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Author Topic: Speaker rating advice  (Read 2215 times)

Guy Morris

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Speaker rating advice
« on: October 04, 2011, 06:24:24 am »

Hello

As a d&b user these days I never really need to concern myself over the amp/speaker power issue and my other stock is Lab Gruppen  FP+ series where they rate their outputs as continuous power with tables for setting the amps to the correct output for whichever speakers are being used (very versatile) However I recently decided to resurrect my original Turbosound TMS series which has been mothballed for sometime, the initial idea was to sell it but frankly it sounds so good  for certain applications I decided to bring it all back up to spec and maybe get it earning again!  Going through the spec sheet I noticed the speakers are rated as RMS with a PROGRAM rating listed as well. eg 450w RMS  and 900w Program, but I'm not sure what the term 'program' in this case means?(never see it these days on spec sheets)

What amp power would you suggest should be used for a 300w RMS 18" and a 150 w RMS mid high?  (TMS 4) I have always worked on the principle of the amp output matching the speaker RMS rating with the Sub amp being marginally higher to allow for the LF dynamics.

As I will be using the Lab Gruppens to power these using the dip switch settings to obtain the correct output I'd welcome suggestions of best safe practice output rating to protect the drivers from any overdrive but do not want to underpower them either! If I recall the original drive amps were C Audio RA 3000 for LF and RA1000 for Mid high and I remember that that the LF amp did run out of steam quickly!

The boxes are being run via BSS FDS 360 with 250 X/o cards originally specified by Turbo.

The other year I had the pleasure of meeting Tony Andrews at PLASA, now he would have been the man to ask!

Advice welcome

Thanks


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TJ (Tom) Cornish

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Re: Speaker rating advice
« Reply #1 on: October 04, 2011, 09:22:23 am »

Hello

As a d&b user these days I never really need to concern myself over the amp/speaker power issue and my other stock is Lab Gruppen  FP+ series where they rate their outputs as continuous power with tables for setting the amps to the correct output for whichever speakers are being used (very versatile) However I recently decided to resurrect my original Turbosound TMS series which has been mothballed for sometime, the initial idea was to sell it but frankly it sounds so good  for certain applications I decided to bring it all back up to spec and maybe get it earning again!  Going through the spec sheet I noticed the speakers are rated as RMS with a PROGRAM rating listed as well. eg 450w RMS  and 900w Program, but I'm not sure what the term 'program' in this case means?(never see it these days on spec sheets)

What amp power would you suggest should be used for a 300w RMS 18" and a 150 w RMS mid high?  (TMS 4) I have always worked on the principle of the amp output matching the speaker RMS rating with the Sub amp being marginally higher to allow for the LF dynamics.

As I will be using the Lab Gruppens to power these using the dip switch settings to obtain the correct output I'd welcome suggestions of best safe practice output rating to protect the drivers from any overdrive but do not want to underpower them either! If I recall the original drive amps were C Audio RA 3000 for LF and RA1000 for Mid high and I remember that that the LF amp did run out of steam quickly!

The boxes are being run via BSS FDS 360 with 250 X/o cards originally specified by Turbo.

The other year I had the pleasure of meeting Tony Andrews at PLASA, now he would have been the man to ask!

Advice welcome

Thanks
In rough terms:

"RMS" or "continuous" or "long term" relates to the driver's ability to handle some kind of low crest factor signal for a long time without burning up.  Think sustained bass notes of certain types of dance music, etc.

"Program" is usually 2X the continuous number, and takes into consideration that most music does not resemble continuous noise (though some does ::) ), and therefore the driver can handle more power than the continuous rating while playing back normal music.

"Peak" is usually 2X the program number, and relates to the speaker's instantaneous ability to handle high power for short durations.

These numbers are simple representations of complex phenomena, and you don't know what they really mean unless the manufacturer tells you how they tested. 

You can read through hundreds of threads on this and the old forum dealing with how to power loudspeakers.  In a few sentances, here's a brief summary:

"A too small amplifier contributes to loudspeaker damage, and a larger amp will be "safer" than a small one." - This is a false statement that comes from folks believing that a smaller amp would be more likely to be run into clipping, which increases the average power to the driver, etc.  In reality, the moron who allows a small amp to clip will surely allow the larger amp to clip as well.

"Clipping causes speaker damage".  This is also a false statement, at least as an axiom.  Clipping only causes speaker damage if the resulting power exceeds the driver's thermal or excursion capacity.  A driver will happily produce a square wave indefinitely if the power level of that square wave does not exceed the driver's capability.

These fallacies aside, there is a general best practice of having an amplifier capable of at least 2X the continuous rating of the driver, to allow for some headroom and get a little more out of the speakers.  If the amp is kept out of clipping, this is usually a safe situation.  There isn't any magic about 2X the continuous number - you can use a huge amp on a small driver without issue, as long as you limit the output of the amp to be within the driver's capability.

To more directly answer your question, you can calculate using the input sensitivity and the gain of your amplifiers to determine what input voltage will produce the level your speakers can handle.  Set up limiters to keep you in that vicinity, and then use your ears, eyes, and nose to make sure that your speakers are happy.  If your speakers are distorting or start to smell, they are being overdriven.

Note that due to the logarithmic nature of the relationship between amplifier power and dBSPL output, turning down just 1 or 2 dB can make a huge difference on how hard your speakers are working, and be easier on your power supply as well.
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DomHarter

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Re: Speaker rating advice
« Reply #2 on: October 04, 2011, 12:52:47 pm »

Hi Guy,

Send an email to Chris K techsupport@turbosound.com with your exact configuration and he will give you the limiter setups for your labs, please make sure you list which gain settings you have picked on the amps

Alternatively download this excel

http://www.turbosound.com/helpdesk/index.php?_m=downloads&_a=viewdownload&downloaditemid=90&nav=0

It has the settings for TMS under legacy products and a simple limiter calculator

Hope this helps
Dom Harter
Turbosound

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Brad Weber

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Re: Speaker rating advice
« Reply #3 on: October 05, 2011, 05:43:35 am »

TJ hit on the basics.  The test signal most commonly used for speaker power testing is shaped to have a particular frequency response and intentionally clipped to have a 6dB crest factor.  The continuous or long term power rating is the result of that testing.  The peak power rating is then based on the 6dB crest factor of the test signal, thus the peak level is 6dB or 4 times to continuous or long term rating.  The program power rating is, as TJ noted, some recognition that a 'real world' music signal may fall between those two extremes and thus it is typically calculated to be midway between the continuous and peak power ratings.

The proper amp rating is the one that provides sufficient output and headroom while not stressing the speaker.  If you have a specific application then it may be possible to calculate the appropriate power (actually voltage) for that application.  The 2X the continuous rating of the speaker 'rule of thumb' is intended to address situations where there are no specifically defined applications or there may be a range of applications involved.
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Guy Morris

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Re: Speaker rating advice
« Reply #4 on: October 05, 2011, 12:18:28 pm »

TJ hit on the basics.  The test signal most commonly used for speaker power testing is shaped to have a particular frequency response and intentionally clipped to have a 6dB crest factor.  The continuous or long term power rating is the result of that testing.  The peak power rating is then based on the 6dB crest factor of the test signal, thus the peak level is 6dB or 4 times to continuous or long term rating.  The program power rating is, as TJ noted, some recognition that a 'real world' music signal may fall between those two extremes and thus it is typically calculated to be midway between the continuous and peak power ratings.

The proper amp rating is the one that provides sufficient output and headroom while not stressing the speaker.  If you have a specific application then it may be possible to calculate the appropriate power (actually voltage) for that application.  The 2X the continuous rating of the speaker 'rule of thumb' is intended to address situations where there are no specifically defined applications or there may be a range of applications involved.


Thanks guys for the excellent explanations advice and link, that should sort it all ! After the refurbishment I'd hate to mess up  on a rating mistake so caution is wise.

Guy
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ProSoundWeb Community

Re: Speaker rating advice
« Reply #4 on: October 05, 2011, 12:18:28 pm »


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