Hello All, I'm new to DIY audio. My first project is a portable music player / boombox. It will be used for listening to moderate volume music for myself and for small get-togethers and on trips with friends. It is based on a Raspberry Pi 3 with a SainSmart SX400 DAC HAT. The DAC includes an amplifier that will power 2 channels at 20 watts (4 ohms recommended). (SainSmart SX400 Expansion Board for Raspberry PI B+ 3D Printing, Arduino, Robotics | Sainsmart) I should also point out that I'm not a huge audiophile. I spent too many hours around really loud garage bands to have that refined an ear (left). But I do want my project to sound better than most portable speakers you can buy for less than $200.
With that in mind, I am trying to sort out what speakers to buy/use in the project, but I find myself swamped in specs that I'm not sure I understand.
First: efficiency. I understand that the more efficient a speaker is, the less power is needed to drive it to achieve the same volume. So I've eliminated speakers that are less than 92 dBm efficient. Is that going to far? Or should I go farther, considering I've only got a 20 watt amp?
Also, is it true that if I go with a two-way system, I should match the efficiency between the full-range/mids and the tweeters? How close do they need to be - one or two dBm of efficiency?
Second: frequency range. I know that human ears can hear from approximately 50Hz to 20kHz. So it makes sense to get speakers that have a nice flat response across that whole frequency range. Of course, no one speaker really does that job by itself. So I've been looking at a full-range (4" to 8") combined with a tweeter. How low into that freq range do I need to go to be pleased? (I listen to mostly rock and metal.) Is a full-range driver that drops off at about 100Hz good enough? Is a 4" or 6" or even 8" speaker really going to reproduce the 50-100Hz range anyway (especially with only 20 watts driving it)?
On the upper range (tweeters), how do I figure out where to do the crossover? Or should I forget the tweeters altogether and just get a pair of real broad frequency range full-range drivers? How high up do I need the full-range to go to be happy with the sound? Is dropping off at 15kHz too early?
I haven't designed the enclosure yet, so I haven't picked sealed or ported. And I'm not terribly size constrained either. It's not going to be one of those pocket-sized units like is so popular with bluetooth speakers. Those always seems to sound tinny and small. Though I would like it to be smaller than carry-on luggage.
Any explanations / advice / recommendations would be appreciated.
Thanks,
Tom
With that in mind, I am trying to sort out what speakers to buy/use in the project, but I find myself swamped in specs that I'm not sure I understand.
First: efficiency. I understand that the more efficient a speaker is, the less power is needed to drive it to achieve the same volume. So I've eliminated speakers that are less than 92 dBm efficient. Is that going to far? Or should I go farther, considering I've only got a 20 watt amp?
Also, is it true that if I go with a two-way system, I should match the efficiency between the full-range/mids and the tweeters? How close do they need to be - one or two dBm of efficiency?
Second: frequency range. I know that human ears can hear from approximately 50Hz to 20kHz. So it makes sense to get speakers that have a nice flat response across that whole frequency range. Of course, no one speaker really does that job by itself. So I've been looking at a full-range (4" to 8") combined with a tweeter. How low into that freq range do I need to go to be pleased? (I listen to mostly rock and metal.) Is a full-range driver that drops off at about 100Hz good enough? Is a 4" or 6" or even 8" speaker really going to reproduce the 50-100Hz range anyway (especially with only 20 watts driving it)?
On the upper range (tweeters), how do I figure out where to do the crossover? Or should I forget the tweeters altogether and just get a pair of real broad frequency range full-range drivers? How high up do I need the full-range to go to be happy with the sound? Is dropping off at 15kHz too early?
I haven't designed the enclosure yet, so I haven't picked sealed or ported. And I'm not terribly size constrained either. It's not going to be one of those pocket-sized units like is so popular with bluetooth speakers. Those always seems to sound tinny and small. Though I would like it to be smaller than carry-on luggage.
Any explanations / advice / recommendations would be appreciated.
Thanks,
Tom
I wasn't looking to spend quite this much on the speakers... but a pair of these might eliminate my need for tweeters/crossovers and really simplify my design.
Dayton Audio PS220-8 8" Point Source Full-Range Neo Driver
Dayton Audio PS220-8 8" Point Source Full-Range Neo Driver
They have a very broad frequency response and a high sensitivity/efficiency:
Nominal Diameter 8"
Power Handling (RMS)40 Watts
Power Handling (max)80 Watts
Impedance 8 ohms
Frequency Response 40 to 25,000 Hz
Sensitivity 96.5 dB 2.83V/1m
Voice Coil Diameter 1"
Would using them in a 20 watt per channel system be too under powered for them?
What would be the effect of using them with an amp that recommends 4 ohm instead of 8 ohm?
Dayton Audio PS220-8 8" Point Source Full-Range Neo Driver
Dayton Audio PS220-8 8" Point Source Full-Range Neo Driver
They have a very broad frequency response and a high sensitivity/efficiency:
Nominal Diameter 8"
Power Handling (RMS)40 Watts
Power Handling (max)80 Watts
Impedance 8 ohms
Frequency Response 40 to 25,000 Hz
Sensitivity 96.5 dB 2.83V/1m
Voice Coil Diameter 1"
Would using them in a 20 watt per channel system be too under powered for them?
What would be the effect of using them with an amp that recommends 4 ohm instead of 8 ohm?
Thanks guys! I appreciate the info.
Mike, I'd love to do 2 per side, but I'm just not willing to sink $480 into just speakers for a portable unit. $240 is a pretty steep for this project. In fact, I was thinking of dropping down to the 6 1/2" version of that speaker and save about $60... but I'm not sure I want to sacrifice the low-end.
Mike, I'd love to do 2 per side, but I'm just not willing to sink $480 into just speakers for a portable unit. $240 is a pretty steep for this project. In fact, I was thinking of dropping down to the 6 1/2" version of that speaker and save about $60... but I'm not sure I want to sacrifice the low-end.
Sorry about that... I meant to include a link to the speakers I was thinking of...
FaitalPRO 4FE35 4" Professional Full-Range Woofer 8 Ohm
Mike
I agree. It is definitely sweet between 80Hz and 1kHz. It goes a bit nuts above 1k.
But to be honest, I haven't found much better. The others that I've looked at all drop significantly and quickly below 100Hz, and most get funky the higher they go above 1k or 2k. Isn't that the trade-off of going with a full-range speaker?
I guess that's kinda the underlying question: is it unrealistic to expect a full range speaker to perform better than that?
Mike, thanks for the suggested speaker. Those would save me a bundle of cash, even buying four of them. But I don't understand how an SPL of 91dBm will give me 97dBm by combining two per channel? Can you elaborate?
It works in two ways. First, when you run speakers in parallel, you lower the impedance. In this case, running two 8-ohm speakers in parallel will result in a 4-ohm load. That will add 3dB. Second, by adding a second speaker, you'll double the cone area, which should give you another 3 dB.
Mike
Mike
Thanks! I didn't know about the second speaker adding 3dB, but now that I think about it, that's not surprising at all.
When running speakers in parallel, is it typical to run the positive and negative wires from both speakers back to the amp and combine them there, or run one set to the first speaker and then connect the positives and negatives of the first speaker to the second? Or doesn't it really matter?
It doesn't matter other than which is easiest. I usually run the wires from one speaker to the other: pos to pos and neg to neg. You can do it off the speaker terminal too.
Mike
Tom, just to give you a little more info...
3dB is a doubling of acoustic energy. So anytime you double the number of drivers, you double the acoustic energy. So two drivers would be +3dB from one driver, and four drivers would be +3dB from two drivers ect.
Watts work the same way. Let me explain a bit more in-depth. The average speaker driver has an efficiency of 84-86 dB at 1 watt at 1 meter. Let's use 86dB 1W/1M for an example. 2 watts = 89 dB, 4 watts = 92 dB, 8 watts = 95 dB, 16 watts = 98 dB, 32 watts = 101 dB, 64 watts = 104 dB, ect.
You can quickly see that the difference between 500 watts and 1000 watts is also +3dB.
Now to calculate dB at listening position, a point source will drop -3dB every doubling of distance. Humans usually sit about 8-10 feet from TV's & speakers, as this is a evolutionary "safe" distance. So we can make an equacated guess that you will be about 3 meters away from speakers set up in a normal stereo triangle, which would be around -4.5dB if I did my math right.
Example: We hypothetically bought 84 dB 1W/1M rated speakers. Let's assume the manufacturer gave this specification for one speaker (normal for DIY speaker drivers). We use two speakers for a stereo pair, giving us 87 dB 1W/1M. We give the speakers 4 Watts of power from an amplifier, giving us 93 dB 1W/1M. We sit 3 meters away giving us 88.5dB at the listening position- a bit louder than average.
The average listening level most people prefer is 83-85dB at the listening position.
Point being, unless you want to get really loud, you don't need that much power.
Oh also, +10dB is perceived as double the loudness.
3dB is a doubling of acoustic energy. So anytime you double the number of drivers, you double the acoustic energy. So two drivers would be +3dB from one driver, and four drivers would be +3dB from two drivers ect.
Watts work the same way. Let me explain a bit more in-depth. The average speaker driver has an efficiency of 84-86 dB at 1 watt at 1 meter. Let's use 86dB 1W/1M for an example. 2 watts = 89 dB, 4 watts = 92 dB, 8 watts = 95 dB, 16 watts = 98 dB, 32 watts = 101 dB, 64 watts = 104 dB, ect.
You can quickly see that the difference between 500 watts and 1000 watts is also +3dB.
Now to calculate dB at listening position, a point source will drop -3dB every doubling of distance. Humans usually sit about 8-10 feet from TV's & speakers, as this is a evolutionary "safe" distance. So we can make an equacated guess that you will be about 3 meters away from speakers set up in a normal stereo triangle, which would be around -4.5dB if I did my math right.
Example: We hypothetically bought 84 dB 1W/1M rated speakers. Let's assume the manufacturer gave this specification for one speaker (normal for DIY speaker drivers). We use two speakers for a stereo pair, giving us 87 dB 1W/1M. We give the speakers 4 Watts of power from an amplifier, giving us 93 dB 1W/1M. We sit 3 meters away giving us 88.5dB at the listening position- a bit louder than average.
The average listening level most people prefer is 83-85dB at the listening position.
Point being, unless you want to get really loud, you don't need that much power.
Oh also, +10dB is perceived as double the loudness.
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OK. So your 4 watts gives you 88.5db at your listening chair. Fine. But the "average" music signal needs at least another 14 db for headroom. That necessitates a 100 watts per channel amplifier.
Not true. If you have a clean signal with a 0 Dbfs sinewave at a given volume output, the amplifier will never clip because digital sound will not be above 0dbfs. This is how car audio enthusiasts tune subwoofer amplifier gain, but usually with a sinewave around -10dbfs.
Also, if we have a maximum level of 88dB at the listening position in an average home, the noise floor will be about 45dB or a bit lower. That's 43dB of dynamic range.
If you want to talk about dynamics, you're much better off lowering the noise floor in your room than megawatt amplifiers imho. 20dB is a great goal. The first watt of power will always be the most powerful, almost always having a dynamic range of 30dB+ from the noise floor, and probably contain the most detail. I have noticed that 86dB at the listening position in a quieter environment sounds substantially louder too.
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A wide-band residential noise floor of 45dB or lower might be a bit of wishful thinking? I have an app on my iPhone and iPad by Studio5 Digital that includes a rudimentary SPL meter, and FFT/RTA - it's quite interesting to be sitting at my office desk at break time when no machines other than the HVAC system running, and see fluctuations in the 65-70dB range, and just the typing on keyboard peaking at over 75dB A. What is even more interesting is the spectral content showing how much of that energy is below 100.
Noise in daily activities is definitely interesting!
Not to descredit you in any way, as I've done the same with my iPhone, but obviously using an iPhone as a mic won't exactly be accurate- although they can give you some interesting relativity based information. I got the 45dB from the average of a few sources; a few I can't find right now
NPC Resources: Typical Noise Levels
decibels, dB - Word Information
Room Acoustics and Noise Floor| JaguarAudioDesign.com Blog |
The Best Tweak - Make Your Room Quiet - Audiophile Review
http://image.slidesharecdn.com/nois...iation-health-effect-12-728.jpg?cb=1338793664
Acceptable <i>dB<sub>A</sub></i> Noise Level
Oh also, fun fact. Diesel Semi's and Trains create infrasound.
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