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Group Delay

Discussion in 'Amps and Cabs [BG]' started by warwickbass, Mar 28, 2003.


  1. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    Ok I know what group delay is, and have read that 25ms is bad, resulting in mud. But whats good, whats avarage... what about 22, 20, 18? and so on.

    And while im at it, i couldent find much on the "Phase Plot" in the WinISD help file or here on Talkbass.

    And Xmax... i read that 5.5mm is bare min for bass, but whats good? especially for a B-string.

    Thanks.
     
  2. Chuck M

    Chuck M Supporting Member

    May 2, 2000
    San Antonio, Texas
    I'm familier with most tech terms used in describing the performance of amplifiers, however, I've never heard of group delay. Could you be referring to slew rate?

    Chuck
     
  3. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    This is form one of bgavin's posts

    And one of the tabs on the plot window of WinISD is a graph for "group delay"
     
  4. Group delay is a defined term that represents the slope of the phase response.

    Phase is the time difference (delay) between the signal at the amp vs the signal as produced by the speaker cone. A 25ms delay means the signal produced by the cone is 25ms later (behind) the signal at the amp. This amount of delay is perceived as significant mud or blurring. GD is frequency dependent, and sounds blurry because the bass is "late" and the highs are "on time".

    Sealed boxes have much lower (less) group delay than vented boxes.

    GD in vented boxes peaks at/below the tuning frequency and GD varies by driver. The JBL E145 in SBB4 is 9.89 msec at 31 Hz. The Eminence Magnum 15LF is 16.17 msec at 31 Hz. The JBL E155 in vented SBB4 is 8.0 msec, which is typical of a good sealed box design. The Delta 15a in optimal-flat vented is 25 msec at 31 Hz.
     
  5. Captain Awesome

    Captain Awesome

    Apr 2, 2001
    PDX
    Bgavin --Do you have the group delay of the Eminence Kappa Pro 15 LF?

    Also, is group delay a big deal for frequencies above 40 Hz?
     
  6. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    So should i be to the understanding that i should shoot for around 8ms to get good crisp clear bass?

    > 25 Bad
    |
    |
    > 15 Good
    |
    |
    > 8 Best

    Would this then be accurate?
     
  7. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    My thread's Still kickin :bassist: ...Bump...
     
  8. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    That's a good little diagram actually. I just happen to have a 15" JBL E145 as mentioned in Bgavin's example, built a cab for it, and it's a monster. No mud, but big , pant flapping botttom end that would compete with some 18's. My eminence loaded Fender cab sounds like a wet fart in comparison.

    Primusdude asked about the relevance of 40hz. This is open to debate by I believe group delay is relevant for all frequencies under 100hz. It's dependant on the frequency that the box is tuned to. Not a lot of commercially available bass cabs are tuned to 30hz. Say for example the box is tuned to 50hz, then group delay would come into play at somewhere at 50hz and below. So it would likely to have a relevant group delay at 40hz.

    Having said that, some people like it muddy. There's a lot of room for personal preference in bass sound.
     
  9. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    ok cool now that thats taken care of (thanks by the way) any takers on the Xmax And Phase Plot.

    ya ... Groop delay is only a problem if the little graph says it is.

    p.s. this is all in prep for a cab im gonna build for a low B. im gonna try and make it collapsible, that way i can have a low and loud cab and it dosent matter all too much how big it is. its gonna be a pain but im gonna give it my best shot.
     
  10. Here is the GD plot for the Kappa Pro 15LF in both Flat and BB4 alignments:

    Link to Kappa Pro 15LF Group Delay Plots

    The BB4/SBB4 alignments are similar to the D2 sealed alignments: both have the tighest (fastest) group delays.

    The vented BB4 tuning is 2.91 cubic feet at 46 Hz.
     
  11. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    Your all most likely sick of lookin at this thread, But im gonna give it one last shot. Someone here has to have some info on my other two questions (maybe i should post them seprately :rolleyes: I'll try that later maybe). So here it goes...

    ... Bump ...
     
  12. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Dude your questions are more involved than you realise. I'm far from a guru on the subject and I've spent hours and hours reading books and researching internet sites. I still only understand half of the science involved. What I'm trying to say is that there are no short answers and there's more to T/S perameters than "what Xmax is best for 5 string".

    I'l try and explain Xmax - maximum speaker movement before the speaker starts to fail and/or distort. There is no magic figure here because different manufacturers achieve their 31.5hz frequency different ways. You can line up 5 different speakers capable of 31.5hz and they'll all have different Xmax. The trick is to note Xmax and make sure you stay within it. This is done by having correct box volume and porting (if applicable).

    I don't fully understand Phase so I'm not even going to try and explain.

    Have a look through This Website for further info.
     
  13. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    I understand what Xmax is.. i just dont know how to apply it... i dont know hot to tell if X ammount of millameters Xmax will be enough for this or that speaker to produce X frequency at what ever volume... or what ever else is involved in figureing out how long my Xmax needs to be. If that makes any sence to ya.

    I intend on buying "the loudspeaker design cookbook" but im currently really low on cash so im trying to get done what i can. basicly every thing i know is from this site and the web. (find myself schooling my friends and the dudes at GC now :cool: .

    As far as i can tell WinISD does not factor in the Xmax of the given speaker in any way what so ever. unless im missing something.

    And the Phase Plot i havent seen anything on that anywhere becides WinISD, which just gives me the graph and no insight on whats up with it. so i just figured I'd toss that out there.

    I am however very thankfull to everyone who has helped me here. and I will check out that site you linked as soon as i have the free time.
     
  14. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    Ha ha i just clicked on that link of yours.... i actually just posted that on talkbass about a week ago telling people they should check it out. I didnt find a whole lot usefull to me at the moment.... but definately future use of that site. I'll give it another look tho and see if I missed somehting usefull to me at the moment.
     
  15. Captain Awesome

    Captain Awesome

    Apr 2, 2001
    PDX
    Xmax is the maximum linear excursion of the driver, also called the "voice coil overhang." AFAIK Xmax is the distance the cone can travel, in one direction while still under the voice coil's complete control. Xmech, on the other hand is how far the cone can actually travel, in both directions, without starting to fart or eventually cause damage. The Xmech is typically a lot longer than the Xmax.

    I have an Avatar 2x10 cabinet loaded with Eminence Delta 10's. On the Eminence website it lists the Xmax as something pretty short, like 1.6 mm. The Xmech is a lot longer, like 20mm or something. I know I can push the speakers a lot more then the Xmax and the volume continues to increase without any farting or audible distortion, and as far as I know it hasn't caused any damage at all.
     
  16. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    I'm reading it as we speak. The info comes thick and fast and it's a heavy read. It requires a fair bit of assumed knowledge and the language is not as simple as it could be. I'm planning to go back and re-read it once I've finished so hopefully more of it will sink in.
     
  17. geshel

    geshel

    Oct 2, 2001
    Seattle
    Whether or not an Xmax is "enough" depends on the box you put it in. What you need to do is, get a graph of cone excursion v. frequency at a given power. For this, you need WinISD Pro, which I think is just in Alpha. With this, you can put in a power level, and see how far the cone moves at a given frequency. If it's outside of Xmax, it'll be at least somewhat distorted. If it's outside of Xmech, the driver will bottom out and possibly get damaged.

    So, one driver might have a higher Xmax than another, but require a box that allows more cone motion, and actually distort earlier than the other one! It's all very interactive.

    As for the "phase plot", I don't think it'll be too useful for you. Actually, Group Delay is just another (more useful) way of looking at the phase! The Group Delay is just the slope (angle) of the trace on the phase plot. So, more drastic changes in phase yield higher group delay.

    The phase plot would be useful if you were combining two cabinets that were to cover the same range - you'd want to make sure that they're not going to be more than 90 degrees or so out of phase with one another.
     
  18. warwickbass

    warwickbass

    Dec 8, 2001
    Minnesota
    You mean they took the little "cone excursion v. frequency at a given power" graph out of WinISD when they made the second one :confused: . That however is exactly what im lookin for.

    I cant believe thats what the phase plot is for, i was like.... the only phase I know about is if two different speakers are in phase with each other. With my obviously limited knowledge the graph didnt look like it would have anything to do with that. Shows ya how bad i need to get a job and to buy that book.

    I noticed that most speaker sites dont list Xmech, why is this.. i would assume that once i download the old version of WinISD that I would most likely need the Xmech along with the Xmax of the given driver to find out if it will work for me.

    Oh well Ill do that when i get the chance and hopefully i wont have to badger you guys with my thread anymore :D . You were all very helpfull tho thank you very much.
     
  19. You can get an Xmax plot from Robert Bullocks "DOS BOX" program, or Brian Steele's spread sheet.

    Link to The Above on My Site

    All T/S data is only relevant at 1 watt, or what they call "small signal" level. Xmax will never be exceeded at 1 watt.

    Xmax is the maximum amount of voice coil movement (1-way) where the same amount of voice coil remains in the gap, as does at rest. When you push the coil farther out, less of the coil is in the magnetic gap, and this introduces non-linear behavior.

    Link to Xmax Types


    There are three types of Xmax arrangements. Underhung, Equal, and Overhung. The link above is to an obsolete JBL tech note that shows each type, and the JBL driver associated with that type. The E145 is largely underhung, which is the most expensive method, but also provides cone control. Note that JBL uses the word "overhang" interchangeably from opposite points of view. The long gap, shorter coil arrangement of the E145 type is "underhung".