You need to update your version so that you can specify the density of water also 🙂.
You could always just seal the port with a passive radiator, and wait for the explosion... 🙂
It was about the terminology of fluid/liquid/gas and started while talking about passive radiators, see above. I think its resolved and the "compressibility of liquids" was just a side note.
Oh, I'm still getting educated. Finding papers on the relationship of the active versus the passive cone excursion are not so plentiful. Plenty of simulation math papers. But they start as simulations without any real world examples.
To be clear, I have limited design experience with Passive-Radiators. Designed a few, worked with a few. My poor little brain needs a refresher. And I am trying to find practical applications papers. So many are behind paywalls now. Frustrating! Philips Research which used to be a treasure trove is now gone. Money money money.
I should have phrased differently 🙂 I meant the "fluid/gas/liquid - termonilogy topic" is resolved (in my humble oppinion), not your quest with passive radiators 🙂
I am sure you have gathered a lot - did you alrady stumple acrros this one:
https://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=9148050&fileOId=9148052
Yes, hiding scientific or technical info behind paywals is a counter move against progress....
Are you refering to the Philips Jornal of Research that was discontinued in the 90s ?
oh, in case you are not already into it: Akabak even has a passive radiator element, so you could do simulations with this and investigate the exkursion of it...
I am sure you have gathered a lot - did you alrady stumple acrros this one:
https://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=9148050&fileOId=9148052
Yes, hiding scientific or technical info behind paywals is a counter move against progress....
Are you refering to the Philips Jornal of Research that was discontinued in the 90s ?
oh, in case you are not already into it: Akabak even has a passive radiator element, so you could do simulations with this and investigate the exkursion of it...
No, I have the complete Philips Research journal downloaded when they started to hide it. I was referring to the online availability of Philips research.
As for simulation I do indeed trust David's program. My little brain needs to have a grasp on the mechanics of this. I do understand port unloading and peak flows and such in a vented system. I need to create the mechanical versus theoretical relationships in my mind in order to remember it properly. It is both a handicap, a limitation and a blessing. Once I understand it, I will have it forever, To get that understanding takes a lot of effort looking at and exhausting all the questions I come up with in the process of understanding. It's useful to have an encyclopedic memory. It is not always easy to satisfy the file requirements to get it 😉
If there was a high speed camera recording of a passive radiator system being swept through the various resonance frequencies of the system, so you could see where the driver and PR have their max and min excursions, maybe that would help getting a more intuitive understanding?
I'm working on two PR systems right now. I will try this and see. I'll use the Linkwitz wedge micrometer and try and learn something.
Yes, Davids hornresp is very accurate and very potent 🙂 My mentioning of Akabak evolved from my thinking that Akabak is able to tamper with the different elements of the whole system in more detail and it is almost unlimited in what you can add in terms of parts and elements. Stuff like the pressure differences or the individual excursions and theyr delay dependand on the air-mass load in between the radiators are easy to examine.
I love your approach of completely understanding stuff and building a model in your head. I try to do the same - takes a lot of work initially but once something is fully understood, one knows it for life. Of course - at the same time - the list of things I don't understand is getting bigger - so I never run out of learning-todos for the future... "the more I know, the more I know what I don´t know" 🙂
Hello! If designing an enclosure for a specific range, say 30-100Hz and I input 800W at 8ohm, Xmax is within limits but Driver Power under Tools menu shows a peak exceeding 800W. How should I approach this. I understand that this is a peak at certain frequencies but should I keep it in mind and lower the system input because of this?
Another question - 2 drivers in parallel, as I understand Driver Power shows only one drivers power in this scenario?
Thanks
A
Another question - 2 drivers in parallel, as I understand Driver Power shows only one drivers power in this scenario?
Thanks
A
Probably because impedance is below 8 ohm at that frequency.
Thermal power limit depends on countless factors, such as enclosure ventilation, voice coil movement, duration of power input ....
Depends on how many peaks there are, and by how much they exceed 800W, but to be on the safe side, yes.
(In practice the input signal voltage Eg will be varying not constant, so the peaks may not actually occur that often).
Correct.
Also keep in mind that power rating is very much a thermal thing: how the voice coil heats up and how long it can take that heat. Power rating is typically measured by driving the speaker with band filtered white noise of a certain RMS value for a specified time. (AES standard is 2 hours IIRC.) A driver can take quite high short term power spikes compared to the AES rating. Also, as the driver heats up Re increases and input power goes down (I think HR can take that into account?).
There are so many factors in how much a driver can take in a specific application, including nonlinearity of the driver, nonlinearity of the air flow, how the heat can escape the enclosure, the crest factor of the program material, and so on. So don't rely on any simplistic models of power dissipation for fine tuning. Also remember that HR results are single frequency values, and you would not drive the speaker at full power at a single frequency anyway (unless it was for some non-music application).
The best way (and probably the only reliable way) to test this, if you want to push the limits, is to do a power test according to the standards, and that typically means sacrificing a driver or two in the process.
There are so many factors in how much a driver can take in a specific application, including nonlinearity of the driver, nonlinearity of the air flow, how the heat can escape the enclosure, the crest factor of the program material, and so on. So don't rely on any simplistic models of power dissipation for fine tuning. Also remember that HR results are single frequency values, and you would not drive the speaker at full power at a single frequency anyway (unless it was for some non-music application).
The best way (and probably the only reliable way) to test this, if you want to push the limits, is to do a power test according to the standards, and that typically means sacrificing a driver or two in the process.
https://sengpielaudio.com/calculator-efficiency.htm
Start here.
Then after you pick your jaw up off of the ground think through a few points.
Yes, a loudspeaker is incredibly inefficient. Your 800 watt peak is indeed about 780 watts of heat. Is the voice coil able to dissipate this much power? It literally depends on the duty cycle of the power levels. If there is a 7 db crest factor then you will have at low power point of about 150 watts and a high power point of about 800 watts. The reality is that most loudspeakers in a reasonable sided home are very loud at 30 to 50 watts. And the voice coil is perfectly capable of surviving this.
Determining factors for power handling are many. Size of voice coil being the primary one. But also the diameter of the voice coil wire, the BL factor and the Re. If the manufacturer gives you the B in the gap you can actually reverse calculate a lot of this.
Bjorn mentions power testing. I have done a lot of this. We used to for pro sound applications use pink noise. An evil torture test that kills the best drivers in rather short order. I remember a 100mm voice coil motor that died within 5 hours of 800 watts RMS pink noise. But that told us the absolute limit. When we added crest factors into the mix and realistic drops in output similar to the IEC and AES standard which I discovered later the driver could survive a lot longer.
As a simple point. Don Keele used to test loudspeakers for Audio magazine. He would use a bridged Crown Macro Reference to do impulse testing. Everything survived multiple kilowatts for short musical peak durations. https://www.stereophile.com/content/crown-macro-reference-power-amplifier-measurements
Back in the days when RMS meant something! The amplifier did have a crest factor of 3db so you can do the math.
As a Audio designer I can tell you that to little power is almost always the killer for loudspeakers. That and now with powerful DSP so easy to purchase, incorrectly set limiters for voltage output of the amplifiers.
If you are designing for Pro-Sound or garage band applications there is much more to consider.
Last point I keep seeing repeated is that a bass reflex enclosure has cooling.
In reality is is little to nothing. This depends on the voice coil centring on the magnetic gap centre. Generally a loudspeaker motor is stronger on the pull into the frame direction. I have to work out many perturbations in a motor to get that even for both push and pull. Most manufacturers live with it. You see this on the voice coil offset tests from Klippel. It is this small miss match that is usually less than 1mm that creates an actual air flow in the port.
Think about it. Your diaphragm moves in the ideal world equal amounts forward and rearward. What is pushed out gets sucked back in. The only air exchange will be turbulent flow.
Again apply simple physics for air flow. You cannot force air into a rigid container without there being an inlet, and an outlet. Basic forced air flow principals used all over the world. Air is blown into a room where there is a means for the pressure to be equalized. In colder climates we have a forced warmed air flow, and a cold return in a forced air heating system.
Yes the port is acting as both in a loudspeaker enclosure. Yes there is a air compression. And yes there is a rarefication of the air. The net difference or actual air flow is the offset amount. The volume can be calculated via your SD and multiplying it by 0.1 to 0.3mm. This is the actual theoretical air exchange.
Start here.
Then after you pick your jaw up off of the ground think through a few points.
Yes, a loudspeaker is incredibly inefficient. Your 800 watt peak is indeed about 780 watts of heat. Is the voice coil able to dissipate this much power? It literally depends on the duty cycle of the power levels. If there is a 7 db crest factor then you will have at low power point of about 150 watts and a high power point of about 800 watts. The reality is that most loudspeakers in a reasonable sided home are very loud at 30 to 50 watts. And the voice coil is perfectly capable of surviving this.
Determining factors for power handling are many. Size of voice coil being the primary one. But also the diameter of the voice coil wire, the BL factor and the Re. If the manufacturer gives you the B in the gap you can actually reverse calculate a lot of this.
Bjorn mentions power testing. I have done a lot of this. We used to for pro sound applications use pink noise. An evil torture test that kills the best drivers in rather short order. I remember a 100mm voice coil motor that died within 5 hours of 800 watts RMS pink noise. But that told us the absolute limit. When we added crest factors into the mix and realistic drops in output similar to the IEC and AES standard which I discovered later the driver could survive a lot longer.
As a simple point. Don Keele used to test loudspeakers for Audio magazine. He would use a bridged Crown Macro Reference to do impulse testing. Everything survived multiple kilowatts for short musical peak durations. https://www.stereophile.com/content/crown-macro-reference-power-amplifier-measurements
Back in the days when RMS meant something! The amplifier did have a crest factor of 3db so you can do the math.
As a Audio designer I can tell you that to little power is almost always the killer for loudspeakers. That and now with powerful DSP so easy to purchase, incorrectly set limiters for voltage output of the amplifiers.
If you are designing for Pro-Sound or garage band applications there is much more to consider.
Last point I keep seeing repeated is that a bass reflex enclosure has cooling.
In reality is is little to nothing. This depends on the voice coil centring on the magnetic gap centre. Generally a loudspeaker motor is stronger on the pull into the frame direction. I have to work out many perturbations in a motor to get that even for both push and pull. Most manufacturers live with it. You see this on the voice coil offset tests from Klippel. It is this small miss match that is usually less than 1mm that creates an actual air flow in the port.
Think about it. Your diaphragm moves in the ideal world equal amounts forward and rearward. What is pushed out gets sucked back in. The only air exchange will be turbulent flow.
Again apply simple physics for air flow. You cannot force air into a rigid container without there being an inlet, and an outlet. Basic forced air flow principals used all over the world. Air is blown into a room where there is a means for the pressure to be equalized. In colder climates we have a forced warmed air flow, and a cold return in a forced air heating system.
Yes the port is acting as both in a loudspeaker enclosure. Yes there is a air compression. And yes there is a rarefication of the air. The net difference or actual air flow is the offset amount. The volume can be calculated via your SD and multiplying it by 0.1 to 0.3mm. This is the actual theoretical air exchange.
Re power testing: you're right Mark, pink rather than white noise. But often band pass filtered to the actual working range of the speaker (for single units, probably not for systems). It's noisy. At Celestion we had a separate, well insulated shed outside the factory for this.