BillFitzmaurice.info

Hey now! I'm looking to power up two J-array tops & two slim T39s for a simple pa system for block parties & whatever else is (hopefully) happening some time later this year...I do hope you're all well by the way, let me also say that...

So the tops would be 8Ω Beta 12As (250W) & the subs 8Ω BP102s (200W). I have two power amps already from different bass rigs & I'm trying to decide which would suit me better here - a first-gen Peavey IPR3000- non-dsp with a built-in 4th order LR crossover at 100Hz...or an old Ampeg SVP1500- no built-in crossover, but banana jacks! There was an updated version later with speakons, so this guy would be from the 80s or early 90s. But still works great. The ampeg is stable to 2Ω on each channel, I'm not clear about the peaveys, are they as well? Naturally I would rather have the amp coasting along.

They each express their output ratings differently & I'm having trouble figuring out if either is more suitable for this kinda deal. I understand I'll be using voltages to set it up finally, but I've forgotten some of this basic math down the years..is either one a better fit based on the numbers?

Peavey:
1,490W RMS at 2 ohms (both channels driven)
840W RMS at 4 ohms (both channels driven)
440W RMS at 8 ohms (both channels driven)

Ampeg:
Per channel, stereo mode
2 ch (20-20kHz) 8 ohms: 230W
2 ch (1kHz) 8 ohms: 280W
4 ohms: 425W
2 ohms: 560W
Mono mode
(20-20kHz) 16 ohms: 460W
(1kHz) 16 ohms: 520W
8 ohms: 850W
4 ohms: 1120W

With each cab being 8Ω, I'll end up with 4Ω per channel, correct?...5Ω for the two subs, call it 4Ω for our purposes, I'm easy.

The T39 plans detail a simple 150Hz crossover if I want to go that route, but is Peavey's 100Hz a better way to go? Happy to hear any opinions, math, you name it.

Cheers for getting through all that
xoxoxo

I would use the crossover in the Peavey. Run in mono - one side for tops, the other for subs. You will definitely need a limiter for the sub channel as that amp is going to put out over 50 volts and the BP102s can't take that.

Bruce Weldy wrote: ↑Tue Mar 16, 2021 3:40 pm I would use the crossover in the Peavey. Run in mono - one side for tops, the other for subs. You will definitely need a limiter for the sub channel as that amp is going to put out over 50 volts and the BP102s can't take that.

+1.
The BP102 8 ohm drivers can take a maximum voltage displacement limit of 35V.
BTW, the BP102 8 ohm is 200W rated in an open baffle, not in a horn sub.
In a horn sub, the BP102 8 ohm can only take a maximum of 153W

That would only leave around 7V as headroom if you were to use the Ampeg. While I have done something with an amp with similar specs in the past, if you're thinking you might turn up, you want some headroom.

+1 on the limiter as well. It's mandatory, so, you might and could also use all the DSP processing available in a used Driverack. That's Limiter, Graphic EQ, crossovers and RTA all in a 1RU space...

I appreciate the input, fellas. So. Out of curiosity, when they say 440W RMS at 8 ohms, both channels driven, do they mean 2x440, each channel being 8Ω, or is it less straightforward? I remember buying the Peavey knowing it was overkill for my needs at the time & knowing that's the right way to go. Again, I understand watts are only calculated from voltage anyway.
I used to get this stuff ))

It's funny, I've gone on to understand far bigger things & pushed out the easy stuff. I'm like Kelly Bundy hahah

Grant Bunter wrote: ↑Tue Mar 16, 2021 7:14 pm BTW, the BP102 8 ohm is 200W rated in an open baffle, not in a horn sub.
In a horn sub, the BP102 8 ohm can only take a maximum of 153W

That 200w rating is thermal, not mechanical. The voltage limits we use are for thermal or mechanical, whichever is less. In a ported box the BP102 mechanical limit is 17v.

Bill Fitzmaurice wrote: ↑Tue Mar 16, 2021 9:50 pm

Grant Bunter wrote: ↑Tue Mar 16, 2021 7:14 pm BTW, the BP102 8 ohm is 200W rated in an open baffle, not in a horn sub.
In a horn sub, the BP102 8 ohm can only take a maximum of 153W

That 200w rating is thermal, not mechanical. The voltage limits we use are for thermal or mechanical, whichever is less. In a ported box the BP102 mechanical limit is 17v.

Just to make sure I'm getting this right for future:
While the thermal limit for the BP102 is 40V (200W@8 ohms), the mechanical limit in a T39 is 35V(153W@8 ohms)?

That's correct. The mechanical limit is usually lower than the thermal limit, sometimes by a very wide margin. That's why you can't use the thermal limit to determine maximum voltage.

Bill Fitzmaurice wrote: ↑Tue Mar 16, 2021 9:50 pm That 200w rating is thermal, not mechanical. The voltage limits we use are for thermal or mechanical, whichever is less. In a ported box the BP102 mechanical limit is 17v.

And would that equate to just 36W?? If I'm getting it.

Lesknow wrote: ↑Wed Mar 17, 2021 7:32 am

Bill Fitzmaurice wrote: ↑Tue Mar 16, 2021 9:50 pm That 200w rating is thermal, not mechanical. The voltage limits we use are for thermal or mechanical, whichever is less. In a ported box the BP102 mechanical limit is 17v.

And would that equate to just 36W?? If I'm getting it.

That's correct. But, his example is that driver in a ported box. In the T39, it's still 35 volts.

Absolutely, just testing myself with the math.

Lesknow wrote: ↑Wed Mar 17, 2021 8:47 am Absolutely, just testing myself with the math.

Well, you can worry over the math or just use this and save the time.....

http://www.sengpielaudio.com/calculator-ohm.htm

Bookmarked, thanks

Lesknow wrote: ↑Wed Mar 17, 2021 10:25 am Bookmarked, thanks

I bookmarked it shortly after arriving at this forum over 10 years ago....

I bookmarked it but can't find the bookmark amongst the hundred or so I have.