Jump to content
The Klipsch Audio Community
ClaudeJ1

Quarter Pie Bass Horn: Measured FR, How2Build, and Hornresp

Recommended Posts

if he were to test horns on tubes vs. horns on SS, which he did not do.

 

 

He tested amplifiers configured with a wide range of "damping factor".

 

What do you think testing a tube amp would have shown him about "damping factor" that he missed otherwise?

Share this post


Link to post
Share on other sites

 

if he were to test horns on tubes vs. horns on SS, which he did not do.

 

 

He tested amplifiers configured with a wide range of "damping factor".

 

What do you think testing a tube amp would have shown him about "damping factor" that he missed otherwise?

 

 

 

 

I think that in general, damping factor is a non-issue irrespective of the amplifier used.  

 

A while back I was thinking about a speaker's overall impedance curve not being flat and the actual damping factor of a low power single-ended triode (SET) amplifier that can change and be higher at certain frequencies and less at certain frequencies in the overall frequency response of the speaker.  Essentially, the way I understand it is that with a SET amplifier the damping factor tends to track the speaker's impedance curve "potentially" having an impact on the frequency response.

 

For example, take something like the Klipsch Forte, although high enough sensitivity for a SET amplifier, has an impedance curve that is all over the place and varies widely.  I believe that the Forte impedance curve drops to a low of 4 ohms at 150 Hz and rises to a peak of about 106 ohms at about 2,150 Hz. 

 

I believe that this impedance rise in the midrange of the speaker’s frequency response will cause the frequency response to rise with a SET amplifier with high output impedance (“Z”).  For example, if an amplifier has an output Z of 8 ohms and the speaker impedance load is 4 ohms at 150 Hz, we have an estimated damping factor of 0.5; however, at 2,150 Hz we have an estimated damping factor over 13.

 

Going from 0.5 to 13 seems like a fairly large spread over a four octave range.  While I am aware of high quality SET amplifiers that do not have a problem driving Forte speakers, what does this potentially mean in relation to a low-quality SET amplifier with high output impedance driving the Forte’s at 150 Hz? 

 

While I believe in my example that there can be some impact with the change in damping factor over the entire frequency range of the speaker paired with very low power SET amplifiers, now where I think the damping factor is mostly a non-issue is because I believe the majority of the problems encountered with SET are most likely due to crappy output transformers that are sold with inappropriate primary inductance levels and misleading specifications regarding any correlations of transformer bandwidth and output power tested over the frequency response range. 

 

Here are the papers that I considered below by Pass,  Augspurger, and Pierce that all seemed to provide some level of empirical evidence that a damping factor above 20 should be a non-event and have minimal impact. 

 

 

Although he is working with full range drivers with very light cones and strong motor structures, from the link below Nelson Pass indicates;

 

http://www.firstwatt.com/pdf/art_cs_amps.pdf

 

“[Critical damping -- that resistive combination of electrical source impedance, suspension friction and acoustic load -- occurs when you apply a step pulse to the voice coil and the cone’s motion doesn’t overshoot. Under-damping results in bass notes that hang around a little longer than the amplifier intended. Over-damping has good transient bass control but also suffers a significant loss of bottom end response. Generally, we want something in between, something closer to critical damping. Whether we over-damp or under-damp seems to be a matter of taste.

 

High-efficiency full-range drivers are more easily damped than other types due to their powerful efficient motors and light cones. Looking at their bass response curves, we conclude that they are easily over-damped, resulting in excessive loss of bottom end. This partially explains the preference for tube amps with such loudspeakers. Anyway, this assortment of observations arrived at a confluence when I hooked up a Son of Zen amplifier (Audio Electronics 1997 #2) to a pair of Fostex 208Es in sealed enclosures. The Son of Zen operates without feedback and has an output impedance of about 16 ohms. This nets a damping factor of 0.5, miniscule compared to the 100 to 1000 you can achieve with regular solid-state amplifiers.

 

With the low damping factor, the Fostex became a totally different speaker. It suddenly had bottom end response and a better top end. It still had the same annoying upper midrange that had Dick Olsher (www.blackdahlia.com) devise his passive equalization network. The low damping factor didn’t cure the upper midrange faults but it seemed to work improvements everywhere else. A year later, Kent has acquired about 20 different full-range mid to high efficiency drivers for us to play with (that’s part of his job description) and we’ve spent as much time exploring them as we reasonably could, trying different things to coax the best sound out of them with a current-source amplifier and various passive parallel networks.]”

 

 

 

From the George L Augspurger paper at these links;

 

http://www.butleraudio.com/damping1.php

 

http://www.butleraudio.com/damping2.php

 

“[it should be obvious at this point that the quoted damping factor of an amplifier is important only if the figure lies somewhere below 20 or so.  Changing the damping factor from 2 to 20 does change the performance of the loudspeaker system (for better or for worse, depending upon the speaker). But trying to prove that a damping factor of 200 is somehow better than one of 20 is pretty unconvincing because the effective difference in the particular case cited is only that between 1.25 and 1.32.]”

 

 

 

From the Dick Pierce paper at Audioholics at these links;

 

https://www.audioholics.com/audio-amplifier/damping-factor-effects-on-system-response

 

https://www.audioholics.com/audio-amplifier/damping-factor-effects-on-system-response/damping-factor-effects-on-system-response-page-2

 

 

“[several things are apparent from this table. First and foremost, any notion of severe overhang or extended "time amplitude envelopes) resulting from low damping factors simple does not exist. We see, at most, a doubling of decay time (this doubling is true no matter what criteria is selected for decay time). The figure we see here of 70 milliseconds is well over an order of magnitude lower than that suggested by one person, and this represents what I think we all agree is an absolute worst-case scenario of a damping factor of 1.

 

Secondly, the effects of this loss of damping on system frequency response is non-existent in most cases, and minimal in all but the worst case scenario. Using the criteria that 0.1 dB is the smallest audible peak, the data in the table suggests that any damping factor over 10 is going to result in inaudible differences between that and one equal to infinity. It's highly doubtful that a response peak of 1/3 dB is going to be identifiable reliably, thus extending the limit another factor of two lower to a damping factor of 5.

 

All this is well and good, but the argument suggesting that these minute changes may be audible suffers from even more fatal flaws. The differences that we see in DFeq8-16.gif figures up to the point where the damping factor is less than 10 are far less than the variations seen in normal driver-to-driver parameters in single-lot productions. Even those manufacturers who deliberately sort and match drivers are not likely to match a DFeq8-24.gif figure to better than 5%, and those numbers will swamp any differences in damping factor greater than 20.

 

Further, the performance of drivers and systems is dependent upon temperature, humidity and barometric pressure, and those environmental variables will introduce performance changes on the order of those presented by damping factors of 20 or less. And we have completely ignored the effects presented by the crossover and lead resistances, which will be a constant in any of these figures, and further diminish the effects of non-zero source resistance.]”

Edited by Fjd

Share this post


Link to post
Share on other sites

Well horns are done! 75% done on the 4 x 6watt Pass class A modules. Awaiting the call to say the horns are ready. Last things to get are the minidsp and tweeters, still unsure on what to get. Almost settled on the Opendrc, 8 channel and raal ribbons.

Then try and make it all work together! 987198bd191cbd321e6ad8435c8a7522.jpg

Sent from my D5833 using Tapatalk

360b0499629d715c3f9882fe98f51f88.jpg

Edited by nzlowie

Share this post


Link to post
Share on other sites

When I was trying active crossover setups in my system I was measuring QPies response with different power amplifiers.

One of the pair I checked was Yamaha M-4 and Nikko Alpha 130.

Yamaha M-4:

Power output: 120 watts per channel into 8Ω (stereo)

Frequency response: 1Hz to 100kHz

Total harmonic distortion: 0.005%

Damping factor: 200

Input sensitivity: 1V

Signal to noise ratio: 118dB

Nikko Alpha 130:

Power output: 100 watts per channel into 8Ω (stereo)

Frequency response: 10Hz to 50kHz

Total harmonic distortion: 0.03%

Damping factor: 50

Input sensitivity: 1V

Signal to noise ratio: 110dB

I made several measurements (in my listening room with microphone placed at my listening seat) , only swapping amplifiers. Microphone, speakers, test signal were always the same.

I noticed that Nikko response was consistently worse by 10db at 90 Hz field.

Do you think that it is an example of damping factor influence?

post-60882-0-82800000-1459672396_thumb.j

Edited by Mariusz_

Share this post


Link to post
Share on other sites

I think that in general, damping factor is a non-issue irrespective of the amplifier used.  

 

 

Damping factor isn't irrelevant ..... however it certainly isn't the issue most people seem to think it is .......  and it only becomes an "issue" when it is not considered in the system design.

 

ie.  if you take a speaker, and you connect a high damping factor amplifier, and then a low damping factor amplifier ....  they will produce a different frequency response.

 

People doing "listening tests" will of course say they prefer one over the other, and decree that one therefore has "higher performance" than the other.    For example, people say that higher damping factor sounds "tighter" - what is actually happening is that there is a peak in the bass around system resonance with a low damping factor amp, which is not there where you use a high damping factor amplifier   (and a peak in the bass sounds "more boomy" when subjectively auditioned).    Which is "correct"?   Which is "better"? .....   Neither.    It is just the frequency response, it can be whatever you want.     We can correct the peak (or lack of peak) by redesigning the box, or applying EQ, or changing the box absorbtion.....   the point being is that if the damping factor is considered in the overall design, then we will have exactly the response we want....   and if it's not  (ie.  if someone is switching in amps with differing damping factor, and subjectively evaluating) --- then it's simply 'which one do you like most?!'

 

If play a tone which is at system resonance.... and we stop it suddenly, then the rate the cone returns to rest depends on the amplifier damping factor   (at the system resonance, the mechanical damping -> 0)  ..... and we see that for various damping factors, the cone returns to rest either too fast or too slow....   and that there is a specific value of damping, for which the cone return to rest is not distorted.      ie.  it is nonsensical to say that high or low damping factor is the goal .... but rather a specific value of damping which the speaker wants.

 

 

 

Going from 0.5 to 13 seems like a fairly large spread over a four octave range.  While I am aware of high quality SET amplifiers that do not have a problem driving Forte speakers, what does this potentially mean in relation to a low-quality SET amplifier with high output impedance driving the Forte’s at 150 Hz? 

 
It's a misnomer to consider that an amplifier with a high output impedance is low quality.
 
Yes, an amplifier with a high output impedance, will cause the frequency response of the speaker to follow the speakers impedance curve .....  sometimes that can be desirable.... and if not the frequency response can be corrected in the speaker design (eg. crossover,  box, horn, etc.).
 
Of course, like you've highlighted, if we take a speaker (the Forte is a strong example) .... and we try a low DF amp, and a high DF amp .... they will sound different to each other.    A speaker like the Forte, with such a huge hump in the electrical Z, was obviously designed to only be used with an amplifier that didn't have a low damping factor.....    people shouldn't be tempted into listening to the difference, deciding which one they "like", and making generalisations about performance based on this experience.
 

 

While I believe in my example that there can be some impact with the change in damping factor over the entire frequency range of the speaker 

 

Indeed.    Regardless of the change in frequency response caused by the combination of the speaker impedance and the amp output impedance....   there is a certain small amount of non-linear distortion which is also avoided when driving the speaker with a current source (low damping factor) vs a voltage source (high damping factor).

 

....  but almost always, the stark difference that people are hearing are simply the differences in frequency response.

 

 

 

Pass - I don't think he goes far enough.    Rather than being a corner case related to full range high sensitivity drivers ....   All speakers are somewhat overdamped.     This is the result of us being given voltage source amplifiers.    We were given these so that our amps would sound the same no matter which speakers they were connected to  (they were not influenced by the speaker impedance).

 

Augsperger -   Yes! .... the important point is that moving the damping factor between 2 and 20, will be  "better or worse depending on the speaker".      The point is that neither a high (20) or low (0.2) damping factor is "better".    It just depends on how the system is designed.

 

Pierce  --  Trying to make the case that moving the DF won't have an effect.    Sometimes, yes.    With a speaker which has reasonable impedance peaks .... and with an amp which has a very high output impedance .... There will be a (quite) significant effect .... so perhaps a poor generalisation.      Well, probably reasonably common in practice, but unhelpful for those people trying to understand what damping factor "is" and what it "does".

Share this post


Link to post
Share on other sites

When I was trying active crossover setups in my system I was measuring QPies response with different power amplifiers.

One of the pair I checked was Yamaha M-4 and Nikko Alpha 130.

Yamaha M-4:

Power output: 120 watts per channel into 8Ω (stereo)

Frequency response: 1Hz to 100kHz

Total harmonic distortion: 0.005%

Damping factor: 200

Input sensitivity: 1V

Signal to noise ratio: 118dB

Nikko Alpha 130:

Power output: 100 watts per channel into 8Ω (stereo)

Frequency response: 10Hz to 50kHz

Total harmonic distortion: 0.03%

Damping factor: 50

Input sensitivity: 1V

Signal to noise ratio: 110dB

I made several measurements (in my listening room with microphone placed at my listening seat) , only swapping amplifiers. Microphone, speakers, test signal were always the same.

I noticed that Nikko response was consistently worse by 10db at 90 Hz field.

Do you think that it is an example of damping factor influence?

 

 

No.  If the low damping factor of the Niko was influencing the response ..... what you would see is a peak in the frequency response, where there was a peak in the impedance.

 

I would guess that what you're seeing is a measurement error or variance.    Try taking a bunch of additional measurements, and see if this type of variance is common?!

Share this post


Link to post
Share on other sites

5 times with Nikko, 5 times with Yammi. Always the same outcome.

And finally I chose Nikko which sounded better to me.

Edited by Mariusz_

Share this post


Link to post
Share on other sites
Well horns are done! 75% done on the 4 x 6watt Pass class A modules. Awaiting the call to say the horns are ready. Last things to get are the minidsp and tweeters, still unsure on what to get. Almost settled on the Opendrc, 8 channel and raal ribbons.

 

This will be a sweet setup. Nice job on the Quarter Pies. Looking very good indeed. Prepare to have superior horn bass definition! 6W is plenty of power for 85 db listening at the sweet spot since I used to use only about 50 Milliwatts. Lots of headroom.

 

It's still difficult for peope to understand that a 60 Watt amp is only twice as loud as a 6W amp, and that horns are typically 13 db more efficient than direct radiators, requiring 1/20th the power. So for those who have a typical 100 Watts per channel on direct radiators, the horn guys need only 5 Watts to do the same job with 20 db less distortion.

Share this post


Link to post
Share on other sites

Hi guys

 

I'm working with a speaker guru to finalize my tweeter choice. He's asked for the SPL efficiency of these bass horns with the Kappa 15c driver. Can someone please provide this?

 

it's been discussed before that these work up to about 500hz, correct? I was planning on setting the crossover at 400hz.

 

Thanks

Share this post


Link to post
Share on other sites

I'd probably lean towards a high-ish crossover point and a 2-way speaker  (as opposed to need to go to a 3-way) .... however, it is good to keep the crossover point as low as possible.

 

The slope of the eventual rolloffs is very important piece of the puzzle for this decision (but your guru will appreciate that)

Share this post


Link to post
Share on other sites

I wasn't really sure why he wants to know about the bass horn, i thought he would be more worried about integration with the mid horn?

I'll ask this in my reply to Russell Storey, was waiting for info before getting back to him.

Sent from my D5833 using Tapatalk

Share this post


Link to post
Share on other sites

Hi guys

 

I'm working with a speaker guru to finalize my tweeter choice. He's asked for the SPL efficiency of these bass horns with the Kappa 15c driver. Can someone please provide this?

 

it's been discussed before that these work up to about 500hz, correct? I was planning on setting the crossover at 400hz.

 

Thanks

It's about the same as an MWM and the original Khorn bin......app[rox. 104 db@1Watt (2.83 volts?) but it depends on the chosen method of measurement.......peak, trough, average, sine, pink noise, what?

Share this post


Link to post
Share on other sites

http://s56.photobucket.com/user/dkleitsch/media/130Avs2226vsLE15A.gif.html?sort=3&o=110

 

As we can see, the  D130 has the same efficiency below the mass corner of the 2226, even though it is about 5dB more efficient as a direct radiator.

 

The mass corner is all that matters (in a horn). In fact, the lower the efficiency, the higher the maximum SPL is likely to be. They reason for this is the x-max is higher on the lower efficiency driver.

 

The D130 is more efficient above the mass corner of the 2226 (about 250hz), about 5dB more output in the 500hz region.

 

The mass corner on the K33 is less than 200hz.

 

The LE15A has the same mass corner as the 2226, but is 3dB less sensitive because it is 16Ω.

 

That is why Klipsch drivers are usually 4Ω.

 

http://s56.photobucket.com/user/dkleitsch/media/CCSSDX15.gif.html?sort=3&o=166

 

The CSS SDX15 is 87.3 dB/2.83V as a direct radiator, but a pair in the horn are 114dB/2.83V at 35hz!

 

(this is a cornerhorn the same height as the Klipschorn, with two 32 cm mouth openings, only slightly bigger than a Klipschorn)

Edited by djk

Share this post


Link to post
Share on other sites

And my QPie-based system has been finished. At last I am done with horn stands and with some minor but visible finish.

Claude, thank you for initiating this project.

post-60882-0-01980000-1460916904_thumb.j

post-60882-0-58540000-1460916921_thumb.j

post-60882-0-92660000-1460916932_thumb.j

Edited by Mariusz_
  • Like 1

Share this post


Link to post
Share on other sites

And my QPie-based system has been finished. At last I am done with horn stands and with some minor but visible finish.

Claude, thank you for initiating this project.

You are welcome. If they sound as good as they look, then you are all set!

Share this post


Link to post
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...