Higher Effiency vs Lower Ohm Load

[1aespinoza 10+ year member]

Is it just me? Isn't this common knowledge for the old heads on here??

TBH I assumed the higher power handling in a sealed enclosure was due to cone travel limitations. I also do understand that higher power going through a voicecoil creates higher inductance which correlates with higher impedance. So if you need higher power to move a sub in a sealed enclosure it will directly affect impedance. I assume that is what is colloquially termed as "box rise".

 

[Jimi77 5,000+ posts]

TBH I assumed the higher power handling in a sealed enclosure was due to cone travel limitations. I also do understand that higher power going through a voicecoil creates higher inductance which correlates with higher impedance. So if you need higher power to move a sub in a sealed enclosure it will directly affect impedance. I assume that is what is colloquially termed as "box rise".

Now we're talking about 2 types of power handling - mechanical vs thermal. Power handling may increase in a sealed enclosure due to limiting cone travel. In the case of a ported enclosure, thermal power handling increases (at FB) because the port introduces a peak in impedance. So hypothetically, a 1 ohm sub could read 5 ohms at the port frequency. This allows competitors to blast a 2kw sub with 10kw from the amp and everybody "ohs and ahs" about how XYZ sub can take so much over rated power, when in reality the sub was really getting something closer to rated power. You can model the change in impedance in box building software - I'm pretty sure winISD gives you the impedance curve based on the enclosure and you'll see it change as you alter the enclosure. You see some pretty impressive results from bandpass enclosures with small drivers because they have 2 peaks to play with.

Bose made a really high q sub for OEM systems (~1.0), which is another way to play with impedance curves. The Q and highish FS on the sub allowed it get pretty loud for a wimpy OEM sub. The sub had a peaky impedance curve, then you cram it in small sealed enclosure and the impedance curve gets even more peaky. That allowed Bose to bass boost into the frequence and the sub had pretty impressive output for what it was. There was a thread about that sub on DIYMA if you want to learn a little more about how you can use impedance curves to "cheat" the system.

 

[1aespinoza 10+ year member]

You see some pretty impressive results from bandpass enclosures with small drivers because they have 2 peaks to play with.

So this is the reason HexiBase gets good results with small drivers.

 

[metalheadjoe 10+ year member]

So you're unaware that a subwoofer's impedance changes in an enclosure? Okay.

I thought this was common knowledge. For example, tuning a ported enclosure introduces a spike in the impedance curve, which is why one can make a sub handle 3,4,5x "rated power" for burps. This is why subs can handle 2x what they might handle in sealed enclosure when placed in a peaky ported enclosure. Is it just me? Isn't this common knowledge for the old heads on here???

I'm aware of the common misconception parroted by people without any proof or understanding. I have yet to see any evidence that such a phenomenon exists. It would be easy to prove: put a subwoofer in a box and measure power at a given frequency. Put the subwoofer in a different box and measure power at the same frequency.

Subs handle over rated for burps because they are burps. "Isn't this common knowledge for the old heads on here???" I understand you're trying to rally support because you can't offer any logic, theory, or evidence.

TBH I assumed the higher power handling in a sealed enclosure was due to cone travel limitations. I also do understand that higher power going through a voicecoil creates higher inductance which correlates with higher impedance. So if you need higher power to move a sub in a sealed enclosure it will directly affect impedance. I assume that is what is colloquially termed as "box rise".

You assumed correctly. The difference in output is because a sealed box becomes a vacuum as the sub extends and becomes pressurized as the sub retracts. The box pressure wants to hold the sub in place.

How does higher power create higher inductance?

Now we're talking about 2 types of power handling - mechanical vs thermal. Power handling may increase in a sealed enclosure due to limiting cone travel. In the case of a ported enclosure, thermal power handling increases (at FB) because the port introduces a peak in impedance. So hypothetically, a 1 ohm sub could read 5 ohms at the port frequency. This allows competitors to blast a 2kw sub with 10kw from the amp and everybody "ohs and ahs" about how XYZ sub can take so much over rated power, when in reality the sub was really getting something closer to rated power. You can model the change in impedance in box building software - I'm pretty sure winISD gives you the impedance curve based on the enclosure and you'll see it change as you alter the enclosure. You see some pretty impressive results from bandpass enclosures with small drivers because they have 2 peaks to play with.

Bose made a really high q sub for OEM systems (~1.0), which is another way to play with impedance curves. The Q and highish FS on the sub allowed it get pretty loud for a wimpy OEM sub. The sub had a peaky impedance curve, then you cram it in small sealed enclosure and the impedance curve gets even more peaky. That allowed Bose to bass boost into the frequence and the sub had pretty impressive output for what it was. There was a thread about that sub on DIYMA if you want to learn a little more about how you can use impedance curves to "cheat" the system.

Impedance is a function of frequency. That's why your 1 ohm sub could present a 5 ohm load at port frequency or at any other frequency depending on the coil. Frequency changes impedance, not the box.

I'll give you the benefit of the doubt and assume you meant "blast a 2kw sub from a 10kw amp", because as stated you contradict yourself in the same sentence. That 10k amp is meant to put out 10k at a certain impedance. I agree that the amp will not make 10k at all impedances. Again, the amp's output depends on frequency, not the box.

Common knowledge can be wrong.

 

[1aespinoza 10+ year member]

How does higher power create higher inductance?

 

[metalheadjoe 10+ year member]

View attachment 59100

I know about eli the iceman. I thought we were talking specifically about inductors (coils) and alternating current. Tell me about power, not current.

 

[spokey9 5,000+ posts]

Speaker impedance curve explained with examples - Audio Judgement

The impedance chart of speakers holds valuable information. Speaker impedance curve explained so anyone can understand.

audiojudgement.com

 

[metalheadjoe 10+ year member]

I don't understand why everyone is so defensive. I am here to learn and don't mind being corrected

Speaker impedance curve explained with examples - Audio Judgement

The impedance chart of speakers holds valuable information. Speaker impedance curve explained so anyone can understand.

audiojudgement.com

Your article confirms that impedance varies with frequency.

 

[1aespinoza 10+ year member]

I know about eli the iceman. I thought we were talking specifically about inductors (coils) and alternating current. Tell me about power, not current.

Well current and voltage make power; and an amplifier's output is AC. The voicecoil is an inductor inside of a ferrite core like a toroud. Only difference is this core is magnetized to repel the voicecoil whereas the toroid's core becomes temporarily magnetized.

 

[Jimi77 5,000+ posts]

I'm aware of the common misconception parroted by people without any proof or understanding. I have yet to see any evidence that such a phenomenon exists. It would be easy to prove: put a subwoofer in a box and measure power at a given frequency. Put the subwoofer in a different box and measure power at the same frequency.

Subs handle over rated for burps because they are burps. "Isn't this common knowledge for the old heads on here???" I understand you're trying to rally support because you can't offer any logic, theory, or evidence.

You assumed correctly. The difference in output is because a sealed box becomes a vacuum as the sub extends and becomes pressurized as the sub retracts. The box pressure wants to hold the sub in place.

How does higher power create higher inductance?

Impedance is a function of frequency. That's why your 1 ohm sub could present a 5 ohm load at port frequency or at any other frequency depending on the coil. Frequency changes impedance, not the box.

I'll give you the benefit of the doubt and assume you meant "blast a 2kw sub from a 10kw amp", because as stated you contradict yourself in the same sentence. That 10k amp is meant to put out 10k at a certain impedance. I agree that the amp will not make 10k at all impedances. Again, the amp's output depends on frequency, not the box.

Common knowledge can be wrong.

And the frequency where impedance will peak can be changed by the enclosure. How much the impedance will peak can be changed by the enclosure. By changing orders, we can introduce multiple peaks in response. The impedance will always be higher in an enclosure than free-air/IB, unless there some enclosure affect I'm unaware of.

Are you denying that enclosures change impedance curves?

 

[metalheadjoe 10+ year member]

And the frequency where impedance will peak can be changed by the enclosure. How much the impedance will peak can be changed by the enclosure. By changing orders, we can introduce multiple peaks in response. The impedance will always be higher in an enclosure than free-air/IB, unless there some enclosure affect I'm unaware of.

Are you denying that enclosures change impedance curves?

Impedance is not impacted by enclosures. I thought I was very clear about that. Prove me wrong rather than assuming common misconceptions are facts.

 

[spokey9 5,000+ posts]

I don't understand why everyone is so defensive. I am here to learn and don't mind being corrected

Your article confirms that impedance varies with frequency.

The enclosure affects resonate frequency and that in turns effects impedence across frequencies.

it's part of the reason when you take a true 4 ohm sub (for example) place it in a box and play music the impedence would rarely show 4 ohm. Even with a tone the same sub in the same box would show the 4ohm until the coils started to heat up then you'd see rise there as well.

It's a big reason why you can sometimes cheat an amp by wiring lower than it's rated because the box is part of the driver and affects the impedence the amp will see

 

[metalheadjoe 10+ year member]

The enclosure affects resonate frequency and that in turns effects impedence across frequencies.

it's part of the reason when you take a true 4 ohm sub (for example) place it in a box and play music the impedence would rarely show 4 ohm. Even with a tone the same sub in the same box would show the 4ohm until the coils started to heat up then you'd see rise there as well.

It's a big reason why you can sometimes cheat an amp by wiring lower than it's rated because the box is part of the driver and affects the impedence the amp will see

Resonant frequency can refer to vibrations or electronics. I agree enclosure can impact resonant frequency in terms of vibrations. Vibrations don't have anything to do with impedance. If you are saying a box changes electrical characteristics of a circuit, tell me how. The commonly-quoted misconception is that box impacts impedance, which is the electronics use of the term.

How about this: Tell me how a box impacts impedance without mentioning frequency. It is ACTUALLY proven that impedance is a function of frequency, so let's exclude that and stay focused the "box rise" misconception. Show me a circuit where a sub played at a frequency in box-A has a different impedance than the same sub played at the same frequency in box-B.

 

[spokey9 5,000+ posts]

Considering impedance changes as the coil moves...anything that effects coil movement (like a box) effects impedance...

 

[Jimi77 5,000+ posts]

Here’s impedance plots using speakerboxlite and an Alpine Type R sub. The impedance is altered when the sub is placed in different enclosures.

Red = ported, Green = sealed, Orange = IB/free air, Blue is band pass.