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| Techno Babble or Sound Advice (you Decide) |
Deciding on the correct amplifier / speaker combination can be daunting for the first time buyer and not that much easier for the person wanting to upgrade!
The choice of manufacturer, desirable facilities, power needed, and place of purchase are at the heart of the initial decisions to be made. Without hearing and seeing your preferred product, in a realistic environment, it can be very difficult. There are sales outlets that are reluctant to remove products from the packing box, let alone connect them up! Comparing technical specifications is often a route taken, however advertised specifications can be questionable, and comparing specifications expressed differently is always difficult, as very few specifications tell the full story in any event.
A grasp of the basics will enable you to avoid disappointment later and narrow down your choices. The massive range of amplifiers and speakers can be overwhelming. A few, well directed, questions will also enable you to decide on the competence of your supplier's advice. We would always advise you to trust your ears and eyes and not buy without hearing and seeing your chosen product in use.
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| MIXER DESKS -V- MIXER AMPLIFIERS |
Mixer desks have their place for multiple microphone and line input application such as studios, home mixing and bands. They are often the first suggestion put forward as a P.A. solution but not in every case the best one. Many of the cheaper products have poor tone control designs, are noisy and have a confusing layout to add to their problems and a host of features that will never be used. Even with a well-designed mixer desk, after a lot of knob twiddling and feedback the result can still be a poor quality sound due to the operator's failure to understand the product fully.
Most users if asked the following have not got a clue, and do not really want to know!
How do you set up the parametric equalizer to reduce microphone feedback?
Should you select a mixer with a wide or narrow Q parametric?
How do you set up the mixer gain controls to ensure the correct dynamic range?
How do you check the channel gain on the VU display and what level should it be?
How do you set up the graphic equalizer to correct for some nasty room acoustics?
They just want it to work!!
This is quite understandable but begs the question do they really want a mixer desk Yes it does look the part - BUT you have to learn to drive it! The solution to the problem is quite simple. If you don’t really require all those channels and unused features don’t buy a mixer.
A high power, rack mount, mixer amplifier with an inbuilt digital signal processor is probably all you need.
(NOT the type that is a powered mixer desk on its side and looks like a double decker bus with knobs on)
Add a good quality, high SPL (Sound Pressure Level), compact; speaker system and the advantages are numerous
- You do not have to know the answers to the four questions above, and a few more you will encounter
- You do not have to pay for unused channels when you only require two or three channels.
- You do not pay for a seven band graphic equalizer with bands too wide for reducing acoustic problems. These equalizers often end up switched out as an easier option to achieving a better sound.
- You do not pay for a bigger, more expensive, flight case to protect all the knobs you do not use.
If you buy the correct mixer amplifier you will, have a more compact system that is, easier to setup, easier to use and easier to carry. Check out our web page for ideas and solutions. The V12 series of amplifiers in 2U rack mount goes up to 650 watts per channels that’s a massive 1.3Kwatts and is available in a compact console with inbuilt radio mics and USB media player.
Having made the decision of mixer desk (powered or unpowered) or mixer amplifier, the next question is HOW LOUD? Deciding how loud is not a simple question. Some manufacturers suggest suitability based on the number of persons within the venue but this fails to consider the room size, shape or the acoustic absorption. Loudness is subjective. Remember it is always possible to turn the level down but not possible to exceed the systems maximum power. Over estimate and have some reserve, is the sensible option. Knowing your largest potential venue and the power level others use is useful. It is however important to understand how amplifier and speaker specifications are expressed in order to make the correct decision. |
Amplifier output power is usually measured in R.M.S. watts into a defined impedance, usually 4 or 8 ohms. Unfortunately several standards exist for expressing wattage ratings. R.M.S watts are the heaviest duty and all other wattage ratings, particularly when used for advertising purposes, should be treated with suspicion. It is imperative for the same wattage system to be used for the speaker system power rating.
Speaker impedance must also be considered. Speaker impedance is the load placed upon the amplifier. Amplifier output power is measured just before the clip point, this being the point of maximum undistorted output power. The problem is amplifiers can produce almost double their power ratings when severely overdriven. This is a condition that is undesirable for ears, amplifier and an inappropriately selected speaker system.
McGregor amplifiers have their power rating expressed in R.M.S. watts.
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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. I.e. is NOT non-stop rave music played at maximum power?
Speakers are normally rated in R.M.S. watts or Programme Watts. 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 it has no 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.
Unfortunately modern music recorded on CDs can exceed programme power ratings. This is due to the C.D. as a recording media having such a wide bandwidth and extended dynamic range. Considering all of the above the safest power rating option is R.M.S. watts measured to the AES standard
McGregor speakers are R.M.S. rated and can be used on similarly rated amplifiers.
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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, signal content arriving at the speaker. This 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.
Switching out the limiter is not a solution and will only result in signal clipping i.e. distortion.
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Most speaker systems end up with an impedance of either 4 or 8 ohms. The speaker impedance is the amplifier load placed upon the amplifier. The lower the ohms the greater the amplifier loads. The manufacturers maximum load specified should not be exceed. Most amplifiers have their output stage optimized to transfer max power into a 4 Ohms and about 70 percent of the max power into an 8 Ohms. Some amplifiers are designed for maximum power into a 2 Ohms. 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.
Ensure the selected amplifier can produce the claimed 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 a 4 Ohms and approx 70% into 8 Ohms.
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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. (Referenced at 0dB.) A speaker response claiming 40Hz - 20 kHz looks good at first sight, but unqualified it may be that at 40Hz the sound is -20dB 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.
(-6dB is half as loud when considering a VOLTAGE specification, e.g. tone control variation).
McGregor amplifiers and speakers have their full specifications listed.
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SPL is short for sound pressure level and is used to express speaker 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 / 1 metre
Remember -3db of power is half as loud, so if assessing two speakers one at 100dB and the other at 97dB, the 97dB speaker is half as loud as the 100dB speaker. You would now require an amplifier twice as powerful to achieve the same loudness. This is a very important consideration when selecting a speaker system. Low SPL speakers are in existence for a few reasons. Mostly they are cheaper to make and suit low-tech mass production techniques; alternatively they have been deliberately designed this way. Sacrificing SPL can provide extended frequency response and improved sonic quality but for every 3dB lost you have to double the amplifier power.
McGregor speakers are high SPL selected and enclosed in carefully tuned cabinets to extract the maximum SPL without compromising frequency response.
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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. |
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