Stereo overheats with Bluetooth, but not radio

I have a new stereo, with 5 new speakers surround. It overheats at high volume and shuts off, but only when Bluetoothing from computer. It doesn’t do this when playing loudly from the built in radio. I’m generally aware of what can cause overheating, speaker impedance, poor wire connnection, etc. But this question is specifically: what could be causing this to happen with Bluetooth but NOT radio?

I’m going to take a WAG, so somebody else can correct me, but I have had this problem and concluded that the FM stations severely roll off the music at the bass end. They also usually compress the audio a bit. Again, somebody more informed about FM radio can confirm or deny this.

I came to this conclusion when I found that my amp was running much hotter when I listened to CDs and FLAC audio files. I then A-Bed a couple songs from radio and my FLAC files to find a noticeable difference in both bass and dynamic range. More bass and greater dynamic range requires more power. More power means more heat.

Haven’t seen the “rolled off bass” thing, but that doesn’t mean your tuner isn’t doing it. And yes, FM stations tend to compress the hell out of the signal, but that has the effect of increasing the average power of the music content.

True, symmetrical compression (especially with modern digital processing) can increase RMS values, if desired. But it’s more likely that the musical material is being compressed to limit peaks while keeping quiet moments quiet. One can experiment with digital audio editing programs that accurately calculate the RMS value to experience this.

Symmetrical compression was very popular when we used tape, but not so much anymore.

Again, I’m not an engineer at an FM station and you may be, so I apologize if I’m making a fool of myself.

The nature of compression used by an FM radio station tends to be partly dictated by the desired audience, the expected listening environment, and the music played. FM stations all tend to use their own carefully drafted compression settings. But one thing that can usually be said, the intent is to make the music sound loud, and sound loud within the constraints of the FM medium. Often it is also processed to sound loud when listened to in sub-optimal conditions.

CDs can be anything. Depends greatly upon when they were recorded and the music genre. Modern popular music has the living heck compressed out of it, and sounds peculiarly bad. Classical music tends to have very limited compression applied. Classic rock - anything recorded up until the 90’s say, is often well recorded with compression used judiciously, only where needed. The crest factor across all of these can vary remarkably. The power versus frequency distribution can vary remarkably as well.

It is quite possible that the compression applied by the OP’s preferred radio station is good enough to provide a satisfactory perceived volume at lower actual power levels than the digital source.

But there are a lot of variables here. Without knowing more about the music tastes and other factors it is hard to say what the underlying cause might be.

I just re-read my posts and I think I’m being unclear about the basic point I was trying to make: compressed music played at the same apparent volume generally puts less demand on an amplifier.

To see why, consider a single, simple musical transient at 60 Hz. Let’s say that it occurs twice, once at 70 dB and once at 90 dB. We then compress the music to make the first transient 76 dB and the second 84 dB (a change of +/- 6 dB each).

If the first transient requires 1 watt of power for 70 dB, it will require 4 watts of power at 76 dB.

If the first transient requires 1 watt of power for 70 dB, the second transient must require about 100 watts of power to play at 90 dB. (A 20 dB increase requires 100 times the power.) Reducing the second transient to 84 dB reduces the power requirement to about 25 watts.

Therefore, we “cost” the amplifier an additional 3 watts increasing the first transient, but “saved” it 75 watts decreasing the second transient. The amplifier is much less likely to overheat. Amplifiers are rather like the sleds at truck pulls in that the demand on the amplifier increases dramatically as we (attempt to) increase the output.

Needless to say, this is a totally unrealistic and greatly simplified scenario, but I think it captures what I was getting at in my first post.

Yup. The usual rule of thumb is that a perceived doubling of loudness requires ten times the power. Yet careful tweaking of a compressor can make things sound a lot louder without the power.

Very deep bass takes a phenomenal amount of power, yet a bit of careful compression and frequency response shaping (even without such tricks as harmonic generation to introduce missing fundamentals in otherwise frequency limited output) can produce a highly satisfactory bass without nearly so much power.

But with thinking about power one finds things are never easy. Overheating is typically an RMS power question. Over a reasonable period of time to account for thermal lag. Worrying about transient peaks by themselves often doesn’t matter so much. They matter when considering limited of power handling, which mean ultimate output swings of the amplifier, but perhaps more importantly damage to speaker drivers. A very low frequency full power swing can cheerfully slap the bass driver’s voice coil into the pole piece and kill the speaker on the spot.

OK, back to the original problem the OP had: overheating. The post doesn’t say whether the receiver is in a cabinet, but a cabinet often reduces the free flow of air over/through the receiver. You need airflow for those heatsinks.

What I did for one of mine is buy a laptop cooler. It’s basically a thick pad with two fans in it. The one I have is USB-powered. I then plugged a USB power supply into the switched AC outlet on the back of my receiver. Turn the receiver on and the fans start up. However, many newer receivers don’t have switched AC outlets.

The cooler sits on top and draws air through the top vents of the receiver. Much cooler operation.

You can also buy fancier fans that are designed just for this purpose, including ones that are controlled by a thermostat, but they are considerably more expensive. My whole setup was less than $18.

It is in a cabinet. Hadn’t thought of a laptop cooler, that should hopefully solve the issue. Thanks!