Port Tuning and Winisd

KJMO

KJMO

Feb 6, 2015
1,962
1,945
5,081
58
#1
The enclosure is about 3.7 cubic ft, with two Genz Benz 10pr300s from Avatar. It's sealed now, and Winisd says it should have pretty poor output below 100hz, which gels with what it actually sounds like. I thought it would be fun to try to put ports in, so I modeled it with 2 ports and it says they should each be 4x4 to get 52hz tuning. I ordered two 4x4 ports, and they're huge! Could that be correct? Before I cut out the holes, I thought I'd check.
 
#2
I always use Boxsim to calculate the port length.
The length also depends on the position of the ports, if they are e.g. close to the corners they get shorter, in the middle they would be longest. The amount of damping inside the cabinet will also alter the tuning a bit (more damping lowers the tuning).
If you use two 4" round ports(inner diameter is slightly smaller) their length should be approx 2.5" to get the 52hz tuning.
 
#3
Another way to tune the length would be to install the ports and play a sine sweep below 100hz and watch the cone movement. Cone excursion should minimize near the tuning freq. You can then start trimming the ports a little at a time until cone movement minimizes at the desired tuning freq.
 
#5
seamonkey said:
Word is those are not 10pr300s, you might want to hunt down the real TS specs, Avatar might have them.
Click to expand...

I used the right TS specs. It doesn't list xmax though

I wonder about using just one of the ports? I also wonder about the tuning frequency. How do you choose it? That's the one winisd spit out, and when I change the tuning the performance doesn't seem to change that much, except that it gets a little weirder.
 
#6
KJMO said:
I used the right TS specs. It doesn't list xmax though

I wonder about using just one of the ports? I also wonder about the tuning frequency. How do you choose it? That's the one winisd spit out, and when I change the tuning the performance doesn't seem to change that much, except that it gets a little weirder.
Click to expand...

To do a thorough job you need to be sure to look at the cone excursion and/or max power screens, and the port velocity one, but the first two require knowing Xmax. Be sure the crank the input power setting up if using excursion as your metric. WinISD doesn't tell you what tuning to use, it just defaults to one specific alignment or another if you don't choose one for it.
 
#7
The only information I have about choosing port tuning is that it should be close to what the "fs" is, which is 56.9. Should I tune it more like 55Hz? Or is there a better way?

Also, the reported xmax is supposedly around 4, but I've seen it stated it's closer to 2 or 2.5. How could you possibly get super geeky when the numbers aren't really known?
 
#8
KJMO said:
The only information I have about choosing port tuning is that it should be close to what the "fs" is, which is 56.9. Should I tune it more like 55Hz? Or is there a better way?

Also, the reported xmax is supposedly around 4, but I've seen it stated it's closer to 2 or 2.5. How could you possibly get super geeky when the numbers aren't really known?
Click to expand...

Super geeky people measure that stuff for themselves.
Yel_wink.gif


Paging @AstroSonic , @Arjank. As usual, just depends on what tradeoff set you prefer though.
 
#9
KJMO said:
I used the right TS specs. It doesn't list xmax though
Click to expand...
You've already visited the relevant thread, disagreements and all; the voice coil overhang, measured conservatively as winding depth minus mag gap depth divided by two...plus .34 random millimeters (for good measure?), is listed as "max linear amplitude" in the 35810-S0 Report.pdf file, and amounts to 2.59 mm. If you instead accept Faital's optimistic, but perhaps representative of their woofer's clean(ish) excursion behaviour, reported Xmax datum, it's the same as regular 10PR300s, namely 4.92 mm.
(The Xlim does clock lower than in the regs though - 10.25 vs. 14 mm.)

I'd ask @agedhorse which number he'd follow if he were in your DIY shoes.
 
#10
I already stated my opinion in the other thread. There's more to this topic than a single simplistic number, and the results of this driver certainly support my opinion.
 
#11
agedhorse said:
I already stated my opinion in the other thread. There's more to this topic than a single simplistic number, and the results of this driver certainly support my opinion.
Click to expand...
Oh, FWIW I agree, I just meant which number to keep in mind when choosing dimensions and tuning.

Actually I'd also model the box with @fdeck's speaker design program and especially his waveform based excursion curve - after all, inputting, say, 200W worth of bass guitar signal does not equal 200 watts of fundamental.
 
#12
Thanks so much. That's all really helpful. Aged Horse, I read all the stuff you wrote, and I really appreciate the insight you provide. I wish there was a way to get hold of the dimensions for the cabs that had the GB faitals, since that's probably the only way to really get the most out of the speakers. But I can see why that is going to be hard to come by.

I'll give fdeck's program a try. I really like this stuff, even though I probably won't ever really understand it ;-) Thanks!
 
  • Like
Reactions: seamonkey
#13
Hopefully someone is still around, but I have two questions: The fdeck calculator graphs out db's and cone excursion, so looking at that, the cone excursion is way beyond xlim with 200watts at 20 or 30Hz. Does that mean I can't put 200watts into the cab with that vent setup without ruining the speakers? Second, I was wondering if you can put one 4x4 port on the front, and one on the back? Seems I've seen that it can be done.
 
#18
Haphazard said: (The Xlim does clock lower than in the regs though - 10.25 vs. 14 mm.)

So I was looking at the excursion graph, and it goes beyond that down low. I probably just don't understand. I may just drill the holes and see what it sounds like. Maybe I'm just doomed to have speakers in a box, although I think at least I'll be a long way from having "chuff".
 
#19
KJMO said:
Hopefully someone is still around, but I have two questions: The fdeck calculator graphs out db's and cone excursion, so looking at that, the cone excursion is way beyond xlim with 200watts at 20 or 30Hz. Does that mean I can't put 200watts into the cab with that vent setup without ruining the speakers? Second, I was wondering if you can put one 4x4 port on the front, and one on the back? Seems I've seen that it can be done.
Click to expand...
Not unusual (EDIT: at least to exceed Xmax) unless the chosen tuning is very low (which has tradeoffs, as any other choice in life). Do both excursion curves, "peak" and "waveform based", exceed Xlim?
[Disclaimer - the following is tentative and open to correction by others, I ain't no expert nor do I play one on TV and I certainly don't want you to blow speakers because of my bad advice!]
If it's only the former it should just mean the fundamental can't exceed 200 watts, but for that to happen the total signal should be significantly over 200W. If it's also the latter (Mr. Deck's approximation of a real world signal input), yeah, no, I wouldn't do it! Your amp might already have built-in high pass filtering, but if it hasn't, go order an HPF unit, again by @fdeck.

AFAI've read, yes, you could put a port on the front and one on the back. Port placement matters in some, specific, respects. E.g. if on the back, you need some inches of clearance, like one port diameter or such, from a wall or other obstructions (optimally there should be about the same clearance at the inside end of the duct, between the opening and the surface directly facing it); if you can see the cone from the outside it means some midrange can escape the port and influence the tone in ways difficult to predict, so you might want to avoid it; if the port is close to a cab surface it lowers predicted tuning so the tuning should be checked after and length shortened accordingly - basically my advice is: make port ducts equal in width and length (dissimilar ducts can and are used for specific reasons - but by people who know what they're doing...) and their placement similar as far as distance from corners and so on.

(Another suggestion, one that I'm shamelessly parroting, just as everything else in this post, might be to use port placement as ways to improve cooling of the drivers, by putting one on the bottom and one on the top. Probably not vital though.)


EDIT: as far as (what I'd interpreted as) Xlim, the .pdf reads:
Code: 
SPE-B9 (-) Max Mech.Amplitude (±mm) 10,25
 
Last edited:
You must log in or register to reply here.
Top Bottom
Back