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Optimal 21" reflex tuning

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URL: https://forum.speakerplans.com/forum_posts.asp?TID=106405
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Topic: Optimal 21" reflex tuning
Posted By: Augusts
Subject: Optimal 21" reflex tuning
Date Posted: 19 July 2021 at 10:46pm
Yello!

fun question - how would you tune your 21" bass reflex subs and why, I have three choices
SPL shown is at AES level (2000W). These are touring subs, one driver per cab. 350L volume, and I have four of them. Also how much people do you think four of them would satisify in a techno party?
Also dnb, all kinds of electronic music.

Space is a thing here, the boxes have been routered, now I can adjust the tuning a little.. I have a way of doing it. I originally made them the orange line, but started thinking that 126 db is what a decent 15" sub outputs at 50-60 hz

Some part of me says that spl is the way, but the other part says that music goes down to 20hz even if the notes (accents) themselves are not there but sinus leftover info is there and some sound effects are there too sometimes. but yes sometimes. 
Help would be appreciated. Tnx
August




Replies:
Posted By: Conanski
Date Posted: 20 July 2021 at 12:44am
What is the cone excursion like at that drive level for those 3 tunings?
For me it's the Orange line. Flat response makes for the most universal tool.. suitable to a wide range of genres. If you tune the boxes higher but need them to go lower for a particular show you risk damaging the drivers, but it's easy to EQ in a 50hz bump if a certain genre likes it. 


Posted By: toastyghost
Date Posted: 20 July 2021 at 4:44am
Assuming all other things like port velocity, displacement, thermal behaviour and distortion are equal (they aren’t) - blue line. It’s got almost the same output at 30 Hz as the orange one.

I’m a massive fan of the lowest extension possible, because it’s a big improvement in perceived sound quality - people turn it up less if it plays low - but I wouldn’t consider a 4 dB broadband sensitivity reduction worth it for ~ 3 Hz extra extension.


Posted By: Augusts
Date Posted: 20 July 2021 at 6:13am

You are right, I can't use the green line because of port velocity, but the blue one is fine.


Posted By: Augusts
Date Posted: 20 July 2021 at 6:16am
Excursion, that is with HP filters. I am also turning towards the blue line because of spl gain


Posted By: JonB67
Date Posted: 20 July 2021 at 12:38pm
Depends how you want to use the cab.

For me, its blue. 

If you look where blue gains over orange its over the whole useable spectrum
 If you look where orange is over blue its all below f3, not totally irrelevant but not much general use either. They're so close at 30, a couple hz isn't going to warrant losing the spl across the range.


Posted By: John Boom
Date Posted: 20 July 2021 at 5:44pm
You able to get group delay plots? Group delay plots might make you like the orange graph...


Posted By: Elliot Thompson
Date Posted: 20 July 2021 at 5:54pm
Each starting point is different. You need to have a matched starting point in order to have a fair comparison to determine the true roll-off curvature. If the graphs were all dB matched at a particular frequency, you will see a more clearer picture. The picture below is an example of all speakers having the same starting point, with changes occurring once, the cabinet gain comes into play.



Best Regards, 


-------------
Elliot Thompson


Posted By: Augusts
Date Posted: 28 July 2021 at 5:30pm
Thanks for all the input guys, I'm going with the blue plot. Seems the best!



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