Tuning a Cabinet for Drop Tunings

Discussion in 'Amps and Cabs [BG]' started by Barbaric.Eric, Aug 24, 2017.


  1. Hey all,
    I'm working on a cheap little cabinet-swap project and am looking for some suggestions.

    I will be installing 4x 10" Fender speakers (+ tweeter and all electronic guts) into an unloaded Ampeg 410he cabinet, which I got for dirt cheap, thus creating a 4ohm/1000w peak cabinet which matches my Ampeg SVTCL visually.

    I have calculated that the original Fender cabinet was tuned to 58Hz via the shelf port along the bottom. I was going to try and straight match 58Hz with the new cabinet but after some research online this seems a little high.

    I currently have two 4" flared ports coming in the mail which will allow me to tune the Ampeg to anything between 42Hz and 54Hz (due to port length limits and cabinet dimensions).

    I plan on using this with my band that tunes down to Drop C (CGCF) with the occasional drop to A. for that low beefy phatness. I am wondering if a cabinet tuning closer to 42Hz (or alternatively 54Hz) would be more beneficial for drop tuning... or perhaps somewhere in the middle ground? This will be my first project experimenting with cab port tunings so I would like some input on how a slightly lower tuning (or slightly higher tuning) will effect the sound and which would be a wiser starting point considering the low tuning before I start chopping and experimenting.

    Thanks gang!
     
  2. I should also add that while researching I've read that the cabinet tuning doesn't need to have a specific link to the notes you play (random example: If your band plays songs written around the root of A often, it isn't necessarily wise to tune your cab to 55Hz to match that often-used A note). Is this true?
     
  3. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    As far as choosing a tuning frequency goes, here are some things I might look at:

    - How far down is the modeled response at the first overtone of the lowest note you'll be using? Like if the lowest note is drop-A, then how far down is the cab at that 55 Hz first overtone?

    - What does the excursion-limited power handling look like? For instance tuning near 55 Hz might get us the loudest possible first overtone, but at the expense of large excursions if significant energy south of 55 Hz is put into the cab. A good lowpass filter can let you get away with a higher tuning frequency than you otherwise could, otherwise 44 Hz is a probably a good ballpark tuning frequency for drop-A from an excursion standpoint.

    - The general shape of the low-end response curve... for example, I try to avoid a significant falloff in loudness as we walk down the scale, so I don't want a big upper-bass hump, but I don't want a "saddle" in the upper bass either. Those are just my personal preferences. If there's an upper-bass hump, that can limit how much improvement you can make with tone controls or EQ.

    - How important is low-end clarity? In general, the less contribution we have from the port, the better the low-end clarity. Typically a lower-than-optimum tuning frequency will tighten up the low end a bit.
     
  4. Thank you for the input, you're post has shed some light on how to not just take a shot in the dark at tuning.

    Low end clarity is definitely a big one for me so I think my starting point will be 42Hz (which will leave the port tubes the longest so they can always be cut back slightly to tune higher if desired).
     
    DukeLeJeune likes this.
  5. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    Hey it's always a shot in the dark to a certain extent! But you are very welcome.

    If the flared ports coming to you are Precision Ports, their actual internal diameter really is as advertised, 4 inches (such is not always the case with ports). This would give you the option of using expandable plumber's test plugs as port plugs. So you might be able to design the cab to have two usable tuning frequencies: A higher one (both ports open) for gigs where you need all the low end boostage you can get, and then a lower one (one port plugged) for gigs where a tighter low end would work better.

    And you can plug both ports if the room is really boomy.

    Here's a shot of a cab with three 3" Precision Ports, one of which is plugged:

    gi.mpl?u=2112&f=hathor_1533_back.jpg
     
    Last edited: Aug 28, 2017
    Barbaric.Eric likes this.
  6. This is exactly why Talkbass is a great resource, despite various grumblings here and there.




    Bravo Mr. @DukeLeJeune



    :thumbsup:
     
    Barbaric.Eric and DukeLeJeune like this.
  7. BogeyBass

    BogeyBass Inactive

    Sep 14, 2010
    as far as ported for lower tunings, you go down to 30 hz for more transient. but a 30hz driver would be better choice , this is 15" or 18" territory.
    they have 30 hz 10" speakers. sensitivity is low and they loose highend. but 30hz 10" have been used for known ported 10" cabs on market.

    as far as lowering the tuning with a 50/55hz driver for better transient such as the fender factory . lowest i would go would be 45/40 hz and it would improve lower transient for drop tune.

    your mainly hearing second octave in lower notes, so 30ish fundamentally is more 60ish in audible range of those speakers.
    likewise yes the 58hz tuning is in that range so the reflex/ported will have a effect on those note transients. so if you go little lower to 40/45hz transients will slightly improve in the 60 hz range of what your hearing. the lower fundamentals will still cause more excursion though so expect a slight power handling loss with lower tuning.

    rule of thumb is usually no lower than 10hz below driver resonate frequency. likewise above. so if factory is around 58hz assumption without actual data would be a 46/55 resonant frequency driver. most likely tuned at resonance or slightly higher in typical practice. be fair say we are talking a 46 to 53ish driver. again making me assume its bandwith product is on the lower side in the 80s and do fine in sealed too. which i would try before drilling holes.

    but yes good call a flat out 40 or 45 hz tuning is about as low as youd wanna go.
     
    Last edited: Aug 26, 2017
    Barbaric.Eric likes this.
  8. Hey gang,
    Thanks for all the helpful insight thus far, I've been letting it sink in this past week or so. But I do have one more question before I finalize my decision to operate on this cabinet (measure twice, cut once right?)

    So my two 4" flared Precision Ports have been sitting on my kitchen table, and every time I see them they are giving me weird vibes... I have a gut feeling that they are too large (diameter) for this application.

    I know there are downsides to having too small of a port diameter, such as "chuffing", but are there disadvantages to having too large of a port diameter (my uneducated guess: too much boom)?

    I have a couple ads posted right now to sell them to hopefully fund two 3" Precision Ports but I honestly don't feel confident that I'll get any bites, and holy smokes these things are pricey to get into Canada right now. So I am on the fence whether to start cutting holes for the 4"s or take a $$ hit and source out some 3"ers. The Fender guts are already installed in the Ampeg. After work tonight I will be installing the dampening material and giving it a little low volume test-run as a sealed cab, just to hear how the speakers handle it and to see if it sounds any good. But I would like to still port this just to try and match the original Fender cab specs closer, but those two pesky 4" ports have me nervous.

    I'm not sure if this is relevant info for this question, but both ports will be 6" long once installed, they are 4" ports with flared ends out to ~6" at each end to get the desired tuning freq.
     
  9. ThisBass

    ThisBass

    Aug 29, 2012
    Germany
    Unfortunatelly it's nearly impossible to predict "chuffing" with cab modellings.
    Most of the time "random" chuffing is caused by transient noise that is very natural for every stringed instrument. Transient noise is generated by every curve envelope decay and it's frequency range underruns the Fundamental of a played note.

    Port chuffing (if it's an issue) can easily be removed by a HPF you may add to your signal chain.

    No, large port diameter size is not a chance to get too much boom.
     
  10. DukeLeJeune

    DukeLeJeune rational romantic mystic cynical idealist Supporting Member Commercial User

    Nov 24, 2008
    Princeton, Texas
    Owner & designer, AudioKinesis; Auth. mfg, Big E (Home Audio only)
    I would guesstimate the internal volume of the 410he cabinet at 4 cubic feet. Two 4" diameter flared ports, each 6" long, will tune that cab to about 43 Hz. Two smaller diameter ports of the same length will tune it lower, and imo lower is not the direction you want to go.

    The main downside of too large a port diameter is that the require length could end up being too long to fit in your box. That is not the case here. So I don't see any downside to your original port diameter choice.
     
  11. Tuning lower for drop tunings will often result in a reduction in excursion limited power handling in the lower mid-bass. in addition the Xmax of the drivers was chosen for a target deep bass extension. Very often, their Xmax will be insufficient for lower tunings. They'll be fine at low volumes though. But that's probably not what you are after.

    A practical approach with quite satisfying tone is to design for a strong response down to the second harmonic (around 60 Hz), as Duke suggested. This is achievable with a wide range of drivers. OTOH, if you really want some audible fundamental energy into the 30's (Hz) at relatively high sound levels (a very challenging performance goal), you'll need a fairly large box with at least 2 premium, high excursion drivers. And you'll need to do some modeling to get the tuning and box volume right. With the right driver choice it can probably be done with your 410 cab. There will probably be some loss of efficiency and maximum volume.

    Lots to think about. :)
     
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  12. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    I'm concerned that you think this cabinet/driver combination will be good for 1000 watts (RMS), especially with dropped tuning. Educated guess is closer to 500 watts, realistic expectations will go a long way towards your project's survivabity in the real world.
     
  13. blubass

    blubass

    Aug 3, 2007
    Modesto Ca
    Current: Blackstar, DR strings, Nady. Previous endorsements with: GK, Rotosound, Ernie Ball, Cleartone, EMG, Dean, Dava Picks, Rebel Straps, Dickies
    Been there, done that. I've looked for cabinets with lower tunings before I started understanding more about cabinet design and the frequencies that cabinets reproduce. IMO you'd be far better off using a HPF on any cabinet that you like the tone of. Cabinets that handle and reproduce low tunings aren't always tight and articulate at those frequencies. As such, you have a lot of mush in those low frequencies eating up power that could be better used to help the bass cut through at more usable frequencies. Best of luck.
     
    AstroSonic likes this.
  14. If the speakers are suitable for a sealed cab I would install the speakers and leave the cab that way. I have the 410he and tune lower than you guys. I put eminence bp102 200w tens in mine. For my originals hard rock band we use B and low A tunings. I've even messed with low f# in the past. Best option for low tunings imo is actually to run a higher tuned sealed cab on stage, run a xlr to foh so the PA is getting all the 20-100hz content and let the PA do the heavy lifting. Low tuned cabs have their place. They are nice if the bass doesn't run through a PA system with subs. But when combined with a PA system with powerful subs low tuned cabs are more of a headache than a benefit. Low frequencys coming out of the subs bleed back into the stage because basically everything below 100hz is omnidirectional. So if you're standing near the subs you'll hear and feel those super low frequencies anyways. And the low frequency bleed from the PA subs combined with a low tuned cab onstage is a recipe for a muddy sound. When using low tunings you want clarity not mud. Unless you're playing drop tuned reggae or something lol.
     
    Last edited: Sep 4, 2017
    5StringBlues likes this.
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