Dual Voice Coil Parameter Adjustments

[BlueWizard]

I'm sure this has come up before, but I did search and apparently 'dual', 'voice', and 'coil' are such common terms that it returned thousand (OK hundreds) of post, none of which directly addressed this issue. ...or none that I could find.

While still in the pure fantasy stage, I'm considering building a 3-way tower using TWO 16ohm-wired DVC woofers, so I can have a final impedance close to 8ohms. Likely, since I can't find 16 ohm mids, it will be a WWMT configuration.

The two I am considering in this particular fantasy, are the Dayton SD270-88 10" and the Dayton SD215-88 8".

I have one spec sheet that gives the parameters with the coils in parallel, that helps in general, but doesn't help me specifically. The other spec sheet gives the parameters of the individual coils, and that would help, if I knew what to do with it.

So, to the basic question -

Can someone give me a concise no-nonsense statement of how to adjust the various T/S parameters so I can enter them into a modeling program?

Re and Le would seem straight forward. Just treat them like any resistors or inductor in (in my case) series. Can't imagine that Xmax would change, or that Pe would change.

But I would suspect that the various 'Q' parameters would change and perhaps BL, but in what fashion I can't fathom.

So, could some one give a clear concise statement of how these various parameters would change when wiring a Dual Voice Coil speaker in both PARALLEL and SERIES?

Thanks for the time and effort.

Steve/bluewizard

[ocool_15]

Check in:
"The Unofficial Speaker Workshop Manual"

OPTIONAL: IMPACT OF DUAL VOICE COIL ON THIELE SMALL PARAMETERS:

[Rybaudio]

The seven fundamental electromechanical parameters are:

Mm
Rm
Cm
Sd
Bl
Re
Le

The first four are mechanical parameters and thus do not change with voice coil wiring. The last two are electrical properties of the voice coil and they behave thus (half for parallel double for series). Bl is the ratio of the force on the cone to the current through the voice coil; for parallel coils (compared to a single coil) you have 2x current and 2x force so Bl stays the same and for series coils you have 2x force and 1x current so Bl is 2x.

Thiele/Small Parameters (Qe, Qm, Fs, Vas) can be derived from these; they all stay the same.

[BlueWizard]

Ocool_15:

Would have helped a lot if you had provided a link.

I can only assume, by "The Unofficial Speaker Workshop Manual" you mean this -

http://www.claudionegro.com./download.html

Second from the bottom -

File name: SW manual 2.0.zip

Description: The unofficial Speaker Workshop manual, by Jay Butterman. Version 2.0.

As to the second OPTION, Google could find nothing by that name.

EDITED: Oops...

That's a chapter in the Speaker Workshop manual, unfortunately it simply references a spreadsheet DVC parameters.xls which isn't provided.

A search of Google for "DVC parameters.xls" also turns up nothing but it would certainly be good to find.


Rybaudio:

Thanks for the help. But let me make sure I understand what you said -

"Bl is the ratio of the force on the cone to the current through the voice coil; for parallel coils (compared to a single coil) you have 2x current and 2x force so Bl stays the same and for series coils you have 2x force and 1x current so Bl is 2x."

2x the current and 2x the force, BL stays the same?

2x the force and 1x the current is a BL of 2x?

Not that I don't trust you, but on the surfaces that seem counter intuitive. But then my intuition was never great.

Thanks again.

Steve/bluewizard

[Pano]

In practical terms, on the DVC drivers I've measured:

These remain the same
Fs
Vas
Mms

The two coils in series vs one coil:

Re x 2
Le > x2 (don't know why)
Qms About the same
Qes ~ 1/2
Qts ~ 1/2

I suppose if the two coils were exactly identical, then the Qms, Qes, Qts changes would be more exact.

Hope that helps.

[jupiterjune]

While still in the pure fantasy stage, I'm considering building a 3-way tower using TWO 16ohm-wired DVC woofers, so I can have a final impedance close to 8ohms. Likely, since I can't find 16 ohm mids, it will be a WWMT configuration.

PHL makes (hopefully not 'made') sixteen ohm midwoofers. Zalytron used to have them.

[ocool_15]

Originally posted by BlueWizard


I can only assume, by "The Unofficial Speaker Workshop Manual" you mean this -

http://www.claudionegro.com./download.html

Second from the bottom -

File name: SW manual 2.0.zip

Description: The unofficial Speaker Workshop manual, by Jay Butterman. Version 2.0.

As to the second OPTION, Google could find nothing by that name.

EDITED: Oops...

That's a chapter in the Speaker Workshop manual, unfortunately it simply references a spreadsheet DVC parameters.xls which isn't provided.

A search of Google for "DVC parameters.xls" also turns up nothing but it would certainly be good to find.

I double checked and using the same link you have. Double click on the "DVC parameters.xls" Icon and it opens in excel. The sheet looks to be embedded in the word document.

[Rybaudio]

Originally posted by BlueWizard
Rybaudio:

Thanks for the help. But let me make sure I understand what you said -

"Bl is the ratio of the force on the cone to the current through the voice coil; for parallel coils (compared to a single coil) you have 2x current and 2x force so Bl stays the same and for series coils you have 2x force and 1x current so Bl is 2x."

2x the current and 2x the force, BL stays the same?

2x the force and 1x the current is a BL of 2x?

Not that I don't trust you, but on the surfaces that seem counter intuitive. But then my intuition was never great.

It is correct. To look at it another way, suppose each voice coil has length L and you hold the current going into the system (call it I) constant. In the series configuration you'll have 2L of wire with the current I flowing through it, hence a force of 2BLI on the cone. In the parallel configuration, you'll also have 2L of wire but in this case you'll have I/2 current going into each one, hence BLI force on the cone. Thus the series configuration has twice the net BL.

The problem your intuition may be encountering is thinking of Bl as some sort of efficiency or strength factor. If that is the case, you need to look at Bl^2 / Re instead; that is the same for parallel and series configurations and in those cases it is twice that of a single coil.

BTW, I should be clear about something from above- when I say the T/S parameters stay the same, I mean they are the same for series and parallel wiring. If you only drive 1 voice coil they will be different.

[BlueWizard]

Thanks for all the responses, I really do appreciated it. Like I said, I'm sure it has been covered before, but I suspect it was a secondary aspect of another discussion. In any event I couldn't find it.

Now, I and others have a nice concise statement of the problem and a solution.

I did try the Spreadsheets again in "The Unofficial Speaker Workshop Manual", and THEY DID WORK.

I'm not sure why they didn't work before, or why I thought they didn't or wouldn't work, but it is working fine now. So, that is a new valuable resource for myself, thanks for the suggestion.

I also want to thank people for taking time out from serious discussions to answer what I'm sure you consider a rookie question.

Regards to all.

steve/bluewizard

[forr]

Its ethymology gives the real meaning of Bl : it is the product of the magnetic flux density in the gap by the length of the wire immersed in it. Bl is expressed in Tesla-meters unities.

It is antinomic to claim that with a dual-voice speaker, the Bl changes when the coils are wired in series or when wired in parallel as the whole length of the wire has not changed. The formula for the efficiency also shows that it is unaffected.

With an unknown speaker you have no way to measure its Bl.

The ratio of the force on the cone to the current through the voice coil is a parameter directly and quite easily measured on speakers, expressed in Newton/Ampere. It should be called "force factor" (FF), never "Bl"

What changes between a series connection and a parallel connexion is the impedance, the first one being four times the second one. So for a fixed voltage coming from the power amp of the usual voltage source type, there is four times more current in the parallel connection than in the series connexion, hence four times more force. So the sensitivity changes, 6 dB more for the parallel connection.

A few monthes ago, I planned to start a new thread about the confusion between Bl and FF. I didn't it but here it is a good place to discuss about it.