Refurbishing speaker cabs

You just hit the raw nerve on PA systems. Hooking it up and making it work is easy. Actually working ON them is a b*tch.

Speaker systems are a complex and very much intertwined collection of components and technology. The reason you can’t find much information on “standard” this spec horn goes with this spec low driver on the internet, is because there is no standard.

Companies spend lots of time calculation stuff and then finding matching components or working from selected components and then matching those to the rest.

If you change only one component (regardless of what) you change the entire package. There are just too much factors in play. Apart from the “bite me in the nose” obvious ones like power handling, impedance and frequency range, there is the cut-off curves, there is speaker efficiency, there is radiation point (ideally you want the radiation point of all your drivers to be in (vertical) line to prevent all kinds of phase problems. For the crossover there is the order (1st, 2nd, 3rd etc.), the quality of the components (coils and condensers), crossover frequencies. And that is just the surface of it.

I know quite a bit about this, both in practical and theoretical sense, but I would be hard pressed and very uncomfortable to offer any concrete advice.

In factories, they will calculate a basic test model based on the specific components, then they will go and test, test and test again. In the meantime making all kinds of small adjustments on any of the aforementioned parameters.

With low end drivers replacing driver a) with driver b) with the same specs will most likely work. As soon as you get to the mids and highs that is no longer the case. And changing crossovers in an existing speaker is not something I’d take very lightly.

In all honesty, I gave up on amp/speaker combi’s about 10 years ago when active speakers came of age. It’s the best of both worlds, it’s easy, it’s components matched by the manufacturer, if you have more than one you have instead backup if one fails, if you use (highly recommended) speakers with D-Class multi-amping (i.e. one amp for every driver/frequency range, typically bi-amped or tri-amped) there will be an electronic crossover/digital sound processing in there. You use simple XLR cables (usually lighter than speakon cables) and you can easily daisy-chain without worrying about impedance and amp loads. Finally with todays digital amps, the weight of an active cabinet is hardly any higher than that of a good passive enclosure (I am not talking about low end ‘cardboard’ speakers of course).

I had just started to say “if you ARE really set on doing this yourself, here’s a few pointers …” but then I realised it’s a hornet’s nest I don’t want to get into.

Assuming you have something like the ZP15s (or it’s predecessor), I can see how you’d want something more. A 15″ with only 200W RMS (my Mackie HD1221s have 500W RMS with only 1 12″!) and a sensitivity of 95dB is slightly less than impressive. I am gonna guess the price makes up for that, but still. They sound and look big, without giving you the big sound you are looking for. If you stuck in 300W RMS (an increase of slightly over 50%), then the questions are indeed is the crossover capable of handling the extra power (without causing a change in the audible signal or burning out shortly) and is my horn still up to par (if it is, it was overpowered with the original driver, so safe to say your speakers are now low end heavy).

I know from your other post that you play for family and friends only at non-paying gigs (really gotta change that guys, if only asking a small fee for the gear), so money can be tight. I understand you have two amps and for speakers. I suggest you have a look at something like these (since you seem to like the big cabinets 😀 ) http://www.mackie.com/products/hd1531/ . Three-way, 900W RMS (1 will get you trough a gig if something happens to the other) for excellent sound quality and banging power. I just picked these because I know them fairly well (and own a pair of 1221s from the same series). Maybe time to sell the 4-speakers and two amps and trade-up to two very good active speakers?

Roughest idea possible:

See if you can find the exact specs for the horn. One question is really important here, are you actually putting more power into the speaker now then you were before the woofer upgrade?

Why is this important? Say you have 200W RMS amp and matching speakers. Now you stick a 300W woofer in the same enclosure but you change nothing else. Effectively you are still only supplying 200W RMS to the speaker. In which case you can pretty much replace the horn by a type with roughly the same specs (frequency range – impedance and power handling capacity). Depending on the efficiency (sensitivity) improvement of the woofer (lets say it went from 95 to 98dB), you might want to get a relatively equal (this is one of the hard parts as calculating with dBs is not linear but logarithmic) sensitivity improvement from your horn.

If however you have for example a 300W amp that you were running at 2/3 power on your 200W speakers and you are now going full blast on the new 300W speakers, then the high end will receive more power too. Generally speaking the crossover filter will have the same ratio when it comes to splitting the low and high end signal. This means you will want to get a horn with a higher power handling (also about 50% of it’s current power handling) as well as the sensitivity improvement.

Finally, on the specs I think I saw the speaker enclosure was 8 Ohm impedance. Your current drivers are 4 Ohm. Is this the same as the old ones? If the old ones were 8 Ohm, your amp is now outputting significantly more than into an 8 Ohm system.

Sorry you consider this a can of worms, but speaker technology really is a mathematical exercise linked to lots of trial and error in test environments (dead rooms and such). I can’t go any rougher than this. That would mean telling you to just stick something remotely similar but better quality in and see if it plays.