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Old 06-25-2008, 08:10 PM
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Default Confused about Threshold vs Volume?

Many newbies go out and buy a detector that has an adjustable, audible threshold and are confused by its function or proper use. The situation gets even more confusing if the detector also has a volume control. Oh wait, you also bought a nice set of earphones and they also have a volume control. What to do, what to do.

Ok, first, lets look at what is this so called threshold and what purpose an adjustable threshold serves. Then we can tackle what to do with the volume control. Setting both properly maximizes your ability to get as much depth as you can from your detector.

Not all detectors sold now a days have an adjustable threshold that you can hear. These latter machines are termed "silent search" detectors. Basically, they are quiet running until you sweep over a target and then they beep at you.

You can think of the threshold as a type of squelch control as found on a CB or short wave radio. Without a squelch control circuit on a radio, the speaker would be putting out a constant stream of hizzing noise when you are not tuned in to a station. This can be annoying. By dialing up on the squelch control, we are basically telling the radio that we don't want to hear a signal until it reaches a certain strength. The hizzing noise coming from the speakers is suppressed because it is low energy background noise and the radio is quiet until you tune in an actual signal. By the way, on some detectors the manufacturer calls the knob that adjusts the threshold a "tuning" knob. Now you know why.

If you dial in even more squelch, you'll start to miss some of the weaker signals from far away stations.

This is exactly how the threshold control works in a metal detector!

With a silent search machine, the "squelch" control is factory set to suppress the small signals and allow signals with a strength above the threshold setting to get through and make a "beep". If you bought a detector with an adjustable threshold (good for you!), you want to set it such that you can barely hear the threshold sound on your earphones. The sound is hard to describe, but it sounds like bees buzzing your ears. By having the threshold at this setting, right on the edge, you are guaranteeing that very weak signals (like from deep targets) will be able to get through the threshold control. This gives a machine with adjustable threshold a slight depth edge over a silent search machine, everything else being equal. This is because a very weak signal may not get through the "squelch" setting of the silent search machine.

You don't want to make the threshold any louder than what you can barely hear. If the threshold hum gets too loud, you'll miss the real small signals again. This time because they are drowned by the louder threshold buzz.

If like some other folks you can't stand that constant low level buzzing sound of the threshold, you can always back it down a hair until it is not audible anymore. Essentially, you'll be running the detector as if it was a silent mode machine. But you pay a price for doing so. First, you'll lose some of that depth advantage you had over a silent search machine. If you back off on the threshold to just make it inaudible and no more, then you haven't lost much depth. Second, you'll lose some potentially valuable information. You see, when you go over a ferrous item, the threshold sound will usually null (will go quiet) momentarily. When this happens, your detector may not detect a valid target for some time after that. This elapsed time is called the recovery time and varies by the detector model used.

When you hear the threshold null out, you know you went over a ferrous item and you need to slow down and or change your sweep direction lest you miss a valuable target buried nearby the ferrous item. With a silent search machine you won't know it's happening.

Ok, now that we understand threshold, lets look at volume. This is again, just like a radio. Your detector may or may not have a volume control (separate from the threshold or tuner). If it doesn't have one, you definitely would want earphones with volume control. If you have volume control in both the detector and the earphones, then set one at max volume and set the other one to actual use conditions.

My MXT does not have a volume control but it has a very powerful (read that loud) audio amp. So, I set the volume control on my earphones to produce as loud a beep as I can without it being painful. I do this by just dropping my digger on the ground and sweeping over it and advancing the volume control until it as loud as I want, without hurting my ears.

Then I set the threshold control until I can barely hear the buzz. As a side note, if the threshold is erratic instead of stable, the Gain is too high for the ground you are sweeping. Back off on the gain until the threshold is stable.

That's it! Hope you found this useful. For information on understanding the sounds your metal detector makes you might want to look at
Understanding the sounds from your detector.

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  #2  
Old 06-25-2008, 08:13 PM
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Very informative... you had me @ the CB comparison... made perfect sense!

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Old 06-25-2008, 08:21 PM
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Originally Posted by sectshun8 View post
Very informative... you had me @ the CB comparison... made perfect sense!
Thanks.

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Old 06-25-2008, 08:39 PM
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excellent description of threshold
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Old 06-25-2008, 08:40 PM
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Can you say that 10 times in a row really fast Rudy . Great post & very informative. I know from alot of reading and alot of experience that if a person really wants to get every last bit of umph detects in all metal mode with a slight threshold hum, but myself I prefer a silent search mode. I just never could get used to detecting with a constant hum although my Tesoro Sidewinder (that I just got) has a threshold based all metal mode. Thanks for the post Rudy. Steve.
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Old 06-30-2008, 02:02 PM
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Now this makes perfect sense as to why some Minelab X70 users suggesting now to tune the threshold so high. Thanks for the explanation.
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Old 06-30-2008, 02:28 PM
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Great post! I have been confused about these features on my Sov GT, but I now understand what the threshold hum represents and how the threshold knob differs from the volume knob.

What I can't figure out is why the threshold volume level slowly increases as I hunt without me touching any of the controls; enough so that I need to continue adjusting it down every 20 minutes or so. What I also don't understand is why the threshold volume goes from inaudible to painfully loud with maybe a 1 degree turn of the knob. Any insight from the Sov users out there?

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Old 03-24-2010, 03:17 PM
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Thanks Rudy great explanation .. I like the squelch example

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Old 03-25-2010, 11:41 AM
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Originally Posted by pescadore View post
Thanks Rudy great explanation .. I like the squelch example
You are welcome.

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Old 07-03-2010, 09:37 PM
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I wish I could have had this post to read back when I first started detecting. It would have been so helpful to me. I'm glad you compared it to the squelch on a cb as this will help me to explain this feature to others.

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Old 07-03-2010, 11:24 PM
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Originally Posted by frhamlet View post
I wish I could have had this post to read back when I first started detecting. It would have been so helpful to me. I'm glad you compared it to the squelch on a cb as this will help me to explain this feature to others.
Glad it was of some help to you.

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Old 08-14-2010, 01:48 PM
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Threads like this are the reason why I joined this forum.

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Old 08-14-2010, 11:06 PM
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Originally Posted by PSYS View post
Threads like this are the reason why I joined this forum.

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Old 02-06-2011, 02:17 PM
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Nicely said!

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Old 02-06-2011, 08:09 PM
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Thanks for bumping this, I'm going to be paying a lot more attention to the threshold this year.

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Old 07-22-2011, 07:28 PM
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Sorry for bumping an old post, but this seems like the best place for my question.

I just bought a Sand Shark (P.I.) and I want to get as much depth as possible so I run the Pulse Width (gain?) setting maxed. When I adjust the threshold knob, I can start to hear the threshold at about 30% but it is unstable and breaking up, kind of sputtering, it isn't until I turn it up to 60% or so that the threshold hum is a stable hum. I then adjust the volume so scanning a surface quarter is loud, but the threshold is now far louder than "barely audible"...

I can lower the volume to make the threshold barely audible, but a surface quarter will be much quieter. I imagine lowering the pulse width would allow me to get a stable threshold at a lower setting, but that would defeat my purpose of max depth..

Does it matter how loud the threshold is or is it just making sure to have it at the lowest stable setting?

Anyone want to help point me in the right direction?

Edit: With it set like above with the lowest stable threshold, max gain, I can't seem to get the threshold to null in my test garden... I get good depth on normal beeps, but it goes from positive change in threshold (beep) to no threshold response as I raise the coil... I thought there would be a null area in between getting a beep and no response...
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Old 04-12-2012, 04:17 PM
Terry Soloman Terry Soloman is offline
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First, Set your Pulse Width at 3/4 - not Max. Now set your volume at half, and THEN set your threshold to where you can just hear it over the background noise. You will find that on some beaches, you will be able to use maximum power, and on some you won't. Important to relax, and learn from every target.

Also, MAKE SURE that you have set the tone to the proper frequency for YOUR ear! The ability to tune the freq to your personal hearing is a huge plus, so take advantage of it!

Originally Posted by Crumble View post
Sorry for bumping an old post, but this seems like the best place for my question.

I just bought a Sand Shark (P.I.) and I want to get as much depth as possible so I run the Pulse Width (gain?) setting maxed. When I adjust the threshold knob, I can start to hear the threshold at about 30% but it is unstable and breaking up, kind of sputtering, it isn't until I turn it up to 60% or so that the threshold hum is a stable hum. I then adjust the volume so scanning a surface quarter is loud, but the threshold is now far louder than "barely audible"...

I can lower the volume to make the threshold barely audible, but a surface quarter will be much quieter. I imagine lowering the pulse width would allow me to get a stable threshold at a lower setting, but that would defeat my purpose of max depth..

Does it matter how loud the threshold is or is it just making sure to have it at the lowest stable setting?

Anyone want to help point me in the right direction?

Edit: With it set like above with the lowest stable threshold, max gain, I can't seem to get the threshold to null in my test garden... I get good depth on normal beeps, but it goes from positive change in threshold (beep) to no threshold response as I raise the coil... I thought there would be a null area in between getting a beep and no response...
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Old 04-12-2012, 04:41 PM
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Very good information. I have been confused about this, but that helps a lot.

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