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Old 30th April 2011, 12:59 AM   #1021
Djim is offline Djim  Netherlands
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Martin, thanks for posting the extended SS15 with 3,06m pathlength elsewhere Maybe you could post it under its own thread (and/or here ;-) as it could be the answer (at least it looks promising) for some people before it gets lost between all suggestions...

Quote:
Originally Posted by Xoc1 View Post
In the UK the Eminence 3015lf is currently retailing at about £137
As an alternative I think that the Precision Devices 15" Neo. PDN15BR40 looks to be a good match. It retails at approx £158, is rated at 700W AES, & has a X max of 10.5mm. Maybe more importantly it has a 4" voice coil compared with the Eminence 3".
As usual no figures for thermal compression.
The only quoted thermal compression figures I can find on Precision Devices site are for the PD1850 18" (1.6db at 800W) and the PD1851 (1.7db at 1000W)
The low thermal compression of the PD 18" drivers is no doubt helped by the 5" voice coils.
I would like to add something. Since we can't argue their thermal compression figures since they lack any further information it seems dynamic compression figures are not mentioned either. What I do know is that in tests other PD’s were not better scoring in (lower) pwr compr figures then 'Italian' drivers so it looks like 2,4dB to 3dB total pwr compr. at AES cont. power rating is very likely.

Last edited by Djim; 30th April 2011 at 01:03 AM.
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Old 30th April 2011, 06:56 PM   #1022
Xoc1 is offline Xoc1  United Kingdom
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Djim thanks for pointing out that the PD thermal compression figures do not give the complete picture.
The PDN15BR40 driver on paper seems to have low efficiency at a quoted 96dB/W but when simmed in a TH like the SS15 seems to have the same 'magic' as the Eminence 3015LF in as much as the efficiency of the sim at 1 watt is maybe 2 db more than most drivers. This combined with its increased power handling suggests to me that it is a good substitute driver for the SS15.
As for the 18" extended SS15 layout C/E/X PA Flat to 30 (FT30) PA TH Awesomeness it was posted as a direct response to Crescendos request for a more compact design. I did not really want to dilute this thread with more variations on a theme.
The SS15 style layout is difficult to fold consistently. I am developing this idea still further with all the amassed knowledge that is available on the forum. Albeit at a slow pace as I am very busy at the moment with work.
It's a case of lots of time and no money - or money and no time!
Eventually my target is to build a pair of TH cabs for myself.
I have a mate who has built 8 off PD1850 FLH cabs who can get PD drivers at a good price and has good joinery skills, so eventually I should get around to producing my own killer project to document and share
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Old 1st May 2011, 02:28 AM   #1023
Djim is offline Djim  Netherlands
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Martin, the 96dB sensitivity for the PDN15BR40 shows it is build for low frequency just like the classic RCF L15P200AK and others. These drivers may look less sensitive but in fact if you look to the > 80Hz bandpass they should have better sensitivity then most other drivers. Sensitivity data as part of Thiele-Small are often measured by AES standard bandpass from 100 to 500Hz. That is why these specialized extended LF drivers look less efficient when it comes to sensitivity. For years this has been discussed in the AES organisation but still there is no specialised extended LF bandpass (40-100Hz) measurement standard.

Anyway, Iíll try to get some pwr compr. info about this PD driver so I can do some more accurate modelling with the SS15. The only worry I have is its relative low Bl force. In the SS15 this driver could face some physical difficulties especially at high power but I will check that out.

Your 18Ēextended SS15 seems to work for 15Ē drivers also. +5dB at 40Hz and just -1dB overall compared to Jbellís SS15. In stacks your extended will even more blossom since its 1/3WL is at 38Hz (Jbellís SS15 1/3WL is > 47Hz). I guess you didnít choose 38Hz consciously but this is a very good choice since it stays above the Fs of many drivers.

8 PD1850ís in FLHís, sounds like a Turbo fan to me . Time or no time, you seem to manage to pull out some interesting designs in between all that work.
Attached Images
File Type: jpg JbellSS15_vs_Xoc1SS18.jpg (72.8 KB, 726 views)

Last edited by Djim; 1st May 2011 at 02:40 AM.
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Old 1st May 2011, 04:15 AM   #1024
djk is offline djk
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Click the image to open in full size.

Note that at LF all the drivers are basically the same efficiency, even though there is 9dB difference mid-band (200hz~400hz). The least efficient driver ultimately has the greatest x-max, and thus the greatest bass output. No-=% is only for the octave between EBP and the mass corner.

Click the image to open in full size.

Note that the least efficient driver has the most SPL in the 70hz region, and that the most efficient is going to need at least 3dB more power to have the same output (graphs at 80V RMS drive level).
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Last edited by djk; 1st May 2011 at 04:19 AM.
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Old 1st May 2011, 07:23 AM   #1025
Djim is offline Djim  Netherlands
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Djk, I'm not sure what you are trying to say. In your example you are using drivers of the same brand that were using the same measuring method for measuring sensitivity. Also your example is from different 'type' of drivers and just one could be called an extended LF driver (I know, not a real definition but some European companies use it for their drivers with a dedicated LF task - high Xmax drivers).

In case of Xoc's example both drivers 3015lf and PDN15BR40 have similar Xmax, similar BL and similar mass but different 1w/1m sensitivity data. When you both load them in a SS15 both will have similar 1w/1m sensitivity.

1.) Isn’t the difference in sensitivity because Eminence uses Quote: “the average output across the usable frequency when applying 1W/1M into the nominal impedance.” While Precision Devices uses a standard AES protocol of 50Hz-500Hz, 1W/1m for measuring sensitivity?

2.) Doesn't that mean if you look to the <80Hz area from so called extended LF drivers you can compare the sensitivity better in the sub frequencies?

Last edited by Djim; 1st May 2011 at 07:40 AM.
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Old 1st May 2011, 12:20 PM   #1026
AndrewT is offline AndrewT  Scotland
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The cone area determines the LF output.
This applies whether the driver is very efficient or off ordinary efficiency or of low efficiency.
The efficiency further up the frequency range is determined by the parameters that control efficiency, only one of which is cone area.

Djk seems to be pointing out that improvements in the upper range efficiency are influenced by parameters that reduce LF output. I think he is suggesting that the parameters that give the required LF output, i.e. cone area and optimised parameters that give medium upper range efficiency tend to allow for a better low end performance than if all parameters are optimised for highest efficiency.
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Old 3rd May 2011, 02:30 AM   #1027
Djim is offline Djim  Netherlands
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Thanks Andrew but the confusion was because his second picture didn't show up first. So his second part looked a little odd with the first picture.
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Old 3rd May 2011, 05:30 AM   #1028
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Thank you for taking the time to explain - I appreciate it and now understand what you were saying

Is there a tool/instrument/device to measure the xmax of a driver while loaded in an enclosure?

Quote:
Originally Posted by Djim View Post
Crescendo, I have to apologise for my fuzzy explanation. Besides the language barrier and between all kinds of work, it still difficult to explain in a few words but Iíll try.When people (including myself) talk about power compression it is not always clear what part of the pwr comp. they are referring too:

1.) Thermal power compression: which is the result of electrical values. More power input means more temp rise (which leads to increase of resistance and such)

2.) Dynamic power compression: which is the result of physical values. The higher the excursion becomes the higher the dynamic power compression values become.

When a driver is forced to go below its own Fs excursion will (dramatically) rise as frequency drops. When the driver Fs is higher than the Fs of the system, the Xmax will be reached with less power. But the confusion started when I stated
Instead I should have stated: If your TH's 1/3WL is much below the Fs of the loudspeaker in free space, the thermal pwr comp levels will be lower as max excursion will be reached with much less power. The dynamic compression figures will be higher as max excursion will be reached with less power.

Now back to your question;
No, I expect the L15P200AK with its lower Fs will have less thermal power compression then the 3015lf at the same power in a SS15. Besides power compression I do have my doubts about the 3015lf Xmax data as given by Eminence. Nobody seems to know how Eminence today calculates their Xmax any longer.What I do know is what people show me in their measurements and these give me reasons to believe that the total power compression figures are higher then 3dB at Xmax.

Therefore I would like to see a side by side comparison of an SS15 loaded with 3015lf and L15P200AK.

Hopefully this makes more sense and is less confusing
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Old 3rd May 2011, 05:37 AM   #1029
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Also, I may be willing to purchase 1 or 2 L15P200AK drivers to test against my 3015LF drivers. What guidelines would deem this battle legit?

I'm thinking, same: enclosure, testing equipment, day, distance, power level
And test different: power levels, distances..

If we can (collectively) agree on these things, I'll heavily consider buying the driver(s).

I see that most of the time, a wide open outside space is preferred. But, is it mandatory? Maybe if the position of the enclosure outside and the structures around it aren't TOO close and are constant, valid test may be made.

Thoughts?
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Old 3rd May 2011, 05:39 AM   #1030
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Quote:
Originally Posted by CRESCENDO View Post
Thank you for taking the time to explain - I appreciate it and now understand what you were saying

Is there a tool/instrument/device to measure the xmax of a driver while loaded in an enclosure?
Davy measured displacement in a horn-loaded cabinet using a radar a while back.

It is a lot easier with a tapped horn - you can usually see or touch the cone.
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