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3ll3d00d

Should I go ported?

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3ll3d00d    72

only in sketchup atm, trying to decide exactly how best to size it so it fits where I want it to go + I have to space to build it + tune is where I want + not really wasteful of sheets of wood. The design has been complicated somewhat by the fact I might now build a screen wall and hence put the sub in a different place as well

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3ll3d00d    72

I've made progress on the cab, the bottom (on the right of the pic) is glued on & am have the rest at the dry fit stage just to make sure it all fits together properly. Obviously that centre brace will have the middle cut out once I get the top of. Bit of a squeeze making this in my shed :)

 

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Ricci    652

Great! I had almost forgot about this build. I am looking forward to what you think of it compared to the UXL's. 

BTW I am hoping to have some high power data for the 21DS115 put up sooner rather than later.

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3ll3d00d    72

dropped the driver in for a quick test

https://imgur.com/a/GtvrX

suggests tune is ~18Hz, modelled was ~19Hz

I guess that peak at ~110Hz is 1st port resonance? model suggested that would land around 130Hz if so so not sure why that is a way off.

Plugged a similar model into tl.app and that does show a peak around that point.

 

Edited by 3ll3d00d

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SME    211

The tune can be found precisely by looking for the nearby zero phase crossing.

I'm guessing the stuff at 110 Hz or whatever is the port resonance if it comes close to the modeled.  If the port opens nears the rear of the cabinet, its length may be effectively extended by it, which would lower both the tune and resonance.

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3ll3d00d    72

I had planned on the tune coming down a touch from the model based on port location but you know it never occurred to me to think that would also bring the first resonance down too, blindingly obvious now you mention it :lol:

0 degrees is about 16.5Hz btw

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SME    211
49 minutes ago, 3ll3d00d said:

I had planned on the tune coming down a touch from the model based on port location but you know it never occurred to me to think that would also bring the first resonance down too, blindingly obvious now you mention it :lol:

0 degrees is about 16.5Hz btw

Another thing you can do is run a sine sweep with the mic right next to or slightly inside the port.  The resonance is very easy to see that way, as is the tune usually.

I believe the 0 degree phase should line up with the impedance minimum.  If it doesn't it may be a sign of slight measurement error.  It's probably not a big deal for you though.  16.5 vs 17.5 Hz isn't really a big difference.

I bet that thing is going to kick some butt.  Are you going to run it with another SpeakerPower amp?

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3ll3d00d    72

atm I have an inuke3000 and an sp1-6000 so I will use the sp1 on the dual uxl at the rear and have the inuke bridged for the 21. Sadly US goods are pretty expensive since Brexit so I doubt I'll get another speakerpower amp, it's probably overkill anyway. I'm not sure what I'll do long term, it depends whether I keep both UXL or not. I have a feeling 2 18s behind me will be overkill (though they make a handy behind sofa shelf) so may end up selling one of them. If so I'd probably look at also selling the speakerpower. The peavey ipr2 7500 seems a reasonable mix of price & power & features, they are about £1300 here whereas an sp2-12000 will be closer to £3k landed. 

meanwhile, raw in room response

https://imgur.com/a/X4Sw0

NF is the one with the big dip in the 20s

21 looks pretty similar to the modelled response

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SME    211

Overkill?  What's that?

Seriously, I thought my 4 x 21" subs would be overkill for 16 Hz+, even as I worried about getting enough output below there.  It turns out my floor is pretty much inert under 10 Hz, and not very exciting in the 13-18 Hz range either.  So I'm planning to add Crowsons some day.  All the same, the content above 16 Hz is very clean and sounds better louder, I think.  All the while, the placement locations gives poor response  for  80-120 Hz, so I'm quite glad I have all the extra headroom.

As far as the Crowson's and my couch are concerned, I'm thinking of cutting some plywood sheets to set the sofa on and putting the Crowsons under those.  I think that'll raise the sofa by 2" or so, which isn't bad.  I don't know whether I want to do 2 or 4 Crowsons.  Only 2 may be plenty for me.  I don't need things to get too crazy.  I just want to fill in where the floor isn't active, including the single digits.

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Kyle    62

Four 21's would be overkill for me, i can't even use my 12" sub past -15dB w/o my kids getting scared watching voltron, lol.

 

 

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3ll3d00d    72

admittedly I haven't reduced the capacity in my system at any time yet but I think I must be at the point where moar genuinely is overkill (at least without changes that allow me to put more subs in the room anyway). I did have a pair of low teens xmax 12s behind me which gave solid response down to ~14-15Hz in the NF position whereas I now have a pair of high xmax 18s so that yields something like 5-6x the Vd. This is quite a large uptick. Admittedly part of the reason is to get a larger radiating area so even that impact across the sofa but it remains to be seen whether my wife appreciates that :)

anyway back to the subject of this thread... I ran some quick tests today to check for port noise, I went to ~112dB (at the LP) with no noise at all & you could just about feel the air if you put your hand on the port. I used REW's CEA-2010 signal for that test at 16, 20 & 25, the only distortion product visible (at that ~112dB level) was 40-50dB down so basically non existent. I'll push that some more another time just to see what happens.

I haven't had a chance to properly run through some listening sessions yet so will leave any subjective commentary til later.

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