Sensitivity loss with compression drivers

[jazzmessengers]

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?

[wvu80]

13 minutes ago, jazzmessengers said:

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,

 

I'm not normally a big "charts and graphs" guy, but I think I'd like to see the charts and graphs on that one.  Otherwise, we are talking about opinions, or feelings about what is being heard.

 

What I would reply to the posters on the other forum, is my facts don't care about your feelings. 

[derrickdj1]

33 minutes ago, 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?

Sure if you are cutting or boosting a lot, there will be a change in the operating sensitivity.  The question is, dose it make a significant difference in your use of the speaker?

[jazzmessengers]

15 minutes ago, derrickdj1 said:

Sure if you are cutting or boosting a lot, there will be a change in the operating sensitivity.  The question is, dose it make a significant difference in your use of the speaker?

 

I believe with the K-402 and TD-4002 (I imagine 4001 as well) you need a decent amount of boost over 8 KHz (someone please correct me where exactly this occurs), where the large format compression driver naturally starts to fall off. I don't think they need any other EQ (boost or cut) below that since both are pretty linear.

[Quiet_Hollow]

3 hours ago, jazzmessengers said:

How accurate is this statement, and how much sensitivity loss is there?

Not at all. The sensitivity doesn't diminish with positive changes in EQ, rather it's headroom (ie, desired playback level subtracted from in-room freq response minus any boosted EQ plus total power handling all expressed in dB).

 

The loss is proportional. For example a +3 dB boost in EQ yields a 3 dB reduction in headroom. Where the K402 is concerned in the home environment, this is typically not an issue in terms of capability.

2 hours ago, jazzmessengers said:

 

I believe with the K-402 and TD-4002 (I imagine 4001 as well) you need a decent amount of boost over 8 KHz

 The K402 requires EQ for the typical Jubilee application because it behaves naturally as a low pass filter when driven above ~6 kHz.

[Marvel]

Since most compression drivers have to be attenuated in the home, wouldn't we more than likely roll off the lower end of the driver and not boost the high end?

 

Bruce

[Chris A]

10 hours ago, 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?

Which forum?  (Not that I really want to know...)

 

1) How can you decrease the sensitivity of the driver+horn?  This isn't a very good question, it seems.

 

2) Why are you fastened on the idea of sensitivity?  Sensitivity of what?  Perhaps sharpening your thinking a bit might help to reformulate the question to something that actually has physical meaning.

 

3) What kind of hi-fi setup has issues with insufficient amounts of available gain? There are Jubilee owners running barely enough amplifier power (and therefore gain) to drive the bass bins and compression drivers - less than 3 w/channel.  Is this what you're worried about?  This includes passive crossovers.  Nothing can be more demanding of "sensitivity" than this.  

 

Chris

[Chris A]

From diyAudio...http://www.diyaudio.com/forums/multi-way/287641-hlcm-horn-loaded-compact-monitor-13.html#post4967244

 

Quote

[user: jpak]

I have been thinking about the Klipsch K-402 controlled directivity horn above a straight midbass horn. I know it's not really your thing; the K-402 used all the way up will require EQ to boost up the treble with whatever 1.5/2" driver, resulting in loss of sensitivity. Still sensitive enough for my use. Someone else here created a thread and was doing the same thing, though he hasn't updated it in a while. His requirements were more stringent than mine, since I have a decent amount of space to work with.

I think that the poster of this was referring to using passive crossover with EQ, and since passives don't "boost", but only attenuate everywhere else (a crazy approach when you think about it), the effect of using passives with passive EQ require more input voltage for a given on-axis SPL due to that attenuation that's embedded in the passive crossover/balancing network.  This is typical practice for passive crossovers using multiple ways--to attenuate everything down to the least sensitive way's level.

 

If you're using active digital crossovers (the recommended path), of course, this isn't an issue--you simply set gains, crossover filters and PEQs in the crossover, using something like REW measurements to guide you, and you're done. 

 

If you're using EQ upstream of passive crossover networks and amplifiers to flatten response (similar to Bose 901s have done for decades with a box that goes into the preamp's monitor loop), this also isn't an issue--assuming that you have sufficient preamp and/or EQ gain available, but you lose the ability to correct for the time delay/phase mismatch at the crossover point.

 

Chris

 

P.S.  I believe that "someone else" referred to in the quote...was probably me.  See:

 

[jazzmessengers]

12 hours ago, Chris A said:

Which forum?  (Not that I really want to know...)

 

1) How can you decrease the sensitivity of the driver+horn?  This isn't a very good question, it seems.

 

2) Why are you fastened on the idea of sensitivity?  Sensitivity of what?  Perhaps sharpening your thinking a bit might help to reformulate the question to something that actually has physical meaning.

 

3) What kind of hi-fi setup has issues with insufficient amounts of available gain? There are Jubilee owners running barely enough amplifier power (and therefore gain) to drive the bass bins and compression drivers - less than 3 w/channel.  Is this what you're worried about?  This includes passive crossovers.  Nothing can be more demanding of "sensitivity" than this.  

 

Chris

 

Why the third degree

 

It was DIYAudio when I was doing searches on constant directivity horns. I realize there are a lot of subjectivist posts that are unsubstantiated which is why I asked here. As for why I asked it first off curiosity and I'm always up for learning something and secondly my favorite amp is a 1-1.5 watt DHT driving DHT SET which I could use on an actively crossed over compression driver/horn.

 

The thread you linked to was one of the posts I was referring to.

[wvu80]

21 hours ago, Quiet_Hollow said:

The loss is proportional. For example a +3 dB boost in EQ yields a 3 dB reduction in headroom.

 

Is the obverse true as well?  If gain was decreased by -3 db, would there be a +3 db increase in headroom?

 

My common sense tells me "no" but I'm sure I don't fully understand the principle as to how all that works.

[Chris A]

1 hour ago, jazzmessengers said:

Why the third degree ...I realize there are a lot of subjectivist posts that are unsubstantiated which is why I asked here...my favorite amp is a 1-1.5 watt DHT driving DHT SET which I could use on an actively crossed over compression driver/horn.

 

Your term "third degree" indicates torture: I certainly wouldn't characterize the response quoted in your post as that.  Perhaps you respond with hyperbole?  (I generally try to keep the usage of rhetoric to cases where it's necessary.)

 

I was referring to the ambiguous usage of the word "sensitivity" on that diyAudio post.  I find that those type of posts create a lot more confusion than is necessary, so I responded to mark that usage of language for what it is.  Words have meaning--especially technical words. I make no apologies for directly addressing apparent meme usage of the word "sensitivity" in the diyAudio post.  Perhaps you will see why I did this if you stick around for a while and read how one or two confusing usages of the term echoes through posts here.

 

I suppose you can use any amplifier that you want to actively bi-amp K-402/2" compression driver combination on top of...?  I'd certainly use amplifiers with more available power headroom that are able to reproduce concert-level transients which the K-402 horn-driver is capable of--but that's just me. 

 

Of course, I'm making the assumption that accuracy of reproduction (PWK's goal...and also mine) is the objective that you seek.  Perhaps I assumed this in error?

 

Chris

[jazzmessengers]

55 minutes ago, Chris A said:

 

Your term "third degree" indicates torture: I certainly wouldn't characterize the response quoted in your post as that.  Perhaps you respond with hyperbole?  (I generally try to keep the usage of rhetoric to cases where it's necessary.)

 

I was referring to the ambiguous usage of the word "sensitivity" on that diyAudio post.  I find that those type of posts create a lot more confusion than is necessary, so I responded to mark that usage of language for what it is.  Words have meaning--especially technical words. I make no apologies for directly addressing apparent meme usage of the word "sensitivity" in the diyAudio post.  Perhaps you will see why I did this if you stick around for a while and read how one or two confusing usages of the term echoes through posts here.

 

I suppose you can use any amplifier that you want to actively bi-amp K-402/2" compression driver combination on top of...?  I'd certainly use amplifiers with more available power headroom that are able to reproduce concert-level transients which the K-402 horn-driver is capable of--but that's just me. 

 

Of course, I'm making the assumption that accuracy of reproduction (PWK's goal...and also mine) is the objective that you seek.  Perhaps I assumed this in error?

 

Chris

 

It seems like you've taken personal offense by my post, I did not mean third degree as in you were literally torturing me, hence the use of smiley. I did think the "sharpening your thinking" was a bit unusual, since I thought it was a reasonable thing to ask.

 

I meant sensitivity in the truest 2.83v measured definition not as a meme or something abstract. I was genuinely curious about it so I asked, I even mentioned measurements in my first post so it would be clear I was asking about the objective definition.

 

I'll not debate the accuracy of tube amps, SET amps or whatever. I am looking for accuracy, I personally think you can get that from a good low power amp assuming it is well designed (IME not the vast majority of commercially designed ones) and there is plenty of headroom. Which is where my question regarding sensitivity (true definition) comes in because I was wondering if I would have enough headroom with my current amp. If it didn't no big deal, I don't have any particular dogma I subscribe to and wouldn't mind swapping to a higher power amp. I know that the speakers and room will always be the largest determinant of sound quality.

[wvu80]

40 minutes ago, jazzmessengers said:

It seems like you've taken personal offense by my post,

I did not mean third degree as in you were literally torturing me, hence the use of smiley.

I did think the "sharpening your thinking" was a bit unusual, since I thought it was a reasonable thing to ask.

I took it that way as well. 

 

No smiley face escapes my gaze. 

[Chris A]

 

When you look at the above cumulative SPL vs. frequency plot for a typical music track, you might notice the difference in values from 70 Hz to 20 kHz - and they're about 50 dB different.  This fits the empirically derived -5.1 dB/octave (-17 dB/decade) decrease in SPL.  This occurs on every track that I've hand demastered--currently numbering about 10K.

 

When you think about this for a moment, it might create the insight that, in terms of power capabilities of any amplifier type, the high end can be boosted by 10 dB or more and you really don't see any real increase in load on the output terminals of the amplifier. 

 

This should answer your question about using extremely low power amplifiers with the K-402 and 2 inch compression drivers (bi-amped). If you didn't have any issues with other horn-loaded loudspeakers, you're not going to have issues with the K-402/2" compression driver.

 

However, if you boost the opposite end of the spectrum relative to the high end (around 400-500 Hz) you will be able to measure increased power output by the amplifier. 

 

In any case, with most 2" compression drivers on the K-402 horn, figures like 110-112 dB/2.83 V inputs are typical.  That's not much required input power-direct coupled to the amplifier channel. However, if using passive crossovers, the first thing that happens is that you insert -5dB to -6dB worth of attenuation on the HF channel (either using higher reactance or resistance).  That's a lot of power going not going into the drivers.

 

I'd still like at least 50% power headroom under all listening conditions, and that's beginning to get marginal at less than 2 W/channel output on the HF channel.  You need about double that power output level if using a bass bin with 105-106dB/2.83V sensitivity--direct coupled.

 

Chris

[Quiet_Hollow]

9 hours ago, wvu80 said:

My common sense tells me "no"

"No" in the sense that the system doesn't magically sprout power somewhere along the chain, but "yes" in terms of overall performance.

[USNRET]

Pardon the interruption. @Quiet_Hollow Check for PM.

[Quiet_Hollow]

in progress.

[jazzmessengers]

On 2/6/2017 at 2:32 PM, Chris A said:

 

When you look at the above cumulative SPL vs. frequency plot for a typical music track, you might notice the difference in values from 70 Hz to 20 kHz - and they're about 50 dB different.  This fits the empirically derived -5.1 dB/octave (-17 dB/decade) decrease in SPL.  This occurs on every track that I've hand demastered--currently numbering about 10K.

 

When you think about this for a moment, it might create the insight that, in terms of power capabilities of any amplifier type, the high end can be boosted by 10 dB or more and you really don't see any real increase in load on the output terminals of the amplifier. 

 

This should answer your question about using extremely low power amplifiers with the K-402 and 2 inch compression drivers (bi-amped). If you didn't have any issues with other horn-loaded loudspeakers, you're not going to have issues with the K-402/2" compression driver.

 

However, if you boost the opposite end of the spectrum relative to the high end (around 400-500 Hz) you will be able to measure increased power output by the amplifier. 

 

In any case, with most 2" compression drivers on the K-402 horn, figures like 110-112 dB/2.83 V inputs are typical.  That's not much required input power-direct coupled to the amplifier channel. However, if using passive crossovers, the first thing that happens is that you insert -5dB to -6dB worth of attenuation on the HF channel (either using higher reactance or resistance).  That's a lot of power going not going into the drivers.

 

I'd still like at least 50% power headroom under all listening conditions, and that's beginning to get marginal at less than 2 W/channel output on the HF channel.  You need about double that power output level if using a bass bin with 105-106dB/2.83V sensitivity--direct coupled.

 

Chris

 

I would be going active, there would be a different amp for whatever bass horn below it. When I've looked at spectrals for classical music I've noticed the same thing, the most energy is the in that upper bass/lower midrange.

 

I'm not chained to the idea of using my 2 watt amp, the FirstWatt SIT is another I've been looking at.

[Chris A]

If bi-amping, no issue using a 1-->1.5 W amplifier on the compression driver. 

[djk]

If you use an electronic crossover and bi-amp a speaker like a Klipsch Cornwall with a 50W amp on the bass and a 10W amp on the mid and hf it will play as loud as a 400W amp through the passive crossover.

 

The 4:1 benefit for bi-amping is only there when the spectrum is divided ahead of the power amps and when the division point is near the mid point of the spectral distribution of energy.On a voltage basis the division occurs around 250hz.This must be weighted by the peak to average ratio so that the equal energy point for above and below the crossover is about 500hz.This is also affected by the slope of the crossover.For the example of the Klipsch Cornwall it has a 600hz crossover point.If the drivers were the same efficency then 50W + 50W would = 200W through the passive crossover.In reality the HF is 10dB more efficent than the LF so we only need 50W + 5W to = 200W.If the HF remains undistorted it will mask distortion from the LF amp driven slightly into clipping.