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1802 sub port experiment

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I was told my specific setup(horn mouth flush of front wall) is still considered 1/4 space with the wall and floor boundary. 

 

Roy, do you see anything out of place with the performance I am seeing in my room? Response has never looked better, both raw and eq’d. I feel I may have something out of order causing my driver to bottom out. Any suggestions for setup/tuning parameters I should change? I wasn’t expecting to ever find the limit of this sub and if I did, I was thinking it’d be closer to 130db. Based on the advertised continuous/max spl numbers I can’t help but think I’ve messed up some numbers in the xilica. 

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On 4/14/2019 at 11:34 PM, glens said:

 

Beyond manufacturing costs vs. MSRP?

Drivers are not that expensive to need to eliminate some to meet a price, I would think anyway.

Not at this level of performance and what it's expected to do to a large space against the competition.

 

This is a complete guess by me, I really don't know but to me it makes sense.  Alot of time and expense goes into designing speakers it seems, one driver for a gain in performance is not much money for what's expected from it. Just guessing 

 

But it does sometimes sound silly to me to try some drastic things just to try them after so much has been tried before it even is sold. The other half is what else have you affected with the changes, there is so much to consider.

It makes my head hurt just thinking about what some changes do compared to what else was given up or changed that I don't really understand. It's why I like designs that have been "worked out",  yes that's a technical term I like.   :huh:

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5 hours ago, AHall said:

Today I found out that this sub will bottom out around 118db for bass heavy music when not using a HPF. So I decided to unplug the ports and let it run as it was designed.

 

You had two plugged out of, what was it, 7?  Not much difference, I'd think, in terms of how when you get below the point that the ports offer resistance the driver is pretty much running undamped.  Wouldn't the rated output vs. frequency require a high-pass at the bottom end for this design implementation?  Were you running with or without one when you got driver bottoming?  Beside the fact you stated it was without - I was more or less wondering whether this was a test being undertaken or routine operation.

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7 hours ago, Chief bonehead said:

Is a room half space?  Does tuning change with air mass loading?  Also the 1802/1502 are not sealed horn loaded subs. They are vented systems that are hornloaded. 

Right...if you're talking about going down a half octave to ~19-20 Hz, then the quarter space of the room (i.e., a typical case with the sub against a wall and sitting on the floor) is doable.  If however you're thinking of trying to get 10-12 Hz--more than an octave below half space cutoff--then you will likely need eighth space loading, i.e., a room corner.  But at these frequencies, there is some blurring of the differences between quarter space and eighth space since even at mid-wall, you're probably within a quarter wavelength of being in the room corner at 10-12 Hz (23.5-->28 ft quarter wavelength), so it gets a little unclear in terms of predicting what's going to happen.

 

Also, since you're talking about a ported design, at some low frequency I would guess that you're going to get 180 degree inversion of phase from the ports internally, so that really becomes the limiting factor in bass extension.  A purely front loaded horn with sealed back-chamber would see that 1/2 wave cancellation from the length of the horn itself (as is seen in the Jubilee bass bin at ~20-25 Hz). 

 

Additionally, the preliminary measurements of harmonic distortion below ~20 Hz show that you're already getting to diminishing returns with the 1802 in its benign ported condition.  It may be worthwhile to replace the internal ports with another identical 18" driver (probably wired in series in order to keep the impedance from going too low, or even bi-amping the woofers) and get what you get in terms of resulting frequency response smoothness--and use the Xilica to smooth out what you get. You may be able to EQ using IIR filters, but you can't do much about phase response below ~100 Hz--which is audible.  I find that flat phase response is your biggest friend in the deepest subwoofer frequency band in terms of perception of very deep bass.

 

Chris

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2 hours ago, Chris A said:

Right...if you're talking about going down a half octave to ~19-20 Hz, then the quarter space of the room (i.e., a typical case with the sub against a wall and sitting on the floor) is doable.  If however you're thinking of trying to get 10-12 Hz--more than an octave below half space cutoff--then you will likely need eighth space loading, i.e., a room corner.  But at these frequencies, there is some blurring of the differences between quarter space and eighth space since even at mid-wall, you're probably within a quarter wavelength of being in the room corner at 10-12 Hz (23.5-->28 ft quarter wavelength), so it gets a little unclear in terms of predicting what's going to happen.

 

Also, since you're talking about a ported design, at some low frequency I would guess that you're going to get 180 degree inversion of phase from the ports internally, so that really becomes the limiting factor in bass extension.  A purely front loaded horn with sealed back-chamber would see that 1/2 wave cancellation from the length of the horn itself (as is seen in the Jubilee bass bin at ~20-25 Hz). 

 

Additionally, the preliminary measurements of harmonic distortion below ~20 Hz show that you're already getting to diminishing returns with the 1802 in its benign ported condition.  It may be worthwhile to replace the internal ports with another identical 18" driver (probably wired in series in order to keep the impedance from going too low, or even bi-amping the woofers) and get what you get in terms of resulting frequency response smoothness--and use the Xilica to smooth out what you get. You may be able to EQ using IIR filters, but you can't do much about phase response below ~100 Hz--which is audible.  I find that flat phase response is your biggest friend in the deepest subwoofer frequency band in terms of perception of very deep bass.

 

Chris

 

I would like to know the results of the dual driver configuration since it was already tested. I wonder if the factory bracing would be adequate in a sealed configuration. It seems like all the designs I’ve seen of sealed subs have massive amount of bracing to prevent enclosure flex and resonance. 

 

UlTrBLN.jpg

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Also I’m not sure if a second factory driver would be correct in the dual configuration due to the volume. There is 13.75cu/ft inside the chamber. 22x24x45”. 

 

As best as as I can tell the driver is an eminence. Labeled 4ohm. I haven’t had a chance to look through the whole line up and compare the pictures and specs. 

 

 

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15 hours ago, AHall said:

The butterworth HPF seemed to maintain good response and rapidly dumped anything below that. I figured I would try it to see if it helps the issue. 

 

This is the current eq’d response and peq I’ll be trying. Open to criticism as always. 

 

That response graph looks very respectable. Using a High Pass (subsonic) Filter is a good idea.

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11 hours ago, Chris A said:

Right...if you're talking about going down a half octave to ~19-20 Hz, then the quarter space of the room (i.e., a typical case with the sub against a wall and sitting on the floor) is doable.  If however you're thinking of trying to get 10-12 Hz--more than an octave below half space cutoff--then you will likely need eighth space loading, i.e., a room corner.  But at these frequencies, there is some blurring of the differences between quarter space and eighth space since even at mid-wall, you're probably within a quarter wavelength of being in the room corner at 10-12 Hz (23.5-->28 ft quarter wavelength), so it gets a little unclear in terms of predicting what's going to happen.

 

Also, since you're talking about a ported design, at some low frequency I would guess that you're going to get 180 degree inversion of phase from the ports internally, so that really becomes the limiting factor in bass extension.  A purely front loaded horn with sealed back-chamber would see that 1/2 wave cancellation from the length of the horn itself (as is seen in the Jubilee bass bin at ~20-25 Hz). 

 

Additionally, the preliminary measurements of harmonic distortion below ~20 Hz show that you're already getting to diminishing returns with the 1802 in its benign ported condition.  It may be worthwhile to replace the internal ports with another identical 18" driver (probably wired in series in order to keep the impedance from going too low, or even bi-amping the woofers) and get what you get in terms of resulting frequency response smoothness--and use the Xilica to smooth out what you get. You may be able to EQ using IIR filters, but you can't do much about phase response below ~100 Hz--which is audible.  I find that flat phase response is your biggest friend in the deepest subwoofer frequency band in terms of perception of very deep bass.

 

Chris

And no room gain?  I would like to see your distortion data since you say it is approaching diminishing returns. I large cinema auditoriums with no boost, the 1802 easily digs into the midto upper teens. Dual drivers is a step in the wrong direction. The kpt1515 is the 1802 cabinet with dual 15’s and goes down to about 35. A sealed box is not as efficient as a vented box. 

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19 hours ago, AHall said:

I was told my specific setup(horn mouth flush of front wall) is still considered 1/4 space with the wall and floor boundary. 

 

Roy, do you see anything out of place with the performance I am seeing in my room? Response has never looked better, both raw and eq’d. I feel I may have something out of order causing my driver to bottom out. Any suggestions for setup/tuning parameters I should change? I wasn’t expecting to ever find the limit of this sub and if I did, I was thinking it’d be closer to 130db. Based on the advertised continuous/max spl numbers I can’t help but think I’ve messed up some numbers in the xilica. 

And what about room gain?  When you put the door back on did you make sure it sealed correctly?  One huge misconception about vented systems is that they don’t have to air tight. The best way to take advanatage of the low end of a vented system and do it efficiently is to boost at the tuning frequency. With a horn sub this large and in your specific room, it will be dry different than say in the lab. Best way is to run an impedance curve to find the tuning of your sub. 

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40 minutes ago, Chief bonehead said:

 I would like to see your distortion data since you say it is approaching diminishing returns.

1051953332_KPT-1802-HLSMid-WallHarmoniicDistortion(ListeningPosition).thumb.jpg.be6c07645f952387d1c9f316477b7312.jpg

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1 hour ago, Chief bonehead said:

And what about room gain?  When you put the door back on did you make sure it sealed correctly?  One huge misconception about vented systems is that they don’t have to air tight. The best way to take advanatage of the low end of a vented system and do it efficiently is to boost at the tuning frequency. With a horn sub this large and in your specific room, it will be dry different than say in the lab. Best way is to run an impedance curve to find the tuning of your sub. 

 

Next week when I get back home from work I’ll double triple check the sealing of the back of the cab. I didn’t notice any damage or disfigurement of the seal. Also was very careful to center the board and tighten evenly. I’ll have to have someone help me figure out the impedance curve. I can email REW files to whoever is willing to look at all the specifics in the measurements that I do not understand. 

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2 hours ago, Chris A said:

1051953332_KPT-1802-HLSMid-WallHarmoniicDistortion(ListeningPosition).thumb.jpg.be6c07645f952387d1c9f316477b7312.jpg

Very different than my distortion data so obviously I did something wrong....

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I have nothing better to form an opinion.  Plotted data doesn't appear to exist on this site for the unit and I don't see any other HD plots for the KPT-1802-HLS in quarter space or half space loading, especially for harmonic distortion levels inside 5 metres microphone distance (i.e., in a home-sized listening room).  It would really help to bring that "blessed data" to the table for 4 to 5 m microphone distance to be relevant to home hi-fi listening rooms.

 

In the mean time, here is a plot of the harmonic distortion levels from a KPT-KHJ-LF (Jubilee bass bin) for comparison's sake.  I've been impressed by the cleanness of its output relative to subwoofers, and I've consistently moved the crossover frequency downward over time relative to crossing subwoofer output because of that.  Presently, I cross at ~30 Hz to the DIY horn-loaded subs that form rigid false corners directly behind the Jubilee bass bins:

 

1830657320_KPT-KHJ-LFin8thSpaceLoading(1m)HarmonicDistortion.thumb.jpg.a105bebbe9fddd02e3511c9cec5289e7.jpg

 

Chris

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1 hour ago, Chris A said:

I have nothing better to form an opinion.  Plotted data doesn't appear to exist on this site for the unit and I don't see any other HD plots for the KPT-1802-HLS in quarter space or half space loading, especially for harmonic distortion levels inside 5 metres microphone distance (i.e., in a home-sized listening room).  It would really help to bring that "blessed data" to the table for 4 to 5 m microphone distance to be relevant to home hi-fi listening rooms.

 

In the mean time, here is a plot of the harmonic distortion levels from a KPT-KHJ-LF (Jubilee bass bin) for comparison's sake.  I've been impressed by the cleanness of its output relative to subwoofers, and I've consistently moved the crossover frequency downward over time relative to crossing subwoofer output because of that.  Presently, I cross at ~30 Hz to the DIY horn-loaded subs that form rigid false corners directly behind the Jubilee bass bins:

 

1830657320_KPT-KHJ-LFin8thSpaceLoading(1m)HarmonicDistortion.thumb.jpg.a105bebbe9fddd02e3511c9cec5289e7.jpg

 

Chris

 

Is there a standard for conducting a distortion reading or more desirable way to do it to produce better results? On couch or floor? Low spl, high spl, normal listening spl? Distance? Raw or with peq?

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On 4/18/2019 at 9:23 AM, Chris A said:

Not your best posting, Claude.  Issues embedded...and assumptions that are not correct.

 

Chris

No assumptions there. Ownership experience and measurements. I also helped build and test 7 Spuds (5 for friends, and 2 for my Son in law). If having owned two of the superior "Super Spuds"/DTS-10's is part of "wrong assumption", then why do you have 2 Spuds "pumping air" behind your Jubes?? Judge not a ye shall not be judged.

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1 hour ago, Chris A said:

I've been impressed by the cleanness of its output relative to subwoofers, and I've consistently moved the crossover frequency downward over time relative to crossing subwoofer output because of that.  Presently, I cross at ~30 Hz to the DIY horn-loaded subs that form rigid false corners directly behind the Jubilee bass bins:

Now THIS I agree with, having Owned Khorns for over 30 years and briefly owning Jubes for a year (had to downsize the speakers to fit a Home Theater Screen between on a short wall. The available space dictates EVERYTHING and it's ALL a COMPROMISE.

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1 hour ago, AHall said:

Is there a standard for conducting a distortion reading or more desirable way to do it to produce better results? On couch or floor? Low spl, high spl, normal listening spl? Distance? Raw or with peq?

 

Adam, perhaps Roy will share his views on that subject soon.

 

In the mean time, I'm guessing that he will probably say something like "put it on the ground in a field" then use some higher-priced microphone and conditioning electronics at some measurement distance.  Klipsch's anechoic chamber doesn't do much below 100 Hz due to its limited interior dimensions relative to subwoofer wavelengths and thickness of absorbent material necessary to be 90% effective in absorbing subwoofer acoustic energy, so you've got to move outside for these measurements (as is the case with virtually all anechoic chambers except those huge ones for aircraft measurements funded by the military that the major national labs and defense contractors own).  But infrasonic noise shouldn't be a limiting factor when measuring outside in a country setting.  In my neck of the woods, however, we've got gas drilling rigs and multiple interstate/major state highways surrounding us that never seem to find the "off button".  So outside subwoofer measurement isn't a real option in places like where I live.  So we measure inside to get a better noise floor environment.

 

However, measuring harmonic distortion (HD) I believe is fair game in a home-sized listening room.  Moving the microphone as far away from the source as the home-sized listening room will permit is part of that story (as you have done) in order to get out of the near field to the degree possible.  This is a subject that will not go away for home hi-fi enthusiasts and is very different from commercial cinema where it is comparatively easy to move 2 wavelengths away to measure out of the near field. 

 

Harmonic distortion is usually not the measure of merit that we seek (rather it's modulation distortion and compression distortion), but when the harmonic distortion is within ~20-30 dB of the fundamental, then we've got to pay attention, since this will change the timbre of the subwoofer to something that's not in the original recording.  I've heard this issue many times in-room, and it's something that buyers need to pay attention to, IMHO, especially those wishing to "keep it clean" as PWK used to say. 

 

There is an option within REW to measure harmonic distortion using a stepped sine option within the RTA facility.  The noise floors and relative harmonic distortion levels are much lower using this method.  When you get a chance (and a little time in a quiet house--since these are long measurements) you can try this approach to get much better results.  Here's a measurement that I did last fall using stepped sine on my right-side Jubilee (the drop-out at 15 kHz was due to intervening noise at the very end of the stepped sine sequence).  The green trace is the actual averaged noise floor of the room.  These measurements take something like 5 minutes each:

 

435593916_RightJubileeSteppedSineMeasurement(1m).thumb.jpg.5f5c69d47b4e7a704d9ffded8125945c.jpg

 

From the REW help facility:

Quote

Although much, much slower than a log sweep, the stepped sine measurement can measure low distortion levels much more accurately than a sweep, particularly at high frequencies and for higher harmonics. Stepped sine distortion measurements show distortion components up to the ninth harmonic, THD and the noise floor, in the same way as the sweep-derived results, but also include THD+N (total harmonic distortion plus noise and non-harmonic distortion) and N (noise and non-harmonic distortion) alone. Note that the noise floor plot shows the spectral content of the noise measured with no signal playing. The 'Noise' in the N and THD+N shows the summed level of all non-harmonic distortions and noise across the frequency span for each test frequency. It consequently sits much higher than the noise floor plot.

 

Chris

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42 minutes ago, Chris A said:

 

Adam, perhaps Roy will share his views on that subject soon.

 

In the mean time, I'm guessing that he will probably say something like "put it on the ground in a field" then use some higher-priced microphone and conditioning electronics at some measurement distance.  Klipsch's anechoic chamber doesn't do much below 100 Hz due to its limited interior dimensions relative to subwoofer wavelengths and thickness of absorbent material necessary to be 90% effective in absorbing subwoofer acoustic energy, so you've got to move outside for these measurements (as is the case with virtually all anechoic chambers except those huge ones for aircraft measurements funded by the military that the major national labs and defense contractors own).  But infrasonic noise shouldn't be a limiting factor when measuring outside in a country setting.  In my neck of the woods, however, we've got gas drilling rigs and multiple interstate/major state highways surrounding us that never seem to find the "off button".  So outside subwoofer measurement isn't a real option in places like where I live.  So we measure inside to get a better noise floor environment.

 

However, measuring harmonic distortion (HD) I believe is fair game in a home-sized listening room.  Moving the microphone as far away from the source as the home-sized listening room will permit is part of that story (as you have done) in order to get out of the near field to the degree possible.  This is a subject that will not go away for home hi-fi enthusiasts and is very different from commercial cinema where it is comparatively easy to move 2 wavelengths away to measure out of the near field. 

 

Harmonic distortion is usually not the measure of merit that we seek (rather it's modulation distortion and compression distortion), but when the harmonic distortion is with ~20 dB of the fundamental, then we've got to pay attention, since this will change the timbre of the subwoofer to something that's not in the original recording.  I've heard this issue many times in-room, and it's something that buyers need to pay attention to, IMHO, especially those wishing to "keep it clean" as PWK used to say. 

 

There is an option within REW to measure harmonic distortion using a stepped sine option within the RTA facility.  The noise floors and relative harmonic distortion levels are much lower using this method.  When you get a chance (and a little time in a quiet house--since these are long measurements) you can try this approach to get much better results.  Here's a measurement that I did last fall using stepped sine on my right-side Jubilee (the drop-out at 15 kHz was due to intervening noise at the very end of the stepped sine sequence).  The green trace is the actual averaged noise floor of the room.  These measurements take something like 5 minutes each:

 

435593916_RightJubileeSteppedSineMeasurement(1m).thumb.jpg.5f5c69d47b4e7a704d9ffded8125945c.jpg

 

 

Chris

 

Once we establish an acceptable  measurement method I’d love to see a step by step work method so I could get my data out there for you guys to dig into. Realistically I only care about these pro components being used in a home setting because that’s how I’m using them. Distortion levels included. I know all the designs I’m using are well engineered and regarded, but distortion/performance levels in room are what matters. That way I can adjust or correct dsp, gear, and treatment to reach 100% optimization in my system. I do acknowledge the open field and design numbers are very important so we can analyze what has changed by putting them in a normal room. Whether it be for the better or worse. 

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Thanks to these forums Adam and I have become very good friends and we both have very similar setups:  Jubes & 1802/1502.

 

After several weeks of chatting with Adam, sharing response curves and ideas, I'm starting to see a pattern. (some of you have seen the post I created with questions/concerns about the response of my 1502 sub.)

 

The two subs seem to be VERY similar in response..  This has been mentioned before by Roy, i think he has mentioned that the 1502 is identical except 3db down.

 

What i'm finding is that taking measurements at the sub mouth or somewhat nearfield ( my listening position is about 60" infront of the sub.  Sub is behind me like Mike Beasley has his)

The sub naturally rolls off right around 30hz.     With some PEQ manipulation I CAN get a flat response down to 20hz but with sacrificing SPL.  

Should subs like these create a lower response at the horn mouth?

 

Last night i did some more testing and when running sweeps of the natural response of the sub ( no peqs) the response  did extend further down to the 20hz point once i was around 4m from the face of the sub.

 

When  Roy mentions the 1802 will achieve mid teens in a Auditorium without boost.   Is this a direct result of needing a room with  enough volume to allow the sub to fully bloom those lower octaves while achieving the published SPLs?   If this is the case, it almost seems as if at 4m/13' distance from the sub face is the sweet spot  to get down into the 20s.   

 

 

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What is the longest dimension of your listening room?  This will determine the transition to "pressure zone" region or band.  In my room, that transition happens at ~14 Hz...calculated using:

 

     1132 ft/sec / (2*39.5 feet))--a half wavelength calculation. 

 

Above this frequency band, you've got the "sparse mode region" of the room (usually up to 100-300 Hz, depending on room volume and reverberation time), and above that, the "dense mode region".  At the commercial cinema scale, there is no real "transition to pressure zone" due to the room's dimensions since they are quite large by comparison to home hi-fi sized rooms.

 

Chris

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