I have a pair of 8 Ohm speakers, and I an using an Audiohead AH1000 amp, now if the speakers were 4Ohm, I can push the 500W per channel at the speakers, but because they are 8 Ohm, I am getting about 300W, is it possible to buy a dummy 8Ohm load to connect to the speakers to give me a 4 Ohm load?
Cheers
guys.

It's possible, but not really practical. The only real way of doing this is to buy a 8 Ohm wirewound resistor rated at 200W+, and mount it on a large heatsink (A fan may be required to cool it as well). Then plug it into your Amp alongside your existing speakers.

It will work, and basically do the job that you are looking for, but technically you'll be no better off and would still only get roughly 300W from your existing speakers, since the additional Wattage created by running at 4 Ohms would be wasted as heat from the resistor!. So you'd be no better off volume wise.

The only real way of doing this, and getting the benefit would be to either change your one pair of speakers to 4 Ohm types, or buy another pair of 8 ohm speakers to add to your existing ones.

Or upgrade your amp.....

Cheers Guys, I think I will leave it alone for the time being, Until I get a few gigs under my belt. Then it will be invested in some nice powerful lightweight speakers.
Cheers.

I think the term "dummy load" put you astray Mr Pointon, what the man is looking for is an "impedance matcher" and yes they do exist, although it is years since I saw one.

It presents a 4 Ohm load to the amp and directs the 4 Ohm output of the amp to an 8 Ohm speaker. They range from the ridiculously cheap (and dangerous to your amp) to ones costing several thousands of Euro. They are damn hard to get though.

Touching further on the speakers issue...

It's better (if you have the room to allow for this) to buy an additional set of 8 Ohm speakers and ADD these to your exisiting setup.

This is due to the fact that placing two cabs next to one another will give you a boost of +3db per channel.

Simply swapping out for a pair of 4 Ohm speakers, will not give you any gain, unless you really go to town and buy a very efficient pair. The downside is that some 4 Ohm drivers are less efficient than their 8 Ohm counterparts.. this depends greatly on manufacturer and model numbers,, but is common.

The other option as already stated is to change the amp to give you an output of 500W rms with an 8 Ohm loading, or buy a second amp the same and run them in Bridge mode if they allow it.

Decent speakers should not change there resistance on the wire coil. This is a constant length and only when the coil is breaking down will the physical resistance change.
The reason the resistance appears to change, is that when a coil moves in a magnetic field, it generates an electical current, this in turn will upset a multimeter because it get confused with the test voltage, and the inducted voltage. If you move the coil out of the magnet then the resistance will be constant.

This is why phasing of speaker is important too....

Dummy loads are a strain on the amp. and unless you need to heat the venue! i would never use one.
Amps are designed to run at a certain wattage at a certain resistance. So simply put, an 400w per side amp at 8 ohms with a pair of 400w speaker rated at 8 ohms is ideal.

The best option for SwanSide is to get anoth set of 8ohm speakers and use them as well as the existing one for larger shows. - A set of bass bins may be better than a set of full range cabinets...

Well, almost..

The ins and outs are very intricate, it is not cut and dry as audio output in the realm of watts is non linear.

But in a way you are also correct.

It is unwise to over power a speaker, however the way in which the audio is produced and the varying differencies of energy consumed by both high and low frequencies means you need to allow for the overhead.

I'll try and explain with a short example;

You have a full range speaker, freq 40Hz - 20Khz, 500W rms cont (800W prog).

If you use a 500W rms output to power the speaker you will not be able to achieve the 500W output without saturating the amplifiers PSUa nd output transistors. This is due to the fact that at 500W the Bass will consume far greater current than the higher frequencies which make the produced signal audible and intelligable.

What will happen in the amplifier will clip on practically every beat, which is not good for both amp or speaker. Due to the cunsumption of the bass freq you will in fact get a much lower output from the amplifier for a full range sound.

This is why it is advised to allow for overhead on amplifiers, so should you wish to produce a 500W rms signal to the speaker it will do so and the overhead will allow the bass frequencies to consume the required current without it detracting from the higher frequencies.

This is far more beneficial than driving an amplifer at close to max, due to the clipping which is harmfull to speakers espeicially at high outputs for long durations.

I'll post some information soon, when I find where I saved it to which explains wattage and speakers in more detail..

Obivously, it is unwise to get a 500W rms speaker and shove 800W rms into it,, although you will be surprised that doing so would probably last a lot longer than shoving a nasty maxed out 500W saturated, clipped signal into a 500W speaker.

RMS is fine so long as the signal is a nice clean sinusoidal waveform... introduce clipping and it becomes a nasty almsot square wave which will damage the speaker.

This is why when I started my posting in this thread I stated Pro Sound Systems, where this is very normal... obivously for most day to day people the temptation of cranking everything up full will always be there.

This also... going sideways a little bit here is where Compressor limiters come in handy, as you can set the max limits before the signals get to the amps,, thus even if you have a higher rated amp set to max levels, the comp/limiter will prevent the clipping and provide a nice smooth sound and allow you to get maximum efficiency out of the speakers.

I hope to have the other info I mentioned posted here very soon.

It's all relevent information, which if studied can give many a better understanding of the mysteries of amps and speakers...


HOW MUCH AMPLIFIER POWER DO I NEED?

There is no exact answer to the question of how much amplifier power you should use
for a particular loudspeaker. Actually, there are three separate and very distinct issues
regarding selecting amplifier power for loudspeakers.

1. LOUDSPEAKER POWER HANDLING RATING

The power handling rating specifications means that the loudspeaker has
passed standard power handling tests. In these tests the loudspeaker is “exercised” to
a point of damage or failure. The power rating resulting from this test is intended to be
used as a point of comparison with the power ratings of other loudspeakers. This rating
does not necessarily correspond to the best amplifier size to use nor is it a measure of
the "safe" amplifier size to use under actual operating conditions.

Discussion:
Power handling test primarily determines the limit of a loudspeaker’s
thermal power handling. This limit is the point where a sustained input signal
(measured as an RMS voltage) causes permanent damage to or failure of the
loudspeaker due to heating. During this test, the loudspeaker is also subjected
to peak input levels of up to 6 dB above the RMS level of the input signal. To a
certain point, these peak levels test the loudspeaker’s peak handling capability.
The pink noise signal used for full-range loudspeaker testing is shaped to a
standard EIA (Electronics Industry Association) frequency response. This
response shape emulates the average frequency response of typical musical
programs.
Nonetheless, this shaped pink noise signal cannot be considered representative
of all real audio signals nor how a loudspeaker will react to those signals.
Generally, it is a more stressful signal for a loudspeaker to reproduce than typical
music or speech signals in terms of thermal limits. However, some audio signals,
such as rock and dance music and even some classical music, can have content
that is more stressful than the shaped pink noise signal.
Because there are no universally accepted standards, most professional
loudspeaker manufacturers use different test methods to arrive at a power
handling specification. In spite of this, these different tests can yield surprisingly
close numbers. The ratings are known variously as the thermal, continuous,
RMS, average, AES, EIA, or sustained power handling. Differences in power
ratings are often simply a result of differences in testing methods or test
equipment, rather than actual differences in the loudspeaker capabilities. Thus,
loudspeakers within a factor of about +1.5 of each other in power handling can
usually be considered of equal capability. A factor of +1.5 is equal to about a
+1.5 dB difference in output. For example, a loudspeaker rated for 600 watts and
a similar one rated for 900 watts are likely to be equally capable in terms of
power handling for real audio signals.
Note that “music”, “program”, “peak”, or similar power ratings are usually two or
more times the thermal (or RMS, continuous, etc.) power rating. However, these
ratings are rarely the result of actual measurements. Usually, these ratings can
only be considered as an indication that the loudspeaker can handle peak inputs
that are higher than the maximum rated thermal power limit.

2. SELECTING AN APPROPRIATE AMPLIFIER SIZE

The amplifier for your loudspeaker should be sized according to both the sound levels
required and the type of audio signals that will be reproduced. If you are unsure of how
to determine these things, consult a qualified professional.

Discussion:
Do not confuse the specified power rating with the maximum sound level that can
be achieved. This is a function of BOTH the amplifier actually used and the
sensitivity of the loudspeaker. Thus, a loudspeaker used with a 100 watt
amplifier with a sensitivity of 97 dB (1 watt @ 1 meter) will achieve the same
maximum output as loudspeaker used with a 200 watt amplifier with a sensitivity
of 94 dB (1 watt @ 1 meter).
Loudspeaker drivers, particularly compression drivers, can usually withstand
momentary power peaks well in excess of power handling testing. Some very dynamic
audio signals have high momentary peak levels such as from percussion instruments.
Some audio signals, such as speech, have large moment-to-moment variations in levels.
To fully exploit the peak capabilities of the loudspeaker and to avoid amplifier clipping,
an amplifier larger than the power rating may be needed to reproduce the peak levels in the
audio signal.
For audio signals with low dynamics, such as heavy metal rock or highly
compressed music, an amplifier with a rating at or below the power handling
specification might be needed to avoid overstressing the loudspeaker’s thermal
capabilities.
On the other hand, a loudspeaker rated at 500W continuous (or RMS,
continuous, etc.) might be used to reproduce background music at low levels. In
this case, perhaps only a 25 watt amplifier would be needed to reach the desired
acoustic level.
Thus, the power amplifier size actually required for a given application may be
considerably more or considerably less than the amplifier wattage specified as
the power handling.
As a rule of thumb, where the full capability of the loudspeaker is needed to
achieve appropriate acoustic output levels, use an amplifier that is
twice the loudspeaker’s power handling specification. This assumes that its
operation can be properly controlled (See Section 3). This allows the amplifier to
reproduce peaks 6 dB above the specified power handling. This is consistent
with both the test signal and the amplifier output capabilities used for
power handling tests. However, this recommendation does NOT guarantee
trouble-free operation. That is the next issue discussed.

3. PREVENTING LOUDSPEAKER DAMAGE

Preventing damage to or failure of a loudspeaker is not a function of amplifier size nor
the loudspeaker’s power rating. Preventing damage is a function of operating an audio
system so that a loudspeaker is not stressed beyond its limits. If an audio system is
operated improperly, damage to or failure of a loudspeaker can occur even with an
amplifier sized well below the loudspeaker’s power rating. Contrarily, if an audio system
is operated properly, damage to or failure of a loudspeaker can be avoided even with an
amplifier sized well in excess of the loudspeaker’s continuous (or RMS, average, etc.)
power rating.
Discussion:
Proper audio system operation includes being aware of the types of audio signals
being reproduced, controlling output levels accordingly, and operating all
electronic equipment so that no electronic clipping occurs within the signal chain.
Examples of improper operation include:
1. Sustained microphone feedback
2. Applying equalizer boosts at frequencies beyond the operational range of the
loudspeaker.
3. Applying excessive equalizer boosts within the operational range of the
loudspeaker.
4. Allowing electronic clipping anywhere in the electronic chain including the
mixing console, signal processing equipment, or the power amplifiers.
5. Allowing loudspeakers to be “pushed” to a point of obvious distortion.
6. Reproducing sustained tones, like synthesizer notes, at full amplifier output.
Each of the foregoing examples can easily result in damage to or failure of a
loudspeaker regardless of the loudspeaker’s power rating or the size of the
amplifier used. It is the responsibility of the audio system operator to
ensure that all equipment in the system is operated within its capabilities.
That is the only way to ensure that loudspeakers do not get stressed
beyond their limits to the point of damage or failure.

APPENDIX: ABOUT LOUDSPEAKER “POWER”

Power tests done by most professional loudspeaker
manufacturers, are not really power tests but voltage tests. The quantity invariably
measured for such tests is the RMS or average voltage of the input signal. Power is
calculated from this number using the traditional formula:

"Power = voltage squared / nominal impedance"

However, the result calculated from this rarely has a basis in reality because of the
following reasons:
1. The nominal impedance is rarely equal to the actual impedance of the loudspeaker.
In fact, a typical loudspeaker’s impedance usually varies considerably over its
frequency range.
2. The loudspeaker is usually a reactive load. This means it behaves, depending on
the frequency, as both an inductor and capacitor. Voltage and current are not in
“sync” in reactive loads, so the actual power cannot be calculated without knowing
what the phase angle is between the voltage and current. This must be included this
in the power equation so it becomes:

"power = (voltage squared x cosine phase angle) / impedance"

Unless this formula is used to calculate the power for each frequency within the
operating range, the total power calculated will not be correct. Usually only one out of
the four terms in the above equation is measured, and that is the voltage. If only one
term is known, you cannot solve this equation.
The bottom line is that for a given power specification at a given “nominal” impedance,
the voltage is the same whether you are looking at a loudspeaker or amplifier
specification. For example: for 200 watts at 8 ohms, the test voltage would be 40 volts
RMS whether this refers to an amplifier or loudspeaker.
In effect the power ratings we use in audio are merely surrogate numbers for what is
actually measured – voltage. However, power ratings are perfectly fine to use as a
matter of accepted convention and convenience for purposes of comparing different
amplifiers and different loudspeakers. Just keep in mind that, scientifically, they do not
represent the actual power into a loudspeaker.

Good post

Overall, good advice. except the dangerous part in section 2 of the cut'n'paste, which suggests that an amp twice the power of the speakers is used. No, no, no, no, no, no.... and no. If taken out of context, that one suggestion is utterly disasterous. Fine for labs and audiophiles in controlled conditions eg: fixed db tests.

I'd disagree the inclusions of "Mysteries" with regards to speakers and amps. After all, its no mystery that if you give your speakers more than they can handle, they'll suffer - and some speaker re-cone place gets a sale.

ChrisP has had many a repair customer who's read a copy of "Max power" and blown a speaker.

Whilst I've no doubt that the cut'n'pasted formula's are accurate - there is one, big, unavoidable, variable in the equation. And thats...Music. Our systems play music, not math.

Unlike 1khz test tones, or pink noise, music has peaks and troughs - its gotta, otherwise we wouldnt be able to watch our LED VU meters bounce up'n'down in time to the music. What works well (and safely) time and time again in lab conditions, can sometimes bear less than 100% relation to true conditions.

Combinations of bass frequencies every beat, with powerful vocals on chorus's etc, strong instrumental solo's, equalisation and added effects all affect the overall energy being passed out of the mixer, into the amps (via other signal processing, such as equalisers, crossovers etc).

"Pushing" speakers is living on a knife edge, since you never know if a dodgy lead, crackly rotary control/potentiometer, mixer fault, or a microphone either accidently dropped (TTHHUUDDD!!!!!) or walked in front of a speaker (WWEEEEEEEEEEEEOOOOOO) is going to send a huge surplus through your mixer onto the amps, and ultimately the speaker.

Not what you need on a Friday night, with less than 24 hours to source replacement drivers. This is the bottom line really - accidently go "too far" and you'll cause damage. Anyone fancy blowing a speaker on the first night of their Christmas gigs this year?

If your amplifier is over-spec'd compared to your speakers, and you normally run the amps with their attenuator (volume) controls turned down by say 25% from maximum, theres still the potential for problems.

For example: If you're playing a larger venue than normal and feel the urge to nudge the amps controls "up" a little bit - you're then narrowing, still further, your safety margin, between dynamics and disaster. The equation that applies here is simply Logic + (Will power + fear) = system safety.

Rather than "mysteries" in audio - its more accurate to consider that there are "variables"

I also agree wholeheartedly with HeadlineDJ's suggestion of Compressor/limiters - great idea and less than one gigs money to buy. Theres a review of the Behringer MDX2600 here on DJU and I'll happily show members how to set one up at the DJU meet-up/jumble sale in February.

When I was a lad (Oi less of it - it wasn't THAT long ago ) , I was fortunate to be mentored by a DJ who was also a Sound Engineer. Sadly, the guy has since passed away but in the time that I was fortunate to know him, he taught me a lot about Dj'ing as well as speaker, amps and PA systems. Advice which went far beyond lab figures, with their test tones, and filtered, heavily regulated mains supplies where they try to create real life real application situations whilst never being more than 300 yards away from the canteen!. .

Whilst I would be the first to agree that it would have been some time since this Guy ever attended a college course! and he certainly didn't walk on water, but he did have over 30 years in the business, gained from using the earliest Valve amplifiers, to the first Harrison Mos-Fet Amps and just before his death - a nice PA Stack driven from Chevin Amps.

In the time that I worked with him, I saw him set up and run everything from a 500W PA for the W.I fete, to whatever was his largest PA system at the time, for the local party in the park or battle of the bands held on carnival weekend. He was the sort of guy who would take the time explain every step of the set up, from Di Boxes to the settings on the Compressor Limiters. These sort of people are few and far between but at no time did I see him running Higher wattage amps into smaller wattage speakers.

His philosophy was that you can't get 30 gallons of fuel into a 20 gallon tank, and the same applies to speakers. He used to say (in his down to earth Yorkshire accent) that if it 'wer possible t' get 1000 watt from t' 500w speaker we'd all save a rite load of money.

I've used the same advice for my own (abeit smaller) Rig for the last 16 years or so and also passed this advice on to many others and touch (formica covered) wood i've never lost any driver (HF or LF) through anything more than old age or progressive upgrades.

Sound Advice (Pardon the pun) is something that even the experts disagree on, you only have to watch 2 experienced sound engineers having a chat, to see exactly what I mean!. I'm always happy to read new advice, and fully accept that if it's working for you - then you must also be doing something right type of opinions provided they are based on real life situations and not facts and figures on paper.

However in the real world of smokey, badly laid out - 'acoustically challenged' venues, and vocalists and music of different styles, I don't agree that the 'experts' setting the parameters whilst working in clean, warm Laboratories can get it entirely accurate. I mean is it possible to re-create every application on paper or in the Lab that the speaker may be subjected to in use?. From the Squeeky 13 Year Wannabe Vocalist who actually sounds like a Cat stuck in tumble dryer - to the heavy metal thrash band who think that the clip light has to be permanently lit for the amplifier to do anything!. These are everyday situations in which a hired PA rig, or even a DJ's hired out 1000W rig may encounter. Not to mention Amps running on less than stable mains supplies, which if 'scoped resemble Ads' heartbeat when he's asked to buy a round at the pub . And finally, the burning question....have the speaker manufacturers tested the performance of their product in these situations on every single amplifier on the market?. Okay so it's sounds like an advert for Daz, but it's worth thinking about.

It's exactly the same as Car Manufacturers, how much BHP appears at the flywheel looks good on paper, and sells cars. But how much do you actually get with 70,000 miles on the clock, 4 large suitcases, the family and 16 stone Aunt Gladys sat in the back! . You won't find that information on paper .

I agree with C.P. here... I have also worked with a various sound engineers. I have also done a college course on studio design and equipment (I'm also in a band so i need to know all this) There are various differing ideas on how a sound system should be setup, Two of which were covered on the course. But in the real world... You need your own personal experience with you own setup. We can all say "You don't wanna do it like that! you wanna do it like this" (to quote Harry Enfield ) but unless you know the system, the way its setup and the accoustics of the venue... then it is down to how good your ears are.

We all have opinions and are entitled to them.

However... All of us have missed an important part of the original post:

Wow, I have been busy for the last couple of days guys, and came home tonight, and I am flabergasted, I was going out, but I have loads of reading to do now, All I can say is a big thanks to everybody for there info, I did forget about the power handling of my speakers, sorry, they are as Gary says 600W each, But I was taking to the missus last night, and we both agree, I will do a couple of gigs, then look for a proper pair of speakers, with the insight that I will, one day want to upgrade my amp.

Thanks again guys.