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Therefore, you will likely need to attenuate the tweeter to blend properly with the woofer and achieve a flat response. This adjustment is usually handled within the design of the speaker’s passive crossover network. I believe this response is incorrect since it assumes that both drivers have the same efficiency. I think the AI is correct that the 4W tweeter will pass twice the current and hence twice the power, but this does not in itself mean that the tweeter will produce 3dB more sound. This would only be true if both had the same efficiency. The fact that both are rated to produce the identical sound pressure level of 89dB established during actual tests must show that the tweeter is half as efficient as the woofer. In my opinion, the AI is ignoring this information and assuming that if the tweeter draws twice the power, then it must produce twice the sound pressure level. (P. T., Casula, NSW) ● Your question states that, fed with Advertising Index Altronics.................................35-38 Blackmagic Design....................... 5 Dave Thompson........................ 103 DigiKey Electronics..................OBC Emona Instruments.................. IBC Hare & Forbes............................ 6-7 Jaycar............................. IFC, 12-15 Keith Rippon Kit Assembly....... 103 Lazer Security........................... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.................. 9 Mouser Electronics....................... 3 PCBWay....................................... 11 PMD Way................................... 103 SC PICKit Breakout Board........ 103 Silicon Chip Back Issues........... 57 Silicon Chip Binders.................. 58 Silicon Chip PDFs on USB......... 65 Silicon Chip Subscriptions........ 59 Silicon Chip Shop.................90-91 The Loudspeaker Kit.com............ 8 Wagner Electronics..................... 10 104 Silicon Chip the same voltage, both drivers will produce the same sound level. But since you stated one has an 8W impedance and one has a 4W impedance, at a fixed voltage level, the 4W speaker is running at 2W and the 8W speaker is running at 1W. That means the 4W speaker is 3dB less efficient than the 8W speaker. However, because their sensitivity rating is being given relative to a voltage, if you connected them in parallel and drove them from a voltage source, they would give roughly the same sound output level. The lower efficiency of the 4W driver is cancelled out by the fact that it will draw more power when driven with the same voltage as the 8W driver. Still, this is an odd way to specify efficiency; it’s more commonly specified as a decibel level at a specific power level (typically 1W). You might be surprised to find that if you test this in the real world, the speaker output levels may not be well-matched if connected in parallel. Whether the tweeter will need attenuation depends on the actual measured on-baffle responses and the crossover. Toroidal core spec for electric fence I’m going to build the “New High Power Electric Fence” project from the April 1999 issue (siliconchip. au/Article/4577). I’m having trouble understanding which E30 ferrite cores I should use. I found several sizes available, for example: NEE30/15/14, NEE30/15/11, NEE30/15/7 and NEE30/11/11. The numbers between the slashes indicate the width and thickness of the core. These measurements substantially alter the Ae and Le parameters of these cores. The article doesn’t include the Jaycar store code, so I don’t know which one to use. Can you help me by providing this information? (N. B. E., Sao Paulo, Brazil) ● The 30/15/14 cores you mentioned are suitable. Jaycar doesn’t sell this size of core, so there wasn’t a catalog code to provide. HV supply wanted for testing capacitors Are you going to design a high-­ voltage power supply, say 50-300V DC at up to 3mA? I want to charge capacitors to test them. (R. M., Melville, WA) ● The Insulation Tester circuit (May 1996; siliconchip.au/Article/5007) has a high-voltage generator that could be easily modified to provide a 50-300V DC supply. By removing (shorting out) one of the 4.7MW resistors in the feedback divider, you can get output voltages of 500V, 300V, 250V, 125V or 50V (switch positions 1 to 5) at the cathode of diode D3. Everything after diode D3, including the lower half of the circuit, is not required. Alternatively, use the circuit we designed specifically for testing capacitors, the Electrolytic Reformer & Tester from August & September 2010 (siliconchip.au/Series/10). The circuit board and programmed PIC microcontroller are still available. Substituting tantalum for aluminium caps I am currently building the Audio Signal Injector & Tracer from June 2015 (siliconchip.au/Article/8603) and am having difficulty finding electrolytic capacitors short enough to fit in the case. Is it feasible to use tantalum capacitors instead (100μF 16V and 1μF 16V)? (J. A., Townsville, Qld) ● Yes, you can use tantalum caps instead of aluminium electrolytics for SC the Signal Injector and Tracer. Errata and on-sale date for the next issue Ultrasonic Cleaner part 2, October 2020: in the winding instructions in Fig.9, the reference to pin 19 should say pin 8 instead. Scale Speed Checker for model railway, January 2026: the 120Ω resistors should be in series with pin 2 of the connectors for the IR sensors (and the photodiodes), not pin 1 (the collectors). Also, the IR LED anodes and cathodes should be swapped. Next Issue: the April 2026 issue is due on sale in newsagents by Monday, March 30th. Expect postal delivery of subscription copies in Australia between March 27th and April 13th. Australia's electronics magazine siliconchip.com.au