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Cone excursion question |
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toastyghost ![]() The 10,000 Points Club ![]() ![]() Joined: 09 January 2007 Location: Manchester Status: Offline Points: 10894 |
![]() ![]() ![]() ![]() ![]() Posted: 28 April 2021 at 12:14am |
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The short answer is put your subs where you have to. Fly them if you want, it doesn’t change the fact that the listener is very likely to be essentially ground plane. |
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0krizia ![]() Registered User ![]() ![]() Joined: 15 February 2016 Location: norway Status: Offline Points: 79 |
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Does this mean that subs should not be stacked on top of each other? If the tuning frequency of a sub can be changed by the ground it is placed on, it should become phase issues when subs are stacked
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smitske96 ![]() Young Croc ![]() Joined: 16 February 2016 Location: The Netherlands Status: Offline Points: 1036 |
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This ^^^ My last build had a factor 0,65 difference (+- expected) in regard to the winISD predictions. Eventually nothing beats practice. |
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0krizia ![]() Registered User ![]() ![]() Joined: 15 February 2016 Location: norway Status: Offline Points: 79 |
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I dont have a place to test the sub(s) unless im renting them out, but I placed one in my car, went into the forest where im not bothering anybody and used some test tones through my car amplifier while the back was door open so i could look at the cone from the outside of the car. Ill do another test with the sub outside the car tomorrow or so and see if it makes any difference, thanks for your comment
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JulianDA ![]() Registered User ![]() ![]() Joined: 29 May 2018 Location: Soest, Germany Status: Offline Points: 110 |
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Did you think about the "elongation" of the Port by placing it on the ground? This can quickly result in a tuning that is a few Hz lower than predicted...I would also advise to only use winISD as a tool to get a rough estimation for portlength. Then build a prototype, measure the impedance and correct the portlength so it reaches your desired tuning.
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0krizia ![]() Registered User ![]() ![]() Joined: 15 February 2016 Location: norway Status: Offline Points: 79 |
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Today I downloaded an frequency app where I can play one frequency at the time, it turns out the “new” Winisd is faulty aswell! I gave the sub mentioned in this post about 150w and played one frequency test tone at the time while observing the cone movement close up, the cone was almost standing still at 37-38 hz! That is 4-5hz below what winisd simulation show! The internal volume has everything from wood thickness to handles, ports and driver volume included so the net volum is correct. Looks like im done with winisd, any suggestion for a better more accurate software?
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Meat Substitute ![]() Registered User ![]() ![]() Joined: 10 July 2020 Status: Offline Points: 64 |
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Did you measure the impedance curve of the box you built? As the above poster has said, every nominal tuning of a box I've ever had from a design software has been wrong. If you haven't measured then you should try. Fairly easy to do with some resistors and a multimeter if that's all you have. Once you have the impedance curve, post it up. From that folk here should be able to give you better advice based on the data.
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Elliot Thompson ![]() Old Croc ![]() ![]() Joined: 02 April 2004 Location: United States Status: Offline Points: 5107 |
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I stopped using WinISD nearly 20 years ago because the port tuning was never correct once measured under real-world testing. These were the days when the Pro version was not around. Nevertheless, you would need to know the impedance curve of the driver in the box (I have yet to find a simulator that can get that correct once you literally measure the driver in the box) at the given frequencies. You may be feeding the driver more power than expected. Also, pending on the size in addition to, the thickness of the materials used for the ports, you will lose room in the internal chamber of the cabinet, leaving the driver with less room than you might expect. There are lots of variabilities in which, can be taken into the equation. However, I would suggest venturing to another software and, make a comparison of the two. By doing this, it will confirm if WinISD is indeed the problem or, something else. Best Regards, |
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Elliot Thompson
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0krizia ![]() Registered User ![]() ![]() Joined: 15 February 2016 Location: norway Status: Offline Points: 79 |
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I didnt think of this, im sure this is a part of it.
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0krizia ![]() Registered User ![]() ![]() Joined: 15 February 2016 Location: norway Status: Offline Points: 79 |
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Maybe "moving in free air" was an exaggeration. The reason I was thinking it happens above tuning is because of the large ports. The way I understand the physics of ports is that air compression inside port(s) have a significant impact on cone excursion around port tuning since it determine the air pressure the driver is working in. A 1" port in a dual 18" sub will make the enclosure work more or less like a sealed enclosure, a 10" port in a single 4" sub will make the driver work more or less in free air right above tuning, and in free air at and below tuning. When ports have almost the same surface area as the driver, and when the driver play right above tuning, alot of the pressure escape through the port, if the port(s) are too large, there is next to no compression inside the port so the driver works in an environment with next to no pressure.
Edited by 0krizia - 09 April 2021 at 8:55pm |
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DMorison ![]() Old Croc ![]() Joined: 14 March 2007 Location: Aberdeen Status: Offline Points: 1616 |
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It might just be down to how you are testing this. If you're using sine waves at known voltages (measured after the amp as per madboffin) then yes, something's wrong with either the model or your build. However, if you're using normal program material, then it could just be a side effect of the fact that most (mainstream at least) music styles have much less content down under 40-odd Hz compared to levels higher up, where often the kick drum might be the loudest thing in the bass range, perhaps in the 50-80Hz range, which would explain your findings. HTH, David.
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Peter Jan ![]() Young Croc ![]() ![]() Joined: 16 December 2008 Location: Belgium Status: Offline Points: 1014 |
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Boost at tuning frequency does indeed take advantage of the low cone movement at tuning. One thing has not much to do with the other, the SPL advantage comes from boost at tuning, not from (extra) large ports. You do need to make the ports big enough to avoid chuffing/breathing that could be the result of too much power, compared to port size or I should say port diameter mainly. You do need to make the ports large enough to keep speed of air going back and forth in the port under a certain value... WITH the added boost, because I see people forgetting about that part while simulating. Add 6dB at 42 Hz (your port tuning) also means 4 times the power at 42 Hz and thus 4 times more air pushed back and forth in the port. And something also not so much thought about... when boosting at port resonance, you will feed the speaker voicecoil that much more power (with a capable amplifier) at and around that frequency. The speaker will suffer no ill effect of boosting at port tuning on a mechanical level (keeping excursion at bay), but can easily run over it's electrical limits (burned voicecoil).
The cone will only move less (even about standstill) AT tuning only . A BR port is a very-small- bandpass resonantor, resonating in counterphase with the rear movement of the speaker, thus adding to what comes out of the front of the speaker as a result. Below and above tuning it will have (gradually and fast drooping off) less of an effect. Below tuning it will go out of resonance and start behaving as nothing more than a giant airleak. The frequency of air flowing in and out has become so slow, it just ooses in and out with relative ease. Above tuning, it will also go out of resonance, but the port can't follow the faster moving air going in and out with rising frequency, air comes to an almost standstill and acts as an airplug. The speaker is going to "see" about the same conditions as if the port isn't there / closed off, but still working within the conditions of that "closed-off" enclosure and the amount of cone excursion that result from that particular frequency and the power at that frequency.
"Moving in free air" is going on a bit below the 42 Hz tuning, not above. 55Hz is about completely out of the reach of a 42Hz tuned port, so the cone will move accordingly to the enclosure it sits in and the amount of power fed into it. Also when boosting at port tuning, keep in mind that the boost Q should be pretty high (=narrow bandwidth) or the boost will also have an effect on frequencies a good deal below and above, where the speaker has no (mechanical) benefit of the port anymore, but will move according to the frequency, the power and the condition it sits in. |
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