EchiDna Posted April 9, 2022 Share Posted April 9, 2022 On 05/03/2021 at 16:50, stevie said: Here's a diagram of the crossover. It doesn't get any simpler than this. I've assembled the circuit using a (chocolate block) terminal strip. So - no soldering needed. I'll post a frequency response of the finished system and of the assembled crossover later today. The Pulse 10 is wired directly to the input and this circuit connects to the HF unit. Seems my build is being hamstrung by a mis-labelled 4.7k ohm resistor and the horn is not getting any signal at all! That will teach me to build something without measuring the devices... before I buy the correct 4.7ohm item, is there an ideal wattage? is 5w large enough? Cheers Quote Link to comment Share on other sites More sharing options...
stevie Posted April 9, 2022 Author Share Posted April 9, 2022 5W isn't enough. Use 17 to 20W to be on the safe side. Quote Link to comment Share on other sites More sharing options...
EchiDna Posted April 9, 2022 Share Posted April 9, 2022 Thanks Stevie, will see what I can find in that range... Quote Link to comment Share on other sites More sharing options...
agedhorse Posted April 9, 2022 Share Posted April 9, 2022 6 hours ago, EchiDna said: Seems my build is being hamstrung by a mis-labelled 4.7k ohm resistor and the horn is not getting any signal at all! That will teach me to build something without measuring the devices... before I buy the correct 4.7ohm item, is there an ideal wattage? is 5w large enough? Cheers 10 watts will be plenty, multiply the (~25W) RMS power rating of the compression driver by~ 1/3 (the ratio of 4.7 ohms / 8 ohms) and you will see a maximum power dissipation of about 8.25W, which is pretty much the absolute worst case that the resistor will see. In actuality, given the crossover frequency and the power spectrum density for bass guitar, it will be about 1/2 of this value. I have used this formula and approach in commercial speakers for decades without any problems. 3 1 Quote Link to comment Share on other sites More sharing options...
stevie Posted April 10, 2022 Author Share Posted April 10, 2022 While it's true that the resistor in the crossover isn't going to see much more than 8W, I'm a great believer in overspecifying resistors in power speakers, having seen too many burnt-out crossover boards in the past, where the resistors have overheated and taken everything else with them. The best place to get these in the UK is Blue Aran, where a 4.7 ohm 20W resistor costs 79p. 1 Quote Link to comment Share on other sites More sharing options...
nilebodgers Posted April 10, 2022 Share Posted April 10, 2022 1 hour ago, stevie said: While it's true that the resistor in the crossover isn't going to see much more than 8W, I'm a great believer in overspecifying resistors in power speakers, having seen too many burnt-out crossover boards in the past, where the resistors have overheated and taken everything else with them. The best place to get these in the UK is Blue Aran, where a 4.7 ohm 20W resistor costs 79p. Yes, a bigger resistor is very cheap. Back when I did some serious design on PA speakers I used the 20w axial ceramics (paralleling when I needed more safety margin) and they survived years of thrashing without a single failure. 2 Quote Link to comment Share on other sites More sharing options...
agedhorse Posted April 10, 2022 Share Posted April 10, 2022 When using heavier parts (like 20 watt resistors), provided the smaller part is properly specified, I see more mechanical damage from the larger parts being not well secured to the PCB. With the larger resistors, they must be mechanically secured in addition to being soldered. All it takes is the cabinet falling over to cause such mechanical damage. 4 Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted April 11, 2022 Share Posted April 11, 2022 (edited) I think that the responses from @Stevie and @agedhorse highlight that design choices usually have benefits as well as downsides. Edited April 11, 2022 by Chienmortbb 1 Quote Link to comment Share on other sites More sharing options...
Stub Mandrel Posted April 11, 2022 Share Posted April 11, 2022 Make sure the resistor is mounted so air can move freely around it. 1 Quote Link to comment Share on other sites More sharing options...
agedhorse Posted April 12, 2022 Share Posted April 12, 2022 On 11/04/2022 at 05:27, Stub Mandrel said: Make sure the resistor is mounted so air can move freely around it. It still needs to be mechanically secured or damage to the leads and/or PCB will result when the cabinet takes even a minor tumble. Most 20 watt parts have bumps in the bottom for this purpose, most 10 watt parts do not, and don’t need it with FR-4 PCBs. 1 Quote Link to comment Share on other sites More sharing options...
Dad3353 Posted April 12, 2022 Share Posted April 12, 2022 Another option is to use an array of smaller, lighter resistors, calculated to have the same overall resistance and power handling, but less subject to shocks. As the power is shared, they have less need to be 'in the air', and thus less prone to damage. Four 4.7 Ohm 5W resistors in series/parallel, for example. Just a thought. 1 Quote Link to comment Share on other sites More sharing options...
agedhorse Posted April 13, 2022 Share Posted April 13, 2022 1 hour ago, Dad3353 said: Another option is to use an array of smaller, lighter resistors, calculated to have the same overall resistance and power handling, but less subject to shocks. As the power is shared, they have less need to be 'in the air', and thus less prone to damage. Four 4.7 Ohm 5W resistors in series/parallel, for example. Just a thought. Yes, this is sometimes done for mechanical reasons (especially with surface mount components, which obviously doesn't apply here). Smaller components have lower individual mass combined with a lower center of gravity. 1 Quote Link to comment Share on other sites More sharing options...
Stub Mandrel Posted April 13, 2022 Share Posted April 13, 2022 8 hours ago, agedhorse said: It still needs to be mechanically secured or damage to the leads and/or PCB will result when the cabinet takes even a minor tumble. Most 20 watt parts have bumps in the bottom for this purpose, most 10 watt parts do not, and don’t need it with FR-4 PCBs. My concern was that it doesn't end up surrounded by acoustic wadding. Quote Link to comment Share on other sites More sharing options...
stevie Posted April 13, 2022 Author Share Posted April 13, 2022 This is all a bit of a strawman. The instructions for assembling the crossover are on page 3. We're not using a PCB; we're using a chocolate block. The resistor is fitted against the chocolate block and taped (or tie-wrapped) to it, and the chocolate block is then screwed to the cabinet. If you wire it up this way, there is no chance of the resistor wires breaking. The heaviest component isn't actually the resistor - it's the coil. And the advice there is to screw the coil directly to the cabinet. 2 Quote Link to comment Share on other sites More sharing options...
agedhorse Posted April 13, 2022 Share Posted April 13, 2022 7 hours ago, stevie said: This is all a bit of a strawman. The instructions for assembling the crossover are on page 3. We're not using a PCB; we're using a chocolate block. The resistor is fitted against the chocolate block and taped (or tie-wrapped) to it, and the chocolate block is then screwed to the cabinet. If you wire it up this way, there is no chance of the resistor wires breaking. The heaviest component isn't actually the resistor - it's the coil. And the advice there is to screw the coil directly to the cabinet. My comments were general in nature, all heavy components need to be securely mounted regardless of how they are used. I would not recommend using tape to mount a component that's likely to get hot. Quote Link to comment Share on other sites More sharing options...
Stub Mandrel Posted July 30, 2022 Share Posted July 30, 2022 Placemarker Quote Link to comment Share on other sites More sharing options...
Bigwan Posted March 22, 2023 Share Posted March 22, 2023 Resurrecting this as I'm looking to put two of these cabs together. Have the drivers so need the wood and crossover components. Never did I think it'd be so hard to find decent plywood in Northern Ireland. Thought I was sorted with a company that would cut panels of 12mm Baltic Birch to size and post for a reasonable price (as in sub £100 for the 2 cabs), but of course they won't post to Northern Ireland. Anyone got a lead on somewhere that will? While I COULD buy some rubbish plywood locally and do the cutting myself, buying in "kit" form would increase the likelihood of me actually doing it 10-fold! Quote Link to comment Share on other sites More sharing options...
tauzero Posted March 22, 2023 Share Posted March 22, 2023 Did you try https://www.woodsheets.com/ ? I don't know if they supply to NI but they provide a cutting service. Quote Link to comment Share on other sites More sharing options...
Bigwan Posted March 22, 2023 Share Posted March 22, 2023 2 minutes ago, tauzero said: Did you try https://www.woodsheets.com/ ? I don't know if they supply to NI but they provide a cutting service. Trying them just now Quote Link to comment Share on other sites More sharing options...
Bigwan Posted March 22, 2023 Share Posted March 22, 2023 22 minutes ago, tauzero said: Did you try https://www.woodsheets.com/ ? I don't know if they supply to NI but they provide a cutting service. YES!!! Ordered! 1 Quote Link to comment Share on other sites More sharing options...
tauzero Posted March 22, 2023 Share Posted March 22, 2023 Excellent! Quote Link to comment Share on other sites More sharing options...
Downunderwonder Posted March 24, 2023 Share Posted March 24, 2023 On 23/03/2023 at 01:11, Bigwan said: YES!!! Ordered! You need to be careful ordering birch that it is actual birch ply and not just veneer. Quote Link to comment Share on other sites More sharing options...
Bigwan Posted March 24, 2023 Share Posted March 24, 2023 50 minutes ago, Downunderwonder said: You need to be careful ordering birch that it is actual birch ply and not just veneer. I guess we'll see... Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted March 25, 2023 Share Posted March 25, 2023 looking at the Woodsheets site it looks good. They seem to be using high quality plywoods and from their offer are CNC machining from consistent quality materials, and charging accordingly. One of the indicators is that they are using sheets with multiple cores. The cheaper boards generally use fewer thicker plies. Let us know how you get on with them and if they provide a good service others will want to go to them. Looking forward to your build 1 Quote Link to comment Share on other sites More sharing options...
Bigwan Posted March 31, 2023 Share Posted March 31, 2023 On 25/03/2023 at 08:22, Phil Starr said: looking at the Woodsheets site it looks good. They seem to be using high quality plywoods and from their offer are CNC machining from consistent quality materials, and charging accordingly. One of the indicators is that they are using sheets with multiple cores. The cheaper boards generally use fewer thicker plies. Let us know how you get on with them and if they provide a good service others will want to go to them. Looking forward to your build It MAY look good... But looks like I'll never know. "Birch plywood is out of stock" email just received... Quote Link to comment Share on other sites More sharing options...
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