1 sub vs 2 subs?

[THATpurpleKUSH 5,000+ posts]

Yes to all.

Ok, well how do you explain people gaining spl or metering the highest with a sub up/port rear or sub forward/port to the side, like what suv's, hatches and non blow through pickup trucks use.

 

[keep_hope_alive Premium Member]

easy. they have a poorly designed system and no idea how it behaves. they experiment and see what happens. in all cases, they are not realizing the full potential of their system. If Nate Munson can break 170dB with a single 10" and people struggle to break 150dB with multiple large woofers - you see what i'm talking about. SPL competitions are exercises in who can apply physics to their advantage.

vehicles are dynamic systems. change placement and many things change. the pathlength between cone and listening position vs. port and listening position vs. both port and cone to reflecting planes to listening position, etc. in your example, the change in position/orientation resulted in constructive phase interference at some frequencies.

Rotate a box and you will get different results because you change reflections. In a closed environment such as a car reflections dominate response characteristics. it's like dropping a pebble in the bathtub. what starts as a circular wave quickly turns into chaos as reflected waves interact with each other.

the problem with the cabin and frequencies of interest is that constructive and destructive interference cause variations in response at measured locations. this is why you may peak with a certain frequency at the dash but a different frequency at the seat. why rotating a box changes response.

regardless, the goal of a ported box is to get constructive interference at the measurement location. but ports cause both constructive and destructive interference. it is why they have such a sharp roll-off. the "tuning frequency" is simply the length were constructive interference ends and destructive interference begins. the wavelength below that point is longer and you get the rear wave cancelling the front wave. but really, a tuning frequency is relative to the port vs cone position relative to the listening position and vehicle reflections.

it's a dynamic system.

 

[Dirtrider4eva 10+ year member]

I see, so in your opinion, in my Celia hatchback, what port sub style would be best? Sub up port to cabin? For a 7 cube box I would be limited to that. A 5 cubic box I could do port and sub in any direction.

 

[Why So Cereal? 5,000+ posts]

easy. they have a poorly designed system and no idea how it behaves. they experiment and see what happens. in all cases, they are not realizing the full potential of their system. If Nate Munson can break 170dB with a single 10" and people struggle to break 150dB with multiple large woofers - you see what i'm talking about. SPL competitions are exercises in who can apply physics to their advantage.
vehicles are dynamic systems. change placement and many things change. the pathlength between cone and listening position vs. port and listening position vs. both port and cone to reflecting planes to listening position, etc. in your example, the change in position/orientation resulted in constructive phase interference at some frequencies.

Rotate a box and you will get different results because you change reflections. In a closed environment such as a car reflections dominate response characteristics. it's like dropping a pebble in the bathtub. what starts as a circular wave quickly turns into chaos as reflected waves interact with each other.

the problem with the cabin and frequencies of interest is that constructive and destructive interference cause variations in response at measured locations. this is why you may peak with a certain frequency at the dash but a different frequency at the seat. why rotating a box changes response.

regardless, the goal of a ported box is to get constructive interference at the measurement location. but ports cause both constructive and destructive interference. it is why they have such a sharp roll-off. the "tuning frequency" is simply the length were constructive interference ends and destructive interference begins. the wavelength below that point is longer and you get the rear wave cancelling the front wave. but really, a tuning frequency is relative to the port vs cone position relative to the listening position and vehicle reflections.

it's a dynamic system.

I haven't seen one of these type posts from u in a while.....good read man once again. I wanna be like u when I grow up

 

[keep_hope_alive Premium Member]

I see, so in your opinion, in my Celia hatchback, what port sub style would be best? Sub up port to cabin? For a 7 cube box I would be limited to that. A 5 cubic box I could do port and sub in any direction.

Traditionally, hatchbacks benefited most from sub and port in the rear, for loading along the hatch. Same concept, you want the port and sub to combine coherently. I would have a slot port at the rear with the sub right in front of it. Will effectively lower tuning a bit.

 

[THATpurpleKUSH 5,000+ posts]

easy. they have a poorly designed system and no idea how it behaves. they experiment and see what happens. in all cases, they are not realizing the full potential of their system. If Nate Munson can break 170dB with a single 10" and people struggle to break 150dB with multiple large woofers - you see what i'm talking about. SPL competitions are exercises in who can apply physics to their advantage.
vehicles are dynamic systems. change placement and many things change. the pathlength between cone and listening position vs. port and listening position vs. both port and cone to reflecting planes to listening position, etc. in your example, the change in position/orientation resulted in constructive phase interference at some frequencies.

Rotate a box and you will get different results because you change reflections. In a closed environment such as a car reflections dominate response characteristics. it's like dropping a pebble in the bathtub. what starts as a circular wave quickly turns into chaos as reflected waves interact with each other.

the problem with the cabin and frequencies of interest is that constructive and destructive interference cause variations in response at measured locations. this is why you may peak with a certain frequency at the dash but a different frequency at the seat. why rotating a box changes response.

regardless, the goal of a ported box is to get constructive interference at the measurement location. but ports cause both constructive and destructive interference. it is why they have such a sharp roll-off. the "tuning frequency" is simply the length were constructive interference ends and destructive interference begins. the wavelength below that point is longer and you get the rear wave cancelling the front wave. but really, a tuning frequency is relative to the port vs cone position relative to the listening position and vehicle reflections.

it's a dynamic system.

Thank you so much! I love when you post this kind of stuff. I swear between you and audioholic I have learned more from just a handful of your guy's posts, than I have spending countless hours reading the thousands of posts from others over the years.

 

[hispls 5,000+ posts]

A port works by combining the rear wave with the front wave, but after a period of time/distance so the two are in-phase. That is why you gain 3dB.
Waves combining in-phase is what I call "coupling". If the port and cone are separated by a distance, they will create separate waves with separate centers, the coupling will not be coherent at some frequencies.

Funny how you almost never see a top tier SPL box with port and sub on the same side....

OP, if soft parts are not matching you must only run 1. Use the one with the aftermarket recone if you want half a chance at holding 2K for any period of time.

 

[TaylorFade 10+ year member]

yep.
boxes with ports on different faces are missing the point entirely, IMO

I'm not sure I can agree with you there.

Funny how you almost never see a top tier SPL box with port and sub on the same side....

Exactly.

Seems to me that your coupling theory would indicate that you wouldn't want the sub and port very close to one another. One is 180* from the other. Unless there is some harmonics or some such that I'm ignorant of.

Most SPL competitors spend a crap ton of time trying to accomplish the coupling of which you speak. To get the front and rear wave to arrive at the mic or listening position at the same time. It's incredibly beneficial. And about 99% of the time not accomplished by sub and port in close proximity unless it's a wall. And that's only because it's a wall.

I've actually seen some interference graphs. Fascinating. They weren't focused on sub and port locations. IIRC, it was comparing monopole and dipole pressurization, but it was clear to see the interference pattern of the dipole (vented alignment).

 

[keep_hope_alive Premium Member]

all good points, guys. my opinions are just that. there is a combination of fact and opinion in everything i say. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

lots of people have ports on opposite faces. usually it stems from physical space. then people see others doing it and copy the design without ever understanding why. some do it on purpose and have a very good reason (though they are the minority). ports on opposite faces can/will affect the realized tuning frequency depending on the orientation in the vehicle. that may be a good thing, but it likely wasn't modeled. as far as i know, we don't have commerically available software that will not only model box performance, but also allow you to import a 3D model of the vehicle to calculate interference. you are welcome to perform the calculations yourself - but very few ever will. to me, that is the difference between understanding and experimentation.

just recognize what the port is actually trying to do (combine rear with front), and everything should make more sense. then you can decide what orientation you want based on the physics that govern the results.

yes, interference patterns are very cool! i saw some computer modeling at an ASA conference that was very neat.

i am certainly simplifying this whole process and focusing on one key aspect of vented enclosure implemetation. there are other benefits such as reduced back-pressure which helps increase available excursion, the impedance mis-match between port and space, etc.

 

[keep_hope_alive Premium Member]

Seems to me that your coupling theory would indicate that you wouldn't want the sub and port very close to one another. One is 180* from the other. Unless there is some harmonics or some such that I'm ignorant of.

in general, you do want the port and cone close, you do want the rear wave to combine with the front to create one new wave - not two separate waves that have to combine later. the port length is what allows the rear wave to travel a further distance and be in-phase with the front wave.

think of it in terms of path length. visualize or calculate the wave (peaks and valleys). wavelength is 1125ft/sec divided by frequency. when a rear wave travels 1/2 of a wavelength (at a particular frequency) it is now in-phase with the front wave.

putting the port at the rear increases the distance travelled by the rear wave (before it combines with teh front wave) and thus can lower tuning frequency.

the concept of "loading" is just taking advantage of reflections as soon as possible so they too are in-phase with the original. it's why putting a sub in the corner of a room excites all room modes.

and room modes... that's another subject entirely.

just think that if all of this goes into the placement of one sub and one port - how much more complex the system becomes when you have multiple subs and multiple ports?!? when you have different path lengths from each sub to the port - they are effectively tuned differently and they will interact before they even have a chance to leave the port. it becomes very complicated very quickly. i believe simplicity is king, install is 90% of the success, and the vehicle is the weakest link.

some of this is stuff i have read in textbooks, but most is just my thought process in how i'm trying to understand these very dynamic, non-linear systems. i could be wrong. but i did stay at a holiday in express...

 

[itsblown 10+ year member]

in general, you do want the port and cone close, you do want the rear wave to combine with the front to create one new wave - not two separate waves that have to combine later. the port length is what allows the rear wave to travel a further distance and be in-phase with the front wave.
think of it in terms of path length. visualize or calculate the wave (peaks and valleys). wavelength is 1125ft/sec divided by frequency. when a rear wave travels 1/2 of a wavelength (at a particular frequency) it is now in-phase with the front wave.

putting the port at the rear increases the distance travelled by the rear wave (before it combines with teh front wave) and thus can lower tuning frequency.

the concept of "loading" is just taking advantage of reflections as soon as possible so they too are in-phase with the original. it's why putting a sub in the corner of a room excites all room modes.

and room modes... that's another subject entirely.

just think that if all of this goes into the placement of one sub and one port - how much more complex the system becomes when you have multiple subs and multiple ports?!? when you have different path lengths from each sub to the port - they are effectively tuned differently and they will interact before they even have a chance to leave the port. it becomes very complicated very quickly. i believe simplicity is king, install is 90% of the success, and the vehicle is the weakest link.

some of this is stuff i have read in textbooks, but most is just my thought process in how i'm trying to understand these very dynamic, non-linear systems. i could be wrong. but i did stay at a holiday in express...

I always enjoy reading your post. I see you're an acoustical engineer and Im actually considering majoring in it but its all kind of iffy any advice? Also questions about vented enclosures and enclosures in general. How far should the opening of the port and sub woofer be from the wall its unloading on. In my case the back of hatchback with subs and port facing the hatch I know it probably changes but what happens if its too close too far away?

 

[hispls 5,000+ posts]

Unfortunately the port and woofer are only 100% in phase with eachother at one point anyway. Also pathlengths of frequencies in the sub 60hz range make phase issues minimal over such small differences. It's not like mids and tweets where the crossover point has a half wave of a couple inches.... we're talking about half waves of 8 feet or more to have complete destructive interference.

OP, Port should be at least a port width away from walls when installed. Even a port width away generally will act as an extension of the port, too close and the port won't load properly at all and the box may begin to act like a leaky sealed box.

 

[Dirtrider4eva 10+ year member]

Traditionally, hatchbacks benefited most from sub and port in the rear, for loading along the hatch. Same concept, you want the port and sub to combine coherently. I would have a slot port at the rear with the sub right in front of it. Will effectively lower tuning a bit.

i see. so having a box firing directly into the front of the car wouldn't allow propping loading? correct?

and having a single sub and port facing the hatch rear is my best current use?

Funny how you almost never see a top tier SPL box with port and sub on the same side....

OP, if soft parts are not matching you must only run 1. Use the one with the aftermarket recone if you want half a chance at holding 2K for any period of time.

this is what confuses me, how just about every thing i see is subs up, port front or back.

also i was planning for recone man. just got it at a steal.

OP, Port should be at least a port width away from walls when installed. Even a port width away generally will act as an extension of the port, too close and the port won't load properly at all and the box may begin to act like a leaky sealed box.

 

[hispls 5,000+ posts]

Subs up and port back (or to side/corner) seems most popular in hatchbacks. Considering some of us aren't scared to build dozens of boxes and try them in any conceivable position to figure out what's optimal, don't re-invent the wheel. I can say from personal experimenting subs ad port forward is a colossal failure in my Jeep. Subs and port up is decent, but sub up and port towards a corner has been best for me.

Really I see loads of top end home theater towers that port out the rear or have passive radiators firing out a side. I think B&W and the like probably have good reasons for doing these designs, but this illustrates the point that good sound isn't conditional on ports and drivers on any particular plane with eachother.

Make sure both subs have matching softparts if you plan to use the pair.

 

[Dirtrider4eva 10+ year member]

Subs up and port back (or to side/corner) seems most popular in hatchbacks. Considering some of us aren't scared to build dozens of boxes and try them in any conceivable position to figure out what's optimal, don't re-invent the wheel. I can say from personal experimenting subs ad port forward is a colossal failure in my Jeep. Subs and port up is decent, but sub up and port towards a corner has been best for me.
Really I see loads of top end home theater towers that port out the rear or have passive radiators firing out a side. I think B&W and the like probably have good reasons for doing these designs, but this illustrates the point that good sound isn't conditional on ports and drivers on any particular plane with eachother.

Make sure both subs have matching softparts if you plan to use the pair.

Ok,

And yeah they would. Well if I have them firing into a corner(s)

My trunk is widest near the hatch wall due to wheel wells,

So would ports go to both corners or one? I would love to build a dozen boxes, but I don't own a tl, nor have the time to build so much. //content.invisioncic.com/y282845/emoticons/crap.gif.7f4dd41e3e9b23fbd170a1ee6f65cecc.gif