Post by: Antone Atmarama Bajor on October 20, 2005, 03:33:07 PM
Ok I did a bunch of sweeps on various drivers yesterday.
among them TAD TL-1603's, JBL 2225, JBL 2245 in 4645 cab, and of course Eminence Lab 12's in my BS-212 Cabs.
Test setup:
TEF 20
Old P2 Laptop running SL 6.7.9.4
Alesis Matica 900 Bridged Mono
Fluke DMM
Crown XXX omni microphone placed 32.8' away from speakers hovering ~ 2" off the ground.
Issues:
I Didn't have calibration data for mic until last test. Volts per pascal was set at default .01 and needed to be .011. The final test was the JBL 2225's. I tried changing these values under "current settings" it seemed to make about .5dB difference
but I seem to be measuring ~5-6dB more than predicted. If anyone knows how I can make those corrections after the fact it would be greatly appreciated. I Corrected This Using Calculation tools at
http://www.sengpielaudio.com/calculator-soundlevel.htm
This site was very helpful.
I am not sure at what the high cut should be doing a 1/2 space ground plane measurements. Everything things to start rolling off in the low mid 100's.
Here is an overlay of four cabs tested:
I'm not sure How Bass Box determines its Normalize Amplitude 0dB point but it claims I'm at 0dB around 43Hz -7dB around 20Hz and +1.5 around 100Hz. I'm measuring (6Hz resolution) -6dB @20Hz relative to 43Hz and +4.4dB @100Hz. I guess that would actually put me ~-10dB @20Hz. I'm wondering if getting 3dB more than predicted @ 100Hz has something to do with the dimensions of the two cabs being about 3.5'X4'???
More to follow
Antone-
Update the 2225 sweep says 8 Ohms at 20VRMS this is incorrect it was two drivers in parallel so 4 Ohms @ 20VRMS.
The 4Labs were wired in series parallel so 6 Ohms @ 24.5VRMS.
I tried to keep everything @ 100Watts @ rated Z.
Post by: Antone Atmarama Bajor on October 20, 2005, 03:35:40 PM
Post by: Antone Atmarama Bajor on October 20, 2005, 03:39:41 PM
These are my THD measurements (I didn't do noise there was plenty of ambient noise around)
Post by: Antone Atmarama Bajor on October 20, 2005, 05:22:55 PM
Still the weakest point of these cabs is the Group Delay is in the mid 20's of ms at around 20Hz. Can't have everything well maybe I can tweak with some digital processors servo feedbacks and all pass filters. But that would just make everything Later than on time.
Antone-
P.S. Oh please I don't wanna be Duane Dibbley.
Post by: Antone Atmarama Bajor on October 21, 2005, 02:22:46 PM
I know I'm going to have to retake the sweeps with the mic calibration set (Unless some one here is a TEF guru and knows a correction factor I can apply).
The part about this cab that I'm most impressed with is that it is a reflex cab with very low Harmonic Distortion Below 20Hz down to about 16Hz.
I know you guys are all a bunch of bass horn gurus. That will be my next project.
Antone-
Post by: Antone Atmarama Bajor on October 22, 2005, 02:58:20 PM
So anyhow. Let me know if there is anything close to as efficient down in the 30Hz and Bellow Range. The only things that come to mind are Danley Subs, Contra Bass, And Genelec.
These things must make a wicked low car sub with all of the in cab gain.
Antone-
Post by: Johan Rademakers on October 25, 2005, 05:33:30 PM
Wkr Johan Rademakers
Post by: Antone Atmarama Bajor on October 25, 2005, 05:38:08 PM
Antone-
Post by: Antone Atmarama Bajor on October 25, 2005, 05:57:44 PM
Thanks those are some cool drivers.
Though A vented Box with the tumult 18 would have ~the same output as my 4X12 Lab subs @ 20Hz in almost exactly the same Volume. The best part about the tumult 18 is its huge XMAX would keep it in the gap across its entire power bandwidth and than some. A Sealed single 18 Tumult would however have slightly more output @ 20Hz Than a single Vented Lab 12 using roughly the same volume box, but thats mainly due to 2X the LABS RMS. But I'm sure the single 18 would sound Tight in a sealed box!!! Too bad they are 4X the price of 1 Lab 12. But it looks like a reasonable candidate for many projects!!
Antone-
Post by: Antone Atmarama Bajor on October 27, 2005, 02:09:41 AM
Toms Tapped Horn seems to be the only thing in existence that is as efficient at 20Hz in such a small Volume.
4 Lab 12's or 1 Adire Tumult 18" are the ~ the same vas. Seem to be the best I have modeled yet. It is becoming apparent to me that Reflex cabs are not the way for significant output bellow 40-50Hz. Unless you have a lot of space and a lot of power available.
I think Tom has designed the only true compact sub with significant output in the 20Hz Range. I could come within 4 or 5dB of the DTS-20 with close to the same volume cab. Or close the Gap by 2dB with a 20 or 30cu' Cab.
There has to be another way to accomplish this in a compact package with High output and High fidelity.
Antone-
Post by: Walt de Jong on October 27, 2005, 01:45:14 PM
Best regards,
Walt
Post by: Antone Atmarama Bajor on October 27, 2005, 02:05:00 PM
I don't think that conical or linear expansion is very effective at coupling the sound energy. Isn't some logarithmic expansion a little more effective? Like a Tractrix? Or Hyperbolic? It sounds like your talking about recombining the rear wave of the driver at some wavelength relation ship with a separate chamber that reenters the horn at some point?
Interesting. What about making a high gain cab for something like the Eminent Technology Model 17. That seems like a very smart idea. High fidelity HVAC?
Antone-
Post by: Walt de Jong on October 27, 2005, 02:17:43 PM
For example Ciare 12.00SW looks like a good candidate. If you got good loading on the cone in the very low frequencies you need less x-max, but in general more is better. Also note that you do not need a driver with very low Fs to get down to 16Hz.
Best regards,
Walt
Post by: Antone Atmarama Bajor on October 27, 2005, 02:35:33 PM
How do you calculate the change of the drivers Fs due to horn loading???
Antone-
Post by: Michael_Elliston¶ on October 30, 2005, 01:47:34 AM
| Antone Atmarama Bajor wrote on Fri, 28 October 2005 07:05 |
A nice little 18' horn. I don't think that conical or linear expansion is very effective at coupling the sound energy. Isn't some logarithmic expansion a little more effective? Like a Tractrix? Or Hyperbolic? It sounds like your talking about recombining the rear wave of the driver at some wavelength relation ship with a separate chamber that reenters the horn at some point? Interesting. What about making a high gain cab for something like the Eminent Technology Model 17. That seems like a very smart idea. High fidelity HVAC? Antone- |
Exponential and hyperbolic are of the same family.Conical basshorns,when not 'infinite' horns seem to operate similar to exponential types. Tractix arent used for bass due to lack of low output see volvotreter.de 'downloads'
Most folded horns consist of several parabolic or conical sections in series approximating an expo flare.
http://www.geocities.com/xobt/basshorns/basshorns.htm
Mike.e
Post by: Antone Atmarama Bajor on October 31, 2005, 01:43:37 PM
I wish a little 18" 20Hz horn was possible with some serious output.
It be like an air cannon. Danger do not get close to the sub. It will shoot a hole through your chest.
Antone-
Post by: Too Tall (Curtis H. List) on January 01, 2006, 12:23:33 PM
| Antone Atmarama Bajor wrote on Mon, 31 October 2005 13:43 |
I always like to think of it as a faceted approximation of an exponential flare. I guess its sorta connical I would just call it linear expansion. The curved bends parabolic? Hmm. I'm sure inside the horn there will be hotspots at the foci of the bends at very specific wavelengths. I wish a little 18" 20Hz horn was possible with some serious output. It be like an air cannon. Danger do not get close to the sub. It will shoot a hole through your chest. Antone- |
Hi Antone,
So you didn't build a horn (LAB sub) because it was too big to move, too heavy or too complex to construct?
If you "play out" you want the smallest physical box you can get what you need out of.
What happens when you put the LAB 12 in a smallish sealed box and use a Linkwitz transform (You would of course need active electronics to do this)?
http://www.trueaudio.com/st_lkxfm.htm
Post by: Antone Atmarama Bajor on January 01, 2006, 08:49:18 PM
I am planing on doing a lab sub in a sealed box.
I wasn't sure if I should do the linkwitz Transform or a dual integrator. 4Lab subs in an ~3cu' Cab can produce ~110dB @ 20Hz. I think it would be good for 1/4 or 1/8th space loading to get several dB of Gain.
The only problem with a lab box with a Q of .707 is its tuned to around 50Hz so an integrator would make it only useful to ~ 50Hz.
Is the linkwitz transform a 12dB per octave Slope?
I could get as much output @ 20Hz as the BS-212 with a sealed box if I had optimal boundary loading.
I could get much greater SPL with a lab 12. But I would need to corner load it to get smooth response down to cutoff (Or have 4 of them). I would also need a delay to align them with my top boxes. 2 BS-212's are almost as large as 1 Lab 12 (No where near as efficient except bellow 30Hz). I think the BS 212's are great for a stage rig. They radiating surface is shallower so more practical than a horn sub.
The biggest problem I have with them is if I'm not careful I can over excurd them in the 30Hz range (just above port resonance) They don't overecurd gracefully (Are there any drivers that do?) They sorta Clack. A sealed box would help control that problem.
Anyhow thats why I built the BS-212. I think its probably close to the best most portable (as two separate cabs) direct radiator "SUB" that anyone can build for the cost (Not specifically my design but just the volume tuning and driver).
Using larger drivers Like the Adire 18's would require a very large enclosure that would not be very portable especially if you wanted to do a diff configuration since this would double the required Volume.
But is it musically Relevant? It sure feels good.
Blah Blah Blah
Happy New Years.
Antone-
Post by: Too Tall (Curtis H. List) on January 02, 2006, 09:54:14 AM
| Antone Atmarama Bajor wrote on Sun, 01 January 2006 20:49 |
The BS-212 is the first speaker cab I've ever Built. I wasn't ready to build something like the Lab Sub. I am planing on doing a lab sub in a sealed box. I wasn't sure if I should do the linkwitz Transform or a dual integrator. 4Lab subs in an ~3cu' Cab can produce ~110dB @ 20Hz. I think it would be good for 1/4 or 1/8th space loading to get several dB of Gain. The only problem with a lab box with a Q of .707 is its tuned to around 50Hz so an integrator would make it only useful to ~ 50Hz. Is the linkwitz transform a 12dB per octave Slope? I could get as much output @ 20Hz as the BS-212 with a sealed box if I had optimal boundary loading. I could get much greater SPL with a lab 12. But I would need to corner load it to get smooth response down to cutoff (Or have 4 of them). I would also need a delay to align them with my top boxes. 2 BS-212's are almost as large as 1 Lab 12 (No where near as efficient except bellow 30Hz). I think the BS 212's are great for a stage rig. They radiating surface is shallower so more practical than a horn sub. The biggest problem I have with them is if I'm not careful I can over excurd them in the 30Hz range (just above port resonance) They don't overecurd gracefully (Are there any drivers that do?) They sorta Clack. A sealed box would help control that problem. Anyhow thats why I built the BS-212. I think its probably close to the best most portable (as two separate cabs) direct radiator "SUB" that anyone can build for the cost (Not specifically my design but just the volume tuning and driver). Using larger drivers Like the Adire 18's would require a very large enclosure that would not be very portable especially if you wanted to do a diff configuration since this would double the required Volume. But is it musically Relevant? It sure feels good. Blah Blah Blah Happy New Years. Antone- |
I have not played around with it so forgive me if I am in error. That is why I sent along John Murphy's web page.
First to the room and any loading from floor, walls or in corners a sealed box is the same as a ported box.
My simplistic understanding is you start out with a driver in a sealed box, so you have a 12dB/oct slope. The Linkwitz transform moves that down in frequency, but maintains the 12dB slope.
So it may be possible that you could tune a ported box a little lower, but with a ported box's 24dB/oct slope. So considering a shallower slope perhaps the Linkwitz transform will not get the last couple of cycles of low end.
Or maybe the LAB 12 driver is not suitable candidate for a Linkwitz transform?
If you have the software you might run the numbers.
Post by: Antone Atmarama Bajor on January 03, 2006, 03:48:05 AM
The only problems I'm foreseeing is that For a live Bass Guitar Rig, Boundaries won't always be available. And Sheet rock walls start becoming acoustically transparent to Low Frequency Energy in the Low 30's. So there will not be as much 1/4 or 1/8th space loading at the lower frequencies.
I am going to build a couple of sealed boxes soon and play with some dual integrators and Linkwitz transform circuits. I'll let you know how it turns out.
The CGN 1808 Looks like it would work nice in a Linkwitz Transform or Dual integrator, the box wants to be tuned to 90Hz so linkwitz transform my not be necessary unless you want to go higher with it like for an LFE channel.
I'm liking the lowered Harmonic Distortion of doing Differential Loading. My bi-amped rig is almost too clean for Bass guitar. None of the good extra harmonic distortion from the Bass fundamental being lower than Cab resonance, or all the cone breakup modes.
Antone-
Post by: Too Tall (Curtis H. List) on January 03, 2006, 10:24:14 AM
| Antone Atmarama Bajor wrote on Tue, 03 January 2006 03:48 |
The only problems I'm foreseeing is that For a live Bass Guitar Rig, Boundaries won't always be available. And Sheet rock walls start becoming acoustically transparent to Low Frequency Energy in the Low 30's. So there will not be as much 1/4 or 1/8th space loading at the lower frequencies. Antone- |
My understanding was that the box you just built is a reflex. If so, then a sealed will act the same when loaded by wall boundaries or corners and wall construction. The big advantage is it should be smaller.
Post by: Antone Atmarama Bajor on January 03, 2006, 12:54:18 PM
But not all stages have convenient walls to couple your closed box subs too. Especially outdoors. Sheet rock will let a lot of the sub bass pass through it instead of act like a perfect reflective surface. In Theory you can get all the gain of boundary loading, but theories rely on perfect circumstances.
Antone-