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Blown Tweeter in an Acme?

Discussion in 'Amps and Cabs [BG]' started by martens-koop, Jul 20, 2004.


  1. martens-koop

    martens-koop

    Oct 10, 2002
    Saskatoon
    Greetings!

    I bought an 8ohm B2 series II used at christmas and have been really blown away by the low end, but not so much by the top end... Geoff St. Germaine came by the shop lately and said that he also noticed that the top end was QUITE lacking in comparison to the other Acmes he has played through... Neither Geoff nor Sheldon could notice a difference as I rolled off and on the attenuators... this was done several times with several different methods of playing (slap, and finger)

    I took the tweeter and the horn out, disconnected them and tested them with a meter, and got a fairly good reading (4 or 6 ohms or something)... I'm wondering if possibly my lightbulbs are blown out.. or possibly the crossover?

    any tips on how to get in there without wrecking anything? -I understand that there's a bit of wacky bracing inside these cabs that should not be messed with... I couldn't find a way to get the back access panel off (the one with the attenuation dials etc..)

    any ideas you have would be really helpfull!

    anyways, all replies are appreciated!!!

    JMK
     
  2. Steve

    Steve

    Aug 10, 2001
    The light bulb is accessed by removing the speaker next to the logo badge.

    The speaker has a sticky gasket that all but glues it to the baffle. You'll probably need to CAREFULLY wedge a screwdriver under the edge of the basket to get it started loose.

    Do yourself a favor and get your replacement bulb from your local Harley-Davidson dealer. They resist the effects of the vibration about 3 time as long as a standard 1156 bulb.

    Can you tell I've changed a BUNCH of Acme bulbs?
     
  3. metron

    metron Fluffy does not agree

    Sep 12, 2003
    Lakewood Colorado
    Give Andy @ Acme a call.
     
  4. Or AcmeBass@aol.com

    Andy replies personally. I read in the manual that it's nearly impossible to blow the tweeter or midrange with the protection circuitry built into the crossover.

    Don't worry too much about poking around inside the cabinet. You'd have a hard time moving any of the braces - they're really wedged in there. It's also a good idea to look around anyway so you're not talking out of your a$$ when people want to know the science of why you sound so good.
     
  5. martens-koop

    martens-koop

    Oct 10, 2002
    Saskatoon
    thanks for the replies... when I had the tweeter and horn out, I was in a hurry, so I never tried to remove the ten inch speakers...

    I was really surprised to see that both the tweeter and the horn had their own special enclosure and that the horn had a bit of fibre glass insulation stuffed into its little cylindrical compartment...

    is this normal for most cabs? (have separated compartments for the different speakers...)

    anyways, next time I have it at the shop I'll open up the cab and look into the lightbulb issue...

    we actually have a harley davidson dealer just up the street... maybe I'll take the bulb in their to see what they know...

    jmk
     
  6. Steve

    Steve

    Aug 10, 2001
    It's not normal only because actual speakers are kind of odd for the high freq. Horns are sealed so it's not an issue but a small speaker will get beat to death by air pressure othewise.

    The Hartke cabs with high freq. speakers are in their own enclosure and I imagine the EA cabs are as well
     
  7. martens-koop

    martens-koop

    Oct 10, 2002
    Saskatoon
    well, I'm happy to announce that I followed everyones advice and pulled out the speakers to reveal that "yes indeed my lightbulb was blown" A replacement bublb revealed sounds and tones from this cab that I didn't even imagine existed...


    next question I need answered is: how much are those speaker cones supposed to move? I can play between the nut and the 5th fret on the G string and they really move like crazy... is that normal?

    also, when playing fairly low (B - E) the speakers distort when I really push them... there is no clipping from either the preamp or the power amp.

    I thought this might be a battery issue on the preamp, but It also does it in passive mode when I crank things... I'll swap out the batteries and see what happens...

    anyways, thanks everyone for all the help!!! jmk
     
  8. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    That's weird!

    Sounds like you're running out of excursion, i.e. you're asking the cab for more bottom than it can provide. Turn down the bass knob, turn down the volume or add a high pass filter to solve the problem.

    Alex
     
  9. metron

    metron Fluffy does not agree

    Sep 12, 2003
    Lakewood Colorado
    The cones in my Acmes moved a ton and I had the same problem with the speakers distorting. They were also never loud enough and I was always buried in the mix. I never had a good experience with the Acmes (including buying them from Andy :rolleyes: ) so I sold them.
     
  10. Ditto Alex...

    The drivers in Acme cabs are capable of moving ALOT. Generally, the longer the excursion, the deeper the frequency being reproduced (it's all about wavelength), so when you beat on the B and it's cranked, it's possible that some subsonic frequencies below 30 hz are trying to come out...possibly a harmonic below the fundamental trying to escape.

    Are you running the Stewart bridged? If not, you may not have enough wattage to properly drive the speakers. Even though the amp isn't clipping, that doesn't necessarily mean you aren't running out of headroom for the speakers.

    Does the Stewart have a High Pass Filter, where frequencies below a certain point will be rolled off? My QSC has filters at 30 hz and 50 hz, so I set it at 30 hz, and get all the fundamental without any of the power hungry subs.
     
  11. Inseam

    Inseam

    Jun 17, 2004
    Pittsburgh, PA
    The Stewart does not have a filter, at least not the Stewart World 1.2.

    It sure helps to cruise these forums! I just got an Acme and had no idea there was a lightbulb in there. Had to do a web search to figure out what you were talking about.
     
  12. martens-koop

    martens-koop

    Oct 10, 2002
    Saskatoon
    my 1.2 does not have a filter... nor does my preamp... incidentally, I have been running bridged.

    today at work (after work in case sheldon is reading this!) I AB'd my newly "fixed" rig against the Eden rig, and then AB'd my stewart into the Acme and my Stewart into the Eden 210... for a while I thought I was going insane, because I absolutely loved the sound of the Eden 210... then I swapped over to the Acme 210, and I loved it too. back and forth I went. eventually I thought my ears must be shot..

    I could TOTALLY hear a massive difference, but I wasn't able to judge which I liked "better". I guess I'd have to say that the Eden cab with my rig had a whole of of snarly rock and roll aggression... whereas I must be noticing (in the acme) what everyone refers to as the uncolored nature of the instrument. wow...

    I think If I played mainly in a rock and roll band, I'd do the Eden, but as most of my playing is church related with a "rock twinge" I'm still happier with the Acme... (to be fair, I have never taken the Eden to church to see what it does there... but a person can handle only SO much fooling around until you say (or your wife says) okay thats enough... just be happy and quit spending money.

    does anyone know how hard it would be to build a low pass filter? (or is it a high pass filter?) I want the one that lets in everything over 30hz!!!

    is it in the realm of a relatively experienced solder-jockey?

    jmk
     
  13. Inseam

    Inseam

    Jun 17, 2004
    Pittsburgh, PA
    I remember reading somewhere that Behringer makes a relatively inexpensive piece of gear that has the filter. I know that name is a dirty word around here, and it might be a whole rackspace thing, but it was $100 or less.

    I'm also curious about filter options in case I need one someday. I've got the Stewart-Acme rig too, but I just got it and don't know if I'll really need to push the cab enough to worry about a filter.
     
  14. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    It's High Pass. You don't specify wether you want active (before amplification) or passive (after amplification), but I strongly advise against passive when your talking about frequencies as low as 30Hz. The parts just get too big, heavy and expensive.

    You can get active filters from Parts Express.
    CLICK HERE and do a search for FMOD.
     
  15. You might also look into crossovers. You could put a crossover between your preamp and power amp, and just run the "high end" to your power amp. Make the crossover point at 30 hz and you're set. HOWEVER, I don't know that anybody makes a crossover with a 30 hz setting.

    The other option might be to get a cheapo graphic or parametric (Presonus EQ3B is $99) Equalizer and CUT everything below 30 hz. Otherwise, you just need to be a lot less agressive with your preamp EQ. See the posts by guyplaysbass, he plays the Low B-4 and will cut his bass freq's and turn his volume up. Acme's behave much differently than most every other cabinet out there...but you've learned that already!
     
  16. martens-koop

    martens-koop

    Oct 10, 2002
    Saskatoon
    hi petebass: I posted a letter, but don't see it up here, so I'll do it again... those Fmod devices look neat.... would you wire it in between the bass and the preamp unit, or between the preamp and the power amp? my inclination would be to put it in right before the power amp...

    the unit seems to be geared more towards line level equipment (it uses RCA connections) does this imply a problem when used in this setting? or does a person just make up a bunch of adapter cables and call it good?

    Mo-Phat: I like your idea about a cheapo parametric eq... I've also thought about a single rack space 1/3 octave eq, but even used, around here those things run about $100... I'm really attracted to the cheaper option... (I've cruised the internet for plans on how to build one, and saw one diagram that looked do-able... but now I can't find that site again!!!

    maybe it was all just a dream...

    jmk
     
  17. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    Dang they are indeed RCA's. I'm pretty sure they come in 1/4" jack as well, but I couldn't see them on the parts express website. Perhaps you could contact them.

    They're designed to go in before the amp.

    The EQ idea is not a bad one. I'm a bit like guyplaysbass in that I tend to cut some lows from my rig with EQ. It works wonders in controling speaker cone excursion. However, if you don't do it correctly, it can rob you of what I believe most acme users were searching for in the first place
     
  18. martens-koop

    martens-koop

    Oct 10, 2002
    Saskatoon
    Hi... I've been looking into high pass filters and am going to try to make my own I think... Because of the slope of cut off and because my math skills aren't the greatest, I came up with a design that uses 28hz as the frequency turning point. using a 390K resister and a 15nF cap.


    I was about to check the availability of these components, when suddenly I realised that there must be dozens of (perhaps even limitless?) combinations to arrive at the same frequency cutoff. Obviously things like the input imedance of the power amp would come into play here. I suppose the output strength of the preamp would also be relavant too... I'm using a Stewart World 1.2 (20K input imedance) and my question is this: does anyone know how to recalculate the component values in order to optimize the results based on the other equipment in the chain?

    should this be on a different thread? or a different forum even?

    thanks... jmk
     
  19. martens-koop

    martens-koop

    Oct 10, 2002
    Saskatoon
    correction... input impedance for the stewart 1.2 is 10K ohms not 20K...


    jmk
     
  20. Tim__x

    Tim__x

    Aug 13, 2002
    Alberta, Canada
    Yes, but more on that later.

    Nope.

    The input-z acts as a resistor in parallel with our filter resistor. So with a 0.47uf Cap and no resistor you'll get a cutoff point of 33.87hrtz. Of course this design is dependant on the power amp you use and if you ever change amps you'll have to redesign it which is why you might want to consider a buffered high-pass.