Home Brew powered sub.

[Douglas R. Allen]

I had the need for a smaller powered sub for drum monitor,smaller rooms, and to loan,lend to friends.
I had 2 6.8 cubic foot sub boxes loaded with a fresh set of these.

Peavey 1808-8 CU BWX 18" Woofer Speaker Driver 294-307

I saw that QSC was blowing out the power amp module for their HPR151w subs. At first I was going to pick up 2 for spares for my HPR181i subs.

WP-001516-00

But after some testing it seems the low cut filters were higher and the limiters seem to be set sooner/longer time constant because they were designed for the smaller 15 inch woofer. I figured I'd put them in the unpowered boxes that I had and see how they worked. I would still have these available to replace a bad HPR181i sub amp while it was sent out for repair should that ever be needed.

The amp modules required their own chambers so I added those to the boxes. This brought them down to about 6.25 cubic feet. The box tuning changed to about 48hz. This worked out well as the steep lowcut filters on the amp seems to be set at about 50hz.

The boxes have a 6db down point at about 45hz and 6db down at 140hz as well. This is pretty much the same freq. response as the HPR151w boxes the amps were designed to go in. There is a 6db peak around 83hz. I'm unsure if this is eq voicing put in by qsc to give a givin' response in their box or a peak in my box/speaker/amp combo. You can see it in the smaart capture. This was a rough measurement in my home so I will take another look when weather permits outside.

QSC - HPR Series - HPR151W

Overall I'm happy with the boxes. The phase response is close enough that I can use them with an hpr181i sub if need be.

This turned out to be a low cost powered sub project that should work well for its intended use.

Douglas R. Allen

"I was unsure as to where was the correct place to post this so please move as needed"

 

[Art Welter]

Re: Home Brew powered sub.

I saw that QSC was blowing out the power amp module for their HPR151w subs. At first I was going to pick up 2 for spares for my HPR181i subs.



But after some testing it seems the low cut filters were higher and the limiters seem to be set sooner/longer time constant because they were designed for the smaller 15 inch woofer. I figured I'd put them in the unpowered boxes that I had and see how they worked. I would still have these available to replace a bad HPR181i sub amp while it was sent out for repair should that ever be needed.

The boxes have a 6db down point at about 45hz and 6db down at 140hz as well. This is pretty much the same freq. response as the HPR151w boxes the amps were designed to go in. There is a 6db peak around 83hz. I'm unsure if this is eq voicing put in by qsc to give a givin' response in their box or a peak in my box/speaker/amp combo.

Douglas R. Allen

Douglas,

Price seems pretty good, what kind of voltage can the amp do before packing up?

You could determine the amp EQ by testing it independently at a low drive level with a load resistor (a space heater or toaster work well if you don't have anything else handy) and some clip leads to your Smaart input to determine what the plate amp is actually doing. A 6db peak around 83hz would be an odd thing to design in, but Quilter is not shy about creating "bang for the buck", 80 Hz gives a good "boom boom" effect.

Art

 

[Douglas R. Allen]

Re: Home Brew powered sub.

Douglas,

Price seems pretty good, what kind of voltage can the amp do before packing up?

You could determine the amp EQ by testing it independently at a low drive level with a load resistor (a space heater or toaster work well if you don't have anything else handy) and some clip leads to your Smaart input to determine what the plate amp is actually doing. A 6db peak around 83hz would be an odd thing to design in, but Quilter is not shy about creating "bang for the buck", 80 Hz gives a good "boom boom" effect.

Art

Art;

I have a DI that is designed to handle speaker level inputs. (Via 40db pad) Would this work as well? Never tried it but was thinking about it. Start at the lowest level of course.

The Plate Amp is rated at 700 watts at 8 ohms. I believe it is a RMX1450 redesigned as a plate and run in bridge mode. The 1450 is 800 watts at 8 ohms bridged. This sounds about right as with no fan it would run cooler with just an 8 ohm load.

http://www.qscaudio.com/products/amps/rmx/rmx.htm

On the powered subwoofer information page it states

"Power module based on the best-selling RMX series amplifier technology provides 700 watts of class H power"

http://www.qscaudio.com/products/speakers/hpr/hpr181i.htm

For the single !000 watt program speaker I have loaded in the box it provides pretty good get up and go within its freq. range. I'll have a look at the eletrical output if I get a chance today.

Douglas R. Allen

 

[Mark DeArman]

Re: Home Brew powered sub.

I'd only be worried if they happen to have some heavy EQ (above +3dB). Might cause some headroom problems. I'd take the previous reply's advice and measure them with a resistor. You might even be able to get the programmer for the "DSP" (quotes are important,) if the DSP solution is cheap enough, for 50$-100$. Lots of the SoC DSP solutions are fixed routing matrix systems which are easy to modify. Not like a real DSP which there is programming involved.

 

[Tim Weaver]

Re: Home Brew powered sub.

You can use the DI to feed smaart, but you still need to have the speaker hooked up to keep things running right. This will still work since the smaart feed is pre speaker.

 

[Douglas R. Allen]

Re: Home Brew powered sub.

Some friends of mine played last night. They let me try the subs out and mix them.
They have the JBL JRX118sp subs that they normally use.

http://www.ebay.com/itm/JBL-JRX118SP...item20c5393351

For tops they have the PV 2-15 and horn. I gave the sub and tops a listen. I thought the sub was high cut quite high. Even in the 250hz range or so it was still putting out quite a signal. On the tubby side.
I listened to the tops and felt something was just not right. It sort of sounded ok but the horns were very loud in relation to the lows. I couldn't get the expected level out of either speaker. I looked the speakers over to find a Parts Express 2 way crossover with no cd horn eq had been put in them. Popping a handle off I found a Peavey 22xt driver duct taped to the horns in place of the 14t horn that should be in it. Black widdow speakers were in place at the bottom speaker location. Also as the crossover was just a 2 way someone had run the 2 15s in series.
The crossover did have a horn level knob so I turned it almost off to get a good blend. Set up like this I thought the speaker sounded better. Horns were soft sounding in the highs. I put a high shelving eq starting a 2k with a 6db boost to make up for the missing cd horn eq. This made them sound ok. I used my CS800s amps with built in crossovers to power the tops 100hz and above.

Leaving their subs in place "In case" I put the tops on my subs and did the show. (they made great monitor/amp stands) I'm not a fan of subs on each side of the stage but it put the tops just high enough to get the job done. I had some very large power alleys in the room but everyone was happy with the sound.

The subs;
Subs really did work great. The QSC amp modules never ran more than just warm/cool. The boxes pounded harder than they had before. They moved a fair amount of air for the size. Before I had 800 watts per box but the 700 watts provide by the qsc amps seemed tighter yet as deep. I believe the low cut filter at around 45hz instead of the 40hz I used on the amps for them before may be part of it. Of course the room I used them in comes into play hear as well. To be honest I found a rattle on the bottom where the port is that I never noticed before. They did come alive. I'm sure not having long speaker cable runs also added to the tight sound.

Overall everything worked better than expected. Nice small subs for shows just like this. Had fun

Douglas R. Allen