Dual voice coil for baffle-step compensation?

[martinbls]

Hi All!

I must say I'm not a fan of huge inductors in series with a mid-woofer to compensate the baffle-step. That's why I wonder, why aren't dual voice coil drivers more popular theses days? The use of a small inductor for the midrange crossover and a large inductor for adding the right amount of spl in the lower frequency region would mean to not give away any effeciency in the midband region. Further more, a higher crossover frequency would be possible to add small tweeters.

Of course, adding another driver (like in a 2,5-way design) would also compensate for the baffle-step, but at the expense of higher costs and a much larger volume (in fact, twice the volume one driver would require).

Any thoughts on this?

Martin

[CharlieLaub]

Not too bad of an idea, really, except that most drivers that are dual coil are designed as subwoofers, and these are typically not useful above about 250Hz. You are only part way through the baffle step transition at that point.

What driver did you have in mind?

-Charlie

[jerome69]

Visaton - GF200 ?

[CharleyW]

The original D'Appolito design (Speaker Builder, 1984 I think) used Focal drivers with dual voice coils to address baffle step compensation.

[CharlieLaub]

Note that I said "most" DVC drivers. I am sure you can find some like the Focals that can do it. BTW a pair of these just sold on Ebay USA last week...

-Charlie

[rabbitz]

Infinity has done that in their Infinitesimal 0.1.

http://www.infinity-classics.de/tech...ical_sheet.pdf

[martinbls]

Hi Guys!

I didn't have any particular driver in mind. My question was merely aimed on the fact that there are only very few designs which take advantage of a dual voice coil driver nowadays and I just wondered why that is. Perhaps there is a serious drawback I'm not aware of.

Although, one driver that comes to mind is the Monacor SPH-170 TC:

hifisound eShop*-*MONACOR SPH 170/TC POLYPROPYLEN*

This driver might be better suited in a closed volume, rather than vented. Especially in this case a second voice coil might come in handy for lower frequency reinforcement.

[martinbls]

SPH-170 TC in 16l closed:

[speaker dave]

Using a dual voice coil for baffle step compensation won't really give you a different end result.

It sounds like you want to make a 2 1/2 way system with a single woofer (large inductor/small inductor for the two voice coils). The end result can't be any different than shaping the response with the right network and a single voice coil.

You can make it such that the output of one voice coil has just the right mid range sensitivity but you have to then heavily roll off the second unit.

No one would do this commercially because the cost would be higher (dual voice coil and dual network) for the same result.

David S.

[system7]

Seems to me you have 3 passive choices for Baffle Step Correction. Lets say 10" baffle needs about 3-6dB correction around 500Hz.

You can have two bass units and a tweeter in a 2.5 configuration, but you rolloff one at about 500 Hz and the other around 2.5kHz to match the tweeter. As here in the Ellam-25 by Troels Gravesen:
ELLAM-25

You can cross over to an attenuated midrange at 500Hz, as in the Gale GS401A:
Classic monitor designs?

You can add the standard RL circuit, as in Rod Elliott's design for a fostex FR unit:
Fostex FX120 DIY ML-TQWT (Transmission Line) Speaker Project

A last option is to do it electronically with a filter. Quite simple really, if you like to tinker...as in Morgan Jones' FR Fostex setup:
Arpeggio Loudspeaker

As speaker dave says. Using dual voice coil will amount to the same thing as a 2.5 loudspeaker with baffle step compensation. IIRC, dual; voice coil is really only useful in Professional PA speakers. The classic RL circuit has a nice side-effect in raising source impedance in the higher registers IMO. Makes for an easy amplifier load.

Oh, I nearly forgot. You can include baffle step in a crossover filter with a bit of cleverness with notch filters which tame a typical 800Hz bass/mid peak from small cabinets.