Dual passive AV15 sub


  • Member
    dB on #1413

    @teecee wrote:

    How do you technically explain the passive?

    This is the first time I’ve made a box sealed, ported it, and then put in the PRs. It’s good to witness the changes.

    See this thread for a little more info. I’ll be putting up tech articals soon to further explain. Lot happening at the moment.

    http://www.aespeakers.com/phpbb2/viewtopic.php?t=353


    Member
    paulspencer on #1414

    100% of ALL vents compress. Most compress significantly well before the user is aware they are. I’ve measured significant port compression with vents as large as 1/2 the diameter of the driver at levels you would be surprised to see.

    100% of drivers, and 100% of ports and 100% of passive radiators have power compression! The question is do vented subs have more compression than passive radiator subs?

    Now there are a few secrets I won’t divulge.

    I don’t see how you can claim they are linear without backing that statement up. I also don’t see why this would be a secret if you have this information.

    True enough. Unfortunately many end users will continue pushing their systems well after the onset of significant levels of distortion. The human ear is fairly insensitive to L.F. distortion products (by virtue of being relatively insensitive to L.F. period) AND most peoples ears aren’t trained to detect significant L.F. distortion

    This depends on who you are talking about. If an acoustic double bass musician listens to classical or jazz music with instruments reproduced they hear all the time, their ears are trained by the original to hear what it sounds like. Very LF – well, we lack reference points to compare LFE sound effects. When it comes to comparing subwoofers, it depends on what you are used to hearing. Many are not used to hearing low distortion bass.

    I do think low distortion in subs is still more imprortant than most think. One reason relates to the FM curve. The bottom octave appears to be where there is most distortion. Harmonic distortion products occur higher in the spectrum, well outside the passband of the subwoofer, up in the range where the ear is more sensitive. Hence the distortion product can be more audible than the fundamental! Consider a 40 Hz tone – 5th order distortion products will be at 200 Hz!


    Member
    dB on #1415

    @paulspencer wrote:

    @paulspencer wrote:

    100% of drivers, and 100% of ports and 100% of passive radiators have power compression! The question is do vented subs have more compression than passive radiator subs?

    I’m tired and not don’t have the energy to argue. Ports can work well. PR’s can too. However, every single comparison between two different systems – 100% – will have different results if the compared systems are different.

    Ports can be excessively non-linear. PR’s can be pushed into non linearity. I’ll try to find the numbers to a few AES papers you ought to read on the subject. Unfurtunately I cannot divulge any of the port vs PR studies I performed while at my previous employer. If you’d like you can ask Thomas Danley of Servo Drive how linear ports are. In fact ask him about the measurements he performed that absolutely baffled and stumped him…

    For most intents and purposes, people using typical 3″ and 4″ diameter ports on 12″ or larger subs between 2.5 and 5 cubes, a correctly implemented passive radiator has far less compression.

    If I get time – just for you – outside of trying to get some leggs back under AE, I’ll re-creat a few of my previous studies with my own gear so I won’t be enchroaching on my previous employers intellectual property rights.

    FYI I have a patent pending on a port variant – I’ve studdied and studdied and studdied the merrits and demmerrits of ports and PR’s. Both have strengths and both have weaknesses. The average even AVID hobbiest however WOULD be surprised at how signifigant ports compress. I used two very short 4″ diameter very double flared ports for a pair of modest excursion 10″ midbass drivers in a 4 cubic foot net box, and was still un-sattisfied with the port compression. Any more area though and I ran into too many internal port resonances / cabinet mode pile-ups…

    I’m guessing in your mind one well designed 4″ double flared port with 2 cubes per 10″ driver should be adequate? In my case I had to live with them as I ran out of time.

    @paulspencer wrote:

    I don’t see how you can claim they are linear without backing that statement up. I also don’t see why this would be a secret if you have this information.

    Because I am legally not allowed to divulge that information – and John and I JUST yesterday cemented our intent for this relationship – and neither of us has ever outside of my last job performed studdies we can publically release. Chances are we will be too busy to in the iommediate future.

    @paulspencer wrote:

    Many are not used to hearing low distortion bass.

    Very much true. FYI I use acoustic bass players for double blind listening – their ears are quick to pick out delayed or smeared transients.

    @paulspencer wrote:

    I do think low distortion in subs is still more imprortant than most think. One reason relates to the FM curve. The bottom octave appears to be where there is most distortion. Harmonic distortion products occur higher in the spectrum, well outside the passband of the subwoofer, up in the range where the ear is more sensitive. Hence the distortion product can be more audible than the fundamental! Consider a 40 Hz tone – 5th order distortion products will be at 200 Hz!

    ABSOLUTELY agreed – and the reason John and I are trying to make this thing work. Far too many consumers have never even HEARD the bottom octave reproduced at anything but whisper levels, and equate doubling and trippling to ‘bass’. Your typical boombox baby.

    I am very very tired – John and I were up till 3 a.m. working on A.E. and got up at 6 am.

    Hang out a while – you’ll get to know me. Better yet, head over to DIYSubwoofers and pull off posts under my name from 6 years ago – you’ll get a feel for where I stand and likely not feel such need to call me out.

    Here’s a link:

    http://tinyurl.com/95ytd

    please keep in mind I was still a DIY zealot while I made most of those posts.

    I generally use double passives the next size up from the driver with PR’s and ports almost half the diameter of the drive unit if porting..

    Anyway – am signing off for now. Happy viewing.


    Member
    paulspencer on #1416

    Deon,

    When you are tired and cranky its easy for disagreeing as prodding or arguing fo the sake of arguing. We don’t know each other, but I’m not the kind of person who is argumentative, looking to debate for the sake of debate, or waste people’s time. Although in this thread I’ve been more argumentative than usual.

    My view has been that PRs are worthwhile only where you can’t implement a vent that doesn’t chuff. So far I haven’t seen anything to demonstrate superior performance of PRs.

    I have felt that vents often get bad press, not so much due to their failings, but due to poor design and implementation. I’d be interested to conduct blind listenting tests comparing sealed vs vented subs where they are calibrated to the same response. I may at some point conduct a study like that.

    Thanks for the links. I’m out of time now, but I’ll certainly have a look when I get the chance.

    Another person to share the load at AE speaksers seems a welcome change. I have been wondering for a while now when John would get someone else in, as has clearly been over-stretched.


    Member
    TeeCee on #1417

    @db wrote:

    @teecee wrote:

    How do you technically explain the passive?

    This is the first time I’ve made a box sealed, ported it, and then put in the PRs. It’s good to witness the changes.

    See this thread for a little more info. I’ll be putting up tech articals soon to further explain. Lot happening at the moment.

    http://www.aespeakers.com/phpbb2/viewtopic.php?t=353

    That information explaining how ports work is very interesting. It really seems rather simple when explained that way.

    What I didn’t understand is that cone excusrsion is reduced due to (in the case of a PR) the vacuum put on the box by a PR. My question was if a port did the same thing.

    I guess what’s so curious is that no matter how you orient the PR or port, the PR’s motion or the port’s action is always in phase with the active with respect to the volume of the box. It seems like it would have varying phase depending on it’s orientation with respect to the active.

    What about phase with respect to a room? Does it make more sense to locate ports or PRs on the same wall of an enclosure as the active? Does it matter at all?

    What’s also so curious is that the resonance created by the port or PR is greater than the damping effect on the active. Well at certain frequencies surrounding the enclosures tuned frequency.

    Is any of that in the right direction or am I not getting it?


    Member
    dB on #1418

    @teecee wrote:

    What I didn’t understand is that cone excusrsion is reduced due to (in the case of a PR) the vacuum put on the box by a PR. My question was if a port did the same thing.

    Yes. While in phase they are both compressing and rarefacting the air inside the enclosure – which reduces the drivers cone motion. At and around Fb, the port and active are in phase just as a PR and active are, below Fb they become more and more out of phase till they are both 180 out – at which point the driver is completely unloaded by the back air spring. You’ve heard people talk about being carefull Not to drive a system too hard below Fb I’m sure.

    @teecee wrote:

    I guess what’s so curious is that no matter how you orient the PR or port, the PR’s motion or the port’s action is always in phase with the active with respect to the volume of the box. It seems like it would have varying phase depending on it’s orientation with respect to the active.

    Location in enclosure has little effect on the phase. Driver electromotive strength, driver Fo, mechanical and electromagnetic Q, springiness of the internal airspring of the box, and the lossy-ness of the port or passive, along with the surface area of said port/passive all effect ‘phase’ and ‘Q’ of the ported system.

    @teecee wrote:

    What about phase with respect to a room? Does it make more sense to locate ports or PRs on the same wall of an enclosure as the active? Does it matter at all?

    Generally people aim ports in a different direction than intended listener, as high frequencies and internal box noises can leak out the port if any are made. As to whether it’s better to aim at the listener or not – a 20hz signal is some 56 odd feet long. 40hz some 28 feet. Orientation doesn’t matter for acoustics so much as room shape and size, location of sub in room, and listeners location relative to all three.

    @teecee wrote:

    What’s also so curious is that the resonance created by the port or PR is greater than the damping effect on the active. Well at certain frequencies surrounding the enclosures tuned frequency.

    And as a result – it what reduces the drivers cone motion around Fb. This is exactly the ‘trick’ that allows the ported enclosure to generate more SPL at it’s resonance than a sealed system.

    @teecee wrote:

    Is any of that in the right direction or am I not getting it?

    Your learning 🙂


    Member
    R. Buszka on #1419

    Technically, a reflex box is a complicated mass-spring system. The enclosure contains the active driver, a confined mass of air, and some type of passive radiator (whether it be a weighted diaphragm or the air mass contained in your more typical port tube — the term “passive radiator” is usually used to refer to the diaphragm type but it can mean both for technical purposes). The woofer cone moves, and the compression and rarefaction of the air inside the box sets the passive radiator in motion. As the frequency gets closer to the tuning frequency, the passive radiator and the box begin to resonate more and more, and this resonant action works to damp the motion of the driver cone, and minimize its excursion. At the tuning frequency of the box, the excursion of the passive radiator being used is at a maximum, and the excursion of the driver is then at a minimum, because the air in the box is already being pressurized by the passive radiator to the point where the woofer cone can’t move as much. The result is much greater low frequency output, but the resonant nature of this output means that transient response is not quite as good as with a sealed box. I have a theory, however, about why the big passive diaphragms can have a sealed-box sound: As the mass of the diaphragms gets larger and larger, it gets harder and harder to move them from rest until you get really close to the tuning frequency, and then they start doing their thing. I really like my 3 cubic foot box with the AE Speakers AV12 and the two 15″ 1400g AE Speakers passive radiators, driven with 500 watts. It’s a combination that seems balanced and synergistic, and it gives me more output than I could hope to use in my little room.

    Sorry, I took too long to write my little explanation.


    Member
    paulspencer on #1420

    Deon,

    I’ve had a chance to read some of your posts on diysubwoofers.org and find that I tend to agree on most of what you have written there that I’ve seen.

    I’m guessing in your mind one well designed 4″ double flared port with 2 cubes per 10″ driver should be adequate? In my case I had to live with them as I ran out of time.

    A member of the diy audio forum has done some experiments on port chuffing, and has come up with some formulas. For a given vent diameter and flare radius he has come up with formulas to determine maximum velocity where chuffing will become just audible. He’s made a calculator tool, which is handy.

    http://www.users.bigpond.com/bcolliso/port-flares.htm

    An example:
    4″ vent with 36mm flare radius >>> 21m/s is the max
    A high excursion 10″ could probably get quite a bit more velocity than that.

    I think a 4″ vent with some 72mm flares could work ok for the AV12 (I’ve tried it) but there is still some compromise – 150mm vent would be more like it, but that just gets huge.

    If you have any more info or links on studies in port/PR compression I’d be very intersted to see it.

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