DIY bluetooth speaker

[audioguru]

Below the resonant frequency of the speaker system, the output level drops.
The size of the enclosure affects the resonant frequency.
A small enclosure increases the resonant frequency then the bass level drops and the mid bass level increases until it sounds like a boomy bongo drum.

The article I posted said that if the enclosure is too small then a port (or passive radiator) does nothing.

 

[SentinelAeon]

Can u comment my idea bout creating a speaker where u can dynamicaly make the box bigger ? Like drawer but that its closed on all sides so air cannot go through ? Should this in theory work ?

 

[audioguru]

If you can make a sealed box with adjustable size then it would be good to judge the amount of bass you will get.
Most speaker enclosures I have seen use acoustical absorbent material filling so that sounds do not echo around like in an empty garbage can.
Physics shows that acoustical filling material converts sound power into heat which makes the enclosure seem larger with a lower resonant frequency (more bass).

 

[SentinelAeon]

Great, i will start working on that design after u calculate the size of enclosure for my speakers when i get them. And then i will test if it actualy changes the sound when i retract the box. I could easily make it so that the speaker is twice the size of the retracted. Fun times ahead. Oh as for acoustical filling material, i didnt think that would help the bass ? Cause if it will, i will fill the speaker with foam or something

 

[SentinelAeon]

Ok, i got my woofers. Now i need a formula that will calculate the size of enclosure i need if i want a certain frequency

 

[SentinelAeon]

Crap, the speaker has good bass but is so silent on 2x25W that its barely usable. Im guessing the culprit is the sensitivity reading ?

 

[audioguru]

If a woofer is not in an enclosure designed for its spec's then it will not produce bass.
The sensitivity of the Dayton 4" woofer is 81.9dB at 1W and a distance of 1m.
25W is about +13.5dB so the total is 95.4dB (loud) at 25W and at 1m. At 2m it will be 89.4dB and at 4m it will be 83.4dB which is not loud. This is the maximum sound level of the beats in music, average music sounds about -10dB less.

I found a speaker enclosure design calculator that produces this ported box (a passive radiator will use the same box size):

 

[SentinelAeon]

U said 81.9dB at 1W at a distance of 1m. But the site says 81.9dB at 2.83V at a distance of 1m. I am guessing that is why the speaker is so silent. Btw, 81.9dB at 2.83V .... how do i convert this to dB per 1V, so i could compare it to other speakers ?

edit: forget what i said, i just checked and 1W sensitivity is same as 2.83V. So i just checked, the visaton 3" speakers i was comparing it to is 88dB at 1W. Ok so 3dB means x2 the loudness ? So judging by this, visaton speaker is many times louder then the woofer speaker i bought.

Btw, i know it should be put into enclosure but i actualy tested it outside enclosure and it still produced decent if not almost good bass. I guess im used to less bassy speakers so i sense bass faster.

Anyway i will have to sell those speakers because they are to silent sadly. If i put this speaker on left and visaton on right, all i can hear is the visaton speaker sadly :/

 

[audioguru]

+3dB is double the power which sounds only a little louder. Since we can hear a wide range of loudness from a whisper to a nearby jet airplane then our hearing's sensitivity to loudness is logarithmic. 10 times the power (+10dB) sounds twice as loud.

Isn't your Visaton 3" speaker 4 ohms? Then it is double the power of 8 ohms which is +3dB.

Without an enclosure then the sounds from the rear of a speaker's cone goes around and cancels the sounds from the front of the cone.

Didn't you buy 4 of those 4" woofers from a place that nobody ever heard of (in China?) and the woofers are also made in China?

 

[SentinelAeon]

I ordered a lot of speakers lately. I ordered 4 woofers from place that no one heard of but im not sure if its a scam or not, i informed paypal of them and will see how it goes.
I ordered 2 of those woofer from a legit place and got them from them. I also ordered 4 new speakers from some youtube video. As for visatons 3", i have both 4 ohm ones that max at 15, but i also got 3" 8 ohm that max at 30/50W. I am the king of speakers xD

 

[SentinelAeon]

Just to clarify, 81.9dB (woofers) vs 88dB (visaton 30W) is about 6dB difference. So if 10dB is twice as loud, we could say the visaton is about 0.6x as loud as woofer ? Because when i turn both speakers on or switch 1 off to compare, u can hear visaton is a LOT louder

 

[SentinelAeon]

Ok for future speakers that i buy. Lets say my visaton play at 88dB per 1W (2.83V) at 8 ohms. 2 questions:

1) is it safe to assume that if my next 8 ohm speaker is at least 85dB per 1W (2.83V) that its loudness will be similar to visaton and can therfor combine it ?
2) if i use 4 ohm speaker, what db rating i need per 1W (2.83V) for it to be same as 85dB per 8 ohm ?

 

[audioguru]

A higher sensitivity of +3dB is a little louder. Twice the power is +3dB.
(2.83V squared)/8 ohms= 1.0W. (2.83V squared)/4 ohms= 2W. Then the 4 ohm speaker is a little louder than the 8 ohm speaker and if both speakers are in parallel then their total load on the amplifier is 2.67 ohms that might kill the amplifier.

 

[SentinelAeon]

I wont run them parallel dont worry. The only reason i am asking is to just set a BOTTOM sensitivity level that is still acceptable for me. To clarify, 81.9dB from dayton woofer i bought is completely useless to me, while visatons 88dB is very acceptable. So i am trying to find the values that will give me the sensitivity i want so i can browse speakers and find the ones that are acceptable. OK so on the other forum someone already answered to me and i would like u to double check this for me.

So we said 3dB is barely audiable difference. So if we say 88dB from visaton is very very good, we can also say 85dB is still quite good. Ok, double check this:

- 85dB at 8 ohms per 2.83V (1W) is about the same as 88dB at 4 ohms per 3.84V (2W)



To clarify, if i see 8 ohm speaker, if its 85dB or more, its acceptable and for 4 ohm speaker, if its 88dB or more, its acceptable.

 

[audioguru]

A 4 0hm speaker plays 3dB louder than if it is 8 ohms.
I notice that a speaker's sensitivity is measured at 2.83V/1m not at 1W. 2.83V makes 1W into 8 ohms so you can see that speaker that a 4 ohms speaker is louder than the same 8 ohm speaker. The different coil changes many things, not just the impedance. The sensitivity difference here is 2.2dB, not 3dB.

 

[SentinelAeon]

Ok so if i see a 4 ohm speaker and compare it to 8 ohm speaker, i can just take the sensitivity values in dB and compare it to eachother ? Like different types of speaker with this values:

Speaker type 1: 8 ohm speaker sensitivity 85dB
Speaker type 2: 4 ohm speaker sensitivity 88dB

Does that mean that speaker of type 2 that is 4 ohm is 3 dB louder then speaker of type 1 that is 8 ohm ? Meaning if i plug them in into the same amp,have it as same volume, all same, it will be 3dB louder ? Or i have to add or subtract some other number ?

 

[SentinelAeon]

Ok ok, i think i finaly got it, ignore the last message and answer this one.

we have dayton tcp115 speaker, 4 ohm and 8 ohm variant. I got the data from their page:

8 ohm: 81.9 dB (1W)
4 ohm: 86.8 dB 2.38V (2W)

Ok so now we have data. 4 ohm speaker uses twice as much power because impedance is twice as small. And twice the power is 3dB. So we can take the value we have for 4 ohm speaker, remove 3dB from it and we get the value 83.8dB. We now see that at same wattage, there is a 1.9dB difference between the speakers. Can we now directly compare this speakers like this:

8 ohm: 81.9dB per 1W
4 ohm: 86.8dB per 2W ---> 83.8 per 1W

Can we now assume that 4 ohm speaker has a 1.9dB better sensitivity then 8 ohm speaker, that is, for each 1 watt, it has 1.9dB better sensitivity. That is, if they both use the same amount of power, 4 ohm speaker will be a tiny bit louder.

 

[audioguru]

You cannot say a 4 ohm speaker uses the same power as an 8 ohm speaker because a modern amplifier output is a certain voltage, not a certain power like an old tubes amplifier.
You cannot say, "for each 1W" because the amplifier volume control sets its output voltage and the speaker's impedance sets its power.

I do not know if foreign speakers have their sensitivity rated at 2.83V like local speakers, they might be rated wrongly at 1W.
If a 4 ohm speaker has its sensitivity rated at 2.83V then its power is (2.83V squared)/4 ohms= 2W so it is a little louder than if it was 8 ohms.

 

[SentinelAeon]

Ok ok but lets say in this imaginary laboratory we have 2 magic amplifiers on which we can say, ok, play this speaker as loud to limit its power usage at 20W. Dont ask me how amplifier does that, it just does. Is then my upper calculating correct ? 1.9dB more for the 4 ohm speaker ? Or at least something around this value, so i can continue my quest in finding a good speaker with high sensitivity. Help me out here.

 

[audioguru]

The input level, volume control, power supply voltage, speaker sensitivity and speaker impedance set the maximum output loudness.
Usually a modern amplifier produces a higher maximum output power when the speaker impedance is low.

In most of my speakers, the tweeter has a higher sensitivity than the woofer so the tweeter is attenuated.