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Author Topic: Which subs to buy? Paralysis by analysis  (Read 19105 times)

Ivan Beaver

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Re: Which subs to buy? Paralysis by analysis
« Reply #10 on: October 05, 2014, 04:41:13 pm »


Perhaps because they call the peak +6db? Or it's -3db from the average across some unknown freq range.  The fun of spec sheets.
If the low freq number is not directly tied to the sensitivity number-then they don't mean anything-or they could mean "anything".

For example:  If you want higher sensitivity number to put on the spec sheet-then that means that the low freq number ALSO will be higher.

Or if you want a lower freq number-then the sensitivity number will be lower.

You DO NOT (or shouldn't anyway) get to choose the numbers independently.

ONCE AGAIN you see the IMPORTANCE of showing the actual MEASUREMENT-so the user can "choose their own numbers" from the graph or interpret how they want to read it.

For example: If you have a measured response you can look at it and see what the sensitivity is at a particular freq and then "do the math" and figure out how loud it can get at that freq.

Without a measured response-you have NO IDEA how loud it is at a particular freq. and no way to even begin to guess-unless you measure it yourself.

I know I harp on this a lot- BUT IT IS IMPORTANT-at least as a first step to figuring out the actual performance of a particular loudspeaker.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Ara Ayrassian

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Re: Which subs to buy? Paralysis by analysis
« Reply #11 on: October 05, 2014, 05:06:13 pm »

Danley doesn't rate their subs with 1W 1M. They use 2.83V.  Which for an 8 ohm cabinet is essentially 1W/1M.  But for a 4ohm cabinet it's more like 2W/1M.  So a TH-118 would have to be derated by 3dB to compare "spec for spec" to other 4 ohm subs.... Which isn't the best practice anyway. Your best bet is to do exactly what you did, and listen for yourself.


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Prior to having Danleys I had a pair of JBL 4719A subs I purchased a pair of TH115's 4 ohm and when I did a A & B test there was absolutely no comparison the Danleys were a overall winner.
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Ivan Beaver

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Re: Which subs to buy? Paralysis by analysis
« Reply #12 on: October 05, 2014, 05:37:48 pm »

Danley doesn't rate their subs with 1W 1M. They use 2.83V.  Which for an 8 ohm cabinet is essentially 1W/1M.  But for a 4ohm cabinet it's more like 2W/1M.  So a TH-118 would have to be derated by 3dB to compare "spec for spec" to other 4 ohm subs.... Which isn't the best practice anyway. Your best bet is to do exactly what you did, and listen for yourself.


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If you want to "play a little game", take a look at the Th118 spec sheet.

http://www.danleysoundlabs.com/danley/wp-content/uploads/2012/04/TH-118-spec-sheet2.pdf

Look at 93ish Hz.  see that impedance peak?  Now look at the amplitude at that freq.

The sensitivity is around 109dB with the 2.83V input.  Which is less than 1 watt at that freq.  So figuring the impedance is around 9.2 ohms-the voltage required to get 1 watt is a little over 3 volts.  The difference between that voltage and 2.83V (the applied voltage) is around 0.6dB.

So using the "1 watt" method-the cabinet produces around 109.6dB with 1 watt (at one freq) below 100hz.

So the cabinet "could" be rated at 109.6dB below 100Z 1W/1M and still not be lying.

AND WHILE WE ARE AT IT-what does the 1M really mean?

Danley does not measure the subs at 1M.  If we did, then the ACTUAL MEASUREMENT would be HIGHER.

We measure subs at 10M (a 20dB loss in distance) and drive at 28.3V (a 20dB increase in level) so they cancel each other out.

So this brings us to the REAL reason for specs.  What is that?

In my opinion, it should be used so that an sound designer can get an idea of what a particular product will perform like at some distance (NOT 1M) away from the cabinet.

If Danley were to use the actual SPL measured at 1M, then at say 20M away the SPL somebody would measure would be LESS than the calculated SPL-using the 1M spec.

But by using the 10M measurement-and "back calculating" you end up with a number (all be it lower than what it actually measures at 1M) that WILL calculate out to longer distances-so the number presented is actually USABLE and not some "inflated number" that looks good on a spec sheet.

Now this works the opposite way as well.

Take the Danley SH25.  If you were to actually measure it at 1M, you would read LESS than the rated sensitivity by almost 6dB.

So is this number false?  NO.  The number is used to figure out how loud the cabinet will be at a longer distance-and it is measured a distance away and again, back calculated to 1M

So why is the measured number lower?  It is because of the depth of the horn.

In the SH25 the acoustic origin is physically almost 1M behind the grill.  So it has undergone a good bit of "expansion" before it even gets to the grill-so the mic is actually close to 2M away from the acoustic origin or source.

But if you use the rated sensitivity and figure out the SPL at say 20M-the number you would measure is the same as the calculated.

Once again-it is IMPORTANT to understand what the numbers actually mean and where they come from-how they are determined etc.

The numbers should translate into the REAL WORLD in a way that is useful to a designer.

If not-then they are pretty much useless.

PS  I know that some other manufacturers use the same methods-but not all.  Hence the reason to know where the numbers come from.

Are they on the spec sheet to look good-or to actually MEAN something useful?

That is often a tough question.  Who put them there-the engineering team or the marketing team?
« Last Edit: October 05, 2014, 05:46:46 pm by Ivan Beaver »
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

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David Sturzenbecher

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Which subs to buy? Paralysis by analysis
« Reply #13 on: October 05, 2014, 07:23:26 pm »

If you want to "play a little game", take a look at the Th118 spec sheet.




No thanks, I'm good. Nothing you haven't preached on numerous times before.  Most of my use for spec sheets anymore is to find out how much something weighs, so I can tell someone else how heavy it is so they can lift it for me... And to maybe get an idea of how to power something. But typically I already know that from the last job. There are much better methods for finding out all the other stuff. You can't tell how good a speaker sounds from a spec sheet. I have heard speakers with really good specs sound really bad.




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Ray Aberle

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Re: Which subs to buy? Paralysis by analysis
« Reply #14 on: October 05, 2014, 07:40:53 pm »

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Not to mention it is difficult to look at spec sheets when they don't download properly. I wish website designers wouldn't require special "somethings" in order to use their sites.....
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Bob Leonard

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Re: Which subs to buy? Paralysis by analysis
« Reply #15 on: October 05, 2014, 07:45:42 pm »

Really Ivan, WTF, does every reply have to be a sermon?

OP,
Any of the subs you listed will do a decent job for you. I would look towards the SRX728 which are obsolete, but can be found, and will do a very good job. The only thing you may not like about the 728 is the size and weight, but it is a formidable dual 18" cabinet that many of us rely on with great success and very, very few failures. The STX 828 is also a great sub with the same capabilities as the 728. The drivers are not the same, and the 2242 used in the 828 will produce good quality sound at slightly lower frequencies than the 728, but either sub will produce very high quality sound capable of rolling your socks up and down at high levels.
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Ray Aberle

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Re: Which subs to buy? Paralysis by analysis
« Reply #16 on: October 05, 2014, 07:53:52 pm »

Really Ivan, WTF, does every reply have to be a sermon?

OP,
Any of the subs you listed will do a decent job for you. I would look towards the SRX728 which are obsolete, but can be found, and will do a very good job. The only thing you may not like about the 728 is the size and weight, but it is a formidable dual 18" cabinet that many of us rely on with great success and very, very few failures. The STX 828 is also a great sub with the same capabilities as the 728. The drivers are not the same, and the 2242 used in the 828 will produce good quality sound at slightly lower frequencies than the 728, but either sub will produce very high quality sound capable of rolling your socks up and down at high levels.

Sales? lol.

Is a dual 18" OK for the OP? The 728s are 168lbs... just wanted to make sure. A pair of the 718S will make it easier to deal with, if the weight ended up being a concern...
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Kelcema Audio
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Peter Morris

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Re: Which subs to buy? Paralysis by analysis
« Reply #17 on: October 05, 2014, 08:48:45 pm »

Danley doesn't rate their subs with 1W 1M. They use 2.83V.  Which for an 8 ohm cabinet is essentially 1W/1M.  But for a 4ohm cabinet it's more like 2W/1M.  So a TH-118 would have to be derated by 3dB to compare "spec for spec" to other 4 ohm subs.... Which isn't the best practice anyway. Your best bet is to do exactly what you did, and listen for yourself.


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Agree, and FWIW I donít think its good practice either, just about every other manufacture specifies 1 watt per meter referenced to the nominal impedance. E.g. - 2.83 volts for 8 ohms and 2.0 volts for 4 ohms.

We measure how powerful speakers (and amplifiers) are in watts, and itís logical to compare their efficiency relative to watts.
 
I understand impedance, and all the issues Ivan discusses.  I just think what Danley is doing can be misleading, especially for those people who donít fully understand the specifications.
« Last Edit: October 05, 2014, 09:17:32 pm by Peter Morris »
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Ivan Beaver

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Re: Which subs to buy? Paralysis by analysis
« Reply #18 on: October 05, 2014, 09:17:15 pm »


Not to mention it is difficult to look at spec sheets when they don't download properly. I wish website designers wouldn't require special "somethings" in order to use their sites.....
I don't have anything "special" on my computer-just the normal stuff-whatever that is.

Are you trying to use something "special" or different"

It would be nice to know what operating system-what browser you are using so problems like this can be addressed.  without that knowledge-there is no way to even think about looking at the problem.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Sammy Barr

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Re: Which subs to buy? Paralysis by analysis
« Reply #19 on: October 05, 2014, 09:19:30 pm »

The QWs are very good subs and match very well with the qw4s. I used that setup today and they sounded great. The VR is better still. Easier to move, more internal bracing, better drivers. Both speakers are reasonably priced and are very durable.
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Re: Which subs to buy? Paralysis by analysis
¬ę Reply #19 on: October 05, 2014, 09:19:30 pm ¬Ľ


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