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Save' inoney with th!s,easy-to-assemble ~it,. Peerless PSK60/2 2-way hifi loudspeakers Based on high quality but well-priced Peerless drivers, these compact loudspeakers will be just right for many hifi enthusiasts. Despite their small size, they deliver big performance! By TOM MANNING* When you consider the high price of good quality commercial hifi speakers, it is not surprising that kit speakers are as popular as ever. You save money as well as getting the satisfaction of building your own. This new *Scan Audio Pty Ltd, PO Box 242, Hawthorn, Vic 3122 . . 16 SILICON CHIP design uses components from Peerless, a name well known to many hifi enthusiasts, as this Danish company has been manufacturing quality speakers since 1926. Peerless speakers · have been unavailable for a number of years in Australia and only recently have returned to the market as a regular stock line from Dick Smith Electronics. But while it is good to see the famous Danish brand back on the market, there have been no current designs using Peerless loudspeakers. That is about to be remedied with the publication of this article. It is worth noting that while Peerless as & brand name has been more or less absent from the Australian scene for a few years, Peerless drivers are used in many famous speaker brands, such as Dali, Jama, Richter, Jansson, Bang and Olufsen, Celef, Yamaha, Vandersteen and Krix. If you were able to look inside the cabinets of these loudspeakers, you would find that Peerless drivers turn up in some Left: shown here on a bookshelf, the Peerless PSK 60/2 loudspeakers will perform equally well on stands or when wall-mounted using adjustable brackets. The bass/midrange driver selected for this design is the Peerless 174WF woofer, a 165mm unit with a cone made of polypropylene. This material is used extensively these days because of its rigidity and high degree of selfdamping. The cone has a soft foam roll surround which ensures a low frequency resonance and good damping. The 25mm high temperature voice coil enables the driver to handle relatively high power; up to 60W RMS, depending on the design of the enclosure. Thiele/Small parameters very expensive and esoteric designs indeed! This first Peerless do-it-yourself design will be an ideal match for the Studio Twin 50 Stereo Amplifier published in the March and April 1992 issues of SILICON CHIP. When driven by an amplifier such as the Studio Twin 50, the dynamic range from these Peerless speakers will be more than adequate for the vast majority of enthusiasts. Designated the PSK 60/2, which stands for Peerless Speaker Kit - 60 watt/2-way, these loudspeakers could serve as the main pair of speakers in your home, or as extension speakers or rear speakers in a surround sound system. They would be a good upgrade of the speakers supplied with many small rack hifi systems. They are small enough to be placed on your bookshelf, on stands or fixed to the walls with adjustable brackets. Woofer selection There are many factors to be considered when designing a new loudspeaker. One of the most important is the bass driver to be used in the sys- tern. At one time, the tendency was to select the largest possible woofer, say a 12-inch (30cm) unit, and then try to design the enclosure around it. These days, the approach is normally to use much smaller woofers, in the knowledge that a small driver in the correct size enclosure is a much better choice than a large woofer in too small a box. Most audio enthusiasts are aware of the pioneering research done in Australia during the 70s by Neville Thiele and Richard Small. Thiele documented the theory behind speakers in vented boxes, which was later expanded on by Small who analysed sealed and passive radiator designs. All good modern bass speakers are now designed with this analysis in mind. The key factors are: (1). · The free air or natural resonance, F 0 , of the driver. This is the low frequency at which the driver's impedance comes to a peak and where it exhibits the greatest cone excursion for a given applied voltage; (2). The total Q factor, Qt, of the Specifications Model ........................................ .................... ........ Peerless PSK 60/2 System .......................... ........................... ...... .......... 2-way bass reflex Woofer .............. ... .... .... ............ .. ......... .. ...... . 165mm Peerless 174WF Tweeter .... ........ ................ .. ............................... 25mm Peerless BOOT Rated Power ......................................................... ....... ....... 60W RMS Sensitivity ............................. ....................................... 88dB (1 W/1 m) Frequency Response ....................................: ... 55 - 20,000Hz (±3dB) Crossover Frequency .... ............ .............................. ............... 2500Hz Tuning Frequency .. ....................................... .. .... .. ....... ...... ......... 45Hz Impedance .............. .......... ...... ............ ... ............ ... ................... 8 ohms Internal Volume .... .. ........ .. .......................................... ............. 14 litres Dimensions ................................. ...... 420 x 215 x 235mm (H x W x D) Weight ................. ...... .............. .. ........................ ...... .. .... ....... ... ... 6.5kg JANUARY 1993 17 BrOel &Kj<Er Potentiometer Range: __ ~ d B Rectifi er : ~ Lower Lim. Freq.: _ _ . 50 _25 Measuring ObJ .: dB l74HF 26/72 6! woofer II ___ . Wr. S peed: ____lQQ mm /sec . Pape r Speed: ___ _]_ mm/ sec. - . ---:7 ~-- .d - - - - 4Q lQHz Q . -~ 'r----1 - --, -- -- -- ·-'-- 1;75 [2 ---· - - '--" _ '-·-"··-'· I I dB B 1- -- -1 --I- L.-tj__J_ ·----t-t-:t--i-••t f---- f-- - ~~:-t-± - ---==-- - ~~~ - ·---. - _ ------/ .___:. -- - -_-::: _ a~,oQ . --. - ;;:;.J;:z:' :=:~' ~ ~ . - - -- - 2010 ===·::x:. ::::::=::___ Ree. No.: _ l _ 10 Date: 20.2.90 s;gn.:....KL_ 0 · - ·--· - · \· --l---+ ➔ ·---+--+­ r---i---1------+----+--+--+ - - - f..---.-.-- -+-· i..- 1--------l---+- -+---I- - _..._ .__,_l- 5 ~ .,.-- --+ 20 10 2 15 +----+___±::--+-+-+ 0 0 40 D A B C L,n. B C Un. ( 1612 / 2 :'231._ A Fig.I: this diagram shows the frequency response of the Peerless 174WF woofer when mounted on a flat baffle. The smooth curve shows its impedance characteristic. Its free air cone resonance is 48Hz, corresponding to the peak in the impedance curve. · Briiel & Kj<Er Potent iom et er Rang e: _~ dB Rectifier: ~ Lower Lim. Freq.: _ _l O _ Hz Wr. Speed:__J_QQ__mm/s ec. Pape r Speed: _ _ 3_mm/ sec. 50~25 Measuring Obj.: dB~__dH I 80DT 26/ 55 10,75 ·-t dBklB f- - tweJ!1.e.r-_-= 4 0. o~ 6 60 - ~-- . ---·~.t----+---+--=;= 1--f +--+--+ +- ~ --+-,-+-J.- Roe. No.: _ l _ 10 - + -t----t-l-4-- 5 -----1____..- Sign .:....K.L____ OP0124 - t- •-+-+- ,__, Oat e:...2D.,_Ll0 0 --+ +--+---y of-· 1 50 1 ~ult iply F~~q . Sc~I~ by: _ _1 ~__oo z:~olevel: _1_k_H_z~7□~~~B._ _ _ 5 _ 10 20 40 D A B C Un. A B C Un. (1612 / 2112 ) Fig.2: this diagram shows the frequency response of the Peerless 80DT tweeter. The smooth curve shows its impedance characteristic. Its resonance is 1080Hz, corresponding to the peak in the impedance curve. driver. This is the "quality factor" at resonance and indicates the combined effect of the driver's electrical and mechanical damping. (3) The equivalent volume, Vas, which is the volume of air (in litres) needed to obtain the same stiffness as the driver's suspension. Expressed more generally, Vas is an indication of the "springiness" of the suspension system. The Thiele/Small parameters for the Peerless 174WF are FO , 48Hz; Qi; 0.55 ; and Vas, 22 litres. Calculations with the relevant formulas indicate that an enclosure volum~ of 14 litres and a tuning frequency of 45Hz are suitable choices. The tuning frequency or box resonance, fB , is the frequency at which the air mass of the enclosure reso- nates with the air mass in the port. At this frequency, the driver's mechanical excursion and impedance will be L ..::____J ~ '°" ,.:, RL (a) C II f"" RL (b) Fig.3: low pass & high filters are the building blocks for crossover networks. The inductor in series with the resistor at left (a) blocks high frequencies & therefore functions as a low pass filter. The capacitor in series with the resistor at right (b) blocks low frequencies & therefore functions as a high pass filter. Price & availability The Peerless PSK 60/2 loudspeaker kits will be available exclusively from selected Dick Smith Electronics stores. The prices are as follows : Complete kit for two speakers, including cabinets .. ...... .... ............ $399.00 Complete kit for two speakers, without cabinets ........................... $269.00 Woofer only (DSE Cat. C-2106) .. ......... .......................................... $79.95 Tweeter only (DSE Cat. C-2101) ... .. ............................................... $49.95 18 S1ucoN CmP at a minimum, but the output from the vent (port) will be at its greatest. This can be seen from the impedance plot of the system (Fig.8), where the impedance dips to a minimum between the two low frequency peaks. Tweeter selection The choice of a suitable tweeter for a 2-way speaker can present designers with problems. The tweeter needs to be at least as efficient as the woofer and its frequency coverage must complement that of the woofer so that the overall frequency response of the system is as smooth as possible. As can be seen from the chart diagram of Fig.1, the 17 4WF woofer has a reasonably smooth response over most of its range, culminating in a small peak in the 2-3kHz region. Its efficiency is quoted as 88dB at 1 metre, for an input of 1 watt. A suitable match is the Peerless 80DT dome tweeter. Its efficiency is slightly higher, at 89dB, and as its response plot of Fig.2 shows, it is quite smooth over its bandpass, with a resonance peak just above lkHz. Thus, it can be teamed with the Peerless 174WF woofer without using an overly complicated crossover network. The BODT tweeter features a 25mm This photo shows all the components for one loudspeaker system: the prefabricated cabinet & grille cloth frame, one woofer, one tweeter, one plastic port, the crossover/terminal panel assembly & various self-tapping screws. voice coil with an aluminium former and a woven textile dome. Crossover design Selecting the woofer and its box size and matching it with a suitable tweeter is the relatively easy part. The crossover design is the hard part and, more than anything else, determines the sound quality and tonal characteristics of a speaker system. In a 2-way system, low pass and high pass filters are combined to divide up the frequency spectrum. The simplest low-pass filter consists of an inductor in series with the woofer, while the simplest high-pass filter is a series capacitor with the treble driver. This is illustrated in Figs 3(a) and 3(b) respectively. Now, let us say we have a crossover frequency of ZkHz, an arbitrary figure but one that is used often enough. In order to obtain an overall flat fre R1 5.60 5W INPUT PEERLESS 80 OT TWEETER Fig.4: the complete crossover network has a 6dB/octave low pass filter for the woofer and a 12dB/octave high pass filter for the tweeter. The resistor provides some attenuation to match the tweeter sensitivity to that of the woofer. quency response, we require each driver's output to be reduced to half power (-3dB) at this frequency. The values of the components in the crossover network must be such that their reactance equals that of the drivers at ZkHz. This should provide a flat frequency response when the outputs are added together. In addition to inductive and resistive effects, the mechanical and acoustical characteristics of the drive units makes the task of building crossovers less than easy. If we applied the results of the above example to our speaker system, the frequency response WOllld probably exhibit an excessive amount of output at around ZkHz, due to the fact that both drivers have peaks in this region. The solution may be to roll off the woofer below ZkHz, and then cut in the tweeter at around 3kHz or so, ef- JANUARY 1993 19 Men~1uing Oh1ect ,_ .PS I( ::. .6J2 / df-:..!.·-?l_~ -~/_ ) __ _ ---~ _q__ dfj t.evel lkrnge: lm~Jc:HJance Range: _2___~: Zero Ze,o M ern>u1i11g 'N • . • ____ M Co t1t J11 ;. 1, Level (FuncJom~nta l): _ ---·- _____ rlB Level (Harmonic ). ______ ____ dB ,• r,m 'f /\)( 1~ :,1,1-,,.:: <J _ . ________ ITif'n / 56 C 120 60 30 12 25 10 80 40 60 30 5 6 40 5 20 10 2 +P Fig.5: this diagram shows the electrical response of the PSK 60/2 crossover network when connected to resistor loads. The reactive nature of the speakers will modify this response. ONLINE: Uented/15 dB Graph ESCAPE: Select Graph CASD Driver Para.rieters: Fs (Hz): 48 Qts: .55 Vas (U: 22 Box Para.Meters: Ub(U:14 Fb (Hz): 45 O.L:? Filter Para.~ters: Fp (Hz):NONE O.:NONE Cursor (Use F1-F4): -25 ID Hertz: 100 Do you uish dB: 2.26 50 10D saa (c) SDS Fig.6: this is the computer predicted bass response of the Peerless 174WF woofer in a 14-litre enclosure. The response is 3dB down at 55Hz & slopes at 24dB/octave below that. fectively eliminating the peaks in each driver. The simplest type of crossover is a first order type, providing a roll-off of 6dB per octave beyond the crossover frequency. This means that above the 20 SILICON CHIP Final design The final design uses a box measuring 420mm high, 215mm wide and 235mm deep, giving an internal volume of14 litres. The port is a slightly tapered unit of 45mm internal diameter and 114mm in length. The computer predicted bass response of the woofer has the -3dB (half power) point at 55Hz, with a slight peak in the response at 100Hz - see Fig.6. The measured frequency response of the Peerless PSK 60/2 loudspeaker system is shown in Fig. 7. The response is within ±3dB from 100Hz to 20kHz. The slightly ragged response below 500Hz is due to reflections in the measuring room. The impedance plot of Fig.8 shows a typical response, with a minimum of close to 6Q at 45Hz (the tuning frequency) and a maximum of 24Q at 85Hz. This means that it will cause no problems at all with typical stereo amplifiers. Subjective performance to sa.ve response gra.ph? (YIN) Da.te: 10-28-1992 load drops by 6dB for each halving in frequency. This is why this type of crossover is referred to as a '6dB/octave' filter. The crossover network finally designed for this speaker system is shown in Fig.4. It employs a 6dB/ octave filter for the woofer but a 12dB/ octave filter for the tweeter, to prevent it from receiving too much signal at its resonance of just above lkHz. Hence, the tweeter is coupled to a network consisting of a 10µF capacitor and a 0.4mH inductor. The 5.6Q in series with the tweeter network provides a degree of attenu,ation in order to match the sensitivities of the two drivers and provide a good overall balance in the sound. The electrical response of the crossover network into 8Q loads is shown in Fig.5. crossover frequency, the low pass section of Fig.3(a) provides a 6dB decrease in signal voltage across the load with each doubling (an octave) in frequency. For the high pass section of Fig.3(b), the signal voltage across the The subjective performance of the PSK 60/2 is very good indeed. The speakers have a relaxed and neutral sound quality, with smooth and tight bass performance. The midrange and treble response is particularly detailed and clean . .Because of the relatively small cabinet size, stereo imaging is particularly good. Assembly procedure The PSK 60/2 is supplied as a complete kit, with cabinet woodwork and Fig.7: this is the measured frequency response of the Peerless PSK 60/2 loudspeaker system. The response is within ±3dB from 100Hz to 20kHz. The slightly ragged response below 500Hz is due to reflections in the measuring room. Br liel & Kja. r M easuring Ob i.: Peerless PSK 60/2 Impedance ...1.L Ree . No .c Da te c28/10/92 S 1~ OP 0124 10 20 Hz 50 Mu lti p ~y Fr eq. Sca le by: __ 10 0 _ __ 20 0 _ Fig.8: the impedance versus frequency characteristic of the Peerless PSK 60/2 loudspeakers. The minimum impedance is just on 6Q so these speakers will not present any load problems to solid state amplifiers. all components for two speaker boxes. The kits will be available exclusively through Dick Smith Electronics. The cabinets come as a flat pack which is simply wrapped around the rear panel and glued. Alternatively, you can purchase all the hardware, drivers and crossovers, etc, and then build the cabinets your- self. The general cabinet details are given in the diagram of Fig.9. If you elect to make your own cabinets, you will need reasonable woodworking facilities. We think that most builders will use the cabinet kits as they are well made, relatively inexpensive and give a professional finish. Assembling the kit of the PSK 60/2 The crossover networks are supplied fully assembled and attached to the spring-loaded terminal panels. No soldering is required - you just clip the leads to the driver terminals. is quite straightforward. No woodworking ability is necessary and you need only a Phillips head screwdriver and a roll of masking tape. Making the cabinets First, unpack and lay out all the various components (drivers, crossover parts and cabinets) and check that you have everything. Don't fully unpack the cabinets until you are ready to assemble them, to avoid the risk of getting them scratched. Tackle the assembly of the cabinets one at a time. The method of assembly is shown in Fig.10. You'll need a large, flat area to w ork on - the kitchen table or a hard floor, for example. Put down newspaper or plastic sheeting to protect both the cabinet and your work area. The cabinet sides come as a continuous length of vinyl coated 16mm-thick particle board, with the four panels separated by V-cut grooves - the vinyl coating holds th.e panels together. Lay out the long continuous side piece and note which are the two side panels (the longer ones), and which are the top and bottom. The bottom panel is the short piece at one end. When the cabinet is folded up, the join is at the bottom. Run a generous bead of the PVA glue supplied in the hardware kit into J ANUARY 1993 21 Fig.9: this diagram is included for those who wish to build their own cabinets. 70 HOLES: A • 146 DIA. B • 63 DIA C • 46 DIA. 150 420 7.5 TOP, SIDES, BOTTOM AND BACK 16mm HIGH DENSITY PARTICLE· BOARD BAFFLE 18mm HIGH DENSITY PARTICLE BOARD BAFFLE MOUNTED IN 8.5 x 18 REBATE MACHINED IN TOP, BOTTOM AND SIDES BACK HAS 50 DIA HOLE IN CENTRE FOR CONNECTIOR. 140 MOUNT BACK IN 8.5 x 16 GROOVE MACHINED IN TOP, BOTTOM AND SIDES 5.5 FROM REAR EDGE OF ENCLOSURE DIMENSIONS IN MILLIMETRES PEERLESS PSK60/2 LOUDSPEAKER SYSTEM 22 SILICON CHIP 1. Lay out the wraparound side piece on a flat surface & run PVA glue into the three V-cuts, the two ends & the rear panel rebate channel. 2. Wrap the sides around the rear panel (finish side outwards). 3. Hold the final corner together with masking tape. 4. Install the foam damping, run glue around the front panel rebate & install the front panel. Note: the small vent port (not shown in this diagram) should be next to the final join. Fig.10: this diagram illustrates the procedure for assembling the cabinets. Make sure that you install the front panel with the grey vinyl coating facing outwards & so that the final join in the cabinet is towards the bottom. each V-cut and the rear panel rebate channel but not the front panel rebate. Run a bead of PVA glue on the end V-cuts, too. Place the rear panel, with the black (finish) side outwards, into the rebated channel of the top panel. Now carefully wrap the sides around the rear panel, taking care not to stress the corner joints. Press the final side and bottom panel together and hold it in place with several strips of masking tape run around the corner - see Fig.10. If a little PVA glue oozes out of the joints onto the veneer, you can wipe it away with a damp cloth. Otherwise, it is easily peeled off once the glue has dried. Now run a generous line of glue into the channel for the front panel. You can then push-fit the front panel into position, making sure it goes in with the woofer hole downwards and with the grey vinyl coating on the outside. You should now leave the enclosure to dry for at least five hours. The next step is to fit the crossover and rear terminal panel assembly which is supplied as a complete unit with the kit. This is simply screwed into place on the rear panel with four countersunk screws. Next fit the damping material you'll need a piece of 25mm thick high density polyurethane foam to cover the rear panel only. This is supplied with the kit. Cut a hole to clear the crossover and driver wires and place it against the back panel. Because it is cut slightly oversized, it will sit firmly, otherwise you can glue it to the back panel. Mounting the loudspeakers You can now terminate the crossover wires to their respective drivers. The tweeter leads (grey + grey with Making your own crossover network If you're maKing your own crossovers, you will need to wind your own inductors. This can be done by hand, using bobbins with a diameter of 38mm and a coil length (between cheeks) of 41 mm. You could make your own bobbins from scrap timber. L 1, the 2.5mH choke, is 305 turns of 1mm enamelled copper wire. L2, the 0.4mH choke, is 104 turns of 1mm enamelled copper wire. All the crossover components can be hardwired and glued to a piece of timber. This can then be glued or screwed onto the -rear panel of the enclosure. JANUARY 1993 23 PARTS SUPPLIED IN HARDWARE KIT 2 Peerless 174WF woofers 2 Peerless 80DT dome tweeters 2 PSK-60/2 crossover networks mounted on terminal panels 2 bass reflex ports, 45 x 114mm 2 foam pieces, 25 x 185 x 390mm 8 male/female grille clips 2 Peerless badges 2 Peerless specification labels 1 bottle 125ml PVA glue 2 fig.8 connecting wires 1 strip black rubber feet (8 pcs) Screws for drivers & terminals Instruction manual Tools you will need Phillips head screwdriver Hammer Strong PVC or masking tape black trace) should be pulled through the tweeter hole and the woofer leads (red+ red with black trace) go to the woofer. Carefully check the polarity of each driver. The wire with the black trace is positive for both the woofer and tweeter. No soldering is required -you simply push the wire clips onto the relevant terminals on the speakers. Check your wiring once it's finished, then screw the two drivers in place using the self-tapping screws supplied. No gasket is necessary for the woofer or tweeter as the vinyl coating of the baffle does this job, as well as being decorative. Now you can push the pre-cut port assembly into place. This should be a firm fit. Fitting the grille cloth frame While the kits will have the cloth fitted over the grille cloth frames , you will have to fit the plastic clips. The baffle has four female clips while the grille cloth frame has four male clips. Fit the male clips first. These are fragile and can be broken if treated incorrectly. The recommended way to do it is to fit a female clip over each male clip and then lightly tap the base of the female clip to drive the male clip into its hole in the grille cloth frame. Do this for each of the four male clips. This done, remove the female clips 24 SILICON CHIP This photo shows how the speaker cabinets should appear when they are assembled. Note that the female grille clip sockets have been fitted to the front panel. and tap them into their four holes in the front panel. The grille cloth frame can then be fitted over the front panel and the speaker is finished. Do a final check. If you're sure everything is together correctly, hook them up, select some music and sit back and enjoy your new loudspeakers. We're sure you'll be impressed with them. Don't overdrive them As noted above, the Peerless PSK 60/2 loudspeakers can be used with amplifiers with an output power of up to 60 watts per channel. Even so, it is advisable never to turn your amplifier up to full volume, regardless of its power rating. An amplifier which is run into clipping, even for a short period, is capable of damaging the speaker voice coils. If the Peerless PSK 60/2 loudspeakers are used free standing, we strongly recommend that they be placed on stands so that the tweeters are at ear level when you are seated in your usual listening position. Not only will this allow you to better appreciate the trebl~ but it will prevent the likelihood of muddy and over-emphasised bass which happens when speakers are too close to the floor. For the same reason, we recommend that you don't place the speakers close to the corners of the room; it may boost the bass but the result will be "muddy" sound. SC