Hornresp: driver excursion? - diyAudio
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Old 10th December 2005, 08:00 PM   #1
e-side is offline e-side  Netherlands
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Default Hornresp: driver excursion?

Hello,

I'm wondering if the calculated excursion in Hornresp is reliable or not. To me it seems that the given excursion in hornresp is fairly high, the driver's xmax is always too low in my case. Does anybody have an idea?

best regards

Erwin
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Old 11th December 2005, 02:48 AM   #2
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Default Re: Hornresp: driver excursion?

Quote:
Originally posted by e-side
Hello,

I'm wondering if the calculated excursion in Hornresp is reliable or not. To me it seems that the given excursion in hornresp is fairly high, the driver's xmax is always too low in my case. Does anybody have an idea?

best regards

Erwin
All the horns I've built with the help of McBean's program have performed exceeding well. Of course I haven't built any where I'd expect more than 125-130 db out of them.

Which driver? Can you post a screen shot of your input perimeters?
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Old 11th December 2005, 08:58 AM   #3
e-side is offline e-side  Netherlands
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In this screenshot I used a driver with high qes (0.98) and high qts (0.74), so it's not an optimal driver for horn design, but it's going to be used for a horn with a very narrow frequency range, 40-100 hz.

According to hornresp, the driver will have an excursion of 7 mm at 50 W of power. The driver's xmax is about 6 mm, so it's maximum excursion will be exceeded already.

I can't imagine that the excursion will be as high as this when the driver is mounted in a sealed box (and this is the case in a front loaded horn), or am I wrong here?

BTW i also simulated horns with drivers with low qes (0.19) and qts (0.2), but the predicted excursion here's also too high, even at low power levels.

regards

Erwin
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Old 11th December 2005, 02:16 PM   #4
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Yes, it is usually pretty reliable. As a check, go simulate this as a bandpass box with a port the area of your throat and the length of the horn. You'll see a peak in xmax at ~37hz with ~7mm of excursion at 50 watts.

This is typical (to see a peak in excursion at resonance). This peak is below the cutoff frequency of the horn, so it is really outside the range you should be operating the horn in. Therefore it should not be a problem if you filter correctly. If you want more protection for the driver without a filter, make the rear chamber smaller, say 20L. This will move resonance higher, change the low end response, and reduce excursion below resonance. It is also typical to see thish large excursion at low power levels, at least in some cases. You've made the system more efficient - it requires less input to move the cone, especially at low frequencies where the driver is not really loaded much by the horn anymore.

Further, xmax is usually only an indication of the overhang or underhang of the coil. As soon as the coil moves from rest, there will be distortion. It is usually accepted that the xmax number gives an approximation of when the distortion will start increasing to objectionable levels. But typically a speaker can actually move farther than this. It's typically given as the mechanical xmax or the mechanical limit or something like that. So at xmax, your speaker should not be damaged - it just probably won't sound as clean. If you approach the mechanical limit, you will likely damage the speaker.
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Old 11th December 2005, 02:20 PM   #5
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This driver's motor is too weak - not a good horn driver IME although you will have 120+ db capabilites at 50 watts it will be at it's mechanical edge. Take the back chamber down to 18 liters and it will load better with less cone movement..

Using this weak driver like this in a horn down to 40 cycles isn't the best way to get good bass.
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Old 11th December 2005, 06:48 PM   #6
e-side is offline e-side  Netherlands
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Quote:
Originally posted by Magnetar
Using this weak driver like this in a horn down to 40 cycles isn't the best way to get good bass.
You're right. It surely isn't the most optimal driver for horn loading, although I already made a horn with a high qes driver, and it sounds very nice.

Anyway, it's clear for me now. Thank you both for the replies.

regards

Erwin
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