Jump to content

Sensitivity loss with compression drivers


Recommended Posts

On February 5, 2017 at 10:18 AM, jazzmessengers said:

This is something I've read from a few different posters on another forum, but with no measurements to back it up. What they're saying is a compression driver that needs to be EQ'd quite a bit, for instance the EQ required for a controlled directivity horn in the treble will diminish the sensitivity. How accurate is this statement, and how much sensitivity loss is there?

 

My guess at what they're getting at is that for a given compression driver, a constant directivity horn will typically be less sensitive (on-axis) at high frequencies than a horn with a collapsing coverage pattern.  The difference in sensitivity will follow the difference in Directivity Index between the two horns. Since equalization is typically referenced to the least sensitive part of the horns useable passband - it follows that the constant directivity horn will be equalized to an overall lower sensitivity.   

 

If the equalization is done properly - the efficiency of the system in both cases should be retained.  And if the horns are of similar size, the power response in both systems should be very similar, too. My point here is that you're simply sacrificing sensitivity for a wider coverage pattern at high frequencies. However, nothing else has really changed. 

 

Kerry

  • Like 1
Link to comment
Share on other sites

1 hour ago, dBspl said:

Since equalization is typically referenced to the least sensitive part of the horns usable passband - it follows that the constant directivity horn will be equalized to an overall lower sensitivity.   

Using what, and crossing with what?  Passive or Active?  Are you reporting sensitivity relative to the output of the EQ or its input?  Why? 

 

Does the gain (or attenuation) of the EQ count in the calculations.

 

I believe you've lost the reference to the meaning of "sensitivity" in your argument.

 

Chris

Link to comment
Share on other sites

  • Moderators
43 minutes ago, Chris A said:

Using what, and crossing with what?  Passive or Active?  Are you reporting sensitivity relative to the output of the EQ or its input?  Why? 

 

Does the gain (or attenuation) of the EQ count in the calculations.

 

I believe you've lost the reference to the meaning of "sensitivity" in your argument.

 

Chris

Your telling Kerry, who worked with Paul,  learned from Paul, and a (the?) top engineer at KGI, who actually designs speakers that sell, at a profit, he's lost in his argument?  

 

I guess there is a difference between doing it in the real world, and on paper. 

Link to comment
Share on other sites

38 minutes ago, dwilawyer said:

Your telling Kerry, who worked with Paul,  learned from Paul, and a (the?) top engineer at KGI, who actually designs speakers that sell, at a profit, he's lost in his argument?  


I didn't take it that way.

 

It sounded to me like Chris was asking if the variable of EQ was taken into consideration when Kerry made his analysis.

 

Which I had to read three times before I could even begin to comprehend what Kerry was saying.  B)

  • Like 1
Link to comment
Share on other sites

8 hours ago, dwilawyer said:

Your telling Kerry, who worked with Paul,  learned from Paul, and a (the?) top engineer at KGI, who actually designs speakers that sell, at a profit, he's lost in his argument?  

 

I guess there is a difference between doing it in the real world, and on paper. 

Sure there is, and I'm also sure that Kerry understands the implications of the questions posed above.

 

If you don't talk about what you're trying to do in terms of powering and crossing loudspeakers, talking about sensitivity really has little meaning.  If you're (probably) thinking from the standpoint of passive crossover use--then the concept of sensitivity is important. 

 

However, if you're thinking from the standpoint of active crossovers and having embedded gain, then the concept of sensitivity loses its standing in the argument, and SPL on-axis (or power response) vs. frequency in regard to extremely limited tube type amplifiers or flea-watt chip amps (which Klipsch Professional Products doesn't do, but plenty of guys on the forum are doing) becomes the discussion of interest.  I'm reasonably sure that Kerry isn't talking about those type of applications--but I would hope that he can speak for himself, instead of having legal counsel trying to carry an engineering argument forward via non-engineering means (argumentum ad verecundiam).

 

If you also don't take into consideration the dramatic decrease in music power vs. frequency (like I showed above in the "purple mountain" plot) you'll not understand why you can get away with the EQ used on 2" compression drivers to run them "full range" from ~425 Hz to 15-20 kHz without adding another way--with severely underpowered amplifiers like most SETs and chip amps.  This is what Roy has shown to us on the 2-way home Jubilee (and I'm sure that Kerry understands and uses, too, e.g. KPT-942, et al.), and that almost everyone outside of that small group of engineers at Klipsch in the DIY world seem to have trouble understanding why it works--and works extremely well.

 

"Everything should be made as simple as possible...but no simpler..." A. Einstein

 

Chris

  • Like 1
Link to comment
Share on other sites

It seems like we're making this out to be more complicated than it is. For a given compression driver, the on-axis sensitivity of a constant directivity horn will be less at higher frequencies than a similar horn with a collapsing coverage pattern. This difference in sensitivity is inherent in the driver/horn design. If the target magnitude response is the same in both cases, then that difference has to be made up somewhere - regardless how you go about it. As a result, you should always be able to measure that difference at the driver terminals.  

 

The constant directivity horn will always require more power at high frequencies to achieve the same on-axis SPL.  

 

Kerry

Link to comment
Share on other sites

17 hours ago, dBspl said:

Since equalization is typically referenced to the least sensitive part of the horns usable passband - it follows that the constant directivity horn will be equalized to an overall lower sensitivity.   

I think this was the source of the problem--the idea that you can do something to the driver/horn assembly to change "its sensitivity".  You can't change the horn/driver sensitivity unless you stick something into the mouth/throat of the horn or driver exit (thus lowering acoustics output in terms of SPL or power, and thus lowering "sensitivity").  It's set, whether collapsing polar or constant coverage horn displays frequency-varying "sensitivity' measurements.

 

If you're talking about measuring "sensitivity" at any point upstream than just across the driver's terminals (implying either a passive or active crossover...or any other internal gain or attenuation devices of any kind...are inserted into the circuit), then to make any sense of the word "sensitivity", you have to

 

1) tell the reader if you're doing that, and "sensitivity" no longer is being measured across the driver's terminals

2) tell the reader what kind of crossover (active or passive) is being used, and

3) tell the reader how much gain (positive or negative) is being used as a function of passband frequencies-for all frequencies being used.

 

Any any case, you're not actually changing the sensitivity of the horn/driver, you're changing the place and electrical/electronic circuit from which you're measuring "sensitivity".

 

Chris

 

 

Link to comment
Share on other sites

One important paper which educated me was Don Keele's describing his work on constant directivity horns.

 

http://xlrtechs.com/dbkeele.com/PDF/Keele (1975-05 AES Preprint) - Whats So Sacred Exp Horns.pdf

 

Generally, mid drivers do not have a flat output above 3000 or 5000 Hz - except maybe the very top end models, IMHO.  Therefore, the focusing of "collapsing polars" makes up for it in the horn.  This focusing is like the Maglite flashlight which can increase on-axis intensity by narrowing the polar.  .

 

Pages 25 and above of the paper show that he had to equalize (boost the high end I'd think) the EV driver used to get a flat response on a plane wave tube.  He then used that to drive one of his constant directivity horns to get a flat output at the mouth.  Because there was no focusing by the horn, the driver had be made flat in response.

 

WMcD

 

 

Link to comment
Share on other sites

2 hours ago, Chris A said:

Any any case, you're not actually changing the sensitivity of the horn/driver, you're changing the place and electrical/electronic circuit from which you're measuring "sensitivity".

 

I think it's pretty easy to agree that I'm not as technical as you however, that said....  I agree with this 100% and drive my wife nuts as she says....  "Well Richard, you should know what I mean..."

 

No honey....words have specific meanings... If you tell me your wrist is broken, you are saying it's broken, not sprained...and my reaction might be slightly different.

 

 

  • Like 1
Link to comment
Share on other sites

1 hour ago, Chris A said:

As always, I yield to the Wisdom of Richard...;)

 

And I yield to the wisdom of Richard's wife, who sounds remarkedly like my wife with whom I have never won an argument by listening and responding to what she said instead of what she meant:ph34r:

Link to comment
Share on other sites

4 hours ago, Chris A said:

I think this was the source of the problem--the idea that you can do something to the driver/horn assembly to change "its sensitivity".  You can't change the horn/driver sensitivity unless you stick something into the mouth/throat of the horn or driver exit (thus lowering acoustics output in terms of SPL or power, and thus lowering "sensitivity").  It's set, whether collapsing polar or constant coverage horn displays frequency-varying "sensitivity' measurements.

 

If you're talking about measuring "sensitivity" at any point upstream than just across the driver's terminals (implying either a passive or active crossover...or any other internal gain or attenuation devices of any kind...are inserted into the circuit), then to make any sense of the word "sensitivity", you have to

 

1) tell the reader if you're doing that, and "sensitivity" no longer is being measured across the driver's terminals

2) tell the reader what kind of crossover (active or passive) is being used, and

3) tell the reader how much gain (positive or negative) is being used as a function of passband frequencies-for all frequencies being used.

 

Any any case, you're not actually changing the sensitivity of the horn/driver, you're changing the place and electrical/electronic circuit from which you're measuring "sensitivity".

 

Chris

 

 

 

I'm simply using a voltage reference to state sensitivity. Since an amplifier is a constant voltage source, you can "de-sensitize" the driver/horn combination however you wish. Your point is that the power response doesn't change, which is true, but I also mentioned that in the second paragraph of my original post.

 

Kerry  

Link to comment
Share on other sites

In other news... if you are using tube amps with multiple taps for different impedance loads, there are some very interesting things you can do with how you hook up your speakers - if you have separate LF and HF connections on the speakers you can use the different taps to manage relative attenuation. Just scroll down to the first and second illustrations to see where he's going, then go back and read from the beginning.

 

By the way, I have never seen these possibilites detailed like this anywhere else.

 

VinylSavior - speakers impedance and taps

  • Like 1
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...