Do these TS values look acceptable?

All elders,

I have just tested my woofer and mid for TS parameters. I have given the figures below. Since I am a first-timer, I want someone to tell me whether the values appear acceptable:


Midrange:

6", cone dia 4.75, cloth surround, paper cone.

Free Air Parameters: Re=7.5; Fs=97; Z=58.58; Qms=7.03;
Qes=1.03; Qts=0.9

Test Box Parameters: Fb= 93; Qmc=7.59; Qec=1.24; Qtc=1.07



Woofer: 8", Cone Diameter 6.25, Re=7.4 (including series resistance of the test leads), foam surround, paper cone

free Air Parameters: Fs=45; Z=29.64; Qms=3.04; Qes=0.94; Qts=0.72

Test Box Parameters: Fb=96; Z=16.68; Qmc=3.34; Qec=2.66; Qtc=1.48.

I have difficulty in getting my Vas Vb right (figures do not look convincing, my maths here is alright). What would be my Vas and Vb for closed and reflex boxes?

Can I Use two of the above woofers for a central subwoofer to operate within 200Hz and employ the mids to take on from there?

Please help.
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
The first set look a bit fishy, the resonance should go up in a closed box, not down.

Make sure your test box is tight, with no air leaks and has no damping material in it.

The second set make sense, and are indicative of a Vas about 3.4 times the test box volume.

These woofers have a Qts to high to be useful for hifi purposes, IMO. To make vented boxes you need a Qts below ~0.45, and sealed should be less than 0.6 or so.

Your woofers will make sound, but you will have peaks and/or dips in the response near rolloff
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
r_s_dhar said:
Midrange:

6", cone dia 4.75, cloth surround, paper cone.

Free Air Parameters: Re=7.5; Fs=97; Z=58.58; Qms=7.03;
Qes=1.03; Qts=0.9

Test Box Parameters: Fb= 93; Qmc=7.59; Qec=1.24; Qtc=1.07


Some confusion here. Are you testing these in a closed box or a vented box?

Fb is generally used to denote the tuning of a vented box.

In a vented box, the resonance of the speaker is whatever the box itself is tuned to.

The resonance of an unenclosed speaker is Fs. (free air resonance)

The resonance of a speaker in a closed box is Fc.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
Want a fast way to find the Q of an unenclosed speaker?

I assume you have a microphone and/or an SPL meter.

Find Fs-you already know how to do that. Just to review, it is the point of highest impedance in the bass range.

Put your microphone/SPL meter as close to the cone of the speaker as you can without touching it. Run your test frequencies all the way down thru the midrange down to a point you know is below Fs.

The formula for the output of a speaker at Fs is
20 logQts.

If the Qts of your speaker is .5, then your output will be 6 dB down from the midrange.

If the Qts of your speaker is .4, then your output will be 8 dB down, approximately.

If the Qts of your speaker is .3, then your output will be 10.5 dB down, approx.

And so forth.

This method can be thrown off slightly because there can be cone resonances resulting in peaks. But if you follow the curve, then you can tell when a peak is occurring and compensate. Follow the curve smoothly and you will be surprisingly accurate.

It's a nice double check.

By the way, you can measure the Q of a speaker in a closed box in the same way. But not a vented box.

I don't think you have to worry about the Q of a vented box. The free air Qts of a speaker that you are putting into a vented box is important. Not the Q of the vented box itself, assuming you build it well.



By the way, are you using a microphone and meter or an SPL meter?