300Hz to 3Khz flat. Sealed basket type limits interference from woofers if or other speakers if built into same cabinet, but in ur case, I think you will use a Mid and tweeter in the same cabinet.
Route the low frequency components separately to another woofer mounted cabinet.
U have 1 sub. so U will need to sum the stereo in to a common lpw freq. amp. This is not a problem as most of u might think.

U can built a unit way better than any thing commercial. Just follow my lead and u won't regret it. this I promise u

Below is my unit, it has a 12" 800W low range. A 6" sealed Paper cone mid and JBL power tweeter. All in all this thing sounds so heavenly. By the way they all are driven separately with no passive crossovers.
Woofer Cabinet is Completely sealed separately and air tight
 

Attachments

Last edited:

Thread Starter

Deric

Joined Feb 8, 2010
25
I would love to go as efficient and make it as amazing sounding as possible. but i think , since i have most of the parts here and ready to go, i would like to stick with what i got. i know its not the best situation, but it should work for my learning purposes.
R!f@@ thanks for being kind enough to help me. though i dont want you to waste your own time on me. so if it gets to be a burden i would understand.
 

R!f@@

Joined Apr 2, 2009
9,918
Not at all. I am almost here every night if I am not abroad working.

I will be back and explain some few things tht could change ur mind.
Before tht try to go thu the link in my post 8.
read about bi-amping. Read it thoroughly. It will clear a lot of things
 

Audioguru

Joined Dec 20, 2007
11,248
A single-ended amplifier with a 13.2V supply from a charged car battery produces only 2.2W into an 8 ohm speaker. if the amplifier is bridged like most ordinary cheap car radios have then the power is about 7.7W into 8 ohms.

High power car amplifiers use a complicated voltage stepup circuit to feed high power amplifiers. For 200W into 8 ohms then the power supply needs to be 123V or plus and minus 62V. You can use lower power amplifiers for the mid and tweeters maybe 30W for each mid and maybe 20W for each tweeter. The max current from the 13.2V that feeds the voltage stepup circuit will be about 42A.

Your 8" woofer has low sensitivity. With an input of 200W then it will not be as loud as you think. You need two 8" woofers plus a larger and more efficient sub-woofer.
 

thatoneguy

Joined Feb 19, 2009
6,359
A single-ended amplifier with a 13.2V supply from a charged car battery produces only 2.2W into an 8 ohm speaker. if the amplifier is bridged like most ordinary cheap car radios have then the power is about 7.7W into 8 ohms.

High power car amplifiers use a complicated voltage stepup circuit to feed high power amplifiers. For 200W into 8 ohms then the power supply needs to be 123V or plus and minus 62V. You can use lower power amplifiers for the mid and tweeters maybe 30W for each mid and maybe 20W for each tweeter. The max current from the 13.2V that feeds the voltage stepup circuit will be about 42A.

Your 8" woofer has low sensitivity. With an input of 200W then it will not be as loud as you think. You need two 8" woofers plus a larger and more efficient sub-woofer.

What the guru said.

All high end automotive amplifiers are mostly switch mode power supplies to get the required voltage and current to the speakers through a Class A/B or B final output stage. Due to heat generation of Class A, A/B, power supplies have been taken to the limit with "Class D" or mislabeled as "Digital" Amplifiers.

A very rough description of a Class D amp is that they modulate the SMPS output with the input signal for subwoofers. Class D amps have an amazing output level, with low heat generation.

Building an audio output amplifier that sounds perfect is a bit art, and a lot science, and a lot of money. Trying to do one from a beginner level will be extremely difficult (understatement).
 

R!f@@

Joined Apr 2, 2009
9,918
I did it on my first try. But I did a lot of reading before hand.

If the OP follows properly he can too do it. Provided he has knowledge on assembling and making circuit boards. ( not just few resistors or caps, but plenty of components)

I wud like to show my amp but it is very difficult to reach it. Being big and heavy and is on top shelf, as I have a DSP to control all the levels separately
 

Thread Starter

Deric

Joined Feb 8, 2010
25
"Your 8" woofer has low sensitivity. With an input of 200W then it will not be as loud as you think. You need two 8" woofers plus a larger and more efficient sub-woofer."

I have heard this sub play on a 200w rms amp in a car, but it wont be loud enough with my 200w? whats the difference
 

R!f@@

Joined Apr 2, 2009
9,918
Ur woofer's sensitivity is 84db. To get 200W, you will need fairly high power to get the right amount of sound out of it.
The more sensitive the woofer the less power u will need for high audio output.

At least around 400W, if u plan to use a sealed cabinet but lesser for vented cabinet.
For a worst case, meaning higher power for powerful bass at 40Hz minimum, I'll say u cud do well at 300 to 350 watts of power for the bass unit.
Going for high power helps u to avoid unwanted clipping at maximum output and less heat build. This way even at low levels u will have descend bass output.
Proper cabinet design is also essential to avoid excessive corn excursion minimizing woofer damage, bass distortion and good bass response.

What do u have in mind for the bass cabinet?
U need to decide on this first, as the Amp design can be changed for ur woofer.
Others might say this is not true, but power requirements greatly vary for sealed to ported subs. As ported cabinets have a greater range of cone movements, which makes higher power amps a danger. High power amps can be used but the user must be careful on how high the woofer is driven.
By staying at it's limit the woofer will be safe.

As for ur tweeter which is at 87db, is too insensitive to be driven at low power. to get balanced audio together with other speakers, proper power rated amp is a must. And this might vary depending on ur midrange.
Type of crossover u have in mind will also effect the Power ratings for the amp used.

U need to decide the cabinet types and Midrange speakers.
I suggest u buy the Mid first. Then go in building bass woofer cabinet.
If u have it then decide how u wud drive the speakers. Active or passive cross over.

If passive then u need to buy the appropriate ones. Building is almost impossible in ur case.

Going for active cross over and multiple amps is better if u are making.
It is sounds much better too. Makes less heat and u can also be sure on the amount of distortion it will produce.

Using passive crossovers, mid range and tweeter alignments and phase balance is rather hectic.
 
Last edited:

R!f@@

Joined Apr 2, 2009
9,918
By the way. Playing a sub in a car and in a room is completely different.

Believe me when I say, A car ready made sub cabinet will sound really bad if used in a house.
Cabinet has to made in accordance to it's playing environment
 
Last edited:

R!f@@

Joined Apr 2, 2009
9,918
Sealed cabinet. Do u have specs on the cabinet it self. Or did u made it.

Do want to drive the tweeters, Mid and bass separately or Bass separately and Mid- tweeter together
 

Thread Starter

Deric

Joined Feb 8, 2010
25
I made it myself, to correct volume for sealed boxes for this specific sub. I think i would prefer to run the tweeters and mid together to keep it simple. im not too worried if there is some overlap or unused frequencies
 

Audioguru

Joined Dec 20, 2007
11,248
The 8" woofer has a free-air resonance of 43Hz. Its resonant frequency increases in a sealed enclosure and its output drops off at lower frequencies. It might not produce bass frequencies below 80Hz in a sealed enclosure. You need to add a larger and more efficient sub-woofer for deep bass that you can feel.

Your cheap tweeters cost (gasp, choke,wheeze) $1.99 each? Won't they sound very cheap? Like a whistle?
 

R!f@@

Joined Apr 2, 2009
9,918
The 8" woofer has a free-air resonance of 43Hz. Its resonant frequency increases in a sealed enclosure and its output drops off at lower frequencies. It might not produce bass frequencies below 80Hz in a sealed enclosure. You need to add a larger and more efficient sub-woofer for deep bass that you can feel.

Your cheap tweeters cost (gasp, choke,wheeze) $1.99 each? Won't they sound very cheap? Like a whistle?
I totally agree :eek:.

So, if plan to run mid and high together u have to use passive crossover.

U will need a power full amp for bass.
Typically around 300W and a 50W or so for mid-high drivers.
A high pass passive crossover for the tweeters.

An active cross over to cut off bass from the mid-tweeter amp.
A sub woofer equalizer to correct and accommodate low frequency loss and anomalies for ur cabinet.

As for woofer. U cannot make a car sub amp tht could drive ur bass unit with that 20A PSU u bought.
If u plan to make an amp, u have to go for a higher voltage supply.
If u want to buy a standard sub woofer car amp, then u will need tht supply plus a car battery strong enuf to handle bass transients.

Without a battery ur supply will go into short circuit protection if it has tht during bass thumping.
If no Short protection is built in, ur 12V will sag shutting down a ready made amp and also produce severe distortion from a 12V home built amp.

U decide what u want, so I can suggest what u can built
 

thatoneguy

Joined Feb 19, 2009
6,359
The 8" woofer has a free-air resonance of 43Hz. Its resonant frequency increases in a sealed enclosure and its output drops off at lower frequencies. It might not produce bass frequencies below 80Hz in a sealed enclosure. You need to add a larger and more efficient sub-woofer for deep bass that you can feel.

Your cheap tweeters cost (gasp, choke,wheeze) $1.99 each? Won't they sound very cheap? Like a whistle?

Agreed, again.

It takes a different balance of speaker types, amplifiers, and placement to sound good in a theatre living room compared to a car, especially when trying to achieve quality sound, and not simply "big bass" for rap music. Most of the extra power is for transients and dynamic range, NOT for "crank it up" loudness. Both home and mobile systems sound excellent at around 25% volume, at which point the amps will still hit a good fraction of their rated output on transients.
 

Thread Starter

Deric

Joined Feb 8, 2010
25
i am not worried about having a lot of base. i just need a little. i have two 15" subs in my mustang. i have the low end covered when i need it. the tweeters are cheap cause they were designed for a specific application, mass produced, and then found to be the wrong size. the company has been trying to get rid of them cheap for a long time. i got them when they were 20 cents a piece. they are in fact very very loud and havent heard any distortion when i wired them straight to the leads on an in home surround sound. they are better than the tweeters in my mustang set up
 
Top