Started and finished another audio project yesterday afternoon in 5 hours flat!

[formica]

your current configuration (regardless of wiring) is

not a push/pull configuration. You simply have two drivers sharing the

same sealed cabinet.

Mike is correct in calling it a conventionnal sealed subwoofer using

two drivers. Isobarik configurations are mostly used to reduce

cabinet size while preserving performance, at the cost of an additional

dirver.

ROb

(BTW, for those who didn't catch it, push/pull = isobarik configuration)

[chops]

Ok, first of all your current configuration (regardless of wiring) is

not a push/pull configuration. You simply have two drivers sharing the

same sealed cabinet. And you want to wire the subs such that both

drivers create a positive pressure on the outside of the cabinet at the

same time. If one driver is moving in while the other is moving out

then you will end up with a lot of cancellation and all you will be

hearing is distortion. The whole reason we need cabinets in the first

place is to keep the rear wave away from the front wave.

I have attached a graph that shows your predicted output.

Green = a true isobarik configuration

Blue = your current configuration

The SPL's shown are with 50W of input. The sensitivity for green would

be a peak of 88dB and blue would be a peak of 94dB (6dB loss when

moving to isobarik). Green has an F3 of 40Hz with a Q of .531. Blue has

an F3 of 44Hz with a Q of .781.

If you could post the dimensions of your room and how well you think it

is sealed we can calculate what your performance after room gain might

look like.

So what you are saying is that for me to have a "true" push-pull configuration, one driver has to physically be inverted? I hope so anyway because I'm in the middle of inverting one of them right now! LOL

Anyway, my room is 13x17 with an 8' ceiling. There is a hallway opening in the right rear corner of the room, probably about 25' long. (if that helps at all) []

[formica]

So what you are saying is that for me to have a

"true" push-pull configuration, one driver has to physically be

inverted? I hope so anyway because I'm in the middle of inverting one

of them right now! LOL

Nope... it can be done both ways... as long as they share the same

hole. In other words, you'll have to plug one hole... and install

the two drivers in the other (in your case, face to face is the only

way they'll fit)

ROb

[jacksonbart]

So what you are saying is that for me to have a "true" push-pull configuration, one driver has to physically be inverted? I hope so anyway because I'm in the middle of inverting one of them right now! LOL

Nope... it can be done both ways... as long as they share the same hole. In other words, you'll have to plug one hole... and install the two drivers in the other (in your case, face to face is the only way they'll fit)

ROb

That sounds.... uh.... I hate to say it... kinda gay. Not that there is anything wrong with that.

[chops]

So what you are saying is that for me to have a

"true" push-pull configuration, one driver has to physically be

inverted? I hope so anyway because I'm in the middle of inverting one

of them right now! LOL

Nope... it can be done both ways... as long as they share the same

hole. In other words, you'll have to plug one hole... and install

the two drivers in the other (in your case, face to face is the only

way they'll fit)

ROb

Rob,

You are referring to an isobaric configuration, not push-pull. However, according to DrWho, what I have is still not push-pull. That, I don't understand. [:|]

BTW, I now have one driver physically inverted.

[DrWho]

Output with approximate room gain - same driver assignments:

After room gain green has F3 around 16Hz and Blue has F3 around 23Hz.

[formica]

That sounds.... uh.... I hate to

say it... kinda gay. Not that there is anything wrong with

that.

Actually it does... but it wasn't intentional... [:$]

You are referring to an isobaric configuration, not

push-pull. However, according to DrWho, what I have is still not

push-pull. That, I don't understand. [:|]

It's because they are the same thing... isobarik (or isobaric) is the correct term.

BTW, for those who didn't catch it, push/pull = isobarik configuration

ISOBARIC: (isobarik, compound loading) - a method of

using two drivers working in tandem in order to achieve a smaller box

size for a given design. Theoretically, the Vas of the complete system

will be half that of a single driver, which results in a net box size

that's also reduced by half. The sensitivity of the isobaric system

will be the same as that of a single driver, but you've got to spring

for that extra driver! "Clamshell" mounting, where the two drivers are

mounted face to face and one driver is wired out of phase, seems to the

most popular isobaric system used today, as it is the easiest to build.

[DrWho]

So what you are saying is that for me to have a

"true" push-pull configuration, one driver has to physically be

inverted? I hope so anyway because I'm in the middle of inverting one

of them right now! LOL

Nope... it can be done both ways... as long as they share the same

hole. In other words, you'll have to plug one hole... and install

the two drivers in the other (in your case, face to face is the only

way they'll fit)

ROb

Rob,

You are referring to an isobaric configuration, not push-pull. However, according to DrWho, what I have is still not push-pull. That, I don't understand. [:|]

BTW, I now have one driver physically inverted.

Isobarik and Push-Pull are two terms that mean the same thing. I notice

your Danmarx.org reference uses the term "push/pull" in conjuction with

compound loading. It is the only website I've seen push/pull associated

with compound loading, but I suppose I can see how they came to that

conclusion.

Anyways, let's use the proper terms....now that one of your drivers is

inverted you have moved to a compound loading situation - though the

benefits of compound loading are best exhibited when both drivers are

mounted on the same baffle near each other. The idea is that the cone

flexes differently when being pulled in that when pushing air out -

causing some nonlinear distortion. By inverting one of the drivers you

end up with each driver exhibiting different distortions in such a way

that there is phase cancellation (only with the nonlinear distortions).

The rest of the original acoustic signal sums just fine.

Both isobarik and compound mounting schemes result in the same cancellation of distortion.

(btw, I'm not sure compound is the proper term either for inverting one of the drivers...but I have seen it used more often that way).

[Guest " "]

chops, your last sentence is the key to how this experiment is setup.

you provided a couple of links to some sites that were pretty good...and some would do well to review those links.

my expectation is that if these are wired traditionally, and installed traditionally, they will move in the same direction relative to the surface they are mounted to, but not move the same relative to each other.

which would sound better? ...hard to say...I think the way you first had them would sound good if the cabinet size divided by 2 is adequate for the woofers you installed. but according to the links you provided...an actual push-pull, allows the use of smaller cabs, and yes, they swing in the same physical direction. but keep in mind...there is the consideration about the main speaker closest to the out of phase driver...and some possible cancellation of low end near the crossover points if a gentle slope xover is being used.

[Guest " "]

DrWho, I like your explination...any predictions about sound pressure levels using isobarik/compound approach? is it reasonable that although distortion is cancelled out and the quality of sound may be dramatic...there may be reduced sound pressure levels than a traditional config.

[chops]

DrWho, which version of WinISD are you using? I have the Pro version and am trying to figure out how you got the room gain?

[DrWho]

Add a linkwitz transform with .707 for both Q's. F0 should be the frequency that has the wavelength of the longest dimension of your room (in your case, 40Hz?). And then you set the F1 anywhere between 10 and 30Hz depending on how well sealed your room is. I did 24Hz in your case? Whatever results in 10dB at 20Hz. I don't remember off the top of my head.

[DrWho]

DrWho, I like your explination...any

predictions about sound pressure levels using isobarik/compound

approach? is it reasonable that although distortion is cancelled out

and the quality of sound may be dramatic...there may be reduced sound

pressure levels than a traditional config.

Isobarik results in the same maxSPL as a single driver, but requires

double the amplifier power. Another way to think about it is that it is

6dB quieter than a cabinet twice the size (both drivers mounted

normally).

[Clarence]

heee he you said linkwitz...

[Guest " "]

That explains my years gone back experience.

I was expecting more bass at the same power levels or higher power levels.....I got less bass...but did not realize it was cleaner bass with less distortion....so when I rewired traditionally and thought i was getting more bass at the same power levels or at a higher power level...I was actually hearing the uncanceled distortion which gave the perception it was louder.

[chops]

Add a linkwitz transform with .707 for both Q's. F0 should be the frequency that has the wavelength of the longest dimension of your room (in your case, 40Hz?). And then you set the F1 anywhere between 10 and 30Hz depending on how well sealed your room is. I did 24Hz in your case? Whatever results in 10dB at 20Hz. I don't remember off the top of my head.

Cool. Thanks!

I do have a few questions...

So when you entered my sub's information, you did it as a 6.3 cu.ft. enclosure with 2 Dayton drivers, right? (I just want to make sure I'm doing it right on my computer)

Depending on how well sealed the room is, do I go higher or lower from 10-30Hz? IOW, if my room isn't very sealed at all, do I go towards 30Hz more or 10Hz?

And what did you mean by "Whatever results in 10dB at 20Hz"?

Do you think that the hallway in the right rear corner of my room in anyway influences the "F0" at all?

The reason I ask that last question is because this sub is putting out some seriously low bass below 16Hz to the point that you ONLY feel it and hear various things around the house oscillating at unknown frequencies. []

Thanks again!

[colterphoto1]

Chops- kudos for speed and all, but are those really being held together with silicone caulk and drywall screws without any glue or screw blocks? Has your other cabinet of similar construction held up well? I can't help but think that this might self destruct when used in a subwoofer cabinet.

Or is that wood glue that I see in the photo?

M

[DrWho]

Add a linkwitz transform with .707 for both Q's. F0 should be the frequency that has the wavelength of the longest dimension of your room (in your case, 40Hz?). And then you set the F1 anywhere between 10 and 30Hz depending on how well sealed your room is. I did 24Hz in your case? Whatever results in 10dB at 20Hz. I don't remember off the top of my head.

Cool. Thanks!

I do have a few questions...

So when you entered my sub's information, you did it as a 6.3 cu.ft. enclosure with 2 Dayton drivers, right? (I just want to make sure I'm doing it right on my computer)

Depending on how well sealed the room is, do I go higher or lower from 10-30Hz? IOW, if my room isn't very sealed at all, do I go towards 30Hz more or 10Hz?

And what did you mean by "Whatever results in 10dB at 20Hz"?

Do you think that the hallway in the right rear corner of my room in anyway influences the "F0" at all?

The reason I ask that last question is because this sub is putting out some seriously low bass below 16Hz to the point that you ONLY feel it and hear various things around the house oscillating at unknown frequencies. []

Thanks again!

I entered your information with a 6.3 cubic foot cabinet.

The less sealed your room is, the less room gain you experience...so move towards 30Hz.

Whatever results in 10dB at 20Hz means to pick an F0 such that you are getting 10dB of gain at 20Hz....you'll notice that as you move the dial around you get more/less gain at 20Hz. 10dB is just the typical average gain in most rooms.

As far as how low your sub is hitting...well...I would take some measurements before you start making the claims. At least for starters list the music you are listening to and run it through some waterfall plots to see what it's frequency content actually is. And then if you can measure from the listening position you can get an idea of how the system behaves with musical information (by looking at the difference of the two measurements).

I'm not saying it doesn't dig low - I'm just saying that it's struggling at the lower frequencies (much less control) and that there are some psychoacoustics involved that make room gain seem unnatural...basically conlcuding that it's better to have a sub that is flat to 20Hz anechoic than a sub that is 14dB down at 20Hz anechoic. And there are plenty on the forum that disagree with me too so whatever.

[chops]

I entered your information with a 6.3 cubic foot cabinet.

The less sealed your room is, the less room gain you experience...so move towards 30Hz.

Whatever results in 10dB at 20Hz means to pick an F0 such that you are getting 10dB of gain at 20Hz....you'll notice that as you move the dial around you get more/less gain at 20Hz. 10dB is just the typical average gain in most rooms.

As far as how low your sub is hitting...well...I would take some measurements before you start making the claims. At least for starters list the music you are listening to and run it through some waterfall plots to see what it's frequency content actually is. And then if you can measure from the listening position you can get an idea of how the system behaves with musical information (by looking at the difference of the two measurements).

I'm not saying it doesn't dig low - I'm just saying that it's struggling at the lower frequencies (much less control) and that there are some psychoacoustics involved that make room gain seem unnatural...basically conlcuding that it's better to have a sub that is flat to 20Hz anechoic than a sub that is 14dB down at 20Hz anechoic. And there are plenty on the forum that disagree with me too so whatever.

Understood about the room gain setting.

The 10dB at 20Hz thing I'll have to play around with to figure out exactly what you're talking about.

All I have to take measurements with anymore is my old Rat Shack spl meter. I'll have to dig up that correction guide for it so the readings will be somewhat accurate. As far as music, most of it is pipe organ, most of which are pipe organs that are capable of 16Hz at Low CCC, and a couple that are capable of 8Hz. However, some of the recordings pick up the sound of the tremolo, which depending on it's speed will produce a beat somewhere between 10-15Hz. I also have a couple of test CDs (Chesky, Stereophile, Telarc) that I can try, one of which has a signal all the way down to 5Hz.

As for making waterfall plots of any of these, I have no way of doing that. I wish I did though. Is there any free software out there that can do this?

"I'm just saying that it's struggling at the lower frequencies (much

less control) and that there are some psychoacoustics involved that

make room gain seem unnatural"

I wouldn't say that the sub is struggling, especially being the fact that even at the loudest levels, I'm only pushing about 50 watts into the sub, and I can visually see the drivers moving only about a .25" MAX, which that's down around 16-20Hz. That's only about 8mm, and if I remember correctly, these subs can handle 15mm x-max.

And true, I may be wrong about this sub going as low as I think, but I'm sure happy with it. It is definately cleaner, tighter, quicker, more accurate and hits harder than the SVS PB12-ISD/2 did. At any rate, this sub is leaving a smile on my face.

[chops]

This is what I have come up with. Also, according to the calculator in this link, the F0 should be 66Hz for my room...

However, when I put 66Hz into the Linkwitz transform, it says that my sub is down -3dB at 14.69Hz! [*-)][8-)]

Everything between both the blue and yellow are identical except for the F0.

http://www.sengpielaudio.com/calculator-wavelength.htm