rear loaded horn question

[zobsky]

Can someone clarify the following for me:

As I understand, .. most rear loaded horns using a fulll range driver are direct radiating in the mid - high frequencies via the front of the driver whereas the low frequenceies projected from the rear surface of the driver are reinforced via horn loading.

The sound radiating via the front and rear surfaces of the speaker cone are out of phase, . so shouldn't the bass emnating from the horn mouth be out of phase with the mid-treble frequencies? If so, shouldn't this be an issue?

I'm thinking I'm neglecting something fundamental here. Can someone point it out?

Thanks

 

[Kravchenko_Audio]

The trouble with mids and trebles

The low end usually survives it journey through a well designed horn. The horn length is what usually swamps out all the mids and treble stuff. The path length and the sound wavlength are quite different. ie the mids and trebles are shorter than the length of the horn and tend to cancel out to a degree. The other way to attenuate not completely cancel out the unwanted stuff is to stuff the rear chamber on the horn. It will effectively suck up allot of what you don't want.

Mark

 

[zobsky]

Re: The trouble with mids and trebles

The low end usually survives it journey through a well designed horn. The horn length is what usually swamps out all the mids and treble stuff. The path length and the sound wavlength are quite different. ie the mids and trebles are shorter than the length of the horn and tend to cancel out to a degree. The other way to attenuate not completely cancel out the unwanted stuff is to stuff the rear chamber on the horn. It will effectively suck up allot of what you don't want.

Mark

Mark,

I already understand (and agree) with all that you mention.

Let me rephrase
consider the following (over)simplifications

A. assume a horn that boosts all frequencies below say 200Hz. These will pass through the horn and exit via the horn mouth

B. frequencies from 200Hz and above are direct radiating and will reach the listener only via direct radiation

wouldn't the freqencies upto 200Hz and those above this point be out of phase?

 

[BillFitzmaurice]

They are in phase. One of the functions of the rear chamber behind the driver is to act as a low pass capacitive filter, much like a reflex port, delaying the passage of sound and thus inducing a phase shift. Further phase shifting of the rear wave is accomplished in the time domain by the distance it takes the wave to pass through the horn. By the time the front and rear waves actually meet enough phase shift has occured so that the two waves are not subject to phase cancellation. It's not dissimilar to using a half-wavelength baffle.

All frequencies pass into the horn. Some HF attenuation is accomplished by the aforementioned rear chamber, more HF attenuation is caused by phase cancellation within the horn caused by reflections at the horn bends. That cancellation can be overcome with the right corner reflector configuration, but in a rear-loaded folded horn one doesn't really want mid or high frequency transmission anyway, so the best configuration is to have simple bends with no reflectors.

 

[MJK]

I have tried to characterize rear and front loaded horn design and performance. You can read about my findings on my site. I am still working on these documents but in the case of the rear loaded horn, I think that I have a good understanding and description of the phase of the horn output w.r.t. the driver output and the performance of the rear chamber. I am looking for constructive feedback on these documents.

Hope that helps,

Martin

 

[zobsky]

Bill, Martin

thanks, .. that's just the information I needed to know

I wish to understand horn theory before I attempt building one (always hard on myself ).