Speakers & Amp Query

[John P. 0]

Hello everyone,

 

I have Audio Intimidation AKA-1 12 Mk2 speakers - the speaker cabinet indicates a "MAX POWER = 400w" and Impedance at 8 ohms. This information is also listed on the GetInTheMix website, although the WhyBuyNew website indicates "Power Max 250w".

 

I am currently using a QTX Sound pro 600 Amp, which is rated at "Power Max = 300w per channel at 4 ohms". As my speakers (above) are rated at 8 ohms my understanding is that this will reduce Amp power to 150w per channel Max - and about 100w per channel RMS (67% of Max).

 

I have been looking at another Amplifier for something with a more powerful output which I could use with my current speakers and have identified the QTX Sound QA1600 Amplifier as a possible contender. This Amp is listed at "Power Max = 2 x 800w at 4 ohms" therefore this would equate to a max power of 2 x 400w at 8 ohms, and is also listed as "Power RMS @ 8 ohms = 2 x 270w".

 

I realise that the above Amp at full power would probably be working my speakers at the limit, but by limiting the Amp output to say 75-80% (i.e. not turning it up fully) the speakers would be able to cope with the output being fed to them. This would give me approximately 200w RMS per channel from the AMP, effectively doubling the output that I currently have available from the QTX Sound Pro 600 (working at full power). My logic is that the QA1600 would not be working as hard as the Pro 600, thus giving the equipment an easier life.

 

At present I have 2 sets of the Pro 600 / AkA1-12 Mk2 speakers, the Amps run together with the mixer output / input to the Amps run in a daisy chain configuration. My thought is that if the QA1600 Amp can be daisy chained together I could purchase 2 Amps, run them in the daisy chain configuration thus providing double my current wattage available (with the Pro 600's) without the expense of purchasing new speakers. I would like to use 2 Amps as this always provides cover in the event of 1 amp breaking down.

 

I appreciate that that is a lot of information above, but really I want to make sure that my logic is correct and that what I am thinking of doing is technically possible?

 

I would be grateful of any further advice or comments that you may have regarding what I am considering to do.

 

Many thanks,

 

John P.

[McCardle 1]

Maximum figures are pretty meaningless on their own and a realm generally reserved for speakers in the parcel shelves of Boy Racers' Corsa's and home cinema equipment, always go off any RMS figures, if RMS figures aren't published then always be very careful of what you drive through them on the basis of why aren't continuous power handling figures being given?, is the manufacturer embarassed by how puny they are.

 

As you can see, there is often a huge variation in how Maximum figures are interpreted, a bit like MPG figures given by the car manufacturers, they may often look good on paper, but how often does the car actually match those specs out in the real world?. Speaker ratings are generally the same, at least any which state maxiumum or worse still PMPO :scared: .

 

RMS or 'Continuous' figures are the ones to pay attention to, as these indicate the power which the speaker is comfortable at handling for extended periods of time - i.e that 5 hour Wedding. Also bear in mind that music is not a linear power, there are peaks which can be experienced, such as high notes in song vocals, or that karaoke singer dropping their mic. A lot of speakers are tested under lab conditions using a continuous signal, rather than the full frequency range encountered by vocals or recorded music.

 

The speaker manufacturer may also obtain their test maximum values in a different manner than the Amp manufacturer, so don't just assume that a 375w Maximum power amplifier will be the same as a 375w maximum power speaker, as they may have been tested using different methods and different signal freqencies - again you need to obtain the RMS Values of both the Amplifier and the Speaker to make any meaningful comparison. If the speaker inpedance is 8 ohms, then you need to compare the amplifiers' RMS figure also at 8 ohms.

 

but by limiting the Amp output to say 75-80% (i.e. not turning it up fully) the speakers would be able to cope with the output being fed to them.

 

Also, as mentioned in my earlier comment, music is linear with levels from deep bass rolls to high treble peaks and inevitably music is often recorded at different volumes so the chances of the amp staying religiously at its well intentioned setting of 75% - 80% would be pretty slim at least not without a few peaks appearing to escape and break the boundaries. This is the same reason why venue owners don't trust their visiting artists or DJ's to abide by any pre-set ampifier levels, they generally fit electronic means of dynamic limiting in the chain, such as compressor / limiters . Your amp setting also probably won't save your tweeters if little 6 year old Nicki singing happy birthday at Grannies 80th birthday, squeals hysterically down the microphone as she hears hersef over the PA for the first time.

 

For this reason, your system should have headroom and the ability to cope with overloads, should any of the 1001 different possible scenarios play out in our line of work.

 

I wouldn't advise choosing a speaker - amp combination purely on figures based on 'That will probably do' or 'those figures look close enough', certainly not when those figures are maximum ones. For all we know those may be the figures that the speaker handled for 2 fractions of a second before the voice coil in the bass driver died a smokey death.

 

So ignore the maximum figures and look at the RMS ones.

Edited March 4, 2013 by McCardle

[Megasong 0]

First let me congratulate McCardle on his response, it's nice to see constructive advice to a novice asking for help rather than the stuff that often gets spewed out.

 

I am not familiar with any of your equipment so can only speak in generalities but there are some things you really need to think about before shelling out your hard earned cash.

 

For every 3dB extra you get from your speakers you have to throw double the power at them. So going from 100W to 200W will give you a 3dB increase in output. This is an increase that most people will describe as 'a bit louder' 270W will not give you even an extra dB over 200W, you'd need to go to 400W to get 6dB over what you have now and to about 1000W to double the perceived volume which is a 10dB increase. My guess is that you may well not get what you are hoping for with your existing speakers and your proposed new amp.

 

Often the cheapest and best way to gain volume is to get more efficient speakers. I don't know what your's are rated at but the figure to look for is how many dB/1W/1M. Most half decent speakers will be around the 97-99dB mark but there are some - normally costing a lot more - which go much higher. We have mid/tops rated at 111dB and Subs at 109dB.

 

Putting this into perspective again, if your speakers are running at (say) 93dB/W/M which is not unlikely seeing as they do not tell you their efficiency anywhere I can find - I've just tried looking - you'll get a maximum of 117dB at their peak rating of 250W. Assuming program to be half peak you'll have 114dB. Using a pair with 98dB efficiency you'll get 118dB and 122dB respectively without giving them any more power. Also how is it measured, half or full space (if you don't have your speakers pretty much backed against a wall and they're measured half space you can knock off 3dB before you start)

 

Sound drops off quickly as it leaves the speaker, losing about 6dB for every doubling of distance so at 8M (a very small hall) you lose about 18dB at the back, hence whatever the amp your speakers are never going to be very loud in anything but a very small venue.

 

The specification I found also gives a frequency response but does not qualify it at all. I've tested some speakers and found that the published frequency response is (on one occasion) at about the -20dB point using a dBA measurement (closer to human hearing than straight dB) and hence virtually inaudible at the ends of the spectrum, and all over the place (+/- 6dB) as you go through it. You need to be looking for something like 60Hz-18kHz +/-3dB & 50Hz - 20kHz +/-10dB or better.

 

I would strongly suggest spending your money on an alternative set of speakers with known characteristics before upgrading your amp.

 

The other thing you should be careful of is you assumptions about the amp's peak power, this can be many times the peak you may expect from the peak voltage of the RMS volts, a lot of PSUs on more budget amps drop dramatically as the power drain goes up, so if it was running at low volume long enough for the caps to charge fully just before a screetch of someone dropped the mic you could get a significantly greater peak. Gemini amps for example claim an instantaneous peak power of about 10 times the RMS power into 8 ohms.

 

If you wanted to chat about it our number is on our web site and I would be happy to try to help. And no I will not sell you anything. We work with a lot of newcomers to DJing and equipment and have quite a bit of experience in setting them on a better signposted route.

[John P. 0]

Hello,

 

Thanks for your advice folks - very useful indeed. It looks llike I'm going to have to spend lots more to get any real / noticeable benefit, so I'm grateful for the advice you have given - which has saved me wasting cash on something that's not going to do what I expect.

 

I have been looking at some of the packages on the DJkit.com website, in the 1200 watts + section. Not cheap, but then - as with all things in life - you get what you pay for.

 

Right - off to speak nicely to the Wife (bank manager!).

 

Thanks again.

 

John P.

[Megasong 0]

John,

 

I'm pleased you found the advice useful and that you are considering an overall upgrade.

 

If I am right in assuming that you are DJing to make some extra money may I make a few further suggestions. These are based on our experience with new DJs and will hopefully help save you from losing money or spending more than you need.

 

Investment in equipment is significant, especially if you want to be able to cope with most of the gigs that come your way. If you are starting out I would guess you may not have a lot of gigs in the pipeline so your expenditure will be based on prospective work rather than confirmed business.

 

If you start by getting yourself a decent selection of music (this is a must have obviously) or find a company that will hire you a rig with music (even better) that has to be the starting point.

 

Next find out how much it would cost to hire decent quality equipment that will cater for the various types of gig you want to quote for. Most kit will go out for somewhere below 10% of it's cost price for a night's hire and, so long as you're not stupid you can be pretty sure it's work and deliver according to promises otherwise the hire company would go out of business pretty quickly. You'll also know it has up to date PAT testing and servicing.

 

If we assume that the hire company will have paid less than you could for a piece of kit you would have to do - at a guess - 15 + gigs before it would have been cheaper to buy the kit BUT you will have a wider selection to choose from so you could fulfil more types and sizes of gig.

 

If you buy new you will probably lose about 1/3 to half the value of your kit immediately should your venture not be successful, you will also have laid out the money to buy it taking it out of your families hands before getting any returns.

 

If you buy second hand good quality items you stand to lose less but you may have to be prepared for some failures which obviously will not be covered by guarantee. Even with new kit in many cases you could be without it for weeks waiting for a warranty repair.

 

You'd be amazed how many DJs we hire to on a long term repeat business basis. They have no capital outlay, they know exactly how much they will clear on a gig and they have no storage issues. With some larger events we'll even deliver, set-up, collect and take down which often costs less than the additional van hire and expertise they's otherwise have to bring in. With live acts we obviously go even further providing sound engineering (mixing etc) so all they do is turn up and play.

 

If you can find someone local to you who offers a decent hire service and get to know them you'll have no overheads at all, only your direct costs in doing the gig. You may seem to be making a bit less but when you take equipment costs into consideration you may be surprised how little less.

 

Assuming you are successful you would then know exactly what works for you and how much what is getting used and you may well be able to do a deal with your hirer and buy the stuff you have been using from them.

 

There are so many DJs who either try to do it on the cheap and fall by the wayside because their set-up just doesn't cut it or who spend a fortune on kit and then can't get the business to warrant it.

 

In our area there are companies (DJs) desperate to get business and quoting crazy low prices, they'll often get the gig doing someone more professional out of it, but they won't often get repeat business as their performance will not be up to scratch. They can only do this because they've laid out their money and are desperate to get something (anything) coming in to pay for it.

 

Most of these DJs could only quote for the smaller cheaper gigs anyway since their kit couldn't handle a bigger gig so they hit a price ceiling they cannot break through without hiring or buying more.

 

Think long and hard before going on a spending spree, fine once you're established and have the gigs to warrant it but I would suggest not until then.