Horn/Driver Comparisons

[mini]

His theory is that Higher Order Modes (HOM) are very problematic. He regards HOMs as any wavefront that bounces off the horn walls and creates a delayed wave launch, much like edge diffraction on a flat baffle.

Hi,

An old thread found while looking for PT waveguides. Many of You might not exactly imagine what the HOM hype is all about.

Dr. Geddes did a real great job on horn calculations, I mean it. From that he derived a suspicion regarding Higher Order Modes, HOM for short (it is a trade mark for male underwear here in Europe, beware of copyright issues!).

His claim is that HOM has ever since degraded waveguide sound until his own special one was commercially available. The only investigation regarding audibility of HOM has not shown the effect of HOM directly. It is hold as its signature that HOM introduces undulations on the amplitude and phase response. From a certain degree of contamination as to say this is quite audible. So far so good. That we knew before already.

If HOM does not become perceptable by superstition we have to deal with the generated sound field. The only effect is linear distortion so far, namely phase and amplitude aberrations. We know how much of it is critical. Why not forget about HOM then? It's just an other source of the above mentioned linear distortion. As is diffraction at edges (enclosure, horn rim, finite horn length even with the Geddes type), interferences from driver internals, crossovers and a lot more.

Look at the graphs and You might discuss the whole total of linear distortion. Is it critical or not? With most of the more honorable systems one would find that it is not.

HOM for itsself is prone to misconception. The lowest order mode - in contradiction to the higher ones - of wave propagation in a horn is some kind of arbritary:
- with Websters horn theory the lowest order is a plane wave
- with tractrix it is a spherical wave
- with Geddes it is something else

A waveguide is virtually HOM free only when the lowest oder mode is THE mathematically exact solution of wave equation with given boudary conditions.

Geddes is right in saying that his oblate something is one that solves the wave equation exactly. But it does only with infinite horn length with that exactness - as far as I understand the whole deal. With that given even Geddes type waveguides have its hassle with HOM.
Additionally one should not forget that the driver itsself introduces HOM. It is questionable how far a waveguide reacts on that, could it attenuate that - a long way to go ... . As Geddes' waveguide has to deal with HOM anyhow, from what do we tell that Geddes' oblate something is better than prevous designs regarding - as shown above - arbitrary defined HOM?

Look at the graphs and decide from that. Considering HOM as a source of something mystique "bad" is misleading. HOM isn't to well defined and its effect on hearing delight hasn't been shown in to bright light by now.

buy

ehm: If Geddes' waveguide do measure good, they are good. But the same is true for all the others. As expenses with Geddes' solution do not explode as with some fairy tales in audio You may decide by taste first, omitting any HOMology. It seems his SUMMA is an honorable offspring of the 4430 but with a smoother response. in't it?.

[Zilch]

Geddes admits his waveguide has HOMs, and he stuffs it with foam to attenuate them. Not HOMless.

It's almost an angels on a pin thing in context, in my view.

Here's Altec enthusiasts' favorite 902 and horns:



Find me the HOMs.

http://audioheritage.org/vbulletin/s...995#post208995

[Robh3606]

You might have better luck in the time domain.

Rob

[Mr. Widget]

You might have better luck in the time domain.

Rob

We all pick the gremlins we choose to battle.


Widget

[mini]

Geddes admits his waveguide has HOMs, and he stuffs it with foam to attenuate them. Not HOMless.

It's almost an angels on a pin thing in context, in my view.

Here's Altec ...

Hi,

It's obvious that the Altecs sound field will suffer from degraded linearity, if someone is keen on using them. Whether the consumer would feel a degraded delight in hearing his music is an other question. It has a lot to do with believes, whether the perception could be trusted as being correct, true, natural - in contradiction to faulty, wrong, ehm - supernatural

This in mind Geddes' claims on "HOM" are a bit misleading. It's not only a question as "how many angles could rest on the pin". The problem lies in the method of how audio quality is evaluated.

The generated sound field should be related to human hearing. Science, statistical proof, real people, real effect. Speculations on reasons for difficulties with the reproduction are unavoidable. But they should be proven in the end. Unfortunately this is not true with HOM. As long as this is so, HOM - ill defined - should not be held against anything.

Conclusion: "HOM"-talking could degrade Your delight in hearing music via Your very stereo set. Simply by disturbing Your belief that everything is just fine. What a pitty!

Take care

ps, to bring it back to solid grounds: Geddes' waveguide is not to much more linear than EVs HP940. Even in off axis response both are quite similar. The 2352/2447 combo performs better up to 10k. But Geddes' is small, serves home audio with wide distribution, shows no directivity flip 'cause of axial symmetry ... not at least it is relatively cheap! It doesn't need that hype. The foam - measurements?