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If box is tuned to 35hz.. and u send a 50hz tone to it... what happens exactly?

 

Silver Member
Username: Tdeaton1021

Near Tampa, Florida USA

Post Number: 602
Registered: Sep-04
okay so what mi getting at is... if you tune a box to lets say some random number... 35hz... and you send it a higher frequency to it... what exactly is happening? and same question for if you send it a lower frequncy?... sending a lower frequency than the boxes tune it bad for it right??? thats what subsonic filters are for?
 

SUBFANATlC
Unregistered guest
MAN you dont know jacksh!t you wannabe go back to work at best buy were you belong with all the other wannabes
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 4077
Registered: May-04
First you have to understand resonance. Resonance is a point in terms of frequency where the resistance provided by the inertia of the moving mass and that of the suspension are equal. That frequency is referred to as the resonant frequency, in the case of a ported box, this is called the tuned frequency, just for those that don't know that. Since resonance is the point where the two suspensions are equal, it's easy to say that it will mean at other frequencies they are not equal. Simply put, when you are above resonance, the port's suspension is dominant, and when you're below resonance the suspension of the sub is dominant, and the resonant frequency is where they become friendly.

If you're above tuning, the resistance of the air mass (port) is high due to the fact that the port isn't quick enough to react to the quick changes in direction. This results in an inactive port and basically a large sealed box. This is gradual, not instantaneous, for a range of frequencies you still get a minor boost in output.

At tuning, the port becomes active since it matches the resistance of the port matches the resistance of the frequency played (inertia). It uses the speaker cone as a fulcrum for it's own output, and sucks energy through the internal air pressure and loads the speaker in the process. This means higher output, lower excursion for the sub since it's controlled heavily by the port's activity, and low distortion.

Below tuning, the port is no longer adding any significant amount of resistance and the suspension of the sub is higher at this point. While the inertia remains the same, as the excursion requirements become greater and greater at any given output level, the influence of the suspension increases, becoming more of a factor than the port. The port is now a hole in a baffle and doesn't load the driver anymore, causing cancellation and sending the subwoofer to very high excursions due to the lack of control.
 

Silver Member
Username: Tdeaton1021

Near Tampa, Florida USA

Post Number: 611
Registered: Sep-04
thanks jonathan.... great explaination
 

unregistered
Unregistered guest
so Jonathan..

Why not tune to the lowsest frequency the sub can handle?

In some cases 20hz or even down to 5hz.. wouldnt you get the little SPL burst over the sealed box that you mentioned if you above tuning.. and have alot less lack of control and high excursion mentioned when below tuning..

would tuning to 20hz or even lower have better SQ (less spl than higher tune.. but more than sealed) from the ported box vs a box tuned to 35hz or higher?
 

Bronze Member
Username: Basshd

Post Number: 74
Registered: May-05
Utilize a low tuned enclosure, when the subs t/s parameters call for it, usually a low fs, say around mid teens to low 20's is considered "low", would call for a low tuned box. Yes a low tuned enclosure would have "less lack of control" than a higher tuned enclosure, but it is entirely frequency dependant and that is based on the type of music and the frequencies in that music that you listen to. In dolby digital home theater there is a lot of content in the low mid teens,(star wars pod race scene, finding nemo glass tapping scene to name a few) but in "popular music" low-mid teen content is relatively rare. Classical music on the other hand can have organ tones down to 12-16hz! Then you have the "bass" cd's that may have content that low. Otherwise most music does not go that low, so no real need to tune at 10hz, for music.
 

Gold Member
Username: Insearchofbass

Post Number: 2672
Registered: Jun-04
yes thanks for the explanation jon i learned something intresting there
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 4082
Registered: May-04
"Why not tune to the lowsest frequency the sub can handle?

In some cases 20hz or even down to 5hz.. wouldnt you get the little SPL burst over the sealed box that you mentioned if you above tuning.. and have alot less lack of control and high excursion mentioned when below tuning.. "

You've just stated the basis of SQ tuning :-). Like E said, music rarely drops that low, really it's rare for music to drop even in the 20s. Movie soundtracks are a different story, though. Anyway, in order to maintain control you need to keep the tuning frequency above the resonant frequency of the sub itself so that you don't lose driver damping within it's range, that is a factor that weighs in with the frequency you choose as most subs don't have an fs below 20hz, many don't even get that low. Your basis is correct, tuning as low as you need to will add SPL at lower frequencies without adding a lot of stress to the driver mechanically. The main reason people don't do this in car audio is that they're looking for added SPL with music, and that means they typically tune in the 30s and 40s. Another limiting factor is that a 20hz tuning frequency requires a very long port, and more space, which is to another thing to be considered in a car.
 

Silver Member
Username: Tdeaton1021

Near Tampa, Florida USA

Post Number: 617
Registered: Sep-04
so thats why avalanches hit sooo low?... they have a Fs of 15.7 i think...
 

Gold Member
Username: Hdubb

Farmington, Nm Usa

Post Number: 1766
Registered: Nov-04
good explantion. again.
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 4088
Registered: May-04
"so thats why avalanches hit sooo low?... they have a Fs of 15.7 i think..."
That has an effect, but in the case of the Avalanche the bigger factor is that it uses a loose suspension to achieve a high efficiency.
 

Gold Member
Username: Hdubb

Farmington, Nm Usa

Post Number: 1768
Registered: Nov-04
i have a question for you jon, it never got answeered in the let it out thread, what is the benifit of tuning your box closer to the res. freq of the car instead of to the sub?
 

Silver Member
Username: Tdeaton1021

Near Tampa, Florida USA

Post Number: 621
Registered: Sep-04
question on top of that question... how do you know what the resfreq of your car is? lol
 

Gold Member
Username: Hdubb

Farmington, Nm Usa

Post Number: 1784
Registered: Nov-04
i think you have to ask the manufac.. one that one im not sure
 

Gold Member
Username: Insearchofbass

Post Number: 2705
Registered: Jun-04
my basic answer hunter is its all about cabin gain
 

Gold Member
Username: Hdubb

Farmington, Nm Usa

Post Number: 1785
Registered: Nov-04
ahh. god i have soooo man more questions about that stuff, but its like why questions so i wont ask.
 

Gold Member
Username: Jonathan_f

GA USA

Post Number: 4090
Registered: May-04
The car cabin resonates at a certain frequency, so you're tuning the enclosure to that so that you'll get even more SPL, since the car helps it out. Like said above, cabin gain. To determine that, you take a speaker with a known frequency response in a large room (preferably flat freq. response) and you place that in the car. The frequency that you get the highest SPL at is where your res. frequency is, usually it's 60-70hz or so, sometimes in the 50s depending on the vehicle.
 

unregistered
Unregistered guest
so jonathan..

you can safely tune down as low as the fs of the sub.. is that what i am getting? (without causing problems) Even though a sub manufacture my suggest higher tuning. So like the eclipse subs that have fs of the low 20's can u actually tune to 22hz and it sound good? or will it be a waste of space to build that long of a port
 

Bronze Member
Username: Basshd

Post Number: 79
Registered: May-05
To find the resonant frequency of your vehicle, measure the frequency response of your subwoofer system, in open air(outside of the car with no reflecting walls within 10 feet of the enclosure), use test tones starting with 35hz as a basis, use a good spl meter and take readings at 35,36,37hz and so on all the way up to 60hz in 1 hz increments. Record your findings(example 90db at 60, 89db at 59hz and so on). Now install(place) the subwoofer system in the vehicle that you want to find the resonant frequency, do the same test, only this time it will be in the vehicle. Take note of the spl readings at 35,36,37hz and so on. Where there is the largest spl gain is where the resonant frequency lies, for example an 8db gain at 48hz over the "outside measurement" but only a 6db gain at 47hz, would mean that the responant frequency of the vehicle COUPLED with that enclosure lies somewhere near 48hz. Now for base line tuning, you'll need to start with an enclosure tune roughly 8-9hz below the resonant frequency that you found earlier., this is a good place to start with. Every vehicle is different, as well as placement, will determine a long way in how you do in competition(placement within 1-2 inches farther back in a suv for example can make a 1-2 db difference). Port area also matters, the more port area the larger the gain, there are ports in competition vehicles that you can literally crawl in! It is said that a ported enclosure peaks at 7-9hz above tuning ie. a 30hz tuned enclosure will peak at 38-39hz, but experimentation is key here. Keep building those boxes until you can achieve the highest spl reading you can. Now this does not work for a daily driver though, as your subwoofer system will be a somewhat "one note wonder" and will not sound good for your "streetbeats", some competitors "plug" the port holes for everyday music in effect making a sealed enclosure, but it is at best a poor solution, if you use the same woofers for comps as your daily driver, then use 2 different enclosures, one for comps and one for your daily driver. There are exceptions to the rule but keep measuring and experimenting and you'll get it(thats part of the fun of competition).
 

Gold Member
Username: Insearchofbass

Post Number: 2734
Registered: Jun-04
or you could do my plan with the adjustable airspace box and adjustable sealed/ported design with different port lengths and save on building box after box and use his method above for testing the sub in and out of the car...i also have a daily user street box with adjustable ports and a sealed option built into my enclosure for the 12's i used to have...its all flush mounted and carpeted no air leaks and looks nice
 

Gold Member
Username: Insearchofbass

Post Number: 2735
Registered: Jun-04
oh and the beauty of the adjustable box is you could use it in the car and out of the car...cant get any better than that testing wise
 

Bronze Member
Username: Eclipse2005

Vicenza, Vicenza Italy

Post Number: 90
Registered: Dec-04
Very interesting, so if i know that my car Fs is around 65Hz, if i understood correctly i should tune my enclosure at 55-57 Hz for the beginnin. is it right?
 

Gold Member
Username: Insearchofbass

Post Number: 2739
Registered: Jun-04
yes
 

Gold Member
Username: Insearchofbass

Post Number: 2740
Registered: Jun-04
but if you were using my adjustable box sealed/ported you could start wherever you wanted with ease
 

Bronze Member
Username: Eclipse2005

Vicenza, Vicenza Italy

Post Number: 97
Registered: Dec-04
Uhm i didnt get it, how your adjustable box work? Ok to change port lenght is easy but what about if u wanna change the box volume?
 

Gold Member
Username: Insearchofbass

Post Number: 2742
Registered: Jun-04
slide the box forward or backward simple as that.. on a track system of course so it could slide back and forth...the box volumes would be calculated and then written on the outside and marked so you knew what volume you were at
 

Gold Member
Username: Insearchofbass

Post Number: 2743
Registered: Jun-04
picture a box inside a box with the first outer box open on the back side and the second box open on the front side but closed on the back side and whallah
 

Bronze Member
Username: Eclipse2005

Vicenza, Vicenza Italy

Post Number: 98
Registered: Dec-04
But u will have a lot of pressure losses, how do you manage that?
 

Gold Member
Username: Insearchofbass

Post Number: 2744
Registered: Jun-04
with a handle on the back side to slide it back
 

Gold Member
Username: Insearchofbass

Post Number: 2745
Registered: Jun-04
build a good seal.. instead of saying i cant because ask yoursely i can IF... oh and this adjustable box would have removable front faces for if you wanted it for various woofer sizes 6.5 8 10 12 15
 

Bronze Member
Username: Eclipse2005

Vicenza, Vicenza Italy

Post Number: 99
Registered: Dec-04
That's a really interesting idea. I think i'll try to build something like that to test it. i got a question, do u know how to find the Fs of ur vehicle?
 

Gold Member
Username: Insearchofbass

Post Number: 2746
Registered: Jun-04
E explained it very nicely up there the only thing ill add is you could buy either a epic 160 or 150 with a built in spl meter and volt meter or you could do what i did before i knew about them and buy a radioshack digital spl meter for 50 bucks but they only go up to 126 db and the epic 160 and 150 do 150 db and 160 db....for right now im fine with my digital handheld meter i dont need to go all out i just want to see if im gaining at low volumes to keep voltage consistant and get the most spl for as little power as possible eventually i will buy an epic 150 or 160 but i did realize one thing just now if you dont have a hand held meter you cant take readings outside the car using E's method described

ps...write down your spl readings outside the car and inside the car and youll have a good chart to look at ....you may learn even more charting the in car results as you vary the box sizes and port tunes in car and chart them and compare you could also write down notes to what the sound charactersitics were like playing music if you were using the box for that reason and you could get into more but ill stop there (hint clamp meter)
 

Silver Member
Username: Eclipse2005

Vicenza, Vicenza Italy

Post Number: 101
Registered: Dec-04
oK THANKS a lot, I'll try to do it, but i guess i gotta get a SPL meter coz i cant keep going to a shop to be measured...Thanks
 

Gold Member
Username: Insearchofbass

Post Number: 2747
Registered: Jun-04
yw did it cost you to get metered and if you plan on buying the epic 160 let me know i got a link to a site cheap well cheaper than the 300 list price
 

Silver Member
Username: Eclipse2005

Vicenza, Vicenza Italy

Post Number: 102
Registered: Dec-04
Ok thanks and yes it cost about 20 euro that is about 23 dollars....so that's a waste of money lol.
 

Gold Member
Username: Insearchofbass

Post Number: 2748
Registered: Jun-04
heres the two sites i have to the epic 160 in case you were intrested

http://www.sonicelectronix.com/viewitem.php?id=3084&affiliate=froogle
http://www.cbrstereo.com//index.asp?PageAction=VIEWPROD&ProdID=646
 

Gold Member
Username: Insearchofbass

Post Number: 2749
Registered: Jun-04
i just had an idea you could buy the epic 160 and skip the handheld radio shack spl meter by just running longer wires so you could run it outside the car too lol Ghetto i know but it would work lol
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