Active fold back monitors

bob21

@ESBlonde It's not really about that - it's the concept that a concentric speaker will have a better phase response - because time arrival between LF & HF is the same; as opposed to two separate drivers (be they horn loaded, compression driver, piezo, whatever) where the phase response is more screwy - because the sound from the two drivers arrives at different time points..

The combined phase response put into the frequency domain normally gives us comb filtering - which is greater summation or cancellation at certain frequencies.. This changes as you move around (changing the timing between the two drivers, and both drivers and the mic). 

Greater summation at certain frequencies = more volume at certain frequencies - which is likely to mean a greater tendency to feedback at certain frequencies - which gets greater and lesser as you move around.. Therefore, the speakers with the poorer combined phase response will be less stable to feedback.

(The coaxial has the same arrival times throughout the coverage, therefore much less comb filtering (none on paper, but this is a practical exercise) - and therefore more stability as above.) 

Also fwiw, the coverage between hf and lf is generally better on coaxial systems as they're (effectively) mounted onto the same 'horn'..

ICBM

p90fool said:

I have a couple of Wharfedale powered cabs @ICBM , anything I can do to prevent future issues?

Try not to bump them around, mainly. I've also tried adding hot-melt glue to the PCBs to more rigidly support them against the heatsinks, but it didn't make much difference.

That said I haven't seen any dead ones for a while now so it's possible they have actually taken the problem on board and redesigned them in some way.

p90fool

Thanks for that, I'll just tell my missus to be more careful . (not easy for a drummer)

simonk

jesone;1083659" said:

I'm now leaning towards the wharfdale ev x12m over the Alto tx8 and Thomann MA150. I'm worried that the Alto won't be loud or clear enough and the MA150 is feckin' heavy!! Any last thoughts before I pull the trigger on this?

Be reassured the Alto's would be plenty loud and clear enough for vox and guitar unless you are playing at frankly ridiculous volumes.

koneguitarist

I have 3 W audio (wharfdale?) 8"active speakers, been using them about 6 years now, been perfect, loud enough at all our gigs, easy to set up and double as practice PA every year!

ESBlonde

bob21;1084128" said:

@ESBlonde It's not really about that - it's the concept that a concentric speaker will have a better phase response - because time arrival between LF & HF is the same; as opposed to two separate drivers (be they horn loaded, compression driver, piezo, whatever) where the phase response is more screwy - because the sound from the two drivers arrives at different time points..

The combined phase response put into the frequency domain normally gives us comb filtering - which is greater summation or cancellation at certain frequencies.. This changes as you move around (changing the timing between the two drivers, and both drivers and the mic). 

Greater summation at certain frequencies = more volume at certain frequencies - which is likely to mean a greater tendency to feedback at certain frequencies - which gets greater and lesser as you move around.. Therefore, the speakers with the poorer combined phase response will be less stable to feedback.

(The coaxial has the same arrival times throughout the coverage, therefore much less comb filtering (none on paper, but this is a practical exercise) - and therefore more stability as above.) 

Also fwiw, the coverage between hf and lf is generally better on coaxial systems as they're (effectively) mounted onto the same 'horn'..

Yes point source is the ideal. I remember one driver where the horn and cone were ceneed to achieve just that. The fact that nearly all professional monitors still use separate drivers shows that in practice it remains the best solution but as I said earlier, the crossover or more particularly these days the digital processor needs to be properly designed and implemented. Some wedges work better in given situations but largely the two driver system dominates where IEMS have not yet displaced them.

bob21

ESBlonde said:

The fact that nearly all professional monitors still use separate drivers shows that in practice it remains the best solution but as I said earlier, the crossover or more particularly these days the digital processor needs to be properly designed and implemented. Some wedges work better in given situations but largely the two driver system dominates where IEMS have not yet displaced them.

Actually - many of the big pro monitors are coaxial. Just two examples: D&B M4 (which are the current 'in thing' in the industry) are coaxial; EAW Microwedges (designed by Dave Rat) are coax. Pro engineers really care about the phase thing!

Crossover isn't really going to have a significant effect on feedback stability - as long as it's not wildly wrong in frequency or slope (which would more likely present as blown drivers) - the stability is more to do with the drivers. Considering how simple crossover design is, even the cheapest chinese boxes have an acceptable crossover in.

The only reason many monitors are still split driver systems is because 10/20/30 years ago, we didn't understand as much about phase coherency - and it wasn't considered so important in design; and driver design wasn't as sophisticated. Many sound cos are still using older monitors (on the gigs that don't pay as well!) - hence the proliferation of old design monitors around! Same reason as most are using 58s.. Nowhere near the best mic available, but they were paid for years ago, and usually don't get complaints..

mike257

I do like an M4. Lovely things. SM58s can do one though.

ESBlonde

I agree with what you say, the radian/EAW microwedge is the dogs, but so often you see them paired on stage which destroys some of the beauty of point source although they are smooth response anyway. EAW's larger wedges which can be used singley all have multiple drivers iirc. I've not used the D&B M4 since i gave up SR a few years ago now so can't comment. Modern digital processing enables crossover and phase response to be optimised but again it's not perfect but a damn site better than many old school passive crossovers.
At pub rock level, I think a single cone and parasitic tweeter in a £200 wedge is possibly pushing your luck compared to active crossover/dsp and twin drivers. But thems the choices and at that price.
It would be interesting to do some modern comparisons of current wedges available, but my interest is not great enough to spend and find out.

Danny1969

I'm not convinced using a coaxial driver for low and high would be of massive benifit in a typical stage monitor because problems with phase smearing are more pronounced and affected in the lower region, well before the crossover point of most compression horn drivers. A failure in a coaxial driver also means you have to effectively change both drivers as one I suppose and that's gotta be more expensive than replacing a blown typical 1" CD horn 

In terms of volume before feedback it's amazing how the stability of the monitors power amp affects this. I can get a frightening amount of level out of 2 HK darts positioned at the foot of a mic stand, to the point they are louder than the PA with no ringing at all. Try the same with something like 2 x SRM450''s or similar and I can't get anywhere near the same level as the internal amps are nowhere near the same quality

Note I'm not saying loud monitors are a good thing, in fact I dislike them and would rather everyone used IEM's.  Loud wedge sound shit from the audiences point of view as they have to  listen to the back of them and generally loud wedges will mess up the FOH sound. But if you have to use them (and I still work with 2 guys in 2 bands who insist on ludicrous amounts of wedge monitor) then one of the biggest factors in how loud you will get them( beyond mic & monitor  placement) is the quality and stability of the amp(s)

Going back to the Alto's, I was in rehearsal last night with Alto mains and Alto 8" powered wedge. I'm still impressed with them for the money

jesone

Okaaaayyy - so with all that taken into account the Alto TX8's are satisfactory right?

matt1973

The HH wedges seeem to fall nicely into this category. Worth a look perhaps?

simonk

jesone;1085268" said:

Okaaaayyy - so with all that taken into account the Alto TX8's are satisfactory right?

They work extremely well for us (5 piece: 2 guitars, vox, bass and drums with 3 of us doing BV's) - we have four of them. Danny makes a good point about overpowering the PA too.

mike257

Hadn't realised just how cheaply priced the Alto TX stuff was. I'm after some mons on a tight budget for little function gigs (can't afford the nice stuff I get to play with at work for my own rig yet!), if the 12s are half decent then they might be just the thing to keep me ticking over for now.

bob21

@ESBlonde

Anyone who 'needs' more than a MW15 has probably decided that without listening to it

Danny1969 said:

I'm not convinced using a coaxial driver for low and high would be of massive benifit in a typical stage monitor because problems with phase smearing are more pronounced and affected in the lower region, well before the crossover point of most compression horn drivers. A failure in a coaxial driver also means you have to effectively change both drivers as one I suppose and that's gotta be more expensive than replacing a blown typical 1" CD horn 

I'm afraid I have to disagree - firstly, whilst summations/cancellations are greater at say 100hz, the distance between those nodes is huge - not a typical moving-a-mic-whilst-singing-distance.. 

Secondly, I would completely disagree that problems with phase smearing is more apparent at LF - when you notice combing in a PA, it's always above 1kHz...

Regardless though - if it is a benefit to some extent, it's still a benefit - an extra 2% out of the monitor is still an extra 2%.

After all, the likes of D&B, EAW et al don't design things a way for the sheer hell of it - if they think it's enough of a benefit to do so (and use a more expensive to manufacture driver) - then clearly there must be a benefit.

However - you do make a good point, the replacement cost is much greater.. Though, in a decent active box (or a well, digitally, processed passive box) driver failure should be a rare occurrence!

bob21

Should also be pointed out that a coaxial design has no correlation to the quality of the crossover in a speaker, or whether the processing is digital/analog/fairy dust!