Lots of people are trying to make headphones......

[Mel Parker]

that sound great for the Excal and Sovereign but when your looking at an audio output like this there is not much to work with. This is exactly why the audio sounds as bad as it does, there is not a sine wave any where to be had.
This is the picture of the threshold barely audible in the phones with no target.

 

[Mel Parker]

Not much to work with guys.

 

[Mel Parker]

n/t

 

[Mel Parker]

n/t

 

[Tin Fin]

Well presented Mel - and on the mark; how to do?
If it's outside the machine, it would need to be waterproof.
It could be a passive converter, but if it is an active converter, then it would require batteries of its own.

 

[otlew]

Well you can certainly see why the threshold sound is nothing more than an irritating buzz, especially at a higher setting.

You don't mention which machine's audio this O-Scope is displaying, Sov or Xcal. Or does it matter?

Also is this the PP or Disc mode? Or does it matter?

Calling all audio engineers to the emergency room.

 

[Critterhunter]

I remember reading an old post from a guy a while back, where he used some kind of audio frequency analyzer to quantify the various tone respones on the Sovereign. If what he said was true, he found that there were far more types of tones than the human ear could hear? If that's the case, based on say conductivity, then might be a method to a madness of using a little dongle over the speaker to display certain info. On the other hand, it's probably already there- in the info the high resolution VDI provides that can't even be told the difference in conductivity for stuff very close, to my ears anyway.

I've searched and searched for that old post, with various key imaginative key words, because I wanted to refresh my memory on it, but for the life of me I can't seem to find it. If anybody does, please post a link.

 

[tvr]

Mel,
What are the horizontal units on the o-scope setting? I notice the distance between the threshold spikes (period) and the period between the multiple spikes on the quarter are about the same relative grids. Does the period get longer for iron?

I'm wondering if the circuit design uses the head phone impedance as a part of a filter circuit.

Is the scope hooked right to one of the speaker terminals? If it is, it sure would be nice to have a two channel scope with a channel hooked to each side of the speaker, invert one side then sum the two channels and see what it looks like. Sold my scope years ago when money got tight; never replaced it, and sometimes miss it terribly!
tvr

 

[Au79finger]

Those electronically inclined may appreciate the link below.I was seeking advise on the Geotech forum and received this link.It is over my head but I was able to learn what I needed to know about matching speakers/headphones to a particular detector.

Hey Mel,do you have the equipment and knowledge to be able to test the Excalibur's driver output to determine the actual impedance and voltage?Or do you know it?




http://www.arizonaoutback.com/azoroot/shop/custom.aspx?recid=75

 

[Tin Fin]

AU79,

That is one heck of a write up and explains very well what to be aware of; even if you don't get the math, it's well done.

And this is part of what I like about this forum.

 

[Mel Parker]

This was just a quick look at the output to the phones so that I could see what kind of signal I was dealing with, I only tried one target the quarter and nothing else. As far as the the sweep rate and volts per division it was just adjusted to fill the screen for the picture. I might get a little more scientific later on.
Doing this by yourself, holding the camera and taking the picture with one hand while moving the target with the other requires lots of co-ordination more than I have. Like patting your head and rubbing your stomach at the same time.

 

[otlew]

Since the Excalibur specifications list the headphone impedance at 8 ohms (piezo transducers) then based on the very informative article, saying that impedance matching gives the greatest volume is in reference to dynamic speakers.

Are the Sovereign and Excalibur the same devices, just in different packaging? I would guess, almost.

Comparing the two for the headphone specs, Sovereign manual states:

32 to 100 ohm max!

Excalibur manual states:

8 ohms, with no provision for any change in the headphone impedance for obvious reasons.

Quoting from the fine article by Mr. Gohlson

In closing, I suspect that you will notice the biggest difference in headphone loudness (because of the difference in impedance and sensitivity) with your threshold set to some nominal value (same threshold position for both headphones) and no target under your coil (i.e., background and ambient noise only). In my opinion, you should choose a set of headphones that are the closest in impedance to the detector output impedance with the highest sensitivity specification as possible.

Of course this article is about dynamic speakers, which have resitive and inductive components in the impedance if I am not mistaken, while the Piezo is largely a capacitive impedance.

So in the case of the Excalibur wouldn't we expect that the amplifier would be different than that of the Sovereign. Or has Minelab just made it work as best they could considering the requirement when diving for Piezo transducers.

This is the reason I asked Mel about what he had tested, to be certain the O-scope is reading the output of the Excalibur (which I assume to be the case).

Here is very interesting pdf file on Piezo tweeters... Piezo Tweeters.

 

[Mel Parker]

n/t

 

[otlew]

n/t

 

[OldBeechnut]

Thanks Mel good review of the excaliburs audio........

Are the Sovereign and Excalibur the same devices, just in different packaging? I would guess, almost

From this video I have found the two to be different, DOC's amp with the sovereign gives a clipped signal..like there is a blast limiter...the excalibur does not have this.
http://www.youtube.com/watch?v=TAFW8qQpgjo

where he used some kind of audio frequency analyzer to quantify the various tone respones

Critter, Ran several test on Skullies speakers, Very happy with them on the Excalibur but if Mel can pull out more of his magic...I'll take it....

Skullies choices are the Audiosears 2463's , and the Kobitones 500's...All the speakeers that are used in the higher end headsets....

And the Piezo tubes 50mm, good for the PP hunter...with a SPL of over 117 they are hard to match. Good the excalibur has a volume control

 

[otlew]

What are the chances that an isolation transformer could clean up at least some of the signal coming out of the Excalibur? I have read they are used for EMI and RFI in some applications, not sure this is one that it would provide any benefit.