Built a burp box yesterday, 2.65cf with a single 8" pvc pipe (it's what I had laying around at the time). I tried it with 2 different tunings, 38 and 44hz. the first test my box was tuned 38hz and I did a 145.7 on my mic @ i think 53-54hz. So I figured wow I need to tune way higher right? well i chopped the port to 44hz (box volume remained the same) and my score dropped almost a full db, and I even peaked at 54hz again.
Thats all the testing I got done as it was getting dark and I didnt wanna plss off the neighbors. Can anyone try and explain why my score dropped when I tuned closer to my peak hz? From everything i have gathered boxes seem to peak 4-7hz above tuning, and yet mine dropped when I narrowed that gap and was still within 10hz gap from my vehicles peak with this box.
the only thing I can think of why I am peaking 10+hz above my tuning is a mix of my trucks resonating freq and my real small box? with my 4.5cf box tuned @ 40 hz I was peaking at 44-45hz.
Well this box was intended on just a burp box. I only compared it to my daily box (the 4.5cf box) just for comparison. I know it wasnt an ideal burp box, should have had more port area, but it's just the supplies I had laying around and I was bored that day lol. But that is why I started with it tuned at 38hz so I had much room to chop the port, but I assumed that I needed to tune much higher and jumped the gun and cut the port to 44hz.
I dont have anything done to my truck for spl, I still have all my stock interior panels and no deadener. what else can I do to it to prep it? it's a 99 ext cab ranger, im open to all ideas.
a ported box typically does peak above the tuned frequency. Usually just above it. That's normal, and can also be a factor of cabin gain and impedance rise, as well.
i think what is happening to u is normal. i started my first spl builds tuning high and it never worked out. i think the main reason people tune high is because the sub will not move as much when u burp closer to the note the box is tuned to.. and for some spl guys with burp boxes and 20k watts that is the reason there subs hold to together. my set up now is tuned to 36Hz and my hit note is 52Hz. the only way to get it perfect is to make a BIG box and a long port then start cutting off the port and filling the inside of the box and shaping it. as u test in ur car. who knows what will work in ur car. u will just have to try it out
OK, no. The reason people tune boxes around 55Hz for SPL, and use that as the burp test tone is due to vehicle transfer function and cabin gain. These can be easily measured (not guessed) using an RTA and a tone generator connected to the stereo system in the vehicle. What you're doing with trimming the port and reducing boxvolume and guessing at it, is pretty much what was being done in the 1950s, before we had any understanding of acoustics in relation to home audio, when people used fire places to make ported subwoofer enclosures.
apart from all the sub\amp\box install , imo the 2nd half of a good spl set is how the vehicle is prepped , meaning all doors seals are good , trunk lid & trunk area is foamed or matted
adjusting the line drive to ur amps also makes a noticeable difference so u shud experiment with that too ....
Well with my attempted burp box I was getting near full excursion on my power. Does this mean anything? should I go with a bigger box still possibly? I feel that if I went with a bigger box I take a chance of trashing my sub. Rovin I dont have a line driver, but I guess I can play with my gain/volume/subwoofer setting on my hu. I dont really have a whole lot of places to seal up being a small truck, my doors would be about it that I can think of?
lol ya (at that freq should be near dead on with a TL too). I did a 145.5 on my mic with my daily box on a single 1750. Metering is outlaw with mic on windshield.
i understand what ur saying glasswolf but its not so easy to find the perfect note to tune when u have a daily driver. as it gets louder parts of the car resonate at different notes, building spl in a regular car and building an spl concrete car is a lot different.
No, again, it's not different at all. The RTA and tone generator will reveal the transfer function of the car's cabin, no matter what car you have, or how it's been prepared. Also, resonance doesn't change frequency based on a change in amplitude. The resonant frequencies are based on object mass. The mass doesn't change at whim. If you want better SPL in a car, any car, you sound deaden the car. This is done for several reasons. You damp a vehicle to reduce resonation by lowering the resonant frequency, which is done by adding mass, and in some cases, rigidity, and by decoupling the sheet metal of the car from the damping material, allowing it to absorb the energy that would otherwise be resonating the car body. What you're doing by sound deadening a car, is you're increasing the efficiency of the audio system by wasting less energy as vibrating metal or sound heard outside the car, and keeping more of it inside the car. That makes the system louder in the cabin, and for daily use, allows you to use less power to obtain the same moderate volume levels. SPL vehicles aren't all that different from a normal car. They just take things several steps beyond what the typical car owner would do, usually because they have a lot more factory sponsorship money to do it with, or just way too much free time and expendable income.
resonance frequency of a car does change if the amplitude changes. glasswolf do u have a tl? if u play a sweep at low volume and a sweep at high volume the loudest notes will be different. resonance is not always a bad thing for spl. some times resonance can actually help. i think glasswolf knows more about car audio than i do. but in all the spl boxes i have made tuning high into 55Hz killed the score. but then tuning around 35 or 40Hz i would still get a higher hit note of 50 to 55Hz. . maybe because the tuning is not as close to the peak, so the impedance in a tuning like this gets more power to the sub than it would when it was tuned high. gets a little more excursion h on the same note. but i am not 100% sure. what do u think glasswolf? maybe u know something that i don't
on the topic of dampening : i have heard from a few competitors who actually lost .something of a db by over matting or by adding mat to certain areas like the roof
so spl is strange thing : what may work for 1 case may not work for another ...
two things that are probably affecting your scores. you generally hit peak efficiency from an enclosure just above the "tuned frequency," so tuning to 40Hz probably did help, since your peak would be closer to 45Hz in that case. Another issue that may drag down the output at 55Hz would be impedance rise from your enclosure design. Without knowing the math for these calculations, which you may not, or having software to figure it out for you, you'd be swinging in the dark trying to find the ideal tuning points. As for my experience, 20+ years in the industry, mecp master installer, electrical engineer, and former IASCA and USAC pro class competitor. I don't know it all, but I have a fairly good grasp of the basics
In regards to impedance rise, it can really affect the output when you're trying to squeeze every bit out of the system.
All speakers are a design compromise, and thus all are different in order to accomplish certain goals. A speaker designer will often use the impedance curve in order to help optimize other more important driver parameters.
Obviously, because there are so many things that affect impedance of a driver, many manufacturers use conjugate techniques to accomplish a given "nominal" impedance. "Nominal" impedance is used to define an average impedance over the driver's frequency range. It is not a term recognized by the IEC. The IEC uses a concept called "rated value", which allows any "increase" above the rated value, but limits the "decrease". The standard does not allow the impedance to fall below the 80 % of the nominal value at any frequency, including DC.
Typically, you can guesstimate the nominal impedance of a driver by measuring the DC resistance and multiplying that value by 1.3. Example: Most 8 ohm drivers (<-nominal) will measure around 6 ohms DC. Not the most accurate method, but close and it doesn't require sophisticated equipment.
Now, to define order of importance. I'm not going to make this overly complicated, mainly because the equations are available with a google search and it's beyond the scope of this tutorial.
Electrical side: The voice coil DC resistance has the biggest impact on speaker impedance. DCR dominates the resistance of a driver at nearly every frequency. Next is inductance on the electrical side. Stray capacitance is miniscule compared to the others, but still there.
Mechanical side: Keep in mind we're measuring the electrical equivalent of these parameters. Major mechanical limitations boil down to suspension compliance, cone mass, and suspension losses. Your resonance peak (Fs), is dependant upon this mechanical branch, as well as it's relation with the enclosure. And, as you may have guessed, the enclosure is a contributor to impedance, since the enclosure is effectively a part of the suspension of a driver.
Finally you have the radiation impedance (how the driver interacts with the surrounding air). You can't really approximate this with a single lumped-parameter synthesis. It's ELECTRICAL importance is low enough to not worry about (though it is a very important factor, as you could imagine).
What we really want to know is what happens at different frequencies. In other words, how do all those different driver parameters affect the impedance curve?
1. At DC, the impedance is completely dominated by the DC resistance of the voice coil 2. Up to the point of the fundamantal mechanical resonance, the reflected motional impedance begins to dominate and is inductive in nature. The total phase angle of the impedance RARELY exceeds 45 degrees and thus the resistive and reactive (inductive) parts of the impedance are just about equal. 3. At fundamental resonance, the impedance is purely resistive, its phase angle is 0, and is determined by the effective series combination of the voice coil DC resistance and the reflected mechanical losses of (primarily) the suspension 4. Above fundamental resonance, the impedancs drops, has a negative phase angle (rarely exceeding 45 degrees) and is capacitive in nature. The impedance drops until it approaches the driver's "intended" range. The midrange for midbass/midrange drivers (duh) and treble range for tweeters. You'll see this point on the impedance graph of a driver 5, In the intended range, impedance approaches the DC resistance of the voice coil, but is SLIGHTLY higher than that DC resistance for a variety of reasons, typically about 10-20%. This is the region that manufacturers (respectable ones, anyway) use to specify the nominal impedance. The impedance at these frequencies is predominantly resistive in nature and is dominated by the DC resistance of the voice coil. 6. Above this region, the inductance of the voice coil begins to influence the impedance. Note that it NEVER becomes purely inductive, or even remotely close. Over the majority of the range of operation, the voice coil resistance still dominates. Second, eddy current losses in the pole piece dominate quickly, such that the phase angle of the impedance asymtotically approaches about 45 degrees, and NEVER 90 degrees.
Other factors: Obviously, impedance is measured at low levels. The next thing to consider is the fact that as a driver increases it's excursion (output), the coil is moving further from the gap, causing a large Thiele/Small parameter shift. This changes impedance due to the changing mechanical and electrical parameters. Heat also affects impedance. Few measure at these levels, so you're SOL on a graph for that one.
The major driver design options that affect impedance are shorting "devices" (Plated polepieces, faraday rings, shorting rings, etc) and the polepieces (old style polepieces, T-shaped or yoke style, and extended polepieces are the most common). Shorting rings, faraday rings, and polepiece platings are designed to shunt out eddy currents from the voice coil, they effectively lower inductance and flux modulation. They lower distortion dramatically as well. Polepiece design affects magnetic saturation as well as determines the surface area available for cooling.
Phase plugs/heat sinks are often designed to help remove heat from the voice coil. Note that removing heat doesn't really affect measured parameters as much as it ensures that the performance stays more consistent as power and heat increases.
i didn't know u were an EE! that is what im going to school for! i understand about all that u said but i have used programs for boxes and they just turn out as normal boxes.. nothing great that would win any spl comps. so all i know to do is test as much stuff as i can. resonance helps some times. am i right? if i have a big resonating sheet of metal (or something) in my car that resonates at my loudest note, it would make that note louder. do u agree?
so this is happening all over in a daily driving car. on the doors windows and almost everything. so as u turn up ur volume some things that are resonating amplifies more than other things that are also resonating. so because they resonate different and are amplified different it changes ur hit note at different volume. stronger things or smaller things resonate at a higher note. so the big spl cars are like tanks. if u play a higher note it will flex very little. i am NOT saying that the resonance is something u want in ur car. i am saying an spl car that is all around strong (doors, windows) will play those high notes and it will be louder. but for a daily car it will fall on its face when u start getting to high..
i hope what i said makes sense.. do u agree glasswolf?
get a sealed box...throw a sub in it and run a sweep. that will yell you the freq of the vehicle. tune your box 6-10 db lower and viola. decent numbers. keep messing with the enclosure, find the right design, make sure the box is solid and doesnt flex. and test deadener placement. lay a piece down and test. so on and so forth. you can lose SPL from over deadening
If you want an easy box to build that will give you a good starting point. Try 16x16x31.5 w/ an 8" port 11" long. Fire the sub up on the passenger side, port external toward the drivers side wall. Put a large wedge under the sub.
It may not be the best box in your vehicle, but that design works pretty well w/ singe subs in mini-trucks. The last ranger I did like this did 144.6 w/ 1 RF T1-12d4 on a Kx400.1, used 4 4" flares on that one though.
"get a sealed box...throw a sub in it and run a sweep. that will yell you the freq of the vehicle. tune your box 6-10 db lower and viola. decent numbers. keep messing with the enclosure, find the right design, make sure the box is solid and doesnt flex. and test deadener placement. lay a piece down and test. so on and so forth. you can lose SPL from over deadening"
^^^^^ this ^^^^
overdeadening can absorb energy, so simply put, you lose sound (energy) to the absorption materials.
You have to keep in mine that some surfaces like glass, reflect sound, while others, like carpeting absorb energy. the resonant frequency of any object isn't going to change. Not with sound pressure, not with pretty much anything but adding mass, or changing it's makeup in some way. I'm not going to get into how sound damping materials work right now, in depth, but briefly, you have 3 layers. one to bond the material to the surface and add rigidity, a decoupling layer, and a layer to absorb vibrations and add mass to lower the resonant frequency of the object to which the material is bonded.
I don't really trust most box designing software that plots response curves, because it almost always plots the curve anachoically, which is pretty much useless when the box goes into a vehicle cabin.
yes everything has a sympathetic frequency, and it's different for just about everything in the car, but my point was simply that you can measure this, objectively, and use that data when designing an enclosure.
Personally for SPL, I like 6th and 8th order bandpass enclosures, but they sound like cat vomit for anything but single-note burping, when they're built for maximum gain and output.
Hunter -I dont have a TL, I would have to find someone near me to run an accurate sweet. On my mic (dbm2, the ones that were on splmeter.com) I just have to try each freq and remember the results. I was peaking about 45-46hz outlaw style (most events are near me, so thats why I tested outlaw. If a box was flexing, but not coming apart or leaking yet, how much db's would you say on average would you lose? does resin help with spl scores much, or is that just to help seal up the box?
Glass- I've actually been considering grapping a high power 10" or 12" just to try some bandpass builds. I would think a single 15" BP would be a little big for the ranger.
Can anyone give me a little info on "rolling the volume", like tips or even the purpose? someone at a comp to me to stop hitting pause and play because i was gonna hurt my woofer, anyone know whats up with this?
resin helps very little. .2-.4 tenths. putting pvc on your port can help a ton. from .7 to 1.4 db is what i usually see. and as far as your box its dependant. i gained .4 by adding another peice of threaded rod, when i already had 2 in my box.
there are so manhy lil things that can contribute as well. like having you vents closed and settings set to a/c and recirc. air.
if u intend on competing seriously or often it wud be worth paying the 650 bucks for a TL or buy a used one ....what u can do is if u have a friend\s who wud like use of it too : u guys share the cost since in spl the slightest adjustment can give ur score a rise or drop so it wud be VERY convenient to have it at ur disposal ...
there are so manhy lil things that can contribute as well. like having you vents closed and settings set to a/c and recirc. air.
Yep, agree w/ you 100% here hunter. Our van gains 0.1db w/ the glovebox open, lol. Also, .2 or .3 louder w/ the vents on floor and defrost. You just have to test EVERYTHING.
I admire all you spl nuts. It takes so much dedication...
Don't get me wrong.. An sq setup also requires dedication and precision, but when its all said and done i guess you'll have a greater appreciation for music.
well metering is truly the only way to prove that ur sh1t is indeed LOUD
u cant just do a true comparison by ear since with even 2 identical sets the higher tuned box will sound harder hitting than the other which was tuned lower
of course a pure spl set is not very nice sounding on music but it proves how loud it actually is ....