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Author Topic: 120 db at 40 hz?  (Read 1404 times)

Dan Erni

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120 db at 40 hz?
« on: October 05, 2019, 11:52:36 am »

Hello all.  I've got a 30'x50' workshop that I want to equip with a good, loud and relatively low cost (I know, can only have two of the three) sound system.  I've narrowed my search for mains to a pair of 10" or 12" two-way boxes run in stereo, and am looking for a sub (or two if needed) to get me around 120 db at 40 hz.  To be more specific, I want the sub to have fairly flat response to 40 hz or lower.  No much use if it will do 120 db at 40 hz while it's doing 130 db at 60 hz, right, and don't want to force it into unhappy operating range with heavy handed EQ.  I'm avoiding the budget stuff (Peavey, Beringer, etc.), but am not brand loyal/proud - if it will get the job done and stand up to normal use, then it's fine for my project.  This is a fixed installation, so weight/size is not an issue.  To save money I'll be buying used.  All suggestions welcomed.
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Mac Kerr

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Re: 120 db at 40 hz?
« Reply #1 on: October 05, 2019, 12:06:56 pm »

Hello all.  I've got a 30'x50' workshop that I want to equip with a good, loud and relatively low cost (I know, can only have two of the three) sound system.  I've narrowed my search for mains to a pair of 10" or 12" two-way boxes run in stereo, and am looking for a sub (or two if needed) to get me around 120 db at 40 hz.  To be more specific, I want the sub to have fairly flat response to 40 hz or lower.  No much use if it will do 120 db at 40 hz while it's doing 130 db at 60 hz, right, and don't want to force it into unhappy operating range with heavy handed EQ.  I'm avoiding the budget stuff (Peavey, Beringer, etc.), but am not brand loyal/proud - if it will get the job done and stand up to normal use, then it's fine for my project.  This is a fixed installation, so weight/size is not an issue.  To save money I'll be buying used.  All suggestions welcomed.

Hard to know if it will get the job done without knowing what the job is.

Mac
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TJ (Tom) Cornish

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Re: 120 db at 40 hz?
« Reply #2 on: October 05, 2019, 07:18:57 pm »

Hello all.  I've got a 30'x50' workshop that I want to equip with a good, loud and relatively low cost (I know, can only have two of the three) sound system.  I've narrowed my search for mains to a pair of 10" or 12" two-way boxes run in stereo, and am looking for a sub (or two if needed) to get me around 120 db at 40 hz.  To be more specific, I want the sub to have fairly flat response to 40 hz or lower.  No much use if it will do 120 db at 40 hz while it's doing 130 db at 60 hz, right, and don't want to force it into unhappy operating range with heavy handed EQ.  I'm avoiding the budget stuff (Peavey, Beringer, etc.), but am not brand loyal/proud - if it will get the job done and stand up to normal use, then it's fine for my project.  This is a fixed installation, so weight/size is not an issue.  To save money I'll be buying used.  All suggestions welcomed.
Hi Dan - welcome to the forum. I think you are misunderstanding how frequency response works - if a speaker has the capability to do 120dB at one frequency and 130dB at a different frequency, that doesn't mean the frequency response will be out of balance, it just means you don't have to use all of the extra 10dB at the more efficient parts of the speaker's response. This is accomplished by EQ. All speakers require EQ - there is no such thing as a speaker with a naturally flat response.

Any reasonably pro sub should do 120dB of some rating at 40Hz in a small room. You may want to figure out what scale you are referencing - the difference at 40Hz between 120dBA slow and 120dBC fast is really massive - approaching 20dB IIRC. Where did you get that number? Who decides if it is loud enough?

For a specific example, the JBL PRX818XLF claims the following specs:

Maximum SPL Output   134 dB peak
Frequency Range (-10 dB)   30 Hz - 103 Hz
Frequency Response (±3 dB)   35 Hz – 87 Hz

There are many threads on this forum attempting to take numbers like these and arrive at some meaning. Challenges such as if these are measured vs. calculated, at what distortion level, for what amount of time, for what scale, and at what distance the measurement was taken/calculated all make a big difference in what the speaker does. This is one of Ivan's favorite topics. Searching his posts will send you sufficiently down the rabbit hole.

Putting some of the cynicism aside, you may be able to make the following assumptions from numbers like the above:

- If we assume the "+3dB" of the rating is at 134dB peak, 35Hz is probably a "-3dB" point, meaning the speaker can probably do 128dB peak at 35Hz, and probably slightly better than that at 40Hz.
- This measurement is probably done at 1 meter. Sound falls off at 6dB per doubling of distance (outside anyway - you'll get some of this back indoors), so if we take the 128dB peak number as our 40Hz output at 3', then at 50' (4 doublings or 24dB loss) the output would be around 104dB peak at the extreme end of your room.
- If you wanted 120dB peak at the extreme end of your room, you would need to add additional speakers. Adding a second powered sub adds both more cone space and more electrical drive power, so you should get about 6dB additional output per doubling of speaker quantity. A pair would do 110dB peak, and it would take four of them to do 116dB peak. You'd need 6 of them to get to 119dB peak.
- If you don't want peak and want 120 "real" dB, you would need to double your sub count again and you are now at 12 boxes.

If you choose a different sub like a Danley TH118, the specs are as follows:

- 140dB peak at 1 meter
- 37Hz at -4dB

- Assuming the TH118 is at least as loud at 40Hz as it is at 37Hz, that means we can get 136dB at 40Hz at one meter.
- Subtracting our 24dB due to distance loss at the far end of your room you would end up with 112dB peak at 50'. Adding a second TH118 plus an equal amount of drive power either via a larger amp or a second amp gets you to 118dB peak. You would still need 6 TH118s to get 120 "real DB" at 50'.

All of this math aside, I suspect you have never experienced 120dB of any scale. NIOSH allows 120dB exposure for 7 seconds before hearing impairment happens. OSHA is less conservative giving you 7 1/2 minutes before hearing damage occurs. These are broadband numbers and we are much less sensitive at 40Hz than we are at 4000Hz so if all you listen to is 40Hz you are probably safe, but if you run a full range system, unless you are extraordinarily bass heavy, you're still going to be at 100-110dB for mids and highs. OSHA gives you 30 minutes at 110dB, so you can listen to half an album while you work, though I suspect most of your work time will be filled with replacing tools that continuously vibrate off your workbench.

My serious advice is to start with one single 18" sub of good quality active or passive and see if it's enough. If it's not, then get a second.


* No warranties to my calculations are expressed or implied - this post was typed while watching my team get their butt kicked by the Yankees, so my concentration may have been impaired.
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Frank Koenig

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Re: 120 db at 40 hz?
« Reply #3 on: October 05, 2019, 07:51:57 pm »

If you're measuring output at 40 Hz you had better be on the "C" scale or you won't see anything. A weighting is down ~33 dB at 40 Hz from 1 kHz.

https://en.wikipedia.org/wiki/A-weighting

--Frank

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Chris Grimshaw

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Re: 120 db at 40 hz?
« Reply #4 on: October 06, 2019, 03:26:40 am »

Gents, it's also possible to measure SPLs without any weighting. All you need to do is calibrate your measurement mic to your SPL meter at some midband frequency (preferably with band-limited pink noise) (ie, where the SPL meter will be reading "flat), and then run measurement sweeps. The dB scale on the measurements will then be accurate.

120dB@1m@40Hz is perfectly possible with a single ported 15". I know because I've done it, and measured the results. I'd expect a decent commercial 18" to do it just fine - NB I was using one of the best 15"s available, and dumping quite a lot of power into it.

A KW181 won't manage it - it'll only do 115dB at 40Hz when you hit the limiters. You'll need a step up from there - SRX818 might do it, but I haven't measured those.

Chris
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Jeff Bankston

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Re: 120 db at 40 hz?
« Reply #5 on: October 06, 2019, 04:53:37 am »

FaitalPro 18XL1600
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Luke Geis

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Re: 120 db at 40 hz?
« Reply #6 on: October 06, 2019, 05:58:37 am »

If it is a peak # no problem, if it is a # you actually need at distance, then there is no real way to acquire it without using insane amounts of money and subs.

Any mid-range commercial sub will do what you are asking for a peak output reference. A mid-level sub would be JBL SRX/PRX, QSC KW, EV ETX and so on. If you want 120db at 50', you will have to buy a sub capable of 140+db and in considerable quantities.

SPL is a slippery slope. There are many ways to measure it and cheat the numbers. If you know you need only 120db peak from a speaker at a 1m distance, that is an easy number to get to with commonly available units, at 50', not so much.
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Chris Grimshaw

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Re: 120 db at 40 hz?
« Reply #7 on: October 06, 2019, 07:03:00 am »

Luke, as I mentioned above, the QSC KW181 is only capable of 115dB at 40Hz. Two of them would manage it, though.

Jeff, I found the Faital 15HP1060 did the job in a smallish ported box and plenty of power on-tap. I'd very much like to play with the 18" you mentioned, but it wouldn't be strictly necessary to hit the numbers that Dan is looking for.

Chris
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Dennis Wiggins

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« Last Edit: October 07, 2019, 10:32:58 am by Dennis Wiggins »
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Frank Koenig

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Re: 120 db at 40 hz?
« Reply #9 on: October 06, 2019, 11:38:10 am »

Gents, it's also possible to measure SPLs without any weighting

Of course. I just saw mention of dBA somewhere upthread and thought I'd nip it in the bud. Sorry if I was a little blunt. --Frank
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Ed Hall

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Re: 120 db at 40 hz?
« Reply #10 on: October 06, 2019, 05:11:56 pm »

40 Hz has a wavelength of about 28 feet. With dimensions of 30x50 won't there be some substantial standing waves in the room, with places where there will be almost no volume and others where there will be +6dB or more? 

What about corner loading the sub? Would that be 1/8 space and give +9dB just by placement?

So 120dB at 40 Hz at the far end could be achieved depending on where you place the sub and where you measure it, couldn't it?
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Dan Erni

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Re: 120 db at 40 hz?
« Reply #11 on: October 06, 2019, 05:34:42 pm »

Hello all and thanks for the detailed responses.  The room will be my workshop and for listening to prerecorded music.  Planning to pour the concrete floor once the weather breaks after the first of the year.  Approximately 12' to bottom of the roof trusses.  Haven't decided if I will install a ceiling or leave vaulted (insulate and drywall surface).  Walls will be insulated and surfaced with drywall.  I used to DJ, and between gigs (and when I was single  ;)) used to set up my system in my living room and listen to music at fairly loud levels.  System was powered by two Crest Audio V1500 amps driving two 15" two-way mains, transitioning at 70 hz to a pair of subs equipped with two 15" woofers in each cabinet.  I didn't appreciate how good the subs were at the time - they sounded great with very little EQ and would play the lowest bass guitar notes (open E string around 40 hz, I believe - I'm not a player) at about the same loudness/physicality as the rest of the range the subs were asked to reproduce.  I sold that system 15 years ago.  After listening to lots of DJs at weddings and such in the years since, I have noticed that most of their subs play loud, but not deep.  My goal is to set up a loud (hence the 120 db) system that will play deep (hence the 40 hz).  I'm not an expert on acoustics or electrical engineering, but appreciate all of the points raised in the posts above.  To simplify things, I don't expect 120 db on the farthest wall away from the subs.  I also acknowledge that 120 db isn't a sound level that's safe to listen to for extended periods, but want the hardware to have a some headroom so that it presumably will last a while in my application.

I've been scanning posts in different parts of the forum and see things about frequency response data being suspect from many manufacturers, that horn loaded subs mostly play loud but not deep, etc.  I was hoping someone could say that Brand X sub is readily available on the used market, has a good reputation as being reliable, and doesn't have to be abused with an EQ to reproduce a 40 hz note at the same SPL as a 60 hz note.  I know I'm asking for everything to be distilled down to its essence, possibly too much so.  All input is welcome and helpful and furthers my knowledge.
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Sean Anderson

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Re: 120 db at 40 hz?
« Reply #12 on: October 06, 2019, 08:33:20 pm »

Dan, if this is for a listening room, go check out the products from JTR. They make some very nice pro audio and theater subs that will do what you want them to do. If you want to hear clear bass guitar, you really need to be looking at JTR, Danley, high end RCF etc.
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TJ (Tom) Cornish

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Re: 120 db at 40 hz?
« Reply #13 on: October 07, 2019, 08:41:49 am »

Hello all and thanks for the detailed responses.  The room will be my workshop and for listening to prerecorded music.  Planning to pour the concrete floor once the weather breaks after the first of the year.  Approximately 12' to bottom of the roof trusses.  Haven't decided if I will install a ceiling or leave vaulted (insulate and drywall surface).  Walls will be insulated and surfaced with drywall.  I used to DJ, and between gigs (and when I was single  ;)) used to set up my system in my living room and listen to music at fairly loud levels.  System was powered by two Crest Audio V1500 amps driving two 15" two-way mains, transitioning at 70 hz to a pair of subs equipped with two 15" woofers in each cabinet.  I didn't appreciate how good the subs were at the time - they sounded great with very little EQ and would play the lowest bass guitar notes (open E string around 40 hz, I believe - I'm not a player) at about the same loudness/physicality as the rest of the range the subs were asked to reproduce.  I sold that system 15 years ago.  After listening to lots of DJs at weddings and such in the years since, I have noticed that most of their subs play loud, but not deep.  My goal is to set up a loud (hence the 120 db) system that will play deep (hence the 40 hz).  I'm not an expert on acoustics or electrical engineering, but appreciate all of the points raised in the posts above.  To simplify things, I don't expect 120 db on the farthest wall away from the subs.  I also acknowledge that 120 db isn't a sound level that's safe to listen to for extended periods, but want the hardware to have a some headroom so that it presumably will last a while in my application.

I've been scanning posts in different parts of the forum and see things about frequency response data being suspect from many manufacturers, that horn loaded subs mostly play loud but not deep, etc.  I was hoping someone could say that Brand X sub is readily available on the used market, has a good reputation as being reliable, and doesn't have to be abused with an EQ to reproduce a 40 hz note at the same SPL as a 60 hz note.  I know I'm asking for everything to be distilled down to its essence, possibly too much so.  All input is welcome and helpful and furthers my knowledge.
There are a lot of reasonable choices depending on budget, but a non-trivial factor may be local availability.  You may want to approach this from the opposite direction - see what’s available locally and then research that model to see what people’s opinions are.

Once again, you’re still going to need to use EQ. I understand what you are getting at - you don’t want to have to try to stretch a one-note box to some semblance of flat response, but every speaker requires EQ, and every sub smaller than a garden shed is going to be more efficient at 60Hz than at 30Hz. You are going to need to boost at 40Hz or cut at some other higher frequency. Both of these approaches are fine as long as you don’t ask more than the sub can produce.  Many sub spec sheets display the “processed response”  - their flat curves depend on either proprietary amp processing or certain filters the user is expected to use. If you don’t want to have to think about that, getting a self-powered sub hides this from you and presents a flat response. The EQ is still necessary and still there; the manufacturer just did the work for you.
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Dennis Wiggins

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Re: 120 db at 40 hz?
« Reply #14 on: October 07, 2019, 10:28:29 am »

Oops, accidentally my deleted comments re: room resonances and things moving about/falling off shelves with 120dB of 40Hz.
« Last Edit: October 07, 2019, 10:40:11 am by Dennis Wiggins »
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Ivan Beaver

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Re: 120 db at 40 hz?
« Reply #15 on: October 07, 2019, 12:41:29 pm »

Gents, it's also possible to measure SPLs without any weighting. All you need to do is calibrate your measurement mic to your SPL meter at some midband frequency (preferably with band-limited pink noise) (ie, where the SPL meter will be reading "flat), and then run measurement sweeps. The dB scale on the measurements will then be accurate.


This only works if the meter has a no weighting option.  Most of the cheaper meters do not.  In most cases C is the closest you will get to flat, but that still rolls off the lower lows and upper highs.

1KHz is the only point at which all of the curve agree in SPL.  A weighting actually has a boost above 1Khz (in addition to the cutting of the general lows and highs.

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Rob Spence

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Re: 120 db at 40 hz?
« Reply #16 on: October 07, 2019, 01:02:16 pm »

You say “workshop “ but not what kind.

In woodworking shops, dust gets into everything even with good dust collection.
Excess dust in speaker cabinets may shorten lifespans.
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Mal Brown

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Re: 120 db at 40 hz?
« Reply #17 on: October 07, 2019, 02:23:40 pm »

120 dB at 40hz for playback ?  That makes my head hurt... 
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Nathan Riddle

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Re: 120 db at 40 hz?
« Reply #18 on: October 07, 2019, 09:37:42 pm »

I'm not sure about you guys, but I loved having 130Hz at 1M @ 20 SPL's with my wub wub 12cm subs in my car rawkin 1200 Zeus volt-amperes :)

But in all seriousness, 120dB of sub isn't a ton. Mains, yes. I have no desire to mix or listen at that level measured slow dBA.

But if you wanna listen to music in your shop? Anything will do IMO...? JBL SRX or Yamaha DZR seems like a nice relatively reasonably priced MI/Pro level equipment choice?
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Frank Koenig

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Re: 120 db at 40 hz?
« Reply #19 on: October 08, 2019, 06:27:53 pm »

You say “workshop “ but not what kind.

In woodworking shops, dust gets into everything even with good dust collection.
Excess dust in speaker cabinets may shorten lifespans.

Woodshop is bad enough. I would expect a metal shop, especially where there is grinding of ferrous alloys, to be terrible. All those little magnetic bits trying to find their way into voice coil gaps. I do a little grinding now and then and I'm always mindful to keep away from any speakers. --Frank
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TJ (Tom) Cornish

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Re: 120 db at 40 hz?
« Reply #20 on: October 08, 2019, 06:38:55 pm »

Woodshop is bad enough. I would expect a metal shop, especially where there is grinding of ferrous alloys, to be terrible. All those little magnetic bits trying to find their way into voice coil gaps. I do a little grinding now and then and I'm always mindful to keep away from any speakers. --Frank
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Caleb Dueck

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Re: 120 db at 40 hz?
« Reply #21 on: October 09, 2019, 09:21:32 am »

120 dB at 40hz for playback ?  That makes my head hurt...

If we assume 20dB sub haystack - that's 100dB full range.  For live music, that's only 5dB more than I'm used to.  If that's the peak number the system needs to reproduce, knowing the average continuous will be lower - that's realistic and what I would expect my personal fun system to handle. 

If it were me though, I'd get TH118XL's and SH69HT's and call it a day.  Get the Dante version DNA amp, and use whatever computers and other devices for sources.
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Jeff Bankston

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Re: 120 db at 40 hz?
« Reply #22 on: October 09, 2019, 10:25:29 pm »

This thread really hertz. I got to go rent a car to put my woofers in.
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Re: 120 db at 40 hz?
« Reply #22 on: October 09, 2019, 10:25:29 pm »


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