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NWCindy a reply to your four posts below: Lengthy, but maybe helpful to others, too.

October 17, 2018 04:55PM avatar
I did a cut and past of your replies below to try and explain it again. I think Oregon Gregg might be right that you seem to be a little 'befuddled' about search coils.

Thank you for your reply Monte. Yes I usually have been using the 7-inch around coil on the kruzer. In fact I have not put the five in on yet and I have not put it on the large coil.
You have three (3) search coils for your Kruzer. A round, solid, 5" Double-D, a round, open-frame, 7" Concentric and the 'standard' elliptical, open-frame 7X11DD. If you haven't used the 5" DD you should plan on it for trashier sites, especially with a lot of closely-spaced nails and other ferrous debris.

The 5" is terrific on most of these models. I haven't bought one yet for my Anfibio Multi, but that's because I already have the 5" DD on a Relic and the slightly smaller 'OOR' DD on a CoRe and can just grab those units when needed. The Kruzer and Multi-Kruzer share the same coils with the Anfibio series and I likely will buy that 5" DD in the future.

As I've stated, I don't care for most 7X11 or 8X11 coils, and for day-to-day hunting of most places that are not too trashy I prefer to use a mid-sized search coil. I have that on the Anfibio, similar to what I preferred on the Impact and Multi-Kruzer, and that is the round, open-frame 7" Concentric coil, and that's the mid-sized coil you have.

I do have a spare Rod but I kind of like the coverage of a big coil on occasion not all the time but just on occasion. However that 11 by 7 is enormous for me that's too big. so I was thinkingl two things, I think I need just one little bit bigger one for open areas ..
"Just one little bit bigger" than what? Bigger than the 7X11 DD standard coil or a bit bigger than the round 7" Concentric?

You said: "I kind of like the coverage of a big coil on occasion not all the time but just on occasion"... so It makes me wonder just how occasionally would you hunt an open area with sparse targets and use a bigger-size coil in a year? I have a bigger-size standard coil for 10 of my 13 detectors and I generally mount a 'standard' size coil on all of them, combined, perhaps 3-4 times a year and spend maybe a total of 3 hours ... a year ... using all of them, combined.

As I have stated many times anywhere I post, I am just not fond of the 7X11 or most of the standard coils in that size range, like a 950 or10" or 11" or 12". They seldom provide me with any benefits in day-to-day use and I really only prefer a larger-size coil for specific site needs and for contract searches. A decent mid-size coil can often give me all the depth and coverage I need and for what is practical at most sites, and they weigh less and balance better so there is less fatigue.

... and a double d .. doesn't the Double D cover more ground on a big grassy area than a concentric?
Possibly yes and possibly no. It depends upon the search coil's size and how the Double-D and Concentric coil compare. It also depends upon the search coil sweep length because those who like to work a broad, wide sweep will have better overall coverage with a Concentric than a Double-D for most targets. By 'most targets' I am referring to the more typical smaller-target depths where we find things like coins, rings, trade tokens, other jewelry, metal buttons, uniform insignia and such.

It will depend upon the site environment, type of and duration of activity, and any effects caused by trampage or erosion in an area. Everything factored in, the majority of the targets are located from surface/sub-surface down to about a 4" depth. Over 4" and down to the 7" to 9" range you are finding what would be considered 'Deeper Targets.'

I have used Double-D search coils since 1971 and I learned early on their strengths and weaknesses, and through these past decades I have appreciated the fact that some metal detector designs work better with a Concentric or perhaps better withy a Double-D design, and in a few cases a particular detector model can do fine with either type search coil.

I realize one goes down to a cone and one covers the whole thing ...
I think some of your 'befuddlement' Gregg mentioned shows here because you probably do not 'realize' or understand the differences quite correctly. But then many people in this hobby do not know the true difference between the two coil types because they have read posts made by others who, obviously, didn't know the differences either and simply have made mis-statements. Describing the differences in the two coil designs is important because, as I stated, some brands and models do better with one type than the other in comparable sizes.

Search coils are the antennae that project the EMF (Electro-Magnetic Field) about the Transmit winding and the Receive coil is balanced so that it will convey changes in the field and also the EMF that is generated on the surface of a located metal object. The projected EMF of a Concentric coil is rather uniform in shape all around the outer portion of the search coils winding, and the Receive winding is more centrally positioned and usually smaller in size than the Transmit winding and typically a uniform shape within the outer Transmit winding.

Therefore, one benefit of a Concentrically wound search coil is that you will generally get a uniform and consistent audio and visual report regardless of the search coil's position of approach to the target. From the left or from the right, moving straight forward or pulling the coil rearward or at an odd-angle or direction. The response is going to be more consistent.

A Double-D designed search coil differs quite a bit, even though it has Transmit and Receive windings. Note that either type coil design, a Concentric or a Double-D, have been, can be, and are fashioned in a round shape, an 'OOR' or Out-Of-Round shape, a more oval shape or a pronounced elliptical shape. The differences are not in the physical shape of the coil housing but the internal shape and placement of the Transmit and Receive windings.

With the Double-D design, and that description, shortened to DD, is based o the appearance of the two opposing Transmit and receive windings. One appears to be more in the shape of a letter 'D' and the other is a reversed shape and the two sides that are kind of the straighter side of the 'D' are just a bit curved. When the two windings are positioned in the coil housing, the Transmit and Receive windings overlap on those straighter sides.

This makes the overlapped and more reactive portion of the EMF running down the center-line of the search coil from front-to-rear. There are some drawbacks to the Double-D design, especially when hunting sites with a lot of ferrous debris to deal with. A sweep approach from the left and then from the right can result in a more inconsistent and less accurate visual and audio response. That's because from one direction you will have the outer portion of the Transmit field first effected and from the other direction the Receive winding's EMF will be encountered first. Thus you can have a differing influence on the overall target response as it then passes through the overlapped field and then the opposing winding's field.

Thus, a DD design can result in a more inconsistent audio response and visual target information than the more uniform Concentric coils EMF would convey. Add to that the fact that a DD designed coil is usually going to not Discriminate as well, as a Concentric coil of comparable size, nor will it handle iron or magnetic-based targets as well as a Concentric design. And if the coils are of a comparable size and shape, the Concentric coil will usually provide slightly better depth-of-detection than a DD coil.

Advantage? Generally, it is in favor of the Concentric type coils for these reasons.

Now, what about site coverage? Yes, the DD coil might generate an EMF that coverers an area from close to the front of the coil, down the center path to close to the rear of the coil. That appears to provide good side-to-side coverage , but only if the search coil is side-stepped from left-to-right and not swept normally because the arcing angle changes the actual front-to-rear coverage based on the ground that is visualized as being scanned. The Concentric coil's EMF is uniform from any position or angle and that results in better site coverage.

Yes, the Concentric search coil's EMF, when viewed from the side, does appear to have a responsive portion of that generated field that tapers into a narrower portion of the field, but it is not always as 'V' shaped or cone-shaped as some would suggest. A Concentric coils responsive field is close to the outer edge of the search coil and slowly tapers to about 2" to 3" before it makes a more pronounced decrease in coverage down to the narrowest point where a coin, laying flat ,would be located in the center-axis of the search coil.

Well, the Double-D does NOT have a wiper-effect EMF that runs to the full depth, either. Instead, the DD coil's field, when viewed from the side, wouild have more of a bowl-shaped EMF which might stay a little more responsive in the front-to-rear center-line closer to the front or rear of the coil, but nonetheless it still is going to taper off. That's why even with a DD designed coil you can still Pinpoint a target in-line with the center-axis in line with the center of the search coil.

But the responsive portion of a DD coil is not very good off to the left of center or right of center region due to the Double-D design. That's why for most of my life of detecting I tend to work slowly and methodically and my side-to-side sweeps, in most hunting applications, are a length of about 24" to 30" and at times I might stretch it out to a full 3 feet. Only in a Competition Hunt or perhaps working a large open sports field do I use a broader sweep than that

...that's why I thought a double D might be good for me if I'm trying to cover open area on a grassy park or something. you know I hardly ever do Parks but I still want the option of having that kind of coil.
There is 'hurry-up' site coverage and 'most efficient' site coverage. Each of us picks the manner in which we want to work an area. In a Competition Hunting I will often use a 7" to 8" coil and I might work a slightly wider sweep and move a little faster than in a serious site search, but I still want to be in control and monitor my coverage. In Competition Hunts most targets are located from surface to maybe an inch or two so there's no need to a lot of overlapping.

When hunting other places where I want the most efficient and effective coverage, and intended targets are usually smaller, such as coins, trade tokens, jewelry, bullets, etc., etc., I will overlap about every 2nd or 3rd sweep by advancing the coil roughly 25% from what I just covered to no more than 50%. Thu I would be re-sweeping 75% to 50% of the already scanned area, but that can be in my favor, especially in very littered sites.

If it is loose and loamy terrain and there has been good cause for coins and other lost targets to have been repositioned a little deeper, then I might advance the coil roughly an inch at a time and make two or three left-to-right and right-to-left sweeps before advancing another inch. Yes, it takes time to cover a big area, but I can guarantee myself that I've been very efficient on at least a smaller section and might not be leaving much behind. Then I move on to another grid or visualized area of the bigger area.

In your case, you said you don't hunt parks and only very occasionally would use that big 7X11 DD, so just forget about it and store it in a tote in a closet. If you want reasonable coverage in typical areas you hunt that might be more open and target free, make sure they are before you go to a larger size coil. Select the All Metal mode and Ground Balance, or use the Discriminate mode with the Disc. set at '00' or '01' and Iron Volume at '02' to '05' and search an area. If it really is trash free and you're not getting a lot of low-tone iron responses or questionable higher tones, then switch to a mid-size to standard coil.

In your case, the round-shaped 7" Concentric coil is a good choice. If you wanted a slightly larger-size search coil than the 7" Concentric you have two ways to go, in my opinion. Consider the open-frame, elliptical 5X9½ Double-D, or perhaps the newest coil, a round, open-frame 9" Concentric coil. Both wowuld have their advantages and would provide a bit better side-to-side site coverage than the round 7" Concentric you have now. But I would use the 7" Concentric the most for now until you get a good feel for what it can do for you.

So I guess in a nutshell my question is, the 7in oval the Gregg recommended is I believe concentric which doesn't make sense to my brain but I thought that would be a good size however that 9 by 5 I think it is Double D seems to be similar size a tad bigger and maybe it would cover what I'm looking for better?
The solid 4X7½ elliptical coil, not really an oval shape, is a Double-D coil. It's OK, as I mentioned in my initial post, for a lot of Coin Hunting or other applications where iron debris wasn't an issue, but that's NOT the coil Gregg recommended. You have his recommended coil, the 7" Concentric. Gregg witnessed the poor performance with smaller 4X7½ DD coil in the tough challenge Nail Board test with the 1836 silver Half-Dime centered amongst the four iron nails. The 'OOR' and 5" DD coils easily out-performed that coil.

If you're not comfortable with the coverage of the 7" Concentric you have, and you want a good mid-sized coil, I would suggest the elliptical, open-frame 5X9½ DD or possibly the new 9" round, open-frame Concentric. Of those two the elliptical 5X9½ DD will most likely provide the lightest and better balanced feel.

I wouldn't mind having them both but there's no need to have Overkill either on the coils. So for a mid-range size which would you recommend a concentric or double d for covering a lot of ground thanks monte
I agree not to have search coil over-kill and my opinion ios that you have the right coil at the present with the round, open-frame 7" Concentric.

I guess this might help you to understand what's going through my head. Why would they make a 7 inch oval shape concentric coil what would be the purpose it looks like a bigger coil But really only reading a very small amount of land so I don't understand why they would even make that size in concentric?
They don't make an 'oval' shaped Concentric for that detector.

There are basically two elliptically-shaped coils between the 5" round DD and the standard 7X11 DD search coils. They are both Double-D types. The 4X7½ solid body DD and the 5X9½ open-frame DD. The first would be more in the smaller-size category and the latter would be a mid-sized coil.

I think I figured it out. I thought Gregg wanted me to get the 7.5X4 and thought he said it was concentric. I already have the 7 in concentric he likely forgot. Anyway it seems the 7.5 and the 9.5 are both DD coils. So i guess it just means I need to decide which one of those sizes i need.
You have the coil Gregg suggested, the round 7" Concentric. Yes, the 4X7½ nd 5X9½ ellipticals are DD types.

The 7.5x4 would read the entire coil size so that should provide added coverage over the concentric 7 inch correct?
As I mentioned earlier, that is wrong. Just because the 4X7½ is a DD design coil doesn't mean it reads the full length for the full depth of detection, nor does it detect as deep as the round 7" Concentric coil.

Darn it takes longer to type this with new nerve injury to my right shoulder than it does to explain the search coil differences is design, shape of the EMF, and do coil comparisons in a seminar. Much easier in a demonstration. I hope you figured out all I was trying to convey.

Be happy with the 5" DD and 7" Concentric and just get out hunting with them. All will be fine.


"Your EYES ... the only 100% accurate form of Discrimination!"

Stinkwater Wells
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Metal Detector Evaluations and Product Reviews
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'Regular-Use Detector Team' are models from: Fisher, Nokta / Makro, Teknetics, Tesoro and White's
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Note: Detectors are listed alphabetically by Brand. Models are chosen as desired based on search site conditions.
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*** All working well today to make memories for tomorrow. ***

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(503) 481-8147
Subject Author Views Posted

NWCindy, here are some replies to your questions on the Buy/Sell/Trade Forum.

Monte 129 October 15, 2018 05:51AM

NWCindy a reply to your four posts below: Lengthy, but maybe helpful to others, too.

Monte 68 October 17, 2018 04:55PM

Re: NWCindy, here are some repl;ies from your questions on thre Buy/Sell/Trade Forum.

NWCindy 72 October 16, 2018 03:13PM

Re: NWCindy, here are some repl;ies from your questions on thre Buy/Sell/Trade Forum.

NWCindy 58 October 16, 2018 02:58PM

Re: NWCindy, here are some repl;ies from your questions on thre Buy/Sell/Trade Forum.

NWCindy 74 October 16, 2018 02:53PM

Re: NWCindy, here are some repl;ies from your questions on thre Buy/Sell/Trade Forum.

OregonGregg 60 October 17, 2018 06:20AM

Re: NWCindy, here are some repl;ies from your questions on thre Buy/Sell/Trade Forum.

NWCindy 55 October 17, 2018 02:27PM

Re: NWCindy, here are some repl;ies from your questions on thre Buy/Sell/Trade Forum.

NWCindy 70 October 16, 2018 02:51PM

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