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post #31 of 44 Old 03-05-2013, 08:47 PM - Thread Starter
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Originally Posted by splotten View Post

Hello bossobass.

For some reason the graphics in the link doesn’t load in my browser at the moment, but as I recall there was a little advantage in SPL per Watt and a large advantage in distortion at equal SPL in the bigger 200L box. The bit about the distortion was my primary interest as I have read countless times that a small box and the inherent “springiness” of the air-volume inside the box would somehow help the woofer achieve lower distortion levels as opposed to higher. To me, and apparently to Kramskoi as well, that has always been counterintuitive. Mind you I am no engineer, so I might well be wrong, but the graphs, as I recall, showed a large advantage in distortion with that particular woofer in a 200L box, compared to a 75L box.

I am not really sure I answered your inherent question. Feel free to elaborate if I missed the mark :-)

Dan
I think this little paragraph is what you are referring to...
Even though already these tests show pretty conclusively the result of the lower low end sensitivity and the required EQ boost, I decided to take a few extra measurements for the VLF enthusiasts out there (cough...Bosso ). I tuned the signal generator to 8 Hz (all sorts of problems occurred below this, not to mention extremely high THD levels). As the screen below shows, I managed to record ~90 dB @ 8 Hz for the 75L subwoofer. Anything higher and the amplifier would clip wildly, not to mention +100% THD produced by the driver alone. For the 200L subwoofer 90 dB resulted in ~1/2 the THD and 95 dB was also within the limits, albeit with high THD and suspension noise. It's pretty obvious that a single 18" sealed subwoofer isn't capable of producing usable levels of output at these frequencies (without a HUGE room gain).

I'm not one to argue with numbers, especially when done by Ilkka... 1/2 the THD and another 5 dB in output within limits speaks for itself. Yes I have theorized such a thing because a subwoofer in a box too small for itself fights two things in striving to achieve the lowest octave, namely power compression and the air spring, not to mention its own suspension characteristics. The stiffer the spring, the more power that is required up until the voice coil cries no mas...This is why I champion low qts drivers because it allows you to build an enclosure that's relaxed, stretched out and ready to rumble without having to coerce the driver too heavily to do your bidding. It is bad enough that the driver will shortly have to endure the onerous shelving equalization that will herald our attempts to make it flat to some ego-maniacal low Hz level!

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post #32 of 44 Old 03-05-2013, 09:24 PM - Thread Starter
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Pressure at 14 Hz...

However my shack meter is a major cluster-expletive-malfunction so now there is something else to buy this week.

I did run some sine business at 18 Hz and the usual suspects reared their heads in the form of irritable resonances that detract from the VLF experience.

I went down to 16 Hz and the consequent door rattle let me know that I still had pressurization of the room. Since this is the organ fundamental most prized, I was glad to feel some good output here. I then went a little lower to 15 and then 14 Hz. The door kept up its protest so I know that the room will support down to at least that and I now believe that the DSP will make the sub flat to probably 10 Hz. That is not to say that anything terribly exciting will happen while achieving it. A single pro-sound 18" won't get anywhere near the 107 db at 10 Hz that the high xmax 3x15 was capable of. But then it won't require 5.5 kilowatts of power either!

That said, the box is excursion limited as it was designed and the QSC has enough clean power to drive it toward the suspension limits. But that's not what this box is about is it?

The QSC 900 is quieter than my laptop until you start feeding it 16 Hz sine waves, then it's as loud as a hair dryer. I may yet put in the closet where I envisioned it going in the first place. However if it remains silent under "normal" circumstances then it stays put next to "the device".

Continued some listening...James Holden's Lump, The Red Violin Chaconne, Vierne's First Symphony for organ...Ane Brun "Lullaby for Grown-ups", Melody Gardout "If the stars were mine", and Kraftwerk's Elektro Kardiogramm...all renedered in rich, textural slabs of sound that I've so missed since the complete dismantling of the 3x15. Like old friends, they are extremely welcome and hopefully I won't abandon them to soon in the future.

Now I'm waiting on the dsp1124, which will hopefully arrive for the weekend. I will want to compare sound signatures before and after eq shelving. The last bit of uummph added to the presentation.

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post #33 of 44 Old 03-05-2013, 10:11 PM
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Originally Posted by kramskoi View Post

...a subwoofer in a box too small for itself fights two things in striving to achieve the lowest octave, namely power compression and the air spring, not to mention its own suspension characteristics!

and BL modulation distortion induced by the higher current

Noah
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post #34 of 44 Old 03-05-2013, 11:08 PM - Thread Starter
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Originally Posted by bossobass View Post

Hi Dan,

I've been over this a few times and still wondering how the proof in the pudding still escapes most folks. Ilkka's CEA 2010 results of the LMS in 75L. 100L and 200L show an inaudible (+/-) 1dB difference from 12.5-80 Hz. Progressive sine sweep torturing of a subwoofer, especially a cheap DIY version with no protection circuitry, shows compression under extreme duress such that the sub would never see in actual use and nothing more.


Another obvious fact that seems to escape most interested people. When the response is flat to single digits (greatest extension without peaking), Q is irrelevant. How you get there is the question.
Kram, it's great to see you posting. Always interesting stuff. Thanks for that, and I'll be popping in to follow this one as well. cool.gif

Hello Bosso...well it's been a while but I'm back, although I don't have the time I once had to scavenge all the great projects that are done here. I'll try and pop in as much as I can, though schoolwork really puts a dent in my free time.

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post #35 of 44 Old 03-06-2013, 06:07 AM - Thread Starter
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Originally Posted by noah katz View Post

and BL modulation distortion induced by the higher current
Right Noah...As a matter of fact I was flipping through my rather voluminous old subwoofer picture folder and I came across a post by Jakeman. Basically your low end will be determined by Re, BL and enclosure size. It's actually something that was pulled from the Rythmik Audio FAQ.

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post #36 of 44 Old 03-06-2013, 07:26 AM - Thread Starter
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...3.3 cu.ft....and never knew using a block plane was sooooo much fun!!


my humble analyzer...


...the 10 Hz burn...for 33 hours total!


Still needs ebony stain...but this will have to wait for a bit...in the meantime, some ghoulish bass?

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post #37 of 44 Old 03-06-2013, 09:05 AM - Thread Starter
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While this is no indication of how clean the signal might be, this is the data after being put into the REW RS-2055 model worksheet.

It seems my meter might have a short or something but here is the raw:

10.... 78
11.... 80
12.... 82
14.... 83
16.... 86
18.... 87
20hz 87dB

Shaking power is gone at 11 Hz so distortion has fully taken over the signal...above that we have action, with the 14 Hz signal certainly being "all present and accounted for"

These are some higher raw numbers from 11-14...

11....85 /104
12....87 /103
14....90 /104 dB

Again keep in mind that this is a 1200 cu ft room with room gain starting at 40 Hz... the higher raw numbers are certainly above distortion limits with lots of added room resonances added to spl at 14 Hz...

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post #38 of 44 Old 03-06-2013, 01:37 PM
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Quote:
Originally Posted by splotten View Post

Hello bossobass.

For some reason the graphics in the link doesn’t load in my browser at the moment, but as I recall there was a little advantage in SPL per Watt and a large advantage in distortion at equal SPL in the bigger 200L box. The bit about the distortion was my primary interest as I have read countless times that a small box and the inherent “springiness” of the air-volume inside the box would somehow help the woofer achieve lower distortion levels as opposed to higher. To me, and apparently to Kramskoi as well, that has always been counterintuitive. Mind you I am no engineer, so I might well be wrong, but the graphs, as I recall, showed a large advantage in distortion with that particular woofer in a 200L box, compared to a 75L box.

I am not really sure I answered your inherent question. Feel free to elaborate if I missed the mark :-)

Dan

Air spring distortion is predictable by a formula and is mostly 2HD. SPL per watt is a 2-edged sword. If you require less power for equal output on the low end because the box volume is larger, you have less power for the top end, or you must employ sophisticated limiters, as every commercial sealed sub does. You can't have both.

The bottom line is, as Ilkka's CEA 2010 results clearly show, there is no audible difference in maximum THD-limited output between the 3 box sizes from 12.5-80 Hz, using the amplifier Ilkka used.

Ricci got the equivalent to 2-LMS drivers in his tests vs Ilkka's results due to the simple fact that he used a much more capable amplifier than Ilkka used. That should indicate that the signal chain is far more important than the box size.

Quote:
Originally Posted by kramskoi View Post

I think this little paragraph is what you are referring to...
Even though already these tests show pretty conclusively the result of the lower low end sensitivity and the required EQ boost, I decided to take a few extra measurements for the VLF enthusiasts out there (cough...Bosso ). I tuned the signal generator to 8 Hz (all sorts of problems occurred below this, not to mention extremely high THD levels). As the screen below shows, I managed to record ~90 dB @ 8 Hz for the 75L subwoofer. Anything higher and the amplifier would clip wildly, not to mention +100% THD produced by the driver alone. For the 200L subwoofer 90 dB resulted in ~1/2 the THD and 95 dB was also within the limits, albeit with high THD and suspension noise. It's pretty obvious that a single 18" sealed subwoofer isn't capable of producing usable levels of output at these frequencies (without a HUGE room gain).

I'm not one to argue with numbers, especially when done by Ilkka... 1/2 the THD and another 5 dB in output within limits speaks for itself. Yes I have theorized such a thing because a subwoofer in a box too small for itself fights two things in striving to achieve the lowest octave, namely power compression and the air spring, not to mention its own suspension characteristics. The stiffer the spring, the more power that is required up until the voice coil cries no mas...This is why I champion low qts drivers because it allows you to build an enclosure that's relaxed, stretched out and ready to rumble without having to coerce the driver too heavily to do your bidding. It is bad enough that the driver will shortly have to endure the onerous shelving equalization that will herald our attempts to make it flat to some ego-maniacal low Hz level!

Ilkka used an amplifier than has nothing in the tank below 10 Hz, especially when fed pure sine wave tones. It's a no-brainer that THD from the difference in air spring stiffness does not rise by double, making it a simple conclusion that the amplifier and input signal were suspect. When he attributed all of the recorded THD to "the driver only", I knew not to take any of what he wrote very seriously. As I mentioned above, Ricci got significantly higher output from "the driver alone" with magnitudes less THD than Ilkka did:



To be honest, Ilkka tested every sub to 10.3 Hz (TrueRTA doesn't go below that), so when I read that he went down -2 Hz from there to around 8 Hz and called it a VLF exercise, dropping my name no less, it was pretty funny stuff. biggrin.gif

I've used small boxes and high power for more than a decade and have yet to see better performance from any subwoofer system created by any design philosophy. Exact reproduction of available source is what matters to me. My measurement hardware is more accurate than Ilkka's and my tests are real world using actual soundtrack source in an actual room, so I've developed a small hole in my head where, over the years, the adherence to everything Ilkka despite the facts of the matter caused me to scratch. smile.gif

The Irene scene is especially useful for tracking 2HD. With the fundamental at 6.3 Hz, 2HD is at 12.6 Hz. At full reference level, there is less than 2% 2HD at 12.6 Hz and 5% THD in total and, sorry to let anyone down, but the equipment Ilkka used wasn't capable of testing below 10 Hz, as he admitted in 'the paragraph'. And, it didn't require HUGE room gain. The room gain is around 8dB/octave, starting at 30 Hz, which is very typical.



The bottom line is that, if you want low end to the bottom of the format, you have to focus on displacement, the signal chain and adequate power far more so than the box size causing THD. Since it's nearly impossible to stand exactly on the line of enough power and not shredding your new drivers, erring on the side of air spring excursion protection seems like good advice to me.
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post #39 of 44 Old 03-06-2013, 04:27 PM
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Originally Posted by bossobass View Post

The Irene scene is especially useful for tracking 2HD. With the fundamental at 6.3 Hz, 2HD is at 12.6 Hz. At full reference level, there is less than 2% 2HD at 12.6 Hz and 5% THD in total...

What's the SPL of the 6.3 Hz fundamental at reference?

Noah
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it looks like your amplifier is sitting on your stove...hot bass. :-0

"The bottom line is that, if you want low end to the bottom of the format, you have to focus on displacement, the signal chain and adequate power far more so than the box size causing THD. Since it's nearly impossible to stand exactly on the line of enough power and not shredding your new drivers, erring on the side of air spring excursion protection seems like good advice to me."

bosso, yours is certainly one reasonable approach. however, such an approach is not without its problems, particularly for some people for some types of music.

there is an entire site that discusses the problems of the "box". note that it has nothing to do with extension as that is one of the ib's primary strengths.

http://ibsubwoofers.proboards.com/index.cgi

primary faq is here: http://home.comcast.net/~infinitelybaffled/index.html

the lower qt of i.b. systems, open baffle systems, or for that matter any lower qt system is generally described subjectively as cleaner, dryer, faster, and/or tighter for some types of music. while hi q systems are generally described as providing "more" bass, which is preferred by many for home theater and some types of music.

i have not seen a good measurement for this effect, but i will look some more.

i suspect the goal of this build is highest quality music bass that one can get from a box.

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post #41 of 44 Old 03-06-2013, 10:27 PM
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Quote:
Originally Posted by bossobass View Post

Air spring distortion is predictable by a formula and is mostly 2HD. SPL per watt is a 2-edged sword. If you require less power for equal output on the low end because the box volume is larger, you have less power for the top end, or you must employ sophisticated limiters, as every commercial sealed sub does. You can't have both.

The bottom line is, as Ilkka's CEA 2010 results clearly show, there is no audible difference in maximum THD-limited output between the 3 box sizes from 12.5-80 Hz, using the amplifier Ilkka used.

Ricci got the equivalent to 2-LMS drivers in his tests vs Ilkka's results due to the simple fact that he used a much more capable amplifier than Ilkka used. That should indicate that the signal chain is far more important than the box size.
Ilkka used an amplifier than has nothing in the tank below 10 Hz, especially when fed pure sine wave tones. It's a no-brainer that THD from the difference in air spring stiffness does not rise by double, making it a simple conclusion that the amplifier and input signal were suspect. When he attributed all of the recorded THD to "the driver only", I knew not to take any of what he wrote very seriously. As I mentioned above, Ricci got significantly higher output from "the driver alone" with magnitudes less THD than Ilkka did:

Yes, distortion is predictable. That goes for both large and small boxes. I don’t follow your point? I understand that distortion in this type of subwoofers is mostly 2. order harmonics. My understanding is that this type of distortion is mostly created by the uneven motion of the cone in either direction caused by the air spring inside the box. My intuition was that the smaller box will have a stronger spring effect and therefor cause more distortion compared to the same woofer in a larger box. Sadly the graphs in the link don’t load anymore, but as I recall they showed exactly that. - Greatly reduced distortion at -all- measured SPL levels, both below and above 20Hz in a 200L box compared to a 75L box. I do not see this test as purely a torture test even if the system was also driven beyond its capability. The test showed that the system also behaved this way well under its maximum capability.

I am not sure why you keep referring to Ilkka's CEA 2010 results. I haven’t seen those. Do you have a link? I am referring only to the small test in the link I posted before. May be the test you are referring to show something different but the in the link I posted it was clearly shown that the bigger box had much lower distortion at equal SPL levels. It might well be that it is possible to achieve similar, or even better, results otherwise, but in a DIY perspective it is notable that it might be possible to more than halve the distortion just by using a bigger box.

You mention that one should also look into the signal chain. If I understand you correctly, you imply that some of the measured distortion might originate from the signal chain. I am not in a position to judge if this might be the case but again, in a DIY perspective you might just make it easier on yourself if you go with the bigger box as it requires less power to achieve equal SPL and inherently strains the signal chain less. Even if I can’t say for sure how much the signal chain influenced the test I linked to, I have a hard time believing that the amplifier would have caused this much extra distortion in the smaller box. After all it was shown that the distortion was significantly less well above 20Hz and well under the systems maximum capability. You may think otherwise. I happen not to.

By no means am I implying that this is the only way to go. I clearly understand that there are tradeoffs either way you choose, but in a DIY perspective with limited engineering capabilities you might just come out on top if you make it easy on yourself, rather than hard :-)

Dan
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Kramskoi

I see you are about done. Thanks for posting your impressions. I get the feeling that you are happy with the system regarding both SPL and SQ.
Well done.

Dan
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Quote:
Originally Posted by bossobass View Post

Air spring distortion is predictable by a formula and is mostly 2HD. SPL per watt is a 2-edged sword. If you require less power for equal output on the low end because the box volume is larger, you have less power for the top end, or you must employ sophisticated limiters, as every commercial sealed sub does. You can't have both.

The bottom line is, as Ilkka's CEA 2010 results clearly show, there is no audible difference in maximum THD-limited output between the 3 box sizes from 12.5-80 Hz, using the amplifier Ilkka used.

Ricci got the equivalent to 2-LMS drivers in his tests vs Ilkka's results due to the simple fact that he used a much more capable amplifier than Ilkka used. That should indicate that the signal chain is far more important than the box size.
Ilkka used an amplifier than has nothing in the tank below 10 Hz, especially when fed pure sine wave tones. It's a no-brainer that THD from the difference in air spring stiffness does not rise by double, making it a simple conclusion that the amplifier and input signal were suspect. When he attributed all of the recorded THD to "the driver only", I knew not to take any of what he wrote very seriously. As I mentioned above, Ricci got significantly higher output from "the driver alone" with magnitudes less THD than Ilkka did.

To be honest, Ilkka tested every sub to 10.3 Hz (TrueRTA doesn't go below that), so when I read that he went down -2 Hz from there to around 8 Hz and called it a VLF exercise, dropping my name no less, it was pretty funny stuff. biggrin.gif

I've used small boxes and high power for more than a decade and have yet to see better performance from any subwoofer system created by any design philosophy. Exact reproduction of available source is what matters to me. My measurement hardware is more accurate than Ilkka's and my tests are real world using actual soundtrack source in an actual room, so I've developed a small hole in my head where, over the years, the adherence to everything Ilkka despite the facts of the matter caused me to scratch. smile.gif

The Irene scene is especially useful for tracking 2HD. With the fundamental at 6.3 Hz, 2HD is at 12.6 Hz. At full reference level, there is less than 2% 2HD at 12.6 Hz and 5% THD in total and, sorry to let anyone down, but the equipment Ilkka used wasn't capable of testing below 10 Hz, as he admitted in 'the paragraph'. And, it didn't require HUGE room gain. The room gain is around 8dB/octave, starting at 30 Hz, which is very typical.



The bottom line is that, if you want low end to the bottom of the format, you have to focus on displacement, the signal chain and adequate power far more so than the box size causing THD. Since it's nearly impossible to stand exactly on the line of enough power and not shredding your new drivers, erring on the side of air spring excursion protection seems like good advice to me.

Well Bosso, you won't catch me downplaying the issue of displacement. I'm in a much smaller room but the SW is only displacing about 25% of what the 3x15 did. If I had my way it would be a 2x18 that displaces more than the 3x15 and the LMS 5400 x 2 was the plan until the prices skyrocketed on them. Even that blasted 5100 is $900 but it is only one of maybe two or three drivers that meet my requirements for system qtc in a reasonable sized dual opposed configuration. The SW cabinet is only 15" deep and I would only need to make it 3" deeper to do a dual opposed 5100 setup. 4 cu. ft. and a Q = .5...now that is sweet, but $1800?...that is rather sour!

I don't know which version of TrueRTA Ilkka was running but the version I have has a signal generator that goes down to 5 Hz. I do remember earlier versions being limited to 10 Hz. I also have to say that although Ilkka's amp was suspect, it was the control in the experiment and I have a suspicion that a test with more adequate equipment might again see a larger box with less distortion, but not as much as was found in Ilkka's tests.

That said, I concur that the trivialities of THD and enclosure size is rather insignificant in comparison to (Sd x Xmax) x (N)umber of drivers, especially for the stupendous subterranean infrasonics suffused within certain scenes from pictures like BHD! Irene won't sing for anything ordinary or sufficient. She requires something more fiesty and I daresay fanatical. My current little experiment is more about music than anything else but that is precisely where I began with the prior system. It just sort of got out of hand ... as has happened to many of us here on the forum. Do I dare walk those steps again? Well I know I'm on the path because just six weeks ago this project was just going to be a modest dual opposed 10" Peerless XLS design...then a 4 x 8" Tang Band, which soon gave way to my current pro-sound infatuation (first the TD18h+ from AE and eventually the 18SW115), in lieu of the continued, chronic paucity of suitable high xmax drivers. The words "group buy" deflate me like a belated birthday balloon!

Finally, the issue of protection is one I have not really encountered even with low qtc. plus eq boost on the lower end. That is not to impugn the common sense approach of safety first...these are after all some quite expensive motors we put in boxes. So be candid as always Bosso. I've regressed on a lot of these issues but welcome the thoughts and the dialogue.

"Frequency response is NOT efficiency response."

 

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post #44 of 44 Old 03-07-2013, 02:43 AM - Thread Starter
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Kramskoi

I see you are about done. Thanks for posting your impressions. I get the feeling that you are happy with the system regarding both SPL and SQ.
Well done.

Dan
Oh we will see Dan. The sub sounds like the old system but obviously below about 12 Hz the fundamentals are becoming lost in the upper harmonics. I might decide to address this in a bit. Judging by the REW worksheet it runs flat to 10 Hz even without equalization but like I said before, there won't be anything really palpable about it...sort of like the Bag End Infrasub response to 8 Hz.. I'll see how much the sound signature changes with the DSP but there really is'nt anything in sub land that lends itself to my needs. The only alternatives that can dig lower is the uber expensive 5100/ 5400 and the Mach 5 UXL, which is out of stock but will drop in with a Q = .5. I could go 21" but expansion of the cabinet might be required to achieve Q = .5. I guess we will see but I'm happy with the results.

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