Is this right?

[Blackedout]

But I could be wrong on this one... My belief is that ported boxes should be tuned depending on the types of music you listen to, as well as the Frequency response of the woofer. I generally understand the rule of thumb to be 30-33 Hertz for rap, 34-37 Hertz for daily listening of all types of music, and 39+ for rock

When I suggested that someone tune their box 35-37 Hertz because they listen to all types of music, I got this little novel back.

Tuning lower generally provides you with a flatter, more musical response curve. Therefore, tuning low (28-33 hz), is not just for rap music... in fact, the majority of material in rap isn't that low to begin with. In car audio, low tuning like that is normally reserved for classical music and such in SQ applications.

When determining what port tuning frequency you want to go with, you need to take into account things like the resonant frequency (Fs) of the driver, the size of the enclosure you plan on using, the environment in which the enclosure will be placed into, port area and velocity, and the amount of space you have to use. I'll briefly outline these ideas below:

Fs:

While it is certainly possible to tune below the driver's Fs, doing so has the potential to severely limit power handling. For high power applications, tuning 3-5 hz above the driver's Fs is common. For a home theatre setup or something used primarily at low volumes, very low port tuning (as low as 10hz or even lower) is not uncommon, even if the driver's Fs is up around 30hz. However, for a high output system, doing something like this can quickly lead to catastrophic failure.

Enclosure Size:

With regard to enclosure size, a smaller enclosure will exhibit more impedance rise than a larger one, and subsequently, the port tuning will peak at a higher frequency than it would in a larger enclosure. For example - A single 12" woofer in a 1 cubic ft. enclosure, with the port tuned at 30hz may display an actual port tuning frequency up around 38 hz at high volumes. If you put the same 12" woofer in a 4 cubic foot enclosure, once again tuned to 30hz, this time the port may peak at around 31 hz. While mathematically equivalent, in a real world application, they function much differently from one another.

Environment:

Where the enclosure is located plays a big role in how it operates. In the small confines of a vehicle, any frequency with a theoretical quarter wavelength longer than the distance between the face of the speaker and the farthest solid object (generally the windshield), will display significant transfer function (cabin gain). Lower frequencies have longer theoretical wavelengths, meaning that lower frequencies will naturally augment themselves inside a vehicle cabin... this takes away some of the need for very low tuning in an automobile. Also, the pressure created inside the vehicle acts on the port to provide some reinforcement, allowing the enclosure to extend a few hz below its actual tuning frequency. Finally, placement of the ports in the vehicle can effect tuning in much the same way. If the ports (or woofer, to a lesser degree) are firing directly into a solid object (such as the trunk lid or wheelwell), there is significant port reinforcement, again allowing the port to retain control of the woofer at frequencies below its mathematical tuning.

Port Area and Velocity:

Much of the physics of sound boils down to converting velocity to pressure, and vice versa. Therefore, in high output systems you need to take into account the effects of port tuning frequency on velocity. At lower tuning frequencies, port velocity is naturally lower, so you can get away with using less port area. However, as the tuning frequency rises, port velocity increases. To offset this rise is port velocity, you need to use increased port area (which should also result in increased output), but its not always practical, and can lead to "peaky" behavior. Mathematical port tuning frequency comes from applying the ratio of the volume of air inside the enclosure to the volume of air inside the port, in relation to the port's length. Meaning that in a small enclosure, adding port area will cause the port length required to maintain a low port tuning frequency to increase dramatically, which is often not feasible. What all this ultimately comes down to is that for a high output system, attempting to tune the port at higher frequencies with a small amount of port area will result in port velocity that is so high that the port no longer acts as it should. In this scenario, instead of having an additional air mass acting as a "surface membrane" to reinforce sound (which is what a port should do), you wind up with a sealed enclosure with a hole it it (which is definitely not what you are going for). Another big downside to high port velocity is that it causes port noise, which is also not something you want. To simplify things, you have the "old stand by" rule. For the average daily use auto enclosure, you should get decent results by tuning the port roughly 3-5 Hz above the Fs of the driver, and using approx. 10-15 square inches of port area per net cubic ft. of enclosure volume.

Space:

Taking into account the above information, you should be able to see that if you plan on using low port tuning with a lot of port area effectively, you are going to need to start with a relatively large enclosure. Often times, you need to compromise your tuning frequency or port area plans somewhat in order for the enclosure to fit in the allotted space. As always.... everything's a compromise.

Thats probably a lot to take in, but my point is that you can't simply say, "This tuning is for rap, that tuning is for jazz, and this other tuning is for metal". If you are trying to obtain a certain effect, different types of enclosures characteristically display certain traits, which you can bolster or reduce by adjusting tuning, but there's a lot more to it than one would initially think.

Hans

There are some really good points in his novel, but I'm just wondering who is mixed up, for the purpose of learning, not for argument. I was thinking ported boxes aren't really great for frequency response anyway, they peak at one frequency and slowly get less loud the further away from that frequency they are. Other boxes, such as 4th order bandpass, bandpass, and T-lines have a broader Frequency response, right? They are more musical boxes because of this...... I just wanna know if I'm off base, because I'm kinda confused now.

Edited November 4, 2009 by JDirty96

[Decaf]

umm that post was kinda not necessary

this is why its good to have someone who knows what they are doing to design a box for u

u do have to take into cosideration the sub, duh

and ofcourse u have to take into consideration ur car, duh

so it was kinda useless info to me

ported boxes are great when designed around the sub being used

4th orders can be great, but tricky in a car when u are tryin to get 20hz-80hz... the cabin itself will alter ur perspective freq response, i see them best for firing thru rear decks when trunks are sealed and spl applications... i know u can have a great 4th order but its not easy

6th orders are even more finicky, but can yeild some amazing spl numbers... again tho best used for a smaller freq range in cars

the fact that the quoted user said most rap isnt 28-30hz... he obviously doesnt listen to modern rap... where mainstream artists like jeezy has songs peaking at 31hz, 33hz, 34hz

i could go on, but to conclude... u cant just throw a sub in a box and expect greatness... it takes alot more

[Blackedout]

Thanks Decaf. I guess the real question that I'm trying to ask, but I feel like I kinda know the answer, is if I am off base? ~40-43 for rock, 35-37 for daily, and low thirties for modern rap. Dude is trying to say that tuning your box to the low thirties is for all around sound quality, 'with a flatter response' I can see where he's thinking that on one hand, because tuning that low will make your box peak a little above that depending on the car your putting it in........ Probably closer to the 35-40 hertz range. On the other hand, a box that peaks in the low 30s, number wise on a term lab would probably sound like shit on daily music, right?

Also, if you're shooting for a flat frequency response, a ported box is the wrong enclosure, right? They are really peaky from one tone to the next.

[Boon]

Honestly, 6hz difference is going to make 3 tenths of fuck all difference in a daily driver.

My last SPL box was tuned around 55hz and still did close to 150's at 42hz. Didn't go much lower, admittedly

EDIT: Ported boxes can play very flat. If you tune BELOW the natural roll-off of the sub you can get a 'bass shelf' or Extended Bass Response - so it plays flat like a really good sealed box but will drop that extra octave.

Pulling out 3 numbers for rock/rap/daily is way, way too generic.

Edited November 4, 2009 by Boon

[Blackedout]

Thats kinda what I was lookin for.

[thumpintundra]

is it good to get that bass shelf you're talkin about?

[arnold1992]

is it good to get that bass shelf you're talkin about?

i think he means bass shelf as in the frequencies are flat enough it can play a broad range with smiliar output.

[thumpintundra]

so building a box that will play flatter frenquencies is better for a daily set up but will still bump? sorry i'm just now getting into the whole box building thing lol