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stoffergoffer 7th October 2012 03:37 PM

transportable speakers building project
Hey everyone,
I about to start a slightly larger project in the coming months, and I hope to get some assistance here. To make it short i want to build some speakers that I can use when I'm out as a DJ for various parties. I have built speakers before so I have a bit of experience.

I have found the drawings of the speakers on a Romanian website, and the idea is to have 2 subwoofers which each have space for a satellite during transport.

I already have the treble and bass units that I want to use, and as a 10 "unit to the satellite, I thought about using this. In the satellites, I'm going to put 2 of the above tweeters in each and then angle them slightly so the sound covers a broader area.
I would like to just have one wire from the amplifier with the full signal going to the sub and then a small wire from the sub to the satellite. First of all this means that the resistance is very small 4 * 8ohm ~ 2 ohms, unless I put some of the speakers in the series. Secondly, I have put some crossovers in the system. I have an idea of ​​how I put it together:

My speakers are in total (40W * 2 +200 W +250 W) = 530W so the first crossover should be able to withstand this. So first the full signal runs to the sub crossover, and here are the lower frequencies (<200Hz) distributed to the bass. Then the signal runs on to the second crossover where > 3000Hz is handed out to the treble, and the remaining signal then goes to my 10 ".

I'm a little unsure about what happens to the resistance whenever a crossover on. It says on the website that the output impedance is on 8 ohms, (so the crossovers gives the amplifier a total resistance of 4ohm), or do you still just count with speakers resistance, in which case it might be an idea to put the tweeters in series?

One advantage of this crossover design is that I will be able to use satellites without bottom and then the 10 "units suddenly playing bass since the signal goes directly to the tweeter crossover.

Hope that there is someone who has no input or thoughts about my project that will help me and improve it.

picowallspeaker 7th October 2012 05:31 PM

you say that you had built speakers before, but putting together
a jig like that is more than just speakers...indeed it involves
crossovers, amplifiers, cables etc. So, the very first thing is about crossovers,
and also the basic laws of connecting speakers .
The wires should come each from the amplifier, making its output the main
node to attach the various loads , and not in series like you suggested .
Speakon connectors should come handy because they carry 4 poles each .
So lets start from the speakers ; the passive filter @200Hz would work
for lowpass, but I don't think it can transfer much energy to the low/mid;
usually the filtration is done actively, see the IMG on the same site * tilbyder IMG STAGE LINE Elektronisk delefilter - MCX-321/SW til den rigtige pris.
Crossover between the low/mid and the tweeter(s) can be done passive .
About energy transfer ...:rolleyes: I don't think the 15" would really perform as a sub ....I fear that his energy below 100 Hz is still very scarce .

* You'd need another ( stereo) amp

picowallspeaker 8th October 2012 05:56 AM

I forgot about the tweeter :p

It will sound a lot louder than the speaker below ( or up ...! )
It has 107 dB /W/m sensibility , so a 10 dB attenuation is needed
to match with the 95 dB sens. of the woofer, which means it'll receive
1/3 of the power to put the same level out ....I'm a little confused :rolleyes:

Usually the tweeters are high-passed at 18 dB/octave ,thus the crossover
would consist in capacitor-coil-capacitor-(then the Rload which is represented by speaker's Z :) )
The attenuation net, also called
L-Pad for the fact that it resembles an L as the schematic shows a resistor
in series and one in parallel, can be put before or after; in the second case
it could alter the cut-off frequency point and slope as it is 'seen' by the crossover circuit.

The frequency of 3000 Hz is the cut-off point between the (mid) woofer and the tweeter, this means that the tweeter starts to emit even at 2000 Hz , depending from the slope given by the filter (...contoured ); this may not be
good for the particular tw that you have chosen, so it's all about trial and
correct .
Also the mid-woofer will lose some efficiency after the necessary low pass ...
another 1-2 dB .

So be prepared to change completely view on how it should be done, and
rely on the suggestions and information that other members much more
prepared than me and in the 'field' by much time, may give you.

stoffergoffer 11th October 2012 05:49 PM

Thank you very very much for your answers this is a big help to me. As i understand you see 3 main problems:

1. The crossover for the mid and tweeter have a freq on 3000, which means im gonna loose the freqs between 3000 and 4000Hz. picowallspeaker suggests that I use a active crossover.
2. Each speaker should receive the signal directly from the amp, and not be connected in series.
3. The high effectivity of the tweeters will cause them to play louder than the rest, and furthermore the mid will loose some db after the crossover.

Okay regarding the first problem. One important thing about this system is that it has to be easy to put up and down. Therefore i dont wanna have an extra heavy thing to carry around in the form of an active crossover. I will only use passive filters even though i may get a little worse audio.
I have redesigned the electrical circuit, and decided to build my own filters specially made for my speaker-units, they are all 12db/oct (hope thats good enough for my tweeters).

Curcuit drawing

First of all i still use the same crossover for the sub which have a crossover freq at 200 Hz. I could also have built my own, but I found that it was actually cheaper to buy this one. The HP signal then runs to the top speaker where a LP filter is introduced for 4000 Hz so the 10" should be playing around 200-4000Hz, and if connected directly to the amp <4000Hz. Before the sub crossover i have connected another signal that goes to a hp filter for the tweeter.
As you see there are two signals running to the top, therefore i will be using a 4 poled speakon cable :)

The second problem. as i said before this has to be very easy to put up and down, therefore i only want to pull one cable from the sub to the amp. I dont see how i could get the signal for each speaker through a single speakon cable.
I will put each speaker in a parallel connection (as you see on the drawing) resulting in a total impedance on 2 ohms, and i dont see why this would be a bad idea. The amp I plan to use for this, is found here.

Okay, third. You suggested that i should be connecting a l-pad to control the volume of the tweeters and i think i will be doing this, but only later in the process and maybe for all the speakers. The reason for this, is that I will be connecting my mixer to the system and here i can just turn down the treble. I know its not perfect but that will do for now.

I read something about the speakers would change in resistance as they play, and for the filters to work I need to put something to hold the ohms at a constant. Can anybody explain this to me? is the l-pads doing this? Is there anything else i should put before or after the filters?

You also said that you doubt the 15" unit, and i will let you know that i plan to replace this with the unit this cabinet is designed for at a later moment.

If anyone is interested i can post the Sketchup model i made for this particular project :)

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