Why isn't this system LOUDER?

[jhaneyzz]

I have just assembled the following components:

Amplifier:
2.1 Digital Amplifier Board Subwoofer AMP TPA3116D2 50W+50W+100W for 12v 24v car
2 1 Digital Amplifier Board Subwoofer Amp TPA3116D2 50W 50W 100W for 12V 24V Car | eBay

Left and Right channels:
Polk Audio DB521 5.25-Inch
4 Ohm
Power Handling: Peak: 275 watts per pair / 135 watts each & RMS: 90 watts per pair / 45 watts each
sensitivity: 93 dB

Sub-woofer:
Rockford Fosgate R2D4 -10inch DVC
4 Ohm
250 Watts RMS 500 Watts Peak Subwoofer

I am supplying it with 24 Watts of power.

Problem:

It just isn’t loud. It seems like I am driving it with a 5 watt amp.

What am I missing?

 

[Mortenhoe]

What is the audio source? What is the gain configuration on your board?

 

[Bone]

To get more out you need to put more in.

 

[cbdb]

24 watts for a sub isn't enough

 

[JimBeam69]

What is the supply voltage? Probably 12V and there might be your problem.

 

[Gnobuddy]

What is the supply voltage? Probably 12V and there might be your problem.

Exactly. On 12 volts, with 4 ohm speakers, a realistic power for a bridged output amp like this one is actually only about 12 watts RMS per channel.

On 24 volts, you'd get something closer to the promised 50 watts RMS per channel. Power output goes up as the square of the power supply voltage, so doubling the voltage roughly quadruples the output power.

The trick, of course, is finding a 24V power source inside a car, and that too, one that can handle 50 watts of power requirement per channel, plus some margin.

-Gnobuddy

 

[DarpMalone]

I am supplying it with 24 Watts of power.

Do you mean 24 "volts" and not "Watts"?

If so, that's fine. What's your signal source? Is this in your car?

Also, make sure the dual 4-ohm subs are wired parallel for 2-ohms

 

[jhaneyzz]

Yes, sorry. The power supply is 24 Volts 5 amps I believe

I measured it with my multimeter and it was 24v on the nose

 

[jhaneyzz]

The source was the headphone out on my iPhone. Volume set to about 80%

Not going for an automobile install. Making a boom box. Was hoping to get by with 12 Volts, but I can put 2 12v batteries in series if I must.

 

[Jerms]

You may find that you need a preamp. Output levels from mobile devices tend to be lower... Or install a Chromecast audio or a bluetooth board or similar with a DC-DC converter to feed them 5V. Beware of ground loops/noise if you do this. At the least a GLI is likely to be required.

You also have something of an imbalance in the sub. It's 89dB, the coaxs are 93dB. It's a dual voice coil design nominally 4ohm. Running it at 2 is unlikely to suit the amp whilst running it at 8ohms you will have to crank the amp up even higher to keep level with the Polks.

Short answer.... Can you try it with say, a HIFI or even a computer source, maybe a laptop line-out?

J.

 

[easp]

Anandtech measured the iPhone6 full-voulme output at ~1v RMS.

You are going to need to get closer to 24v one way or another. Two fully SLA batteries in series may exceed the operating range of the TPA3116, and/or the caps on your board.

 

[Jerms]

DC-DC boost converter time then.....

 

[Gnobuddy]

Two fully SLA batteries in series may exceed the operating range of the TPA3116, and/or the caps on your board.

Not to mention, add up to a lot of weight. Lead is heavy!

This is a good application for A123 Systems and similar (LiFePO4) batteries, if you can find them at a manageable price.

The ones I've encountered came off the charger at 3.6 volts per cell, quickly settling down to about 3.3 volts per cell. Six cells in series would add up to just under 22V hot off the charger, so should be safe for your electronics. (You do need a charger specifically designed to cope with this cell chemistry.)

Please keep in mind that other types of lithium batteries are quite unsuitable, and many pose a severe fire hazard.

-Gnobuddy

 

[jhaneyzz]

Making progress

Just got back from a business trip with all of your input dancing in my head.

I wired the DVC Sub in parallel and things got MUCH louder. Given that it is midnight here I can’t really crank it up, or hook up a tape deck etc. until tomorrow.


Jerms
You may find that you need a preamp. Output levels from mobile devices tend to be lower... Or install a Chromecast audio or a bluetooth board or similar with a DC-DC converter to feed them 5V. Beware of ground loops/noise if you do this. At the least a GLI is likely to be required.

I’ve been doing some research on available pre-amp boards. You mentioned a Bluetooth board. Are you implying that such a board would have a pre-amp in it?

Looking for suggestions on good boards.

You also have something of an imbalance in the sub. It's 89dB, the coaxs are 93dB. It's a dual voice coil design nominally 4ohm. Running it at 2 is unlikely to suit the amp whilst running it at 8ohms you will have to crank the amp up even higher to keep level with the Polks.

One of the nice things about this amp is that is has a pot for modifying the crossover frequency (I don’t know how electrically kosher that is, but it seems to do what it is advertised to do.) As well there are separate volume controls for the stereo channels and the Sub. Plus a “Master volume control."


Anandtech measured the iPhone6 full-voulme output at ~1v RMS.

You are going to need to get closer to 24v one way or another. Two fully SLA batteries in series may exceed the operating range of the TPA3116, and/or the caps on your board.

I haven’t checked the caps out yet, but this is directly from the TI spec sheet.
(TPA3116D2)
2 × 50 W Into a 4-Ω BTL Load at 21 V

I am loading the left and right at 4 Ω
The sub is at 2 Ω
There are two (TPA3116D2) chips on the amp.
So I don’t really know how to determine the draw or the voltage ceiling.


Jerms
What do you mean by:

DC-DC boost converter time then…..


Gnobuddy

I will definitely look into that battery option.

I have a previous build in a big Samsonite suitcase that I haul around with a luggage cart because it is so heavy.

 

[jhaneyzz]

Some of the Preamps I am looking at are dual rail and need V-0-V input.

Sorry about the Newbie question, but how do you go about supplying that if your power source is a battery?

James

 

[jhaneyzz]

Are Boost converters an option for audio use? I always thought that there had to be a catch somewhere.

 

[Gnobuddy]

...how do you go about supplying that if your power source is a battery?

The simplest way is to use two batteries of the appropriate voltage in series, with the centre-tap being your zero-volt rail.

Other than that, there are switch-mode supplies that can turn a positive rail into a negative rail.

If you're rolling your own, many old (pre-opamp) discrete preamp circuits will run happily off a single supply rail. Performance will not be as good as an opamp, but might be just fine for a portable, battery-operated boombox application.

-Gnobuddy

 

[Gnobuddy]

Are Boost converters an option for audio use? I always thought that there had to be a catch somewhere.

Well, they've been in a lot of car audio power amps for many, many, years. Anything above about 12 watts RMS per channel requires more than a 12 volt rail, so some kind of switch-mode supply is mandatory, and it has to boost the nominal 12V rail from the car battery up to higher voltage.

-Gnobuddy

 

[jhaneyzz]

The simplest way is to use two batteries of the appropriate voltage in series, with the centre-tap being your zero-volt rail.

I am such a noob! Err.... What's a center tap and a zero volt rail?

 

[Gnobuddy]

Err.... What's a center tap and a zero volt rail?

Sorry for the confusion!

Zero volts is another way to say "ground", so "zero volt rail" is just the ground rail. When you said "V-0-V" in your post, the "0" is the zero volt rail.

Let's suppose your dual-rail requirement is (+9 volts), 0 volts, (-9 volts). You can get this by connecting two 9 volt batteries in series, + end of one to the (-) end of the other.

You will now have one (+) end free; that's your +9 volt rail. You will also have one (-) end free; that's your (-9 volt) rail.

And the connection between the (+) of one battery and the (-) of the other - that becomes your zero volt rail, or ground.

The advantage of this approach is that it's very simple. Unfortunately, there are also disadvantages - you need two batteries, so that doubles the battery cost, weight, and bulk you have to deal with.

-Gnobuddy