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Port or leave it alone?

Discussion in 'Amps and Cabs [BG]' started by Stinsok, Jan 22, 2004.


  1. Stinsok

    Stinsok Supporting Member

    Dec 16, 2002
    Central Alabama
    A buddy of mine has a Hartke 2x10 transporter cabinet. It is a sealed design and he asked if porting would make a positive difference in the sound. I told him wait before doing anything because I could get some advice from the good and knowlegeable cabinet builders on the forum. What do you think?
     
  2. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    If he's going to leave the existing speakers in it, I'd say leave it as a sealed cab.

    The designers would have calculated the Efficiency Bandwidth Product (EBP) of the speakers to determine wether or not the cab should be sealed or ported.

    The formula is:- fs/Qes.

    Consensus is < 50 is usually good for sealed and > 100 is suited to ported enclosures.

    So if you take speakers with an EBP <50 and put them in a ported cab, prepare to be underwhelmed.

    The conception that ported speakers are automatically bettter than sealed cabinets isn't necessarily true. My home Hi-Fi sub sounds pretty darn good and it's a sealed cab. It's all about the overal design!
     
  3. Stinsok

    Stinsok Supporting Member

    Dec 16, 2002
    Central Alabama
    Cool, thanks for the reply. "As is" I would describe the cabinet as have more punch than low end. He was using it in conjunction with a 1x15 cabinet, but is thinking he wants to use the 2x10 by itself.
     
  4. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Fair enough. I guess we could find out the T/S parameters of the speakers (if Hartke will release them), then decide wether to use those drivers or buy a couple of 10's better suited for bottom end, then do some calcs on the porting. I'm happy to help but......

    I'm not a fan of using 2x10's on their own unless you're playing quiet gigs only. Even my Eden 2x10 struggles as a stand alone at volume, and that's one of the better 2x10's on the market. Anything we come up with is going to have the same problem.

    Has he tried using the 15 as a stand alone? If it has a horn for the highs, some 15's sound fine on their own with some EQ tweaks. Certainly more usable than a 2x10.

    The other option is to sell his cabs and buy a 4x10.
     
  5. notanaggie

    notanaggie Guest

    Sep 30, 2003
    One good reason for leaving it alone is that a sealed speaker cab has good cone motion control. The air pressure in the cab tends to prevent the cones from moving too far.

    If you port it, below some frequency the cones will have nothing controlling their movement. The cabinet power handling at low frequencies will probably be a lot lower to avoid over-excursion.

    The Hartke folks would have ported it if they could have got better performance that way. Since they didn't, it is doubtful that you will.

    I tried lots of that kind of mod years ago. Most of them ended up worse than where I was before I did it.

    I'd leave it, and if I couldn't stand the cabs, I'd trade them in against something I liked, or sell them.

    BTW, your description of "more punch than low end" would go for just about any Hartke cabs I have messed with. I think they were really developed for the popping style player, and so they have a ton of spank, but not a lot of boom.
     
  6. Stinsok

    Stinsok Supporting Member

    Dec 16, 2002
    Central Alabama
    I looked that particular cabinet up on their website. I wouldn't mess with it either.
     
  7. McHack

    McHack

    Jul 29, 2003
    Central Ohio!
    Drivers that are selected to go into ported cabs, don't necessarily have the same structurally rigid cone,, of a driver in a ported box.

    Ported boxes, really allow the cone to move ALOT, where Suspension boxes (non-ported) boxes have a fixed amount of air inside,, & rely on that air-suspension to keep the cone from farting all over the place...

    If you port,, a suspension cab,, you'll make it fart ALOT earlier than it normally would.
     
  8. Stinsok

    Stinsok Supporting Member

    Dec 16, 2002
    Central Alabama
    Thing one thing he understands is Farting.
     
  9. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    you can't simply port an existing enclosure. Porting will require a different air volume for the enclosure as well, which is typically greater in volume than the same cone in a sealed box. Ever notice how shelf-ported or tube ported cabs are much deeper than sealed cabs? In makes for more airspace.

    You'd basically have to build a new enclosure from scratch or end up with a cab that either wouldn't go low or would blow the cones.
     
  10. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    That's not exactly true. Both ported and sealed cabs use the air behind the cab as a spring. The speaker actually moves LESS in a ported cab if the frequencies fed to it are at the cab's tuning frequency (Fb)or above. Below Fb, the speaker loses the air spring and flaps and farts like crazy. Fart volume depends entirely on how much baked beans you're putting into it.

    Sealed cabs are simpler. The speaker just moves more as the frequency gets lower.

    So if you fed a 40Hz signal into both a sealed and ported cab tuned to 40Hz, the sealed speaker will move much further. Actually the ported speaker will barely move at all. The port will be doing all the work. At this point the cone itself is under a lot of pressure so the cones have to be strong enough to withstand the forces or they will crease or worse.
     
  11. notanaggie

    notanaggie Guest

    Sep 30, 2003
    Pretty true as an explanation, although not how it would be described technically

    May be true, might NOT be true. Often the speaker will move a lot more at some frequency above the box tuning. So you can have a fart-out at a higher frequency if that is true...it may run out of excursion before the assist from the port is effective.

    That's true............at very low lows the speaker just pumps air in and out of the port.




    Actually, maybe not, since the pressure created in the box by movement may hold it back.

    But to keep up with the same acoustic output, yes the speaker has to move farther and farther. At half the frequency it has to move 4 times as far for same acoustic power output.

    Whether the box volume will let it move that far is another story.

    The ELF system effectively feeds more and more power in at the rolloff rate to make a small sealed box produce lows. But eventually it farts out.
    Aint nothing but a horn or a lot of cone area that will really boom with no flapping.

    Check out the Phil Jones folded horn cab....it oughtta tear down walls. Speakers radiate direct in front, but are coupled to a long folded horn behind......I wanna try one.
     
  12. McHack

    McHack

    Jul 29, 2003
    Central Ohio!
    heh, I posted this from work, & didn't have time to elaborate in detail... However, I merely wanted to stress the point that, you shouldn't just port your suspension boxes...

    For all of the detailed reasons we've explained.

    To simplify, just don't do it...
     
  13. Stinsok

    Stinsok Supporting Member

    Dec 16, 2002
    Central Alabama
    Turns out there is another piece to the puzzle. The 10'' drivers in the cabinet are NOT Hartke. Someone replaced them with 2 Dayton Loudspeaker aluminum drivers. As of right now I cannot find any information on them (discontinued?) Anyone know anything about these?
     
  14. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I think Dayton is an OEM brand for Parts Express. Check www.partsexpress.com. I believe that someone told me that Dayton brand speakers are actually made by Eminence.

    If it really is an Eminence and there's an Eminence type spec. number on them...generally a silver label stuck on the edge of the magnet, you can send an email to info@eminence.com and ask for the T-S parameters. You have to have the spec. number, they won't know what you're talking about without it.
     
  15. ESP-LTD

    ESP-LTD

    Sep 9, 2001
    Idaho
    MCM Electronics has some-

    Aluminum cone drivers . I used some of these years ago in sealed boxes (they had a Qts of .5 or better). The rest of the aluminum cone speakers that had had REALLY high Qts figures.

    If memory serves I put a pair in a sealed 2.25' box which had a q of about .7 ; they sounded fine with a 4 string but were about 92db so not that loud; I finally smoked them with too much power for an extended period. I recall at the time thinking they were pretty similar to the Hartke Transporter series. You might see if MCM willl tell you the T/S parameters; I don't have them anymore.
     
  16. Stinsok

    Stinsok Supporting Member

    Dec 16, 2002
    Central Alabama
    Ok folks I need your help. My computer is out and I cannot run WinISD and I can't download it on this computer (work.) Can someone run some numbers for me? Here is what I have for the Dayton 10'' aluminum cone speakers(per Parts Express.)
    Fs:32.5
    SPL: 93.6 1W/1m
    Vas:3.39 cu. ft.
    Qms:.74
    Qes:.23
    Qts:.18
    Xmax: 3.3mm

    The cabinet dimensions are:
    24'' wide
    14" tall
    12'' deep
    Made outof 3/4 plywood.

    I dont have the means to drill any ports bigger than 2". Can someone tell me the port diameters that would work in this situation? Thanks again! :help:
     
  17. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    There's barely enough info there to work with but I've had a go at it.

    By my calcs that cab is about 58 litres.

    First of all those speakers will work better with a ported cab. At the moment that cab is -3dB at 150Hz and -10dB at 58Hz. Which certainly fits my description of "no bottom end".

    I'd port the cab, tuning it to 70Hz. This will yield a -3dB point of 64Hz and -10dB at 53. There's also a slight hump at 78Hz. Still not earth shattering but much better than what he's got now.

    You say you can drill holes up to 2" in diameter. To make it as easy as possible, I've calculated the ports so they are 3/4 of an inch in length, the same as your plywood thickness. That way all you have to do is drill the holes and the plywood itself becomes the vent tube. You will need 3 round holes, each of them 1.82 inches (47mm) in diameter.

    I prefer ports on the front but it's not crucial. If there's no room, put them at the back. Either way, make sure the ports are not obstructed while playing. So if they end up at the back, make sure the cab is at least 2 or three inches away from the back wall while the cab is in use.

    If you can find any more T/S data, let me know and I'll run more scenarios. I'd particularly like to test for cone excursion.
     
  18. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I've never come across that before. I gave it a try and if it's true, asks for a single port that's 0.88235294 in in diameter, and naturally .75 inches long. (0.882355294 * 0.85 = 0.75)

    A port that size would whistle as the air escapes the cab.

    I cheat. I use WinISD Pro for my vent calcs. The formulas in Vance Dickasons book are great but I find it too time consuming when trying to do the math on multiple ports.
     
  19. Stinsok

    Stinsok Supporting Member

    Dec 16, 2002
    Central Alabama
    Thanks very much for the help. The TS parameters I listed were all the information available.