Transmission lines/rear horns- how do they affect xmax?

[Bill poster]

Reading that drive units hardly move in a rear horn speaker- I guess this means much less distortion in the bass region- just wondering if this is the same for transmission line designs?

[planet10]

Depends on the nature of the transmission lines... in the terms narrowest sense it is an aperiodic box which will have similar excursion as sealed, in its broadest sense a horn is a TL, and TLs include everything in between

dave

[Psychobiker]

Just from a sheer engineering level, I would imagine that at specific resonance points that when the line is vibrating at its fundamental (or multiples thereof), there would be very little excursion due to the backpressure within the box?

L

[planet10]

That is one of the concepts of a well tuning taditional TL... the primamry resonance reduces the driver's fundemental resonance.

dave

[Bill poster]

so if the line is tuned to a frequency below the drivers res. freq. then you hit problems?

[freddi]

software can examine - here's a ridiculously large BIB pipe-horn type simulation for a Nirvana 10" with ~50Hz resonance - note the excursion in-band is lowest where the impedance nulls occur and power handling at 45Hz is less than one watt for its specified 1mm xmax. For me it would make more sense to have the Nirvana in a 75 liter Karlson coupler (where it loads better and sounds better) - then if desired, augment the bottom with a reasonable size sealed box woofer.

[planet10]

Originally Posted by Bill poster

so if the line is tuned to a frequency below the drivers res. freq. then you hit problems?

Depends. There are far too many other factors.

dave

[InclinedPlane]

I've heard alot of forum talk about the Karlson design lately. It must be quite good. Wish I could hear one.

[ThorstenL]

Hi,

Originally Posted by Bill poster

Reading that drive units hardly move in a rear horn speaker

That was untrue for any rear-loaded horns I encountered, be they JBL Scoop type PA systems, Hedlund Horns with Lowthers or AER's, LBH's and Beauhorns.

It is true (or more true) for front loaded bass horns that operate the bass driver in a small sealed chamber (common for big PA Bass horns), however such systems often raise the in system resonance much so the resulting horn does not play as low when stacked as one would expect.

TL's and related structures will have resonances (just like a bass reflex box) where they will cause a reduction (often very substantial) of cone motion, at other frequencies no such action takes place.

Indeed I find that I get most mileage from analysing so-called TL's as atypical reflex box with a very low tuning via a large cross-section port and small actual box, plus the various parasitic resonances the long and often folded port causes.

Doing this in simulation seems to fit the actual measured results better than using classic TL Theory.

Ciao T

[PeteMcK]

re:'analysing so-called TL's as atypical reflex box with a very low tuning via a large cross-section port and small actual box' - interesting, Thorsten. So, what roughly proportion of the TL volume would you use as the 'box', and what proportion as the 'port'? or is it an 'it depends' answer? :-)