Burp box...

[hispls 5,000+ posts]

doesnt work that way. You arent gonna meter louder just because you have a bigger port tuned higher. The box size needs to adjust to your port area as well as your tuning. Got a few people doing that with pure garbage results in last year's bass season. A box cannot function both spl and daily purely due to the airspace which needs to adjust accordingly for each purposes. There's a reason why burp boxes are small tiny boxes with high port area and not giant high airspace enclosures. Big airspace and big port did the worse from all my personal experiments.


you might want to check cone excursion tab man. After a certain point, you start losing a lot of cone control and lose all output and it wont even function as a burp box anymore it'll work like if the sub is ran in Infinite Baffle. No pressure build up in the box along with sloppy cone control can make you lose everything along with damaging subs. My big airspace and high port area box the subs stank immediately and the output was slightly better than what my door speakers pumped out....

Seems to me you're making sweeping generalizations here and about box size returning to this 'pressure in the box' line which nobody has yet tried to explain. Do you really think OP is going to push a pair of 12s to mechanical limits at 50-55hz on 1600W because he has too much port area or a 5 cube box?

I would suggest that box size varies greatly depending on subs. Some gain little with increased box volume, others you can go very big.

I've done my own tests where I've built a box for 3 or 4 subs, pulled a sub or two and bunged up the holes and got the same numbers. I can't speak for any other sub and you won't know for sure without testing, but the Shocker Sigs I've been using a 10 is louder than a 12 up to about 2.75 cube, 12 is louder than a 15 up to 4.5 cube, and 15 is louder than an 18 up to almost 8 cube. They like big box and big port, as do similar subs like the DD 95XX which have relatively high FS and are critically over-damped.

That said, you'll hit a point where bigger box will start to lose just because it jacks up the sound wave in the car, and there's always a compromise between box volume and port area taking away from one another AND too large a port often won't behave predictably just due to geometry inside the box and having to crowd it too close to something.

I've seen quite a few guys getting good results with external flared ports that can be swapped out based on application.

The only thing for it is to test everything. With this in mind, it's far easier to lower port area/tuning/volume than go bigger once the box is assembled, if you don't have money for wood to do new boxes constantly plan accordingly.

 

[shredder1 10+ year member]

Seems to me you're making sweeping generalizations here and about box size returning to this 'pressure in the box' line which nobody has yet tried to explain. Do you really think OP is going to push a pair of 12s to mechanical limits at 50-55hz on 1600W because he has too much port area or a 5 cube box?
I would suggest that box size varies greatly depending on subs. Some gain little with increased box volume, others you can go very big.

I've done my own tests where I've built a box for 3 or 4 subs, pulled a sub or two and bunged up the holes and got the same numbers. I can't speak for any other sub and you won't know for sure without testing, but the Shocker Sigs I've been using a 10 is louder than a 12 up to about 2.75 cube, 12 is louder than a 15 up to 4.5 cube, and 15 is louder than an 18 up to almost 8 cube. They like big box and big port, as do similar subs like the DD 95XX which have relatively high FS and are critically over-damped.

That said, you'll hit a point where bigger box will start to lose just because it jacks up the sound wave in the car, and there's always a compromise between box volume and port area taking away from one another AND too large a port often won't behave predictably just due to geometry inside the box and having to crowd it too close to something.

I've seen quite a few guys getting good results with external flared ports that can be swapped out based on application.

The only thing for it is to test everything. With this in mind, it's far easier to lower port area/tuning/volume than go bigger once the box is assembled, if you don't have money for wood to do new boxes constantly plan accordingly.

I am kinda concerned about power levels vs box/vent size... I really don't know what my power level is... LOL!.. it cannot be that much... what can 2 CAB's strapped at 1 ohm produce theoretically in an efficent box with decent... (not great)... electrical?... that seems to be the issue... once I find the right...(efficient box/port for my power???) I'll be doin' ok...

Unfortunately it's not a perfect world and a lot of factors come into play so I'm just tryin' to increase power input and port area when I design this box... do I need to stay around 4 ft3 net?.. If I go to 3.5 ft3 net it does look like around +108 in2 will work with the power I'm inputting...

 

[hispls 5,000+ posts]

I am kinda concerned about power levels vs box/vent size... I really don't know what my power level is... LOL!.. it cannot be that much... what can 2 CAB's strapped at 1 ohm produce theoretically in an efficent box with decent... (not great)... electrical?... that seems to be the issue... once I find the right...(efficient box/port for my power???) I'll be doin' ok...Unfortunately it's not a perfect world and a lot of factors come into play so I'm just tryin' to increase power input and port area when I design this box... do I need to stay around 4 ft3 net?.. If I go to 3.5 ft3 net it does look like around +108 in2 will work with the power I'm inputting...

Assuming you build an efficient box impedance at your peak should be rather high, so not much power really. That's where complex modeling software really falls on its face. Sure they could predict all kinds of stuff well IF (and it's a huge if) you had accurate data for all those variables. Worst of all is that without having built the box and measuring you won't know what your impedance is at any given frequency and it sounds to me like you don't even know exactly where your peak is in the first place.

Theile Small calculations are good to get rough idea of response shape and peak, but anything beyond that is going to be largely theoretical until you've spent enough time and money that you may as well have been flying blind from the get go just trying everything and metering and see what happens.

If those programs were reliable no SPL competitor would ever need to build more than 1 box, they'd just plug in the numbers, build whatever it says and never be able to gain from there.

https://www.stevemeadedesigns.com/board/topic/98191-spl-gains-updates-page-30-routing-the-port/

A lot of the pictures are gone, but this should give you some ideas of things to try. DO NOT rule out anything that lost for him, he tried all these things because others have gained by trying them. Ditto, do not try something and not test assuming it gained. You must change only 1 variable then test.

 

[shredder1 10+ year member]

Cool man... my cabin peak is between 50 - 52 hz... I think I'll test the 4.5 ft3 net one... It may fall on it's face or not... Building a box is no sweat, buying wood gets old real fast tho... BTW... I've seen and actually read that thread before a couple of times... but I haven't seen it in a couple of months... oh yeah... it IS better with pics...

 

[TRaGiK 10+ year member]

I've seen quite a few guys getting good results with external flared ports that can be swapped out based on application.

I'm one of those guys. 6 inch for daily, 8 inch for the meter. 2 DB difference from one to the other.

 

[Jeffdachef 5,000+ posts]

Here it is with a slightly smaller area and less volume... I already increased to 87 in2 and gained over 68 in2... I just am looking for efficiency..

the input power I used is a wish I know... so I kept the port velocity right at the limit...

idk why you use 5000 or any number other than projected clamped numbers.

 

[kr15 5,000+ posts]

Im kind of with Jeff on this.... there is a correlation between enclosure size, tuning, and resonant frequency. Its been proven time and again in my teams applications. Its been confirmed with a few world finals competitors from another team local to us.

Can we make a blanket statement? No... but when im building a burp box, resonance plays a role in the volume I use.

 

[shredder1 10+ year member]

Thanks guys for all the advice... I've got a lot to chew on now... a new theory has presented itself and I cannot explain it without putting everyone to sleep... LOL!.. I'll build and test... I'll probably post within a week how it went anyways... the last theory did gain so I have high hopes for this one...

 

[shredder1 10+ year member]

I do see what you all are saying about box size affecting the output... and vent size being not the ONLY factor... I've been on a mission regarding this for 24 hours now... it does look like a 3 ft 3 net will be a lot more efficient and the input power I'm was using was a pipe dream... I'm still trying out different airspace/port/power combos trying to find one... the port area I need does require some length tho... that is what I'm seeing now... I'm trying to keep it under 30" long if I can... does sealing the interior with resin really help?.. also, the bend in the port poses the question of having single 45 like the second pic or including one on both port walls like the first pic... which one is more efficient?.. should I attempt to kerf the bend if that is even better?.. the ends of the port will be flared... probably a 22.5 degree straight flare on the inside and a basic roundover on the exit... or should I use the straight flares on both sides?.. determining length is no problem this way but it DOES make cutting and assembly a little trickier... is it worth it?

 

[shredder1 10+ year member]

I've yet to get wood... I got a lot of info and it FINALLY started to make sense to me... I do see as the box gets smaller the impedance/power changes in Winisd... the testing is on now... I've tried to come up with something that will WORK... reading that other thread about common chamber raised a few questions in my mind that has made me reevaluate the advice I'm getting... Guess what?.. now I DO understand what you guys are saying FINALLY!.. So I'll post this up and I would really appreciate any input/criticism that you have...Lets see if I've come closer to the mark...

I hope that I'm not being a bother with this as I have learned a lot but do not feel 100% sure regarding this... but I am a lot closer than I WAS beginning this project... I will see by next Wednesday how this works out ... I'm going to flare the port ends inside and exiting... is it worth the effort to kerf the bend inside the port?... and I MAY foil tape the inside... if not I'll seal it with resin... thanks in advance

 

[shredder1 10+ year member]

What you have told me makes more and more sense... if I tune to 39 hz with the appropriate port area, I'll extract the most power... I think I'm at the build and test stage... just make sure I locate the port on the D/S... go as small as I can with a usable port length... and quit asking questions and just build it!... I've read that tuning 1/3 octave below peak is the best way to do this and have a daily... is this true?

 

[kr15 5,000+ posts]

I did some testing with added power today. Same box.

152.2 Legal around 5k.... BUT, it became really inefficient and gained next to nothing above 3k clamped. At last show i did 150.2 in stock 2k clamping 1700w. So an extra 3k ish netted me only 2db. Mainly due to my voulme not being ideal for that kind of power.... still, 152 legal on a pair of 12s isnt bad. But **** that inefficiency....

And now ill be going to 2 15s.. its gonna take a 153.5 or so just to place at world finals in 2k. I just dont think these ferrite 12s will get me there...

That said, please keep updating this as you go. I'll keep checking in

 

[shredder1 10+ year member]

idk why you use 5000 or any number other than projected clamped numbers.

I think I've gotten pretty close... thanks to all the info and advice I've received... I've delayed around a week, digesting a few things and trying a few changes to see what happens... This one is getting built... the comment above really made me reevaluate how I was looking at this... LOL!.. thanks Jeff... it makes a lot more sense now and I'm hoping that this will be the last one I'll build for a while...

Torres

Figuring port layout

Transfer function magnitude

Rear port velocity at 2700 watts

Rear port velocity at 3300 watts

Cone excursion

This I'm hoping gets me at least an idea of what power to use as input when modeling the port... I've been told it's not accurate but better than nothing at least...

2800 at 4300 input... low range

Up to 3300 at 5000... high range...

I'll post what happens when I get it built and metered... see any obvious problems... chime right in please... I'm not starting till Friday... thanks

 

[hispls 5,000+ posts]

I did some testing with added power today. Same box.152.2 Legal around 5k.... BUT, it became really inefficient and gained next to nothing above 3k clamped. At last show i did 150.2 in stock 2k clamping 1700w. So an extra 3k ish netted me only 2db. Mainly due to my voulme not being ideal for that kind of power.... still, 152 legal on a pair of 12s isnt bad. But **** that inefficiency....

And now ill be going to 2 15s.. its gonna take a 153.5 or so just to place at world finals in 2k. I just dont think these ferrite 12s will get me there...

That said, please keep updating this as you go. I'll keep checking in

2dB for doubling power where you sit is about expected. You may well be fighting excursion losing power due to x-max limits, progressive surround causing more resistance, and of course pressure in the vehicle causing more resistance. You're also flexing panels/glass/etc. more losing more, and building more heat everywhere which is inefficient. I'd say you're best bet is resin, armorall, gorilla tape, playing with vents/glove box/etc. type "tricks".

I don't think ceramic magnets are what's holding you back at 5K into a pair. From what I've been told the real impressive gains from neo come much higher power and much higher pressure. Of course you may well gain big just dropping in any different pair of subs... rolling the dice either way.

That said, I'll probably have some extra neo sigs looking for a home late summer early fall if you're looking to give neo a go and can work with D1.4 or d2.8 coils.

I'll post what happens when I get it built and metered... see any obvious problems... chime right in please... I'm not starting till Friday... thanks

I really think you should plan a way to easily adjust volume and tuning down the road, only when you're convinced the box is as good as you can get do you want to start getting permanent with resin and such. You really need to own a meter and keep a notebook if you're serious about getting loud.

 

[kr15 5,000+ posts]

Im fighting ALOT of issues at that level. Dropping to 10.8v, cabin probably just losing pressure, and the box being too big for that power. I have a meter and have tested lots of tricks so far. It is stock class so i can basically do nothing to cabin reinforcement wise except sound deadener.

I do still need to test some seat positions, visors etc.

My inclination with neo is because I have access to a sub builder who is in start up mode with his company. The subs im running he made for burping out of Treo motors. But he also has 4 of his own ferrite motors he builds, plus he is prototyping 2 or 3 types of neo. Radial, wedge and I think column. The wedge is gaining around 2 on drop in over ferrite. He also made one of his motors capable of a neo ring on the pole, basically what DD does on SC option. This sub sees about 1.2 gain on drop in. If i do run neo, they will be his, od id get neo motors and have him build them specifically for my application. He did a pair of 2.5" coil neos for someone for lower power classes and they were extremely loud. 155 legal in a trunk on ~4k.

So part of the reason I even came back to competing (i was away for about 5 years) was to run his subs and help him grow his company. Hes been a friend for about 8 years.

Im going to talk to him tho. He is running out of his own neo motors, and the Sigs might be a fun rebuild for us