UK Internet Radio Build

[ralphsaunders]

Hey all,

I'm very new to this sort of thing, the most I've ever played with electronics has been while fixing my bass/electric guitars; never the less, I've committed to building an internet music radio for a university project.

I'm posting here, as most seem to, seeking advice on what qualities I should be looking for in speakers, amps, and other sound related gubbins that might be required for such a project.

To give you some idea about what I'm trying to achieve, the radio has a Raspberry Pi (small linux computer, the size of a credit card) in it, as well as some buttons. I imagine its size is going to be largely dictated by the dimensions of the speakers that go into it, although the entire unit needs to fit onto someone's work desk (150cm x 50cm) while still giving them space to work.

Perhaps idealistically, I'd like the unit to produce good sound for its size. In the small (and one not so small) docks I've tried for my research, the sound has always felt rather... compressed. Led Zeppelin's Achilles Last Stand (encoded in Apple's lossless codec), has sounded fairly awful on all of them. From what I could see, the units I tried all had two speakers (which I'm guessing would be classed as full range), no bigger than 2" in diameter. This has lead me to believe that perhaps a tweeter + small woofer combination for each channel might be best?

I've put together a list of components that I think might do the job. It's worth noting that I'm limited by UK stockists as shipping from the US is usually rather pricey.

2 X 2 Watt 4 Ohm Class D Audio Amplifier Board

http://www.ebay.co.uk/itm/2-X-2-Watt-4-Ohm-Class-D-Audio-Amplifier-Board-PAM8803-2W-Stereo-Power-Mini-/350660948197?pt=UK_AudioTVElectronics_HomeAudioHiFi_Amplifiers&hash=item51a50570e5#shId

AS06608PS-R Speaker (driving the bass) x2

http://www.digikey.co.uk/scripts/DkSearch/dksus.dll?WT.z_header=search_go&lang=en&keywords=AS06608PS-R&x=0&y=0

Tweeter x2

http://electromarket.co.uk/product/902.310/2.25+Inch+40W+8+Ohms+Square+Mylar+Dome+Tweeter

250W 8 Ohm Crossover Pair

http://www.electromarket.co.uk/product/DR17/Pair+250W+8+Ohm+Crossover+Network+for+QT+Series+Speakers

Do these components fit the purposes I want them for? Are there better ones out there for less or the same amount of money? Would the unit be loud enough for a small office?

Cheers,
Ralph

[johnastockman]

Re: UK Internet Radio Build

Ralph, the one thing I do know is that any off-the-shelf crossover (XO), or pre-made unit, is woefully inadequate to perform that task. The pre-made XO "assumes" that each driver is a constant 4 or 8 ohms, across it's entire useable freq. range. That couldn't be further from the truth. Any driver's impedance will vary across it's preferred frequency range, so it's impossible to get something "designed for a 4/8-ohm driver" to do the intended job. Yes, it'll pass the signal, but it will be far from even acceptable. The XO must be designed specifically for the intended drivers, as each has it's own unique specs and characteristics that must be taken into account when trying to design a XO. I'm not sure what's available in the UK, but look up Wolf, who is a frequent poster here and an excellent speaker designer. I know he has a couple small designs that could work well for your app. I think one is a single-driver arrangement and one is a small 2-way. He knows how to properly design a XO using actual measured data, not using fixed-number algebraic formulas (which is what the pre-made XO's use). Any of his designs will offer a sound quality that is light-years beyond what you linked to. If you have any questions, I'm sure he'd be happy to help. I'd check that out before you commit to any purchases. Good luck and let us know if you have any other ideas/questions.


John A.

[Whitneyville1]

Re: UK Internet Radio Build

To add to John's post, the idea of a 2 watt per channel amp isn't going to get you there. The bare minimum I would consider would be 7 watts RMS into 8 Ohms @ no more than .01% THD from 40-18,000 Hz. There are fine little 15 WPC amps available pre-built for about 12-15 Pounds from China on the 'Net, with power supplies that do much better that I mentioned. Look on eBay for them. The amps are barely larger than four packs of cigarettes (2 high, 2 wide, one deep). The tiny amp is one reason the sound is so compressed. By the time it moves the speaker, it's maxed-out. While listening at just 1/4 watt (.25) average is fine for a desk 'Net radio, the peaks in the music are often 20 or 40 times the "average", and if the amp can't deliver, the sound must be compressed to what the amp is able to provide.

[Markasaurus Rex]

Re: UK Internet Radio Build

http://techtalk.parts-express.com/showthread.php?235790-Quick-intro-and-project-overview-(Android-powered-jukebox)

Ralph you might want to check out my build in the link above. I was pursuing much the same goal as you albeit with somewhat different components. It did turn out great though and would highly recommend the speakers and amp that I used.

[ralphsaunders]

Re: UK Internet Radio Build

Hi again,

It's been a while since I've posted as I've*been busy developing the technology that's going to play a role in this project, so I thought I ought to update the topic with where I'm at as well as current questions/musings.

I must thank all three of you for commenting with what was quite welcome advice. It would have been likely that I was about to make a costly mistake and your responses made me take a second look at what was out there already in terms of small boombox-like projects.

I found several potential designs through users of this forum, as well as another UK speaker building forum, which seemed suitable for my application. Sadly, most of these speaker designs were using drivers which aren't readily available in the UK. This left me with the Sprite (https://sites.google.com/site/undefinition/sprite) by Paul Carmody.

The Sprite looks quite promising for what I want to do —*apart from being quite simple in the amount of components it uses (less chance of failure ftw!), it also looks like there is enough space to fit the Raspberry Pi and other related gubbins in there.

Before I bite the bullet, are there any caveats I should be aware of with this design? When I found the design it seemed it was too good to be true as it was everything that I really wanted.

I'm also wondering if I could make it even smaller still. By my estimation there is more than enough space for the Raspberry Pi and the breadboard I'll be using. If I could make it smaller, it'd make the whole thing more portable, which would be a plus for me. I did notice that Paul mentions the design of the enclosure turned it to 63 Hz and it also gives a volume boost between 70-90Hz. Can I shrink this and still get this affect? How much will this change the sound? How was Paul calculating the tuning of the enclosure? Part of me also wonders if sticking the Raspberry Pi and other components in the space will alter this tuning as well — perhaps even causing potential interference?

There really is a fantastic community here at parts express and it's great to have an archive of support in what can be quite challenging projects.

Cheers,
Ralph

[SirNickity]

Re: UK Internet Radio Build

I'm intrigued by good sound in small boxes. It's really tough to get good output below 200Hz when you're trying to achieve the sizes you see in commercial docks and tiny wall-mount and computer speakers. The internal volume (LxWxH) of the enclosure has a huge effect on the bass output. You can put other things in this space, but be aware that anything you put in the enclosure takes away from the volume of air behind the driver.

Also, avoid sharing airspace between two or more drivers playing different signals. (L and R, or woofer and mid, for example...)

You'll notice that drivers 3" and below have anemic low end, and those 4" and larger have poor high frequency distribution. So, 3" drivers are a good compromise for full-range, single-driver output. They'll also give you the best compromise between low frequency output and enclosure size. 4" drivers will start to require a little more space, and going above that, you'll get less output with the same size enclosure.

It's always good to plan for a subwoofer output and just shoot for 100Hz and up, if size is your main constraint.

[Paul Carmody]

Re: UK Internet Radio Build

I found several potential designs through users of this forum, as well as another UK speaker building forum, which seemed suitable for my application. Sadly, most of these speaker designs were using drivers which aren't readily available in the UK. This left me with the Sprite (https://sites.google.com/site/undefinition/sprite) by Paul Carmody.

The Sprite looks quite promising for what I want to do —*apart from being quite simple in the amount of components it uses (less chance of failure ftw!), it also looks like there is enough space to fit the Raspberry Pi and other related gubbins in there.

Before I bite the bullet, are there any caveats I should be aware of with this design? When I found the design it seemed it was too good to be true as it was everything that I really wanted.

I'm also wondering if I could make it even smaller still. By my estimation there is more than enough space for the Raspberry Pi and the breadboard I'll be using. If I could make it smaller, it'd make the whole thing more portable, which would be a plus for me. I did notice that Paul mentions the design of the enclosure turned it to 63 Hz and it also gives a volume boost between 70-90Hz. Can I shrink this and still get this affect? How much will this change the sound? How was Paul calculating the tuning of the enclosure? Part of me also wonders if sticking the Raspberry Pi and other components in the space will alter this tuning as well — perhaps even causing potential interference?

You have good taste! ;)

You CAN make the Sprite smaller, but I wouldn't. The bass out of it is awesome, and I have found that once you start sacrificing on interior volume on the Dayton ND90 (or Aura NS3), you lose that rich bass, and it starts sounding more and more like a little speaker (I have made several different-sized prototype enclosures for that driver, and so far that ~4 Liters in the Sprite wins, hands down). But if you MUST go smaller, let me know and I'll try to figure out where to compromise, and hopefully keep the integrity of the bass.

The Raspberry Pi probably won't take up much extra space, especially if it's just the circuit board. Just FYI, the rule of thumb I use with vented enclosures is that as long as you're with +- 10% of spec, the end result will sound as it was intended.

Oh, and if I were to ever build another Sprite (which is pretty likely), I'd definitely just opt for the Lepai LP-2020A, now that I've figured out how ridiculously easy it is to pop it out of its shell... it's even practically got a faceplate ready to mount!