# Speaker power (wattage) and consumption

Discussion in 'General Electronics Discussion' started by Ivan's Assay, Nov 20, 2018.

1. ### Ivan's Assay

6
0
Nov 16, 2018
Hey guys, i have one hopefully not much compcicated questions.

In this thread i want to know if this makes any sense and if my understanding is even near correct.

Here we have:

12v 12Ah battery
150/100w 4ohm Speaker

1. Why it has 2 wattages ? Is it 100minimum - 150maximum or speaker 100w need amp of 150w ? Not sure :/

2. if 150w is max speaker output does it mean the following:
12v*12Ah = 144wh
150w:60min = 144Wh:57min (Can it be calculated like this ?)
So according to this calculation will speaker run ~57 minutes on max ? (Of course the amp is going to use more power than 150w if powering 150watt speaker but lets ignore that for now.)

3. If we have 200watt 4-16ohm 2 channel amplifier, can i connect 2x 60w 8ohm speaker to each channel ?
4. Will it work like that and if it can be wired like that will just sound be distorted because of lack of power ? 120w+120w=240w/200w
5. Does series and parallel connection make a difference for watts or is just for ohms ?
6. If i power 10w speaker with 3w amp will amp burn or will sound just be crap ? (Similar to question 3.)
Thanks!

Last edited: Nov 20, 2018
2. ### kellys_eye

4,275
1,146
Jun 25, 2010
Where did you get those specifications from? Post a link.

Various manufacturers use various methods to state speaker power - most such methods result in a vast over statement of their capabilities which really should be stated as continuous RMS.

The figures you give 'may' refer to 100W RMS and 150W peak - not unreasonable for 'genuine' equipment.

The power consumption can only be calculated with knowledge of the amplifier efficiency and this depends on the 'class' of amplifier (A, B, A-B, D etc)

Assuming 100% efficiency AND 100% capability of discharge from the battery AND 100% full power output at all times then your watt-hour calculations are correct.

You can wire speakers in series and parallel (or a combination of) to get a total power handling capacity of the sum of the speakers.

Series and parallel affects the ohms (impedance), not the power.

Using a higher power speaker on a lower power amplifier will cause no harm assuming the correct impedance is used.

Ivan's Assay likes this.
3. ### Audioguru

3,040
678
Sep 24, 2016
Many amplifier and speaker manufactures lie about their maximum allowed power ratings. They makeup the power numbers to be 2 times to 10 times the truth. A car amplifier advertised to produce 200W really produces only 15W per channel for a real total output power of 60W. The output power rating is supposed to be continuous, not momentary and at a reasonable low distortion, not blasting extreme distortion. I had some speaker systems rated at 40W but when they failed the inside speaker parts were stamped only 5W.

Most modern amplifiers have an AC signal voltage output that is almost not changed by the speaker impedance. If the output voltage is 15VAC then the power into 16 ohms is (15V squared)/16 ohms= 14W, into 8 ohms is almost (15V squared)/8 ohms= 28W and if the amplifier can drive 4 ohms the power in the speaker will almost be 56W.

Speakers have a low frequency resonance that is damped by a direct connection to the output of a modern amplifier. Speakers in series ruin the damping causing the resonance to sound boomy like a bongo drum and since the total impedance is higher then the total output power is lower.

Speakers in parallel reduce the total impedance which increases the output power until maybe the amplifier is destroyed.

You never play a continuous tone at full output power continuously. The output level of music and speech have peaks and valleys so the average output power is about 10% to 20% of full power when played loudly. Then you can calculate the length of time a battery will last from its mAh spec's and the efficiency of the amplifier.

4. ### duke37

5,364
769
Jan 9, 2011
The speaker efficiency is very low. The output will be well less than 1W.

5. ### Ivan's Assay

6
0
Nov 16, 2018

it is in Serbian originaly but here is translation:
Technical characteristics:
Dimension: 300 mm
Power: 150/100 W
Impedance: 4 Ohm
Frequency: 30 - 2000 Hz
Sensitivity: 90 dB
Kalem: 2 "in 4 layers
CAPTON is a calamus body
Magnetic Weight: 40 Oz

Happy to hear that.
Of course it can't be perfect but according to this calculation when using D class amp, hopefully speaker will work at least 57 min

6. ### Ivan's Assay

6
0
Nov 16, 2018
Well if this it the case. How i am i suposed to mach speaker and amp without underpowering speaker or even overpowering it and blowing it up ? :/

Is there something that will prevent overpowering so i can connect 200w amp to 3w speaker and make it work propertly ??

7. ### Chemelec

291
47
Jul 12, 2016
Just keep the Volume at Reasonable Levels and WITHOUT Excessive BASS.
BASS Requires the MOST POWER.

Cannonball likes this.
8. ### duke37

5,364
769
Jan 9, 2011
And keep the volume down below clipping level. When the amplier clips it produces high frequency harmonics which can damage the tweeter should one be present.

Just treat the system with respect.

9. ### Audioguru

3,040
678
Sep 24, 2016
You have a high power 12" woofer speaker that is 4 ohms and you have a 12V battery that produces only 13V.
The datasheet shows that a Texas Instruments TPA3220 bridged stereo class-D amplifier IC powered from the battery produces max undistorted output power of only 18W per channel because the battery voltage is much too low. When the battery voltage is 28V then the output power is 150W.

When calculating how long one battery charge will last, think about the output. Is it a full power continuous tone? Or is it music or speech that have power peaks and valleys with an average power of 10% to 20% of full output power?