Amp/Speaker set-up - Am I on the right lines?

[JohnAlex]

Hi, Guys.

 

I have a pair of JBL M350's and a W-Audio DA-1300 but the Amp puts out 390w per channel with an 8ohm load - which is little more that my M350's which are 350w/8ohms.

 

Am I right in thinking that it would be better to run the amp with a 4 ohm loading which would then deliver around 630w per channel? If so, I was tinking of getting a pair of 15"/300w RMS/8ohm Bass Bins which I would then put in parallel with a M350 on each output of the amp - thereby giving me the 4ohm loading and running the amp at around 60% maximum.

 

However, my search of the internet seems to favour a) putting the Bass Bins on one channel and my JBL's on one channel -which seems risky as the 'main music' would die if that chanel went faulty - or b) running the Bass Bins from another amp - which still leaves the DA-1300 feeding my M350's with 390w.

 

My guess is that running the amp in Bridged Mode is of no use as it requires an 8 ohm load and running the M350's in parallel would give me a 4ohm lading.

 

Any advice would be appreciated.

[mike7172]

Hi there,

you could run them at 8 ohms but be careful not to overload the amp,

you'd normally give the box twice the RMS (ish) but as long as your not running your amp into protect constantly you should be okay.

 

with regards to running sub-top per channel, this will be fine as long as your okay with not having control over the low end, but also check that the cabs your using have passive crossovers in em, otherwise you'll end up spending money on a crossover etc etc

 

hope this helps

;)

[Dave SA]

Mike - the OP was talking about running the system in MONO - with 2 x TOP per 1 side and 2 x BASS BINS per 1 side of the amp.

 

What's the application JohnAlex?

[JohnAlex]

Thanks, Mike - that helps a lot. ;)

 

Given that with an 8 ohm load there's not much difference between the amp output (390w) and the speaker rating (350w) then, as you recommend, it seem sensible to look at reducing the amp loading to 4ohms and thereby raising its maximum output to getting on for double the M350's rating.

 

Also, as the M350's 15" drivers are doing quite a lot of mid frequency work, I think going the sub-top route will have the additional bonus of improving the bottom-end response. When you say that I won't have control over the low end, does this mean that tweeking EQ will have little or no effect?

 

Oh, and thanks for the tip regarding passive crossovers.

 

 

John

 

A concurrent post has been automatically merged from this point on.

 

Hi, Dave.

 

Thanks for your input.

 

The application is video disco's, generally at Conferences - so usually fairly large, carpeted rooms with a non-packed audience.

 

The reason I mentioned running the system in mono with 2 x tops on 1 side and 2 x bass bins on the other was that most information I have come across seems to recommend that configuration over 1 x top and 1 x bin on each side - for what benefit I don't know. My thought was that if the tops side of the amp goes down then you loose all the main sound output - and surely, there's an awful ot of signal/frequencies that are being processed by the amp on the bins side that are just being wasted/filtered out by the bins crossover units - Is that good/of no consequence/to be avoided?

 

So, it seemed preferable to me to run 1 x top and 1 x bin on each side - but I'll be guided by you guys who know much more about this.

 

John

[Dave SA]

Firstly, adding another 8ohm box to each channel, dropping the total load per channel to ''4 ohm'' will NOT increase the power going to the M350. In fact, if anything less power will get to each component of the system due to the addition of an extra passive crossover per circuit.

 

You didn't say what the application for the system is. Music playback? Vocal reinforcement? Jazz Band? Heavy Metal? The application will dictate the advice I would offer you.

 

Kind Regards,

Dave Morgan,

Spartan Audio.

[JohnAlex]

Hi, Dave.

 

The application will be music playback. I think I appreciate that the M350's will not be getting (or indeed, need) more power but I started this quest because I thought a M350 on a 390w amp output was a little tight.

 

Seeing that a 4 ohm loading would take the DA-1300's output up to 650w I thought this would mean that a 350w 'speaker drain' would sit nicely at about 60% of the maximum output - rather than being 90% of a 390w maximum output. And, as a bonus, adding a bass bin to achieve the 4ohm loading would also reinforce and supplement the work being done by the M350's 15" driver - probably not a right assesment! ;) .

 

I had not thought about the extra passive crossover 'eating' power as I anticipated the total loading to still be around 350w - just spread over the M350 and a bass bin. Again, my ignorance is showing, I guess, and I very much appreciate your advice and recommendations.

 

John

[MarkPAman]

Seeing that a 4 ohm loading would take the DA-1300's output up to 650w I thought this would mean that a 350w 'speaker drain' would sit nicely at about 60% of the maximum output - rather than being 90% of a 390w maximum output.

 

The sub that you add to get 4ohms will use power too though. It's only got to be 300W to end up using 100% of you 650W, & that's not a lot for a sub.

 

I'd stick to the 8 ohm arrangement & be careful not to clip the amp. If you want to add subs, then get another amp too.

[JohnAlex]

Thanks, Mark.

 

Sounds like a good plan - especially as I guess it's always a good idea to have a second amp then if one dies you can use the other with the M350's and continue the party.

 

John

[jamesperrett]

Am I right in thinking that it would be better to run the amp with a 4 ohm loading which would then deliver around 630w per channel? If so, I was tinking of getting a pair of 15"/300w RMS/8ohm Bass Bins which I would then put in parallel with a M350 on each output of the amp - thereby giving me the 4ohm loading and running the amp at around 60% maximum.

 

No - a sub with a proper passive crossover will still result in the amplifier seeing an 8 ohm impedance.

 

James.

[JohnAlex]

Oh, James - you've upturned the cart just as I thought I had it sorted.

 

I was under the impression that if I put one of my 8ohm M350 (with passive croos-over) in parallel with an 8ohm Bass Bin (with a passive cross-over) on each channel of the amp, then the amp would see a 4ohm loading on each channel.

 

You say it will still see an 8ohm loading?

 

John

[Sound In Gloucestershire]

John, it depends on the subs crossover

 

one way to avoid this is to go into the top first and then down into the bass, this will present a 4 ohm load and the tops will run full range

[JohnAlex]

Hi.

 

Well, that's great info ;) It seems the general opinion is to run the amp with a 4ohm load using a M350 and a sub in parallel. However, if I get a second amp then I can run the subs from that and have the DA-1300 with an 8ohm load each side (as it is now) - but that doesn't solve the DA-1300's maximum ouptput being little more than the M350's.

 

Thanks for your expertise :** laughs out loud **: I think I have a way forward :** laughs out loud **:

 

John

[Sound In Gloucestershire]

its common practice to have a higher power amp than your speakers

 

in this case, the difference is tiny, I wouldnt worry about it, if you see red lights, turn it down! If it sounds bad, turn it down. Plus I highly doubt the warrior actually outputs the full quoted wattage anyway

[abbotsmike]

My advice would be to keep the tops running off the single amp as it is now. Passive crossover, especially at subwoofer frequencies, are horrendously inefficient, and as said, 300w or so is not a lot to give to a subwoofer.

Leave the warrior amp running just the pair of tops, and watch/listen for clipping. ideally you want an amp that does a REAL 500w@8ohms to be comfortable powering tops that can take a real 350w@8ohm. The warrior amps have a reputation for putting out less than their 'rated' power.

If, in the future you decide that you need more bass, then consider buying/building a subwoofer or two, and buy a reputable amp to match (JBL, crown, old peavey, matrix, even some Kam units) I have a small PA rig and a single hornloaded 12" subwoofer easily keeps up with a pair of 10"+1" tops.

[jamesperrett]

John - I think your biggest problem is that you are blindly following advice without knowing whether it is good or bad advice because you don't understand the principles of the subject.

 

Your amp is underpowered for those speakers but that isn't a problem if you don't drive it into clipping. Yes, you can get more power out of it if the impedance it sees drops to 4 ohms but your speakers are 8 ohms and they will actually receive less power if you use some kind of parallel setup that lowers the total impedance. If you want to feed more power to the speakers you have then you need a bigger amp and no amount of connecting speakers in parallel will solve this.

 

Anyone who tells you different is probably as inexperienced as you are.

 

James.