Chip Amp for Sub

[bcmbob]

I am not seeing anything dealing with chip amps used to power subwoofers. Is that not a proper application for this technology? If not, are there any other productive avenues for 300 to 500 W diy sub amps?

[AndrewT]

my low bass speaker runs @ ~100mW.
It was powered by a pair of 170W amplifiers.
It could easily have run on a 60W amplifier and still have ~28dB of overhead for very high bass transients.

[Dr.EM]

The only 'chip-amps' you'll find in this power range will be the class-D types, and even then they may well require extra output devices to perform at this power level.

You are unlikely to see LM3886 and similar class-AB power op-amp chips used to this power level. It'd only be possible by using many paralleled and bridged into a low impedance load at which point (imo) it becmes easier to build a fully discrete amplifier.

EDIT: Andrew is also right though, you are unlikely to need 300-500W of power. It depends on the setup.

[Sebastiaan]

A BPA-300 will do. I designed one used in a commercial sub. Very reliable as long you can cool it.

With kind regards,
Bas

[bcmbob]

The sub I built uses this Hi-Vi driver. My high power comment is based on these published specs.

*Power handling: 500 watts RMS/700 watts max *VCdia: 3" *Le: 1.35 mH *Znom: 4 ohms *Re: 3.4 ohms *Frequency range: 35-150 Hz *Fs: 34 Hz *SPL: 84 dB 2.83V/1m *Vas: .60 cu. ft. *Qms: 4.83 *Qes: .65 *Qts: .57 *Xmax: 15.5 mm

I have gotten good results with my briged Hafler DH-120 in terms of volume. My interest in more power is based on comments that larger amps provide more control over the motion of the voice coil in a driver - resulting in more acurate response. I may have already passed that point of deminishing returns with the setup I have.

I have also seen that many (Bash, Apex Sr, P Express) manufactures offer 300 - 500 - 1000 W sub amps. Is this just overkill for a home 7.1 system?

Dr.EM: Can you give a few more specifics on your comment "it becmes easier to build a fully discrete amplifier". I have built several Dynaco and Hafler amps and would enjoy getting back to doing some soldering. I am planning to build some Statement Speakers HTGuide Forum - Statements Monitors build thread this summer and it seems the new breed of chip and class D offerings might be great to drive them.

[Andrew Eckhardt]

I wouldn't normally recommend anyone interested in fidelity to run their 500 watt driver at 500 watts, not that you really intended to do that.

A bridged DH-120 is probably not the best thing for this woofer. You're running an H bridge of single average sized power FETs into 4 ohms, or virtually loading each channel at 2 ohms. At full power that thing will get very hot. If you've never had problems opening up the thermal cutout in the power supply you don't even need a 300 watt amp, but a real one designed to drive that much into 4 ohms would probably be smart. It might actually sound better too.

[AndrewT]

Originally Posted by bcmbob

*SPL: 84 dB 2.83V/1m *....................... My interest in more power is based on comments that larger amps provide more control over the motion of the voice coil in a driver - resulting in more accurate response.

your problem is that SPL specification. A 4ohm speaker having 84dB/2.83V @ 1m is equivalent to 81dB/W @ 1m.
500W into 81dB is roughly the same as 50W into 91dB. Most PA woofers are much better than 91dB/W @ 1m.
Comparing my previous example of 60W driving a 94dB/W @ 1m speaker, your 81dB/W would need 1200W plus whatever is lost (maybe 1500W to 2400W total input) in power compression to match the SPL. If I were to dedicate a pair of 60W+60W chipamps to the speaker then you would need near 5kW to match it. See the problem yet?

Yes, that speaker should need high power for high SPL but really, it belongs in the bin.

Big Power amplifiers do not have this innate ability.
All Power amplifiers can be built to do this. Power output has nothing to do with it, I would argue the opposite case. So much of the component selection has been compromised to ensure high power delivery that LFcontrol is more likely to have gone out the window.

[tangmonster]

Originally Posted by bcmbob

I have also seen that many (Bash, Apex Sr, P Express) manufactures offer 300 - 500 - 1000 W sub amps. Is this just overkill for a home 7.1 system?

How big is the other amplifiers in your system?
i have a 5 channel system running on 50W max per channel
Currently I am using a +- 80W amplifier for my subwoofer (2 x 12" unknown speakers) I am happy with sub volume but i am still busy building a bpa300 setup as described in this link:

DIY BPA300 6x LM3886 300W audio Amplifier

one last thing.

As my personal rule of thumb to get rms power for most commercial amps take their advertised rms value and divide by 4. If they give a pmpo value divide by 15.

also , take weight into account:
a 500w rms class A/B amplifier will have to weight around 10kg's minimum to even remotely have a chance to give 500w even for a few ms.

The bpa300 is not bad on the efficiency side of things and needs a 500va toroidal weighing around 3.5kg's to reach 294W

[Dr.EM]

Oh, I know what driver that is now

Someone here used it:

HTGuide Forum - HiVi M-series 5.1 HT -- progress

with a 300W class-D plate amp, and that would be my reccomendation if you wish to use such a low efficiency driver. Anything else is going to be big and get hot, which sort of defeats the point of the driver which plays very low in a small box.