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Rules of thumb for how many drivers to order for a project?

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  • Rules of thumb for how many drivers to order for a project?

    Looking to get the wisdom of the board on how many drivers and the "overage" to order for a given project. How many drivers do you order for QC purposes and/or to have a reserve for repair/curious kid fingers should a driver become NLA in the future? For example, I've seen a number of comments about low-cost drivers like the TCP 115s vary widely in consistency so better order a few more to get what you need (e.g. MTM surround system has 8 so better order 10 or even 12). Are there manufacturers or drivers that you think are rock solid on QC and it's rare to have a driver measures outside of a small margin of error, and it's a matter of trust (order exactly what you need) but verify through testing? Is this a matter of cost per driver or is it some manufacturers and batches are just better than others? - Thanks

  • #2
    Seems a simple question on the surface, but the answers will guarantee to get somebodies hackles raised.

    1. Most critical: cost does not necessarily indicate the driver you received will meet advertised specifications. Seas has had wandering breakups on some of their drivers over the years, Aurum Cantus is notorious for producing very expensive drivers with miserable unit-to-unit consistency on some models as well as some models being consistent - but so far off of advertised that it is actually pretty dumb to purchase them blindly, ScanSpeak has exhibited drifting T/S specs, etc. Apologists for the hit or miss QC abound, but the fact remains you cannot depend on manufacturers based on driver prices.

    2. Some variation from advertised do not necessarily matter. In some cases, the modeled response will be close despite different T/S parameters. That means at the point where the cabinet alignment dominates the response the variations become moot. On the other hand, we can generally pick up on sensitivity differences as little as 1db if it is across a large segment of the audible spectrum.

    3. Measure everything. You will be surprised at how hard it is to correlate brand/price with QC. In my experience (I have now measured hundreds of drivers), quite a few Dayton drivers have excellent QC. There are also a few that are strangely out of the park. This had held true for most manufacturers I have measured. The point is: measure everything.

    4. No need to buy extra drivers for QC purposes. If the driver does not meet advertised, that is on the vendor and ultimately the manufacturer to take accountability. As a general rule of thumb, a 5% deviation on a specification is not considered grounds for concern - but that depends entirely on tolerance stack up. Return the ones that do not measure up.

    5. Purchasing additional drivers for futureproofing is a personal decision. ALL drivers below a certain price point (and most at any price point) will eventually be discontinued. Even if they are not discontinued, undocumented changes in manufacturing processes and materials can certainly render the same model number driver effectively a different driver. If the manufacturer does not put a lot of demands on the build house to maintain consistency to original specifications they (the build house) will feel free to substitute materials. It happens. It happens on expensive drivers from time to time, it definitely happens on cheap drivers. Cone coatings, glues, surround thicknesses, spider composition, magnetic charge, top plate alloys. Purchasing extra drivers for futureproofing against damage is best done all at one time to help mitigate the impact of that. On the other hand, building grills and utilizing proper filtering and amplifier sizing will make sure a driver will last a very long time. So save a few bucks and invest in protection instead of cluttering your shelves with "just in case" drivers.
    Don't listen to me - I have not sold any $150,000 speakers.


    • Colonel7
      Colonel7 commented
      Editing a comment
      Thanks for all of your thoughts. Encouraging to know that QC and measuring should be treated the same regardless of price.

  • #3
    I don't see the need for things to match in a system. What I do like is to have drivers that will mount in the same cutouts. For example, I have two different pairs of Morel tweeters that fit the same cutout. They measure different, and the xo likely changes though. The same applies with some Peerless woofers I have. If your system has a sub, the variation in specs on a mid-bass don't really matter a whole lot. It's possible to loose a driver to damage that is NLA. If you have one tweeter, or woofer for example, it might work in a center channel. Sometimes you can find a replacement driver used. I sold some NLA Peerless woofers to someone with speakers that used 4 of them, and two were damaged. I sold mine to him, and bought myself something new to replace them.


    • #4
      The more speakers you make and give to others, the more of an issue this can seem to be. I have a few spare buyout drivers and PRs for just in case, but other than that I don't usually have spares.

      Funny you mention the TCPs, Im building an array with 8 per side and I did purchase one or two extra just in case one had wonky specs compared to the others, which one did, but they are cheap, and I can still use the other off one for something in the future. If they were $$$ I'd just buy what I needed and hope for the best.

      Zarbo Audio Projects Youtube Channel: * 320-641 Amp Review Youtube: *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
      *Part 2 *Gluing multiple curved laminations of HDF


      • Colonel7
        Colonel7 commented
        Editing a comment
        Thanks Tom. If I do order some TCPs I might order a couple extra to have around. I'll choose the best and I could use the extras for a project with my soon to be 4th grader. Q on driver spares: how often if ever do you need them? I'm thinking it would be if I get some they won't ever be needed but if I don't them sure enough they'll be NLA -just the way life works!

    • #5
      Another issue with purchasing drivers is, at least in Oz, price: the $A has dropped considerably since I bought my Dayton and Morel drivers in 2014 and they've almost doubled in price since then. So when I had to buy a replacement it was rather a shock.

      Other brands which aren't imported from the US, such as SB Acoustics, Vifa and Peerless, haven't suffered the same problem.



      • #6
        Only had to order one extra drive on several builds because of QC issues, but that was after I measured or had a rub after a build. I do like to try to move drivers from side to side (cabinet to cabinet) to match spl measurements. Don't get to hung up on this as your crossover components are going to vary as well.
        John H

        Synergy Horn, SLS-85, BMR-3L, Mini-TL, BR-2, Titan OB, B452, Udique, Vultus, Latus1, Seriatim, Aperivox,Pencil Tower