Correct speaker phase in push pull subwoofer

I recently built a push pull T-line sub woofer following someone else's design. Both our designs have both 4 ohm drivers facing the same direction (one mounted outside the enclosure and the other facing the same direction but mounted inside the enclosure (in a I< I< fashion). The originator of the design states that these two drivers should be wired out of phase. It seems to me that they should be wired in phase. which is correct? If the speakers were instead mounted in a I< >I fashion or a I> I<, it would seem that they should then be wired out of phase with each other. Would appreciate advice and an explanation.

Bengui

[Bill Fitzmaurice]

The cones must move in the same direction, so you would wire them reverse polarity if facing each other or facing away from each other, which is the usual way an isobaric is done. Since you opted to have both cones facing the same direction they would be wired normally.

Thanks, Bill

Your clarification is useful and I appreciate your prompt reply. It is as I thought, but I was uncertain since the other chap seemed so definite in his notions.

Bengui

[Bill Fitzmaurice]

bengui wrote:

Thanks, Bill

Your clarification is useful and I appreciate your prompt reply. It is as I thought, but I was uncertain since the other chap seemed so definite in his notions.

Bengui

I'm going on the assumption that the design is isobaric. The usual isobaric has the drivers face to face, separated by only a spacer between their frames, and in that case reverse polarity is a necessity. I could make a better judgement by seeing the design.

Hi Bill,

Unlike the typical isobaric type, my design has both driver cones facing the same direction, . When a positive charge is applied to the positive driver terminals, both cones move forward in unison.

Bengui

[mgboy]

So, what exactly are the advantages to a push-pull system? Do you have to double the volume of the enclosure, like you would if you just had two drivers on the same face?

[Bill Fitzmaurice]

mgboy wrote:

So, what exactly are the advantages to a push-pull system? Do you have to double the volume of the enclosure, like you would if you just had two drivers on the same face?

IMO, for an isobaric, none. The cab volume is halved, but the sensitivity and output is that of only one driver. Back when 3mm was a long xmax and Vas values of 25 cu ft were common isobarics had some value, but modern drivers rendered them obsolete. There is another version of 'push pull', a standard reflex with two drivers facing opposite directions, which is supposed to result in cancelled harmonic distortion. I've never seen corroborating measurements of it though.

[mgboy]

I wasn't referring to either of the alignments you mentioned. Look at this:



That's what I was referring to, and I do believe the OP was referring to having drivers on either end of the box, facing the direction.



Opposed configurations (drivers facing opposite on either ends/sides of the enclosure) due provide resonance control, but I'm not sure if there's any sort of distortion reducing effects - I'd imagine there might be.

[thxgoon]

mgboy wrote:

I wasn't referring to either of the alignments you mentioned. Look at this:


Opposed configurations (drivers facing opposite on either ends/sides of the enclosure) due provide resonance control, but I'm not sure if there's any sort of distortion reducing effects - I'd imagine there might be.

The original poster was talking about push pull in an isobaric transmission line bandpass sort of configuration if I'm reading it right. IOW the images you posted but with one of the drivers inside yet another box with a specially designed port. The advantage of push-pull is reduced harmonic distortion created by the proximity of the voice coil to the magnet. When one woofer is close and moving 'faster' the other is far away and moving 'slower' thus canceling the distortion. That's the idea anyways.

[mgboy]

I must be reading his posts (the OP's) wrong. I'll re-read them.

[Bill Fitzmaurice]

thxgoon wrote:

The original poster was talking about push pull in an isobaric transmission line bandpass sort of configuration if I'm reading it right.

That's why I asked to see details, as push-pull could mean either.

Hello again,

The original sub design that I used can be found on the following:
http://www.teresaudio.com/haven/subs/subs.html

Cheers,
Bengui

[mgboy]

bengui wrote:

Hello again,

The original sub design that I used can be found on the following:
http://www.teresaudio.com/haven/subs/subs.html

Cheers,
Bengui

Well in that case, I believe they should be wired in phase, otherwise they cones would be moving in opposite directions and there would be a direct cancellation. Correct bill?

[Bill Fitzmaurice]

mgboy wrote:

Well in that case, I believe they should be wired in phase, otherwise they cones would be moving in opposite directions and there would be a direct cancellation. Correct bill?

Yes. The would be wired reverse polarity as shown, but if both drivers are outward facing per the OPs version they'd be wired normally. They would be moving in opposite directions, but only because they're on opposite sides of the box. Both are moving either inward or outward simultaneously. BTW, that's not an isobaric alignment.

[mgboy]

Bill Fitzmaurice wrote:

BTW, that's not an isobaric alignment.

Yup - I've got a grasp on isobaric alignments. =)