Using class D automotive amps for making active PA speakers?

[windcrest77]

Is it just me or has anyone else thought of mounting automotive amplifiers as power amps in active speakers? For the following reasons... they are inexpensive, they offer a lot of power in class D (in the thousands of watts), they are compact and made for "bolting in" applications, they are light, offer many selections over the few companies making plate amps, have built in crossovers, etc. Am I missing something here? What would be the drawbacks? I would think the main drawback would be coming up with an adequate 12V DC power supply. I would see using an external power supply to get the 12v DC and not build that into the speaker but keep it separate for weight reasons. If not useable for regular PA speakers, I would see them very useable in making a portable battery-powered PA with a motorcycle battery and trickle charger.

Here is a small selection:

http://www.sonicelectronix.com/viewcat. ... Kgodd07WbQ

Have there been projects posted here using automotive class D? (i'm new)

[Bill Fitzmaurice]

When you investigate the most expensive part of an amp, the power supply, it will become evident why no one does this.

[BrentEvans]

Couple of things:

1. Powered speakers are less than ideal in most situations, especially in light of the new super-lightweight amps from the various manufacturers. One 14/2 is much easier to run than a signal cable AND AC to every cab.

2. The power supply is really a booger. You can't power these things up with a wall wart. Remember that they are designed to operate off a car's alternator, which is measured in the tens of amps to over 100 amps, and many of them really work better with the alternator AND a battery. A 12V 3A power supply from RadioShack weighs 10 pounds and that gets you a consistent power supply of 36w to the amp. Class D amps are highly reliant on power in to get power out. Compare that to the class D pro audio amps.... the whole amp is lighter than the power supply for the car amp alone, and it can actually provide enough power.

3. Power claims in car-audio-land are smelly because they tend to be pulled out of the manufacturer's...

[CoronaOperator]

3. Power claims in car-audio-land are smelly because they tend to be pulled out of the manufacturer's...

Unlike pro-audio amplifiers that claim 5000watts out of a 20amp 120volt source http://www.crownaudio.com/amp_htm/xls.htm

[BrentEvans]

3. Power claims in car-audio-land are smelly because they tend to be pulled out of the manufacturer's...

Unlike pro-audio amplifiers that claim 5000watts out of a 20amp 120volt source http://www.crownaudio.com/amp_htm/xls.htm

That's actually a little closer to reality. Those amps can deliver that much "program power" for long enough intervals to be useful in music program... Of course the continuous rms figure is much lower. There's a lot of tech in the newer amps to buffer and recycle power to get the high program figures.

[DJPhatman]

3. Power claims in car-audio-land are smelly because they tend to be pulled out of the manufacturer's...

Unlike pro-audio amplifiers that claim 5000watts out of a 20amp 120volt source http://www.crownaudio.com/amp_htm/xls.htm

Read a little more and you will find that the XLS 5000 claims 5000Wrms bridge mono @ 4 Ohms. This is the same as 2500Wrms @ 2 Ohms stereo. And, it requires 1950 watts at either voltage.

[CoronaOperator]

Read a little more and you will find that the XLS 5000 claims 5000Wrms bridge mono @ 4 Ohms. This is the same as 2500Wrms @ 2 Ohms stereo. And, it requires 1950 watts at either voltage.

Exactly my point. You cannot in this universe get 5000w continuous out of a 1950w input. Physics doesn't work that way. The Lab Gruppens claim 10,000w out of the same 1950w input. Peavy, beringer, etc, etc do the same. The pro audio industry lies about their specs on amplifiers. 20 ms burst power is not "guaranteed minimum continous power" as crown and others claims. Their specs are rated as ISL rated power.

ISL = "If struck by lightning"

As for sketchy car audio claims: any manufacturer outside of the ones you find at wallmart, parts express, etc spec real world CONTINUOUS power from 20-20k, at less than 1% thd, all day and night continuous 100% duty cycle. These specs are part of an industry standard measument protocol called CEA2006. These amplifiers are rated to a real continous power rating standard that pro audio refuses to adopt. While I agree that many entry level products in the car audio industry are marketing bullsh*t, their are 100's of companies out there that make more honest product claims than pro audio.

/rant over but after 23 years in high end sound quality car audio the bashing of that genre of audio gets old. You owe it to yourself to seek out and listen to a pro tuned SQ car system. Its an experience you won't forget. Unlike home or pro audio, the listener's ears are always within inches of the previous listener. The system can be tuned to a level of imaging and depth that I have yet to hear elsewhere. I mean all sound is comming from eye height hovering above the middle of the bumper focused perfectly. You don't hear anything comming from the speakers, just the stage. Play a good recording on a system of that calibre and you can draw out the stage layout, height of drum riser, and weather the mic is stationary or handheld moving 10" to the right on a high note.

Just to keep on topic to the OP. Power suppies to convert 120vac to 12vdc weigh about a pound an amp. To get 1000 watts out of a 12vdc amplifier you need about a 100amp power suppy. Thats 100 pounds of equipment. To get that 100amp supply to the car amp you would need 4 gauge minimum power cable at $1 a foot, preferable 1/0 gauge cable at $4.5 a foot, you need to run a pos and neg so times that by 2. Then you are paying for the amplifier to have a power supply to bring that voltage back up. As you can see the costs start spiraling. Car amplifiers only make sense when 120vac is not available (back country, car, boat, etc).

As for a motorcycle battery, that is only good for small t-amps comonly available. I can drain my yellow top optima spiral cell car battery in 7 minutes on my car stereo. It consumes about 110amps of 13.8vdc at full power. You're motorcycle battery and trickle charger won't get you through 1 song on a high power amp.

[bassmonster]

A Jack 10, Lepai TA2020, and a deep-cycle battery make for a very potent portable PA.

Jack 10 Beatin' Up the Beach

[technicaldave]

Couple of things:
2. The power supply is really a booger. You can't power these things up with a wall wart. Remember that they are designed to operate off a car's alternator, which is measured in the tens of amps to over 100 amps, and many of them really work better with the alternator AND a battery. A 12V 3A power supply from RadioShack weighs 10 pounds and that gets you a consistent power supply of 36w to the amp. Class D amps are highly reliant on power in to get power out. Compare that to the class D pro audio amps.... the whole amp is lighter than the power supply for the car amp alone, and it can actually provide enough power.

Maybe not a wall wart, but something like a <4lbs computer PSU such as this?

22A at 12v = 264 watts

Using that with an auto amp rated at least 200w RMS, you can run a BFM cab with something like a BP102 and after it's been limited down to it's voltage limit then both PSU and amp will be operating comfortably in their range. Power supply noise at frequencies this low are likely to be negligible.

...and with computer PSU's being chucked by the million into the trash in old PCs, they can be picked up free in the right places.

What have I missed?

[Israel]

Exactly my point. You cannot in this universe get 5000w continuous out of a 1950w input. Physics doesn't work that way. The Lab Gruppens claim 10,000w out of the same 1950w input.

actually considering that it is a power amp 120v equals 3600 watts @4 ohms, 125v should be about 3900 watts. considering that it is not a big jump to the 5000 watts taking on account that it is at 1% thd. but really possible???? maybe on papers should be easier

Maybe not a wall wart, but something like a <4lbs computer PSU such as this?

22A at 12v = 264 watts

I have tried moving car stereos and power amps on pc power supplies, even they are fairly regulated, something happens that the voltage drops too much from some point maybe 22a is a peak figure. They struggle to move a 200w car stereo if i need steady power i connect a small 12v battery (power wheels, pc ups or so) between the supply and the source for voltage regulating even that it is too difficult

As for the question of mounting automotive power amps on speakers to make them active I have played with the idea and it is better to chunk a lightweight power amp and placing it inside a cab (that is what every speaker company does i suppose) and even that it would be easier to use it outboard in a rack

[Ryan A]

Exactly my point. You cannot in this universe get 5000w continuous out of a 1950w input. Physics doesn't work that way. The Lab Gruppens claim 10,000w out of the same 1950w input.

actually considering that it is a power amp 120v equals 3600 watts @4 ohms, 125v should be about 3900 watts. considering that it is not a big jump to the 5000 watts taking on account that it is at 1% thd. but really possible???? maybe on papers should be easier

Volts X Amps = Watts

Most electric outlets in the US are 120 volts and rated 15 or 20 amp. If you go over that the circuit breaker will blow

120 V X 20 amp circuit = 2400 watts

120 V X 15 amp circuit = 1800 watts

2400 watts is the maximum continuous power that any amp will ever put out when using a 120v wall source

Output cannot > input

[technicaldave]

I have tried moving car stereos and power amps on pc power supplies, even they are fairly regulated, something happens that the voltage drops too much from some point maybe 22a is a peak figure. They struggle to move a 200w car stereo if i need steady power i connect a small 12v battery (power wheels, pc ups or so) between the supply and the source for voltage regulating even that it is too difficult

Perhaps if a pair of power supply capacitors were added in parallel to the PSU outputs then it might perform?

[zefrenm]

My dj friend asked me the same thing and I told him you basically left with 2 options make a mini car electrical system with the alternator and battery or take apart an arc welder and build a heavy uty voltage regulator with a lot of capcitors in parallel. Both options seem a little much and he opted to buy a amplifie125r for what he needed

[koturban]

Arc welders rarely run on 120-15.

Can't get around Joule's Law.

[Bill Fitzmaurice]

Arc welders rarely run on 120-15.

Can't get around Joule's Law.

You can't with DC, but as for wattage ratings of amps they can skirt it because they run an AC signal, not DC, so they don't have to deal with a 100% duty cycle.