View Full Version : >>> Need Isobaric Help <<<

O.G. D-Wet
06-09-2010, 02:35 AM
Sorry, when I originally posted this I was REALLLY messed up lastnight! So please excuse any of that BS...

Anyway, my question is about the 3dB loss... I keep reading about a 3dB loss in isobaric applications...
So say I have a sub on 1000w in a car metering 140. This sub is being run off a friend's amp. He needs the amp back but the only amp I have is 2000w amp. So instead of investing in a new amp, I get another sub and change my setup to isobaric BUT still keeping a constant 1000w on each sub... SO my question is, when I get metered again, I will only hit around 137dB??? Or is the decibel loss thing more complicated then that? I'm just kind of curious why anyone would ever iso-load their subs if there's no advantage cept a smaller enclosure

O.G. D-Wet
06-09-2010, 02:51 AM

06-09-2010, 02:55 AM
What da fawk did i just read?

06-09-2010, 03:51 AM

06-09-2010, 08:09 AM
With modern subs, why waste efficiency with isobaric loading? :)

O.G. D-Wet
06-09-2010, 03:42 PM

06-09-2010, 03:57 PM

Isobaric relies on the other sub creating opposing pressure inside the box to decrease enclosure requirements. However, since you added a second woofer you have to power it as well with equal power to your first. Since your power is being split in half you now have a 3db loss in terms of effeciency, you have to put in 2000 watts to the system to get the same output as 1000 in the bigger box. Since your splitting power though, you have 2x the powerhandling. So once you put in enough power to get the pair to have equal power to the original single, you get the same SPL. If your in a situation where you can drop your amps impedence and double power this works fine. Nothing is actually quieter in this case, you simply have to put more power into the system since the woofers aren't working together and you have to power both. Max SPL between 2 woofers iso and a single in 2x the box volume is the same, you just need 2x the power to get there.

However, it does have advantages. From a SQ perspective even order distortion get cancelled out. Also, you can fit designs that wouldn't fit any other way. Let's say you want a 6th order bandpass and you model it to find out you need 8cubes net between the 2 chambers and your working in a trunk. If you want that design to fit isobaric would be the way to go.

Another cute trick is to build a box that normally requires 1 sub. Say 5 cubes net for a 15 is all you can fit. Then, add in 3 extra speakers for a double isobaric loading basically. power. Sensitivity, efficiency, frequency response remains the same, max power quadruples and max output level increases by 6 dB.

Easy way to run 2 15's in an area that can barely support one. Car audio has so much cabin gain that a falling frequency response in a car isn't a big deal. If you actually graph alot of enclosures that people build you'll notice they don't play very low at all. In the home 4 cubes for a 15 or 18 in some cases on here would sound like crap and have no low end bass. That's part of why you don't see isobaric much. That and speaker designers have been designing subs to fit into small spaces and just take retard amounts of power before they break. That's been the trend since kicker in the early nineties.

Anyway in your case your score will change. Your power doubled so you'll still be pushing the woofers just as hard, but the mechanical compliance is way different due to the isobaric loading.

O.G. D-Wet
06-09-2010, 04:06 PM
so then ur NOT actually LOSING 3dB on the meter, correct? just in terms of efficiency. So If I went from one sub sealed to two subs iso sealed, my TL score wouldn't drop from the single sub sealed, correct?

06-09-2010, 04:06 PM
WHy not just keep the sub you have and just set gains to only run 1000 to it?

O.G. D-Wet
06-09-2010, 04:08 PM
WHy not just keep the sub you have and just set gains to only run 1000 to it?

then the enclosure stays the same size... This isn't an issue I'm actually having, It's just a question. I keep reading about isobaric losing 3dB and I'm just trying to understand how that dB is being lost