Burp Frequency...

[PandorasCustoms]

According to an article written over on caraudiomag.com (http://bit.ly/eSooXf) , the basics for SPL competition when using a Ported enclosure primarily involves Distance to the meter

Does this have the same effect when working with a 4th Order Bandpass enclosure?

According to the information supplied over there, a peak tuning frequency of 86hz would yield the loudest Burp freq. in my Explorer.

The enclosure will be 78" from the meter, thus giving you the formula... ((13560/2)/78")=86.923.

Is something wrong with this information?

I have been building enclosures for a while, and have been around the car audio block once or twice, but I have never been a competitor (All previous work was for friends, family, and associates). I am looking at taking a shot at the IASCA iDBL Stock <=160 Cone SA category. And want to make sure I am looking at this math correctly. From what I can tell, even with cabin gain calculated in (Factored with BassBox Pro), this frequency is still my best shot at a LOUD burp. Can anyone shoot this down? I am looking for opinions and arguments before my paper and pen turns to wood and saw blades.

[corey0928]

it usually would be better to look at the resonance (sp.?) frequency of your vehicle, I think explorers are in the 50s if im not mistaken

[PandorasCustoms]

Well, I know for DB Drag I would need to revamp the setup because their max freq. is 80Hz, but IASCA goes up to 100Hz.

And, according to BassBox Pro, with a cabin gain increase of 12db/octave beginning at 90hz, the peak frequency is still 79Hz with my current design.

I have been playing around and modifying the tuning to frequency to 50hz, I can replicate the same volume (SPL) as a 85Hz tuned enclosure.

Still something doesn't seem right...

[fecupe2001]

4 doors 2gen explorers are 51-53 hz man, you wanna try burping @ 79 hz?? that isn´t a panda hommie, my explorer love to peak at 53 hz no matter what i do, funniest thing is that the best score i could get on some testings were with a 39 hz tuning!!!

Anyways, a 4th order bandpass peaks around the front chamber tuning, if you tune it around 48-50 hz it would peak around the resonant frequency of your explorer, here´s a video i posted on my channel finding the resonant frequency of the sexplorer!!!

By the way, you said your box would be placed around 78" of the sensor, it´s a 2 door explorer? are you using the box on the back seat area i guess?

[PandorasCustoms]

Yes, I have the 2-Door Sport 4x4, and IASCA Stock division rules require that all enclosures be staged in the "cargo" area of the vehicle.

I am currently in the process of Dampening everything. Got the doors and rear hatch done thus far. Pulling the interior later this week and doing the floors and roof.

I was hoping to get everything ready for the box build by this weekend, but with these new numbers, I may have to change a design.

Currently, the idea I had was 18" Tall chambers Sealed chamber in the rear and the ported chamber in the front right up against the back seats. The port was going to be on top but facing forward making the total height of the enclosure 22.75", and clearing the back seats. It would also make the port almost level with the top top of the dash. I won't have to modify much as the idea was to make a port design that has limited effect on the actual volume of the enclosure itself. Hence the reason it is top mount, facing forward.

And, yeah, I had heard some others talking about 1st gen X's looking around 51hz which is why I brought this up. It just seemed to be really out of place to be tuned that high when no one else was...

[PandorasCustoms]

Bump... Anyone else have any input?

I have already began to recalculate my Tuning Frequency.

Now, if I go with a Quarter length wave, I end with a tuning frequency of 43.5 Hz.

Would it be better to try and match the wavelength peaks as opposed to the Resonance Frequency? Wouldn't 43.5 meet both criteria? From what I have been reading, Resonance Frequency is +12/db octave. So, wouldn't tuning to 43.5 give me a little more gain over 51 while at the same time meeting the wavelength/distance calculation for the meter placement?

I am going to see if I can't meet up with a guy here in CFL and get a meter in the car this weekend to try and get an actual resonance freq. for my Ex

.

Also, just thought of this, but doesn't dampening the vehicle effect the Res. Freq.? As the vibration of the interior sheet metal decreases, wouldn't this cause an effect on what frequencies cause the most vibration? I am going to try and get everything damped before I go get metered just in case, but just trying to cover all of the bases.

SQ enclosures just seem much simpler...

[Boon]

That 'distance from the meter' thing is conjecture and pure theory, it doesn't work in the real world. It might work in a pipe made of anechoic material so the only thing to consider was the primary wave but cars are full of reflections and a huge variety of materials with different resonances so the distance thing all falls apart.

Dampening the vehicle lowers the resonant frequency and can actually hurt your score. Strategic dampening of panels where energy loss is occuring can help though - so you can't just buy a couple of bulk packs of Damplifier and expect your score to go up.

If you want a pure burping setup you need a setup you can adjust the tuning of then to spend many hours with a saw and a termlab changing the tuning 1hz at a time and sweeping it until you get your peak. The peak freq changes with dB as well.

[RooTxBeeR]

Good thing I am never going into SPL

[AMI CUSTOMS]

You need 1/4 wave from speed of sound, so your theoretical peak with ZERO cabin gain is 43 hz, and that theory does work, I calculated mine in my sierra to be 56.5 and I peak at 57. In my s10 I calculated 63 and peaked at 63. The closer you are to the mic the higher the freq peak will be in theory BECAUSE it takes more energy to moves a sine wave faster thus higher SPL.

[PandorasCustoms]

That 'distance from the meter' thing is conjecture and pure theory, it doesn't work in the real world. It might work in a pipe made of anechoic material so the only thing to consider was the primary wave but cars are full of reflections and a huge variety of materials with different resonances so the distance thing all falls apart.

Dampening the vehicle lowers the resonant frequency and can actually hurt your score. Strategic dampening of panels where energy loss is occuring can help though - so you can't just buy a couple of bulk packs of Damplifier and expect your score to go up.

If you want a pure burping setup you need a setup you can adjust the tuning of then to spend many hours with a saw and a termlab changing the tuning 1hz at a time and sweeping it until you get your peak. The peak freq changes with dB as well.

This is completely understood, and I was aware of the "Over Dampening" aspect. Currently, I know that there is a lot of "energy" wasted in movement of certain panels in my vehicle, so I have been focusing on correcting those first. And, that is good insight on the idea of a "Perfect World" design. I hadn't actually considered it, but it makes sense. If it was that easy, then everyone would theoretically peak the same numbers with the same setup in different vehicles.

You need 1/4 wave from speed of sound, so your theoretical peak with ZERO cabin gain is 43 hz, and that theory does work, I calculated mine in my sierra to be 56.5 and I peak at 57. In my s10 I calculated 63 and peaked at 63. The closer you are to the mic the higher the freq peak will be in theory BECAUSE it takes more energy to moves a sine wave faster thus higher SPL.

Yeah, 43hz is kind of what I came up for the quarter wave as well, but I have no "proof" that this method will yield the best "burp". My theory was that if I run the quarter wave setup then I will gain the benefit of the 12db/octave from the Cabin Gain plus have the frequency aligned to meet at the sensor. I will say that I was sitting in the X last night and running my signal generator at varying frequencies with only quarter volume on the head unit, and 52hz "seemed" the loudest. But, again, in SPL, "loudest" doesn't always mean most pressure. I really need to pick up an RTA for myself, but I am just skeptical about buying a cheap tool that could be inaccurate, and I can't justify an expensive tool for a "hobby".

Also, currently, the enclosure tuning would effect the readings of an RTA, correct? This is why I tried to measure it at low volume because the tuning frequency would have the most minimal effect on the output, but it would still have some. I might just suck it up and go get the RTA...

I did get with a guy here in Orlando who has a Term and we are going to do some different measurements this weekend.

But, I wanted to have an idea and a designs ready for a build before I went over there.