Setting up an amp for a car audio setup without a sub - AVS Forum
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post #1 of 7 Old 07-28-2012, 01:06 PM - Thread Starter
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Hello everyone,

My first post pertaining to my first car audio system on my first car smile.gif.

Have been visiting AVS forum for quite a while now and have taken a lot of help in setting up my home-theater by peeking into different threads. Was waiting until I had something to write, to share, before I joined the forum. Finally I do, and I will begin with a huge-huge thanks for all the information that I could find here.

Since I didn't want to alter the dash of my hatchback, I decided to go for a simple set of 4" Auditor front squeakies. Again with very limited boot space which I didn't want to lose, I settled for plank mounted 6x9 (3-way coax) rear speakers - Earthquake VTEC 693 (330W RMS, 4 ohm) with no subwoofer at all. First of all, whoever's looking for a similar sub-less setup, I would highly recommend these rear speakers because they sound awesome. The bass is pretty punchy and I'll say that once again - really punchy! Really good and worth a look. The head unit is a Sony XAV-601BT.

The rear ones are powered by a Hertz EP2 2-channel amp rated at 60W RMS at 4-ohms. I had a few questions.

1. Since the speakers are rated much higher, do you think I would be better off having a separate bridged amp for each of the rear speaker?

2. Since the speakers are higher rated than the amp, does this mean I can set the gain to MAX, always and I wont end up blowing the speakers?

3. The amp's got 3 filters - LPF, HPF and Full. I know that LPF is for the subs, but which one of HPF or Full would help the rears?

4. Should I turn off the X-over filter in my head unit and use only the one in the amp?

5. Would the 12dB bass boost work with my rear speakers or are they only meant for subs and when LPF is turned on?

Thanks.
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post #2 of 7 Old 07-28-2012, 08:25 PM
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Hi,

1. Yes. Or a single, higher rated amp. the 60W one will get nowhere near the speaker's full potential.

2. Yes.

3. I would leave that on Full, I normally do with just 6x9s. You can try the HPF if it has an adjustable crossover knob and see if it sounds any better, but 6x9s generally sound good on their own.

4. The head unit is more practical to use, set the amp up so that you can make all your adjustments from the head unit. i.e. control the crossover from the head unit and leave the amp straight through.

5. The 12dB boost is useful on 6x9s, if the bass is as punchy as you say I'd turn it on. Isn't there a 6dB boost as well, like a 0 / 6 / 12dB switch? I find most (e.g. 3 or 400W, 4 ohm) 6x9s can't handle 12dB, but 6dB is a definite improvement.

If you can find the space and/or resources for a sub, go for it. The difference is amazing.
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post #3 of 7 Old 07-29-2012, 12:53 AM - Thread Starter
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Thanks @stevenred,
Quote:
The 12dB boost is useful on 6x9s, if the bass is as punchy as you say I'd turn it on. Isn't there a 6dB boost as well, like a 0 / 6 / 12dB switch? I find most (e.g. 3 or 400W, 4 ohm) 6x9s can't handle 12dB, but 6dB is a definite improvement.
Considering I am an absolute noob tongue.gif what I see on the amp is a knob that says 'boost' and its got 0db at one end and 12db at another. The user manual is pretty useless. Does this mean I can set it to 6db?
Quote:
If you can find the space and/or resources for a sub, go for it. The difference is amazing.
Yes, I am pretty inclined at doing that but then after some thorough investigation today, I now know that my ICEs capacity is limited by my front speakers that wouldn't let me go beyond 50% volume. (I asked the dealer for the best he had and that's all he could give me! frown.gif ) Do you think they will burn-in and settle down a bit and allow me to push them a bit more? They're just 10 days old.

Considering the limited volume I can get because of the front speakers, would you still recommend I go for separate amps on each of the rear ones?

Thanks.
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post #4 of 7 Old 07-29-2012, 05:43 AM
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Hi,

On all the amps I have used they have had just a 0 / 6 / 12dB switch, a knob sounds better though as you can choose where to set it. I never used the 12dB with 6x9s as it was too much but the 0dB setting wasn't enough for me. Try it out but I think 12dB is a bit high, its over 3 times the power.

I'm pretty sure speakers don't 'settle in' and operate according to their specs from day 1. How many amps and speakers are you using? It is normal to have low power front speakers, medium 6x9s (both of which you have) and a high power sub, each running off a separate amp (or separately controlled channels on the same amp).

If your fronts are low power compared to the rears, just set the balance on the head unit to a rear bias and as you increase the volume the power should be split appropriately e.g. 25% front 75% rear. Or as you say you can use another amp and set the gain on the front one low and the gain on the rear one high, leave the head unit bias alone. That way the signal strength for front and rear is the same but the rear speaker signal is amplified more.

For example your fronts are 50W running off a 100W amp. Set the gain to 50%. The rears are 400W running off a 500W amp, set this one's gain to 80%. That way the max power of the amp = speaker power, AND the big rears provide high power bass and mid notes while the fronts are free to concentrate on high mid and treble, nothing is strained. The signal comes from the head unit at full power on front and rear channels, when it reaches the amps it comes out of the front one scaled up to 50W full scale, and from the rear one scaled up to 400W full scale, if you see what I mean. The split between front and rear is happening at the amps, the head unit is pumping out a standard signal. I find that best because then any adjustment can be done from the head unit, which is easier than the amp.



Hope that helps. I remember when I was getting started in car audio - interesting and exciting, but confusing and expensive too! I'm an electrical engineer now so understand a lot of what is going on inside the amp etc. but a lot of it is trial and error, there aren't any classes about this at school. I've bust speakers and amps in stupid ways before (remember the amp casing is grounded!!!!!)

Have fun!
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post #5 of 7 Old 07-29-2012, 06:28 AM - Thread Starter
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Thanks very much. That puts a lot of things in perspective for me.
Quote:
On all the amps I have used they have had just a 0 / 6 / 12dB switch, a knob sounds better though as you can choose where to set it. I never used the 12dB with 6x9s as it was too much but the 0dB setting wasn't enough for me. Try it out but I think 12dB is a bit high, its over 3 times the power.

Set it to 6dB and it seemed to be just in place, neither underpowered nor cracking up.
Quote:
How many amps and speakers are you using?
A single 2x channel one for the rear ones only. Front ones are powered directly from the head unit.

What seems exceedingly interesting to me now is what would the front ones sound like if I try and power them up with my existing amp. If it works well, as you said, I will get one for the front ones as well. Possibly a 4x channel this time so that I can consider adding a sub. Though I am still in two minds about losing boot space for a sub smile.gif.

Thanks very much for the help in getting me started on this one.
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post #6 of 7 Old 08-02-2012, 01:39 PM
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The first piece of advice most car audio forums will give someone just starting out on a low budget: Put it all in the front speakers, and skip the rears. The reasoning is: A) When you go to a concert, the band is in front of you. You can use surround sound for movies at home, but in a car, music, news, whatever, will sound better coming from in front of your ears. B) You don't end up having to split the budget to buy 4 speakers or sets of speakers.

I can't find the Auditors you mentioned, but since they're 4" I'll assume they're less powerful than the 6x9s. Some people, even with the above advice, want some rear fill (maybe you occasionally have passengers in back, maybe you just like the way it sounds), so you could put those in the back. The way I'm imagining it, you put the amplified 6x9s in the doors (I don't think you mentioned what kind of car it is, but I hacked up a cheap plastic cutting board to make spacers to fit bigger speakers in my front doors, it's a fairly common practice) and either put the Auditors back in their box, or use them as rears.

My wife has a 99 Nissan Altima (4 door midsize sedan) and I replaced her front speakers with some decent ones, added a small amplifier, and disconnected the rears 8 years ago, and she loves it.
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post #7 of 7 Old 08-02-2012, 11:53 PM - Thread Starter
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Makes sense @gotcha640. Thanks for the same.

To clarify, I own a small hatchback (Suzuki Alto) to help me through the back alleys and ruthless traffic in India tongue.gif.

Since its under warranty, the showroom guy warned me against making any mods to the vehicle as such; including any cuttings and fittings.
I too didn't feel like doing it any way. Hence I stand with a dash that would allow exactly 4" speakers only. So I went for the auditors.
Unfortunately the doors dont have a provision.

As suggested by @stevenred, I am now going ahead with plugging my 2ch Amp into the front ones and purchasing a better one for the rear.
I did try to fit in a small 8 or 10" sub but then it eats up so much of the boot that I wouldn't be able to carry a decent sized duffle bag for the occasional long drive.
So it stands out of question for me now. I do understand that I will miss what the sub could have added to the acoustic environment but I will have to live with it atleast for now until its outta warranty.

Once it is, I will surely think about some 6x9 (maybe, components) in the front, possibly door mounts along with a sub if I could manage a custom mod to fit that in (I am thinking about the spare tire tray for this one biggrin.gif )

So far the sound's been very good, a bit of tweaking with the balance and fader and I can happily say that I do get some very good positioning of the audio.

Thanks everyone for all the help. What a start! smile.gif

I would like to sign-off with just one last question - I heard from people that dash mount speakers pointing straight up, directly into the windshield actually spoil the sound. But a lot cars come with a dash fitment for front speakers so I don't understand whether this makes any sense. Probably a short note or a link to a useful source would be very helpful.
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