Wharfedale i4T connections

[IA76]

Hi

I just needed to sense check this please as it is the first time using this speaker.

The connection terminal labelling is different on speaker vs manual. The full manual can be viewed here.

At 100v am I right in saying that these are the correct connections if we say T1 is at the top and T4 at the bottom?

100v 25w - Live T3 & Common T1

100v 12.5w - Live T4 & Common T1

What is making me doubt this is that T1 which is common if I am right above has a + next to it on the speaker.

Edited November 13, 2023 by IA76

[sunray]

It looks to me that you have the 8 ohm sticker on there, just check it with an impedance meter.

The 6 & 8 have a 100v impedance selector switch, iIwonder if they have started doing the same for the 4. My knowledge of these is fairly dated.

Edited November 14, 2023 by sunray

[IA76]

The 4 doesn't come with the selector switch. The tap is set depending on which terminals you use.

The place I purchased it from have just said for 100v 25w T2 is live and T4 is common 😕

Edited November 14, 2023 by IA76

[DrV]

Is this what you need. It's got all the connections for the whole range

Sorry, re-read your post - that's what you already have

 

Edited November 14, 2023 by DrV

[DrV]

I think sunray is right. But you don't need an impedance meter - just an ordinary ohmmeter will give you an adequate comparative reading. The resistances will be lower than those shown in the table but they should follow the same pattern, using the top terminal as common you should see increasing resistance as you work down the terminal block.

[IA76]

I have access to an impedance meter used for testing 100v systems. These are the reading I get with it set at 20k

T1 & T2 = 1.04k

T1 & T3 = 2.24K

T1 & T4 = 4.74K

What has confused me is that that supplier has advised that to run the speaker at 100v 25w it is T2 live & T4 common which shows 1.04K on the meter and seems to go against the manual (if I ignore the ++-- markings on the speaker)

Edited November 14, 2023 by IA76

[DrV]

I'm not terribly experienced with 100V systems but I understand the basics. If you calculate the power based on the impedances shown in the table they come out correctly. So for 25W you would need 400ohms. Are you sure your decimal point is in the right place? The impedances you quote give you much lower powers. If you have indeed got 104 ohms 224 ohms and 474 ohms then the powers are more realistic.

[sunray]

It is a few years since I used some of these only on one job, so detail is vague, both 8Ω and 100v i4T and i6T or i8T.

both formats look familiar to me although I wouldn't have been able to sketch the detail, I don't recall measuring the impedances but it is highly unlikely I didn't measure before connecting to amps, equally I don't recall there being any impedance discrepancy .

using an impedance meter, ie with an audible signal of 1KHz usually the readings should be:

For 70v,  25W = 200Ω, 12.5W = 400Ω, 6.25W = 800Ω

For 100V  50W = 200Ω, 25W = 400Ω, 12.5W = 800Ω.

Your measured figures  at 100V (70V) give powers of roughly:

1 hour ago, IA76 said:

T1 & T2 = 1.04k   = 10 (5) W

T1 & T3 = 2.24K  = 4.5 (2.25) W

T1 & T4 = 4.74K   = 2 (1) W

 

[sunray]

5 minutes ago, DrV said:

I'm not terribly experienced with 100V systems but I understand the basics. If you calculate the power based on the impedances shown in the table they come out correctly. So for 25W you would need 400ohms. Are you sure your decimal point is in the right place? The impedances you quote give you much lower powers. If you have indeed got then the powers are more realistic.

That's a good point except 104Ω ~ 100W , 224Ω ~ 45W,  474Ω ~ 20W.

[sunray]

All figures off the top of my head so apologies if any silly errors.

 

To really confuse the issue, If you measured from the bottom as com I'd expect to see

Edited November 14, 2023 by sunray

[DrV]

The supplier suggested T2 and T4 which would be 3k7 with the OP's figures. Assuming the d.p. error this is 370 ohms which gives 27W which is 25W within acceptable measurement errors 

[IA76]

using the 2KΩ setting

T1 & T2 = 1.008

T1 & T3 - just displays a 1

T1 & T4 - Just displays a 1

T2 &T4 - 0.013

Using the 200Ω setting

T1 & T2 = 1.008

T1 & T3 - just displays a 1

T1 & T4 - Just displays a 1

T2 &T4 - Just displays a 1

This is the meter

Edited November 14, 2023 by IA76

[sunray]

42 minutes ago, DrV said:

The supplier suggested T2 and T4 which would be 3k7 with the OP's figures. Assuming the d.p. error this is 370 ohms which gives 27W which is 25W within acceptable measurement errors 

Transformer will have a multi tapped winding and coincidentally this particular version works out well, excuse the fact I I've shown it as 100V & 50W, in reality that's what the tapping is despite the fact the transformer and loudspeaker are rated at 25W But I'm far more familiar with 100V than 70V.

From this it can be seen that using com to 50W should be the same as 50W to 12.5W.

 

I knew I'd end up getting a calculator out, working on these figures

turns ratio (n) is √(474Ω/8Ω = 7.7) & √(104Ω /8Ω = 3.6)...  ∴ 7.7-3.6 = 4.1 

working back the other way, Z = n²z = 4.1² * 8Ω = 16.8*8Ω = 134Ω

Power =  V²/r = 100²/134Ω  =  74.656W (From calculator)

I hope I have this correct, but as always E&OE.

[DrV]

1 hour ago, IA76 said:

using the 2KΩ setting

T1 & T2 = 1.008

T1 & T3 - just displays a 1

T1 & T4 - Just displays a 1

T2 &T4 - 0.013

Using the 200Ω setting

T1 & T2 = 1.008

T1 & T3 - just displays a 1

T1 & T4 - Just displays a 1

T2 &T4 - Just displays a 1

This is the meter

Well, I give up! There are too many unknowns. Don't suppose you can open it up and have a look? One thing I would say is that it's unlikely to have an isolating transformer as Ray shows but more likely an auto transformer (cheaper). However he has experience of installing such systems which I don't.

If it is an autotransformer then I would suggest that the speaker itself is connected between T2 and T4. Clearly 100V into .013k would be a lot more than 25W! That also means the supplier doesn't know what they're talking about. 

[IA76]

I contacted Wharfedale direct from their website and they sent me this picture which ties in with the 70v layout in the manual but not the 100v one!

Edited November 14, 2023 by IA76