# i don't really understand tuning frequency...

Discussion in 'Amps and Cabs [BG]' started by lpbassics, Feb 24, 2002.

1. ### lpbassicsGuest

Jan 26, 2002
WI
help me out now.

I need a bassic explanation. I just don't really get what role it plays and how to change it if it's wrong, or what is considered wrong, or if its relevant at all...

thx smart people!

-lp

2. ### notduane

Nov 24, 2000
Location
B=30.87Hz / E=41.20Hz / A=55.00Hz / D=73.42Hz / G=98.00Hz

"Hz" is short for Hertz...as in German physicist Heinrich Rudolf Hertz.

1 Hertz = 1 cycle per second.

To get the "next" note's frequency (e.g., C to C#) in an equal
temperament system (12* notes/octave), multiply (going UP the
scale) or divide (going DOWN the scale) by the *12th root of 2...

1.059463094359...etc.

A is an easy starting point to remember: A0=27.50Hz, A1=55.00Hz,
A2=110.00Hz...A4=440.00Hz, etc.

any o' this hoo-ha help

3. ### lpbassicsGuest

Jan 26, 2002
WI
at the tuning frequency's role in bass cabinets.

but i didn't know thats where A 440 came from, thx!

-lp

4. ### notduane

Nov 24, 2000
Location
d'ohh! Shoulda' checked what forum this was.

bgavin or Gabu can help ya' out.

5. ### tufnuts

Tuning Freq. is a way to say Resonant Freq. It's the Freq. that the system (cab and speakers) is resonant at. This is the lowest frequency you want the cabinet to acurately reproduce. It can be changed after construction by changing cab port diameter, and length. If you are unable to get where you want then, you either build another cab to suit the driver. Or you replace the speaker with one that "fits" (acoustically) with the profile you want the cab to fill.

But bgavin's the man on this one. I still need to finish tuning my cabs...doh!

6. ### lpbassicsGuest

Jan 26, 2002
WI
porting

playin around with winisd and i don't really get what its telling me in the vents section.

number and shape i understand

vent diameter would be like 2" x 5" would be a rectangle 2" x 5"

now vent length... is that the distance that the vent goes into your cab?

vent mach : i have no idea what this means, it usually gives me a "Qes/Pe!" or gives me a low number (ie. 0.20)

also, how can u use porting to change the tuning frequency?

thank you thank you thank you!

-lp

7. ### bgavin

May 3, 2001
Orangevale, CA 95662
You are trying to understand brain surgery as read from the back side of a cereal box. There isn't a short cut to knowledge other than getting it the hard way. Vance Dickason's book "The Loudspeaker Design Cookbook" is a good place to get all the basics.

vent diameter would be like 2" x 5" would be a rectangle 2" x 5"
No. Diameter and square area are different.

now vent length... is that the distance that the vent goes into your cab?
Yes. Total length of the vent, open end to open end.

vent mach : i have no idea what this means, it usually gives me a "Qes/Pe!" or gives me a low number (ie. 0.20)
The speed of the air in the vent, represented as a percentage of MACH 1. You can get away with as much as 10% (0.10) almost all the time. The ideal is 4.5% (0.045). Vent velocity is maximum at the tuning frequency, and under full power (maximum cone excursion). As you move up the scale and/or reduce the power, the vent velocity drops dramatically.

The Qes/Pe warning is telling you the vent is too small for this particular driver at the power setting current in Pe. You can reduce the Pe by changing the power rating of the speaker. This is the same is "turning it down" for WinISD.

how can u use porting to change the tuning frequency?
Longer vents lower the tuning frequency. Shorter raises it. If the length gets too extreme in either direction, then the area of the vent must change. A larger area raises the tuning frequency and smaller area lowers it. The smaller area increases vent velocity, and larger area reduces vent velocity.