Crossoverpoint for horn drivers

[Niklas Nord]

If we take for example one JBL 2451 and cross this one at some 1600hz
instead of 600hz. Anybody knows how much power it will hande then?

That is, a higher crossowerpoint..

[yggdrasil]

Power rating:

- 100w continuous program above 500Hz
- 150w continuous program above 1kHz

http://www.jblpro.com/pages/componen...rvs.htm#2451HJ

[Niklas Nord]

maybe somewhere 200watts then

[spkrman57]

My 2 cents worth here:

1" driver @ 1.6khz

1.4" and 2" @ 800hz

These points allow plenty of safeguarding of the drivers and I have had success with those points.

Ron

[whgeiger]

maybe somewhere 200watts then

NN,

Due to the large crest factor found in musical and other typical program signals, displacement limit set by a RMS power specification is optimistically unfortunate. Also, at 200 watts, a 'pressing' of the driver's thermal dissipation envelope will occur; not to mention, that an unacceptable level of throat induced distortion will be observed.

If more acoustic output is needed, then use a horn/driver array for reliable results. In the P.A. setting, reliability is everything except that intelligibility and inaudible distortion are expected givens.

Regards,

WHG

[grumpy]

200W ? ... you'd be pushing well over 130dB SPL at meter distance. Instantaneously, the voice coil might not become a blown fuse (I recall old Dynaudio tweeter ads showing very brief bursts of 1000W+) , but I hope you're wearing hearing protection.

[Niklas Nord]

Yes but music can well have peaks up to 120db, when listening to
classical music, or some percussion..
Not direcly dangerous to the ear if it´s just peaks and the overall
pressure is some 95db.

Do you mean that 200watt´s would blow the driver?

The thing with throat distorsion is interesting.
I have been asking alot about distorsion in horn drivers, but no one
has been able to give any detailed information about distorsion, and
how it compares to conventional tweeters..

[yggdrasil]

Where are you going to use this driver?

[whgeiger]

NN,

Some comments follow your text.

Regards,

WHG

Yes but music can well have peaks up to 120db, when listening to classical music, or some percussion.. Not directly dangerous to the ear if it’s just peaks and the overall pressure is some 95db.

A high crest factor, but underneath a powerful low frequency component hopefully seen by a robust woofer.

Do you mean that 200watts would blow the driver?

a) At lower frequencies, diaphragm fractured when slammed into phase plug.
b) At higher frequencies, voice coil meltdown marks termination of thermal run-away.

The thing with throat distortion is interesting. I have been asking allot about distortion in horn drivers, but no one has been able to give any detailed information about distortion, and how it compares to conventional tweeters.

Distortion occurring in a horn throat is attributable to the elastic non-linearity of air that is emphasized by
a) its entrapment in the small-enclosed spaces of phase plug passages and
b) the relativity high intensity of acoustic energy that passing through them.

The following formula may be used to characterize 2nd. harmonic distortion.


[D2h] = [k]*[f]/[fc]*(([Wa]/([St]*[N]))^(1/2)) – Second Harmonic Distortion


where


[k] – Empirically Derived Constant
= 0.4 - for conventional exponential horns that exhibit some beaming at high frequencies and thus a relatively flat on axis response.
= 0.2 – for constant directivity horns that exhibit a declining (un-equalized) on axis response.

[fc] – Flare Cut-Off Frequency of the Phase Plug Passages (Hz)

[f] > [fc] - Signal Frequency of Interest (Hz)

[St] – Area of Phase Plug Slits (Adjacent to Diaphragm) (in^2)

[N] – Quantity of Drivers Used

[Wa] – Total Acoustic Output (Ave. Watts)

For direct radiating tweeters, that are less efficient, principal distortion products are related to the non-linearities of diaphragm excursion that are emphasized by the prerequisite increase in volume displacement.

[edgewound]

Here's my take on it and it kinda needs to be qualified....here goes


I'll assume you're using it for hifi or studio monitor use...

if it's a two way system, a good frequency would be in the 1100-1200Hz neighborhood. Why? Because of a thing called "power response". How high you cross it over will determine how great the off axis response is in the upper mid frequencies that come out of the horn and don't beam too much like a flashlight.
You might want to consider an 18db or 24dB/oct hi-pass to keep the lower frequencies from upsetting the diaphragm too much. Now with that said...the driver will be able to try and reach 18-20KHz with a higher xover point since it would be relieved of lower freq duties.

As far as power handling goes...the more power the better...within reason, of course. You want plenty of headroom available to prevent the amplifier from clipping, and as we all know (we should anyway) amp clipping is public enemy number one with with HF drivers...doesn't matter what flavor they are...clipping burns the voice coil...and also sounds really bad .

You want your system to sound clean...so you need pleanty of clean power.

Correct me if I'm wrong, please

Thanks for reading my thesis,

Edgewound

[Niklas Nord]

My questions come from some ideas I have, to build some speakers..
My Auroratowers will be finished this summer, så I must have someting
else to work with, I want a project

Loudspeaker built for hifipurpose, the goal would be as low distorsion as
possible. Then I would like to use a horn driver, and maybe a tractrix horn
couse theose seems to have better caresteristics than conventional horn
as in my K2 s9500.
A two way design maybe is hard to go with, three way if it´s better..

Is there anybody that knows any facts about conventional tweeters, do they
have lower distorsion than horn drivers? If let´s say the horn driver is crossed
somewhere ower 1khz, and the conventional tweeter is crossed ower 2khz.

[Mr. Widget]

Is there anybody that knows any facts about conventional tweeters, do they
have lower distorsion than horn drivers? If let´s say the horn driver is crossed
somewhere ower 1khz, and the conventional tweeter is crossed ower 2khz.

You mention crossover frequencies but not SPLs... based on your earlier posts I believe you also want high SPLs. A conventional dome tweeter with a sensitivity of 91dB/watt will have quite a bit of distortion at 125dB. A TAD 4003 with a sensitivity of 112dB/watt will have the lowest distortion, a JBL 2451 will also have very low distortion.

WIdget

[edgewound]

You've got several variables to deal with as far as what you're looking to accomplish, and what kind of distortion your willing to put up with. It's all a compromise somewhere. The 2451 is going to give you greater efficiency than ANY dome radiating tweeter, such as a Morel or Dynaudio, (if you can find any)or Ceratec, et al... The least distortion inducing horn type available, I believe, would be a conical style waveguide. Since sound waves are spherical in nature, the circular shape of the waveguide will be less prone to reshaping...or distorting, if you will...the physical shape of the sound waves radiating from the horn. The ideal approach, some would advocate,would be a coaxial arrangement, or Duplex as Lansing called it, so all frequencies are emanating from the same acoustic plane or "window", thereby reducing comb filtering or lobing effects of overlapping radiation patterns of separated drivers. Of course the drivers should be time/phase aligned in the crossover network to reduce the effects of phase distortion. Wow...lots of distortion issues to address .


Anyway, I hope these brief thoughts are helpful to you.

Anyone have any other thoughts here?

Thanks, Nik

Edgewound

[Mr. Widget]

...lots of distortion issues to address .

Very good point. I was just thinking of simple harmonic distortion, but there are many forms of distortion. NN, you do pose some interesting questions!

To really get into it, I suppose we need to know more about your requirements, system, room etc.

Widget

[Niklas Nord]

Well, If we think about the K2 s9500, one 375nd and two 1400nd.
I don´t think we will need any ultra high frequency drivers couse we
can´t hear well beneath 16khz, and I´m very happy with the high
frequency in the s9500.

I was whinking of a loudspeaker that would be working from 80hz,
80hz couse there is 16 SUB1500 drivers from 0hz to 80hz in the auroratowers.


(statement, and crazy.. and just right)

well, from 80hz.
And more capable than the s9500 when it comes to SPL. And offcourse
lower distorsion (the s9500 has no noticeable distorsion).

I dont know if the 2451 is the best driver to work with. I would like it to be
crossed higher than the K2, to have lower distorsion.
Maybe the driver in the new K2 s9800 will have better measurements than
the older drivers. Or perhaps some TAD will be better..

I have been thinking of two 1500AL, and maybe two 5" - 10" midranges.

I´m just brainstorming here.