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Author Topic: High power subwoofer performance  (Read 3243 times)

Gareth James

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High power subwoofer performance
« on: March 22, 2006, 11:10:42 am »

Hi folks,

I have been doing some research lately into a very high power subwoofer design and have been trying to find a suitable 12" driver to work with.

Some of the drivers I have been looking into are the Beyma 12LX60, B&C 12TBX100 and Ciare 12.00SW.

With the exception of the LX60 (which is rated at 700w AES) the other two are both rated 1000w. All the drivers use 4" voice coils and have similar Xmax and Xmech ratings. (Thiele-smalls params maybe different but I'm looking to design the car around the engine and not the other way around - so to speak)

However as most will already know, in any aspect of a speaker design power in does not equal power out...

Basically I have been doing research into power compression characteristics of drivers so that I might find the best tool for the job.

Beyma quite handily include a power compression graph (vs power input) on most of their downloadable spec sheets. Having enquired at B&C they very kindly offered to try and replicate as closely as possible the test which led to the following results:

index.php/fa/4349/0/

Now obviously its not an apples to apples comparison as the LX60 is rated at 700w however it does seem to give a good indication as to the losses (and gains) that might be had from picking the right driver.

I am looking into this as I have reached the conclusion that even with amplifier technology becoming cheaper I believe a loudspeaker should warrant its power rating. If half of the power is being wasted due to heat emission then that defeats the point in my eyes... Rolling Eyes

Any thoughts guys?
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Mark Seaton

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Re: High power subwoofer performance
« Reply #1 on: March 22, 2006, 12:46:35 pm »

I would caution against trying to compare such measurements without careful comparison of all the factors involved.  For results to have any meaning, you need to look at the total impedance curve of the driver in the test box.  Then you have to look at the spectrum of the test signal.  

For a simple driver in a sealed box, you will get the worst case power compression driving a sine wave at the Rmin that falls above Fb and before the inductive rise, or at really low frequencies, but there you have to watch out for over-excursion.  You will see the best case for this sealed box example when driving a sine wave at Fb.  If the two drivers have the same in-box Fb, and have similar thermal characteristics, the driver with greater motor strength will have less current through the voice coil at Fb.

Let's remember that it is in fact current through the voice coil that causes heat.  More specifically, current x Re (or Rdc) of the voice coil is what defines heat.  So when the impedance peaks, current goes down, even though voltage is the same.

In the case of a vented box, the worst case is at the tuning frequency.  Here there is both an impedance minimum as well as a minimum of driver excursion.  Of course as that port starts to choke off, excursion and impedance goes up.  Call it thermal protection by distortion. Rolling Eyes  It's also what many amplifier manufacturers expect and design for to maximize power.  If you design a speaker with a minimum of compression and non-linearities, make sure the amp power specs are relevant to your application.  Shocked

In a horn, where we see often a rise in impedance over a wider band, it should come as no surprise that thermal performance will be better.

Personally, and especially while peaking over Tom Danley's shoulder, I've come to realize that while some drivers do behave much better than others, power handling is much more indicative of durability to abuse and how bright you can make the voice coil wire glow with the crazy amounts of power we have available today.  Of course once you get past about 3dB of compression, additional average power really doesn't do much for you.  If you keep going deeper with the investigation, you will probably find that box design and appropriate driver parameters give you a much bigger "lever" on the thermal capabilities than driver construction.  After you maximize that aspect, then you just need a driver that can withstand the level of "abuse" you expect to dish out.

My 2c.
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Mark Seaton
Seaton Sound, Inc.
"Make no little plans; they have no magic to stir men's blood..." - Daniel H. Burnham

Ivan Beaver

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Re: High power subwoofer performance-NICE!
« Reply #2 on: March 22, 2006, 07:19:39 pm »

As in all things audio (and otherwise) you cannot simply give performance specs in a single/simple number.  You have to know all of the details on how it was measured and what was used to generate the signal.

How loud will it go?  How low will it go?  How much power will it take? What is it's coverage pattern? What is the sensitivity? etc.  It all depends----

Nice response.
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For every complicated question-there is a simple- easy to understand WRONG answer.

Can I have some more talent in the monitors--PLEASE?

Ivan Beaver
dB Audio & Video Inc.
Danley Sound Labs

Tamas Tako

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Re: High power subwoofer performance
« Reply #3 on: March 23, 2006, 11:28:53 am »

Hi,

as stated here by the "gurus"  Very Happy  this is not that simple.

The power compression vs input power is not really the diagram you need for this type of enclosure.
If you like to build a sub, you need a Power compression graph of power comp. vs. I2xRdc. I mean considering the efficiency vs. frequency graph and the power comp. vs. input power graph is the correct way.

In addition, you also need to know the Xcursion vs. input power graph to know the total power compression vs. input power at different frequencies.

BTW the power compression of the two different speakers (beyma and the B&C 12") can not be that different that the graph shows... I personaly think this is due to the different measuring method as Ivan stated...


If you really like to design a good subwoofer box, then you first have to determine your goals regarding frequency response, efficiency (sensitivity, pattern control) power ratings, dimensions and shape, applications etc...

good luck,

Tamas
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