Techno Babble

Techno Babble or Helpful Information (you decide)

Deciding on the correct amplification system can be daunting for the first time buyer and persons wanting to upgrade! Deciding on price, size, weight, and manufacturer, place of purchase, backup service, warranty, build quality, desirable features, frequency response and power required are all decisions that have to be made. Hearing and seeing your preferred products in a realistic environment can be very difficult with some sales outlets not even prepared to open the packing box let alone provide a demonstration.

Comparing technical specifications is often a route taken, however advertised specifications are now almost meaningless as a result of marketing spin and the way technical specifications are being expressed. More about this later!!

A quick grasp of the basics will save a lot of disappointment later and help narrow down the overwhelming choice.

We would always advise you to trust your ears and eyes and DO NOT buy without hearing and seeing your chosen product in use.

Powered Speakers

Powered speakers are more compact and do offer a more cost effective solution than non-powered speakers and an amplifier... but at what cost?

The Class D versions with a switch mode power supply do weigh less and run cooler, however they are generally less reliable and considerably more expensive to repair. The Class D amplifier particularly when powered by a switch mode power supply is acoustically inferior to a Class AB amplifier powered by a conventional linear power supply. Power levels claimed by the manufacturers of these products should be very carefully assed as most do not achieve the claimed performances.

The better quality powered speakers do benefit from dual amplifiers, active crossovers, digital signal processing and time alignment. How good, worthwhile or convenient these features are is debatable and can only be gauged by extensive listening and personal preferences. Most powered speakers do not have all these features but all can be incorporated within a conventional amplifier and speaker system if deemed desirable.

Powered speaker manufacturers decide on the most appropriate drivers for their amplifier power rating, thereby removing the decision from the retailer and customer. This can be beneficial but can also have expensive drawbacks if repairs are ever required as many of these drivers are not interchangeable.

Powered speaker suffer from several disadvantages, the most annoying is the requirement of a mains power supply and a screened cable to each speaker, clearly inconvenient. Even less desirable for long-term reliability is the placement of the amplifiers electronic components within a cabinet that vibrates under extreme sound pressure!!

Sales marketing has been the major factor in promoting the powered speaker not the advantages of the concept. We feel the disadvantages outweigh the advantages in most applications particularly where higher power levels are required and a good clear bass response.

Mixing Desks Vs. Mixer Amplifiers

Mixer desks have their place for multiple microphone and line input application such as studios, home mixing and bands.

Mixers are often the first suggestion put forward as a P.A. solution but not in every case the best one especially if your requirements are minimal. A well thought out mixer amplifier with a self contained power supply is often a better solution for the more simple application. The user has less to learn, less to carry, less to go wrong and less to connect. Mixer amplifiers are simpler and more intuitive than flat bed, bulky mixing desks with complex signal routing options that will probably never be used, and can give very good results. Yes mixers look the part BUT you have to learn to drive them so if all those channels and features are not required, buy a mixer amplifier.

High power mixer amplifiers do exist in the McGregor range and are ideal for backing track singers and are also available in console style formats. McGregor also have a range of amplifier solutions for background music and zoning in 1U or 2U rack sizes.

Amplifier Watts

Having made the decision of mixer desk (powered or un-powered) or mixer amplifier, the next question is how loud does it have to go?

Amplifier power ratings were almost always expressed in RMS Watts and once upon a time we could take it for granted that the watts advertised would be RMS, but now SOME specifications read like fairy stories!!

The Electrical Institute Standard method for measuring amplifier power is to drive both channels to 1% passed the clip point with a 1KHz sine wave and express the RMS Volts x RMS Amps as the Output Watts (RMS) into a specified load, usually 4 ohms.

Marketing departments all over the world have been busy trying to redefine the watt to make their products more desirable or seem better value than there competitors product. Buyer beware you are about to enter a minefield of misinformation.

You will have probably already seen some of the following confusing power output descriptions. PMPO, PMP, Burst Power, Peak to Peak Power, Peak Power, Dynamic Power, Instantaneous Power, Nominal Power, Music Power, Programme Power, Continuous Power, RMS Power, and then there is the undefined Watt which could be any of the above. Some of the above have a genuine mathematic relationship to the industry standard RMS power rating and some are simply imaginary. Trying to untangle reality from spin is not what the average purchaser wants to do.

A simple solution to dealing with this type of deliberate misinformation is to ask for written confirmation of the true RMS power of your intended purchase. If the amplifier or speaker is not within spec return the purchase as faulty and demand a refund.

McGregor amplifiers have their power rating expressed in Watts R.M.S. into a defined speaker load. Our speakers will handle the music produced by the equivalent rated amplifier.

Speaker Watts

When choosing speakers it is wise to have some spare power handling capacity.

The old rule of thumb was to rate the speaker system at one and a half to twice the output rating of the amplifier. This is still good advice but improved speaker design and financial considerations have eroded this margin of safety and equal ratings are often used. This is only advisable if the speaker manufacturer has a reputation for correctly rating the power handling of their speakers and the application will not to be too demanding – NOT a good idea for non-stop rave music played at maximum power!!

Speakers are normally rated in R.M.S. power or Programme power (also called Music power). Any other defined or indeed undefined Watts should be treated with the utmost suspicion.

Speaker manufacturers have the problem of defining a rating that will compare with real live material. The R.M.S. wattage rating is good for thermally stressing the speaker but it does not simulate real live conditions, as music has instantaneous peaks to stress the mechanical reliability of the speaker. Programme wattage gets closer to reality as it consists of filtered random generated noise that contains many frequencies similar to voice and instruments. This synthesized signal is controlled to A.E.S. standards by bandwidth limiting and ends up with an R.M.S. to peak ratio of two.

I.e. 100 watts R.M.S. = 200 watts programme or music power.

Unfortunately modern music with its increased bandwidth and modern compression techniques that increase the duty cycle can exceed programme power ratings. Considering all of the above the safest power rating option is R.M.S. watts measured to the AES standard.

McGregor speakers can be used on similarly rated amplifiers.

Clip Limiters

The financial implications of purchasing a speaker system capable of handling twice the R.M.S. output of the amplifier led to all McGregor amplifiers from 1992 onwards being fitted with active clip limiters. The clip limiter function is to limit the amplifier to the sonically acceptable output signal and prevent the overdriven, destructive, clipped signal content arriving at the speaker. The clip limiter reduces the speaker power-handling requirement and improves the sonic quality when the amplifier is overdriven. Our limiters are sonically transparent until the amplifier runs out of power at which point the limiter controls the situation. Consistently operating at the limiter threshold means the amplifier is underpowered for the task and the sound will be compressed. A higher power amplifier should be used to provide more acoustic headroom if the limiter is constantly being activated.

Switching out the limiter is not a solution and will only result in signal clipping i.e. distortion that can damage speakers.


Most speaker systems end up with an impedance of either 4 or 8 ohms. The speaker impedance is the load placed upon the amplifier. The lower the ohms the greater the amplifiers load. The amplifiers maximum load specified should not be exceed.

Most amplifiers have their output stage optimised to transfer maximum power into 4 Ohms and about 70 percent of the maximum amplifier power into an 8 Ohm load. Some amplifiers are designed for maximum power into a 2 Ohm load. These amplifiers will transfer very little power when driving into an 8 Ohm speaker load and should be avoided unless it is intended to run a 2 Ohm speaker system. Speaker loads of 2 Ohms are not that popular as high cable losses can occur between the amplifier and speaker.

A Class D amplifier powered by a switch mode power supply will struggle to produce more than 55% into 8 ohms. If 8 ohm speakers per side are only in use then the Class D amplifier with a switch mode power supply has to produce at least 20-25% more power than a Class AB equivalent for it to sound as loud. Additionally the peak instantaneous level is less impressive.

Ensure the selected amplifier can produce the required wattage into the speaker load to be used not the load you are unlikely to use. Impedance matching is important to achieve the maximum power transfer.

McGregor amplifiers produce their maximum power into 4 Ohms and approx 70% into 8 Ohms.

Frequency Response & The dB

Amplifiers and speakers have their frequency response expressed between a lower and upper frequency.

The ideal graphic response would be a straight line between these two points and is usually reference as 0dB. A speaker response claiming 40Hz – 20 kHz looks good at first sight, but unqualified by say +/- 3 dB the frequency response is meaningless.

The dB is a ratio between two quantities such as voltage or current. In the case of power the ratio is squared.

For example it may be that at 40Hz the sound is -20dB down on the 0dB reference i.e. almost inaudible. The same would apply for an amplifier. Remember that -3dB is half as loud when considering a speaker or amplifier POWER specification and -6dB is half as loud when considering a VOLTAGE specification, e.g. tone control variation.

McGregor amplifiers and speakers have their full specifications listed.

SPL (Sound Pressure Level)

SPL is short for sound pressure level and is used to express a speakers efficiency. One watt is fed into a speaker and the sound output is measured at a distance of one metre. The result is expressed in dBs. i.e. 100 dB @ 1 watt at 1 metre distance.

Remember the following when considering purchasing speakers or amplifiers.
+3dB is twice the power i.e. 100 Watts +3dB = 200 Watts
-3dB is half the power i.e. 100 Watts -3dB = 50 Watts
+10dB is required for the sound to be considered as twice as loud.
Doubling the electrical power (Watts) is not the same as doubling the acoustic output that we hear.
An increase of one Bell (10dB) is accepted as being twice as loud to the average person but this also depends on many other factors and is an approximation.

Also consider loudspeaker compression due to the heat generated in the voice coil. Losses of -3 to -7dB are typical and will occur very quickly in practice. The greater the power applied to a speaker the more heat in the voice coil and therefore the greater the compression.
The higher a speakers SPL @1 Watt / metre, means less power is required from the amplifier to attain a given volume and therefore less compression will occur in the speaker. Speaker sensitivity is often overlooked and is a very important consideration when selecting a speaker system. Continually increasing the amplifier power is ultimately a recipe for disaster.
Low SPL speakers are in existence for a few reasons. They are cheaper to make and suit low-tech mass production techniques but they may have been deliberately designed this way as sacrificing SPL can provide extended low frequency response and improved sonic quality so consider your system application and requirements with this in mind.

McGregor speakers are high SPL selected and enclosed in carefully tuned cabinets to extract the maximum SPL without compromising frequency response.

Some manufacturers are now expressing their speakers maximum output power as being able to reach so many dBs, again an unqualified dB is meaningless. The figure shown will not include any compression, or indicate the standards used to measure the speaker SPL and maximum output.

We hope the above short form information will avoid costly mistakes. The information above has been simplified as far as possible and is not intended to be exhaustive.