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tubesandhorns

2" driver, 1 3/8" horn

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I am upgrading my speakers with a new mid horn and driver.  Right now I have a Fastlane LaScala tractrix (1 3/8" throat), and will upgrade to a BMS 4592 with a Volti FC260ii (2" throat).  I am chomping at the bit, but Greg is pretty tied up and I won't see the horns until later this year... which I understand- so now problem with that.  So my question- can I do this incrementally, that is, what happens if I get the BMS or other 2" drivers now and I either bolt them or use the Eminence HA14-2 to put them on the Fastlanes until the Voltis arrive?  I see posts that describe going from a small driver to a large throat horn, but this is the other way around.  Thanks

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I've never tried it.  I'm thinking it's something I might do if it was the only way to finish a gig or so.  Of course if you've got on hand what you need to try it, why not.  I wouldn't procure anything to do so.  Chances have got to be weighted most toward no net benefit at best, as a guess.

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16 hours ago, tubesandhorns said:

I am upgrading my speakers with a new mid horn and driver.  Right now I have a Fastlane LaScala tractrix (1 3/8" throat), and will upgrade to a BMS 4592 with a Volti FC260ii (2" throat).  I am chomping at the bit, but Greg is pretty tied up and I won't see the horns until later this year... which I understand- so now problem with that.  So my question- can I do this incrementally, that is, what happens if I get the BMS or other 2" drivers now and I either bolt them or use the Eminence HA14-2 to put them on the Fastlanes until the Voltis arrive?  I see posts that describe going from a small driver to a large throat horn, but this is the other way around.  Thanks

 

Since the sized don't match and you are further squeezing  the output, frequency response problems along with pushing the sound through the small throat would likely provide some ugly horn sounding side effects.  You could always try it and see.  Maybe open the throat up to match better if you don't mind modifying the horns you have.

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I’m no expert, but I offer a few observations.  Intuitively, matching a driver to a throat that is smaller than the driver seems like a bad idea, but what about the following:

  • Klipschorn 15” driver attached to ~13x6 slot;
  • Edgar horn described in Speaker Builder; and
  • MEH as implemented by Tom Danley and discussed in the thread started by Chris A?

 

Go to Chris A’s thread to see the sizes of the drivers attached to small throats.

Perhaps the “mismatch” is OK at lower frequencies, but problematic at mid to high frequencies.  Others, such as @Chris A can offer more technically supported answers.

 

9667529A-C02B-4318-9ED1-1EB6B1F01286.jpeg

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24 minutes ago, DizRotus said:

Klipschorn 15” driver attached to ~13x6 slot

 

My (very non-technical) take would be this...

The driver mounted to the slot would make it a compression driver (big driver squeezing through the hole)

 

The driver he's looking to add to the horn might already be a compression driver (inside the driver itself) so compressing a compression driver might give him compressed sound or worse.

 

I've never used the root word compress three times in a sentence before!

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3 hours ago, DizRotus said:

Perhaps the “mismatch” is OK at lower frequencies, but problematic at mid to high frequencies.

Yes.

 

As the compression slot or throat dimensions get close to 1/2 wavelength of the emitted acoustic energy, the restriction or expansion will begin to strongly interact with the emitted acoustic output. You can think of these slots like phase plugs in compression drivers--the plugs are there to prevent cancellations across the diameter of the diaphragm and throat exit. 

 

Here is a plot of what a phase plug does to extend HF performance in a compression driver/horn assembly (horizontal axis = normalized frequency, vertical axis ~relative SPL):

 

1060705094_EffectofPhasePlugonFreqResponse.JPG.552877e5d0a745c356366d8fa5519897.JPG

 

As the design of the phase plug gets better and better, the smoother the resulting frequency response at higher frequencies. 

 

When you suddenly constrict or expand the throat of the compression driver/horn interface, the resulting frequency response begins to get very ragged at higher frequencies.  You also begin to see the effects of all that reflected acoustic energy at those drop-out frequencies interact with the compression driver diaphragm, which cause all kinds of harmonic and other distortion types to be generated. 

 

Chris

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9 hours ago, Chris A said:

Yes.

 

As the compression slot or throat dimensions get close to 1/2 wavelength of the emitted acoustic energy, the restriction or expansion will begin to strongly interact with the emitted acoustic output. You can think of these slots like phase plugs in compression drivers--the plugs are there to prevent cancellations across the diameter of the diaphragm and throat exit. 

 

Here is a plot of what a phase plug does to extend HF performance in a compression driver/horn assembly (horizontal axis = normalized frequency, vertical axis ~relative SPL):

 

1060705094_EffectofPhasePlugonFreqResponse.JPG.552877e5d0a745c356366d8fa5519897.JPG

 

As the design of the phase plug gets better and better, the smoother the resulting frequency response at higher frequencies. 

 

When you suddenly constrict or expand the throat of the compression driver/horn interface, the resulting frequency response begins to get very ragged at higher frequencies.  You also begin to see the effects of all that reflected acoustic energy at those drop-out frequencies interact with the compression driver diaphragm, which cause all kinds of harmonic and other distortion types to be generated. 

 

Chris

Thanks for the chart.  Very helpful in visualizing.

 

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