Best subwoofer deal ever!

HT cOz · « **Reply #60 on:** 24 Sep 2010, 02:29 pm »

Quote from: Rclark on 24 Sep 2010, 07:48 am

I'm on the preorder list for the dac

That DAC looks very interesting. I wonder how it is going to sound? Any chance we could get Danny's OP on it?

Rclark · « **Reply #61 on:** 24 Sep 2010, 05:30 pm »

The cd player sounds awesome and the DAC uses the same dac in the player but with robust upgrades, plus volume control (albeit digitally controlled). It is said to take the cd player to "another level", so I expect it to be very nice. I still probably want to add a Dodd buffer as a final touch but it will be a great starting point and a useful performance boost for my cd's. I'm excited, for $299 it's just too good a deal. Later on, if I decide to go computer I can use the USB port input.

Oscillate · « **Reply #62 on:** 2 Oct 2010, 01:48 am »

Danny stated in Reply #45 "When I say in phase then I am talking about them moving the same direction
at the same time. Polarity on one of them will be reversed"

Danny ...I am very interested in purchasing a pair of the MFW-15 surplus drivers and would like your opinion
on the merits and differences between the two following implementations for a single enclosure:

Compound ~ Push/Pull Dual Drivers. Drivers wired electrically out of phase while mechanically in phase.

Working as you describe above

A good prcatical example would be in the old M&K style of

~~~~~ Versus ~~~~~

Compound ~ Push/Push Dual Drivers Drivers wired electrically in phase and mechanically in phase.

The dual opposed driver mounting style offered from many mftrs. these days.

...thanks in advance

Danny Richie · « **Reply #63 on:** 2 Oct 2010, 11:00 pm »

Technically none of those are really push pull. They are called push/pull quite often but the net effect is the same as if they are both facing the same way. You just have one woofer flipped around backwards.

Facing a driver in a different direction really doesn't change the net effect or SPL levels either. Just as with an all front facing set up the box size needs to be double the same of that of a single driver.

The M&K design really makes no sense as the lower woofer is loaded differently than the forward facing one. It is really in a band pass while the other is not. To compensate for the different loading of the air pressure the Qts of the drivers would have to be adjusted to even them out.

A true compound loading design has drivers on either side of the box both moving in the same direction at the same time. This has the advantage of cutting the air space needed in half and it cancels out at 90 degrees off axis just like an open baffle design. Unfortunately you get the same output levels of a single woofer.

alphaiii · « **Reply #64 on:** 3 Oct 2010, 02:09 am »

Quote from: Oscillate on 2 Oct 2010, 01:48 am

Compound ~ Push/Push Dual Drivers Drivers wired electrically in phase and mechanically in phase.

Danny,
So the above design is what you refer to when both drivers are moving the same direction... and this allows for halving the box volume (relative to a single driver) to get the same SPL, correct?

hayden · « **Reply #65 on:** 3 Oct 2010, 02:18 am »

I'm not Danny but I will jump into the discussion. The last design you show will not result in a space savings. The dual-opposed configuration is used to lower distortion and mechanical forces in the enclosure. You seem to want an isobarik design, which in reality results in a space savings of about 40%.

JP

Danny Richie · « **Reply #66 on:** 3 Oct 2010, 03:14 am »

Quote from: alphaiii on 3 Oct 2010, 02:09 am

Danny,
So the above design is what you refer to when both drivers are moving the same direction... and this allows for halving the box volume (relative to a single driver) to get the same SPL, correct?

No, they are moving in opposite directions. It requires the same air space as two front firing drivers.

Quote

The last design you show will not result in a space savings. The dual-opposed configuration is used to lower distortion and mechanical forces in the enclosure.

This is correct.

alphaiii · « **Reply #67 on:** 3 Oct 2010, 03:49 pm »

Quote from: hayden on 3 Oct 2010, 02:18 am

I'm not Danny but I will jump into the discussion. The last design you show will not result in a space savings. The dual-opposed configuration is used to lower distortion and mechanical forces in the enclosure. You seem to want an isobarik design, which in reality results in a space savings of about 40%.

JP

Quote from: Danny on 3 Oct 2010, 03:14 am

No, they are moving in opposite directions. It requires the same air space as two front firing drivers.

This is correct.

Ok, got it. So to use dual drivers in roughly half the space, they'd need to be wired out of phase (polarity reversed on one driver)... so that when one sub moves "outward", the other is moving "inward".

Not sure why, but I was getting confused by the descriptions...

hayden · « **Reply #68 on:** 3 Oct 2010, 05:26 pm »

No, you aren't quite there yet. Look up the isobarik/isobaric alignment. To get the space savings, one driver has to be enclosed behind the other driver inside the enclosure (in a constant pressure mode.) If both drivers fire to the outside of the enclosure you will not get an space savings.

laserman · « **Reply #69 on:** 3 Oct 2010, 07:48 pm »

Isobaric (most commonly “push-pull”)

An enclosure that uses two woofers mounted face to face, one wired reverse polarity. This alignment effectively cuts the vas in half. The general rule of thumb for an isobaric enclosure is twice the woofers, twice the power, and generally half the box size of dual acoustic coupled design units.

Pros: Very small enclosures, increased power handling, driver non-linearities canceled out (lower distortion).

Cons: Very low efficiency, due to the small size of the recommended enclosures for some woofers an isobaric alignment may not be practical.

Danny Richie · « **Reply #70 on:** 3 Oct 2010, 07:56 pm »

What laserman said....

Plus the same thing is true for one of these if the woofers are wired so that as one pushes air into the box on one side and the other is pulling air out from the other side. In this case then the box size does need to be half of what it is for a single woofer.

laserman · « **Reply #71 on:** 3 Oct 2010, 07:57 pm »

OR -

There's several ways, they don't have to be face to face. They can be front to back, even back to back.

This one is ported, and it appears to be a shelf port. You could probably do the front port with circular ports. As you can see, the plenum between the two speakers is sealed, this is where the push/pull action occurs.

Go on.......

Danny Richie · « **Reply #72 on:** 3 Oct 2010, 08:01 pm »

Quote from: laserman on 3 Oct 2010, 07:57 pm

OR -

There's several ways, they don't have to be face to face. They can be front to back, even back to back.

This one is ported, and it appears to be a shelf port. You could probably do the front port with circular ports. As you can see, the plenum between the two speakers is sealed, this is where the push/pull action occurs.

Go on.......

Yep, that one cuts the air space in half too.

hayden · « **Reply #73 on:** 3 Oct 2010, 08:12 pm »

Quote from: laserman on 3 Oct 2010, 07:48 pm

Isobaric (most commonly “push-pull”)

An enclosure that uses two woofers mounted face to face, one wired reverse polarity. This alignment effectively cuts the vas in half. The general rule of thumb for an isobaric enclosure is twice the woofers, twice the power, and generally half the box size of dual acoustic coupled design units.

Pros: Very small enclosures, increased power handling, driver non-linearities canceled out (lower distortion).

Cons: Very low efficiency, due to the small size of the recommended enclosures for some woofers an isobaric alignment may not be practical.

Another "con": You would obviously need to purchase two drivers. It really depends on your space requirements. I personally don't think that isobarik alignments provide enough space savings to justify the cost/complexity. You would be better off with a simple dual-opposed set-up unless you are looking to save the extra tiny amount of space.

Oscillate · « **Reply #74 on:** 4 Oct 2010, 04:31 pm »

Danny stated in Reply # 70 "Plus the same thing is true for one of these if the woofers are wired so that as one pushes air
into the box on one side and the other is pulling air out from the other side. In this case then the box size does need to
be half of what it is for a single woofer."

So with all these different expressions of a 'true' isobarik alignment, the internal enclosure size wouldn't be just the volume required
for a single driver ...the internal enclosure volume actually needs to be 1/2 of the (Vas) required for a single driver? ...and that is to
make the air in the enclosure compress quicker, making it more 'springy'? ...allowing the driver cones to return to their normal
positions quicker?

Thanks for clearing up the fog surrounding these alignments

Hank · « **Reply #75 on:** 5 Oct 2010, 05:56 pm »

Quote

I can't do much on the amps as I am having to buy them from Rythmik. I'd have to see if Brian would go in on any discounted deals to make it work.

So, I guess Peter and I are the only ones interested in a servo deal

dvenardos · « **Reply #76 on:** 5 Oct 2010, 06:21 pm »

Lots of people would be interested, however, since Danny isn't having the amps manufactured...

Quote from: Hank on 5 Oct 2010, 05:56 pm

So, I guess Peter and I are the only ones interested in a servo deal

jtwrace · « **Reply #77 on:** 5 Oct 2010, 06:27 pm »

Danny
How about a picture of the underside of the amp?

Any qty discount for them?

Danny Richie · « **Reply #78 on:** 5 Oct 2010, 06:32 pm »

I don't have any pictures of the back side of the amp right now.

Anyone willing to order a lot of anything from me can get a discount.

jtwrace · « **Reply #79 on:** 5 Oct 2010, 08:05 pm »

How deep are the amps? Any with XLR inputs?