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AMP/Speaker Maths

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Category: General
Forum Name: Newbie Discussion
Forum Description: Newbie Discussion/Questions. Look less stupid here...
Printed Date: 06 April 2020 at 2:57pm
Software Version: Web Wiz Forums 12.03 -

Topic: AMP/Speaker Maths
Posted By: toomanyairmiles
Subject: AMP/Speaker Maths
Date Posted: 06 October 2019 at 12:38pm
Hi Everyone, newbie here.

I have a Devine D-200 class D amplifier which I currently use to run some old Peavy Hi-Sys 6XT tops (200w / 400w peak at 8 ohms) on a system which is  used for meetings. The whole system was built on a shoestring from second hand parts with the intention of improving components over time.

We now want to use the system for background music at small events and I'd like to get some full range cabs. I'm trying to figure out if my D200 would have enough grunt to power a pair of Martin Audio EM26's (or even if these cabs are a good idea) on its own, or if I should buy a second amp, but I'm getting rather lost in the maths.

The EM26's are 200 watt, 500 peak, the same as my existing speakers, and Martin recommend an 200-300W amp into 4 ohms.

The Devine can run 2x 180W 4-ohm stereo output (RMS), 2x 100W 8-ohm stereo output (RMS) or 1 x 360W 8-ohm stereo output (RMS).

Any advice/alternative plans etcetera is welcome.

Posted By: toastyghost
Date Posted: 06 October 2019 at 2:12pm
It’s enough in that it’ll make noise, but you won’t achieve the maximum peak output of either pair of speakers.

It’s up to you if you think that it’ll be loud enough for the intended usage and coverage area. You can calculate that for guidance from the cabinets’ stated overall sensitivity multiplied by the wattage - or better yet, voltage, available from the amp.

The rating given for a cabinet is usually 1w/1m, although in practice this is kind of a misnomer. It’s good enough for guidance but don’t take it as gospel.

There’s a tool to explain the maths and a calculator here:" rel="nofollow -

Just remember that for background music you don’t need 110dB continuous, far from it. It’s more about a discreet system with good coverage, in my opinion, and that means getting the cabinets up above people’s heads so you’re not killing the people closest to the boxes.

Also there is nothing wrong with under powering a speaker so long as you avoid clipping, through the use of appropriately set limiters.

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Posted By: toomanyairmiles
Date Posted: 06 October 2019 at 3:29pm
Thank you.

I do have them up on a pair of gorilla stands.

I'd intended to buy another amp in the long run anyway, money is scarce until I do some fundraising, and for the current purposes my main issue is lack of full range.

The system was added because we have a number of members with hearing loss and needed both amplification and an induction loop. For its current purposes it makes the appropriate noises, but obviously it was put together on the basis of what was available in the budget/time frame, and it could be far better.

In your view would I be better off adding a second amp or changing the speakers first?

Posted By: toastyghost
Date Posted: 06 October 2019 at 3:51pm
Neither box will have a particularly high level of bass, so may not meet your needs in terms of 'full range'.

The Martin will likely sound better out of the box than the Peavey, just in terms of voicing, but I'd be looking at a cabinet with a larger woofer if you want a bit more bottom end.

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