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Author Topic: Need Help Choosing Sub  (Read 10863 times)

Ivan Beaver

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Re: Need Help Choosing Sub -for example
« Reply #10 on: October 03, 2012, 08:57:40 pm »

details.

The max SPL is another VERY vague spec.  Yes it may get to a particular SPL-at what freq?  How loud will it get in the intended range? 
Attached is a graph from a popular brand 2x18" sub.  It has a rated sensitivity (20-20K) of 109dB.  And will remain nameless.

If you look at the graph-you will see that it is indeed 109dB AT around 1500 Hz.  So no games there. 

HOWEVER at the low end of its rated response (30Hz) is it around 84dB sensitivity.  That is a difference of 25dB.  That is QUITE a lot-especially if you look at power.  It is the difference between 100 watts and 30,000 watts.  Yes you read that correct.  It would take 30,000 watts at 30hz to be just as loud as 100 watts at 1500 Hz.

Somehow big wattage numbers just don't get that large.  What amp would you use?

THIS is why it is important to look at the real response graph and not just the simple numbers.
« Last Edit: October 04, 2012, 07:23:36 am by Ivan Beaver »
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Ian Murphy

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Re: Need Help Choosing Sub -for example
« Reply #11 on: October 04, 2012, 10:13:18 pm »

Thanks for the info.  Yes, I did understand what you meant Frederik.  Even the dB scale can be influenced by a lot of factors: what is the size and geometry of the room they are using, what is the reflection coefficient for the room, are they even using air? and what temperature?  International standards can help, but is anyone verifying they are conforming? 

From what I believe (although I haven't looked at it in 2 years), good car audio subwoofer and amplifier tests usually use a 50Hz sine signal at 0dB input to amp for their power ratings.  RMS is a Root Mean Square value, and it is an accurate average for a periodic function used across the board for basic electrical engineering power rating.  I'm not sure why this isn't a standard for pro audio.  Its very easy to match amplifiers and subwoofers using this value and about 75% of the car audio companies seem to conform to the standard.  I think the only pro audio companies I've seen use RMS ratings for their subwoofers are JBL and Seismic Audio (the company I just found). 

But regardless, it seems like the way to go is either pay a lot of money for a widely recognized brand, get reliable recommendations, or listen to the speakers for yourself.  I wish there were bigger music equipment stores around here but there are not.  I think I may just have to try these Seismic audio subwoofers and listen to them for myself.  I'm sure they won't sound great but hopefully they will do for now.  If I don't like them you can get a full refund as a company policy.
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Ivan Beaver

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Re: Need Help Choosing Sub -for example-Car specs?????????
« Reply #12 on: October 05, 2012, 07:43:10 am »

Thanks for the info.  Yes, I did understand what you meant Frederik.  Even the dB scale can be influenced by a lot of factors: what is the size and geometry of the room they are using, what is the reflection coefficient for the room, are they even using air? and what temperature?  International standards can help, but is anyone verifying they are conforming? 

From what I believe (although I haven't looked at it in 2 years), good car audio subwoofer and amplifier tests usually use a 50Hz sine signal at 0dB input to amp for their power ratings.  RMS is a Root Mean Square value, and it is an accurate average for a periodic function used across the board for basic electrical engineering power rating.  I'm not sure why this isn't a standard for pro audio.  Its very easy to match amplifiers and subwoofers using this value and about 75% of the car audio companies seem to conform to the standard.  I think the only pro audio companies I've seen use RMS ratings for their subwoofers are JBL and Seismic Audio (the company I just found). 

But regardless, it seems like the way to go is either pay a lot of money for a widely recognized brand, get reliable recommendations, or listen to the speakers for yourself.  I wish there were bigger music equipment stores around here but there are not.  I think I may just have to try these Seismic audio subwoofers and listen to them for myself.  I'm sure they won't sound great but hopefully they will do for now.  If I don't like them you can get a full refund as a company policy.
The input level to the amp means NOTHING! in terms of power capacity of the loudspeaker.  Different amps will have different amount of gain-so different output levels. 

It is kinda like saying the size of the tires relates to the horsepower of an engine.

RMS is a VOLTAGE measurement.  When you look at POWER (especially in a loudspeaker) what is "RMS".  Since the impedance of the loudspeaker is different at different freq-the REAL power is going to vary at different freq.

The use a single freq is also TOTALLY useless in terms of power capacity.  It all has to do with the freq.  How is it that you can take a 8 ohm 200 watt speaker and plug it into a 120V outlet and the speaker be just fine?  That should be 1800 watts going to it.

 If the loudspeaker has a high impedance peak at 60Hz, then the actual POWER going into the speaker will not be very much-but the voltage will.  So if you base your spec on the volatge capacity at 60Hz and 8 ohms-then (wrongly assume) that at all other freq the loudspeaker could handle the same voltage-you have some very high numbers-that mean NOTHING!  Change the freq to something at which the loudspeaker is 8 ohms and it goes POOF real quick.

There are all kinds of games that can be played.  And all kinds of ways to make things look like they can do things they can't.

This is where the simple numbers keep giving false ideas.

The car world is probably the WORST market for making false claims as far as performance goes.  Mainly because of the typical customer and their total lack of any worthwhile knowledge.  So thinking that the pro market needs to be more like that is really going out on limb.  Not one I would want to be on.  Yes there are a few real companies with real specs-but they are very few and far between.

However the pro market is rapidly trying to catch up in terms of stupidity and crap products.  Just give us some time.  And between the two areas-the overall sound quality will get flushed down the toilet and we will be back to original Edison quality-except the audience will be deaf from the levels produced by the bad sound.

Just my opinion-others will vary.
« Last Edit: October 05, 2012, 07:46:53 am by Ivan Beaver »
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Ian Murphy

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Re: Need Help Choosing Sub
« Reply #13 on: October 05, 2012, 04:34:50 pm »

The input level to the amp means NOTHING! in terms of power capacity of the loudspeaker.  Different amps will have different amount of gain-so different output levels. 
Edit:Disregard post (if you really want to read, it is quoted below)
« Last Edit: October 05, 2012, 06:08:18 pm by Ian Murphy »
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g'bye, Dick Rees

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Re: Need Help Choosing Sub
« Reply #14 on: October 05, 2012, 04:44:51 pm »

I disagree with some of that.  0dB input means you are at maximum input voltage to the amp, meaning you aren't clipping and that you aren't sending a low signal.  I haven't been around the pro audio network much, and I think there is definitely an exception on these forums, but my take is that a good percentage of people who buy pro audio equipment are musicians looking to power their gear.  They just want something reliable for them that sounds good to them (and many are experienced with what 'sounds good'), so they can go jam and make music.

Not that I am trying to defend car audio, but a good percentage of car audio customers are people that are really good at working with their hands and making customizations.  There is a lot of information on the web about speaker box construction that is pretty accurate.  You may notice that some of these speaker companies will include information about tuning port frequencies for making custom enclosures.  If you aren't familiar, there are actual sound competitions both on SPL and SQL (power and quality) that take place for cars.  They take real measurements for these competitions, so all of these users are generally in a technical or engineering field that are maximizing sound output, or minimizing distortion. 

RMS isn't a VOLTAGE measurement, it averages any time varying function.  It is used for ELECTRICAL power.  I think what you mean is acoustic power output, that is different.  Generally once you filter out anything above 75Hz, using a full signal 50Hz signal is a decent test.  There will usually be some impedance drop near the resonance of the enclosure and typically this low end is filtered out (say 29Hz). 

Lastly, a good specification included in car audio speakers is max volume displacement.  This is a good way to measure acoustic output.  Its pretty basic, more volume displacement in the cone, more bass, simple as that.  It varies at each frequency but basically for the same frequency, the more displacement you get in the air, the louder the sound output.  The only mention I see of this is commercially available pro audio is that speakers are "long throw".

I didn't mean to go on a discussion about pro audio vs. car audio (especially my first post here :(), but I appreciate your input.  I was looking to see if anyone had any 'best buy for the money' tips on speakers (subwoofers for this forum).

Ian.....

Before you dig yourself too deep a hole, check out Ivan's CV.  He is a top industry pro and you should carefully research anything he tells you before you try to "correct" him.  If he tells you RMS is a voltage measurement, you can take that to the bank. 

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Mac Kerr

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Re: Need Help Choosing Sub
« Reply #15 on: October 05, 2012, 04:54:34 pm »

I disagree with some of that.  0dB input means you are at maximum input voltage to the amp, meaning you aren't clipping and that you aren't sending a low signal.  I haven't been around the pro audio network much, and I think there is definitely an exception on these forums, but my take is that a good percentage of people who buy pro audio equipment are musicians looking to power their gear.  They just want something reliable for them that sounds good to them (and many are experienced with what 'sounds good'), so they can go jam and make music.

No. 0dB is not an audio level, it is a ratio between 2 numbers. Without a reference it has no meaning. If you said 0dBm that would be a power of 1 milliwatt. If you said 0dBu that would be a voltage of .775V. If you said 0dBv that would be a voltage of 1V. If you said 0dBfs that would be the maximum output of a particular piece of digital gear, and could equate to anything from +8dBu - +24dBu.

Quote
RMS isn't a VOLTAGE measurement, it averages any time varying function.  It is used for ELECTRICAL power.  I think what you mean is acoustic power output, that is different.  Generally once you filter out anything above 75Hz, using a full signal 50Hz signal is a decent test.  There will usually be some impedance drop near the resonance of the enclosure and typically this low end is filtered out (say 29Hz). 

RMS is a voltage measurement. That value is often used in the calculation of so called "RMS Power", but the power is not RMS, the voltage measurement used to define it was.

Quote
Lastly, a good specification included in car audio speakers is max volume displacement.  This is a good way to measure acoustic output.  Its pretty basic, more volume displacement in the cone, more bass, simple as that.  It varies at each frequency but basically for the same frequency, the more displacement you get in the air, the louder the sound output.  The only mention I see of this is commercially available pro audio is that speakers are "long throw".

I didn't mean to go on a discussion about pro audio vs. car audio (especially my first post here :(), but I appreciate your input.  I was looking to see if anyone had any 'best buy for the money' tips on speakers (subwoofers for this forum).

Lastly, a good way to lose any credibility in these forums is to start a discussion about car audio. It has nothing to do with pro audio, no matter what the people involved in it think.

There have been literally hundreds of discussions on what subwoofers have good value, or very high output, or really suck, and some searching in the forums will let you read hundreds if not thousands of opinions.

Mac
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Jay Barracato

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Re: Need Help Choosing Sub
« Reply #16 on: October 05, 2012, 04:58:17 pm »

I was laughing too hard to respond.
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Jay Barracato

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Re: Need Help Choosing Sub
« Reply #17 on: October 05, 2012, 05:12:58 pm »

I was laughing too hard to respond.

I'm waiting for the other shoe to drop........
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Ian Murphy

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Re: Need Help Choosing Sub
« Reply #18 on: October 05, 2012, 05:24:49 pm »

Ugh, I did dig myself into a hole and I got nothing out of it.  I feel like this was their intention all along...Okay, well hopefully you all at least got some laughs out of this.

Yes Ivan was correct, I didn't read through his post carefully enough.  I'm sure you have infinite more experience with speakers and audio systems than I do, so I'll stop trying to defend anything.  I did a search already on some of these speakers, basically what I got out of it is "XX company is crap, spend more money".  Oh well :-\
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g'bye, Dick Rees

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Re: Need Help Choosing Sub
« Reply #19 on: October 05, 2012, 05:29:47 pm »

Ugh, I did dig myself into a hole and I got nothing out of it.  I feel like this was their intention all along...Okay, well hopefully you all at least got some laughs out of this.

Yes Ivan was correct, I didn't read through his post carefully enough.  I'm sure you have infinite more experience with speakers and audio systems than I do, so I'll stop trying to defend anything.  I did a search already on some of these speakers, basically what I got out of it is "XX company is crap, spend more money".  Oh well :-\

Good for you.  It takes a solid person to 'fess up when they've been hasty.  You are to be commended for taking any lumps.

I wouldn't say "spend more money".  I will stick by my assertion that spending any money on Seismic brand speakers is pretty much a waste.  You could get very good "industry standard" subs used for the price of a new Seismic box. 

I hope you stick around.  This is a great place to learn and ask questions.  It may take some getting used to, but it's worth it.

I wish you success in your quest.
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Re: Need Help Choosing Sub
« Reply #19 on: October 05, 2012, 05:29:47 pm »


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