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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 22nd March 2020, 05:11 PM   #11
jReave is offline jReave  Canada
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The general rule of thumb is that you can play with dimensions if you stay within about 10% of the original.

Attached below shows why this is true in your case. Here are the comparisons of the baffle diffraction with Troel's original dimensions and then with your new dimensions. What's important is to keep the drivers's placement on the new baffle about the same as the old baffle in terms of distances from the cabinet top and sides. You can see that the differences in response are absolutely minimal and therefore, the xo is going to be perfectly fine in the cabinet you have selected.

More important as has been mentioned is getting the port right for the new net volume of your cabinet. Also, bracing is important, more so when you are using good drivers - you don't want the cabinet resonances messing up the quality you are paying for in the drivers. So keep the braces and redesign the port. Get help with that if you need it. And/or use a sub for the LF's.

The other problem not mentioned so far is the over 100mm difference in height. Ideally, the tweeters should be at ear height in your listening position. You will lose a little bit of HF response by being vertically off-axis. So if this is the case, lower your chair, raise up the cabinets a little or perhaps reduce the resistance on the tweeter by an ohm or 2.
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File Type: jpg baffle diffrcation comparison.jpg (63.8 KB, 50 views)
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Old 22nd March 2020, 09:13 PM   #12
Rallen is offline Rallen  Denmark
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Quote:
Originally Posted by Douglas Blake View Post
That was me and I may have misunderstood you...
My comment was based on the understanding you already had the crossovers in hand.

If you are going to have to build a crossover, no matter what, then going with a fresh design specific to your choices makes a whole lot more sense.

Thanks for clarifying. I am currently learning about crossovers for the purpose of designing my own - at some point. For now I'm pretty sure I will be better off with Troels' XO than anything I would be able to design myself ;-)

Quote:
Originally Posted by jReave View Post
The general rule of thumb is that you can play with dimensions if you stay within about 10% of the original.

Attached below shows why this is true in your case. Here are the comparisons of the baffle diffraction with Troel's original dimensions and then with your new dimensions. What's important is to keep the drivers's placement on the new baffle about the same as the old baffle in terms of distances from the cabinet top and sides. You can see that the differences in response are absolutely minimal and therefore, the xo is going to be perfectly fine in the cabinet you have selected.

More important as has been mentioned is getting the port right for the new net volume of your cabinet. Also, bracing is important, more so when you are using good drivers - you don't want the cabinet resonances messing up the quality you are paying for in the drivers. So keep the braces and redesign the port. Get help with that if you need it. And/or use a sub for the LF's.

The other problem not mentioned so far is the over 100mm difference in height. Ideally, the tweeters should be at ear height in your listening position. You will lose a little bit of HF response by being vertically off-axis. So if this is the case, lower your chair, raise up the cabinets a little or perhaps reduce the resistance on the tweeter by an ohm or 2.
That is indeed good news. Thank you very much - both for the conclusions and for your explanations of what to keep in mind.

I have actually spent most of my evening trying to figure out about the reflex port. My hope was to somehow calculate how the port should be modified in order to get the "same" result as Troels' ones. However, I can't really figure out how to do that.

I have gathered various different software to calculate port sizes, but I always hit the wall when I'm supposed to make a decision about which tuning frequency I want. WinISD gave me some suggestions, but I ended up with a tube much larger than the enclosure itself ;-)

The current port in the enclosures I am (re)using is about 68x140mm. Easiest thing would obviously be to just extend or shorten this if thats a possibility, but I'm up for making a new port or adding an additional one.

Any suggestions would be greatly appreciated - thanks already!!
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Old 22nd March 2020, 11:22 PM   #13
Pharos is offline Pharos  United Kingdom
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General rule was that the port length is about X3 the diam.
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Old 23rd March 2020, 12:10 AM   #14
jReave is offline jReave  Canada
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Personally, I like Unibox better than WinISD but it needs Excel.

Unfortunately, vented box F3 is going to be a function of both box size and port length. So you really can't get the same response in a smaller box just by using a longer port. But you can still get a good response with a smaller box albeit with a higher F3. Just tune F3 a little bit higher by increments until you get the best response possible. Most likely that will need a longer port too than the original.

Here's a thought that just came to me. I wonder if you might be able to fashion a new base for each cabinet such that it will raise the tweeter up closer to its original height and by cutting out the bottom of the existing cabinets, also add some extra liters to the net volume.
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Old 23rd March 2020, 09:45 AM   #15
Rallen is offline Rallen  Denmark
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Thanks. I have been thinking about ways to rise the tweeters as well - I will at least add some spikes to add a little more height.

Currently looking at UniBox, which doesnt make me any less confused. I have managed to load the speaker values end enter the volume, but I'm kinda lost from there. Haha Will give it another go later.

Do you have any idea what kind of port measurements I should end up with for the design?

Last edited by AllenB; 23rd March 2020 at 09:47 PM. Reason: Remove excess quoting
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Old 23rd March 2020, 10:17 AM   #16
Rallen is offline Rallen  Denmark
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Woops. Was supposed to be en edition of the above, not a new post..

EDIT: Fiddled a little more with it, but my preliminary conclusion is the same as I got from WinISD. It wants my port to be longer than the cabinet depth for the 22,5-23,5L that my interval volume should be..
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Old 23rd March 2020, 10:35 AM   #17
system7 is offline system7  United Kingdom
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I think you may be agonising over this way too much. It is a fairly narrow baffle and about 50L, but whatever.

I looked at Troels' design as much as he publishes now:
Amish revisted

Interestingly, our Goran did something 25L quite similar:
www.audioexcite.com >> Classic Two – M5

OK, a slightly updated bass 01, but his bass filter is near as dammit the same.

I am no great shakes on reflex, but I think tuning is overrated. There are many different bass alignments. IIRC, smaller boxes get smaller ports You can line a port with a bit of carpet to make it narrower. Or put drinking straws in for a bit of damping.

Wouldn't do much harm to try Goran's simpler tweeter 9500 filter too. I usually just fiddle about with resistors to get level right. All this deep null stuff is overly fussy IMO. Tiny differences. As people have said, 10% change is nothing.
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Old 23rd March 2020, 10:39 AM   #18
Rallen is offline Rallen  Denmark
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Thanks for your input! I did wonder why theres so much difference between Troels' 9500 and 9700 filters when the drivers are supposed to be almost identical :-)
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Old 23rd March 2020, 11:00 AM   #19
system7 is offline system7  United Kingdom
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Troels has done some measurements, and the 9500 is 2dB louder than the 9700:
Why ScanSpeak tweeters 9500 and 9700 aren'

So you'd take out an ohm or two of resistance in the filter.

If the 9700 is a bit louder at the very top, you'd fix that with a little 7.5R plus 1uF Zobel shunt.

All fixable,IMO. I'm not quite clear what the volume of the tower cabinet is internally. But about 20-25L is what most people do.
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Old 23rd March 2020, 11:07 AM   #20
Rallen is offline Rallen  Denmark
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Thanks. I think my enclosures are around 22,5-23,5L internally.
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