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View Full Version : 45's in the corners, how many?



Gunlex
09-21-2007, 05:13 PM
my design is like this

http://i33.photobucket.com/albums/d55/ratherbriding99/upload-1.jpg

I'm going to put a 45 in the port corner, but should i put them in the other corners too? Does this help anything?

Twistid
09-21-2007, 05:14 PM
your mom

twisztdauthorit
09-21-2007, 05:17 PM
yes it helps make the box more ridged and stronger... if ur short on space then u dont need it but it never hurts.

InhumanAcura
09-21-2007, 06:58 PM
yes it helps make the box more ridged and stronger... if ur short on space then u dont need it but it never hurts.

i guess it might add some rigidity..i always put them in to avoid dead spots that the 90 degree angle creates..think about it, do you think air will flow better with a bunch of sharp corners or with some nicely somewhat rounded edges..it just promotes better air-flow..

iamamp3pimp
09-21-2007, 06:59 PM
you wont notice a difference unless you are metering, and even then, it might hurt you.

Gunlex
09-21-2007, 07:44 PM
well, just 1 in the port corner it is then =D

Lakota
09-21-2007, 07:50 PM
you wont notice a difference unless you are metering, and even then, it might hurt you.

x2

iagrdshaka
09-21-2007, 11:26 PM
pour resin in the corners

dleccord
09-22-2007, 01:50 AM
form tubes are better.

yama168
09-22-2007, 02:13 AM
you wont notice a difference unless you are metering, and even then, it might hurt you.

Just curious how would it hurt the metering?. Ive always heard that the 45's help.

Aloha

dleccord
09-22-2007, 03:06 AM
you wont even know the difference. its mainly for looks. but meterings are a different story.

mlstrass
09-22-2007, 03:14 AM
Until someone builds identical boxes tested under identical conditions: one with no 45's, one with MDF 45's, one with resin, etc... then it's all speculation as to how it would meter. I've never read any test results like that. If anyone has them please post up for all to learn.

Until I read othewise I'll continue to use them as knowing how air normally flows a 45 will keep up the air speed/not restrict flow better than a 90.

I've ported/flow benched plenty of cylinder heads in my time and it's the same principle...

Lakota
09-22-2007, 02:15 PM
Just curious how would it hurt the metering?. Ive always heard that the 45's help.

Aloha

One reason is because of the change of volume.

Mr Cabinetry
09-22-2007, 03:24 PM
Until someone builds identical boxes tested under identical conditions: one with no 45's, one with MDF 45's, one with resin, etc... then it's all speculation as to how it would meter. I've never read any test results like that. If anyone has them please post up for all to learn.

Until I read othewise I'll continue to use them as knowing how air normally flows a 45 will keep up the air speed/not restrict flow better than a 90.

I've ported/flow benched plenty of cylinder heads in my time and it's the same principle...

Well, there is plenty of theory and speculation that has been circulated as to ports with 90 degree corners create more turbulence, thereby reducing airflow.

This myth has been around so long that no one has had the stones to step up and say otherwise and with the science to back it.

If anyone on here watches " myth busters " they did a show to prove or disprove the "myth" that a open bed pickup gets better gas mileage with the tailgate down than with the tailgate up.

Anyways, in the course of exercise was discovered that a pickup gets better gas mileage due to what is called a " Trapped Vortex " where by air flow becomes trapped in the closed bed of the truck and in effect this creates a " bubble " to which the air now flows over this " Trapped Vortex or Air Bubble " thus eliminates the air drag.

The same applied air flow dynamics occur in 90 degree corners of a slot port and there's more than enough proof on the internet to confirm this fact.

Also, here's another tidbit to munch on, the dynamic air flow principals are not the same for a ported sub box as those of say HVAC system because in a sub box air in not circulated in the same manner in a closed loop system, because a subwoofer only pushing/pulling air static air by the amount of the subwoofers xmax.

It only feels like the air blowing but in fact the air is only moving are such a high accelerated rate given at which the frequency the subwoofer moves.

W8 a minute
09-22-2007, 08:33 PM
Thank you, Mr Cabinetry.

I've been watching these box building threads and trying to figure out why everyone is treating a ported box like an F1 cylinder head. There is no "flow" or constant rush of air in one direction. The air inside the port resonates back and forth. In fact, if you fill a port with smoke 98% of the smoke will stay in the port until it dissipates.

mlstrass
09-23-2007, 12:41 AM
Thank you, Mr Cabinetry.

I've been watching these box building threads and trying to figure out why everyone is treating a ported box like an F1 cylinder head. There is no "flow" or constant rush of air in one direction. The air inside the port resonates back and forth. In fact, if you fill a port with smoke 98% of the smoke will stay in the port until it dissipates.

VERY interesting, might have to try that some time. I have also wondered what the air inside actually does as the sub is pushing the majority of the air until you get very near/at tuning which is not very often on a low tuned daily box and most music normally listened to. Could be why the smoke just dissipates. Perhaps doing the smoke test and playing tones at/below tuning might offer more insight.

I don't see how the pick up bed analogy relates though. I understand air trapped inside the bed "forces" air to flow over the bed, but there's no air flowing over the air trapped inside a box, so we're actually dealing with the air in the bed if using the mythbusters test. Can you explain more?

I "assume" that the air pulses in/out of the port, but have no idea how far the air travels in/out and how much air from the box is actually expelled each time. Going off of that knowledge or lack of I still feel that a 45" in the corner at the back of the port is beneficial as at some time or another air will be making that bend and I'd prefer it to be a 45 ;)

Any more thoughts as this is rather interesting???

W8 a minute
09-23-2007, 01:17 AM
I have thoughts but no conclusive answers. We tried this with a "disco" smoke machine and it was very interesting to watch the smoke dance in the port. It varies with frequency as you might imagine. IIRC at certain frequencies there was almost no movement in the port at all, like a null, or something. Unfortunately I don't remember the tuning of the box or what frequencies did what. We were just goofing around. Who knows, we might have cured cancer if we weren't smoking all that pot.:groovy:

This was several years ago, ok a decade, and todays subs push a lot more air. But todays subs also require more port area. I would imagine that if the port was too small you could actually push all the smoke out with a beefy sub. But I would also bet that you would have port noise with that box as well.

Edit:
I almost forgot about the 45 degree angle thingies. The only reason (I think) they might be useful is to keep the port area equal the entire length of the port. Thus eliminating any tuning anomalies. But then I ask: Would you hear any difference?

dvrmstrng
09-23-2007, 01:24 AM
personally i think they are useless....air is air....its not going to be "trapped" in a 90 degree angle

Flipx99
09-23-2007, 01:26 AM
I think this is quite interest debate...

I tried using 45s..not sure how much a difference it made.

What I think doesn't help is K-bracing/gussets....It would seem that they would block the air...which is why I use threaded rod.

dleccord
09-23-2007, 03:46 AM
i just havent read anywhere that their bass sounded cleaner with 45s.

iagrdshaka
09-23-2007, 04:13 AM
it's more for improving scores on the meter

mlstrass
09-23-2007, 05:43 AM
W8 a minute,

Quite interesting the things we do when stoned. LOL

I'd really like to see that test done by playing tones right around tuning as I would "assume" the most air moves in/out of the port then.

Either way I'll continue to use one in the corner at the rear of the port and also will use window bracing, etc... I always round over all edges and try to place them so the port isn't obstructed. IMO bracing should be no more of an obstruction then the actual sub itself.

I cut my teeth on DIY home subs, mostly low tuned HT stuff and multiple window braces are the norm and I've never had or heard of an issue with a sub sounding bad because of the bracing inside. Wrong tune is another thing of course.

Seems like we "over think" most of this car audio stuff at times LOL

iamamp3pimp
09-23-2007, 11:35 AM
Just curious how would it hurt the metering?. Ive always heard that the 45's help.

Aloha

its unpredictable.

iamamp3pimp
09-23-2007, 11:39 AM
I have thoughts but no conclusive answers. We tried this with a "disco" smoke machine and it was very interesting to watch the smoke dance in the port. It varies with frequency as you might imagine. IIRC at certain frequencies there was almost no movement in the port at all, like a null, or something. Unfortunately I don't remember the tuning of the box or what frequencies did what. We were just goofing around. Who knows, we might have cured cancer if we weren't smoking all that pot.:groovy:

This was several years ago, ok a decade, and todays subs push a lot more air. But todays subs also require more port area. I would imagine that if the port was too small you could actually push all the smoke out with a beefy sub. But I would also bet that you would have port noise with that box as well.

Edit:
I almost forgot about the 45 degree angle thingies. The only reason (I think) they might be useful is to keep the port area equal the entire length of the port. Thus eliminating any tuning anomalies. But then I ask: Would you hear any difference?
I agree 100%, but doubt that you would hear much difference. but throughout the box...no way

iamamp3pimp
09-23-2007, 11:41 AM
W8 a minute,

Quite interesting the things we do when stoned. LOL

I'd really like to see that test done by playing tones right around tuning as I would "assume" the most air moves in/out of the port then.

Either way I'll continue to use one in the corner at the rear of the port and also will use window bracing, etc... I always round over all edges and try to place them so the port isn't obstructed. IMO bracing should be no more of an obstruction then the actual sub itself.

I cut my teeth on DIY home subs, mostly low tuned HT stuff and multiple window braces are the norm and I've never had or heard of an issue with a sub sounding bad because of the bracing inside. Wrong tune is another thing of course.

Seems like we "over think" most of this car audio stuff at times LOL


Window bracing wont cause any more turbulence than threaded rod......and its much faster and better looking

did i mention cheaper?

Mr Cabinetry
09-23-2007, 01:51 PM
Ah, the meeting the minds are touching on all the interesting points that at one time or another have been debated on and theorized as to what impact all the elements combined do or don't effect subwoofer/enclosure performance/bass response.

Bracing

I've always used " window type " for enclosure's, though, admittedly, I have used bracing with circular cutouts only form the standpoint of where this bracing would be located as to not impede air flow/movement while at the same time displacing the least amount of volume.

Given now that we realize how subwoofer function applies it's mechnical force to the static air volume, the air more or less is in resonance with that of the frequency of the subs excursion when it reaches a certain point.

The air is moving, but not to any great degree that would cause these " turbulence " issues that keep being brought up time and time again, I have always argued that bracing in any form doesn't hinder the function of the static air volume nor the port for that matter.

Slot Ports & 45's in corners

I cannot argue nor dismiss the effectiveness using 45 degree corners in the ports as to the impact of " bass response " whether it improves it over a 90 degree corner.

As mlstrass has already stated that two identical ported enclosure's would have to be built to prove this " theory " out as beneficial or not, speculation as this point provides nothing concrete.

And as also stated, it is highly doubtful that to the human ear, anyone would be able to distinguish such differences.

The smoke thing is very interesting as it would clearly show the forces at work and what is and is not happening.

Idea ( Something from watching Myth Busters )

Build a ported enclosure and use a Plexiglass top for the enclosure, that way it can be seen what is actually happening to air/smoke and more important, make a video of how the air/smoke is moving in the port and around bracing and what not.

This would answer alot of questions, clear up all doubts and either confirm or " BUST " the myths going around.

As to the 45 vs 90 degree corners in terms of the " Air Movement " and the " Trapped Vortex " created, I have rethought the physic's in terms of dynamic air flow vs static air being resonated as the frequency of the subwoofers full excursion .

The air is not reacting as " flow " in one direction, but being both pushed and pulled simultaneously at such an accelerated rate that what we have been referring to as " air blowing out the port " is nothing more than vibration of the air and what we are " feeling " is both compression and decompression of that static air in the same instant.

tooloud4tv
09-26-2007, 09:54 PM
bottom line and this is from personal experience, 45 degree angles help get the air out the dead corners. tried this i did an ok hair Trick with the SAME box i have now, went back and DID 45 degree corners and Resin the whole inside, ITS AN Big Diff in the air movement i can tell u that much, as far as it metering louder? i have no idea that meter is tricky, but to the ear o meter its an winner!

twisztdauthorit
09-26-2007, 10:09 PM
bottom line and this is from personal experience, 45 degree angles help get the air out the dead corners. tried this i did an ok hair Trick with the SAME box i have now, went back and DID 45 degree corners and Resin the whole inside, ITS AN Big Diff in the air movement i can tell u that much, as far as it metering louder? i have no idea that meter is tricky, but to the ear o meter its an winner!

this could be due to a smaller box volumes cuz putting in 45's would loose quite some volume. In turn changing the tuning and all.

But all in all i would put 45's in

mlstrass
09-27-2007, 02:04 AM
I always account for bracing/45's in my designs, so I don't lose any volume. But have never built identical boxes with and without. Since I don't have a meter and don't compete numbers don't really matter to me anyway.
I'll keep doing the 45's just for the "feel good" dbzzzzz they add...:)