We have aTechnics SEHD560 about 2 year old hardly used but on the odd occasion when required and not at full blast the sound cuts out also the decibel meter works in reverse we have had it back to the suppliers on numerous occasions to find no fault I was told there is a safety device to protect the speakers but this can be removed prior to throwing this as new 4hundred quid out fit in the bin can you help
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In-car entertainment systems, especially the types chosen for camper vans, etc., are often capable of quite high power outputs and usually need speakers capable of being driven at those high power outputs without damage.
The trouble is, such speakers usually don't sound so good at the very low volume settings needed for evening and late night use in a campsite environment to avoid annoyance to neighbours.
It is a big problem choosing speakers that sound good at low volume and yet can withstand the higher volume needed to overcome the wind and road noise of driving. There have been many technological advances in speaker design and a hi-fi specialist will undoubtedly be able to make suitable recommendations that are resistant to damp conditions, long-lasting and with cones free enough for good reproduction at ultra low volumes but robust enough to withstand high power outputs and such drive units are likely to be fairly expensive.
For myself I would choose to use a dual speaker system with a multi-speaker system comprising several low-powered speakers strategically placed for low volume use and a fairly standard high-powered system for normal use and a selector switch.
Speaker requirements are likely to be 8 ohm, most modern hi-fi speakers are. A few low-fi systems have used special high impedance speakers and the old hi-fi standard for valve amplifiers was 15 ohm and 3 ohm or lower has been used in televisions a lot.
4 ohm speakers are commonly used where a higher power output is desired at the cost of some quality of sound reproduction but depending on how the sound is listened to can soon overload some amplifiers primarily designed for 8 ohm as it will try and deliver more power into the lower impedance speakers and perhaps exceed the rating.
8 ohms is a safer choice. The lower the wattage rating of the speakers the more efficiently they tend to be able to reproduce sound at low volume levels so for background music in a small domestic environment the average power requirement will be in the order of half a watt so even with a high powered amplifier the volume would rarely be turned up above 1 - 2 on the typical scale of 10 and ten watt speakers would be more than adequate. It is unfortunate that it is almost impossible to obtain quality speakers rated at such an unfashionably low power rating.
With the stiffer cones of a higher power rated speakers the volume has to be turned higher before the speakers become efficient and listening at low levels can be difficult. In a domestic environment a 50 watt rating is perhaps the best compromise as if there are neighbours to consider a ten watt average power output will be sufficient even if the amplifier is capable of higher powers. Just don't turn the volume up more than necessary.
The greater the power rating the more power will be required for efficient reproduction. For electrical and mechanical safety of the speakers the rating should exceed the maximum output of the amplifier but listening at low levels with quality of sound can become virtually impossible.
Sorry I don't know the answer to your question because I don't know the specification of your amplifier but like a car engine that might have a capability of, say, 200 horsepower, in use and for practical purposes that figure is completely immaterial because most of those horses would never be used by a responsible driver. It requires only about 20 horsepower for an average car to maintain 50mph so it hardly matters what the potential power output is as long as it is capable of doing the work assigned to it.
The average person listening to a hi-fi in an average room requires an average power output of around half a watt. It is immaterial if the amplifier is capable of 50, 150 or 500 watts because for comfortable distortion-free listening most of that potential power will never be used.
With hi-fi the problems start with the speaker systems. It is a mistake to use a high power speaker in a domestic environment regardless of the potential amplifier power output. The amp will only produce the power it is capable of if it is driven hard (the volume turned up) and because doing that is anti-social, wasteful and harmful to health and comfort that should not happen but high power speakers tend not to reproduce sound efficiently at low power and so more power must be provided than would otherwise be needed with good low power speakers.
Fashions have changed and it is now difficult to find good hi-fi speakers for the domestic environment that reproduce sound efficiently at low power levels and speakers with a 10 watt rating, the ideal type for small to moderately-sized accommodation, are almost impossible to find these days but it is still possible to find good drive units rated at between 20 and 50 watts that perform fairly efficiently at social volume levels.
There seems to be a failure in your output drive circuit. All electronics fail suddenly and don't show any signs until the defect is noticed except in the cases of intermittent troubles From what you have described an intermittent defect is not the culprit here. Are you using external speakers or the internal ones in the set? If you are using external speakers disconnect them and see if the internal speakers work OK. If it's both channels at the same time it's in the electronics, not in the speakers. This would require internal service. Unfortunately there is no easy fix for that. Have it diagnosed (which they can't properly do in your home unless it's a very obvious problem) get an estimate first. Those sets are very well made and reliable but nothing is perfect. You need a service call or move it to a shop.
> I turn the volume to a low it still has the odd noise
If there is any drive to the speaker at all (volume not turned off), the rattle is probably coming from a broken 'surround;' the part that keeps the cone centered around the outer edge.
Another point of failure is a structure called a 'spider' that is located between the voice coil and cone that ensures the voice coil stays centered.
If there is hum with the volume turned completely down, the amplifier driving the speakers (internal or external) has a failing filter in the power supply.
You may have speakers of an incorrect impedance attached to the unit since the problem occurs when audio signal level is increased and the current goes up.The unit is shutting down to prevent damage. I would check the speaker connections and make sure that the speakers impedance are matched for the unit you are using.