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Author Topic: 120 db at 40 hz?  (Read 1386 times)

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


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