Electro-Voice Michigan MC12A User's Manual
Contents
1. SPECIFICATIONS Frequency Response in Recommended Vented Enclosure 1 Meter on Axis Half Space Anechoic Environment Swept One Third Octave Random Noise 6 dB MC8A 42 20 000 Hz MC12A 32 11 000 Hz Low Frequency Acoustic Power Output vs Frequency Small Signal in Recommended Vented Enclosure 3 dB Down MC8A 50 Hz MC12A 40 Hz 10 dB Down MC8A 37 Hz MC12A 27 Hz Sound Pressure Level at 1 Meter 1 Watt into Nominal Impedance Anechoic Environment 300 2 000 Hz Average MCBA 97 dB MC12A 97 dB Power Handling Capacity Long Term Average MC8A 12 watts MC12A 20 watts Short Term 10 milliseconds MC8A 120 watts MC12A 200 watts Half Space Reference Efficiency MC8A 1 35 MC12A 1 35 Amplifier Power Requirements Continuous Average at 8 Ohms for the Following Average Sound Pressure Levels Mid Band in the Reverberant Field of a Typical Living Room R 200 with Peaks 10 dB above Average Long Term Average Power Capacity not to be exceeded Medium Level 85 dB SPL MC8A 1 watt MC12A 1 watt Loud Level 95 dB SPL MC8A 10 watts MC12A 10 watts Very Loud Level 105 dB SPL MC8A 100 watts MC12A 100 watts Maximum Level MC8A 120 watts 106 dB MC12A 200 watts 108 dB Impedance Nominal MC8A 8 ohms MC12A 8 ohms Minimum MC8A 7 5 ohms MC12A 8 ohms Thiele Small Driver Parameters Nominal see Special Note on Low Frequency Perfor2. mounting MC8A 7 in MC12A 11 in Net Weight MC8A 4 b 2 oz MC12A 5 lb 7 oz ELECTRO VOICE COMPONENT SPEAKERS Electro Voice component speakers have traditionally provided the hobbyist and professional with the flexibility of custom installation as well as the oppor tunity for simple building block system expansion and improvement A comprehensive group of cone speakers mid frequency horns and drivers horn tweeters crossovers and accessories is available Additionally all Electro Voice component speakers offer conversion efficiencies substantially higher 3 to 8 dB than typical bookshelf home speaker systems This high efficiency is essential for most professional audio applications In the home it permits accurate reproduction of the high sound levels of live music or for more normal listening levels the use of amazingly small amplifiers for satisfactory reproduction Electro Voice cone speakers have now been thoroughly revised to reflect the latest knowledge of rational optimized low frequency speaker enclosure design The result is a combination of extended low distortion bass response high efficiency and modest cabinet size simply not available in other component speakers PRODUCT DESCRIPTION The Michigan MC8A and MC12A speakers are designed to provide full range high fidelity reproduction at modest cost Both speakers are appro priate for home music systems and the smaller MC
3. sympathetic vibrations from affecting overall system performance Proper bracing technique splits a rectangular panel into two equal rectangles with the brace placed along the panel s longest dimension Good bracing materials are 2 X 2 dimension lumber or 4 inch widths of 3 4 inch plywood placed on edge Three mutually adjacent inside surfaces of the enclosure top one side and rear should be lined with a one to two inch thickness of glass wool or similar acoustic absorptive material to prevent internal reflections from affecting mid frequency performance No absorptive material should be placed over or within the port The location of the speaker on the mounting baffle is relatively unimpor tant but close to ear level mounting will provide best mid and high frequency performance in the listening room The enclosure s height width and depth may be changed as long as 1 the internal volume remains the same 10 and 2 extreme differences between any two dimensions are avoided The required port area can be obtained by any convenient combi nation of width Y and height X as long as its long dimension is no more than five times the short dimension The port is normally located on the front baffle board but may also be on any other box surface that has free access to the listening room For most accurate box tuning the port should be no closer than several inches from the nearest adjacent enclosure wall The port s
4. cut advantages over a sealed system in the areas of efficiency box size low frequency limit and distor tion These results make the choices of box size low frequency limit efficiency power handling capacity and maximum acoustic power output rela tively easy to make In fact Thiele even presented in tabular form quite a number of possible vented box choices having optimum performance charac teristics see A N Thiele Loud speakers in Vented Boxes Part J Audio Eng Soc Vol 19 May 1971 p 388 By applying the work of Thiele and Small Electro Voice engineers developed a computer program which easily quickly and accurately predicts the performance of any speaker box system in the frequency range where the diaphragm is acting as a simple piston The upper limit for this operation is usually the frequency at which the dia meter of the diaphragm becomes a large fraction of a wavelength The Thiele Small Driver Parameters shown in the Specifications section include the speaker characteristics re quired by the computer program to develop the small and large signal per formance of a given speaker and enclosure combination For more information on this subject ask for Bulletin 10B It includes addi tional vented enclosure recom mendations for Electro Voice component speakers and a detailed bibliography of the work of Thiele Small and others Also where the Thiele Small Driver Parameters are know
5. line the lengths listed above must be halved If it is desired to run the speaker line under a carpet TV twin lead may be used for short distances Transformer Installation MC8A For constant voltage distribution systems an Electro Voice TM5 TR5 or TR15 line matching transformer may be directly mounted on the MC8A frame using the holes provided with two 6 32 x 1 4 self tapping screws PERFORMANCE IMPROVEMENT WITH BUILDING BLOCK KITS While both the MCBA and MC12A will provide quite adequate sound repro duction under most circumstances an improvement in performance can easily be realized by adding a tweeter and mid frequency speaker The tweeter will provide the most dramatic improvement and should be added first through the use of an HF 1 High Frequency Building Block Kit The HF1 includes a TW35 horn tweeter CR35 crossover level control wiring harness and mounting hardware In addition to extending the high frequency response beyond the limits of normal audibility the HF1 provides more precise definition of high frequency wave forms and much improved high frequency dispersion in the listening area The improved disper sion makes it possible for the listener to move considerably off the central axis while experiencing very little change in sound quality The MF1 Mid Frequency Building Block Kit comprised of an MR10 horn driver CR10 crossover level control wiring harness and mounting hardware provides addition
6. proximity to the speaker is unimportant SPEAKER INSTALLATION AND HOOKUP The MC8A and MC12A are designed for installation on the inside surface of the mounting baffle As with all quality speakers care should be taken in mounting if best results are to be obtained Drill four mounting holes and cut the mounting baffle opening in accordance with the dimensions given in the Specifications section To mount the speaker four carriage bolts with nuts and washers may be used The MC8A frame will accommodate a 3 16 20 bolt and the MC12A will accommodate a 1 4 20 bolt Wood screws are not recommended Secure the speaker to the baffle board just tightly enough to compress the speaker gasket Excessive tightening is not neces sary since the compressible gasket will form a satisfactory seal with only nominal pressure To avoid any significant amplifier power loss in the speaker lines and undesirable change in low frequency response wire size must be properly chosen 18 gauge stranded wire commonly called lamp or zip cord is satisfactory for lengths up to 38 feet limiting the loss in sound pressure level to an insignificant 0 5 dB If longer speaker lines are required use progressively larger wire sizes 16 gauge to 60 feet 14 gauge to 96 feet and 12 gauge to 150 feet These lengths assume the 8 ohm impedance of one speaker Two speakers in parallel have an imped ance of 4 ohms so if connected to the end of a single speaker
7. 8A may be used com mercially in high quality ceiling mounted sound systems High frequency output is enhanced by a centrally mounted free edge cone whose dimensions and mass have been care fully chosen for maximum performance improvement The free edge cone is small and light so it is able to respond to the extremely rapid high frequency motions of the voice coil which the large main cone cannot follow The MCB8A and MCi2A have die cast frames which offer long term stability not found in stamped frame speakers Also the MC8A s frame is drilled to accept Electro Voice TM5 TR5 and TR15 line matching transformers The characteristics of both speakers have been carefully developed to work well in vented bass reflex enclosures of small or reasonable size In the recom mended 2 4 cubic feet vented enclosure the MC8A provides essentially flat response to 50 Hz with usable output down to 37 Hertz The larger MC12A in its recommended 6 cubic feet enclosure has essentially flat response to 40 Hz with usable output to below 30 Hz In addition the MC8A may be housed in the small sealed ceiling mounted boxes used in commercial applications RECOMMENDED ENCLOSURES The MC8A and MC12A have been designed for mounting in vented boxes appropriate to the speaker charac teristics The use of a vented box with its tuned feature complements the per formance of the speaker and provides maximum low frequency performance consistent with si
8. al improvement in performance after installation of the HF1 The MF1 further reduces the fre quency range which must be reproduced by the cone speaker reducing harmonic and intermodulation distortion in the system The MR 10 s diffraction horn improves dispersion in the listening area in addition to increasing efficiency The improved mid frequency performance provided by the MF1 is especially important because instrument and voice harmonics which determine the char acter of the sound are found in this frequency range SPECIAL NOTE ON LOW FREQUENCY PERFORMANCE The recommended enclosures and associated performance specifications displayed earlier were determined in accordance with the definitive analysis of A N Thiele R H Small and others The performance of speakers in sealed enclosures including acoustic sus pension types has been well understood for some time In contrast vented systems have been designed using not much more than cut and try methods with little real engineering know how However the above mentioned analysis has changed this picture completely Thiele showed the similarity between a speaker in an enclosure and an electrical high pass filter circuit Application of well known filter analysis techniques led to quite accurate performance calcu lations for any speaker mounted in any vented or sealed cabinet Moreover it was shown that a properly executed speaker vented enclosure combination held clear
9. ice inc 1987 Litho In U S A Part Number 53013 613
10. mance section fs Free Air Resonance Frequency MCBA 75 Hz MC12A 50 Hz Qes Electro Magnetic Q at fs MC8A 0 87 MC12A 1 2 S Mechanical Q at fs MCBA 1 95 MC12A 2 2 Ors Q Q Total Q at f pi s s Ams MC8A 0 60 MC12A 0 78 Vas Volume of Air Having Same Acoustic Compliance as Driver Suspension MCB8A 1 05 ft3 MC12A 5 1 ft3 Half Space Reference Efficiency MCBA 1 35 MC12A 1 35 Peak Displacement Volume of Diaphragm Sp X max MC8A 1 9 in MC12A 4 7 in3 Sp Effective Diaphragm Area MC8A 30 in 2 MC12A 75 in2 Electro Voice a MARK IV company MCSA MC12A MICHIGAN Component Speaker s Xmax Peak Linear Displacement of Diaphragm MC8A 0 063 in MC12A 0 063 in PE max Thermally Limited Maximum Input Power MC8A 12 watts MC12A 20 watts Re DC Resistance of Voice Coil MC8A 6 5 ohms MC12A 7 5 ohms Cone Diameter Nominal MC8A 8 in MC12A 12in Voice Coil Diameter MC8A 1 in MC12A 2 in Magnet Weight MC8A 10 oz MC12A 130z Magnet Material MC8A ceramic MC12A ceramic Dimensions Overall Diameter MC8A 8 1 4 in MC12A 12 1 4 in Overall Depth MC8A 33 16 in MC12A 3 1 2 in Mounting Bolt Circle MC8A 7 5 8 in MC12A 11 9 16 in Mounting Hole Diameter Four Evenly Spaced Holes MC8A 7 32 in MC12A 0 28 in Baffle Opening Diameter Note Frame does not permit front
11. n Bulletin 10B shows how to choose the size and tuning of a vented enclosure and how to determine the low frequency response of vented and sealed speaker systems using scientific pocket calculators a MARK IV company WARRANTY Limited Electro Voice High Fidelity Speakers and Accessories are guaranteed for five years from date of original purchase against malfunction due to defects in workmanship and materials If such malfunction occurs unit will be re paired or replaced at our option with out charge for materials or labor if delivered prepaid to the proper Electro Voice service facility Unit will be returned prepaid Warranty does not cover finish or appearance items or mal function due to abuse or operation at other than specified conditions Repair by other than Electro Voice or its authorized service agencies will void this warranty For correct shipping address instructions on return of Electro Voice products for repair and locations of authorized service agencies please write Service Department Electro Voice Inc 600 Cecil Street Buchanan Michigan 49107 Phone 616 695 6831 Electro Voice also maintains complete facilities for non warranty service of E V products Specifications subject to change without notice ELECTRO VOICE INC 600 Cecil Street Buchanan Michigan 49107 MANUFACTURING PLANTS AT E BUCHANAN MI Mi NEWPORT TN W SEVIERVILLE TN Ml REDMOND WA E GANANOQUE ONT Electro Vo
12. ustic power output vs frequency is 10 dB below the maximum mid band output due to either thermal or displacement limitations Dimensions for the two recommended vented enclosures are shown below Vg MC8A 2 4 ft3 MC12A 6 ft3 Inside Depth D MC8A 13 in MC12A 17 5 16 in Inside Width W MC8A 16 1 4 in MC12A 21 13 16 in Inside Height H MC8A 20 3 4 in MC12A 27 1 2 in Port Area XY MC8A 12 in2 MC12A 16 in2 Port Depth L MC8A 2 3 4 in MC12A 4 3 4 in fg f3 fio fie Hz Hz Hz Hz 0 120 88 0 58 88 92 80 50 50 37 43 40 34 40 27 An outline drawing of a typical enclosure is shown below ENCLOSURE CONSTRUCTION Speaker enclosures should be con structed of rigid materials such as void free plywood or particle board In general 3 4 inch thick material is most satisfactory although smaller enclosures approximately 2 cubic feet and under may be successfully constructed of 5 8 inch material It is mandatory that the joints between the pieces of wood be strong and well sealed Simple butt joints secured with wood screws or nails and white glue are very satisfactory Removable panels should be secured with wood screws and weather stripping tape For joints longer than about 3 feet internal glue blocks may be appropriate In the largest boxes greater than about 6 cubic feet bracing is usually required for the largest expanses of wood to prevent
13. ze and speaker para meters A vented box not only increases the low frequency power output but also reduces distortion for a given level The MC8A may also be used in the small sealed enclosures found in ceiling mounted distributed speaker systems When used in this way low frequency performance is considerably reduced but is usually adequate for commercial applications In the listing below we have attempted to choose a typical vented box size that best complements the MC8A and MC12A Other vented box sizes and tunings are quite feasible and may give performance more suitable for a partic ular application Two small sealed enclosures for the MC8A are also shown For further information refer to the Special Note on Low Frequency Performance section of this sheet and ask for a copy of Bulletin 10B Enclosure Type Sealed Sealed Vented Vented Explanation of Symbols Vg Net internal enclosure volume not including volume displaced by bracing port or speaker Variations of 10 are acceptable fg Helmholtz resonance frequency of box vent combination f3 Frequency at which the small signal normal listening levels acoustic power vs frequency is down 3 dB relative to the mid band output f49 Frequency at which the small signal normal listening levels acoustic power vs frequency is down 10 dB relative to the mid band output f Usable low frequency limit the frequency at which the large signal maximum aco
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