Crossover components choice

[Threadbare]

I want to build the Tarkus design and have the designer's building notes from his website. There is a circuit schematic and a list of components. I am particularly befuddled by which capacitors to buy. The list doesn't specify much apart from value. Some are polypropylene and some are electrolytic. Most electrolytics are polarised but the schematic doesn't show any polarity markings. Do I assume they are bipolar types and just whack 'em in. Also there are no voltage recommendations for them, nor wattage figures quoted for the resistors.

I can read a schematic and solder, have done it professionally years ago, but I'm not a design engineer so cannot magic up the missing information from a theoretical direction. Can anyone shed any light on what components are actually required?

Thanks in advance.

[DanP]

If using electrolytics, they must be bipolar, though poly caps will last longer and might sound better. I'd say use a minimum of 100V caps (50V is probably fine if you have some laying around). For the resistors, use non-inductive audio resistors with a minimum ratimg of 10W. Basically anything that PE sells in their crossover components section will work well.

Dan

[Threadbare]

Thank you Dan. That is very helpful. So either use bipolar or upgrade to a decent polypropylene if the value is available.

[killa]

Dan is correct. Paul probably used electrolytic because they were large values and electrolytics are a lot cheaper than poly caps.

[Threadbare]

That is the most likely reason. He used modestly priced drivers in the design as well. For that I am grateful.

[Threadbare]

I have ordered the crossover parts and now just firming up on the enclosure dimensions. Paul states the top box volume is 13 litres and the bottom one is 62 litres. I have calculated using his internal measurements they are actually 17.75 and 65.75 litres. Has anyone made the calcs and come up with anything different. The reason I ask is because I want to do simple rectangular shapes instead of sloping. Very easy to do if I know what volumes to aim for. His stated volumes don't really tally with the angled dimensions given. Or do they?
I have a feeling by the time I work this all out one or more of the drivers will be discontinued.

[PWR RYD]

I think his stated volumes are net volumes. You are calculating the gross volumes. The net volume is what is left of the gross volume after you subtract the space consumed by the port, the driver's magnet, internal bracing, etc.

[PWR RYD]

I would calculate his gross volumes, like you already have, then build your rectangular boxes with the same gross volumes. What is more important is that you keep your baffle widths and relative driver positions on the baffles the same as Paul did. A box volume +/- 5% will be inaudible.

[Threadbare]

Thanks for that, Craig. It makes sense now.

[PWR RYD]

I just took a look at Paul's crosover for the Tarkus. C5 is 125 uF. I would definitely just use a 125 uF, 100 V, non-ploarized electrolytic cap there. A 125 uF film cap would be huge, expensive, and might not make any audible improvement in that part of the circuit. C2, the 65 uF cap, is where you might want to splurge a little and pay for a film cap. All of the other caps are small enough I would definitely use film caps. I have had very good luck using the Audyn Q4 caps that PE sells. They are reasonably priced, always measure within spec, and have nice sturdy leads. I think they sound good.

[Threadbare]

I've already ordered the parts but thanks for the comments. I am still just finding my feet in the "audio" side of electronics. I have built things and repaired things over the years but never had the opportunity to learn about design so any input I get here is welcomed and appreciated. I just steer clear of any topics that might involve snake oil and subjective nightmares about which colour is best for cable ties.

[Dave Bullet]

What I've gathered over the years:
1. Crossover components in series with the drivers seem to be the focus for upgrades than those in parallel
2. Lower frequency sections tend to opt for cheaper components. Either this is price driven (larger values) or we are less sensitive to variations in bass "quality"
3. If you want to upgrade - series caps in the tweeter.... and less so but possibly midrange circuit are what people do
4. for all parallel legs - higher resistance inductors (remember to subtract / allow for inductor DCR) and non-polar / bi-polar electrolytic caps are fine. Ideally your XO simulation software will allow you to measure power dissipation across the circuit so you can see if you have a load issue needing to parallel resistors etc...

[AEIOU]

A "parallel" component is just as much a part of the circuit, has an equal effect just as much as a series component. Think about it, -6dB (First Order) for only one series component, add a second parallel component and it is another -6dB for a total of -12dB. In other words the parallel component is just as responsible for total distortion as the series component.

[Threadbare]

I think his stated volumes are net volumes. You are calculating the gross volumes. The net volume is what is left of the gross volume after you subtract the space consumed by the port, the driver's magnet, internal bracing, etc.

After months of delays, bad health issues and pandemic lockdown I'm about to start cutting the mdf and went over the calcs for dimensions once more to make sure. Using Paul's published dimensions for the squared off version of the lower box using 3/4" material brings the gross volume to a whopping 72 litres! Are you sure this is correct? His comments about the build on his site mentions 62 litres. That's a lot of room for the port tube and single driver.

[Chris Roemer]

Earlier you wrote:
"Paul states the top box volume is 13 litres and the bottom one is 62 litres. I have calculated using his internal measurements they are actually 17.75 and 65.75 litres."
Uh... I DO get 65.7L for the lower box, but (off his orig. drawings) I get 13.4L for the top. He must've felt the magnet & port (in the bottom) consumed about 4L (230 cu.in.).

Working off his description of a rectangular bottom box, I get 65.7L (the EXACT same I got for his angled box). Again, this is gross internal volume.
A 4"id x 13" long port (from 4" PVC) uses up about 210cu.in. - leaving about 20ci for the Peerless motor/cone. Seems reasonable (enough) to me.

[Threadbare]

Thankyou Chris. I will check again until I get the figures to work as they should.