Help needed with tweeter/crossover

[nosse]

Hello.

I'm building a mobile sound system (boom-box) on behalf of my fraternity.
I'm total newbie and the first version was kind of embarrassing.

Now I'm left with:

- two p.audio HP-10W woofers
http://www.ljudia.fi/Archive/Product...-%20Tiedot.pdf

- two two-way first order crossovers (2000hz)

- two complete **** piezos

- a 25w car amp



I think I'm going to do a closed box for the woofers measuring 12,8 liters. Do I get significant advantage if I make it for example 20 liters?
I'm going for mono system so that signal is made mono before the amp, so I can drive another woofer with 25w and a woofer tweeter circuit with another 25w.
So woofers get total of 50w. I'm going to have to make/buy high pass filters for the woofers, ideas welcome.

And then the real problem. I was thinking about Selenium st-200 as the tweeter, but I'm not sure if it can do 2000hz and 16w without blowing.
Should I look for another tweeter, or should I try to get a 4000hz high pass. There was some problems with piezos and crossovers, but I'm not certain which degraded the sound.

http://www.ljudia.fi/Archive/Product...-%20Manual.pdf

Another problem is modest budget of 100eur( 135$ ) Some loosening is possible though.

I'm sorry for my English and I thank in advance for your help.

[jerome69]

Hi

I think I'm going to do a closed box for the woofers measuring 12,8 liters. Do I get significant advantage if I make it for example 20 liters?

Yes Better Bass. optimum is 34L for one woofer in a closed box.

DT220 : consider use the HP10W 96dB full range -> / 4kHz
105dB SPL / 8ohms -9dB 4kHz for a 6dB crossover R=15ohms C=1uF

[nosse]

Thanks for advice.

Does larger internal volume help bass in 100hz - 300hz region? I have to cut away practically everything below 100 hz as excursion of the HP-10W allows only 107hz as lowest when given 25 watts.

My last box was enormous 130 liter monster and it has severe xmax problems. I thought that smaller box will only cut power from lower frequencies.

[jerome69]

Originally Posted by nosse

Does larger internal volume help bass in 100hz - 300hz region?

No, it is the contrary

Originally Posted by nosse

I have to cut away practically everything below 100 hz as excursion of the HP-10W allows only 107hz as lowest when given 25 watts.

My last box was enormous 130 liter monster and it has severe xmax problems.

130L is too large for a closed box.
For two woofers in the same box : optimum is 40/50L closed box.
If you already have a 130L box, you can try a Bass Reflex box reduced to 100L@48Hz. The vent is very easy to make : 10cm diameter is 3cm long. 9.5cm is 2cm, 9cm is 1.5cm long. You don't have need a tube, but only a hole in the wood

Originally Posted by nosse

I thought that smaller box will only cut power from lower frequencies.

Yes

[AEIOU]

Piezo tweeters don't absolutely need a crossover. Bt they can and will benefit from a properly implemented crossover. Further you cannot just use an off the shelf crossover with a piezo tweeter. The impedance of a piezo tweeter is way, way higher than the usual 4 or 8 ohms. Only the larger professional grade piezo tweeters will go as low as 2,000Hz. Expect an octave higher for budget, cheap, inexpensive piezo tweeters.

[picowallspeaker]

Ultimate advice
It is impossible for a 25 cm paper cone to reach with uniform output ,specially regarding off-axis ,the high frequencies . If those are reproduced by a single unit , using a waveguide of the same diameter (25 cm) would allow a low cut of about 2 KHz ,allowing the use of an high power -little device (compression driver). It can also be found in Pro and Dj equipment .

[jerome69]

Yes but when you have a limited budget, you keep it simple.

[nosse]

The monsterbox has a port and two woofers, the woofers sound good but it's too big to be portable. The piezos actually naturally go somewhere around 1500hz, I had the whole system measured in anechoic chamber, and the piezo area of the frequency response curve looked really zigzag. It might sound like I have so much "professional" help that I don't need you guys, but you are helping a lot.

I have had two signal engineers and one former professional live mixer to help me, but none of them have actually ever built a speaker.

Thanks again.

[picowallspeaker]

Piezos are not hi-fi ,not in the band you intend to use them . Could be used above 10-15 KHz ,taking for granted you'll hear them only on axys ,nothing else . Building a wave guide with a dead speaker cone and some plaster can be very easy and inexpensive ,or they are sold for 10-12 $ .
Yes ,for high quality applications compression drivers are expensive ,as they are the only ones that can couple to the air from throat to mouth of a waveguide with velocity .
Then ,measuring a speaker in anechoic chamber can be quite useless ( depending on the applications ) as it doesn't take into account room interactions ....

[nosse]

It's going to be mobile speaker, so I cannot take room interactions into account. It will probably be played outside most of the time.