Since it would seem that most people here and quite a few installers don't have an idea on tuning a box for a subwoofer I thought I'd show my math work on the subwoofers I want to put into my zenclosure $99 ebay box.

I measured the box's inside dimensions as:

21" wide
9.25" high
4.75" deep at the top
8.9" deep at the bottom

Running the math I came up with 0.75 cu.ft.

My box has two 10" holes which will mount a speaker about 7 5/8" deep a bit less due to the slope.

I looked up the figures for some of the more popular woofers and then ran the calculations for the sound flavor in my box. Depending on what sound you're looking for you should choose a different Qts, a higher one will give a more boomy sound while one closer to 0.707 will give you a more accurate one.

The two speakers I have highlighted give me pleasing Qts numbers - even better than ones costing many times more. Also note the efficiency number - to get 3 dB more sound I could pick the Infinity speakers or run twice the amount of amplifier power into the Rockford Fosgates. I'll probably go with the 10VQ with the high Q core insert and then sample the low Q core for a bit lower bass.

Boxes and subwoofers interact with each other and changing the box or the speaker will give greatly different sounds. Using the Qts figures will give you a better chance in getting it right.



The lines on the graph show frequency response on the X-axis (side-to-side for you drop outs) and audio amplitude on the Y-axis (up-and-down). The light gray line shows the Qtc response of a 1.5 - about 4 dB too much bass at 120 hertz - double too much. Also notice how quickly the line drops off never even getting below 60 hertz at all. This is going to sound poor.

In contrast look at the 0.9 Qtc with a slight less than one dB mound centered around 80 Hz and a gentle slope that is 3 dB down by about 43 hertz. This is a good honest sounding speaker/box combination that will give you gut wrenching low bass.

 

I purchased polyfill at Walmart and glued it to the inside walls of my understrut (ebay) box. The result was amazing. Both my 10's hit harder and lower.

I used the try-it-and-see method.

 

hey i have to jl 10in w6s wit the ebay under the strut box, do u think adding the plyfill from wallmart will make any difference in sq ?

 

Polyfill will make the box feel bigger to an extent. Most manufactures recommend 1" of fill on the 5 walls of the box without the speaker. Make sure that you allow your woofer to breath if it has a vented pole - a hole in the back of the magnet structure and do not let the poly rest against the speaker's moving parts including the fine wires that run from the terminals into the speaker's coil.

 

Paul, did you take into account the displacement of each pair of subs in your calcualtions? I'm alittle surprised that the response curves are as flat as they are considering the small amount of airspace available.

I bought Mike's box for a single 10 some time ago and have really been pleased with it. Using an Adire Audio Koda 10 and it still seems pretty punchy.

Anyway, thanks for the graphs and research.

 

It's impossible to measure the basket, magnet, and cone's displacement without sinking them into some water ... I wouldn't even do that to speakers sent to me for free testing.

I did some WASG (wide @ss scientific guessing) and figured that the displacement with the woofers would drop to around 0.60 which would cause the woofer's peaks to rise a bit more. That's why I'm looking for the lowest possible Qtc as calculated.

Most of the speakers I tried have a high Qts designed for small box enclosures. Notice how the JL Audio 10W6v2 which is no slacker of a speaker gave too high (IMHO) Qts numbers. In a bigger box those guys are going to be much more happy.

 

Your WASG was really close. With the 10VQ, box volume is dropped to .606 ft3.

What program are you using to generate response curves?

 

So paul, doing those dimensions with just 1 10" woofer should work? i always though the more woofers the bigger the box? but im sure im waaay off on that assumption. LOL

 

My numbers are with TWO woofers. You can not use these same numbers for a one woofer set up. With two woofers they work together - the two motors of the woofers are pushing or pulling at the same time. They will interact with each other.


Here's the java calculator that I've been running backwards. It's designed to enter in the three physical speaker parameters (Qts, Vas, and Fs) and then the desired Qtc which will then tell you how big to make the box (Vb). Since we know what the Vb is I was just working the Qtc up and down until I matched the volume of 0.75.


http://www.carstereo.com/help/Articles.cfm?id=26

 

Yep Paul, the box volume I referenced was with 2 of the woofers installed.

Not sure if you are familiar with this program, but you might find it fun to play around with.

http://www.linearteam.dk/default.aspx?pageid=winisd

 

Thanks I heard that program is good.

 

I'm doing the ebay under strut bar 10" w/ 1 alpine type r.....do you think I need the poly fill? The box is sealed.

 

Forgot to add - these plots are for the passive box with a "perfect" speaker. Any bumps or lumps in response caused by the speaker's weaknesses will be put on top of this nice smooth plot. I can't correct the manufacture's issues with response but can put it in the box which will sound as "correct" as possible.

 

I looked for the Alpine Type R 10" speaker's parameters and couldn't find them.

If you have the Qts, Vas, and Fs that would make life easier.

 

Damn paul, you are the box genius around here. thanx for all the help man!

 

I'm not sure what the Qts, Vas, and Fs are? What do those stand for?

 

Thanks, I do what I can.

 

A.N. Thiele and Richard H. Small defined most of the relationships and terms we now use to describe what happens in a speaker and between a speaker and a particular enclosure's type and size. Their work has become the standard for speaker measurement criteria in which all manufactures now use which allow you to do a direct characteristics comparison of different speakers.

Qts - The opposing forces from the mechanical and electrical suspensions acting against each other is the total Q of a speaker in free air at resonance (Fs).

Vas - Represents the volume of air that when compressed to one cubic feoot exerts the same force as the compliance of the suspension in a particular speaker. The compliance or stiffness of the driver suspension is determined by the surround and the spider. It is simply a measurement of its stiffness.

Fs - This is the free-air resonant of a speaker; it's the frequency that the speaker wants to vibrate at. This is a result of the weight of the moving parts (cone, etc) in balance with the stiffness of the speaker's suspension. At a speaker's Fs the speaker will over emphasize (make louder) that frequency and cause crossover points to change due to impedance variances. For accurate sound reproduction these frequency peaks must be controlled (kept flat).

Qtc - Put a speaker into an enclosure and you then change how that speaker will act due to the resistance of the air pressure inside of the enclosure. When the speaker cone moves in or out the air pressure within the enclosure will put a resistance on its movements. The size and type of enclosure you build will depends upon the Qtc value you desire.

From this guy's web site: http://www.members.shaw.ca/loudspeak...iel-small.html which explains all the Thiel-Small parameters.

 

noob question here, but are all of these figures with the box being sealed? anyone recommend porting the box at all?

 

one more ?- what would the differences be between having the chambers seperated or not?