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04-15-2005 Post mapped to one branch of Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,295
Joined on 05-28-2004

Post #: 1
Post ID: 910
Reply to: 910
An ultimate horn profile?

Looking at the variety of exponential, parabolic, conical, tractrix, hyperbolic and whatever ales horn profiles out there I was thinking that we probably incorrectly approach the entire subject of horn profile analyses.

We listen the horns and we feel it is indicative enough. We apply to the horns an abstract logic and pretend that our horns are noses of submarine, winds of airplane or the jet propulsion exits. Yes, the theories are bult around all those commercial applications but those commercial application target completely different goal then we do in audio. In those commercial application the behavior of the exposed curves is the only thing that is important. If those application pay attention to air pressure that passes along the curve then they care about it only in a reference to the body of the curve, and the do not recognize the pressure wave as a self contained precious entry. Also all those commercial application and all engendering thinking that associated with it deal with essential parallel source of air. This is never a case with our audio horns.

Consequently, the mentioned (and few other reasons) made me to review our thinking about “an ultimate horn profile” and about our ability to interpret the auditable result and project those interpretations to the horns.

It is undoubtedly that the major characteristic of sound reproduction is a shape (profile) of the front of pressure wave. The engineers do not like to talk about it because they can’t objectively measure or visualize it. However, let pretend that the front’s profile is the key. If so, then it would be easy to understand that there is nothing more devastating for the front of a pressure wave then steps within sequential horn opening. Any, deviation from constant explanation rate would format the front of pressure wave and presumably screw the sound (let presume that inside of compression chamber there is no reformation of the wave’s front, that is not exactly true)

Ok, that was kind of all well-understood things but what we do after we understood it? We take a “wining profiles horn” and attach it to a random driver and then we build our theories how those profiles behave. We “kind of” forget that the compression drivers already have the built-in beginnings of the exponential channel. Each driver has own build-in opening rate and own length of the wave-channel. The only thing that we actual use is the diameter of the throat but we even not care that before the exit the driver might have 5”-6” of horn sitting right inside. Did I mention that we not really know or care what rate this inner-horn?

The point that I am trying to make is following: when we take for instance the Altec 802 and palace it into 1” tractrix and then “compare” it with 2” JBL 2440 then…. beside the differents in the drivers do we also deal with the COMPLIANCE of the specific “inner-horn” with the profile of our “outer-horn”?

Dose it means that the “ultimate horn profile” would be a profile that would be a DIRECT AND FLAWLESS CONTINUATION of the GIVEN SPECIFIC DRIVER?

Rgs,
The caT


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
04-15-2005 Post does not mapped to Knowledge Tree
slowmotion


Oslo, Norway
Posts 60
Joined on 07-22-2004

Post #: 2
Post ID: 913
Reply to: 910
Re: An ultimate horn profile?
Hi

 Romy the Cat wrote:

<P>Dose it means that the “ultimate horn profile” would be a profile that would be a DIRECT AND FLAWLESS CONTINUATION of the GIVEN SPECIFIC DRIVER?</P>
<P>Rgs,<BR>The caT</P>


Actually you can make a new driver throat to match your chosen horn
profile . So instead of starting your horn at the driver, you start the horn at the phase plug, and your driver is the beginning of the horn, just like it should be.
You may need to remagnitize your driver after doing this.

cheers,
Jan
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cv
Derby, United Kingdom
Posts 173
Joined on 09-15-2004

Post #: 3
Post ID: 914
Reply to: 910
Re: An ultimate horn profile?

Ah Romy, did you not know that the old JBLs, RCAs (and possibly S2 as well) all have an internal flare rate of 160Hz? This is but one reason why I'm asking Martin Seddon to make me a pair of 160Hz horns...

...just had a look; it may have been 180:
http://www.audioheritage.org/html/projectmay/technology/435be.htm

Ah well, what's 20Hz between friends.

You're right of course - we want to preserve continuity. This is something Earl Geddes has suggested is easier to do with the newer generation of "pancake" drivers, if I remember rightly, as far as his waveguide design goes anyway (superficially, it's really just a conical with more horn like smooth throat transition).

04-15-2005 Post does not mapped to Knowledge Tree
slowmotion


Oslo, Norway
Posts 60
Joined on 07-22-2004

Post #: 4
Post ID: 915
Reply to: 914
Re: An ultimate throat profile?
Hi Chris, all

Yes, about 180Hz, which is why a friend of mine had new 120hz
driver flare rate throats fabricated for his 288Bs , for use with 120Hz horns.
Since most of the drivers out there are designed for PA , it pays to modify them for use in the home... Wink

cheers ,

Jan


04-15-2005 Post does not mapped to Knowledge Tree
slowmotion


Oslo, Norway
Posts 60
Joined on 07-22-2004

Post #: 5
Post ID: 917
Reply to: 914
Re: An ultimate horn profile?
Hi

 cv wrote:
You're right of course - we want to preserve continuity. This is something Earl Geddes has suggested is easier to do with the newer generation of "pancake" drivers, if I remember rightly, as far as his waveguide design goes anyway (superficially, it's really just a conical with more horn like smooth throat transition).


Well, if I remember correctly , Geddes don't care about the how waveguide loads the driver, since he uses big SS amps with very low output impedance.
It's all about coverage , If I understand correctly.
Since he uses them if 2-way systems split at 1000Hz,
a pancake driver is just about right Wink

cheers

04-15-2005 Post mapped to one branch of Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,295
Joined on 05-28-2004

Post #: 6
Post ID: 919
Reply to: 914
Center your drivers, boys.

 cv wrote:
This is but one reason why I'm asking Martin Seddon to make me a pair of 160Hz horns...
Another problem….

Chris, be carefully with those large 160Hz horn and S2. The guys who make then have no instruments to center the mounting holes very precisely (wood-turning machines apparently do not furnish this level of precision, not to mention the concrete pouring machines :-) As the result, if you have a compression driver with own channel, and the driver is not exactly centered within your external horn (a fraction of millimeter does mater) then you would have a slight suck-off at middle. For instance my horn has a centering mechanism   (courtesy to John Hasquin) that allows centering the driver. I use a high resolution RTA (0.25db at 1/12 octave) running a sweep and moving the driver. Wherever I get a perfectly flat response at 4kH there I would consider the drive in the centered. Moving the driver within 2-3mm introduce an octave wide drop between 3kH and 5kH with minus 2-3 db at 4kH. Some of the drivers are less sensitive and particularly the drivers where the throats at the end of the phase plug but if you driver has own inner-horn than the centering it within the outer-horn become very important.

Rgs,
The caT


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
04-15-2005 Post does not mapped to Knowledge Tree
cv
Derby, United Kingdom
Posts 173
Joined on 09-15-2004

Post #: 7
Post ID: 921
Reply to: 919
Re: Center your drivers, boys.

Very good point - I will direct Martin's attention to this. Visually, it looks like he did an excellent job on the 340 Hz horns, and the 160Hz horns will be rolled off at 1k anyway but nonetheless, will see what he reckons. Actually, no need - I just remembered: he got a machine shop to turn a threaded mould in ally, with a precise 1.5" plug protruding at the end; he then moulded the horn throat around that in resin. So in theory, it should be pretty damn precisely centred by design as the horn threads on to the driver (or is it the other way round?). Still, when I get some measurment equipment setup I'll check the 3-5k response to be sure.

JMLC has mentioned the need for precise centering in the past, and it's another thing that struck me about all the WE 555/594 users etc - they take what may or may not be wonderful drivers then attach them to some discontinuous *throat adaptor* using something that was salvaged from a shower hose...

04-15-2005 Post does not mapped to Knowledge Tree
JLH
Indianapolis, IN U.S.A.
Posts 42
Joined on 07-20-2004

Post #: 8
Post ID: 922
Reply to: 917
Re: An ultimate horn profile?
Hey Boys,

 Remember even if you use a modern "pancake" compression driver, you still have no control over the flare rate the manufacturer used within the phasing plug. And most of the time they are not willing to tell you, or they don't even know! I've seen some companies design the phase plug by computer to get the "best" performance while completely disregarding any basic horn design rules. They just manipulate the phase plug until they get the specs they want. They do this because they know Moron sound contractors will buy based on specs and not on sound quality.

      In addition, the idea of an ultimate horn profile does not make any sense. Each and every horn profile has its own strengths and weakness. Depending on your goals, and the drivers you have, one profile will be "better" than the others. However, once you change your goals, or the driver, room, source, etc. a different profile will become the "best". There are no absolutes in Audio, only varying degrees of perfection.

Rgs, JLH
04-15-2005 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,295
Joined on 05-28-2004

Post #: 9
Post ID: 923
Reply to: 922
The ultimate what?

 JLH wrote:

  In addition, the idea of an ultimate horn profile does not make any sense. Each and every horn profile has its own strengths and weakness. Depending on your goals, and the drivers you have, one profile will be "better" than the others. However, once you change your goals, or the driver, room, source, etc. a different profile will become the "best". There are no absolutes in Audio, only varying degrees of perfection.
Actually, John.

I did not pitch the “ultimate horn profile” as a competition between the profiles and I rather called this thread like this satirically. The point was the we are considering the advantages of one curve over another but forget that we have the major  “step” between the internal and external curves of drivers with completely unpredictable sonic consequences.

The caT


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
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   Target    Threads for related reading   Most recent post in related threads   Forum  Replies   Views   Started 
  »  New  LeCleach vs. tratrix and ...Zigmond Froid..  LeCleach vs. tratrix and ...Zigmond Froid...  Horn-Loaded Speakers Forum     0  14539  12-09-2005
  »  New  Some horn writing by Thomas Dunker. ..  Some horn writing by Thomas Dunker. ...  Horn-Loaded Speakers Forum     0  32409  01-14-2006
  »  New  An Interview With Dr. Bruce Edgar..  An Interview With Dr. Bruce Edgar...  Horn-Loaded Speakers Forum     0  42167  07-10-2007
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