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Class D Switching Power Amplifiers and Power D/A conversion

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Old 10th November 2010, 06:33 AM   #761
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Originally Posted by bluewhale View Post
Saturnus, I built a truly portable battery operated speaker one year ago with a bass response that cut off around 80-90Hz.. We used it at Burningman. It had an eminence 8cx, and we found that for dance music it was quite nice. In fact, people said it boomed even though part of the beat was cut off.

I do recognize that indoors you can get a gradual 15db or so boost down to 20 Hz with all the surfaces in a typical room, but it is graduated. Room response curves show that the effect increases as the bass gets deeper. At around 70 Hz, where the kick beat in most music ends, there isn't that much of a boost. I'd have to check to make sure, but I don't believe it will be 4 times the output.
For simplicity you can consider the room boost an inverse 1st order filter at roughly 120Hz for semi-free field use as we're talking about here. So it's +3dB at 120Hz, +6db at 60Hz, +12dB at 30Hz and +15dB at 20Hz. So yes, it needs 4 times the output to compensate for the loss of the +6dB boost at roughly 60Hz. Please note that the boost actually starts at roughly 200Hz (120Hz*Pi/2).

Last edited by Saturnus; 10th November 2010 at 06:36 AM.
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Old 10th November 2010, 06:43 AM   #762
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Interesting. Could they be coupled with a piece of wood and some glue somehow?
Yes, but it would be more difficult to implement. If high quality neo drivers are wanted then speakers such as P.audio SN10MB are perfect drop in replacements for the P.audio HP10Ws. They're not lighter though, actually they weigh slightly more, but they're better quality with twice as good sensitivity (+3dB) over the HP10W. They also cost about 5 times more a piece though.
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Old 10th November 2010, 07:09 AM   #763
kblnig is offline kblnig  Denmark
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[QUOTE=Saturnus;2359586]
I also have to agree with you on the piezos. Usually they're considered utter crap, and rightfully so, but there are gems among them that can easily compete with even the best dome tweeters on the market. Since the Zomax HP100s that I used in the Boominator isn't produced anymore, I'm also leaning towards a CTR one. But I also have my eye on a P.audio tweeter horn.

Hi Saturnus. Have you yet come up with any piezos worth trying now that the HP100s are sold out?
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Old 14th November 2010, 09:09 PM   #764
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Saulty, I'm also planning to design a monophonic boombox with a cabinet dimension similar to yours, and I'm wondering if you still think the CTS/Motorola piezo tweeter is efficient enough to keep up with the Fatality driver you employed. How is the fidelity, and did you find it could cross over as low as 1.5k without issue? Basically, if you had to do it all over again, could you recommend said tweeter for the application?

Also, may I ask why you went for the far more expensive Class D Audio board over Hifimediy's, T3 1.0 tk2050/bt1597 Tripath board? I know that requires a 48v power source for maximum output, but in all other parameters, it does seem ideal.

Ps... I'd settled on the speaker drivers before I saw this thread. Either coincidence, or a clue that they've got the best parameters for the application - at least at a moderate price point.
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Old 15th November 2010, 02:48 PM   #765
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Hi Saturnus. Have you yet come up with any piezos worth trying now that the HP100s are sold out?
Yes. The CTR KSN1001A, the -01A one because it's extremely easy to integrate as all it takes is a 76 diameter cut-out and some glue on the back to flushmount it.. Still tinkering with it to get it sounding right.

Alternatively you can try some of the many many replicas/replacements of the same, or the -05A version, but I've yet to find any that has more than just acceptable sound quality. Also note that most of the replicas/replacements don't match the 94dB/w/m sensitivity of the original CTS one.

Last edited by Saturnus; 15th November 2010 at 02:50 PM.
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Old 15th November 2010, 07:50 PM   #766
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Hi.
What about this?

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Old 15th November 2010, 08:47 PM   #767
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Hi.
What about this?

http://www.ljudia.no/hyttalerelementer-s82124/piezo-c78561/qlm-1005-p78564/"]http://www.ljudia.no/hyttalerelementer-s82124/piezo-c78561/qlm-1005-p78564/
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Old 15th November 2010, 09:19 PM   #768
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Originally Posted by saxomann View Post
http://www.ljudia.no/hyttalerelementer-s82124/piezo-c78561/qlm-1005-p78564/"]http://www.ljudia.no/hyttalerelementer-s82124/piezo-c78561/qlm-1005-p78564/
Bad link but I figured out what it was anyways. Run of the mill replica of the KSN1005A. Not one of the worst around but I'd only recommend the originals unless someone can send me a replica of the KSN1001A that actually sounds acceptable.
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Old 15th November 2010, 09:58 PM   #769
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Originally Posted by Saturnus View Post
Bad link but I figured out what it was anyways. Run of the mill replica of the KSN1005A. Not one of the worst around but I'd only recommend the originals unless someone can send me a replica of the KSN1001A that actually sounds acceptable.
Hi.
Could you bother to tell me witch speakers and amp you would choose if you didnt need battery suply? I will mostly use it in a Volleball arena and at work building houses.
How could i conect a mic and volume controll for it (the mic that is).
Prisiate your help. I have tried to find a deasent boombox to by, but i dont think
it exist.
Bjoern
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Old 16th November 2010, 06:50 AM   #770
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Well, after much experimenting I keep coming back to the conclusion that the current design is basically perfect in every way. There's only one minor change and a few refined details.

The minor change is that the handle/port is now replaced with a plastic slot handle where the end is cut off so that it duplicates as a port just as in the original design but just a lot more easy to make. You can even vary the length to fit tuning demands.

Boominator mark.II recommended parts:

Woofers: P.audio HP10W (no alternatives)
Tweeters: CTR KSN1001A (or replicas)
Amplifier: 41Hz Amp6basic (or other TA2020/TA2021 based amp)
Batteries: up to 3 12V 7Ah SLAs in parallel internally (or Li-ion pack fitting in size)

Boominator Signature recommended parts:

Woofers: P.audio SN10MB series II (no alternatives)
Tweeters: P.audio PHT407N (or similar high dispersion, high sensitivity and high quality tweeter horn)
Amplifier: 41Hz Amp9basic (or other 4 channel Tripath based amp)
Filtering: active at 2.4KHz with passive correction (or mix PLLXO and passive filters)
Batteries: up to 3 12.8V 6.8Ah LFP packs (no viable alternatives to the LFP pack, they're superior in every way to any other battery type)

Both versions can solar panel integrated or loose on top if so desired. I recommend a standard cheap 15W "12V" amorphous panel where the casing is stripped off for integration.

For 24V or higher operation on the Signature (or if you have another amp on the mark II), I recommend switching to an external power supply and not use the internal batteries.

You can naturally mix and match as you like, and even use alternatives I haven't listed but I can't guarentee as good a result if you do.

Last edited by Saturnus; 16th November 2010 at 06:57 AM.
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