Karaoke Forums

Hi Folks

Following on from a earlier thread regarding my son upgrading his PA system - He now has a Yamaha MG16/6FX desk and a QSC GX5 (2 X 750W into 4 ohm) power amp mated with a pair of peavey Hi sys 2 speakers. He has yet to give the system a good try out but is trying to sort a local hall for a band practice/PA setup this week.

My question is with the above power amp etc. when he adds a crossover and Bass amp what sort of power output should he be looking at? Should it be similar to to QSC around 1500w or slightly more or less?
He reckons the bass amp is not as crucial as the power amp so he may look at a cheaper unit i.e. Kam etc. around £225 UK for a 1500w any thoughts?

Big thanks again for reading this.

Paul

Yes that should do it.
Really you want a lot more for the bass.
Here in the UK he is not going to come close to turning his tops up that much.

When I run subs I prefer to run twice the power to sub. So your giving 750 watts per channel to your tops, the subs should get about 1500 watts. But then this is completely dependant on the sub you choose.
The bass amp IMO is a crucial point as it is going to need to be able to push the power without problems ie heating up/shutting down/etc. Make sure it is going to be able to stand the riggers of a dedicated sub amp, it's going to be pushed hard. I know nothing of KAM amps, but in a previous question it looked as though it wasn't as clean of an amp as some others in the same price range.
But you should wait on what to get for your sub until you know which subs you are getting.

_________________
LIKE Lonman on Facebook - Lonman Productions Karaoke & my main site via my profile!

I'd second what Lonman said, as a general rule about twice as much power for the subs as the top end. However, one thing to consider here is when you've got 750 a side pushing the top ends, I highly doubt you'll ever get close to pushing those things with that much power. The low end frequencies are what take the most power to reproduce. Once you've offloaded that to the subs, the top end cabinets will not need nearly as much power to get to the volume level you need. Therefore it is totally conceivable that you could get away with less than 1500 a side for the low end.

_________________
DJ Tony
Let It Rip Karaoke

He could even get away with 1 sub to start with - I ran many live shows with only one.

_________________
LIKE Lonman on Facebook - Lonman Productions Karaoke & my main site via my profile!

I have learned there are two kinds of subs: those worth the money, and those that are glorified stands for your tops. Don't waste money on cheap subs, just wait & save until you can justify something good. I am not familiar with the products that may be priced nicely in the U.K. but I think the JBL SRX subwoofers are great in terms of output, truck space / mobility, and efficiency. Easily worth the price.

_________________
Jeff Wheeler, moonlight DJ/KJ

One bass per person with a corn on the cob, mashed potatoes, and some Kool Aid should be plenty.

_________________
C Mc
KJ, FL

Hi folks

As per lonman my son said he may actually just run 1 Sub for a while and see how it sounds and if required add a second sub later.
Would that require a AMP that can sum the bass into 1 output as opposed to just running 1 channel of a stereo amp?

Cheers

Paul

It's still going to be completely dependant on which sub you decide to go with as to which amp you will want to run. Since you are running Peavey already, look into the SP series subs. Then get an amp to match the 'program' power rating - either in a bridge mode or a per channel mode.

_________________
LIKE Lonman on Facebook - Lonman Productions Karaoke & my main site via my profile!

You will want a crossover with a sub output.

_________________
Jeff Wheeler, moonlight DJ/KJ

well im jumping in late here, I agree with others about more power to the subs than the tops, also that cheap subs are a waste of money. better to buy one good sub than two cheepos. Im also a believer that your sub amp needs to be the best amp you have. it will take the most abuse and clip the soonest. if you can afford to buy a stereo amp that as enough power per side to push a sub then when you upgrade to another sub all you need is the cord to plug it in.

I run a 2 way mono crossover, i crossover to my subs somewhere between 75 and 200 hz depending on the room

_________________
the voices arent real, but they have some good ideas

Hi Folks

Big thanks again for all the good info.

Cheers

Paul

I just sold my 2 new JRX 18s for 500.00, so now I can get a single SRX 18s for around 900.00. From what I gather here I will be better off, plus one less sub to carry around, right?

Yes, I think so. At low power and above about 55Hz, two JRX118S would be better than one SRX718S; but when you get down to 40Hz (and a lot of modern music does, especially the "break music" many KJs play) or up to about 300 watts RMS (combined) the SRX will perform better than two JRXes, and the SRX still has room to get louder and lower. And as you mentioned, it is much smaller than two JRXes and makes your load-in a little easier.

If you were previously running the two JRX subs on one amp channel in a 2Ω configuration, you may not see a benefit above 55Hz. If you had one per side in a dual 4Ω setup, bridge your amp into the 8Ω SRX and give it as much juice as you want. I power my 728s, which are almost identical to two 718s, with 2400w RMS each, or 1200w RMS per driver.

If you do not have a Speakon bridge adapter or patch panel, and don't want to make one yourself, a guy on eBay sells 1 foot adapters for about $30, http://cgi.ebay.com/10-Ga-Bridge-mono-S ... 359d273bb2

_________________
Jeff Wheeler, moonlight DJ/KJ

Actually I have never had the JRXs hooked up yet. Was getting ready to as Tony (letitrip) helped me with making all the connections in another thread.
It's just a killer that I sell 2 new 18" subs for 500.00, and buy a single 18" for 900.00 . But thats one of those "get what you pay for things" I guess.
Anyway I'm excited now to move up to the SRX. I never wanted the JRXs, but did get a smokin deal on em. Thanks!

I learned that lesson the same way you did, I bought two Behringer subs for $350ea and put them under $900ea tops and realized the subs were not even useful, as those tops out-ran them through the whole frequency range. I still have them but I don't use them very often and am always tempted to put them on Craigslist.

_________________
Jeff Wheeler, moonlight DJ/KJ

Thanks for the info Jeff, and sorry to the op for the hijack..