Hi-Fi Audio Equipment
Being a serious audiophile, Tushar has invested in high-end audio products from reputed manufacturers such as Bose, Nakamichi, Shure and Pioneer. Tushar has designed/assembled and marketed professional audio equipment under the brand name of Naik Audio over the past twenty years, his designs include cassette decks, power amplifiers, graphic equalizers, active cross-overs, audio mixers, tone-arms for turntables, pre-amps for cassettes, pre-amps for ceramic and magnetic pickups, 2-way and 3-way speakers (both infinite baffle and bass-reflex).
Bose 501 Speakers Nakamichi RE-10 Tuner-Amplifier
Tushar still offers his consultancy services for issues related to audio engineering and industrial automation. (write to Tushar on naiktushar@hotmail.com for consultancy services).
Tips for Audio Enthusiasts and Electronic Project Builders
Speaker Placement & Alignment (Phasing)
Stereo Power Amplifier Construction
How to select good components for your home-made speaker system
Tools and equipment required to start assembly at home
Butterworth Fourth-Order Vented Speaker Enclosure Design Formulas
Everybody (especially youngsters) loves throbbing bass output from their speaker systems. If you have a readymade amplifier/tuner/speaker system then, nothing much can be done to enhance the bass response of the overall system. Maximum what you can do is just try to relocate the speakers in room corners (close to the wall but about 6 inches away from both side walls) and use the added bass reproduction due to the phantom images of the speakers on three sides of the corner. One has to also check the wiring of the speakers from the amplifier output. If these wires are connected in out of phase order, then the overall bass response of the system shall be degraded due to low-frequency signal cancellation (if both the signals - from left and right speaker - are out of phase - 180 degrees phase shifted). After doing all this, if you are still not satisfied with the bass response of your system, then its time for you to spend some fortune and purchase a boom-box - a sub-woofer (preferably active type, since it has an inbuilt power amplifier alongwith the 8 - 12 inches woofer).
But, if you have a (DIY) home-made hand-built amplifier and speakers, then there are many bass improvement tips. First of all, you have to check if the diameter of the woofer is at least 8 inches and the magnet is considerably bulky and deep (you need a long-throw voice coil to get a deep and rich bass response). Once that is confirmed, then see if the enclosure volume is sufficient to give you a good low frequency response (see my download page for speaker enclosure design software). The best low frequency response is produced by properly designing a single port bass-reflex or a sixth-order band-pass enclosure. The damping material (such as freely available glass-wool - from any air-condition or refrigerator repair workshop) should be neatly placed on the inner walls of the cabinet to reduce any booming or jarring effects. Too much of glass-wool shall "deaden" the sound, whereas less amount of glass-wool shall result in a bit booming sound. There is no calculation for this and one has to use a Trial-n-Error method till you get a clean bass reproduction. On the other hand one must see the amplifier equipment. First of all, reduce number of coupling capacitors in the overall signal path from input to output. One can always eliminate the input capacitor from the power amplifier as their is always a output capacitor at the output stage of a cassette deck or a CD/DVD/VCD player. Then check on the power supply reservoir capacitors, (these are actually the main filter capacitors which are connected just after the bridge rectifier of the power supply section of the amplifier). Usually these are rated at 2,200 uF. During momentary bass peaks, the power amplifier's output stage demands a momentary high current which can be 5 - 6 times higher then the power transformers current rating. In such an event these reservoir capacitors acts like a current bank and supply the extra current for a split second (which gets charged at the next cycle from the power transformer). Therefore, if due consideration is given to a power supply filter/reservoir capacitors then, one can get a more detail, clean and powerful bass response from a good quality woofer. Usually, a pair of 10,000 uF x 2 capacitors (or whatever suits your pocket !!!) can do the trick and are sufficient enough for addressing the momentary peaks of a bass signal.
If you have ready-made speakers then check if they are fitted with paper cone tweeters. If they are, then its advisable to purchase silk dome tweeters from the market (such high quality tweeters are available from manufacturers such as Philips). Then carefully un-install the cone tweeters and install the new dome tweeters in those cavities of the enclosure. You may have to design a adaptor plate to install a new retro-fit dome tweeter to the existing enclosure. The old un-installed paper cone tweeters can be used as output devices for your 555-based mosquito repellent circuit (just joking !!!).
Speaker Placement & Alignment (Phasing)
The proper stereo imaging and the concept of a virtual sound stage in a drawing room cannot be obtained if the speakers are not placed properly, or if the phasing of the left and right speakers is not correct.
Placement
Speakers should not be placed at the corners of the room since they tend to give a colored sound because of the effect of the phantom images of the speaker on the other 3 sides (this can be used as a blessing when you require a improved bass response but have no tools to attain it). Speakers should be placed at least 12 - 15 inches away from the corner walls. Floor standing speakers must be raised to a level such that the tweeters are at the ear level at a sitting position of a listener in a drawing room (like 1.2 M from floor). If you have bookshelf speakers, then one has to properly position them at ear level or at an height facing the listener at an angle from the wall. Usually, speakers must be placed on nicely supported solid stands with spikes at the feet. If necessary, you can load the base of the speaker stand with sand, stones or old telephone directories !!! Last but not the least, there must be atleast 6 feet distance between the two stereo speaker enclosures. This same philosophy applies for a 5.1 or a 6.1 speakers setup used in a home-theatre environment.
Phasing
If you have invested in a high end or an expensive speaker system, but if the bass response emerging out of these speakers is not up to the mark or satisfactory, then the first thing to check is the correct wiring and phasing of the speakers with the amplifier's output terminals. The "+" output terminal (marked as red) of the amplifier must be connected to the "+" terminal of the speaker and similarly the negative terminals must match. In some cases the "+" terminal of the amplifier may get connected to the "-" terminal of the speaker - and then the problem starts. Technically or electrically its not dangerous for your speakers and you cannot damage your precious speakers because of this mistake. But, you may have to suffer a degraded bass response and non-existent virtual sound stage. If you have home assembled the speakers as an enthusiast then speaker phasing can be found out by conducting a simple test as follows. Take a single pencil cell (AA battery) and pair of small wires (preferably red and black), then connect the black wire to the negative terminal of the battery and the red to the positive terminal. Then connect the black wire to one of the terminals of the speaker (lets say right hand side terminal) and then for a momentary period (not more then 1-2 seconds) connect the red wire to the other speaker terminal and then carefully notice the direction of motion of the woofer cone. If it comes out from its mean position, then the speaker terminal at which the red wire is connected is the positive input terminal of the speaker. Repeat the same for the other speaker and then connect the speaker wires accordingly to the amplifier's output terminals. Phasing problem is solved !!!
I personally recommend to use high-end speaker cables to connect the speakers to the amplifier. Its actually the vital link between the two, and if its of poor quality then you may have poor dynamic range and sluggish speaker response. Invest in good quality speaker cables, such as from Monster Cables (they cost around US$ 6 - 7 per meter, Indian Rupees 300 - 400 per meter, but its worth the investment).
Stereo Power Amplifier Construction
Many good quality stereo power amplifiers can be constructed at home and they can sometimes sound far better then commercially available amplifiers. If one takes some basic care in selecting the right circuit and premium quality electronic components, then building a power-amp at home is a couple of weeks job. You can always rely on kits from Maplin, Heathkit, Radioshack or Visha (in India) to get the basic components and PCBs. Make sure that you always use a glass-epoxy PCB with green mask on it for your audio work. I personally recommend to use the TIP 3055 / TIP 2955 based circuits for the power amplifiers for the hobbyist who want to work with power transistors. Whereas, the people who like to get a simple but powerful circuit working in "no-time" must go for Sanyo's hybrid stereo amplifier chips such as STK4141 etc. These power amp ICs are nicely trimmed for accurate signal amplification. You may also try low-cost chips such as TBA 810, TDA 1010 or TDA 2020 for 8W, 10W, 20W power output respectively. Use a good quality power transformer and huge (high capacity) power supply capacitors such as 10,000 uF. Always select a power amplifier circuit with a dual power supply for better bass response. If you are planning to use a Baxandall tone control circuit (for Bass and Treble control) then its better to use one which is built around a couple of BC148 transistors. Avoid LM741 op-amp based tone control circuits, as they have inherent "noise" problems. If at all, you want to use op-amps then make use of specially designed op-amps for audio applications such as NE5532, NE 5534 or the TLC range from reputed chip manufacturers such as Philips, Sanyo, National. Do not do compromise at component level as the final result shall be frustrating for you. Because, everything shall work, but it shall lack the quality !!! Always use MKT, Polyester or Mylar capacitors, metal film resistors, and nickel-gold platted terminals for your RCA inputs. The internal amplifier signal wiring must be done using a shielded cable and try to route the input signal cables as short as possible and away from the mains power transformer (this lets you to avoid un-necessary mains hum - 50 Hz/60Hz). Its a good practice to install series small glass fuse in the output for speakers, the rating must be calculated based on the maximum RMS power handling rating of the speaker. Use a "de-thump" circuit in the power amplifier section, so that the speakers get connected to the power amplifier after a predefined basic time delay of 3 - 4 seconds (which is usually used for charging the internal circuit capacitors). Using the de-thump circuit protects the expensive speakers from getting burned due to inrush of high transient current. Last but not the least, use a cooling fan if deemed necessary with the aluminum heat-sink installed at the output stage of the power amplifier. This cooling fan can be purchased from a computer spares shop, its the same fan that they use in cooling the power supply modules of a PC (maybe you can salvage one from a old computer power supply).
How to select good components for your home-made speaker system
Basically, you must decide the budget for the purchase of drive units (Woofer, Tweeter or Mid-range) and then hunt for the drive units from your local market. While selecting a Woofer one has to always see that its from a reputed manufacturer such as Philips, Alda, Wharfdale, Peerless, Lowther, KEF, etc.(if you are in India, then I recommend you to purchase Luxco brand of Woofers available with Precious Electronics at Lamington Road, Mumbai) please do not purchase low-cost woofers with better (glossy) looking cones but has a sheet metal pressed frame (basket) and a comparatively small magnet. A good Woofer has a aluminum die-cast frame and a bulky magnet piece at the back. Try to see if you can buy a Woofer with a rubber-baxtrene cone and a fabric surround. I personally dislike the rubber surround as it tend to disintegrate over a period of time, finally degrading sound quality and introducing heavy distortion. "Surround" is the flexible rim which connects (or rather suspends) the speaker cone from the metal rim of the frame. See that the cone is thick (if its made out of paper-pulp) and has at least one corrugation at the centre. All new Woofers with higher power handling capacity are manufactured with heat-sinking fins at the magnet. While purchasing a new Woofer, conduct this small test to see if the "voice-coil" is not touching the side walls or has a "bottoming" problem. To do this, please place the Woofer on a table top with the magnet at the base and then gently push the woofer cone inwards with five fingers placed at equidistance on the cone. Keep your ears very close to the cone and notice if you hear any scratching noise when you push the cone. If you hear a scratching noise, then it means that the voice-coil is touching the side walls and you must discard that drive unit and try another one (naturally if the salesmen of that shop allows you to do so !!!)
There is not much to look for when you select the tweeter, specially when you are going for a dome tweeter. Just see that you purchase from a reputed manufacturer. When you are purchasing a paper cone tweeter, you must see that he cone diameter is not more then 2.5 inches (Tweeters with larger cone diameters are useless and have a limited high-frequency response) preferably with a thin polyester or a Mylar surround.
The next component which plays a major role in a speaker system is the network, which is used to segregate the low and high frequencies from the incoming signal from amplifier's output to the separate drive units such as a Woofer and a Tweeter. There are 2-way and 3-way networks available in the market from various manufacturers. Please do not try to make your own speaker networks at home, because it requires some specially made inductors (coils/choke) and making an inductor at home (with the right inductance value) is not at all easy.
The final thing is the right cabinet for mounting the drive units (speakers). Select only Nova-Teak type of wood for your enclosures. The thickness of the wood depends on the Woofer wattage. For eg. anything upto 20 Watts RMS can be handled by a 0.5 inch wood, 21 Watts to 50 Watts with a 0.75 inch wood and anything above 51 Watts upto 200 Watts RMS in 1.0 inch wood. Over the years, I have been searching some exotic materials and enclosures to house woofers and have done some real tests and the results were stunning !!! (see my download page for speaker enclosure design software) Avoid chip-board or plywood to assemble speaker enclosures.
You can try mounting your woofers in an old discarded set of Bongo or a Congo (the instrument used by musicians, which looks like an African snare drum). Just rip off the skin from the top and make a wooden adaptor plate to rest on the Bongo top which shall finally hold the woofer in place. You may kep the bottom end of the Bongo open (as it is) to act like a bass-reflex enclosure (provided the Bongo is standing on a tripod and is a bit raised from the floor) or you can close it with a wooden circular piece to make an infinite baffle type cabinet. Don't forget to place some glass-wool in the Bongo.
You can try the same thing with the drainage pipes available freely in the market (may cost US$ 3 - 4, Indian Rupees 120 - 130 a piece). These pipes are made out of ceramic material (therefore no jarring or booming effect) and are very solid and heavy. They are usually dark brown in color and has a extended flange type end to cascade with a similar pipe for making longer pipe lines.
Instead of ceramic pipes, you may try thick walled PVC pipes used for sanitation drain lines. You can make a decent sixth-order band-pass speaker enclosure using a PVC pipe of diameter 8 - 10 inches, by suspending the woofer at the center of the pipe. The two chambers formed due to placing the woofer at the center of the pipe acts like two resonant cavities and can be properly tuned by punching ports in each chamber to match the frequency response that you are expecting. (Such pipes are available with the local building material supplier at a price of US$ 4 - 5, Indian Rupees 300 - 400 per meter.
Tools and equipment required to start assembly at home
Some basic tools and equipment is necessary to start or convert your backyard into a hobbyist den :
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Screw drivers set (Philips type and standard)
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Nose pliers
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Tweezers
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Wire Stripper
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Cutter
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Set of multicolor hook-up wires
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Crocodile Clips
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Soldering Iron (preferably from Goot)
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Good quality solder wire and flux
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Adjustable blades
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Files (small and big)
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3 1/2 Digit Multimeter
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Analog Multimeter
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Signal Injector (can be assembled at home)
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Old general purpose (full-range) speaker unit (without any enclosure)
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Pair of RCA and EP connecting cables
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Hacksaw
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Electric Drill Machine
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Measuring Tape
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Rubber Solution and some glue
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Nickel-gold platted terminals (RCA, Phone and Banana type)
You can cheaply convert your existing CD player into a make-shift audio signal generator by purchasing a test frequency CD and playing it on a portable CD player and using its line out or speaker out terminals. If you do not get a test CD for audio test frequencies then you can make one, by saving some fixed frequency sinusoidal waveforms on a CD in native audio CD format. Frequencies such as 20 Hz, 50 Hz, 100 Hz, 250 Hz, 500 Hz, 750 Hz, 1KHz, 3 KHz, 5 KHz, 8KHz, 10KHz, 12KHz, 15KHz, 18KHz, 20KHz are used in testing audio equipments.
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Dr. Amar G. Bose - Founder of Bose Corporation, USA Dr. Amar Bose son of a freedom fighter and a political dissident who immigrated from Calcutta (India) during the 1930s was brought up in Philadelphia. He became more attached to technology at a tender age of thirteen when he started repairing model trains to support the income of his family. Dr. Bose later started repairing transistors and entered Massachusetts Institute of Technology (MIT) for graduate education. He completed his BS in Electrical Engineering in 1950 and has an idea in his mind to invent a stereo loudspeaker that would reproduce a sound that audience hears at a great concert hall in a domestic environment. Bose's early patents won him great respect within the industry; but he needed capital in order to do further research and begin production. In time, Bose received financial support from MIT professor Y. W. Lee, and founded Bose Corporation (1964). He first invented the 901 (R) Direct/Reflecting (R) speaker system in 1968, it was the first stereo loudspeakers that utilized the space around them instead of reproducing sound as if in vacuum. Bose then developed Auditioner (R) audio demonstrator, which takes the specifications of a given room, hall, or other space and demonstrates precisely how a given Bose speaker system will sound in that space even before it is built. Bose's sense of spatial acoustics also helped him conquer the car stereo market, with systems that transformed the on-the-road listening experience. Dr. Amar Bose has earned over two dozen patents, and he still works full time, directing a more than $550 million company, whose products can be found in Olympics stadiums, Broadway theatres, the Sistine Chapel, and the Space Shuttle (where his noise cancellation system protects the astronauts from permanent hearing damage). Bose also teaches electrical engineering and computer science at MIT, and is a local celebrity in the fields of electronics and education. After
initially questioning why loudspeakers with advanced technical
specifications failed to reproduce the realism of a live
performance, Dr. Bose began his 12-year study of speaker design
and psychoacoustics. The Bose Corporation introduced the Bose
901 Sound System, which set a new standard for sound quality and
promptly received worldwide acclaim. |
Tushar still offers his consultancy services for issues related to audio engineering and industrial automation. (write to Tushar on naiktushar@hotmail.com for consultancy services).