Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Rebuilding the Enigma...
Rebuilding the Enigma...
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 11th July 2019, 08:22 PM   #81
ICG is offline ICG  Germany
diyAudio Member
 
ICG's Avatar
 
Join Date: Jul 2007
Location: I had a Déjà Moo - I've seen that BS before!
Quote:
Originally Posted by Brian Steele View Post
Hmm, so what else is distortion but what you just mentioned ?? Good grief man, are you trolling me or something?
Distortion can be of a higher order, which will be filtered by the inheritend bandpass, it can be mechanical noise, air compression in the port (which will result in audible higher frequencies because it's not 'filtered'), it can, no, it WILL be non-linear distortion and, ofcourse, direct mechanical noise, which will be audible and there will be distortion because of the power compression too. Exceeding the max excursion results in a LOT non-linear distortion. All of which are audible, regardless of it being a BP or not.

Quote:
Originally Posted by Brian Steele View Post
Yes, *some* mechanical noise may make it out of the port - most of it however is filtered like basically everything else above the bandpass subwoofer's upper cutoff frequency, because the vented chamber acts as the LP filter - and ANY sound that originates in that chamber is subjected to that filter, including any distortion and mechanical noise generated by the driver.
That's a gross misunderstanding of the BP principle. And that's a severe misunderstanding of the sound of a BP subwoofer. Compression does changes the sound, mechanical stress does sound different. If you keep ignoring the changes in sound, it will result in a killed sub, no matter what you do otherwise. The logical solution is to just use 2-4 subs instead - which can deliver the needed spl. To gain 1-1,5 dB by modifying the sub is simply futile. Put there more subs and everything's fine. Using the same or a different driver will simply not give you the needed headroom. Period.

Quote:
Originally Posted by Brian Steele View Post
The Enigma is actually pretty good at doing just that, as is measured out of band noise is 15~20dB below its passband, when measured with a sine sweep. Even when driven to its 10% THD limit in its passband (which occurs around 40 Hz, and at 23.3V, the equivalent of 70W into 8 ohms (the driver's power rating, btw), measured distortion at higher bass frequencies (where most bass in music is found) is significantly lower. At 50 Hz it's just above 2% and above that it's around 1% or less. Good luck hearing that when playing sine waves, much less music . When playing most music, the only indicator that this sub is at its limits is that it just stops getting louder.
You surely haven't measured the THD at the used spl. At PA levels the thd often exceeds 30% and for a BP it typically exceeds even 40% or more. That's still fine since the ear is extremely insensitive to distortion in the bass or even more in the sub-bass. What's more important is the source of the distortion. K2 or even K3 is not that 'harming' in the bass. Non-linear distortion is much, MUCH worse though. And that's where you can recognize your sub is at its limit. Learn how the non-linear distortion sounds and you'll be able to save your subs from destruction.
__________________
I had a Déjà Moo - I've seen that BS before!
  Reply With Quote
Old 11th July 2019, 08:55 PM   #82
Brian Steele is offline Brian Steele  Grenada
diyAudio Member
 
Join Date: Nov 2007
1. There is very little vent compression within this subwoofer's design limits. (See post #54). Any noticeable compression would have have shown up in the linearity testing.

2. The subwoofer is NOT being driven at "PA levels" It's been driven by a 100W amplifier (See post #60) and it's been tested to remain under 10% THD in its passband up to 70W. And that THD was measured without the use of 30 Hz HP filter I enabled for the subwoofer's operation in the bar, so unless they suddenly decide to feature sine waves instead of music on their background audio system, distortion generated by the subwoofer will remain at or below 10%.

3. ANY distortion created by within the vented section of the bandpass subwoofer WILL be filtered by the acoustic HP filter once it is outside of the filter's passband, period. The filter does not know and does not care if that distortion is linear or non-linear - if that distortion manifests itself at frequencies higher than the passband, it will be subjected to the acoustic filter.
__________________
www.diysubwoofers.org
  Reply With Quote
Old 12th July 2019, 03:15 AM   #83
ICG is offline ICG  Germany
diyAudio Member
 
ICG's Avatar
 
Join Date: Jul 2007
Location: I had a Déjà Moo - I've seen that BS before!
Quote:
Originally Posted by Brian Steele View Post
1. There is very little vent compression within this subwoofer's design limits. (See post #54). Any noticeable compression would have have shown up in the linearity testing.
Compression does not show in linearity. It shows in impulse response and distortion.

Quote:
Originally Posted by Brian Steele View Post
2. The subwoofer is NOT being driven at "PA levels" It's been driven by a 100W amplifier (See post #60) and it's been tested to remain under 10% THD in its passband up to 70W. And that THD was measured without the use of 30 Hz HP filter I enabled for the subwoofer's operation in the bar, so unless they suddenly decide to feature sine waves instead of music on their background audio system, distortion generated by the subwoofer will remain at or below 10%.
HAHAHA! You've built the subwoofer of the century! Congratulations!
Seriously, most subwoofers pass the 10% distortion below 5W @30Hz. Yours isn't an exception. It is very obvious you've never measured distortion on a subwoofer.
Seriously, put there 2 or more subs. That will help a ton more than any modifications you're doing. It's used as a PA and it's clear it isn't enough.
Seriously, that sub is used beyond its capacity. That's not your fault but denying that it happens doesn't change that.

Quote:
Originally Posted by Brian Steele View Post
3. ANY distortion created by within the vented section of the bandpass subwoofer WILL be filtered by the acoustic HP filter once it is outside of the filter's passband, period.
Anything that is created by the port WILL exit the port because the port is the filter, period. If you haven't realized that, you don't know how a BP works.
__________________
I had a Déjà Moo - I've seen that BS before!
  Reply With Quote
Old 12th July 2019, 04:11 AM   #84
Brian Steele is offline Brian Steele  Grenada
diyAudio Member
 
Join Date: Nov 2007
Quote:
Originally Posted by ICG View Post
Compression does not show in linearity.
Clearly you have no idea what "linearity" means.


Quote:
Originally Posted by ICG View Post
Seriously, most subwoofers pass the 10% distortion below 5W @30Hz.
Maybe most of YOUR subwoofers are like that, LOL. This one measures differently .


Quote:
Originally Posted by ICG View Post
Yours isn't an exception. It is very obvious you've never measured distortion on a subwoofer.
I've both measured and posted the measurements here. It's very obvious you either don't know what you're talking about, or you're trolling. I'm going with the latter for now. Stay off my thread from now on please. Your posts are adding no value to the content.
__________________
www.diysubwoofers.org
  Reply With Quote
Old 13th July 2019, 02:48 AM   #85
Brian Steele is offline Brian Steele  Grenada
diyAudio Member
 
Join Date: Nov 2007
Quote:
Originally Posted by BP1Fanatic View Post
Technically, a BR, BP4, BP6, and TH could all be a 7 board enclosure not including bracing.
If you put some rather severe limits on the shape of the enclosure .
__________________
www.diysubwoofers.org
  Reply With Quote
Old 13th July 2019, 03:14 AM   #86
BP1Fanatic is offline BP1Fanatic  United States
diyAudio Member
 
BP1Fanatic's Avatar
 
Join Date: Jan 2009
Location: Columbus, Ohio
I'm just stating enclosures outside of Sealed and BR don't have to be complicated to build.
  Reply With Quote
Old 13th July 2019, 03:44 AM   #87
Brian Steele is offline Brian Steele  Grenada
diyAudio Member
 
Join Date: Nov 2007
I thought I might share some more info on the distortion / linearity testing just in case anyone's interested, and also provide some background on why I chose to use a 30 Hz HP filter with this build.

For my linearity tests, I usually run some quick sine sweeps (not long enough to heat up the voice coil by any noticeable amount) and use REW (test signal set to -3dB) to measure the frequency response and distortion until it reaches about 10% in the passband (for the Enigma, the passband is about -3 dB +1.5 dB from 38 Hz to 115 Hz). Note: This requires some careful positioning of the mic to get right, which also requires a bit of experimentation - too close to the subwoofer and the mic gets overload, too far from the subwoofer and too much of the environment gets into the measurements. The start and end of the sine sweep also needs to be chosen carefully so you don't end up trying to push the driver significantly pass its excursion limits outside of the subwoofer's passband.

Once I've established the best position for the mic, I redo the measurement, and for each measurement cycle I drop the test signal by 1 dB or 3 dB, depending on how much detail I'm looking for. I usually stop around -24 or -27 dB. I then adjust the measurements in REW by the same amount that I dropped the signal. If the subwoofer remained perfectly linear for each signal level, the measurements will also align perfectly (yes, I'm assuming that the mic remains linear throughout the measurements. In any case, if it doesn't, it will make the results look worse, not better). Vent compression shows up pretty quickly in these tests, based on some of the results I've seen. So does any in-line limiting that may be in place (like the lightbulb type protection that Bose likes to use). Another thing - I choose 10% THD as my limit, but it's perfectly acceptable to choose a higher distortion point, particularly if the subwoofer is destined for PA use.

As for the choice of the 30 Hz filter?

The first image shows Enigma2's distortion when driven at a level equivalent to 70W into 8 ohms. While distortion at 40 Hz is around 10%, distortion at 30 Hz is almost 32% at the same signal level and continues to rise below that, and it consists primarily of odd-order distortion, a clear sign that the driver is exceeding its linear excursion limits.

The second image shows Enigma2's distortion at 6dB below the "70W" reference. Distortion at 30 Hz is now much lower, at just under 12%. So, it stands to reason that if I use a HP filter at 30 Hz (e.g. 24dB/octave, -6dB at the corner frequency of 30 Hz), then I wouldn't have to worry about the driver being overdriven at any frequency at or below the subwoofer's passband, once it's driven at 70W or below.

In reality, I am being over-cautious doing this, as the vast majority of music doesn't feature any information below 40 Hz (and a good portion of that doesn't have much below 50 Hz either), but I wanted the new driver in the Enigma2 to have the best chance of survival, given the environment that it's going to be used in (and what tends to happen at that bar). Maybe after a few months, if it has survived intact, I'll move the HP filter down to about 20~25 Hz, to minimize its impact on the subwoofer's passband.

The third image shows what the impact of such a filter can have on the distortion profile. No, that's not the Enigma - that's the measured distortion for one of my brother's KSubs. The KSub is an active 4th order bandpass design using 2 12" drivers, and from the distortion profile, it looks like there's a 35 Hz (or even higher) HP filter applied. The inband distortion of this KSub was quite a bit higher than I expected, but I didn't have the time to take it apart and find out why.
Attached Images
File Type: png 20190712-enigma2(1).png (49.3 KB, 69 views)
File Type: png 20190712-enigma2.png (46.8 KB, 49 views)
File Type: png 20190712-ksub.png (47.7 KB, 49 views)
__________________
www.diysubwoofers.org
  Reply With Quote
Old 13th July 2019, 04:22 AM   #88
Brian Steele is offline Brian Steele  Grenada
diyAudio Member
 
Join Date: Nov 2007
For comparison purposes, here's a linearity test of the Bose AM7 bass module that was replaced by the Enigma2. The result is not as clean as the Enigma2's, and I suspect at least one of the drivers in the AM7 bass module has some sort of mechanical damage. Not only is it noticeably non-linear around 50 Hz, but the non-linearity is the reverse of what I'd expect to happen (instead of the output compressing, it actually expanded a bit as signal level was increased from -24 dB to -3 dB). And there's definitely some sort of limiting going on at -3dB - check how the graph deviates from the others about 200 Hz.

I'm going to be picking up the AM7 bass module tomorrow to take a closer look at it, and to see if I'm correct about the drivers.
Attached Images
File Type: png 20190712-bose.png (74.2 KB, 48 views)
__________________
www.diysubwoofers.org
  Reply With Quote
Old 13th July 2019, 03:48 PM   #89
BP1Fanatic is offline BP1Fanatic  United States
diyAudio Member
 
BP1Fanatic's Avatar
 
Join Date: Jan 2009
Location: Columbus, Ohio
Quote:
Originally Posted by Brian Steele View Post
As for the choice of the 30 Hz filter?

In reality, I am being over-cautious doing this, as the vast majority of music doesn't feature any information below 40 Hz (and a good portion of that doesn't have much below 50 Hz either)
I HATE when you so called audiophiles make that statement. You should state the majority of the music YOU listen to isn't below 40hz. There is plenty of Hip Hop, Dubstep, and EDM music below 40hz. If you are such an audiophile, then you should design your speaker system to play the lowest note of a piano or pipe organ. So called audiophiles should listen to ALL types of music. And no, I don't consider myself an audiophile. If it ain't Hip Hop or basshead instrumentals, then it don't get played in my crib or rides. Basically, I prefer beats only seeing that most people ain't saying nothing worth a d@mn.
  Reply With Quote
Old 13th July 2019, 05:18 PM   #90
Brian Steele is offline Brian Steele  Grenada
diyAudio Member
 
Join Date: Nov 2007
Quote:
Originally Posted by BP1Fanatic View Post
I HATE when you so called audiophiles make that statement.
LOL - I wouldn't call myself an audiophile. You'll never hear me waxing on about how cables make a difference for example. I just know what type of music the bar plays, and little or none of it features any information below 40 Hz, much less 30 Hz, and even if it did, their main system wouldn't be able to reproduce it anyway. Their main system, for example, which they seem happy with, features KSubs for bass, and those are already -6 dB @ 48 Hz and -10dB @ 44 Hz. And their customers don't appear to be leaving the bar because the subs don't go 10 Hz deeper .

For home use my DIY sub digs a lot deeper (it easily gets down to 20 Hz), but it's also big and inefficient - not really the best match for use in that bar, though it might be fun one day to plug it in there to see if the customers notice any difference .
__________________
www.diysubwoofers.org
  Reply With Quote

Reply


Rebuilding the Enigma...Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Another enigma with my "Enigma" Brian Steele Subwoofers 9 4th November 2018 07:27 AM
Audio Analogue Enigma service manual hamradioman Solid State 0 21st August 2015 02:24 AM
Help With DEQ2496 For Subwoofer (Enigma) Gwho Subwoofers 7 15th October 2013 01:11 AM
Someone with Enigma 3 and a scanner: Can you help me? Hybrid fourdoor Music 0 21st September 2003 10:22 AM
I'm rebuilding my amp Lisandro_P Everything Else 2 4th July 2002 08:53 AM


New To Site? Need Help?

All times are GMT. The time now is 10:55 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki