Ventilator x-over

[JohnDoe]

Ventilator features says:

"Same 800Hz crossover as the original".

How does that sound, if you run it stereo out to a set of 2-way powered monitors, with something like 2400Hz x-overs?

[Jim Alfredson]

The output of the Ventilator is full range.

 

The Leslie 122 had a passive crossover network which divided the signal from the output of the Leslie amp in order to direct low frequencies to the woofer and high frequencies to the horn. The Ventilator emulates this. It separates the signal from the input into two bands and processes each band separately in order to emulate the two rotors (upper and lower). Then signals are then recombined at the output stage, before the digital to analog conversion.

 

In other words, the crossover of your monitors doesn't matter.

[kanker.]

It might be interesting to see what a Vent sounds like through a speaker with an 800Hz crossover. Someone should hook one up to a Leslie and find out

[Baldwin Funster]

Running your Vent into a pair of 2way monitors with a similar crossover frequency and similar or identical drivers as a 122 sounds very much like a physical leslie. Sometimes you might even fool yourself into thinking you moved some air.

[Skinny]

Sometimes you might even fool yourself into thinking you moved some air.

[AnotherScott]

Running your Vent into a pair of 2way monitors with a similar crossover frequency and similar or identical drivers as a 122 sounds very much like a physical leslie. Sometimes you might even fool yourself into thinking you moved some air.

One of the interesting thing about the Mojo/Hamichord version of VB3 is that you can split its Leslie sim to send LF and HF out separate outputs. If you sent them to a pair of stacked speakers, I would think that that would be about as authentic as you could get, spatially. (Though the crossover frequencies aren't an issue.)

[Delaware Dave]

Keep in mind that because the crossover on the powered speaker is 2400Hz, the low rotor sim of the Vent will come completely out of the woofer of the powered monitor, while the spinning horn simulation of the Vent would be split between the woofer and the compression horn on the monitor, the split point being around 2400Hz. Sonically, if you only had the 8' drawbar out, the change over from woofer to compression horn would occur around the D7 key.

[Jim Alfredson]

Since neither speaker is moving, I don't see why it would matter. Does a recorded Leslie sound bad if you play it back on a home stereo system without an 800Hz crossover?

[Delaware Dave]

Well, a tone coming out of a woofer would probably have a different color than that of a compression horn. I'm thinking the tone coming out of a compression horn would sound thinner and brighter while the woofer would replicate that sound fatter and warmer. So the crossover point could have a play in the tone you hear coming out of the powered speaker, depending on where that crossover point is set.

[AnotherScott]

Sonically, if you only had the 8' drawbar out, the change over from woofer to compression horn would occur around the D7 key.

Remember that the crossover is not a hard and fast line with frequencies below coming out of one driver and frequencies above coming out the other. There is a gradual slope as one fades out and the other takes over.

 

Regardless, I don't think crossover point makes any difference here. Unlike a Leslie, 2-way PA speakers are designed to have a nearly imperceptible transition through the crossover point between the two drivers. As Jim basically said, they are designed to reproduce a full range signal. If properly engineered, the crossover point is basically indiscernible, and the speaker system as a whole should just send out what it gets in... in this case, essentially "reproducing" the effect of a particularly distinctive 800 Hz crossover. I guess there is the issue that frequencies at different points along the spectrum are coming from different points in space, but in a two way speaker, the physical distance between the HF and LF drivers is far smaller than that in a Leslie 122 anyway. So if that's what you want to simulate, a pair of full range speakers, one about 2 feet over the other, driven by the Mojo/Hamichord split as I described, is probably the way to do it.

[CEB]

It might be interesting to see what a Vent sounds like through a speaker with an 800Hz crossover. Someone should hook one up to a Leslie and find out

 

Go all double Lez. That could be wild.

[Delaware Dave]

Scott, you are missing (or not understanding) my point. 1khz is a distinct pitch in the sound spectrum. Although a 12" woofer or a 2" compression driver can both reproduce that pitch is not the issue; it is how the reproduced pitch will sound to the human ear. The 1khz pitch being reproduced by a 12" speaker will have a different timbre than how that pitch's timbre will sound coming from a 2" compression horn due to a number of factors: size and construction of the cone, the materials used in the construction, the shape of the cone; these all influence the timbre. Therefore the x-over point of the powered speaker can influence how the pitch of the note d5 sounds (its distinct timbre) depending on whether it is being reproduced by the 12" woofer, a piezo horn or a combination of the two due to the slope of the x-over as determined by the capacitors and the diodes used in the setting of the x-over point and its slope. So how 1khz will sound when being reproduced by a 12" speaker will be different than how it sounds coming out of a piezo even though both pitches will be 1khz. So the x-over point does have an impact on what you hear (from a timbre perspective).

[Skinny]

Go all double Lez. That could be wild.

There was this one time in college...

[AnotherScott]

The 1khz pitch being reproduced by a 12" speaker will have a different timbre than how that pitch's timbre will sound coming from a 2" compression horn due to a number of factors: size and construction of the cone, the materials used in the construction, the shape of the cone; these all influence the timbre.

Slightly simplified, but I think the gist is right:

 

Dispersion and distortion characteristics may differ between those two drivers, but as long as you're not driving them to audible distortion, a pure 1 kHz pitch (i.e. a sine wave) should sound the same on both (though its relative level may differ off axis). A change in timbre means a change in overtones, and a sine wave has none, so the change in timbre you're talking about should not exist.

 

OTOH, if you're trying to reproduce a sound with overtones (no longer simply a 1 kHz pitch), sure, a note will sound different depending on which driver you send it to, but at least on-axis, there's no problem having the fundamental mostly coming out of one driver and the harmonics the other based on where those frequencies occur relative to the crossover frequency, as long as flat frequency response is maintained in the speaker system. Now, the crossover design is one factor in deviations from flat frequency response, but I would not assume that an 800 Hz crossover would have any inherent advantage here just because that's what the Leslie and Vent use internally. The flatter the response of the final speaker, the better, regardless of where its crossover is.

 

So getting back to that earlier post, the speaker just needs to reproduce the full range input signal as accurately as possible, the "crossover effect" between the rotor and the horn is already "baked into" the source, I don't see any advantage in "duplicating" it. It would almost be like saying that the best way to view a sepia image is through sepia glasses... no, the best way to view a sepia image is through accurate, neutral (clear) glasses. (I know, the analogy is imperfect!)

 

And getting back to dispersion, none of it is like a leslie anyway. With a real Leslie, off axis sounds just like on axis, because the speakers are moving. So everyone hears the same sound out of each driver no matter how off axis they are (up to the point where the wood gets in the way)... they just hear it at different times. ;-)

[Losendoskeys]

I'll stick with my Motionsound 145 for home and Vent for gigs.

Simples!

[MuzikTeechur]

I think my head is going to asplode.

[Bill H.]

Actually I think JohnDoe might be on to something here, although I'm not sure and can't prove it. The subtle distortions produced by the high frequency driver in a real Leslie might sound more authentic when run through a compression driver and horn rather than a paper cone woofer.

 

If any of you guys are running across JBL SRX712s for stage monitors and want to do a little experimenting, try running your Vent through that and A/B it to your K10, K12, or whatever you're using for keyboard amplification.

 

SRX712's are very common for stage monitors in upper end installs and touring systems, and are crossed over at 1200hz - which is at least getting close to 800hz. Might be revealing.

 

...or not. But I kind of have this hunch that it would be.

[Jim Alfredson]

If you can hear the crossover point in your speakers, your speakers suck.

[Bill H.]

I'm not talking about hearing the crossover point itself, but hearing the difference in a speaker that's crossed over at 1200hz versus one that's crossed over higher.

 

Speakers that are crossed over lower definitely have a different sound to them, and that sound might be flattering to the high frequency horn sim of a Vent.

 

Maybe. Just a thought.

[Baldwin Funster]

Ive used a vent through 2 way studio monitors, 2 way stage monitors, 3 way extended bass speakers, 1 way in ears and headphones. It aleays sounds about the same accounting for the overall tone of the speaker system and it always sounds good if not great. I'm sure all of these had different crossover freqs,some active some passive. I'd say that it REALLY HASN'T MATTERED what the crossover is if its part of a properly designed system. Even if a difference could be perceived, when heard in context IT REALLY HASN'T MATTERED.

 

Sorry for shouting.

 

 

[AnotherScott]

The subtle distortions produced by the high frequency driver in a real Leslie might sound more authentic when run through a compression driver and horn rather than a paper cone woofer.

If those subtle distortions are built into the modeling and are therefore already part of the sound that's coming out of the Vent, you'll hear them no matter what driver you reproduce them through. That's the point... if the Vent is accurate to the sound you want (distortion and all), then I'd say that the best thing to put it through is whatever will add the smallest amount of additional coloration of its own, regardless of how that is achieved. Now, no speaker is perfectly flat, and people may prefer the sound of the Vent through one speaker system rather than another, as it will sound different through different playback systems. But I think that whether you happen to like it more through a QSC or a JBL or whatever will have far more to do with the overall tonal characteristics of those speakers than how close their crossovers are to 800 Hz.