| johnmark |
OK ordered four Atlas12 and can't wait to install them in my pair of dipole cabinets.
Does anyone know how high in frequency these Atlas 12 can be used.
With the light cone and low Le, I would think they could be run up to 250 hz easily unless there is a cone breakup mode.
I will be using these Atlas 12 with a Fostex FX120 or Adire WR125s fullrange driver on an open baffle and would need to crossover in that range.
JM |
|
|
| simon5 |
| I know he must be busy, but you should call Chad to ask about that. I think it will be ok to crossover at 250 Hz. |
|
|
| DcibeL |
| Yes I'm sure 250Hz would be just fine, but why? |
|
|
| Tweeker |
The red line on the chart is the closest one to your situation, is the .52 qts in a very large 11.4cu foot sealed box. This is alignment has a box volume over 2.5 * vas, well on its way to infinite baffle, especially given the frequency. Be sure your cabinets dont act as transmission lines at these frequencies, it can lead to very lumpy response.
 |
|
|
| johnmark |
I was just wondering if anyone has actually measured the response (not simulated) above 100 hz to know if there are cone resonances.
My dipole cabinets are half way between an H frame and U frame. The backs are heavily stuffed with fiberglass to hopefully damp resonances like Tweeker warned of.
I will post a pict when I get the drivers.
My plan is to use the dipole cabs from about 250 hz down to 50 hz and use a conventional sealed or vented box from 50hz and below.
I think Linkwitz also suggests this on his site.
I need to run the woofers up high enough to avoid stresssing the full range driver also planned for an open baffle.
JM |
|
|
| ThomasW |
| quote: | | With the light cone and low Le, I would think they could be run up to 250 hz easily unless there is a cone breakup mode |
Our testing indicates that the Le is almost 3 times higher than the published spec. |
|
|
| simon5 |
| Interesting... I hope Chad will be available soon to comment this. |
|
|
| johnmark |
Well I got my four Atlas 12's and put a pair each into my 3 cf sealed boxes.
The walls of the boxes are lined with high density fiberglass glued on with silicone. The cavity is not stuffed. I hooked them up in parallel and drive them with my adcom amp. They are fed from an active crossover off my receiver's preouts. I cut them off at 90hz.
What I heard was muddy, one note bass. Very dissapointed. They are not nearly as good as single NHT 1259 for comparison. I also compared them to a pair of 10" audax drivers that were originally in the same cabinets and the Audax were cleaner and more musical, but did not have the xmax needed to play as loud.
I tried the different Q configurations which you can adjust with the second VC, but this did not clear up the 1-note sound. I also tried to load them aperiodically by drilling some small holes in the box, but no improvement. I also tried them in a dipole cabinet, but the 1 note sound persisted.
Maybe these drivers are better suited as a car subwoofer (thumper)? They are very attractive drivers and appear well made, but they seem to have a very stiff suspension to my manual prying.
I was hoping to use them up to 200hz but this would be out of the question from what I heard.
I hope that I can return these.:bawling:
JM |
|
|
| SY |
Yow! Two of these stuffed into a 3 cu ft cabinet seems excessive. The Vas is about 128 liter (call it 5 cu ft). For two drivers, that's nearly 10 cu ft. With a Qts of 0.5, that makes your Qtc...
I think I know why they're boomy. |
|
|
| johnmark |
In low Qts mode they are suppose to have a Qts of .33 per the website, Vas 128.5l, Fs 23.2
with 3 cf I should be somewhere around .7 for system Q unless my calcs are way off ?
Even if I fracked up my Q calc, this would not explain why they sounded poor in a diploe cabinet also.
JM |
|
|
| SY |
Sorry, I didn't see the low Qts option. With Vas/Vb = 3.3, Qts = 0.33, you should indeed land near a Butterworth alignment. A pretty high f3, but room gain would help some
Have you verified the T-S parameters? And I assume you broke in the suspensions? |
|
|
| DSP_Geek |
| quote: | Originally posted by johnmark
Well I got my four Atlas 12's and put a pair each into my 3 cf sealed boxes.
The walls of the boxes are lined with high density fiberglass glued on with silicone. The cavity is not stuffed. I hooked them up in parallel and drive them with my adcom amp. They are fed from an active crossover off my receiver's preouts. I cut them off at 90hz.
What I heard was muddy, one note bass. Very dissapointed. [...]
JM |
Just from a sense of curiosity, how well braced are the boxes and what dimensions are they?
Francois. |
|
|
| tiroth |
| quote: | Originally posted by ThomasW
Our testing indicates that the Le is almost 3 times higher than the published spec. |
I just measured Atlas 15.
Tool: Philips PM6303A Automatic RCL meter
Frequency: 1kHz
Spec Le: 0.86mH
Measured: 1.86mH
With sense coil shorted: 360mH
Inadequate shorting rings? |
|
|
| johninCR |
| quote: | Originally posted by tiroth
I just measured Atlas 15.
Tool: Philips PM6303A Automatic RCL meter
Frequency: 1kHz
Spec Le: 0.86mH
Measured: 1.86mH
With sense coil shorted: 360mH
Inadequate shorting rings? |
I'd say they have some serious explaining to do. I'm really glad I procrastinated in buying anything. Apparently Dan hit the nail on the head with his comment about not all XBL2 drivers are created equal. |
|
|
| danvan |
| quote: | Originally posted by tiroth
I just measured Atlas 15.
Tool: Philips PM6303A Automatic RCL meter
Frequency: 1kHz
Spec Le: 0.86mH
Measured: 1.86mH
With sense coil shorted: 360mH
Inadequate shorting rings? |
Don't get me wrong, I don't know much about measuring specs...but shouldn't you measure any spec in the frequency range of the driver? 1kHz seems a bit high for a subwoofer. I would think that would affect the results a bit...though perhaps not enough to justify Ascendants measurements. |
|
|
| tiroth |
Personally, I'm not getting too bent out of shape, but there do seem to a number of problems with the T-S measurements. Others have pointed out that the change in parameters with the Qts adjustment don't seem to make sense. Le for instance is the same for all Qts settings, whereas I would have expected exactly the results I saw.
I think this is probably an honest mistake and not any attempt to mislead customers. Still, if there is a serious discrepency, it should be corrected.
I'm not certain of the usual test procedure for Le, although I thought it was often 1kHz and then a second factor at 10kHz. It does change with frequency. I'd certainly appreciate some independent confirmation of these measurements. |
|
|
| ThomasW |
We measured 2 different samples of the Atlas 12" driver. Stated Le is .86 mH.
The 'nominal' Le measured with VC #2 open, 2.45mH |
|
|
| Brian Tatnall |
Thomas or tiroth,
This thread was linked to the Ascendant forum by internet troublemaker of sorts, however there seem to be some valid concerns here. Could either of you bring it up in the Ascendant forum since you guys did the testing.
Thanks,
Brian Tatnall |
|
|
| ThomasW |
| Which thread is it? |
|
|
| tiroth |
| I've registered at that site. As soon as I am approved by the mods I will post the measurements with a linkback here. |
|
|
| tiroth |
Here is Simon5's thread re: TS parameters.
http://forum.soundillusions.net/showthread.php?t=50282
He also back-calculated TS based on Qts.
http://forum.soundillusions.net/showthread.php?t=50982
This is fine, but I would like to see real, accurate TS measurements. I think the original ones were wrong due to back-calculating as opposed to measuring, and I suspect the Le discrepency is the result of applying a formula as opposed to measuring. Either that, or the build shop did not build to spec.
I don't really care about the effect of Le on impedance because I have a lot of EQ at my fingertips. What does concern me more is that higher Le may indicate inadequate shorting rings, which could mean higher distortion.
I think everyone should keep things in perspective though. The Atlas may not be a $400 driver, but it certainly looks like it could be a great $100 driver, and that's what it costs at the moment. I won't have time for a while to do any real testing, but my initial tests seem to indicate that it perhaps gets a little more excursion than Shiva before making that wonderful "thwap thwap" sound, and at 15" it is moving a LOT more air. |
|
|
| johnmark |
Just to let you know, I got a call from Chad at Ascendant and there was no hassle about returning the drivers. I would not hesitate to do business with them.
JM |
|
|
| ThomasW |
If Simon5 want to fantasize about the T/S parameters, that's fine by me.
Our goal was distortion testing, so we didn't run a full set of T/S parameters. We ran the Le for since the distortion numbers indicated an Le that was quite a bit higher than the published specs.
For most people this isn't a problem. It could/would be a issue if one wanted to run the driver above a standard 80Hz XO point. |
|
|
| crippledchicken |
| quote: | Originally posted by johnmark
Just to let you know, I got a call from Chad at Ascendant and there was no hassle about returning the drivers. I would not hesitate to do business with them. Chads a very honest person and will, treat you right i have to agree.
JM |
;) |
|
|
| simon5 |
| quote: | Originally posted by ThomasW
If Simon5 want to fantasize about the T/S parameters, that's fine by me. |
I don't want to fantasize, I'm trying to help.
johnmark, if you didn't return the drivers already, I think you should try one driver per 3 cu.ft box with lowQ. I would like to hear your opinion on this. |
|
|
| crippledchicken |
| quote: | Originally posted by simon5
I don't want to fantasize, I'm trying to help.
johnmark, if you didn't return the drivers already, I think you should try one driver per 3 cu.ft box with lowQ. I would like to hear your opinion on this. |
that's what the forums are for to help each other as, no one person can have all the answers! i appreaciate all the help i've got. keep up the good work! crippledchicken
:) |
|
|
| johnmark |
Sent them back.
Decided to stick with the single NHT 1259 per side and use a lower cut-off freq. The suspension of the Atlas 12 seemed very stiff to me but probably needed some extended run-in time. I am not able to leave my subwoofer running all day for several days however.
JM |
|
|
| Mark Seaton |
| quote: | Originally posted by ThomasW
We measured 2 different samples of the Atlas 12" driver. Stated Le is .86 mH.
The 'nominal' Le measured with VC #2 open, 2.45mH |
Hey Thomas,
Do you recall at what frequency you had measured this?
What many might not be considering is that in the vast majority of loudspeakers, inductance falls with increasing frequency. Some programs allow to better model the nature of this shorted inductance. Note that almost all manufacturers list the Le as a calculated Le at 1kHz, not a curve fit. With the common specification given this way, the ONLY way I would expect to see more accurate numbers would be with an additional spec at some lower frequency. Due to the interactions with lower frequency impedance resonances, the best method is by curve fitting rather than discrete measurements. |
|
|
| DcibeL |
| ThomasW or Trioth, any chance I could get you to measure the inductance of the Atlas 12" when the 2 Ohm coil is wired in series with the 4 Ohm coil? I am just curious. |
|
|
|
