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Old 3rd May 2011, 06:41 PM   #1031
Djim is offline Djim  Netherlands
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Crescendo, there is no commercial tool for measuring Xmax. I have seen different methods from high speed cameraís or lasers to a simple paperclip with a ruler so its up to your imagination and your budget. Just keep in mind the more complicated you make a measurement the more can go wrong.

If you want to compare the L15P200AK with the 3015lf you need power. In sensitivity test (1w/1m) they probably measure the same. At full continue sine wave power for the 3015lf (450Watt IEC standard) you can expect to see/hear a difference in favour of the RCF. The cause is the expected higher power compression of the 3015lf at this point. Also it wouldnít surprise me if you will see a bigger difference below 60Hz then in the higher frequencies. It is this part of the bandpass Iím particularly interested in.

The RCF also has quiet some headroom left since that driver should be able to handle 750Watts continue sine wave power. For music power you will need an amp of 1500 Watts (peak) to get the full power out of the L15P200AK. But as usual in both cases use your ears to hear if the sound doesnít get distorted.

The reason a open space (2Pi) is preferred is to make sure no external factors like reflection from objects/buildings will take place. Especially in room measurements can have dramatic effects on your measurement. For instance 1 meter change in position indoors can give completely different results. Therefore measuring outside and if possible as far as possible from any building or objects is preferable. Sand walls/bluffs have less influence then structures. Sand has the ability to absorb sound waves.

Few notes:

1.) Good measurements start with good planning and preparation.
2.) Both drivers have a different resistance (Re) which means you need to calibrate them independently to get 1w/1m.
3.) If you donít have access to a True RMS meter specialised for audio measurements you canít measure music or complex audio signals. With standard multimeters (true RMS or not) you can only measure sine-waves. True RMS is not really necessary although it should give you more accurate results (the difference isnít as big as many people suggest here on the forum).
4.) Use a quality amp for high power measurements to make sure you can Ďfeedí the drivers with clean power.
5.) Make sure your power supply cabling is able to handle the power the amplifier needs. Also make sure the loudspeaker cable is short as possible and able to handle the heavy loads.
6.) Always write down (logbook) every step, every change in your measurements.
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Old 3rd May 2011, 10:10 PM   #1032
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My QSC RMX2450 can supply 1300W rms FTC/1500W rms EIC @ 8 ohms/0.1% THD (bridged). Would that be acceptable?

First of all, my plan is to test outdoors. The further other objects are, the better. But, how far must they be (at least) to deem the experiment valid?

The steps above sound good and do-able to me. I do not own an RMS meter though. Not sure what type is recommended and/or if they are pricey either. I would definitely be interested in investing in one if it won't break the piggy bank.

Anyone get wholesale prices on RCF goods?
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Old 3rd May 2011, 11:13 PM   #1033
Djim is offline Djim  Netherlands
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There is no general rule for distance of objects/buildings. It also depends on how big they are and the direction of the wind. Just try to get as far away as possible but if you post your measurements make a small map of the surroundings so everybody is able to see the influences.

You don’t actually need a True RMS meter if you measure with continue sine wave signals around 50Hz. If you calibrate power (by measuring AC Voltage) start at point where the impedance is the lowest in the HornResp prediction. In case of the SS15 that is around 45Hz (that is also close enough to your multimeter calibration point of 50Hz).

Any relative cheap multimeter will do. However, the more digits behind the dot the more accurate is suppose to be. That’s why I prefer to use a multimeter with at least 3 digits behind the dot so you can calibrate to 2,830 AC/Volts. If you use a meter with only 2 digits behind the dot you can end with 2,839V or 2,821V in a worst scenario.

Most people here on this forum set their amp to 2,83Volt for their SS15 but that is actually not correct. That’s why they measure higher 1W/1m SPL figures as predicted by HornResp. If you want to compare with other members here on DIY you should use this ‘incorrect’ method.

If you want more correct measurements you need to measure first the Re of the driver + the connected loudspeaker cable. It will be around 5,4Ohm (1watt = 2,3238 Volts in this case). For a handy online calculator you can use this link.
This method only works for continues/frequency stable sine waves. Complex signals or signals of different form can only be measured with specialised equipment.
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Old 26th May 2011, 11:07 PM   #1034
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Quote:
Originally Posted by Djim View Post
You seem to use the old specs of the driver that show better Thiele-Small parameters.

The Kappa Pro-15LF-2 at 53 volt has a theoretical HornResp excursion of 10,5mm. The reality is this drivers suffers from at least 3dB pwr/dyn compression at Xmax. This means you will need twice the power to reach Xmax in reality.

Xmax theoretical = 40V at 6,12Ohm = 265Watt
Xmax theoretical -3dB pwr/dyn compression = 530Watt

Like I said at LEAST 3dB so powering this driver to its 600 watts continues power rating is absolutely NO problem!

That's why I said people are way to much concentrating on theoretical Xmax while they don't seem (or want?) to understand the impact of power/dynamic compression. Although I never work with Eminence the 3dB seems to be the (lowest) value I get from other users.
As far as I know only RCF and 18Sound include pwr compression data with their drivers.
If I'm getting this right, though it will take more power to get the Kappa Pro 15LF-2 to reach xmax due to compression, it will still only put out the modeled SPL at its xmax (125dB @ 100Hz @ 6.7mm xmax, for example) -- if I'm understanding this correctly from our other thread:
Quote:
Originally Posted by Djim View Post
Excursion is directly coupled to SPL and power not. So less excursion (because of pwr comp) results in less SPL.
If this is correct, the Kappa Pro 15LF-2 at xmax is 3dB quieter @ 100Hz than the 3015LF at xmax (128dB @ 100Hz @ xmax)

Since both drivers are susceptible to either types of compression, the Pro 15LF-2 might make it closer to xmax (in turn, closer to the modeled SPL) a little easier than the 3015LF since it's further from its thermal limits than the 3015LF at their modeled xmax -- the Pro 15LF-2 is still quieter at xmax, however.

Am I narrowing in on this correctly?
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Old 27th May 2011, 12:04 AM   #1035
Djim is offline Djim  Netherlands
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Quote:
Originally Posted by CRESCENDO View Post
If I'm getting this right, though it will take more power to get the Kappa Pro 15LF-2 to reach xmax due to compression, it will still only put out the modeled SPL at its xmax (125dB @ 100Hz @ 6.7mm xmax, for example) -- if I'm understanding this correctly from our other thread:

If this is correct, the Kappa Pro 15LF-2 at xmax is 3dB quieter @ 100Hz than the 3015LF at xmax (128dB @ 100Hz @ xmax)

Since both drivers are susceptible to either types of compression, the Pro 15LF-2 might make it closer to xmax (in turn, closer to the modeled SPL) a little easier than the 3015LF since it's further from its thermal limits than the 3015LF at their modeled xmax -- the Pro 15LF-2 is still quieter at xmax, however.

Am I narrowing in on this correctly?
In my quote about the 3015lf I was using info from others. I don't know the exact numbers for Eminence drivers. All I know is that Eminence doesn't supply enough information and what they supply is not confirming AES standards. But it looks like you got it right in theory.

The thermal capabilities of a driver are set out by the AES power ratings. Therefore if you need to reach Xmax (BL70%) or even Xvar (BL50%) in reality you need to check the power ratings of the driver if the voice coil is capable of handling the power. That's why I stated that people shouldn't focus so much on Xmax and instead focus on the power ratings. And again, if the Fb of the system is below the Fs of the driver it will be different.

Normally when they design a quality PA driver they search for a balance between power ratings and excursion. In other words, a well designed PA driver should reach its Xmax around its AES continue power rating and its Xvar around its max power (and still have enough crest factor to deal with power peaks). But the reality is that not every brand use this principle of balancing their drivers.

Last edited by Djim; 27th May 2011 at 12:15 AM.
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Old 29th May 2011, 02:17 AM   #1036
Djim is offline Djim  Netherlands
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Exclamation Cheap 80 Euro alternative for Eminence 3015lf

For the European DIY builders on a very tight budget there is a cheap alternative driver for the SS15, the DAP AB-15 that you can find for about 80 Euro's.

Although factory specs suggest it is rated as 400W continue and 800W max, I wouldn't go beyond 500Watts that much. Still, for the price for one 3015lf you can have 2 Dap's.
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File Type: jpg SS15_DAP_AB-15_01.jpg (94.0 KB, 708 views)
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Old 9th June 2011, 05:52 PM   #1037
jbell is offline jbell  United States
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As requested, here's links to the plans. (is there a moderator way to add this info the post1???)

http://www.diyaudio.com/forums/attac..._aug18_dwg.pdf

http://www.diyaudio.com/forums/attac...le_revised.pdf

These come from post 74 and post 622. Kappa pro 15lf2 works in place of the (now) more expensive 3015lf, as do several other drivers.

Thanks to all who contributed.
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Old 23rd June 2011, 06:49 PM   #1038
Djim is offline Djim  Netherlands
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Default Fiction or truth?

Jbell, a while ago you asked why the LF output looks different from predictions, especially below 1/3WL. I’m working on a possible answer that I want to show.

Think of flutes, remember? 1/6th extension outside the cab, (1/3 WL) 50Hz – 1/6th = 50 – 8,3 = 41,7Hz (ring any Jbells yet, try the harmonic tests with same Voltage from 40 to 44Hz by 1/2Hz steps)

Now the big question, what if the main system works as a Tapped Horn but the driver also sees an Offset Horn in the same construction. Now let’s see what HornResp says:


Click the image to open in full size.


You can clearly see where the two designs cross each other 41,7Hz (coincidence?). You can also see the LF extension below this point. Also look carefully to the +60Hz knee in the response of the offset horn. Now think how these two graphs can influence and integrate with each other (and what would the possible outcome be if you add both).

Compare those findings, to what you have measured with your Smaart and see if you find any resemblances (Ps did you make measurements without Low-cuts yet)?
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Old 23rd June 2011, 07:07 PM   #1039
jbell is offline jbell  United States
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Hmmm.... have to think on that a bit. I do know I've asked if I need to take 'horn bubble' into account, because every TH plays just a bit lower than hornresp says, and I've been told it's already accounted for... But yes flute and 1/6th -- got it.

I will tell you, because I've done 1hz sine wave tests... 42hz is the edge of the cliff. It's freefall from there on down.

For whatever reason... I have only done tests with my high pass on, even the current 32hz 24db/oct high pass. I guess I just have this feeling in the back of my mind, that I'll disable the high pass, and then a surprise will happen later... (oops, sorry dad... cooked your sub... but it was fun while it lasted !!)

I'd rather keep the high pass, and the password protection on the crown... just for my peace of mind.

Last edited by jbell; 23rd June 2011 at 07:09 PM.
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Old 23rd June 2011, 07:17 PM   #1040
Djim is offline Djim  Netherlands
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Don't go below 20Hz (not interesting anyway) or above 15V (41W for your driver) and you'll stay under 10mm excursion.

Last edited by Djim; 23rd June 2011 at 07:26 PM.
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