What sized amp for subwoofers?

**jmiyake** · 10-17-2006, 06:01 PM

About a week away from finishing my two ported RS390 Dayton High Fidelity subs. Shopping for a pro-amp to power them. I have decided on buying a Crown XLS amp... but I keep going back and forth on how much power to buy.

Two 15" RS390 HF subwoofers in two separate 195 liter ported enclosures tuned with 6" tube to about 16.5hz.

What sized amp would you buy?

James

**Jethro** · 10-17-2006, 06:16 PM

So those ports are what, like 38" long?!?!

If it were me, I would run ~500 watts to each one (1000w total).

> About a week away from finishing my two
> ported RS390 Dayton High Fidelity subs.
> Shopping for a pro-amp to power them. I have
> decided on buying a Crown XLS amp... but I
> keep going back and forth on how much power
> to buy.

> Two 15" RS390 HF subwoofers in two
> separate 195 liter ported enclosures tuned
> with 6" tube to about 16.5hz.

> What sized amp would you buy?

> James

**jmiyake** · 10-17-2006, 06:27 PM

The speakers are 4 ohms rated at 500w rms to 700max.
The amps are rated thus from manufacturers website:

Power Output (1 kHz*)
---------Stereo-------------Bridge-Mono
-----------8 Ohm---4 Ohm--8 Ohm
XLS 802- 500W 800W 1600W
XLS 602- 380W 600W 1200W
XLS 402- 300W 450W 900W
XLS 202- 200W 300W 600W

**jmiyake** · 10-17-2006, 06:32 PM

> So those ports are what, like 38"
> long?!?!

36.5" long.

**thomasw** · 10-17-2006, 07:07 PM

Usually you can answer this question with your box modeling program. Programs like Unibox and WinISD show the amount of power needed to drive the sub to full excursion

**bogie** · 10-17-2006, 07:32 PM

That ain't enough amp. Go bigger. I've clipped my XLS602 with a pair of Q15s... I'm probably gonna get a Behringer 2500.

> About a week away from finishing my two
> ported RS390 Dayton High Fidelity subs.
> Shopping for a pro-amp to power them. I have
> decided on buying a Crown XLS amp... but I
> keep going back and forth on how much power
> to buy.

> Two 15" RS390 HF subwoofers in two
> separate 195 liter ported enclosures tuned
> with 6" tube to about 16.5hz.

> What sized amp would you buy?

> James

**wg_ski** · 10-17-2006, 07:34 PM

> Usually you can answer this question with
> your box modeling program. Programs like
> Unibox and WinISD show the amount of power
> needed to drive the sub to full excursion

*And* remember that those ar 1kHz power ratings. Power at >2x line frequency will be less by about 20%. I suspect the big one can only do about 650W at 20 Hz unclipped.

**wg_ski** · 10-17-2006, 07:37 PM

> That ain't enough amp. Go bigger. I've
> clipped my XLS602 with a pair of Q15s... I'm
> probably gonna get a Behringer 2500.

The RMX2450 (what the EP2500 is a clone of) *is* 650W @ 20-20k, unclipped. It might not be big enough either :-).

**mikebw** · 10-17-2006, 07:53 PM

Be aware that these QSC's do have a fairly audible fan, which is good for the amp, but depending on where you put it you may be able to hear it, although probably not while the bass is cranking... have fun!

**paul_n_oneal** · 10-17-2006, 08:04 PM

Get one of these and never look back

<A HREF="http://www.musiciansfriend.com/produ...Amp?sku=480827">http://www.musiciansfriend.com/produ...Amp?sku=480827</A>

Paul

**Jethro** · 10-17-2006, 08:34 PM

BassBox6Pro shows full excursion will be reached at just under 500 watts (above tuning frq).

> Usually you can answer this question with
> your box modeling program. Programs like
> Unibox and WinISD show the amount of power
> needed to drive the sub to full excursion

**corbettplatt** · 10-17-2006, 09:45 PM

> About a week away from finishing my two
> ported RS390 Dayton High Fidelity subs.
> Shopping for a pro-amp to power them. I have
> decided on buying a Crown XLS amp... but I
> keep going back and forth on how much power
> to buy.

> Two 15" RS390 HF subwoofers in two
> separate 195 liter ported enclosures tuned
> with 6" tube to about 16.5hz.

> What sized amp would you buy?

> James

Well I am building a single sealed RS390 HF in 5.5 cubic foot box and will be powering it with a Bash 500 watt amp. So I am very interested in what you come up with. I looked at a ported design but it seemed like the Q value pointed to a sealed enclosure.

**wingnut** · 10-17-2006, 11:39 PM

> About a week away from finishing my two
> ported RS390 Dayton High Fidelity subs.
> Shopping for a pro-amp to power them. I have
> decided on buying a Crown XLS amp... but I
> keep going back and forth on how much power
> to buy.

> Two 15" RS390 HF subwoofers in two
> separate 195 liter ported enclosures tuned
> with 6" tube to about 16.5hz.

> What sized amp would you buy?

> James

Better to over-power than under-power. My gut-shot is 250 - 500 watts. Remember, more power gives you more headroom (not more overall sound). Transients sound more articulate, with better punch. The fact in the matter is you NEVER use more than about 1/10 of your amp power rating for any significant period of time.

A 5-watt amp sounds no different than a 5000-watt amp most of the time.

AJ · 10-17-2006, 11:56 PM

Yeah, but that 5000 watter sure does warm the room in the winter time. Better run a dedicated line from the pole...

**jmiyake** · 10-18-2006, 09:59 AM

Provided Link: QSC amp selection tool

Interesting QSC recommends the amplifier be 1.5 to 2 times the continuous rating of your speakers. So for 500 watt speakers they recommend 1000 watts per channel!

Do you agree with this?

**wingnut** · 10-18-2006, 10:27 AM

> Yeah, but that 5000 watter sure does warm
> the room in the winter time. Better run a
> dedicated line from the pole...

Jacks up the electic bill too! Anyway, I can be extreme, at times, to make a point -- certainly was here. But I did own a 5 watter at one time in my life (actually, it was 8 watts/channel). My first stereo rcvr as a kid was a second-hand Sansui. You wouldn't think it could play very loud, but it rocked (or so it seemed -- maybe my hearing was still good then). Your right. 5000 watts is much more toasty this time of year than the other!

Toby

**wg_ski** · 10-18-2006, 11:18 AM

> Interesting QSC recommends the amplifier be
> 1.5 to 2 times the continuous rating of your
> speakers. So for 500 watt speakers they
> recommend 1000 watts per channel!

> Do you agree with this?

I've seen the recommendation as much as 4x the speaker's continuous capacity. If the amp is overdriven, the thermal load on the speakers is higher. The more headroom you have in the amps, the less likely the system is to be overdriven. This is true of both pro and home sound systems. You see 8" woofs with 60 watt ratings being used with 250W amps all the time and it doesn't bother anything if it's not turned up to distortion.

In the pro world, the speakers (including subs) are high pass filtered to prevent overexcursion. This for the most part removes mechanical failure mechanisms, leaving just the thermal to be dealt with. For HT subs, limitations are almost never thermal - it would be just too blasted loud. You size the amp so it won't bottom the sub out with the expected source material. Which may contain a lot of sub-20-hz. And most long-throw subs don't have a lot of headroom between x-max and where they physically bottom out so it's easier to do than with typical 'pro' speakers.

**Paul O** · 10-18-2006, 02:01 PM

What they don't tell you is you have to use good system limiting with this type of power, you need an oporator with good system knowledge that knows where the speaker limits are, and he/she has to pay attention at all times. Revome any one of these three and you'll blow stuff up real quick. Also note that due to the very uncompressed nature of live music, greater dynamic headroom is needed to prevent amp clipping. Having 1000 watts available to drive a single speaker sure sounds like a lot, but that's only 9db of headroom from 125 watts.

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