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Discussion Starter · #1 ·
Hi all,


I am in my final year of product design at uni. For my major project i am designing "interactive wireless speakers", which amount other features are to be small enough to be held in the hand and played with. The speakers will dock onto a base station to charge and will also dock an ipod, similar to the new Griffin Evolve speakers (evolvespeakers.com). Each speaker will house a full range driver, its own battery and an RF receiver.


The focus of the project is more on the fun, music and mood, playful side of the product rather than the audio quality. However without some audio quality the product is no good in the first place.


I have to hand in a final design and a prototype which is as close to fully working as possible. In terms of getting it working I am not a electronic engineer so i can either break apart current products or use kits and house them in my casing design.


Im looking for advice on speakers and amplifiers and possible batteries and wireless components too if people are knowledgeable on that.


Im looking at using around 2 - 2.5 inch speakers to keep the case size down. from the research i have done so far I need to use 4ohm speakers rather than 8ohm as they are battery powered and each speaker will be a full range driver.

Something simiular to the Visaton FRWS 5 4 OHM ( visaton.com/en/chassis_zubehoer/breitband/frws5_4.html )


Im guessing the RF signal coming into the speakers, transmitted from the base is going to need amplification before going to the speaker so i was looking at using something like a Kemo M031 Universal amplifier 3,5W ( kemo-electronic.com/en/module/m031n/index.htm )


In terms on battery and wireless technology i have very little knowledge. I know that i want a recharagable battery that will last between 5 - 10 hours. Each unit is chanrged by dropping it onto the base station (like the griffin evolve). The wireless signal needs to give a range of around 100 - 150ft.


I need some guidance to see if i am roughly on the right track or there is something else i should be looking at.


Thanks.
 

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 http://www.amphony.com/products/h1000.htm


you probably need one transmitter and two sets of headphones ( for stereo speakers that aren't wired to each other )


or use a different system, depending on your range requirements etc. but this is the only cheap digital system that i know of.

http://www.google.com/products?q=son...&hl=en&show=dd


sony makes several models of speakers that are powered directly by headphone level signal


splice the speakers together with the headphones into wireless speakers


but then you would have a problem with recharging it ...


so you could just get this:

http://www.google.com/products?q=son...&hl=en&show=dd


and some bluetooth transmitters:

http://www.google.com/products?q=blu...&hl=en&show=dd


but i guess it wouldn't be much of a project then haha !

Quote:
Originally Posted by boyceUK /forum/post/15421322


I need some guidance to see if i am roughly on the right track or there is something else i should be looking at.

how about get something to work FIRST then worry about sound quality.

Quote:
Originally Posted by boyceUK /forum/post/15421322


Im looking at using around 2 - 2.5 inch speakers to keep the case size down. from the research i have done so far I need to use 4ohm speakers rather than 8ohm as they are battery powered and each speaker will be a full range driver.

Something simiular to the Visaton FRWS 5 4 OHM ( visaton.com/en/chassis_zubehoer/breitband/frws5_4.html )

the optimum impedance of speaker will be that which the amplifier you're using is designed for. most walkmans are designed for 16 ohms. but more importantly then impedance you will need sensitivity. large drivers are usually more efficient than small ones and if you want a small efficient one you will probably need something specifically designed for a battery powered device ( such as those sony speakers ).


flat response ( good sound quality ) and high efficiency are somewhat mutually exclusive. you visaton is only 80db efficient. frankly for such a small driver you don't have much options.

http://www.madisound.com/catalog/pro...oducts_id=8364


( there are both 4 ohm and 8 ohm versions in sizes 2, 2.5 and 3 inches )

http://www.madisound.com/catalog/pro...products_id=83


( this also comes in different sizes )


fostex is more efficient but bigger, heavier, more expensive, etc:

http://www.madisound.com/catalog/pro...oducts_id=8480


EJ Jordan make good compact full range drivers:

http://www.ejjordan.co.uk/drivers/
 

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Discussion Starter · #3 ·
Thanks for taking the time to give a detailed reply vasyachkin,


As i say im a designer so rather than most people on here looking for volume and perfect sound quality my project is more about the styling, fun and making music interactive. I am looking to create something similar to this;




However, this was only a concept whereas mine will need to work and recharge.

and am currently working on the sketching and CAD for my own designs.

Quote:
Originally Posted by vasyachkin /forum/post/15422192


splice the speakers together with the headphones into wireless speakers

One of the first things i did in the project was to buy a pair of Sony MDR-RF850RK Wireless headphones and a Philips SBA1500/00 Portable Speaker System and replace the earphone drivers with the drivers with the drivers out of the philips speakers which worked as the philips speakers were originally designed to work with earphones power. They also come with a amp (the disc you can see in the picture) designed to fit between the MP3 player and the speakers. Which again worked with the RF circuit and gave louder, better quality sound.

The sound quality from these speaker and/or amp was ok but im guessing better could be a achieved with better quality parts like those we've suggested.

Quote:
Originally Posted by vasyachkin /forum/post/15422192


but i guess it wouldn't be much of a project then haha !

Using current products and taking them apart is not a problem as if i was designing for mass production is would be be custom made but this is just a one off prototype. Also the parts i take out have to fit into my designed case work, like the pic shown above.

The problem with taking products apart is i will end up paying a lot more than, specially when i have 6 speakers all with their own RF receiver and amp. I would need to spend a lot on headphones. lol

Quote:
Originally Posted by vasyachkin /forum/post/15422192


the optimum impedance of speaker will be that which the amplifier you're using is designed for.

Well at the stage the speakers or amplifier have not been chosen. the constrains are;

1) that each speaker, battery, RF receiver and amp must fit into a 10cm sphere case.

2) the combination of components must give a battery life of at least 6 hours.

3) constraint 1 & 2 come first but the volume and quality should be that of a small pair of PC speakers form each sphere speaker.


The Philips speaker i took apart and a set of Connected Essentials HPL200 Wireless Speakers that i also took apart both use 4ohm speakers and i read the reason why car speakers were 4ohms is because, "In the car stereo market, virtually all speakers are 4 ohms. The reason is due to voltage limitations available in cars (namely the 12 volt battery)."
 

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Quote:
Originally Posted by boyceUK /forum/post/15426496


The Philips speaker i took apart and a set of Connected Essentials HPL200 Wireless Speakers that i also took apart both use 4ohm speakers and i read the reason why car speakers were 4ohms is because, "In the car stereo market, virtually all speakers are 4 ohms. The reason is due to voltage limitations available in cars (namely the 12 volt battery)."

well there are two effects here


low available power supply voltage ( 12V in car or 3V in a walkman ) favors lower impedance speakers.


on the other hand high power also favors lower impedance speakers.


my subwoofer is 1 ohm for example because it is 5000 watts. but a walkman's output is only between 0.005 and 0.020 watt which is why most walkman headphones are 16 ohms.


your philips speakers arent the kind i described because they come with their own amplifier. they have a full 1 watt of power, or about 50 times higher power than a walkman - that's why they have lower impedance ( 4 ohms versus 16 ohms ).


but you don't have to worry about any of that. you should simply look at the specs of the amp for the impedance that it likes and the specs of the speaker and make sure they more or less match.


your battery life will depend on


amplifier power ( 1 watt, 2 watts , 5 watts etc )

amplifier type ( class AB, H, D etc )

speaker impdeance load ( 4 ohm, 8 ohm etc )

playback sound level

speaker sensitivity

and obviously your battery capacity


of course ideally you want class D amplifier for anything battery powered, but i don't know if you will find one in suitable power range.


if you can't have class D then you will need to match the power of your amp as closely to the power at which you will actually use the speakers as possible. because regular ( Class AB ) amps are more efficient when they are driven closer to full load. in other words if you plan to use 0.5 watts of power you will get much better battery life with 1 watt amp than 2 watt amp.


if i understand you correctly you're just trying to improve on the sound quality of these philips speakers.


if that is the case you should at least be able to put it into words what exactly do you find wrong with the sound of philips ?


by the way if that philips amp really has 1 watt that should be enough. the quality may suck, thats for you to judge.


i would say that as far as AMPLIFIERS go roughly speaking:


10% THD - cheap generic electronics such as desktop speakers, portable radios etc ( $1 - $20 )

1% THD - good desktop speakers, minisystems, DJ amplifiers ( $50 - $1000 )

0.1% THD - hi-fi amplifiers, old skool amplifiers ( $100 - inf )

0.01% THD - modern high end amplifiers ( $200 - inf )


so if your phillips amp puts out 10% THD and you swap it for an amp that does 1% THD that may have a point to it - by that i mean it would be audible even on a 2" speaker. but if it already has 1% and you swap it for a 0.1% amp ... probably won't hear the difference unless you hook it up to real speakers.

http://www.madisound.com/catalog/pro...products_id=85

http://www.madisound.com/catalog/pro...oducts_id=8478


calculate the volume of a 10 centimeter sphere and model the bass response in it for each driver of interest using any of the free programs like unibox.


some drivers may require different box design ( vented, sealed, aperiodic ) and some may be better suited for a 10 cm sphere than others. thats what modeling is for - to find out.


but i can tell you right now that 2.5" peerless is probably your best bet.

http://www.madisound.com/catalog/ind...sort=3a&page=2
 

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Discussion Starter · #5 ·

Quote:
Originally Posted by vasyachkin /forum/post/15436527


your philips speakers arent the kind i described because they come with their own amplifier.

Maybe you cant tell from the picture but the the philips speaker come in 2 parts. the Speakers >> Cable >> 3.5mm jack on the end. the second half is the amp part which is not directly connected to the speakers. Amp >> Cable >> 3.5mm jack. So you can just use the speaker directly into the headphones socket on your ipod or if you want more volume you can plug the amp into the headphones socket and the speakers into the amp.

anyway, either way my spherical speaker will each need battery, amp and speaker.

Quote:
Originally Posted by vasyachkin /forum/post/15436527


but you don't have to worry about any of that. you should simply look at the specs of the amp for the impedance that it likes and the specs of the speaker and make sure they more or less match.

But if ive not decided on either the speakers or the amp which decision comes first? surely there has to be one area that is better suited to the size i am looking at and the fact i want battery powered.

Quote:
Originally Posted by vasyachkin /forum/post/15436527


if that is the case you should at least be able to put it into words what exactly do you find wrong with the sound of philips ?

they dont create enough volume, not a long way off i want tho. towards the top end of their volume they becomes more and more distorted.

Quote:
Originally Posted by vasyachkin /forum/post/15436527


calculate the volume of a 10 centimeter sphere and model the bass response in it for each driver of interest using any of the free programs like unibox.


some drivers may require different box design ( vented, sealed, aperiodic ) and some may be better suited for a 10 cm sphere than others. thats what modeling is for - to find out.

This sounds interesting and definitely something i should include in the investigation of my project. are you saying i need to buy both of those 2 drivers you have linked to test them or they can be fully modelled using this program?

could you elaborate on this a bit please.

Quote:
Originally Posted by vasyachkin /forum/post/15436527


but i can tell you right now that 2.5" peerless is probably your best bet.

Looks good to me too, are you suggesting to go with the 4 or 8 ohm version?

I can't see from the data the wattage. it says "Long-term Max Power (IEC 18.3) 60 W" but surely ther're not 60W?
 

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Discussion Starter · #6 ·
Just had a very helpful convocation with the man at http://www.audio-components.co.uk/ who helped clear things up for me.

He said that the 2.5" peerless is very well suited and suggested i went for the 4ohm version as the sensitivity was better. So i ordered one of those.

He also suggested putting around 4 or 5 W through it to get a nice bit of sound out.

and that from 4 x 1.5v rechargeable batteries i should expect to get a few hours use from it.
 

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Quote:
Originally Posted by boyceUK /forum/post/15461316


Maybe you cant tell from the picture but the the philips speaker come in 2 parts. the Speakers >> Cable >> 3.5mm jack on the end. the second half is the amp part which is not directly connected to the speakers. Amp >> Cable >> 3.5mm jack. So you can just use the speaker directly into the headphones socket on your ipod or if you want more volume you can plug the amp into the headphones socket and the speakers into the amp.

that makes sense.

Quote:
Originally Posted by boyceUK /forum/post/15461316


But if ive not decided on either the speakers or the amp which decision comes first? surely there has to be one area that is better suited to the size i am looking at and the fact i want battery powered.

so you want to know what impedance do speakers in small portable radios have ? probably either 4 or 8 ohms. i don't think there is any optimum impedance. it depends on the desired power output and available power supply voltage.


modern electronics can step up the power supply voltage from that of the battery. high power car audio amplifiers do this - they take 12V power and step it up to something like 80 volts to deliver higher levels of power into a speaker. cheap portable electronics are likely to avoid this complication and try and use whatever voltage the battery provides ( lets say 3 volts ). so it really depends on the amplifier design, i don't think you can generalize some kind of optimum impedance for all amplifiers.

Quote:
Originally Posted by boyceUK /forum/post/15461316


they dont create enough volume, not a long way off i want tho. towards the top end of their volume they becomes more and more distorted.

well the peerless speaker should be stronger as its designed primarily for use in flat screen televisions which usually have at least 5 watts of power. but don't be surprised if the distortion was actually coming from the amplifier.


so you would be fine with the peerless speaker and also i think you would be fine with just 1 watt of power BUT it has to be clean power. you may have trouble finding a clean 1 watt portable amp. when people look for clean sounding amps they usually look for amps that weigh 100 pounds and draw 500 watts from the outlet.

Quote:
Originally Posted by boyceUK /forum/post/15461316


This sounds interesting and definitely something i should include in the investigation of my project. are you saying i need to buy both of those 2 drivers you have linked to test them or they can be fully modelled using this program?

could you elaborate on this a bit please.

no need to buy both drivers. the software will plot the bass response by itself using only manufacturers' specs. it would then allow you to choose which driver produces the flattest response in a 10cm sphere. but i can do the same calculation in my head and based on that i recommended the 2.5" peerless. so if you trust my judgement you don't have to use the software but it may be interesting for you.

Quote:
Originally Posted by boyceUK /forum/post/15461316


Looks good to me too, are you suggesting to go with the 4 or 8 ohm version?

I can't see from the data the wattage. it says "Long-term Max Power (IEC 18.3) 60 W" but surely ther're not 60W?

use whichever impedance the amp that you will be using is rated for.


as i said this is a driver designed for use in flat panel televisions. such TVs typically use about 5 watts of power. yes 60W is probably an optimistic figure but this driver is fairly strong. you might drive it into distortion but you won't be able to burn it out. its much stronger than your project requires.

Quote:
Originally Posted by boyceUK /forum/post/15461580


Just had a very helpful convocation with the man at http://www.audio-components.co.uk/ who helped clear things up for me.

He said that the 2.5" peerless is very well suited and suggested i went for the 4ohm version as the sensitivity was better. So i ordered one of those.

He also suggested putting around 4 or 5 W through it to get a nice bit of sound out.

and that from 4 x 1.5v rechargeable batteries i should expect to get a few hours use from it.

i would suggest using less power to conserve battery life. yes the driver can handle 5 watts but bigger amp will drain batteries faster. try to find power consumption in the amp's specs and compare it against milli-ampere-hour rating of the batteries. you should be able to figure out how long it will run for based on that. lithium batteries will give you longest life. just make sure you aren't using a wrong charger for the batteries.


if you can buy a camcorder or a digital camera rechargeable lithium battery ( of the same voltage that your amp needs ) and a charger built specifically for that battery then it would probably be ideal. lithium ensures you have best possible power from small weight and size and a dedicated charger ensures your battery gets charged properly. of course there may be cheaper solutions but they wouldn't be quite as fool-proof. you probably don't want the battery with all the acid and stuff exploding in your hands if you pair it with a wrong charger.
 
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