When is a 1000W speaker not a 1000W speaker?

[Nakatomi]

I've got a little job on at the moment of repairing a Mackie Thump 15A. It doesn't power on. So, I grabbed the schematics & had a good old nosey around. The LF amp, usually the strongest amp in a bi-amped active speaker is based on a TDA8924 chip! Maxed out, in bridge mode that IC is good for 240WRMS. Add the HF side, using a TDA7294 which when given 100V (which it ain't) can deliver 100WRMS into 8 Ohms.

Ah, so that's (in theory) only 340WRMS you say. Good. Then we come to the power supply. Split rail 28V at 5 amps. That'll give us about 280W!!! That's quite some way from your 1000 Watts isn't it, Mr Mackie? Even in their spec sheet they say the LF amp is 400W RMS. NOPE. Not when the chip amplifier can only deliver 240WRMS. Very very very naughty Mackie.

Anyway.. after having a good butchers at the guts of this speaker I'm not convinced these are as bad as people say. Build quality isn't awful & most components are pretty well rated. Except for the fault this one has - which is a dry joint on the AC input cable receptacle on the PSU board. Oh and the rectifier diode mounts left something to be desired - being that the leads were under stress & one was completely broken off when I removed the assembly from the heatsink.

[Excalibur]

Justin, you haven't quite grasped the idea of advertising, have you? Let's say we're kicking out 250w RMS, eh? That seems doable from your figures. Immediately we can double that to 500w by using Programme as the rating. So far,so good. Now the bit where we're pushing the boundaries of truth a little.
Peak Music Power Output. PMPO. We can double up again to the magical Kilowatt, but although this figure looks impressive, it can only be achieved for a fraction of a nanosecond, by overdriving it to destruction, and picking up the bits afterwards.

It's a true figure, in that respect, but absolutely and totally useless. My van may be capable of 85mph, but I don't expect it to be able to hold that speed for any length of time without drastic consequences!! :eek:

Don't forget what young Dicky found when he took an active QTX sub to bits. If memory serves, we didn't hit 100w, never mind a 1,000!! :)

[funkymook]

And we all know watts have nothing to do with volume don't we.....

[Nakatomi]

Part of my post said that mackie claim (in the product manual) that the LF amp is 400W RMS. That's a blatant lie. This isn't turning one definition of a watt into another. It's an outright LIE. Specs are well known to use smoke & mirrors (RMS vs program vs peak vs peak music power etc) but RMS should mean what it says.

[Excalibur]

And we all know watts have nothing to do with volume don't we.....
Not strictly true. Given the same speaker, an amp giving 500 watts rms will be louder than one giving 250 watts rms. Now whether you can hear the increase in volume is by no means certain.

You are of course absolutely correct that given two different active cabs, there's no reason at all why the one with the higher power use should be louder.


Part of my post said that mackie claim (in the product manual) that the LF amp is 400W RMS. That's a blatant lie. This isn't turning one definition of a watt into another. It's an outright LIE. Specs are well known to use smoke & mirrors (RMS vs program vs peak vs peak music power etc) but RMS should mean what it says.

Oh dear me. :o:o:o:o:o:o:o:o:o:o:o

In my attempt at levity, I overlooked this salient point. Unforgivable. Justin, I apologise unreservedly.

Mind you, I've seen the same cabs have different rms figures quoted in many different places. :daft:

[ukpartydj]

Very naughty... if this is true that their "xxx watt speakers" are actually incapable of ever being that powerful isn't that a violation of trading standards?

[Nakatomi]

Very naughty... if this is true that their "xxx watt speakers" are actually incapable of ever being that powerful isn't that a violation of trading standards?

Could be but I suspect they'd say "ah. The combination of power supply and amplifier circuits CAN provide 400WRMS, just not for very long". Legal by the skin of its teeth or not I think it's reprehensible.

[ukpartydj]

Could be but I suspect they'd say "ah. The combination of power supply and amplifier circuits CAN provide 400WRMS, just not for very long". Legal by the skin of its teeth or not I think it's reprehensible.

Is this the reason they always say "don't open the casing, your warranty will be void"... and you'll find out we conned you...

[CRAZY K]

Is this the reason they always say "don't open the casing, your warranty will be void"... and you'll find out we conned you...

On a lighter note In the 60s I wanted to uprate sound volume so i was sold a lets say 150watt Sinclair Amp which was put in a box by my disco shop.

Remember the C5?

It sounded less loud than my existing 50 watt unit.

I actually travelled to the Sinclair workshops in Cambridge to confront them and complain--they put it on their bench and measured it with some sort of scope and said look its reading 100 watts rms.

I couldnt do a lot after that but it wasnt very loud and to this date ( a long time ) I have taken the Excalibur route--use yer ears.:D:D:D:D:D:D:D:D:D:D

Ignore all claims and stated specs. :rolleyes:

[Nakatomi]

Not strictly true. Given the same speaker, an amp giving 500 watts rms will be louder than one giving 250 watts rms. Now whether you can hear the increase in volume is by no means certain.

You are of course absolutely correct that given two different active cabs, there's no reason at all why the one with the higher power use should be louder.



Oh dear me. :o:o:o:o:o:o:o:o:o:o:o

In my attempt at levity, I overlooked this salient point. Unforgivable. Justin, I apologise unreservedly.

Mind you, I've seen the same cabs have different rms figures quoted in many different places. :daft:

No bother Peter. I didn't take offence but felt I had to point out I think Mackie are lying. I even checked the revision.. all the boards & stickers on the cab say rev D, so did the manual I checked. So we're not comparing apples with oranges. I know manufacturers sometimes upgrade things & keep product names exactly the same (in the name of what?) but that isn't this.

Anyway, all the above notwithstanding, I managed to fix the blighter & give it a fair old hoofing in my kitchen at home. These things don't sound too bad at all (they're quite punchy but not as loud as my TS115A from Alto) but they do rather run out of headroom pretty quickly, revealing their true output capacity. Nice & light too, and not at all mid/top bitey like the original SRM450. I quite like their inclusion of a parametric EQ of sorts too, tuneable from 100Hz to around 8kHz.

Inside the cab, there are a couple of things they've done which raise questions as to their sanity, such as the power supply PCB being at the top of the plate (the mains input & filter PCB are at the bottom) with the amp module in the middle - meaning the mains power cable has to take a longer route than would be necessary. Construction-wise though, larger components & wires are not only soldered but blobbed with silicone goop to attain some kind of vibration resistance.

I've included some pics of the repair:

17799
Dry joint on one of the pictured pins. A bit poor, that.

17798

Whoops! See what happened there? A diode in a TO220 package just came away from all its legs. Slightly iffy board design not helped by imprecise component lead forming during manufacture.

[ckpr2]

This is why I prefer to design and build my own speakers and amps.

[ckpr2]

Don't forget what young Dicky found when he took an active QTX sub to bits. If memory serves, we didn't hit 100w, never mind a 1,000!! :)

1000 watts is only twice as loud as a 100 watts.
Its down to the ear being logarithmic. Twice as loud needs 10 times the watts.

[CRAZY K]

1000 watts is only twice as loud as a 100 watts.
Its down to the ear being logarithmic. Twice as loud needs 10 times the watts.

Yes watts are a tricky subject as previously posted by me, my newish Yamaha Box Amp is rated as 500 plus 500 and although that's nominal it's enough to drive my UL15s to a deafening level, even if they could do with a more powerful amp probably.

Add in the Monitor feed to a powered sub and there's enough to fill a bigish Marquee as SATURDAY proved.