Q that is too high and other musings...

[jaberwocky6669]

Hello

I have a couple of things that I have been thinking about. I hope that someone will discuss them with me. I am designing my first loudspeaker project for a non-discriminating listener (12 year young child). I used the sealed-box method to determine Vas. Is it absolutely necessary to make the resonant frequency shift by 25%? Also, can a speaker have a Qts that is so high that it would be impossible to correct the peak? Are contour networks used to correct the peak caused by high Q?

(This is the 2nd time that I have posted this message. I waited all night. I hope that it doesn't double post)

[sreten]

Hi,

No you do not have to shift by 25%, but lower is less accurate.
Yes a drivers Qts if too high, is too high, a box only makes it higher.
No, the cost of the components to do this at bass frequencies is prohibitive.

/sreten.

[jaberwocky6669]

Are you familiar with this method of determining a speaker's resonance frequency?

http://hyperphysics.phy-astr.gsu.edu...peakerres.html

I am thinking that I could make this completely pc-based.

[Keruskerfuerst]

Bassunits with Qt>0,5 are usually used for transmissionline cabinets.
Qt can be corrected by an active network.

[jaberwocky6669]

Originally posted by Keruskerfuerst
Bassunits with Qt>0,5 are usually used for transmissionline cabinets.
Qt can be corrected by an active network.

I forgot to include my estimated Qts value! According to my measurements (which may be... off) the Qts for my speaker is 1.459!

Active network, is that an active crossover?

[richie00boy]

That method is fundamentally lacking. It does not tell you to keep the voltage seen by the speaker under 1V, to ensure correct small-signal measurements are taken.

As has been mentioned, if Qts is really bad there are ways it can be compensated for electronically, but this does impinge on the simplicity of the design and always requires an active module to accompany the speaker.

[jaberwocky6669]

Well, I think that I should certainly re-measure the t/s params again to make sure I did everything correctly. I realized that when I determined Fs that the speaker was very close to other objects (less than half a foot!) So, off I go. Thanks everyone for all of your helpful replies. And if anyone has anything else that they would like to add then they are more than welcome!

[jaberwocky6669]

I finally get it! Now I understand why the procedure described at: http://www.epanorama.net/documents/a...arameters.html states that you have to adjust the frequency until you see a MAXIMUM voltage on your multimeter. If the multimeter's voltage reading paralells the ohms then,.... well can't explain it but I understand now. DO you know how long I have been going back and forth between this method or that method? About a year (or more)! And I have the people at this forum to thank too. Thank you!

[richie00boy]

If you want a better explanation what is going on have a look on my website

[jaberwocky6669]

I am checking it out now. I do have one question though. In the PDF about measuring t/s params under figure 1 there is a sentence that states: This can be achieved in a basic fashion by simply 'swamping'... Can you clarify if you did mean swamping or swapping. And if you did mean swamping then what does that describe?