Just bought a Crown XLS 802, Parallel connected speakers test

[stonehedge99]

Hi Guys,

I Just bought a Crown XLS 802 amplifier. Im actually planning to hook up 4 speakers to this amp, 2 on each side L & R respectively. 2 x 8 ohms speakers (Handling capacity 350 rms) on each side will make a 4 ohm load if im right and a total speaker wattage of 700 rms per side. So the crown amp will run at 4 ohms with a power of 800w per side. This is the basic outlay.

I now have 2 of the speakers with me. Can i test the amp for one side alone with 2 speakers. I mean hook speakon from amps right side (or left) runs out into 1st speaker and then speakon from that speaker runs to the next one (creating the 4 ohms load). And can i just test the amp, per side, like this.

Thanks

 

[Call911]

Of course, there's no rule saying you have to plug a speaker into the amp. No speaker means no load.

 

[stonehedge99]

But because theres no load on one side i wont end up burning something up right ?

 

[FMEng]

But because theres no load on one side i wont end up burning something up right ?

No, the amp won't care. The notable exception would be a tube amplifer. They have to have a load or parts fry.

 

[stonehedge99]

Yes exactly, i faintly remembered reading somewhere that it would be disastrous to use an amp with no load. But i didnt remember the specifics thats why there was a lingering fear at the back of my head. Thanks for clearing it up.

Regards

 

[BGW]

Just leave the audio input for the channel you're not using unplugged.

 

[stonehedge99]

I tried out the amp as you all suggested, and it went pretty well. The parallel link of the speakers worked fine. But i just felt the 802 (which incidentally is supposed to be 3 times more powerful than the XLS 202 that i have) i ran both amps side by side and kept cutting amps and alternating. And was a little depressed to find them almost the same volume. I say almost because the XLS 802 was a little audibly louder than the XLS 202, but i was feeling a little let down that it didnt sound 3 times more powerful. Is it possible that i got a bad unit or do they usually sound that way and not very obviously louder ? Or would this be because im using the same 350 rms rated speakers to test both ?

 

[Chris15]

The XLS202 is rated at 300W RMS for 4 ohms and the XLS802 is rated at 800W RMS for 4 ohms.
P(diff) = 10*log10(800/300)
= 4.26dB more powerful.

4.26dB is not much most of the time, but if you're pushing your headroom, it's well and truly the difference between clipping and not clipping...

 

[museav]

I tried out the amp as you all suggested, and it went pretty well. The parallel link of the speakers worked fine. But i just felt the 802 (which incidentally is supposed to be 3 times more powerful than the XLS 202 that i have) i ran both amps side by side and kept cutting amps and alternating. And was a little depressed to find them almost the same volume. I say almost because the XLS 802 was a little audibly louder than the XLS 202, but i was feeling a little let down that it didnt sound 3 times more powerful. Is it possible that i got a bad unit or do they usually sound that way and not very obviously louder ? Or would this be because im using the same 350 rms rated speakers to test both ?

Chris addressed the math and the fact that it is logarithmic, thus a +4.26dB increase in output level expected.

The other aspect is the perceived change in loudness from a change in level. The general 'rule of thumb' is that a 2dB difference in level is a just noticeable difference in perceived loudness, a 3dB difference a generally noticeable change in loudness and a 10dB difference in level a doubling or halving of the perceived loudness. A 4.26dB increase in sound pressure level would usually be considered as being perceived as around 1.34 times as loud, so you would likely be disappointed if you expected it to be 3 times as loud.

 

[Aman121]

Not sure if im heading off topic here, but..
It was mentioned that tube amps will fry themselves if they are run with no load. Is this because they use an output transformer? Would a solid state amplifier with an output transformer have the same issue if run with not load?

 

[stonehedge99]

Thanks. I kind of understand how the perceived loudness may be lower than whats expected.

A quick question though. If i hook up 2 speakers on the left and 2 on the right and each speaker is 350 rms @ 8 ohms. Then whats my actual power output when i hook 2 on each side creating a 4 ohms load. Is it 700 rms at 4 ohms or just 350 rms @ 4 ohms ? I know its a silly doubt and im logically leaning towards 700 rms per side as the answer. But i wanted to just know if i was wrong.

Thanks

 

[FMEng]

Not sure if im heading off topic here, but..
It was mentioned that tube amps will fry themselves if they are run with no load. Is this because they use an output transformer? Would a solid state amplifier with an output transformer have the same issue if run with not load?

A solid state amp driving an un-loaded transformer would be fine. The load presented to the amp is whatever the speaker impedance is, factored by the turns ratio of the transformer. No load on the transformer = no load on the amp. In other words, it isn't the transformer that causes the concern, it is the topology of some tube amps that make them susceptible to damage with no load.

 

[FMEng]

Thanks. I kind of understand how the perceived loudness may be lower than whats expected.

A quick question though. If i hook up 2 speakers on the left and 2 on the right and each speaker is 350 rms @ 8 ohms. Then whats my actual power output when i hook 2 on each side creating a 4 ohms load. Is it 700 rms at 4 ohms or just 350 rms @ 4 ohms ? I know its a silly doubt and im logically leaning towards 700 rms per side as the answer. But i wanted to just know if i was wrong.

Thanks

The power rating of the speaker simply tells us how much power can be applied to the speaker, long-term, before its components fail. It does not tell us anything about how much power it gets from the amp or how loud it is.

How much power the speaker gets is determined simply by the voltage applied by the amplifier and the speaker's impedance. When two speakers are driven from one amp channel, each speaker gets half of the power delivered by the amplifier. The formula for power is the voltage squared, divided by the impedance (in ohms).

At risk of over simplification, a speaker rated for 100 Watts can be just as loud as a speaker rated for 500 Watts. What tells us about how loud a speaker can be is its efficiency, expressed in dB SPL per 1 Watt, specified at some distance away. SPL is sound pressure level.