Audiothings - going back to post #10. Your SPL analysis is still valid, but for just one speaker. With both Left and Right, you should get + 3 dB higher at your listening position. That would be 109 dB for the L+R ScanSpeak mids, and 108 dB for the L+R SB 12" woofers.
(Note: I believe you will get a + 3dB boost from having both left and right speakers playing. But if Pete Basel is correct, you will get a + 6dB boost. Pete and I have not had a chance to discuss this, and I am always open to the possibility that I am wrong)
In my post 11, those dB SPL values are for a single driver measured at 1 meter under standardized test conditions. I should have mentioned that at 40 Hz and above, the SB woofer is above the Xmax limitation and out of the low frequency roll off region. The full 112 dB @ 1 meter capability will be available.
So based on this, I am comfortable that your current design concept will meet the standard of 85 dB (C) + 20 dB headroom.
There are pro audio woofers available which have voltage sensitivities ranging from 92 to 98 dB @ 2.83V/1M... however, no woofer can escape the laws of physics. Those woofers will have a much higher Fs and will have much less bass extension below 40 Hz. They will also require a vented box. However, if 40 Hz is all you need, perhaps a high sensitivity pro woofer would work for you.
If you want to produce high dB and very low frequencies, there is no way to do it except very large radiating area, large voice coil travel, large boxes, and a lot of power. With a pair of SB34 woofers, and with 250 W for each woofer (500 W total), you gain 6 dB (3 dB for doubling the radiating area, and 3 dB for doubling the power). If you do not want to give up any head room at low frequencies, you will need to double your box size to about 7 cubic feet. If you want to stay with your current box size, you will consume some of that electrical power in the EQ process, and you will give up some headroom in the very low bass.
(Note: I believe you will get a + 3dB boost from having both left and right speakers playing. But if Pete Basel is correct, you will get a + 6dB boost. Pete and I have not had a chance to discuss this, and I am always open to the possibility that I am wrong)
In my post 11, those dB SPL values are for a single driver measured at 1 meter under standardized test conditions. I should have mentioned that at 40 Hz and above, the SB woofer is above the Xmax limitation and out of the low frequency roll off region. The full 112 dB @ 1 meter capability will be available.
So based on this, I am comfortable that your current design concept will meet the standard of 85 dB (C) + 20 dB headroom.
There are pro audio woofers available which have voltage sensitivities ranging from 92 to 98 dB @ 2.83V/1M... however, no woofer can escape the laws of physics. Those woofers will have a much higher Fs and will have much less bass extension below 40 Hz. They will also require a vented box. However, if 40 Hz is all you need, perhaps a high sensitivity pro woofer would work for you.
If you want to produce high dB and very low frequencies, there is no way to do it except very large radiating area, large voice coil travel, large boxes, and a lot of power. With a pair of SB34 woofers, and with 250 W for each woofer (500 W total), you gain 6 dB (3 dB for doubling the radiating area, and 3 dB for doubling the power). If you do not want to give up any head room at low frequencies, you will need to double your box size to about 7 cubic feet. If you want to stay with your current box size, you will consume some of that electrical power in the EQ process, and you will give up some headroom in the very low bass.
Thank you
Thank you for sharing the spreadsheet, hifijim!
How does the spreadsheet take the cabinet size and F3 into account?
I am interested because I have similar questions for my build, which uses two 12" woofers per box.
Tymphany NE315W-04 12" - The calculator at HiFi Loudspeaker Design gives me a box of 48L and 45.5 F3, but does not reference SPL or limiting factors such as amp power or X-max...
You can read more about my project at:
Woofer choice for WHW configuration.
Six- Minneapolis.
Thank you for sharing the spreadsheet, hifijim!
How does the spreadsheet take the cabinet size and F3 into account?
I am interested because I have similar questions for my build, which uses two 12" woofers per box.
Tymphany NE315W-04 12" - The calculator at HiFi Loudspeaker Design gives me a box of 48L and 45.5 F3, but does not reference SPL or limiting factors such as amp power or X-max...
You can read more about my project at:
Woofer choice for WHW configuration.
Six- Minneapolis.
In a recording studio it helps if the woofers do not spit the cone across the room when (not if) someone drops a live mic.
This is not a sophisticated spreadsheet... you have to enter the roll-off values into column F by hand. In the case under discussion, I made a model of the SB34 woofer in a 3.5 cubic ft box sealed, and I extracted the dB values from the bass simulation : at 40 Hz it was -1.5 dB... at 34 Hz it was -3.7 dB, etc. This is crude, but it works.
You install the values in blue text: Qes, Vas, etc... in your case, with twin woofers, what is listed is the SPL and power requirements for a single driver. With two in the same box, you will get an extra 6 dB, but you need twice the power.
edit: it also seems to work if you use twice the area (two drivers is twice the area)... if I double the Sd value from 508 to 1016, the SPL goes up by 6 dB, and the electrical power required doubles...
Vance Dickason has a slightly different formula for vented boxes.
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" that two drivers wired in parallel results in 6 dB increase in voltage sensitivity: + 3 dB due to twice the radiating area, and + 3dB due to cutting the impedance in half (double the current)"
That is correct as far as voltage sensitivity.
MaxSPL should go up by 6dB because VD is like voltage, double the voltage and it is + 6dB.
I agree Pete. We get + 6 dB for doubling the volume displaced. I must have had diarrhea of the brain when I wrote this statement
So if a single SB34 can produce 112 dB at 1 meter with 250 W, a pair of them can produce 118 dB at 1 meter with 500 W.
If we double the electrical power to a driver, we get + 3dB.
If we keep the total electrical power the same and use two drivers instead of one, we get +3 dB. Each driver gets half of the power.
If we use two drivers instead of one, and we also double the electrical power, we get +6 dB.
This statement I made in post 21 is also wrong
With both Left and Right speakers playing you should get + 6 dB. That would be 112 for the L+R ScanSpeak mids, and 111 dB for the L+R SB 12" woofers.
So if a single SB34 can produce 112 dB at 1 meter with 250 W, a pair of them can produce 118 dB at 1 meter with 500 W.
If we double the electrical power to a driver, we get + 3dB.
If we keep the total electrical power the same and use two drivers instead of one, we get +3 dB. Each driver gets half of the power.
If we use two drivers instead of one, and we also double the electrical power, we get +6 dB.
This statement I made in post 21 is also wrong
With both Left and Right speakers playing you should get + 6 dB. That would be 112 for the L+R ScanSpeak mids, and 111 dB for the L+R SB 12" woofers.
SMPTE/ITU/Dolby/AES and various other international entities have their own recommendations and standards - but all of them indicate that small rooms are to be calibrated to around 79 dB(C) and large rooms are to be calibrated to around 85 dB(C) for each speaker, with a 20 dB headroom per speaker.
At this time, I'm aiming for 82 dB(C) per speaker at mix position (3m), with a 20 dB headroom. Though it is more likely that I will be calibrating closer to 79 dB, I don't want to be maxing out the potential of the system... These types of systems are often called upon to take some serious abuse, either by accidental mic drops and the like, or to satisfy some idiot producer who doesn't have a clue about the difference between a louder playback and a hotter mix.
I have brought my old windows laptop home... I'll fire up WinISD tomorrow, make some simulations, and come back for more advice...
Thanks for all the inputs...
At this time, I'm aiming for 82 dB(C) per speaker at mix position (3m), with a 20 dB headroom. Though it is more likely that I will be calibrating closer to 79 dB, I don't want to be maxing out the potential of the system... These types of systems are often called upon to take some serious abuse, either by accidental mic drops and the like, or to satisfy some idiot producer who doesn't have a clue about the difference between a louder playback and a hotter mix.
I have brought my old windows laptop home... I'll fire up WinISD tomorrow, make some simulations, and come back for more advice...
Thanks for all the inputs...
I put the data into WinISD and this is what I got.
For the SB woofer - 2nd Order HPF @ 37 Hz (without this, the cone excursion exceeded the limit) and 2nd order LPF @ 220 Hz, 200W.
For the Scanspeak midrange - 2nd order LPF @ 220 Hz, 120W
SPL:
Cone Excursion:
Does this look right?
I seem to be getting ~111 dB @ 1m and the -3 dB point seems to be ~45 Hz...
The woofer will have a ~115L sealed box, be driven by 200W... Dedicated 7" midrange with 120W.
The JBL LSR308P Mkii which is less than 1/4th the size, puts out peaks of 112 dB, - 3dB point @ 45 Hz... 56W per driver... Equivalent or better performance potential than my idea...! Why??
Of course, my idea is sealed and the JBL is vented... but still... why is my super beefy idea barely able to keep up with the so much smaller (and cheap as chips) JBL?
For the SB woofer - 2nd Order HPF @ 37 Hz (without this, the cone excursion exceeded the limit) and 2nd order LPF @ 220 Hz, 200W.
For the Scanspeak midrange - 2nd order LPF @ 220 Hz, 120W
SPL:
Cone Excursion:
Does this look right?
I seem to be getting ~111 dB @ 1m and the -3 dB point seems to be ~45 Hz...
The woofer will have a ~115L sealed box, be driven by 200W... Dedicated 7" midrange with 120W.
The JBL LSR308P Mkii which is less than 1/4th the size, puts out peaks of 112 dB, - 3dB point @ 45 Hz... 56W per driver... Equivalent or better performance potential than my idea...! Why??
Of course, my idea is sealed and the JBL is vented... but still... why is my super beefy idea barely able to keep up with the so much smaller (and cheap as chips) JBL?
The JBL is an active monitor and more than likely has a low shelf filter or linkwitz transform applied (link with filter) to boost the bass end.
Why people make speaker length short. Why not have 24" length ? If cost is no issue ? why limit yourself to small Box tower? I am thinking of making 1x2x2 ( wxhxL) speaker with two full range and one passive radiator.
As Mr Ugg10 alluded to, you are not comparing apples to oranges. You could shrink the size of your concept at least by 1/2. I use the same woofer in a 70 liter box and I have bass extension to flat down to 32 Hz.
If you require a 40 Hz F3 point, you could shrink your box considerably, and then use a Linkwitz Transform eq to get you flat to 40 Hz. With the Hypex amplifier, you have a lot of options.
The JBL LSR308P has a spec of 45 Hz to 20 kHz +/- 3 dB. With the concept you are considering, a frequency response of 40 Hz to 20 kHz +/- 1 dB is achievable. I suspect your harmonic distortion will be less than 0.5% from 100 Hz to 20 kHz, and above 200 Hz it will probably be less than 0.2%. The $250 JBL will be hardly comparable to what you plan to build.
The strength of your concept will not be maximum high SPL, although it will be capable of at least 111 dB. The stength of your concept will be a very flat frequency response, wide uniform dispersion, very low distortion.
You know best what your customers will want for their studios.
Audiothings: another thing to consider is possibly going to a larger woofer. For example, the SB42FHCL75-6 15 inch woofer. It has 60% more surface area than the SB34 12 inch driver. It is about 3 dB more sensitive. At maximum power (300 W) it will make 116 dB at 1 M.
In a 100 liter sealed box it has an F3 of 41 Hz. With a mild Linkwitz transform EQ boost of 3 dB at 40 Hz it would be flat down to 32 Hz.
I am sure there are other drivers to consider, but this is a good example with a lot of potential.
In a 100 liter sealed box it has an F3 of 41 Hz. With a mild Linkwitz transform EQ boost of 3 dB at 40 Hz it would be flat down to 32 Hz.
I am sure there are other drivers to consider, but this is a good example with a lot of potential.
Only when the interference is 100% constructive. This typically happens only at low frequencies, I wouldn't count on much mid boost from two drivers, and besides, you get "zero" boost if a particular sound is only coming from one channel.
Very important question. OP has not indicated the passband in which 117 dB @ 1 m is required.
Eh, it's a 30 mm tweeter. A waveguided 1" dome, or better yet, a 1" compression driver in a horn/waveguide, would likely yield better dispersion.
250 W / 120 W per channel is also probably not enough for what OP needs. I'd be quite inclined to look at using pro audio drivers for this application.
Starting from the top, an Eminence N151M with QSC clone horn: JBL M2 for The Poors
Possibly a B&C 8MDN51 for MF (alternately, an AE Speakers TD8M would be a huge upgrade) crossed at ~1.5 kHz to the HF driver
Many many options for LF... but if you need a 3-way for 117 dB with reasonable SQ and uniform dispersion I think this application would call for a tapered TL; vented (port resonance) and tapped horn (response irregularities) don't really go up too high and an ML-TL might still have port chuffing issues. Vented and TH would work if you crossed from LF to MF closer to 100 Hz but that is a big compromise for the MF driver (power handling vs excursion vs distortion).
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It's not quite clear under what conditions that peak SPL is achieved. Note also the continuous SPL rating of 102 dB. The extra peak SPL is clearly limited, either thermally or otherwise. Additionally, the amplifiers will probably be capable of a little extra power than nominally rated but at drastically higher distortion.
308P MkII | JBL Professional Loudspeakers
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