Ohm's And Amps!

[Paul Ireland 0]

Hi Guys,

 

I can't get my head round these ohms and ratings yet.

 

Here's my set up

 

I've a Thomann T.amp 1400 so 700watts @ 4ohms and 450 watts @ 8ohm

 

My Speakers are HK pro Series

 

Passive system 2 x 500 watt subs @ 4ohm and 2 x 400 watt fullrange tops @ 8 ohms

 

How do i work out the Ohm rating coming from the amp or that the speakers are creating?

 

SO I connect the amp to the sub(4ohm) and the top(8ohm) is connected to the sub!

 

I'm baffled!!!!!!

 

Could i use a bigger or should i be using a smaller amp????

[UKHero 0]

If your subs are 4 Ohm and have a cross over in them then your amp will only see the 4 Ohm load if set up as you say Tops pluged into Subs and subs in to amp.

 

As for the amp Watts to speaker watts you have opened a can of worms as different people will tell you different things. The main thing is you dont drive your amp into distortion or see the clip lights on all the time as this can kill your speakers. If the amp is big enough for the gigs you do and the speakers are rated above the output of your amp then from my POV your fine... But I guarentee others will tell you differently.

 

 

Nik

[djgorey 0]

UK Hero is right about the power of amps - lots of people suggest more powerful amps than the speakers, others recommend the same and others suggest amps that are slightly less powerful than the speakers, but whichever you pick, a clipping amp is what will kill the speakers.

 

As for the impedence, you have to take a step back from the speakers for a bit and look at the physics involved.

 

An amplifer is basically a transformer that raises a small current (input signal from mixer) to a larger current (output to speakers). A speaker acts as a resistor and has a nominal value of resistance, usually in diso speakers this is 4 Ohms or 8 Ohms. Briefly, the value on a speaker is only a nominal figure because the actual resistance at any one time will vary with the frequency of the sound the speaker is trying to re-produce, but we don't have to worry about that at the moment.

 

Now, an amplifer's output is related to the resistance across it - i.e. a speaker. It follows Ohm's law of V=IR where V is voltage, I is current and R is resistance and a derivative of Ohm's Law, P=IV where P is Power.

 

An amplifer will give out more power at a lower resistance so, for example, the Matrix UKP1300 gives out 650w per side with a 4 ohm speaker and 390w per side with an 8 Ohm speaker. This may make you think "Ahh - lower impedence is better" and in terms of getting more power, it is, but that comes at a cost.

 

The lower the impedence, the more stress is placed on the amplifer so some amps will run 2 Ohm loads (4 Ohm speaker connected in parrallel for example), others won't. Whether an amp can or cannot run at 2 ohms, it will last longer running at 8 or even 16 Ohms.

 

It is a trade-off. I run my amps at 8 Ohms without question. This means that the amps will last longer and sound quality is better. However, it means that I also need to take more amplifers with me to a gig to get the same noise.

 

In your case, I don't know if the speakers have a crossover that would mean the amp "sees" 4 Ohms or not. If it does, then great. If not, then you are presenting the amp with 2.667 Ohm. To work out the total resistance you use:

 

1/R(Total) = 1/R1 + 1/R2 + 1/R3 + ...1/Rn

 

If your amp is seeing 2.67 Ohms, then it will be putting out more than 700 per side, but at the expense of reliability.

 

I hope this helps with understand the impedence rating of your speakers.

 

(p.s. I think you need another amp to run the tops by themselves)

[Paul Ireland 0]

UK Hero is right about the power of amps - lots of people suggest more powerful amps than the speakers, others recommend the same and others suggest amps that are slightly less powerful than the speakers, but whichever you pick, a clipping amp is what will kill the speakers.

 

As for the impedence, you have to take a step back from the speakers for a bit and look at the physics involved.

 

An amplifer is basically a transformer that raises a small current (input signal from mixer) to a larger current (output to speakers). A speaker acts as a resistor and has a nominal value of resistance, usually in diso speakers this is 4 Ohms or 8 Ohms. Briefly, the value on a speaker is only a nominal figure because the actual resistance at any one time will vary with the frequency of the sound the speaker is trying to re-produce, but we don't have to worry about that at the moment.

 

Now, an amplifer's output is related to the resistance across it - i.e. a speaker. It follows Ohm's law of V=IR where V is voltage, I is current and R is resistance and a derivative of Ohm's Law, P=IV where P is Power.

 

An amplifer will give out more power at a lower resistance so, for example, the Matrix UKP1300 gives out 650w per side with a 4 ohm speaker and 390w per side with an 8 Ohm speaker. This may make you think "Ahh - lower impedence is better" and in terms of getting more power, it is, but that comes at a cost.

 

The lower the impedence, the more stress is placed on the amplifer so some amps will run 2 Ohm loads (4 Ohm speaker connected in parrallel for example), others won't. Whether an amp can or cannot run at 2 ohms, it will last longer running at 8 or even 16 Ohms.

 

It is a trade-off. I run my amps at 8 Ohms without question. This means that the amps will last longer and sound quality is better. However, it means that I also need to take more amplifers with me to a gig to get the same noise.

 

In your case, I don't know if the speakers have a crossover that would mean the amp "sees" 4 Ohms or not. If it does, then great. If not, then you are presenting the amp with 2.667 Ohm. To work out the total resistance you use:

 

1/R(Total) = 1/R1 + 1/R2 + 1/R3 + ...1/Rn

 

If your amp is seeing 2.67 Ohms, then it will be putting out more than 700 per side, but at the expense of reliability.

 

I hope this helps with understand the impedence rating of your speakers.

 

(p.s. I think you need another amp to run the tops by themselves)

yeah i,ve thought of bringing 2 amps alright but the weight is the only factor there. how'd i set it up? a splitter? as in split the signal from the mixer to the 2 amps ? by the way the sub has a built in crossover does this mean it sees a 4ohm load in total each side ? and if for argument i've the amp up full it's sending 700 watts tothe sub and is the sub sending 700 w to the top? p.s i never drive the amp to clipping .

[superstardeejay 0]

It's important to know whether your subwoofer has a low-pass crossover, or a 2-way crossover. Subs with a low-pass crossover (most cheaper disco grade stuff) do not preserve the impedance and will mean that a 4 ohm bass plus 8 ohm top will give the amp a 2.7 ohm load (as mentioned) which is often too low for your average amplifier.

 

If you have the HK Premium Pro speakers then luckily (being at the higher quality end of the market) they have a 2-way crossover in the bass cabinets which indeed preserve the overall impedance to 4 ohms per side (so 4ohm plus 8ohm = 4 ohm!!). This is designed so you can run a four-box set (like yours) with one amp only, for convenience and efficiency, and the sound will be voiced as HK intended it when they designed the crossovers.

I would personally keep a spare cheap amp in the boot of your car to cover for a failure in mid-party, rather than worry about using 2 amps all the time, as you wont really gain anything except a bad back.

 

The T-amp you mention is perhaps a little underrated for the HK Premium Pro, better to have an amp too big than one too small. The T-Amps have optical limiters so you can't easily clip them for long.

 

Please confirm exactly which model HK boxes you have.

Edited March 16, 2009 by superstardeejay

[Paul Ireland 0]

This is the rig i have

 

http://www.thomann.de/ie/hk_audio_premium_pro_set_1518.htm

 

And i do carry a spare amp also, in fact it's the t.amp 2400, the bigger one is the spare

 

Cheers

 

[superstardeejay 0]

Excellent stuff, though dare I suggest that those speakers deserve an amp a little more worthy? Youve bought some very nice speakers and driven them with a nasty amplifier. Treat yourself!

 

 

[Paul Ireland 0]

Excellent stuff, though dare I suggest that those speakers deserve an amp a little more worthy? Youve bought some very nice speakers and driven them with a nasty amplifier. Treat yourself!

what would you recommend superstar?

[D.X 0]

what would you recommend superstar?

 

I run 15+18s together off a single QSCRMX2450. 2x500w @ 8ohms and 2x750w @ 4 ohms. Should run your rig no problems. That leaves them slightly under powered and many will tell you to over power speakers. Personally, I've never had any problems.

 

If you wanted to over power them get the next model up, the RMX4050. That will have some serious whack.

[JCarey 0]

Paul,

 

You mentioned weight as a factor in the amps you carry.

 

If you decide you really need amps with more kick, check qsc's plx range or crown's xti series.

 

If you have the budget they have both have models with output suited to your speakers and weigh very little. Thomann stock both and carry the specs on their site. As your in Ireland, I know a guy in Tipp who claims he can match the German prices, pm me for his number if interested. Also if you buy on-line keep in mind the euro/sterling rates and the uk's VAT being so low there may be advantages buying from the UK.

 

I have heard the crowns driving JBL SRX speakers, they do a great job.

I have read many positive things about the plx's.

 

Think do you really need to spend? if so good luck with your choice.

 

John

[Paul Ireland 0]

Paul,

 

You mentioned weight as a factor in the amps you carry.

 

If you decide you really need amps with more kick, check qsc's plx range or crown's xti series.

 

If you have the budget they have both have models with output suited to your speakers and weigh very little. Thomann stock both and carry the specs on their site. As your in Ireland, I know a guy in Tipp who claims he can match the German prices, pm me for his number if interested. Also if you buy on-line keep in mind the euro/sterling rates and the uk's VAT being so low there may be advantages buying from the UK.

 

I have heard the crowns driving JBL SRX speakers, they do a great job.

I have read many positive things about the plx's.

 

Think do you really need to spend? if so good luck with your choice.

 

John

Thanks John,

 

I'm still unsure whether i need another amp. Ideally if money was no object I'd get a better quality one but I'm fairly happy with the t.amp at the moment I suppose. I reckon I wouldn't really know what difference it made til I tried it!!!

 

Will keep researching though