Asymmetrical force on the driver, creating distortion (linear as well as IMD)
As well as limiting the xmax.
Use push-pull compound woofers (f2f mounted) for a halved Vas, in case you want a compact enclosure.
Isobaric is obsolete design that is a total waste of a woofer. You are able to match the output of the isobaric with a single woofer in the same box with simple bass boost equalization. Isobaric was done to avoid equalization. It's a bad idea. The limit to the bass output at low frequency is set by the Xmax of the woofer. Putting two woofers in an isobaric configuration achieves the same Xmax and total displacement as with a single woofer. It's dumb and a waste of money. Go look at WinISD and plot the max SPL curves for single woofer and dual woofer in isobaric configuration. It will be identical for any woofer with decent power handling used below 100Hz. I can think of only one company selling a sub woofer with this design for a very good reason. It provides no performance advantage unless you are building a passive subwoofer and must avoid any bass boost equalization at all costs to fit with the audiophile zero equalization single amplifier paradigm.
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More or less what's written in the post above.
With active EQ you can simply get the same freq resp, without an additional woofer as well as wasting power, since you loose quite a bit of sensitivity.
I was under the impression the OP already had more than couple of woofers. Yes, it is basically a waste of hardware, I agree. But here isobaric and PP compound seem to be mixed up. PP compound is not isobaric!
In case you have the necessary hardware, i.e 4 woofers, whereas cabinet size is a major consideration, PP compound (which is not isobaric, which indeed is bull) gives you the same sensitivity and output as a single woofer, but in half the box size, because of the halved Vas of the PP config. Sensitivity does not change as long as te woofers are connected in parallel, but antiphase.
In case you have the necessary hardware, i.e 4 woofers, whereas cabinet size is a major consideration, PP compound (which is not isobaric, which indeed is bull) gives you the same sensitivity and output as a single woofer, but in half the box size, because of the halved Vas of the PP config. Sensitivity does not change as long as te woofers are connected in parallel, but antiphase.
It's either isobaric, or just two woofers working together in a box?
All other ways are fancy names to say the same thing.
The first post is obviously about making a box smaller, therefor the question if isobaric is a good idea.
If M&K is that exactly or not, is not really relevant.
Since a isobaric construction is the same as halving the Vas, our efficiency goes down.
Which again, can be seen if you just simply open a simple software program and simulate the whole thing.
This is the maxSPL of a single woofer vs isobaric setup;
yellow = isobaric
orange = single woofer
So again, in an active subwoofer cabinet, it doesn't make ANY sense to go for isobaric.
Unless you like to waste 4 times more power (it's squared) and waste money on a second woofer.
All other ways are fancy names to say the same thing.
The first post is obviously about making a box smaller, therefor the question if isobaric is a good idea.
If M&K is that exactly or not, is not really relevant.
Since a isobaric construction is the same as halving the Vas, our efficiency goes down.
Which again, can be seen if you just simply open a simple software program and simulate the whole thing.
This is the maxSPL of a single woofer vs isobaric setup;
yellow = isobaric
orange = single woofer
So again, in an active subwoofer cabinet, it doesn't make ANY sense to go for isobaric.
Unless you like to waste 4 times more power (it's squared) and waste money on a second woofer.
The M&K is 2 woofers working together in a box.
Isobarik is mostly about trying to make a smaller box with the woofers you have.
But what hgas been said about there being modern woofers that can achieve the same box size & capability. Without EQ. EQ is a red herring in this case. A tool that can be used on any woofer.
The one thing that is usually ignored is that isobarik will isolate the box somewhat from the driver radiating into free air.
Isobarik has overhead… the small chamber that creates the compound driver. This makes them impractical for small Vas drivers.
dave
Isobarik is mostly about trying to make a smaller box with the woofers you have.
But what hgas been said about there being modern woofers that can achieve the same box size & capability. Without EQ. EQ is a red herring in this case. A tool that can be used on any woofer.
The one thing that is usually ignored is that isobarik will isolate the box somewhat from the driver radiating into free air.
Isobarik has overhead… the small chamber that creates the compound driver. This makes them impractical for small Vas drivers.
dave
I don't really follow what you're trying to say?
I think the use case is pretty simple;
We have a certain budget plus a certain size box that needs to be small.
How can we accomplish this.
Sure, you can do it by wasting extra power and money with a passive approach which is called isobaric.
Or actually do it the smart way, and just EQ it.
What is done now, like usually, is that people go to town with pages and pages of theories.
All nice, but it doesn't help the original problem and it mostly just makes everything very confusing.
Making a very simple problem extremely convoluted.
If you have two woofers already anyway, you might as well put them both in a small box and EQ them.
Even with old woofers this can be done (beats me what the age of the woofer has to do with this?)
That option would still be more beneficial than a isobaric approach.
EQ'ing is a fundamental part of speaker design, not just a "after thought" to compensate little things.
Therefor extremely relevant to the original question actually.
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Many posts suggest EQ is needed to do what isobatrik does, bit that is not the case. EQ is irrelevant to the discussion.
Now, in most rooms, since the room is usually a compromise, EQ is helpful in dealing with anomalies caused by the room. Doesn’t matter the woofer. It is a bandaid for the room. I started with the room design, and do not find any bneed for EQ. Maybe i will need it when i have 4 subwoofers and get response WAY down.
dave
I think you still don't understand what EQ can do.
EQ is extremely relevant to this discussion, that is not a matter of opinion.
EQ is relevant in ANY discussion when someone wants to fit something in a small box.
Things like Linkwitz-Transform can be used. Not only to extend the freq range, but also to compensate.
If that is not available, just a bunch of param EQ's can do exactly the same trick.
Or just any other EQ compensation, either boost or cut.
Possibilities are vast.
If you think EQ only has the function of fixing room anomalies, I would very highly suggested diving a bit deeper in what EQ can do.
Because than you have an awful lot to learn.
Like I said in my previous post, it is fundamental part of the entire speaker design, most definitely not just a band aid.
Efficiency (SPL per Watt) is halved but power handling is doubled.
Also, maximum displacement of two isobaric drivers is same as with single driver.
Not correct. Max SPL is equal. For above two reasons.
Not correct. You need two times more power for same SPL.
You should always try to acheive the required goals without EQ, and then you add teh band-aid. I won’t argue that it can be a powerful tool, but only as a last resort.
Do we even know yet what woofers? And available space? Didn’t see those defined.
dave
Do we even know yet what woofers? And available space? Didn’t see those defined.
dave
I guess math and simulation programs are lying than?
Bastards.... can't trust science anymore these days...
Same SPL, same excursion, same response, this is power graph (well VA graph), green is isobaric.
The other two are LT and a same response made with param EQ's.
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When it introduces loss of information into the system. Which it does in many cases.
EQ is a tool, not a panecea.
dave
EQ is a tool, not a panecea.
dave