DIY bluetooth speaker

[audioguru]

A cheap poorly designed speaker system produces its total resonant frequency louder than other frequencies. The resonant frequency is increased when a speaker is enclosed due to the springiness of the air inside the enclosure. The resonant frequency is played by the speaker for some time after the input signal has stopped. When music is played by this speaker then bass sounds are produced mainly at this one resonant frequency, called one note bass.
Since you have two raw speakers, the speaker that does not produce bass has its own higher resonant frequency and maybe acts like a large hole in the enclosure cancelling bass frequencies from the woofer. A tweeter always has a sealed back.

But in the video, your speaker has a few resonant frequencies and I agree it produces almost no deep bass. The length, width and height of a speaker should be at certain ratios so that sounds do not continue to bounce around inside at one frequency. Stuffing inside also can damp resonances.

 

[SentinelAeon]

Hmm, might be that. But that is also good news for me since i will have less trouble finding some good speakers. Its much easier to get to 80Hz than it is to say 50Hz, right ?

 

[SentinelAeon]

I got a new question. While browsing youtube to learn more about passive radiators i found an interesting video of 2 ridiculous small speakers that seem to have a good bass. Now my question is, how is that even possible ? I know it is all calculated but look at the speaker, it is tiny. And if i read correctly, passive radiators have a certain frequency at which they radiate and they ONLY improve bass if the speaker actualy goes that low. So for instance if speaker is 150-20.000Hz, there will be very little heard from him at like 70Hz and therefor passive radiator will not help much. SO again, how did they manage to get bass from such small enclosure and from such small speakers.

 

[audioguru]

In most of the video there is severe distortion. Either the amplifier is badly clipping, or the voice coils are smashing into the magnet structures, or both.

A little speaker can have thick wire on its voice coil for a high power rating. The heavy wire is heavy so then the resonance frequency is low.
The magnet can be huge and expensive so that the loudness rating is not too low.
Then the amplifier can have a high output power and lots of bass boost if the peak-to-peak excursion of the speaker is a lot.

A passive radiator works the same as a port. If its spec's are correct for the speaker and enclosure, the low frequency response is extended but the cutoff slope is much steeper which reduces very low frequencies because the sound from the passive radiator or port cancels sound from the front of the speaker.
With a passive radiator or port, the speaker does not have a load at very low frequencies and might be damaged unless a filter is used to remove the very low frequencies.

 

[SentinelAeon]

Thank you for your answer, 2 more questions:

1) I saw on soundimports that you can not only buy a speaker, but also a copy of that speaker without magnet - a passive radiator. Therefor, the speaker and passive radiator are identical. Would that mean that they are a good pair, their specs are ok and will therefor work as intended ?

2) I have a question regarding frequency response and resonance frequency. The speaker in question is visaton SL 87 FE which im just putting into a speaker enclosure. So first, its frequency response is 75-18.000Hz which would be awesome for me. But then you see resonant frequency of 120Hz which is very very bad. You said something like, resonant frequency is frequency at which speaker will naturaly move. But i dont understand what you mean by that. Could you explain in simple terms and also compare frequency response with resonant frequency ?

 

[audioguru]

A passive radiator with the cone of a speaker but without the magnet probably does not have the voice coil therefore its cone weight and resonant frequency will be different (higher frequency) than the speaker. I think the resonant frequency of a passive radiator should be the same as the speaker in most enclosures for a little amount of bass extension. The manufacturer or you can add some weights. If you add weight to the cone of a speaker then you reduce its loudness.

The little Visaton speaker produces only a little amount of bass. Its max power is only 15W so it will not be very loud..
87dB at 1W, 1m. 81dB at 4W, 1m. 75dB at 16W, 1m. 69dB at 16W, 2m. Therefore at a distance of only 2m, the loudest beats will be only 68dB without distortion at 15W and the rest of most music will be only 58dB (almost a whisper).

The resonant frequency of a speaker is the frequency that its springiness and cone weight vibrates when excited. Without an amplifier or anything else connected to a speaker, tap its cone and it will go "bong" like a bongo drum. That is its resonant frequency. The springiness of the air inside the enclosure increases the resonant frequency. The frequency response drops at frequencies below the resonant frequency but a passive radiator or port will extend bass response a little when properly calculated but the speaker will produce less levels at very low frequencies.

 

[SentinelAeon]

I opened another woofer i got for lets say, fair price of 20€, since i got 5 more small speakers with it. Its rated 15W, has 5.5ohm resistance so im guessing its 4 ohm. So here is text from another forum i wrote:


Well i just tested the daytons. I bought a cheap 5.1 system and got a small sealed woofer with it. It had good bass, speaker says 15W. I measured the speaker and its 5.5 ohm, while dayton is 7.8 ohm. Now get this:

1) The 5.5 ohm speaker from woofer 4" plays a lot louder than dayton and it draws a total of 25W at maximum
2) the 7.8 ohm dayton 115 4" speaker (8 ohm) draws maximum of 10W.

Now i dont get this. Lets say the woofer speaker is 4 ohm and dayton is 8 ohm. Wouldnt dayton by this calculation draw half the power of the 4 ohm speaker and that would be exactly 12.5W ? Even though 4 vs 8 difference ... thats only 3dB because double the power. And loudness was a lot more then 25% or so. And bass is more or less same with both drivers. For some reason my phone will show both with more or less same loudness but that certainly isnt the case, you can hear the other one a lot louder. My simple dB meter app will show dayton max at 65dB and the other one at 75dB.

I am really interested how much i would get from 4 ohm dayton. Also its interesting i get 10W per channel with 8 ohm daytons, while my amp says 38W per channel when 8 ohm and 50W when 4 ohm. When i tried some other 3" drivers from aliexpress that are 3 ohm, i managed to get a whooping 57W per channel

Also looking at online sheet, i see 4 ohm 115 dayton is 86.8dB and 8 ohm 115 dayton is 81.9. Ok so to compare them, we substract 3dB (double impedance) from 4 ohm dayton and get 83.8dB, which is better then 81.9 from 8 ohm one. Add in double the power because its lower impedance, maybe that will really sound louder. I need to order a pack of 4 ohm ones and test it

end: to sum it up, i will order 4 ohm daytons and see how it goes in an enclosure. They might be usable since they are very cheap. And beside them i would add a full range visaton frs 8 in its own enclosure, maybe add some resistor to make sure its not to loud. Cause visaton is really really loud and probably it will be so loud that u wont hear bass from daytons at all. Or will you ?

 

[audioguru]

Here is the difference in frequency response between a sealed and vented (or with a passive radiator) speaker. This speaker probably has a free-air resonance of 50Hz so it is at least 8" in diameter. The vented response is flat and is -3dB at 30Hz because the enclosure size and vent (passive radiator) are properly calculated.

 

[SentinelAeon]

What is funny though that the small speaker from woofer i got, is in a small enclosure, probably not much bigger then my big speaker i use. And the bass really goes low and is loud. What about i take that speaker from woofer that was in SEALED enclosure. And i calculate its volume. And just make my speaker enclosure of same volume but obviously different dimensions. And see what it gives me. Then i add 2 passive radiators and see if it improves things ? Like i said, i dont have any data from the speaker itself except that bass is really good in its very small enclosure it came with. I also tested dayton 115 in the same enclosure and bass is more or less the same but like i said its less loud. Like i said i really have to order 4 ohm dayton 115 cause it just might give me that 30-40% more i need that would make it awesome (when i say 30-40% more i calculate like this: about 2dB i get from difference between 4 and 8 ohm version. And then another 3dB because 4 ohm version will allow 50% more power which is 3dB. And 5dB is almost 50% more or maybe 40-50% more loudness)

 

[audioguru]

For good bass, a ported enclosure (or one with a passive radiator) is usually larger than a sealed enclosure.
A few hundred posts ago I showed a calculation that the total Q spec of a speaker determines if its enclosure should be sealed or ported. Your sealed speaker might work poorly with a passive radiator.

+3dB (double the power) sounds only a little louder. +10dB (ten times the power) sounds twice as loud.

 

[SentinelAeon]

I know, but 3dB sounds 25% louder, that means 5dB sounds like 40% louder, which is something. Ok, so lets go at it this way. Lets say my speaker of choice is dayton TCP115 4 ohm. It is cheap and highly praised by community. So if i know all the data from this speaker which is readily available. And my volume size of choice is either 0.09ft^2 or 0.18ft^2 (2.5l or 5l ). So now that i know this data, how would i go about finding what is best for my speaker. Either closed, ported or passive radiator. And what kind of passive radiator or what kind of port dimension. Dayton TCP1155 4 ohm shows 76Hz in 0.06ft^3 ported enclosure. So theoreticaly i should be getting at least SOME bass from it, be it 1 note or not, i dont really care so much, as long as it gives apperance of bass as my current speaker does. But i am really new at this calculation things so i really could use your help with this. We have a speaker and we have a enclosure size. How do we proceed from here ? Here is all the data from the speaker:

Order the Dayton Audio TCP115-4 Bass-midwoofer

Buy the TCP115-4 online at SoundImports ✓ Same day shipping ✓ Low shipping rates

www.soundimports.eu

 

[SentinelAeon]

I already found such program and calculated. So what do you think about that, would you change something ?

 

[audioguru]

-3dB at 48Hz would sound pretty good. Just now I played 48Hz on my 3" ported computer speakers and it played but produced almost no sound at lower frequencies. Each enclosure is less about 1 liter. They produce about 3W or 4W each.
At frequencies lower than 48Hz the voice coil might smash against the magnet structure so a highpass filter might be needed.

Can you carry an enclosure as big as 5 liters?

 

[SentinelAeon]

5 liters is probably to much to be portable, but my friend asked me to make him a speaker with good bass and he said he didnt care about the size, so i am making it out of wood also. Btw, i will run that dayton on left channel and full range visaton on right channel. Because i want to protect the full range, i will put it into its own enclosure. And i dont know how enclosure volume is calculated. If i have a 5 liter enclosure and then a very small enclosure of full range, will that mean that the dayton will actualy have 5 liters minus the volume of full range enclosure ?

 

[audioguru]

The full range speaker should be a tweeter that is already enclosed and it must have a highpass filter. Then the woofer should have a matching lowpass filter. The filters are called a passive crossover network.

 

[SentinelAeon]

I am anxiously awaiting my 4 ohm daytons, cant wait to put them to the test. I also decided that when i make en enclosure, i will play around with resonant frequency. Then i will make 2 or 3 different port as the program shows me. I wanna see if i would rather have F3 at 40Hz and loudness a little lower or F3 at 50Hz and little higher loudness. Or even 60Hz F3 and even more loudness. It will all depend on how loud the speaker is. Because on left channel i will have 4 ohm dayton and on right channel i will have 30W Visaton FRS 8 M 8 ohm. And judging by how loud the visaton is .. i will need every bit of loudness from dayton squized otherwise i will just hear the visaton.
Btw i attached a comparison of 4 vs 8 ohm version of dayton TCP115. Interesting, 4 ohm version combined has about 5dB more sensitivity than 8 ohm version. I am wondering what power of capacitor i should use for visaton. Looking at the graph, i can either do it at 3000Hz or 5000Hz. Or maybe even at 1000Hz since dayton isnt that loud from 1000Hz upwards.

1) where would u suggest i make frequency for full range visaton that will cover upper part
2) If i dont make any crossover on daytons, why and how will that be bad ? Lets say i only crossover full range and leave dayton as it is. Why will that be bad ?

 

[audioguru]

The full-range speaker will need a fairly large enclosure separate from the woofer. Its high frequencies are pretty bad and It is too big to be a tweeter.
A real tweeter has its rear already sealed and has a small dome as a cone so it spreads the high frequencies all around like the woofer does with low frequencies.

The woofer response above 3kHz is all over the place and without a lowpass filter will add and cancel frequencies from the other speaker.

 

[SentinelAeon]

Alright so what u r trying to say is, the best way would be to limit the dayton at 3000Hz and then add a tweeter that will cover 3000-20.000Hz ?

I am all for that, its just, the tweeter is so tiny. Will it be able to play as loud as the dayton, will i hear it ?

 

[Nigel Goodwin]

Alright so what u r trying to say is, the best way would be to limit the dayton at 3000Hz and then add a tweeter that will cover 3000-20.000Hz ?

I am all for that, its just, the tweeter is so tiny. Will it be able to play as loud as the dayton, will i hear it ?

Yes, you don't need a big cone for high frequencies, and you don't always need to cut the high frequencies to the bass unit either, it just won't reproduce them. It's fairly common to have an attenuator in the tweeter, to quieten it down to match the bass unit.

But speaker choice, cabinet design, and crossover design are VERY complicated subjects, and as much art as science - which is one reason why quality speakers are expensive, as well as their components been expensive as well.

 

[SentinelAeon]

I thought about adding a resistor if necesary to make them match. The only problem is that i run on batteries and it seems a shame to waste battery life like this