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[MikeHarris]

the Crest 9200 shamed the Crown too.
They did variable rails much better

[duane massey]

Interesting tidbit: when we built the 20hz horns in the mid 70's each one held 5 TAD 1602's. Each woofer was driven by approx 85 watts, and the excursion was so small that you had to shine a flashlight on the cone to even see the movement (if you could stand to squeeze into the throat while it was working).

[Marcel de Graaf]

Interesting tidbit: when we built the 20hz horns in the mid 70's each one held 5 TAD 1602's. Each woofer was driven by approx 85 watts, and the excursion was so small that you had to shine a flashlight on the cone to even see the movement (if you could stand to squeeze into the throat while it was working).

This is efficiency related. Hornloading a driver in the right conditions makes the driver have less excursion for a given output compared to direct/vented system. Its as Ivan mentioned if a speaker has more excursion for a certain frequency, than this speaker must be faster as a speaker with less excursion at the same frequency. Hornloading usually make`s the low frequency part sounding a lot cleaner as there is less distortion produced by the speaker.

We all know the classic 808 kick drum.  This has some high frequency content in the beginning of the waveform followed quickly by a decay off low frequencies. To ideal reproduce this kick drum (and make it absolute tight or "punchy") the high frequencies has to come from the same acoustic center as the low frequencies. I always wondered if it would not be a big  improvement for the listener as this full kickdrum is played back in a different track layer where only the full kickdrum is reproduced by a wider bandwidth subwoofer (multiple drivers). Maybe other problems occur.

Coming back to the low frequency driver itself. I always keep my eyes out for the highest -3db point of the motor structure itself. If you would dismantle the loudspeaker cone and suspension you are left with only the voice coil. This part has only the resistive part of the wire winding and the inductance formed by the coil. The formed circuit has some time delay on its own, usually called the electronic time constant in the world of servomotors. This time constant is the time the motor reached 63% of his max. current to its inital step response. The formule for the time response of the motor alone is L/R and this can be converted back to the real -3db frequency point of the loudspeaker, but be aware this usually not shown in a frequency chart of the loudspeaker, because directivity (and/or a combination from other effects) is make the speaker looking flat. The time constant of the servodrive subwoofer is incredible low.

And than there is the issue the inductance is not constant over its frequency range. It will always be a big can off worms. A good reading about the importance of the subject is in the following link; http://aespeakers.com/designing-for-low-distortion-lambda-001-motor/

gr. Marcel

 

[Jim McKeveny]

Transient response can be objectively quantified by rise time, not sure how much it matters after the LPF of a sub.

JR

Couple decades ago I came across a study that found that people are more sensitive to rarefaction than compression at low frequencies.(Wish I could find it now. It was in pre-internet engineering journal). This certainly implies that absolute polarity is a factor in the leading edge transient VLF experience.

[Art Welter]

Couple decades ago I came across a study that found that people are more sensitive to rarefaction than compression at low frequencies.(Wish I could find it now. It was in pre-internet engineering journal). This certainly implies that absolute polarity is a factor in the leading edge transient VLF experience.

Jim,

If you can find any scientific study that supports your implication, love to see it.

The "leading edge" transient of most VLF experiences is high frequency noise, like the kick drum waveform example below.
Reversing it's polarity, as between the top and bottom example will make no difference in the "experience" of it's VLF envelope.

That said, if a VLF waveform were highly asymmetric, and the speaker reproducing it had large amounts of even-order distortion, it's possible reversing polarity could be audible due to a level change.

Art

[Ivan Beaver]

Couple decades ago I came across a study that found that people are more sensitive to rarefaction than compression at low frequencies.(Wish I could find it now. It was in pre-internet engineering journal). This certainly implies that absolute polarity is a factor in the leading edge transient VLF experience.

Years ago I did a test (based on some people telling me so), that JBL double scoops had more impact when the drivers went backwards with a + input.  The "idea" was that they loaded up the horn first, rather than hearing the front loaded first.

I totally understand how easily our ears are fooled (I have fooled myself quite often), but I swear they did sound punchier when wired in reverse.

With that being said, there are all kinds of places in the signal chain that could reverse the polarity of the signal, nullifying the movement.

I do question my findings back then (it was 25 years or so ago), as I have learned a lot since then that make me wonder about the test.  No I have not done it since.

[Ivan Beaver]

That said, if a VLF waveform were highly asymmetric, and the speaker reproducing it had large amounts of even-order distortion, it's possible reversing polarity could be audible due to a level change.

Art

And just because you can hear it, does not make it better or worse.

The Hi futility market loves to embrace anything that "sounds different", as "It must be better".  Even if it is worse.  Just hearing a "change" is often a big deal.

If you "believe" a piece of gear is better, and it sounds different, then it MUST be better-right??  HAHA

[Jim McKeveny]

If you can find any scientific study that supports your implication, love to see it

I'd like to also. It was @1977-8. The "sub" woofer concept was just making the rounds - Infinity Servo-Statik, Fulton J's, Dahlquist Sub. I dove into the SUNY Stony Brook Engineering Library card catalog to see what research there might be on VLF. What came across was not so much the audio realm as military: shockwaves, non-lethal weapons, etc. The polarity difference wasn't about asymmetry in the source, but in the human response.

[Jim McKeveny]

And just because you can hear it, does not make it better or worse.

The Hi futility market loves to embrace anything that "sounds different", as "It must be better".  Even if it is worse.  Just hearing a "change" is often a big deal.

If you "believe" a piece of gear is better, and it sounds different, then it MUST be better-right??  HAHA

Agreed. This is what I call the "optometrist" effect. "Better? Or worse?...."  'Better now?" ....

[Steve-White]

Years ago I did a test (based on some people telling me so), that JBL double scoops had more impact when the drivers went backwards with a + input.  The "idea" was that they loaded up the horn first, rather than hearing the front loaded first.

I totally understand how easily our ears are fooled (I have fooled myself quite often), but I swear they did sound punchier when wired in reverse.

With that being said, there are all kinds of places in the signal chain that could reverse the polarity of the signal, nullifying the movement.

I do question my findings back then (it was 25 years or so ago), as I have learned a lot since then that make me wonder about the test.  No I have not done it since.

Interesting.  I used to run a pair of single JBL rear horn loaded "scoops" per side in a DJ setup.  JBL E-140's in them, Phase Linear 400 for power with Altec 511 horns.

It could be the simple "Click Test" done with a battery when tuning the enclosures, i.e. how much damping material to stuff them with.  That's a good way to check how well the box works.  Kick drum attack of waveform as to what the amp sees with regards to polarity depends upon how it's mic'd - front or rear as far as the electrical polarity of the "hit".

I would like to listen to such a test and compare different LF designs - might learn something. 

Thinking back, the JBL + or red phase for DC was for the cone to pull in with a positive voltage applied to the red terminal which is the opposite to many other brands.

[ProSoundWeb Community]