Loudspeaker System Design: The Final Details

As promised much too long ago, here are the detailed plans and bill of materials to construct my new loudspeaker system.

The PCB (printed circuit board) layout bitmaps are (or at least should be) correctly scaled so that if you print them out at 1:1 scale you should have the true size of the boards. The mid range/tweeter crossover page size is A3 and the woofer crossover page size is A4.

Far from being printed, I actually built them in a very crude manner by simply taking a single sided PCB blank, marking the cut pattern on it with a marker pen and cutting (with a small angle grinder) rather than etching, the board and drilling the holes. The grey colour corresponds to copper that needs to be etched or cut, whichever way you choose.

The large holes in the PCB’s along side each inductor are for secure mounting purposes which I achieved through the use of nylon cable ties to hold them securely in place (they are pretty heavy owing to the cores). After the fact I discovered that it is important to secure the components via other means to dampen resonances. The approach I took was to use silicone rubber to secure the components to the boards to reduce component vibration. Similarly, when mounting the crossover boards inside the cabinet care must also be taken to ensure that the board vibrations are damped out. For that I simply used some of the packing foam the inductors came encased in.


Final Crossover Design Schematic Diagram




Mid-range/Tweeter Crossover PCB design – (15 by 30 cm in size).


Woofer Crossover PCB design – (10 by 20 cm in size).

The cabinets should be constructed with 18 mm MDF or something similarly heavy and robust. You may choose to build it in a different shape as shown as long as the volumes are preserved and the driver layout is as shown with the mid-range unit mounted above and the woofer mounted below the tweeter.

Although the plan does not show it, I recommend adding extra bracing behind the front facia between the holes cut for the tweeter and mid-range units as the mid-range can give rise to significant cabinet colouration arising from structural vibrations. I found this out after the fact, initially assuming it would be problematic so couldn’t easily retrofit such bracing.

The woofer- mid unit also requires a stand-off to time align it to the tweeter for which plans are shown below. I constructed this from two sheets of 12mm MDF cut to shape and glued together, then painted to beautify. Note that the cusp on the stand-off should point to the centre of the tweeter when the drivers are mounted.

During assembly gaskets are required for the tweeter and woofer-mid range drivers, the standoff and the vent (if you choose to use the “Precision Port” that I used). For this I used un-polished leather which works very well as a gasket material and is readily available from leather craft stores.

The port length should be adjusted to obtain the required 30Hz box frequency. If you use the “Precision Port” in the bill of materials then this is obtained with a pipe length of 30 mm joining the two flanges.

How you choose to mount the PCB’s I leave up to you. In my case I screwed them to the back panel of the cabinet just behind the woofer. making them accessible and constructable without the need of an access port. That was also the reason for two PCB’s because the boards needed to be small enough to be able to maneuver into the cabinet through the woofer port.

The woofer-mid-range enclosure should be filled with accetate wool / Insulation. The stuff I used I got from a haberdashery store which was sold as cushion stuffing material. You could equally well use material meant for thermal insulation. Most of the woofer cabinet should be free of acoustic insulation to obtain the right box Q. In my case I filled the bottom 1/4 of the cabinet with accetate wool which appears to give a box Q pretty close to the design ideal.



Basic Cabinet Design


Woofer-Mid Standoff Design


Bill of Materials

2 of Peerless SDS-830656 5 1/4″ Woofer-Midrange

2 of Peerless SLS-830667 8″ Sub-Woofer

2 of Precision Port 3″ flared port tube kit

2 of Gold Banana 5-way recessed speaker terminal round

2 of Vifa XT25TG-30-04 Dual Cone Super Tweeter

2 of 1 uF 100V non-polarised electrolytic capacitor [ C16 ]

2 of 4.7 uF  Jantzen 400V crosscap capacitor [ C4 ]

2 of 10 uF 100V non-polarised electrolytic capacitor [ C7 ]

2 of 18 uF  Jantzen 400V crosscap capacitor [ C14 ]

2 of 22 uF  Jantzen 400V crosscap capacitor [ C3 ]

2 of 27 uF 100V non-polarised electrolytic capacitor [ C11 ]

4 of 33 uF 100V non-polarised electrolytic capacitor [ C8, C18 ]

2 of 47 uF  Jantzen 400V crosscap capacitor [ C2 ]

2 of 56 uF Jantzen 400V crosscap capacitor [ C15 ]

4 of 80 uF 100V non-polarised electrolytic capacitor [ C5, C6 ]

8 of 200 uF 100V non-polarised electrolytic capacitor [ C1, C9, C12, C17 ]

2 of 250 uF 100V non-polarised electrolytic capacitor [ C13 ]

2 of 400 uF 100V non-polarised electrolytic capacitor [ C10 ]

2 of 0.05 mH Jantzen 16AWG air cored 0.06 ohm DCR inductor [ L9 ]

2 of 1.5 mH Jantzen 15AWG P cored 0.14 ohm DCR inductor [ L1 ]

2 of 0.45 mH Jantzen 16AWG air cored 0.25 ohm DCR inductor [ L2 ]

4 of 0.56 mH Jantzen 15AWG P cored 0.08 ohm DCR inductor [ L10, L11 ]

4 of 3.3 mH Jantzen 18AWG P cored 0.35 ohm DCR inductor [ L3, L4 ]

2 of 5.6 mH Jantzen 18AWG P cored 0.45 ohm DCR inductor [ L7 ]

2 of 12 mH Jantzen 18AWG P cored 0.57 ohm DCR inductor [ L5 ]

2 of 18 mH Jantzen 18AWG P cored 0.83 ohm DCR inductor [ L8 ]

2 of 22 mH Jantzen 18AWG P cored 0.96 ohm DCR inductor [ L6 ]

6 of 0.33 ohm wirewound 5W resistor [ R1, R2, R11 ]

2 of 2.2 ohm wirewound 5W resistor [ R4 ]

4 of 2.7 ohm wirewound 5W resistor [ R5, R6 ]

4 of 3.3 ohm wirewound 5W resistor [ R9, R10 ]

2 of 6.8 ohm wirewound 10W resistor [ R3 ]

4 of 8.2 ohm wirewound 10W resistor [ R7, R8 ]


You should be able to purchase all the parts required through Parts-Express.


Final Thoughts

Having now had my new speakers for 9 months or more and having had many hours listening with them, I can say with complete honesty that I find them a pleasurable listening experience. It is easy to forget that the sound is emanating from loudspeakers and to feel immersed in the experience. I’ve yet to hear with any certainty a audible problem with the sound reproduction of these loudspeakers. If I ever hear disturbing things it is invariably due to problems in the recording itself.

What really impresses me about these speakers are the bass extension, the reproduction of voice and the well balanced sound in the far field. It genuinely fills the living room and open plan kitchen with well balanced sound even though the speakers are not in the living room, but rather situated in my adjacent small “music room”. The bass extension has, on many occasions, indicated low frequency noise problems in recordings that simply aren’t audible through my old speakers.

I have said it before and I shall say it again with confidence. Anyone who has the courage to build this loudspeaker system will be impressed by their performance but I can well understand that such an ambitious project may well be beyond most, if for no other reason than the cost of the components required to build them. The drivers aren’t expensive but the number of components in the crossover escalates the cost of the system, so much so that the crossovers cost nearly twice as much as the drivers! However, skimping on the crossover design will only come at the cost of performance and that really wasn’t my aim so I’d argue the added cost is more than worth it. My system cost me about $1200 and my labour to construct. There is absolutely no way I could get anything approaching this level of performance for that sum of money and I’d argue that I’d be spending in excess of $5000 on a commercial system to obtain similar capabilities.

All in all I thoroughly enjoy listening to my new speakers and have absolutely no desire to replace them any time soon, perhaps never.


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