Tractrix FLH for Alpair 10.3?

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By, well, 'common sense', a horn-like stuff is giving the mated driver a better (higher) air load.

And let's simplify the driver into 'motor' + 'cone'. The load of the motor is the cone and associated air load. Higher efficiency is obtained by better 'transmission' of the force between motor and its load. (and the load can be divided into 2 stages - motor/cone and cone/air, we finally get the sound from air, of course)

Now, let's assume there's a motor that is very powerful, and its cone is relatively light and small. So the actual load of the motor is very light, thus the force of the motor can't be transmitted to the cone effectively. (think of a powerful punch hitting a feather pillow) The cone doesn't get full energy from motor, air doesn't, either, of course.

In this case, a horn (added air load) is a helper to the motor for handing its force to the air more effectively. (now there's a poor but proper jaw taking the punch)

On the contrary, in a combination of a weak motor and heavy cone, it's already quite a load for the motor. As to the inefficient force transmission between cone and air is another issue and makes no difference to the motor itself. The appetite of the motor is nearly full anyway.

Now we add some more load to such a motor, be it even heavier cone or more air, what would happen? The motor can be overwhelmed, or working in a overloaded situation - like a man pushing a car. Yes, it'd move, but painfully slow and can't do instant start/stop. (what is fast start/stop? HF, that is)

Simply put, only powerful motors get the larger benefit from horns (added air load). Horn makes the operation of the whole combination more ideal. Makes sense, doesn't it?

So, the motor strength is related to BL, Re. The motor load is related to Mms. The air load of the cone is related to the Sd. And there're some magical formulas getting all these factors into harmony.

 

[astrojet]

Thanks CLS. Simple enough, even if it all ends with a 'magical formula'.

Off topic, so read no further in case you are bored! I now wonder.... if front horn loading boosts from the horn corner upward for 3 or 4 octaves, and then reflections/interference takes over and reduces the output at about 3 dB/octave, does anybody try to selectively damp/attenuate the high-frequencies (above the 3 or 4 octaves of enhancement) to let the horn pass highs essentially unaffected? Maybe this could be done with a thin coating of pliable or elastic rubber, etc. Even something like a finely textured surface might work.

Probably not, and perhaps a naive idea, but thought I'd ask.

Back to building boxes. I've got a few in the works now, including a Karlsonator and the FHXL.

 

[hollowboy]

I've heard Lowther PM4 in Oris 150 and I like the sound very much.

[...]

One of the very important factor is, it seems no coaxial driver is designed for horn-loaded. They tend to fit in compact boxes for their major application.

Lowther drivers have Fs of 55-60, Qts of 0.2-0.3, VAS 40-50litres, SPL 95-99dB

Boatloads of coaxials have those same stats.

Mine (15" coaxials) are bigger, but of the same rough type (light cone, strong magnet): Fs 50, Qts 0.23, VAS 135litres, 7.03% efficiency (~100dB).

Like Lowthers, their tiny Qts means they need loads of help on the low end. Can't see why a front horn wouldn't work with them, exactly how it does with Lowthers.

 

[GM]

if front horn loading boosts from the horn corner upward for 3 or 4 octaves, and then reflections/interference takes over and reduces the output at about 3 dB/octave, does anybody try to selectively damp/attenuate the high-frequencies (above the 3 or 4 octaves of enhancement) to let the horn pass highs essentially unaffected? Maybe this could be done with a thin coating of pliable or elastic rubber, etc. Even something like a finely textured surface might work.

BLHs are basically limited to ~two octaves, compression FLHs, ~three octaves.

Horns don't 'let' the HF through unaffected since throat and mouth acoustical impedances increase with increasing frequency due to a falling acoustical power at 1/f and why the driver's HF response must rise to compensate.

To minimize these losses due to reflections back to the throat, good horn design dictates a conical HF section and a proper mouth end correction such as Dr. Geddes, the late JMMlC, Tom Danley and others have been promoting in recent years, not to mention RCA's Harry Olson as early as the late '30s.

Peavy's QTW horns 'rim' the mouth with foam same as some DIYers and at least the 'real' Altec have been doing since at least the '70s and the '50s using acoustic fiberglass insulation originally designed to damp heat/AC ducts. Before then, HF sound reproduction was limited to what could be fit on the edges of a film strip, so limited to ~11 kHz, hence no need to deal with this issue.

http://www.excelsior-audio.com/Publications/QTWaveguide/QTWaveguide_WhitePaper.pdf

http://images.sc1.netdna-cdn.com/D/Replacement-Speakers-PEV13-493560-detailed-image-1.jpg

GM

 

[GM]

Like Lowthers, their tiny Qts means they need loads of help on the low end.

Gees, this horn design driver specs 'myth' that a low Qts is required just won't die......... Low Qt motors were required due to the amps back in the beginning either being a impedance matching or at least a high output impedance with variable damping factor [DF] tone controls to boost them even higher, so in today's T/S 'world' this equates to a nearly doubling [or more] of the driver's effective Qts, ergo proper wide range horn design, especially BLHs, dictates a 0.4 to 0.7 Qts once all series resistances have been factored in and why driver Qts has risen in 'lock step' with amp design's decreasing output impedance [increasing DF] over the decades.

GM

 

[IG81]

It would seem like a very strong motor with a medium/high Qt is a possible situation if a very stiff suspension is present, yet this could still be horn material if I'm not mistaken.

Fs = 1 / (2π √(Mms Cms)
Qt = √(Mms / Cms) (1 / Rmt)

You can still end-up with a fairly high mass-corner frequency if Fs is also high due to a low Mms on the same driver, something that I take as an - at least partial - indication of horn suitability.

Perhaps Fs and the Q-parameters, as well as the often mentioned EBP, are only good to get a general idea of a driver's suitability for a specific application. It seems like they are merely incidental to more revealing parameters, or am I just rambling again?

 

[GM]

?? If it's medium-high Qt it by definition is not a 'powerful' motor, just one strong enough to cope with the driver's mass, compliance.

Well, one wants to use the right 'tool' [specs] to do the 'job' properly, so depending on the app one could say that any set of specs could apply.

I made this point fairly early on using MJK's software by showing a FLH sim calculated using Prof. Leach's compression horn design routine with a driver's measured specs of ~83 Hz Fs, 32.85 L Vas, 3.3 Qes/2.446 Qts.

Its size was huge due to the high Qes of course and with a ~1 mm Xmax, not a practical design, but a viable alignment none the less with a driver most folks wouldn't even consider for a narrow BW OB app.

GM

 

[TimbreAudio]

Stumbled across this thread.

Looks like Fern & Roby have made a high XO large mouth horn using the Alpair 7p, and crossing over low to an Alpair 12/12PW.

I wonder how it sounds?

The Horn Speaker System | Fern & Roby

 

[TimbreAudio]

Did anyone get to listen to this at Capital Audio Fest?