subwoofers with dual opposed drivers

[NiagaraPete]

Why neighbour's?

True its fun to piss them off but that could come back to you in ways you don't like.

 

[sarumbear]

It is not used now but it was mainly used in car audio subwoofers. The following is an old Polk design with 4 drivers:

Old School Polk Audio C4 Subwoofer - Four 6x9's in Isobaric Teardrop Enclosure

I wasn't sure if this should go in the Vintage Speaker section or the Car Audio section, but since it's car audio, I decided to put it here.

forum.polkaudio.com

And another one:

Lexus IS-F - 6th order Isobaric Clamshell Bandpass (video page 5)

****DISCLAIMER**** BOX CONFIG SUBJECT TO CHANGE DEPENDING ON HOW IT SOUNDS i am currently ATTEMPTING an oldschool style, Compound (clamshell) Isobaric 6th order Bandpass box. I hope to temporarily put it together outside of the car tomorrow and get and indication of how its going to act. It has t...

www.stevemeadedesigns.com

What a complicated design. What is the benefit?

Isobaric setup effects a driver as follow:

• Vas is halved.
• No is reduced by -3 dB (efficiency).
• Re is halved.
• Le is halved.
• +3 db efficiency for wiring in parallel.

There is no benefit of a isobaric setup other than reducing the enclosure size.

• Advantages :
  • Reduces the box volume to half.
• Disadvantages :
  • The price paid for an extra woofer.
  • Increased difficulty in building the box
  • Amplifier must handle low impedance loads.

 

[Chrise36]

What a complicated design. What is the benefit?

Isobaric setup effects a driver as follow:

• Vas is halved.
• No is reduced by -3 dB (efficiency).
• Re is halved.
• Le is halved.
• +3 db efficiency for wiring in parallel.

There is no benefit of a isobaric setup other than reducing the enclosure size.

• Advantages :
  • Reduces the box volume to half.
• Disadvantages :
  • The price paid for an extra woofer.
  • Increased difficulty in building the box
  • Amplifier must handle low impedance loads.

Size is crucial in car applications. Distortion is supposed to be lower if you can hear any in such low frequencies.Efficiency depends on the tuning of the box you can have great gains in small bandwidth also power handling doubles.My feeling was of a more violent( fast?) reproduction of bass but that is totally subjective.Regarding price you can buy 2 cheap drivers and make one good sub. Also one more negative is amp damping factor is half with half impedance but a class d will not have a problem. If you have 4 ohm drivers you can build either an 8 ohm or a 2 ohm isobaric sub.

 

[sarumbear]

Size is crucial in car applications. Distortion is supposed to be lower if you can hear any in such low frequencies.Efficiency depends on the tuning of the box you can have great gains in small bandwidth also power handling doubles.My feeling was of a more violent( fast?) reproduction of bass but that is totally subjective.Regarding price you can buy 2 cheap drivers and make one good sub. Also one more negative is amp damping factor is half with half impedance but a class d will not have a problem. If you have 4 ohm drivers you can build either an 8 ohm or a 2 ohm isobaric sub.

Power handling doubles but without increase in efficiency what is the point? You just make the amplifier work more.

Why do you say two cheap drivers make a good sub? What parameter of that cheap driver by itself is limiting the sub quality?

 

[Chrise36]

Power handling doubles but without increase in efficiency what is the point? You just make the amplifier work more.

Why do you say two cheap drivers make a good sub? What parameter of that cheap driver by itself is limiting the sub quality?

Usually power handling is what defines prices. Worse power handling usually is cheaper. Regarding efficiency it depends on the design You can have equal or better but in a limited bandwidth. I will try to show you an example when i can.

 

[sarumbear]

Usually power handling is what defines prices. Worse power handling usually is cheaper. Regarding efficiency it depends on the design You can have equal or better but in a limited bandwidth. I will try to show you an example when i can.

When wiring the speaker in parallel the isobaric subwoofer box design has no efficiency loss or gain. The only change is in the Vas.

Vas = 1.4 * 105 *Sd2 * Cms

As it can be seen in the formula above. Altering the cone area of the driver (Sd) or the compliance (Cms), will result in a different Vas. Even though there are 2 speakers, only one is contributing to sound radiation, so the piston size is the same. Now we look at the compliance (Cms). Because the 2 speakers are interconnected by a sealed tunnel between them, their suspension systems are coupled, combining the 2 suspensions, making a twice rigid speaker. In other words, half the compliance. Hence, halving the compliance will only half the Vas value.

 

[abdo123]

What a complicated design. What is the benefit?

Isobaric setup effects a driver as follow:

• Vas is halved.
• No is reduced by -3 dB (efficiency).
• Re is halved.
• Le is halved.
• +3 db efficiency for wiring in parallel.

There is no benefit of a isobaric setup other than reducing the enclosure size.

• Advantages :
  • Reduces the box volume to half.
• Disadvantages :
  • The price paid for an extra woofer.
  • Increased difficulty in building the box
  • Amplifier must handle low impedance loads.

I would really appreciate it if you could make a similar description for dual opposed configuration.

 

[Chrise36]

When wiring the speaker in parallel the isobaric subwoofer box design has no efficiency loss or gain. The only change is in the Vas.

Vas = 1.4 * 105 *Sd2 * Cms

As it can be seen in the formula above. Altering the cone area of the driver (Sd) or the compliance (Cms), will result in a different Vas. Even though there are 2 speakers, only one is contributing to sound radiation, so the piston size is the same. Now we look at the compliance (Cms). Because the 2 speakers are interconnected by a sealed tunnel between them, their suspension systems are coupled, combining the 2 suspensions, making a twice rigid speaker. In other words, half the compliance. Hence, halving the compliance will only half the Vas value.

Yes it is true but we are also adding a bit of mass from the air trapped inside. This halving of the compliance is what i assume to hear as a more instant reproduction but the tuning is what will define the gain for example in this simulation you can tune the box to reach 117 db in 55 hz with rougly 20 liters 4th order isobaric box while with one speaker you are hitting 110db in 47 liters closed box.

 

[sarumbear]

Yes it is true but we are also adding a bit of mass from the air trapped inside. This halving of the compliance is what i assume to hear as a more instant reproduction but the tuning is what will define the gain for example in this simulation you can tune the box to reach 117 db in 55 hz with rougly 20 liters 4th order isobaric box while with one speaker you are hitting 110db in 47 liters closed box.

On principal I won’t comment on subject views. I can say though that Fc doesn’t change with an isobaric setup, nor the maximum sound level. There is just one piston/cone generating sound.

And, the air mass compliance is much much smaller than the Cms of the driver.

 

[sarumbear]

I would really appreciate it if you could make a similar description for dual opposed configuration.

Dual opposed configuration is just two drivers in one box. Standard TS formulas work.

 

[Chromatischism]

Size is crucial in car applications

Also in getting the most out of a box you can actually still ship (PSA).

 

[sarumbear]

Also in getting the most out of a box you can actually still ship (PSA).

Why not use an EQ? Amplifier power is abundant in cars. Only two drivers are generating the sound. Use a stereo amp if you want.

 

[Chromatischism]

Why not use an EQ? Amplifier power is abundant in cars. Only two drivers are generating the sound. Use a stereo amp if you want.

PSA subs are using DSP.

Or are you actually saying EQ can replace more cone area and amplifier power? I am very confused by your statement.

 

[sarumbear]

PSA subs are using DSP.

Or are you actually saying EQ can replace more cone area and amplifier power? I am very confused by your statement.

I am repeating, again. In isobaric the cone area does not increase. Only one of the cones generate the sound waves. What is it that confuses you?

 

[Chromatischism]

I am repeating, again. In isobaric the cone area does not increase. Only one of the cones generate the sound waves. What is it that confuses you?

Ok, but you suggested to just use EQ instead, as if it were a substitute.

 

[sarumbear]

Ok, but you suggested to just use EQ instead, as if it were a substitute.

But it is! The maximum SPL is limited by the driver. The frequency response error that will happen due to smaller than optimum enclosure can be corrected by an EQ/DSP. You just need a higher powered amplifier, which costs less to increase than doubling the driver.

 

[Chrise36]

But it is! The maximum SPL is limited by the driver. The frequency response error that will happen due to smaller than optimum enclosure can be corrected by an EQ/DSP. You just need a higher powered amplifier, which costs less to increase than doubling the driver.

That is too general and might not be necessary in the car because the car amplifies the bass frequencies. That is why closed subs that work in small box were developed. Having the amp draw too much amperage will exhaust your battery. And as i showed before you can make a bery efficient design with huge output from very small boxes with isobaric.

 

[Chromatischism]

I don't know how we got to talking about isobaric subs in a car.

 

[sarumbear]

That is too general and might not be necessary in the car because the car amplifies the bass frequencies. That is why closed subs that work in small box were developed. Having the amp draw too much amperage will exhaust your battery. And as i showed before you can make a bery efficient design with huge output from very small boxes with isobaric.

You showed me an example. How do you know that its an efficient design? If you have the data please share, otherwise you are just assuming. I am instead showing you the math why your assumption is not correct.

Meanwhile, when you parallel the drivers you reduce the resistance hence increase the current drown from the amp. No difference to my suggestion of using a single driver and an EQ, which increases the voltage output of the amp. Result: same battery load.

It is always better to use simple math than assume blind.

 

[sarumbear]

I don't know how we got to talking about isobaric subs in a car.

We are discussing isobarik design, not specifically in a car. I was trying to explain that contrary to some posts on this thread, isobarik is not a design with “opposing” drivers.