calculating cone excursion?

[Jim85IROC]

I'm tinkering with ideas for a subwoofer to compliment my tangband computer speakers. Parts Express has a JBL/Vifa buyout 4.5" woofer for $7 that I'm looking at using in a ported isobarac enclosure.

My original plan was to use the 5.25" Dayton drivers in an isobarac, but I like how this Vifa models, and it costs half as much.

I realize that I'm not going to get room shaking bass out of these tiny drivers, but I'm not trying to. It's just a computer system after all. I modeled this driver in WinISD, and with a 10 watt input, it shows an output SPL of approximately 92dB in the frequency band that I'll be using it. Unfortunately, WinISD (at least my version) doesn't show cone excursion, so I can't tell if this output is actually possible.

Here's a WinISD plot with a 10 watt input. I've got the crosshairs at the -3dB point relative to the output below 100hz:


Is there a simple way to calculate cone excursion given t/s and enclosure parameters at a specific frequency?

[JMB]

Unibox will estimate this if you have enough of the parameters to enter. You can find it at www.danbbs.dk/~ko/ubdwnld.htm

Jay

[kelticwizard]

Below is the Parts Express 299-495, made by Vifa. On sale for $6. I guess that is the one you mean.

It is in an 11 liter ported enclosure, ported at 45 Hz. It is run at 6.5 volts, (10 watts for a 4 ohm speaker). From the curve you posted, I assumed that is pretty close to what you are using.

Parts Express said the outside diameter of the basket was 5", so I assumed the cone was 4" exactly. I think I am probably pretty close.

The green line is the output, the purple line is the cone excursion. As you can see, the Vifa's cone excursion of +/- 3.5mm can indeed put out the bass you are looking for, at least down to 40 Hz or so.

By the way, if anyone else wants to try this, the BL is probably 6.38, according to Bullock and White's BoxModel. I estimated the Sd as .00785 sq m, or 78.5 sq cm.

I used BoxModel to find the Bl factor, then used Subwoofer Simulator, a program written by our won F4ier, to illustrate the cone excursion.
http://www.geocities.com/f4ier/speaker.htm

[sreten]

Transfer parameters to winISD Pro (alpha) which is also
freeware and it will show excursion and power limits.

sreten.

[sreten]

97dB passband ? not a chance in hell, seems pairs not isobaric.

sreten.

[kelticwizard]

I didn't do isobaric, just a single one to get the idea.

This is for 10 watts input, (actually 10.5 watts at 6.5 volts input).

Instead of estimating the vifa "4.5 in" cone area, I went to Vifa's website and looked the Sd of the other 4 1/2 inchers.

It was 58 sq cm, not 78.5 sq cm. Speaker must have an oversized rim. Oops.

So that changes the Sd to 58, and the Bl to 4.71 Tm, (as calculated by BoxModel).

Here is the revised simulation-it's pretty close to the last one.

Here are the other Thiele-small parameters as stated on the Parts Express website:

PE 299-495

Power handling: 35 watts RMS/70 watts max *
VCdia: 1" *
L1: .5 mH *
Znom: 4 ohms *
Re: 2.95 ohms *
Frequency range: 65-5,000 Hz *
Fs: 65 Hz *
SPL: 88dB 2.83V/1m *
Vas: .16 cu. ft. *
Qms: 1.44 *
Qes: .34 *
Qts: .27 *
Xmax: 3.5 mm *
Dimensions: Overall Diameter: 5",
Cutout Diameter: 4",
Mounting Depth: 2-3/8".

[sreten]

Where are you getting the utterly ridiculous 97dB sensitivity from ?

sreten.

[kelticwizard]

The output curve is for 6.5 volts into 4 ohms, or 10.5 watts.

So it would be 87 dB for one watt. Which is actually a bit high, since it really is an 85 dB/watt speaker. But Jim just seems to be interested if the 4.5 woofer can put out the goods around 40 Hz, and the answer seems to be "yes". (Okay, maybe just a little into the nonlinear range).

[Eva]

I don't recommend isobaric layout. Two drivers placed toghether in smaller than ideal boxes [not isobaric] would still have about the same bass eficiency and 6dB higher SPL capability compared to isobaric.

Resulting efficiency in midbass and midrange should be also 3dB higher and less cone excursion for the same SPL should be expected due to mutual loading

[Jim85IROC]

Originally posted by Eva
I don't recommend isobaric layout. Two drivers placed toghether in smaller than ideal boxes [not isobaric] would still have about the same bass eficiency and 6dB higher SPL capability compared to isobaric.

Resulting efficiency in midbass and midrange should be also 3dB higher and less cone excursion for the same SPL should be expected due to mutual loading

Assuming that this isobarac enclosure is 1/2 the size that a single driver would require, that means that running 2 subs in that enclosure in a conventional manner would make it 1/4 the necessary size. How am I going to get any kind of bass from it without massive equalization?