# 4th order Bandpass enclosure making my ears ring???



## chrisW. (Sep 8, 2013)

Ok so I've been running an old school set up of two MTX Thunder 5000 12's in a sealed enclosure and an MTX Thunder 2150x amp. I ran the pair @2.6 Ohms (4Ohm + 8Ohm) and squeezed around 750w rms or so out of the little amp. 

I recently bulit my first 4th order bandpass enclosure using only one of the 12's (the 4Ohm) The enclosure is a 1:1 ratio tuned for sq. Overall the bandpass enclosure doent sound as loud off of 500w as the pair of 12's off of 750w, close but just doent seem to have the same output. But one thing I've noticed is after extended periods of high volume listening my ears ring. Even though the sealed 12's seemed to sound louder they never made my ears ring.

Another thing I've noticed is I've been getting the glance over a lot more with this bandpass from other drivers and pedestrians. One nice thing about my car (Mk6 VW Golf) is that it's incredibly well sound insulated. With my windows cracked and my system up full tilt, a car stopped right next to me barley hears any bass. It's seems the bass coming from this bandpass enclosure is making it way out of my cracked windows a lot better than the sealed pair of 12's.

Is it possible this type of enclosure can seem quieter but actually be louder. This is my first experience with bandpass. Is this typical?


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## amalmer71 (Feb 29, 2012)

SPL and "loud" are two different things.

It sounds like (no pun intended) that the bandpass box is hitting higher SPL in frequencies that don't seem as loud to your ears, but is doing damage (hence the ringing in the ears).

The average person hears down to 20Hz. That doesn't mean everyone does. AAMOF, the average person needs a boost in lower frequencies in order for them to sound "as loud" as mid range frequencies. Same with high frequencies. Our ears revolve around 2kHz to 5 kHz, or there about. Anything below or above that frequency needs to be louder (phons) in order for our ears to perceive them as being as loud as 2kHz to 5kHz.

Read this
Phon - Wikipedia, the free encyclopedia

and this
Equal-loudness contour - Wikipedia, the free encyclopedia

Those just touch on the basics, but it'll give you an idea of what's going on.
Just remember, just because it doesn't "seem loud" doesn't mean it isn't damaging your ear drums.


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## SPLEclipse (Aug 17, 2012)

What are your sealed resonance, vent tuning, and enclosure volume? It might be peaking really high, and that's why it sounds different.

As for the other question, bandpasses load the wavefront into the cabin differently than if you were just playing into open space in the car, so I could see it having a different effect.


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## chrisW. (Sep 8, 2013)

The box doesn't seem to be peaking high at all. The response is the flattest I think I've ever heard. Punchy but plays the lows effortlessly. I bulit the box but didn't design it. I got the plan from a friend who ran it through a box building program and told him I wanted it to be more oriented to sq than spl. It's 15"x15"x24" 1:1 ratio I think it's about 1.2ft^3 or so per chamber with a 6"x9" port

I'm very happy with it just curious about the science behind how the sound is being delivered because it's clearly different than the sealed enclosure


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## Xnewbx (Feb 1, 2014)

Something to note is you won't gain really anything different from a ported enclosure if your ratio is a 1:1. 
Also I appreciate the fact when it sounds loud in the car but not to others. Bass isn't always about impressing people in the lane next to you


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## gijoe (Mar 25, 2008)

Basically what others have said, I think you have very different frequency responses with the 2 setups, so they sound very different. Although the one inclosure doesn't seem as loud, it may have a big peak somewhere that is causing the discomfort. If you have access to an RTA you could measure both and compare them to see what's really going on.


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## chrisW. (Sep 8, 2013)

Xnewbx said:


> Something to note is you won't gain really anything different from a ported enclosure if your ratio is a 1:1.
> Also I appreciate the fact when it sounds loud in the car but not to others. Bass isn't always about impressing people in the lane next to you


I'm aware this design isn't exactly exploiting all the advantages of bandpass. But that's not really the goal. I plan to put the box in my wife's Jetta with the port through the rear deck or through the ski hole. Its only in my car until I source an amp for her and for real world testing although that will be moot once it goes in her car


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## nineball76 (Mar 13, 2010)

I'm confused. Are your subs different? Is one a 4ohm and the other an 8ohm? And these are sharing a chamber? 

sent from Tapatalk, via Sony Z1 badassness!


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## chrisW. (Sep 8, 2013)

No. Single 4ohm 12" in the bandpass.

The sealed box with 2 12's were the same sub but different impedances to get 2.7Ohms(2.66) and get more power out of the amp


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## qwertydude (Dec 22, 2008)

In my opinion an SQ oriented bandpass wouldn't have a 1:1 ratio. That could cause quite a peak depending on the volume and Vas of the speaker. In fact 1:1 with a total volume equal to Vas would end up being a peaky monster. Perfect for SPL burping. This might be why you're getting ringning ears. It may sound quieter because it's not responding with as wide a frequency range like music normally goes but that huge peak can cause ears to ring after listening for extended periods.

An SQ oriented bandpass ought to have a larger sealed section to extend response below the port tuning. That would give you deeper bass. The smaller ported section would also load down the woofer better over a larger range leading to a wider upper bass response. This combo would result in a wider passband with better response below the port frequency.


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## cubdenno (Nov 10, 2007)

Disregarding everything else, a band pass enclosure tends to be lower in distortion if it is built correctly. So while you were cranking your two sealed subs and most likely pushing them into levels of distortion you perceived as "louder", chances are, the two were not as loud as the band pass enclosure. 

So now you have a subwoofer set up that is most likely cleaner and louder. You just don't realize it because reduced distortion levels. 

Shame you never metered the old setup to compare with the new set up.

Also, most sealed systems start rolling off around 50 herts or so. The band pass depending on tuning may not start rolling off 10 to 15 hertz lower and at a higher sensitivity than the sealed. Coupled with your vehicles cabin gain, the lows are playing at a significantly higher spl than what you saw with your two subs in the sealed design.


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## cubdenno (Nov 10, 2007)

qwertydude said:


> In my opinion an SQ oriented bandpass wouldn't have a 1:1 ratio. That could cause quite a peak depending on the volume and Vas of the speaker. In fact 1:1 with a total volume equal to Vas would end up being a peaky monster. Perfect for SPL burping. This might be why you're getting ringning ears. It may sound quieter because it's not responding with as wide a frequency range like music normally goes but that huge peak can cause ears to ring after listening for extended periods.
> 
> An SQ oriented bandpass ought to have a larger sealed section to extend response below the port tuning. That would give you deeper bass. The smaller ported section would also load down the woofer better over a larger range leading to a wider upper bass response. This combo would result in a wider passband with better response below the port frequency.


On paper, the band pass I have for my 15 is tuned for 65ish hertz. The peak you described is true on modeling software. A ridiculously high peak. Like 94/95 db 1w/1m levels. And since the single reflex design rolls off slightly faster than sealed below tuning, in my car I get a nice flat response to 30 hertz with the cabin gain. Plus I can eq in about any response I want at the expense of hitting max output a bit faster. 

End result is I ended up with very clean output at ridiculous levels. While they are huge, I really like the sound of the design. If you have the room, I really recommend single reflex band pass designs.


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## chrisW. (Sep 8, 2013)

Yeah this peak everyone is telling me I have I really don't think exists in the real world application of this box. I think I would notice it. It's plays flatter than any other enclosure I've heard. 

The point of this thread isn't to fix the response of the enclosure. I don't believe there is anything wrong with it. What I am curious to know is, besides the response itself, is a sound wave coming 100% from a port different in anyway to a sound wave coming 100% from a woofer cone? Even at the same volume is it intensified somehow that it will effect ears different or travel differently outside the car? Or are db's just db's? These are the main things I'm curious about.


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## cajunner (Apr 13, 2007)

chrisW. said:


> Yeah this peak everyone is telling me I have I really don't think exists in the real world application of this box. I think I would notice it. It's plays flatter than any other enclosure I've heard.
> 
> The point of this thread isn't to fix the response of the enclosure. I don't believe there is anything wrong with it. What I am curious to know is, besides the response itself, is a sound wave coming 100% from a port different in anyway to a sound wave coming 100% from a woofer cone? Even at the same volume is it intensified somehow that it will effect ears different or travel differently outside the car? Or are db's just db's? These are the main things I'm curious about.


you have made observations.

these observations may or may not be based on things that are true, like facts.

they may be based on conjecture, or opinion.


but that's okay.

measuring your car using something that creates facts, like an RTA or SPL meter, is a way to answer your questions.

not measuring, and wanting people to swish around in your mouth and describe what the gargling sounds like, is not a way to answer your questions.

now, don't get me wrong.


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## chrisW. (Sep 8, 2013)

Not sure what this swishing in mouths business is about or what practices you keep in your free time but I don't recall asking any questions that required a specific diagnosis of my set up in particular. Rather I asked, to the best of anyone here's knowledge, is a sound wave coming exclusively from a port different than coming directly from a cone with no port involved. Now, you could read, and not reply to the thread, or if you must reply, one could reply with "not that I know of."

now, don't get me wrong.


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## cubdenno (Nov 10, 2007)

I am pretty sure you are misinterpreting cajunner. 

His point as I read it is, you have some questions based on your experience with your system. You ask the questions hoping someone can explain what you are experiencing. But without measurements to tell us what is actually going on, all we can do is guess based on the words you typed. Simple as that. If you read cajunners post from past threads, you will see that is how he often tries to get his point across. 

Or at least that's how I have always interpreted his posts...


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## cajunner (Apr 13, 2007)

a sound wave, is a sound wave.

it won't know where it came from, but you might by the way it behaves.

it may be saddled with a lot of harmonics, (sealed) or it might be acoustic filtered, (band-pass) and not have a lot of those higher notes that come from ringing cones.

you might decide one is louder than the other, based on those harmonics being audible, or you might just have an ear infection.

the swishing in mouth, and asking about the gargling sound, is just me saying if you don't measure your findings, how will you know that you are asking the right questions?

when you realize that these answers are more complex than a simple "not that I know of" then you will understand the point I was making.


but that's okay too.


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## cajunner (Apr 13, 2007)

cubdenno said:


> I am pretty sure you are misinterpreting cajunner.
> 
> His point as I read it is, you have some questions based on your experience with your system. You ask the questions hoping someone can explain what you are experiencing. But without measurements to tell us what is actually going on, all we can do is guess based on the words you typed. Simple as that. If you read cajunners post from past threads, you will see that is how he often tries to get his point across.
> 
> Or at least that's how I have always interpreted his posts...


it's not that I mean anyone disrespect, it's just that there is no easy way to tell someone asking questions that are so fundamentally challenged that you have to make up some device to be interpreted, like their question needs to be interpreted, that many don't get the connection.

good show...


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## cubdenno (Nov 10, 2007)

chrisW. said:


> Yeah this peak everyone is telling me I have I really don't think exists in the real world application of this box. I think I would notice it. It's plays flatter than any other enclosure I've heard.
> 
> The point of this thread isn't to fix the response of the enclosure. I don't believe there is anything wrong with it. What I am curious to know is, besides the response itself, is a sound wave coming 100% from a port different in anyway to a sound wave coming 100% from a woofer cone? Even at the same volume is it intensified somehow that it will effect ears different or travel differently outside the car? Or are db's just db's? These are the main things I'm curious about.


Depending on the tuning, the peak will be there. But once installed in car, the cabin gain will totally change the frequency response at the listening position. Again depending on tuning, the peak may be at resonant of your vehicle such that those one note wonder systems you hear.... Anyway, I truly believe it's the reduced distortion that is causing the audible effects you are experiencing. 

There is a phase difference I believe. Don't quote me though and it may be moot. Been partaking of adult beverages and sleepy so it's very possible I am way off base. I know there are a bunch of places that you could google phase differences between sealed and band pass enclosures. Or sound differences. Anyway the point is it would explain better than I could at this point.


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## amalmer71 (Feb 29, 2012)

The flatter response, which may be present because of the bandpass enclosure, may hit lower frequencies with more intensity than the sealed box did, but it may not seem as "loud" to you because (as I explained) lower frequencies aren't as easy to perceive as being "loud" as much as upper bass and mid range frequencies to the human ear.

E.G., The OSHA SPL threshold is 85dB TWA for 8 hrs before hearing protection is required to be provided to all employees at any job in the US. It doesn't matter if it's at 30Hz or 3,000Hz. 85dB is 85dB. The difference is, we don't perceive 85dB @ 30Hz as being loud, but 85dB @ 3,000Hz seems very loud. If someone sat in your car and heard a test tone of 30Hz @ 85dB they'd probably want you to turn it up so they could hear it better. They may not feel the same way if you were to play a 3,000Hz test tone at 85dB. The kicker is, either frequency can cause permanent damage, which is why your ears were ringing.

30Hz may just not seem loud to you. Not everyone hears lower frequencies with the same intensity. Everyone's ears perceive sounds differently. Just as some people like the way Reba McEntire's voice sounds, but I can't stand it. It makes me leave the room when my wife starts playing her music. The tonality of her voice is sickening to me. Things are only as "good" as we perceive them to be.

Your comment about it doesn't seem as loud but made your ears ring leads me to believe this is what's happening. For some reason you're just not hearing the frequencies that are causing the damage to the stereocilia inside the cochlea which causes the "ringing" in your ears. It could be your perception of the auditory spectrum isn't as great as you'd like it to be or it could be a simple matter of cancellation of certain frequencies in your car due to phase shift or other anomalies. Basically how "noise cancellation" headphones work.

It may be as simple as cajunner mentioned; an ear infection.


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## chrisW. (Sep 8, 2013)

Pretty sure I don't have and ear infection 

Ok well I never imagined it was this complex haha... And I'm not on a mission by any means to obtain answers. It was just something I noticed and wondered if there was a simple or even a not so simple explanation. I do appreciate you guy's efforts.


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## cajunner (Apr 13, 2007)

I probably should give my two cents on the original question.

I think the experience of the 2 sealed subs, is that of a good mid bass.

the band pass eliminates some of that lower midrange, it's going to sound "flatter" or "cleaner" but it's also going to make you turn up the volume a little bit, to get back to where the sealed subs used to give you the response that says "I'm there"

This may lead you to drive your front stage harder, to make up for those lower midrange coming out of your previous sealed alignment, and the ringing is a result of this phenomenon.

You're trying to regain the sonic characteristics of the sealed system using an acoustically filtered sealed system, and those notes that are now missing from being acoustically filtered, are missed, for reals.

Everyone that does bandpass coming off sealed boxes, that I know of, had to adjust their system or their listening preferences to suit the new response variable, so it's not an uncommon observation.

that you would believe it to be a different kind of sonic wave, or some other characteristic added to it, is probably pretty normal too.


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## chrisW. (Sep 8, 2013)

Xnewbx said:


> Something to note is you won't gain really anything different from a ported enclosure if your ratio is a 1:1.


1:1 keeps the size down and give the output of a ported enclosure with the power handling of sealed ;-)

I'm using this sub out of nostalgia and it is seeing 500w rms daily but is only rated at 250w rms, 500w peak. This set up wouldn't work as well ported.


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## Treesx4 (Dec 10, 2013)

Man I hate to sound like an old man... But if your ears are ringing.... You need to be careful.... No one like to think about "Safe sound"....
I have a constant ear ringing...It never stops... it gets old... Mine was not from car audio, but from an accident... but it still sucks.... 
If your system can get that loud get some ear phones (check local laws while driving) and then get the wow factor from car next to you at the light.... lol But again sorry for being an old man.... But do what I did and enjoy it any way!!!

And sound waves are sound waves.... the difference in sound is probably where different enclosures peak at!!! That simple!!
Good luck


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## qwertydude (Dec 22, 2008)

I really do suggest getting a DB meter, you can say it's SQ all day long and is the best you've heard but is it really "SQ" and when you eq it can you truly eq it flat? Because large peaks tend to be hard to eq out unless you have a parametric equalizer and know how to use it. Note the weighting and apply a correction factor when playing fixed level test tones with it.

This is why people have a hard time believing that you can have a peaky 1:1 bandpass, ringing ears, and still claim it's "SQ".

Having tuned systems long enough I can tune crossovers and eq's just with my laptop and a test tone generator. But that's because I know what a flat frequency response should sound like.

Try running pure test tones of the same level and you might be surprised at just how peaky a response you're getting. Just playing music won't necessarily reveal these peaks. That's why everyone here is also jumping on that peak because even though you claim it's flat, a peak in the 60 hz range is still going to be a big peak in car because most cars cabin gain starts at 60 hz. So the response curve my experience tells me is that you'll have a peak in the 60 hz region and then another one in the 30 hz region from the cabin gain with a dip in between.


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## BuickGN (May 29, 2009)

I remember the first time I fired up my bandpass I had to back the gain way down. Mine was 1.8 sealed and 2.2 ported I think. I loved the sound but like people have been saying, it wasn't flat. There was a peak at 50hz and not much output below 35hz. It played loud up to 80hz. It took some getting used to because in the beginning I would unknowingly play it louder to make up for the slight loss of low end. 

The bandpass also carried farther like the OP mentioned. At what sounded like the same output which sometimes didn't sound that loud in car I swear it sounded just as loud 20' from the car which I didn't like. Of all my setups, bandpass carried the most and IB the least, being practically inaudible near the car. With the windows down it's like there's a shield blocking sound. I can crank it up and it sounds like there's no subwoofer when standing near the window but stick your head inside and it's loud. I'm very happy with not being able to hear much outside of the car even though I can't explain it. The only thing I can think of is cancellation near the car, especially since the trunk is vented to atmosphere. The only explanation I can think of for the bandpass is maybe it was louder inside then I thought.


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## cajunner (Apr 13, 2007)

BuickGN said:


> I remember the first time I fired up my bandpass I had to back the gain way down. Mine was 1.8 sealed and 2.2 ported I think. I loved the sound but like people have been saying, it wasn't flat. There was a peak at 50hz and not much output below 35hz. It played loud up to 80hz. It took some getting used to because in the beginning I would unknowingly play it louder to make up for the slight loss of low end.
> 
> The bandpass also carried farther like the OP mentioned. At what sounded like the same output which sometimes didn't sound that loud in car I swear it sounded just as loud 20' from the car which I didn't like. Of all my setups, bandpass carried the most and IB the least, being practically inaudible near the car. With the windows down it's like there's a shield blocking sound. I can crank it up and it sounds like there's no subwoofer when standing near the window but stick your head inside and it's loud. I'm very happy with not being able to hear much outside of the car even though I can't explain it. The only thing I can think of is cancellation near the car, especially since the trunk is vented to atmosphere. The only explanation I can think of for the bandpass is maybe it was louder inside then I thought.



just to guess, I'd say the smaller compartment of the cabin, is part of that difference.


when you put a bandpass into the trunk, it makes both the cabin and the trunk the compression chamber, and the sound will be acted upon evenly.


when you separate the trunk from the cabin, you not only decrease wavelength room, you now have two resonating compression chambers acting on the signal.

open the larger chamber by opening a window, or open the smaller chamber by opening the trunk, or open both at the same time, and each change is one more step away from the bandpass's enclosed volume. The bandpass's chambers are fixed, the Qtc is what it is, but with IB the Qtc is going to change as you make changes in the car.

a weird phenomenon I have noticed with air boats, is that as they drive away from you, they will reach a distance where the sound drops off precipitously, it's at least a 20 db change going from say, 100 feet to 110 feet away. 

which is good, because being blasted by an air boat at close range is quite painful to experience, and you can literally see the point at which this cancellation occurs, by the point which people take their hands off their ears.

maybe the wave collapses, maybe the band pass maintains a uniformity to the cabin pressure that isn't affected by the windows being up or down, it's an interesting observation though.


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## BuickGN (May 29, 2009)

I'm sorry, I should have mentioned my bandpass fired through the ski pass with the port fitting tightly and the trunk and cabin pretty well sealed from one another. The IB setup should see about the same area as the bandpass. 

I've heard that bandpass couples differently and that can cause the issue we're talking about. I also should have mentioned the IB becomes louder when you're 40-50' away from the car, that's one thing that led me to think it was cancellation. 

I still want to know if it's possible for one setup to be harder on the ears at the same output at the same frequencies. I don't see how but I guess anything is possible.


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## chrisW. (Sep 8, 2013)

Finally someone else who's experienced the same thing


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## cajunner (Apr 13, 2007)

BuickGN said:


> I'm sorry, I should have mentioned my bandpass fired through the ski pass with the port fitting tightly and the trunk and cabin pretty well sealed from one another. The IB setup should see about the same area as the bandpass.
> 
> I've heard that bandpass couples differently and that can cause the issue we're talking about. I also should have mentioned the IB becomes louder when you're 40-50' away from the car, that's one thing that led me to think it was cancellation.
> 
> I still want to know if it's possible for one setup to be harder on the ears at the same output at the same frequencies. I don't see how but I guess anything is possible.


the IB setup has the rear of the cone exposed to a second cavernous, leaky enclosure. How is that "should see about the same" then?

Unless your IB setup is configured in some fashion that I am not aware of, the bandpass should load the cabin space more efficiently than when the front and back wave reflections are allowed to act upon the cone directly, as in the IB instance.

This is my same point, the cabin is acting as a pressure vessel, that the band pass can fill without being interfered with by reflected waves from the interior acting on the cone.

This is possibly why the resonant mode of a band pass is able to carry outside of the vehicle, the basic integrity of the sound wave is not acted upon to the same degree, interfering with the signal in the cabin.

Also, the caveat is that the tuning frequency is also the most efficient use of power, and a strong coincident peak from the cabin transfer function, with the bandpass's tuning frequency, could cause the phase to combine in the case of the band pass and subtract in the case of the IB, so that any escaping notes from the windows outside of the vehicle, have to "come back into alignment" at a distance equal to the degree they were out of phase inside the cabin.


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## dareo (Dec 17, 2010)

I'm playing with a bandpass setup engineered by JBL, gto1204 bp-d, and it is pretty interesting. Huge peak around 120hz, and very strong output from 60hz on up. This is being used inside right now, so no cabin gains. It hits very fast and hard in mid bass ranges that don't sound loud but with my spl meter on it gets well into the 100s fast.


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## BuickGN (May 29, 2009)

cajunner said:


> the IB setup has the rear of the cone exposed to a second cavernous, leaky enclosure. How is that "should see about the same" then?


That was in response to this:



cajunner said:


> just to guess, I'd say the smaller compartment of the cabin, is part of that difference.
> 
> 
> when you put a bandpass into the trunk, it makes both the cabin and the trunk the compression chamber, and the sound will be acted upon evenly.
> ...


I stated that in both the IB and BP configuration, the trunk and cabin were separated, sealed from one another so that's not a factor.


cajunner said:


> Unless your IB setup is configured in some fashion that I am not aware of, the bandpass should load the cabin space more efficiently than when the front and back wave reflections are allowed to act upon the cone directly, as in the IB instance.


I've pretty much eliminated or at least reduced as much as possible any backwave interference. There is VERY little difference with the trunk open vs trunk closed. Backwave reflections were causing some peakiness in the higher sub frequencies so I took care of that early on. 


cajunner said:


> This is my same point, the cabin is acting as a pressure vessel, that the band pass can fill without being interfered with by reflected waves from the interior acting on the cone.
> 
> This is possibly why the resonant mode of a band pass is able to carry outside of the vehicle, the basic integrity of the sound wave is not acted upon to the same degree, interfering with the signal in the cabin.


This is the best explanation I've heard so far to explain the difference in the sound carrying ability at long distances of the BP.


cajunner said:


> Also, the caveat is that the tuning frequency is also the most efficient use of power, and a strong coincident peak from the cabin transfer function, with the bandpass's tuning frequency, could cause the phase to combine in the case of the band pass and subtract in the case of the IB, so that any escaping notes from the windows outside of the vehicle, have to "come back into alignment" at a distance equal to the degree they were out of phase inside the cabin.


That's pretty much what I was thinking. Anything that escapes from the trunk will cancel out to some degree with what's coming out of the windows. Mine actually seems to do this more when it's parked inside of the closed garage. Windows down with the 15s at xmax produces a very underhelming output when standing in the garage. In every other setup, the sub bass is very loud inside of a closed room. I can open the garage door and it's just a little louder. Pull out of the garage and it's louder still but again, not impressive at all (which is good).



cajunner said:


> open the larger chamber by opening a window, or open the smaller chamber by opening the trunk, or open both at the same time, and each change is one more step away from the bandpass's enclosed volume. The bandpass's chambers are fixed, the Qtc is what it is, but with IB the Qtc is going to change as you make changes in the car.


I forgot to mention it last time but in response to this, you're completely right. However, it happens so low in the FR that it's not noticeable unless you're playing some 20-25hz material and even then it shows up as a slight increase in SPL with a window down. On most music there's no audible difference in the cabin with the windows up or down. Same with the trunk being open, very, very small difference in output and FR. A couple people said it's because the resonant frequency of the subs as a system is so low. I think the subs themselves have an Fs of something like 20.4hz


cajunner said:


> a weird phenomenon I have noticed with air boats, is that as they drive away from you, they will reach a distance where the sound drops off precipitously, it's at least a 20 db change going from say, 100 feet to 110 feet away.
> 
> which is good, because being blasted by an air boat at close range is quite painful to experience, and you can literally see the point at which this cancellation occurs, by the point which people take their hands off their ears.


I lived in New Orleans for 7 years and I've only been on one airboat. I plan on changing that next time I go to visit.


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## cajunner (Apr 13, 2007)

I haven't been on an airboat in over 10 years, but I've driven a little and rode a lot.

As far as an IB installation being able to isolate the back wave from the cabin, that's one thing but the back wave being isolated from acting on the cone in the smaller volume of the trunk, is another.

I'm not understanding how you accomplished that, unless you ran aperiodic mats?

Usually people have the cone between the two volumes, and resonant modes from both cavities are acting on the cone, as well as creating nulls and peaks in the interior volumes of each.

I would imagine the SPL of a good IB system to have a calculable resonant mode in both the cabin and the trunk, and multiples/ratios of the two frequencies corresponding to major and minor response fluctuation in the FR.


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## BuickGN (May 29, 2009)

cajunner said:


> I haven't been on an airboat in over 10 years, but I've driven a little and rode a lot.
> 
> As far as an IB installation being able to isolate the back wave from the cabin, that's one thing but the back wave being isolated from acting on the cone in the smaller volume of the trunk, is another.
> 
> ...


This is just my opinion so it's probably wrong..... I think we have two different problems. One is the slight air spring effect increasing Qtc and reducing efficiency. I think with the size of my trunk and the fact that it's vented to the outside world by the stock vents with the rubber flaps removed, Qtc is very close to Qts. I would think Fs and Fc are very close as well. 

Next is the back wave making it through the cone and making TA harder to get right as well as creating peaks and nulls. Some of these peaks are higher than 120hz even when the low pass is at 60hz/48db. It muddied up the 50-60hz area as well and required massive cuts. I have two king size down filled pillows at the rear of the trunk as well as a fixture with wood of different sizes and shapes glued to it that I've tried. It's just for experimenting with breaking up the back wave, not permanent. Before the backwave treatment there was a big difference between trunk open and closed. I liked the way it sounded with the trunk open better. I thought the change I was hearing was a change in Qtc from opening the trunk. I'm pretty sure that was wrong because once I started trying to break up/absorb the backwave the difference between open and closed was minimal and it sounded a lot more like the trunk being open. 

Right now I have no EQ on the subs except for 20hz +2db which is mostly because my hearing barely goes that low and I like to feel it. I don't remember having the same issues with the W6 and W7s so I wonder if it's because of the sandwich cone and the air gap between the cones vs the thin paper cone of the IB15. 

With them firing into the back seat foam and with the cabin being more than twice the volume of the trunk, it has less of an effect. I can roll the windows down or open the doors and when sitting in the drivers seat there's little to no change. I think the trunk dominates any changes in response and even then it has little effect. 

I was reading about how much sound gets through a 3/4" piece of MDF and while I don't remember the exact number it was way more than I ever would have thought. Something like 12db down from the sub output. I have 2 layers of MDF and I'm adding another when I go with the W7s so I should be ok but if I would have known that much sound gets through the MDF I would have gone 3 deep from the beginning.


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## namesmeanlittle (Nov 20, 2013)

bahahahaha distortion distortion causing hearing loss not spl you can safely listen to music at 110 dbs if you could have distortion normally in the 90 to 95 db range, our ears eventually cause distortion so it is impossible after a certain point. anyway it is a bandpass box in a tin can it has distortion and will never be as loud outside. i have 2 10's in my truck that can be heard 1/3 down a block and barely hit 120 dbs. people think i have super woofers there junk sealed boxes always work better for sq and distance. look at 40's - 60's speakers most are not loud but can be heard at a great distance, they where built to have low distortion. also bandpass means to cut out all but one frequency they work great for that one note after that its all down hill. This is why i always recommend a sealed box if you wanna listen to music. for noise aww hell go for a 6th order a tuck with 2 folded bass horns  bass horns sound ok they just need massive space


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## cajunner (Apr 13, 2007)

BuickGN said:


> This is just my opinion so it's probably wrong..... I think we have two different problems. One is the slight air spring effect increasing Qtc and reducing efficiency. I think with the size of my trunk and the fact that it's vented to the outside world by the stock vents with the rubber flaps removed, Qtc is very close to Qts. I would think Fs and Fc are very close as well.
> 
> Next is the back wave making it through the cone and making TA harder to get right as well as creating peaks and nulls. Some of these peaks are higher than 120hz even when the low pass is at 60hz/48db. It muddied up the 50-60hz area as well and required massive cuts. I have two king size down filled pillows at the rear of the trunk as well as a fixture with wood of different sizes and shapes glued to it that I've tried. It's just for experimenting with breaking up the back wave, not permanent. Before the backwave treatment there was a big difference between trunk open and closed. I liked the way it sounded with the trunk open better. I thought the change I was hearing was a change in Qtc from opening the trunk. I'm pretty sure that was wrong because once I started trying to break up/absorb the backwave the difference between open and closed was minimal and it sounded a lot more like the trunk being open.
> 
> ...


we keep dancing around the basic thing, that of the rear wave in the smaller volume of the trunk, having an effect directly on the cone, not passing through it, not being absorbed by pillows behind it, but the actual standing waves, directly modulating the cone's output.

It doesn't matter what the cone is made of as much, when you're talking about frequencies that are yards long and create pressure gradients that have massive energies, over several feet and sometimes gathering in areas where the decibel levels will change by 10 db, or a power factor of whatever, depending on the vehicle's unique characteristics.

Some would likely call it a desirable feature, map it out with contour software and measurements, and use computer generated response corrections, or even apply a servo circuit directly, if they knew how.

And I bet it would go hand in hand with the phase correction people are already doing in order to get the bass in the cabin to fill in, or leave no serious nulls in the listening area.

I'm not really concerned about changes to Qtc of the cabin, when you introduce or remove the trunk's resonant nodes by closing or opening the trunk. That's where I think the greater part of changes in what you hear are, and not some minute changes in Fs of the system due to pressure differentials. The standing waves, acting on the cone. That you have them firing into an acoustic filter (the seat back) could also help reduce the modulation on the cones by those frequencies that are affected, but at the very lowest octaves the seat doesn't filter much at all.


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## diy.phil (May 23, 2011)

@chrisW if your ears are really ringing (and not a figure of speech), please quickly book an appointment with your doctor for a physical exam, blood test/work and hearing tests. This is something we cannot help you with -- it's a health issue sometimes caused by something else in the changing/aging body, something only your doctor can check and explain, and have some treatments/plans for you. Good wishes to you! (We can only prescribe subs and boxes here.)


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## chrisW. (Sep 8, 2013)

diy.phil said:


> @chrisW if your ears are really ringing (and not a figure of speech), please quickly book an appointment with your doctor for a physical exam, blood test/work and hearing tests. This is something we cannot help you with -- it's a health issue sometimes caused by something else in the changing/aging body, something only your doctor can check and explain, and have some treatments/plans for you. Good wishes to you! (We can only prescribe subs and boxes here.)


I think you misunderstood the point of the thread. It's not about my my ears ringing. The theme of the thread was supposed to be the difference between port bass vs bass off a cone and if the two behave differently. My ears are fine. They ring only a little for a short period of time and only after going full tilt with the system for a while. I'm not worried about it.


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## PcChip (Mar 21, 2021)

I'll necrothread this because I can't find anywhere else talking about this, and it sounds like a question similar to one I have 

Back in the day (2005) I had a great system in the trunk of a ford escort (subs all the way to the back of the trunk firing backwards, rear seats down). It was loud, low, and clean.

Today I'm trying to re-create that sound in my Veloster N (which is a hatchback) 

I've achieved the same loudness, however I'm getting a ringing feeling that comes with it that I never had before in my escort. It makes my ears hurt after listening. Sure, I could just be getting older and my ears are more sensitive now... but I don't think that's it. It almost sounds like the entire cabin or the sub box is ringing, and the ringing is what is hurting. Can a spectrum analyzer confirm this? 

Anyone else know what I'm talking about?


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