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Multi-Way Conventional loudspeakers with crossovers

Reusing crossover design for other enclosure
Reusing crossover design for other enclosure
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Old 23rd March 2020, 11:20 AM   #21
system7 is offline system7  United Kingdom
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Location: Portsmouth UK
Quote:
Originally Posted by Rallen View Post
Thanks. I think my enclosures are around 22,5-23,5L internally.
Goran used 50x110mm in 27L.

I used to buy adjustable ports to take the agony out of adjustments. They have tube within a tube that you can fiddle with. Never could hear much difference!
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Old 23rd March 2020, 04:02 PM   #22
jReave is offline jReave  Canada
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Quote:
Originally Posted by Rallen View Post
It wants my port to be longer than the cabinet depth for the 22,5-23,5L that my interval volume should be..
Longer ports are going to need to be bent. A 90 degree elbow will usually do the job. Many people just use plumbing type pipe from the local box store. And by using an elbow, you can permanently attach 1 end to your cabinet while still being able to pull out and cut the length on the other end of the elbow to make any necessary adjustments to the tuning.

For some reason I can't actually find this design on Troel's site. There also seems to be a bit of a disparity between the official spec sheet and what others are measuring in terms of TS parameters for the woofer. Using AudioExcite's data for the ScanSpeak 18W/8545-00 (is this actually the correct driver?), Unibox comes up with 20L vented tuned to 37Hz and with an F3 of 37Hz too. Port diameter chosen is 6.8cm so the length ends up at 34cm. See Pic 1.

Pic 2 - What I do next is go back and forth between adding more Nominal Power to the driver (Speaker Design tab, up in the top left table) and looking at the driver's excursion (Vented Box tab) until it's as close to xmax as possible without exceeding it for the lowest frequencies the driver will likely see, maybe 30-40Hz for most musical content.

Pic 3 - Once that point is reached, in this case with 40W, you have the reasonable max SPL that the driver is going to produce at 1m, in this case about 102dB. And now this is where you are going to check to see that your port has a large enough diameter to avoid chuffing and other unwanted noises at this SPL. Staying under 8% is good. Staying closer to 5% is better. But if you think that you will never actually play the drivers this loud, you can drop the wattage and reduce the port speed and therefore get away with a smaller diameter port. Notice that when the port diameter is smaller, the port length needed is also reduced.

Just for educational purposes, the next 3 pics show what happens if you only have 15L to work with. A flat response is now achieved when Fb is at 40Hz, F3 is 41Hz and the port is now 6.8cm x 39.5cm. Notice that port speed has been reduced at the same SPL because the tuning is a little higher so it isn't being asked to do quite as much work. Conceivably, you could drop the port diameter a little bit here if you wanted to. And again, even a smaller diameter if you think your max SPL is going to be lower than 102dB at 1m.

Hope that helps.
Attached Images
File Type: jpg SS8545 20LVB.JPG (152.6 KB, 31 views)
File Type: gif VB 20L Excursion ScanSpeak 18W8545-00 CF.gif (22.3 KB, 31 views)
File Type: gif VB 20L PortAirSpeed ScanSpeak 18W8545-00 CF.gif (21.7 KB, 31 views)
File Type: jpg SS8545 15LVB.JPG (150.2 KB, 31 views)
File Type: gif VB 15L Excursion ScanSpeak 18W8545-00 CF.gif (22.1 KB, 25 views)
File Type: gif VB 15L PortAirSpeed ScanSpeak 18W8545-00 CF.gif (21.6 KB, 3 views)

Last edited by jReave; 23rd March 2020 at 04:04 PM.
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Old 23rd March 2020, 07:19 PM   #23
Rallen is offline Rallen  Denmark
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Thanks man!!! I think I can make use of the programs now by looking at your thorough screenshots. I honestly don't understand everything yet, but I start getting some of it, and get some results for the port :-)

The most important thing for now, was to figure out that it is actually possible to get it working with the current port diam, so I dont have to order a new "port assembly" with the other parts.

You mentioned that I could consider lowering the tweeter resistance by 2 ohms to compensate for the listening angle. Is that something you would do? And what resistor would I lower then?

Click the image to open in full size.

Last edited by AllenB; 23rd March 2020 at 09:48 PM. Reason: Remove excess quoting
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Old 23rd March 2020, 09:09 PM   #24
jReave is offline jReave  Canada
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Troel has 2 resistors dropping the tweeter level - R1011 before the xo and R1071 after the xo. You could omit 1 or the other, listen and see which sounds best to you. Or if you assemble the resistors with .5ohm values (resistors in series add their values together), you have options to try just about any combination of alternatives.

I'll note that the resistors before and after the xo affect the FR in just very slightly different ways so removing 1 vs the other should actually sound a little different. But I think the differences are going to be very subtle with such small values so it would be interesting to see if you have a personal preference.
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Old 24th March 2020, 04:32 PM   #25
jReave is offline jReave  Canada
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Or hey, maybe you just need to tilt the speaker back a couple of degrees. That'd be pretty simple.
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