High power tweeters

[Pbassred]

I am putting together a cabinet containing a 15inch 300W bass driver and a horn. I think the crossover frequency should be 3KHz. I have seen some Piezo horns with the boast that, since they are high impeadance, you dont need a crossover network.

.......................but what happens to the HF that hits the bass driver? How much power can a "high impeadance horn output?

How could I balance the output?

What would the effective total impeadance of the cabinet be?

 

[Lars Clausen]

Hi

First i will try to convince you not to use a Piezo Horn. They may be cheap, but will never really provide a useful sound quality or sound pressure level. Even if you should go ahead and use a Pieze, the use of a crossover is still recommended. The Piezo crystal can only take so much power from the Bass and at high power levels the horn is likely to burn.
Use a low cost dynamic horn instead, and 18dB of filtering for the horn. 3kHz is ok. It will sound much better and louder (which i suspect this speaker is mainly intended for)

For the Bass you should definitely also use a crossover to avoid high frequencies out of the bass units operating area, being passed on distorted by the driver. Use 18dB of filtering as well.

The total impedance of the box is still 8 Ohms if the drivers are, because they are only loading the amplifier in their specific frequency area.

If you need to calculate the parts required for this filter, go here:

http://www.lcaudio.dk/com/passivexover.htm

 

[Brett]

I am putting together a cabinet containing a 15inch 300W bass driver and a horn. I think the crossover frequency should be 3KHz.

More like 800-1200. Think about the dispersion characteristics and breakup modes of that large cone.

I have seen some Piezo horns with the boast that, since they are high impeadance, you dont need a crossover network.

Yuk. Ditch the piezo idea and use a compression driver on a suitable flare. PAudio, Selenium, Beyma make modestly priced units that sound quite good if used properly.
But you will need a xover.

but what happens to the HF that hits the bass driver?

There is very little power required at highish frequencies and the inductance of the 15 will see to it anyway.

How much power can a "high impeadance horn output?

Depends on which one. But they'll probably make your ears bleed (because they sound bad)

What would the effective total impeadance of the cabinet be?

There is no such thing as "effective total impedance" because impedance is frequency dependent. With the 15 and peizo it will be low (say 8R) at low frequencies, and very high once the inductance of the 15, and the piezos kick in.

 

[Ken L]

Re: Re: High power tweeters

15inch 300W bass driver

Think about the dispersion characteristics and breakup modes of that large cone

Brett is on the money here - as usual.

Generally, a 12" driver conservative upper limit before beaming is around 863 hz - maximum upper limit due to beaming is twice that.

you also want to try to crossover at the point that the dispersion characteristics of the woofer match or blend with those of the horn.


regards

Ken L

 

[li_gangyi]

anyways...I think piezo sucks...they are only used for low priced stuff...gives an annoying sharp sound and generally lousy sound...there might be certain exceptions...I dun noe of any right now...sa for the crossovers...try the calculator link on top...it works quite well...or go for a Bi-Amped system.

 

[Pbassred]

eeeeek! Kinda what I expected really. What I didn't mention is that these will be 4ohm cabs so the horn needs to be 4ohm also (don't they?). (i'm thinking about hi/low balance)

Since I can't find a 4ohm horn what about 2 X 8ohm ones in parrallel, positioned next to each other? Would the HF sound waves clash?

 

[Brett]

eeeeek! Kinda what I expected really. What I didn't mention is that these will be 4ohm cabs so the horn needs to be 4ohm also (don't they?). (i'm thinking about hi/low balance)

Since I can't find a 4ohm horn what about 2 X 8ohm ones in parrallel, positioned next to each other? Would the HF sound waves clash?

Simply design the xover with a "swamping" resistor in parallel with the 8 ohm HF driver, so the net result as seen by the amp is 4 ohms, ie, an 8 ohm resistor in parallel.

You won't need 2 horns, they will interfere acoustically, and a resistor is about $2.

 

[Pbassred]

Here's where my plan falls over........
I was planning on using the Emenence Delta15 which has an SPL of 101db with the peak up arround 2-4Khz ( so why crossover at less?) . Unfortunately, they only make an 8ohm version

MaKenzie make a 4 ohm unit but the ave SPL is only 98db.

So I can either push 140w in to an efficient driver, or push 200W in to speakers that run 3db less efficiently. Same output

Anyone know of an efficient 4ohm driver?

 

[planet10]

Piezo's need an XO to sound decent -- 22 ohm shunt + suitable cap in series -- are suited for use above 7K or so only (ie PHY-HP K30). A piezo isn't efficient enuff to keep u with either of your woofs which, as Brett says, won't go hi enuff -- when i was doing PA i set the 15s to XO at 300 -350 Hz.

I wouldn't sweat the 4 ohm/8ohm thing. The more efficient driver will still play louder, your amp will be less stressed and typically produce less distortion.

dave

 

[Pbassred]

I wouldn't sweat the 4 ohm/8ohm thing.

Yeah but, ........I want it all!!

another dave

 

[Brett]

with the peak up arround 2-4Khz ( so why crossover at less?)

Because a frequency response chart will tell you about 5% of what it will sound like. A 15 will be breaking up looooooong before 2k and suffering significant beaming by a few hundred Hz.

 

[Ken L]

Here's where my plan falls over........crossover

The crossover design needs to be an inherent part of the process and can be quite complex.

People using compression drivers and horns have been crossing over from 15" woofers to horns successfully for decades, ala Altec, JBL, CAR, etc.

You might wish to consider cloning one of the many variations out there on one of those themes.

There are reasons that those designs have a _cult_ following. It will be extremely difficult to match or better those designs as they have been improved and/or modified over the years.

This is the direction Brett was indicating in the third post to this thread. And IMHO a good direction to go in.

Umm, well at this point- I suggest you not try to re-invent the wheel. All the major factors for driver selection, crossover, impedance matching, , spl differences will mostly have been worked out depending on how you go about it.

regards

Ken L