I have a 12" GCON in a 2.5ft^3 enclosure tuned to 32hz.  I have been lacking in response toward higher frequencies and was curious to know where the drop was happening, as it is quite a steep slope.  I was playing with a tone generator this evening and from 28 to 50hz sounded amazing but as soon as I hit 53hz I lost significant dbs. There was another significant drop at 60hz. Is this due to my box tuning? Can a ported enclosure be expected to produce these frequencies with significant spl? What can I do to get these frequencies to play? Separate subs dedicated to that range? box position doesn't seem to make a difference. Vehicle is a 96 Honda accord sedan.

Three things to check. First verify your tuning is accurate by using your tone generator again and watch to see at what frequency the sub moves the absolute least amount. That will be your tuning frequency and in most cases should be relatively close but just be sure. Have you tried moving the sub around yet? Generally gaps like that in the frequency response are due to acoustic anomalies that cause cancellations and such. The last thing to check is all the settings on your HU and amp to make sure you don't have a low pass filter that's turned down in that neighborhood somewhere.

Checking and verifying the tuning of the enclosure can help ensure there's nothing goofy with the frequency response from being tuned abnormally low or something. Very uncommon issue, but it could happen.

In all likelihood the issue is an acoustic one. You'd be floored by how a few inches or a few degrees of rotation can affect the response of any speaker or sub in a car. They're a horrible environment from an acoustics standpoint.

I'm sure you've checked your settings, but hey, shit happens sometimes. There's been plenty of threads over the years where someone has had an issue like this, fought it for a week or two and then discovered something they thought they had previously checked but missed.

Verify all that stuff and lets see what you have after that. I'm sure others will have other ideas as well, those are just the first few places I would check. Another possibility is that the sub simply doesn't respond well into that range, but I would tend to doubt that train of thought for several reasons.

Thanks for the tips Alton, I am leaning toward cabin gain/acoustic issues but I will move the sub around and check my response.  I checked my HU settings but not the amp...something could have changed while moving my amps around and what not. and I'm sure the box isn't tuned where I think it is, I imagine it's close, but this was my first ported box build...I will check somethings tonight. Thanks again

is  bass boost off?

is  bass boost off?

Bass boost is off

myself and another member on here are experiencing similar issue...

 

http://www.soundsolutionsaudio.com/forum/topic/60448-missing-frequencies/

 

 

Thinking its a null or cancellation.

All installs i have had.. others i know.. competitors, etc.. this is normal in a vehicle tuned the way you are.

 

4th Bandpasses have the ability in a vehicle to literally open the play range.  This sounds opposite of what you would expect but i do not think all of the BPs i've heard are the rarest out there and all the ported enclosures i've heard and built around this country are all wrong.

 

You could do a BP but it's not easy.

 

Simply put, it's the acoustical gain in a vehicle.  You want to overcome it? you need high efficiency or peaks in your response where you are lacking output.. 

IE- above 50hz.  Tuning a 4th order BP or even a 6th which is harder can offer 2 main peaks in the response.

 

Allowing the response to "saddle shape" in between the 2 peaks right in the playable range your vehicle is efficient at will audibly net you a smooth flat output response.

 

It's not easy as to just throw it in and it's fixed..  You need equipment to do this right.

I'm not the BP guy to talk to but if any are here who build them that are here, i'm sure they can help you out.

i assume you're conducting these observations with the front stage disabled? 

 

where are the mid's high passed? could be cancellation issue.  any rear speakers?

 

some ideas:

 

1. temporarily move the box to the back seat and test the response. this could rule out a situation involving the trunk. although, i don't know what the solution would be. 

2. remove speaker from the rear deck. 

3.you could build a ~1 cu ft sealed box and play around with that. easier to test orientations and so forth. 

4.what is the high and low pass xover settings for the sub (what range of frequencies are you depending on the sub to reproduce)? perhaps the car has a steep resonance in the sub 50hz range. so what your hearing is a large peak 30-50hz not a null over 50 hz. or its a combination of both. 

HU is an 80prs. I have tested sub with mids and highs off. no rear speakers. I sealed off the holes in the rear deck where the speakers used to be. sub is crossed at 80hz 12db slope. mids lp @ 60 on a 24db slope, hp @ 5k 12db slope I believe. I am in the process of dialing everything in as this is my first attempt at running active...it is taking longer than expected I will test with the sub in different orientations tomorrow and with the back seat folded down and see what happens. I am building a box for an xcon right now and want to get this figured out before I change my setup, but like hedz, I think it is an issue with cabin gain/cancellation

if the mid and sub is overlapped then there could be cancelation but you're saying that the null still exist with the front stange disable. 

 

if the rear speaker holes are sealed and the rear seats are up than that could be the problem. 

How much do you have to eq down the rest to be equal? Has position changed this much?

I haven't tried to eq down 50hz and below...I will check that tonight. I have been playing with sub position too...I didnt even think that sealing off the holes would cause the issue...I always have the ski hole down so I assumed it wouldn't be an issue.

Everything has some affect.  Coming through the ski hole kind of makes it like a 6th order band pass since there is some length for the waves to travel through the opening, it's like a port.  Close that off and unblock the rear speaker holes and it will affect it completely differently.  There's little to no length involved in getting through the holes, but they're still holes plus the waves will be reflecting off of whatever is above the rear deck.  Be it the glass or the roof both surfaces have their own effect on the sound waves and then there's the angle of the reflection and what it bounces toward from there.  While these reflections can have a much larger effect on higher frequencies due to the shorter wavelength and higher resonant frequencies of the surfaces involved it does still have an effect on low frequencies too.  The holes the bass is traveling through probably affect the end result that your ears perceive more than the reflections would.  I'm not an acoustic engineer at all, but the little I've been able to learn and seemingly understand leads me to that conclusion.

 

I'm absolutely certain that if I'm wrong on that theory Sean, Brad or someone who really actually does know will correct me on that.

the ski pass is probably not creating the resonance effect your describing within the range of frequencies produced by a subwoofer. you might be able to estimate a resonance with this equation. treating the trunk and ski pass as a Helmholtz resonator. 

 

 

v is speed of sound, A is area of ski pass , V is volume of the trunk, L is length of the length of the ski pass. 

Edited October 4, 201311 yr by lithium

Well, I wasn't thinking of the ski pass as having anything to do with resonance, at least directly.  My thought only went to that of a 6th order bandpass as mentioned, though the helmholtz effect would make more sense and could definitely be at the root of the cancellation issues.  The same way it does in the design of mufflers in a car.  I was only trying to refer to the resonances of the materials of whatever reflective surfaces should the OP open the rear speaker holes in the rear deck.  Like I said, sub bass frequencies wouldn't be anywhere near the resonant frequency of the glass and probably not that of the sheet metal either.

 

My original statement still stands though.  Everything in the environment has some affect on the response, especially anything in between what's making the sound and where the listener is hearing it.  Even in an open room the surfaces of the walls, flooring, and even the furniture can affect the response the ear picks up.

Well, I wasn't thinking of the ski pass as having anything to do with resonance, at least directly.

Read up a bit on reflex enclosures, they by default utilize helmolz resonator in design. Exactly why they are built.

I am very curious how much the whole system rolls down. ie, is it everything above 53hz? Real measurements would be beneficial to know the response. No need for calibrated, just relative. Curious also if it behaves linearly (ie same rolloff at different levels).

I haven't experimented enough but 28 to 52hz play loud and clear, there is a steep drop at 53hz and from 53 to 59hz there is not much difference as far as I can tell in output. At 60hz there is another steep drop in spl and it seems there is a gap from 60 to around 120hz where my components start to play nicely. I think 80-120 can be boosted by changing my install but I am trying to keep the doors as stock as I can so I deal with that gap. When I fold my seats down I definitely notice a boost in spl, i have also been trying different box orientations in my trunk...I am finding like most things it all comes down to the install...I can't even count how many times I've heard that, and ALL of my experience proves that statement to be true

Like you said equipment is only a small part of it, a good install will always win. Just keep playing with your current setup until you get to where you want. Then you can adjust the individual components of your system as necessary. 

It is definitely a process with a steep learning curve. At  least I know I will have something to do for awhile.

with eq dont boost, alway cut.