The Boominator - another stab at the ultimate party machine

[Saturnus]

Originally Posted by Andrew Eckhardt

Alrighty, I'm not building any of this stuff but the projects are interesting and I pretty much scanned the whole thread. I saw almost no circuit drawings. Lots of talk about box alignment and tweeter crossovers, but didn't see anything about woofer crossovers.

Folks will want to be sure they have not omitted a high pass filter for the woofer. If your port frequency is at 70Hz, for example, you might want to use a 24db rolloff below that, maybe 60 at the lowest. Where to crossover would be a compromise between sound quality and energy efficiency, and filtering right at the tuning frequency might not be a bad idea, but ignoring a high pass on the woofer when you're losing response in truckloads below 60-90Hz might cost you half the running time in waste heat in the woofers (and lots of dynamic headroom as well, depending on the signal.) Of course you want this to be a signal level crossover of some kind to keep low end that can't be converted into sound pressure out of the amplifiers altogether. Please excuse if this consideration has already been addressed across the board and I missed it.

Fairly sure I mentioned that I have a different input cap on the amp6b that cuts at 60 Hz. You really can't go higher than that before it's noticable, unless you make a more complex filter than just changing the input cap.

Most mp3 don't have much info under around 40 Hz anyways, so it's not a major deal in my mind.

[Andrew Eckhardt]

Do you mean that the compression schemes used dump off the bottom of the band? Because I didn't think that was the case. Sure you need to have the dynamic headroom in the DAC, but in terms of compression I don't think high resolution at low frequencies takes up much space, so it's probably preserved pretty well. I could be wrong.

Far as the MP3 player, I Think that they are designed with the exact same considerations in mind far as amplifier loading and power consumption, only at the headphone level. If you only load the output with a few hundred to a couple thousand ohms you are likely to experience fair flatness down to 20. What actually comes out, of course, still depends on the recording. But you're definitely right, nothing much below 60 is gonna make it out of your speakers except as heat. Below 40 you're bound to increase overall distortion by eating up linear excursion as well.

[Andrew Eckhardt]

Stereophile: Apple iPod portable music player

[Andrew Eckhardt]

In fact I got stuff coming down a 96kbs stream on the psychill station at di.fm right now that Looks to be about 10 Hz and loud. I can't hear it, it's just driving the woofers crazy in my dipole PC speaker setup... and I'm actually using an Ancient SB16. There's not supposed to be anything down there, but I got about 12mm P-P on a ten inch, doing nothing.

[Andrew Eckhardt]

Of course with a simple 6dB/oct filter at 60 Hz you'll still be 15dB down at 10Hz, something like that.

[Havoc08]

Originally Posted by Saturnus

Please note this is specifically for the amp9b or amp6b which has 90% effciency, assuming the source is able to load the amp to -0 dB, and that the music roughly follows the RIAA recording standard.

Yes, but still 400watts into your design...
By experience you are often amazed of how long these digital amps actually run on a 7aH SLA. In real life you rarely listen to max volume on all channels and with your design 4x100 watts is going to be loud!
The mileage of your battery will of course also depend on your music taste as pumpin out heavy bass of course demands more power than a tweeter.

As I mentioned previously the amp 4, amp1b or sure 2x100 watt might be a middle way if the 2x15 watts are too little and the 4x100watts too much.

[Saturnus]

Originally Posted by Andrew Eckhardt

Do you mean that the compression schemes used dump off the bottom of the band? Because I didn't think that was the case. Sure you need to have the dynamic headroom in the DAC, but in terms of compression I don't think high resolution at low frequencies takes up much space, so it's probably preserved pretty well. I could be wrong.

I usually tick the sub-cut when I compress mp3s. That's a 24 dB/octave digital filter cutting at 40 Hz just like most professional amps are equipped with as standard.

[Saturnus]

Originally Posted by Havoc08

Yes, but still 400watts into your design...

Yeah, the Boominator is NOT designed to be fed more than about 50W per side which is about the maximum an amp9b can provide with real music signal.

It's pretty much designed to run on an amp6b or amp9b at both 12V and 24V.

[Andrew Eckhardt]

Originally Posted by Saturnus

I usually tick the sub-cut when I compress mp3s. That's a 24 dB/octave digital filter cutting at 40 Hz just like most professional amps are equipped with as standard.

That works.

[Saturnus]

Originally Posted by Andrew Eckhardt

That works.

Exactly. It's not like I'd ever use mp3s and certainly not an iPod for any kind of serious listening, so I usually use slight dynamic compression and sub-cut on my mp3s since they'd be mostly used for playing on an iPod, either on head phones or the Bomminator.