I have been on a quest to build a medium/large format sealed studio monitor with a comfortable peak SPL potential of ~117 dB @ 1m. I have started a couple of other threads in this regard... regular members may kindly excuse me for the badgering, I assure you that the idea is evolving (with your kind inputs).
The drivers I'm looking at are:
LF - SB Acoustics SB34NRX75-6
MF - Scan-Speak 18M/4631T
HF - Wavecor TW030WA11
DSP and amplification will be courtesy of a Hypex FA-253.
Enclosure volumes TBD depending on site of installation, and crossover points/slopes TBD upon testing - only constant is that the focal point (between the midrange unit and tweeter) will be @ 4' from floor level - the studio standard.
Please take a look at the above idea, and help me understand what challenges I will be dealing with here.
The drivers I'm looking at are:
LF - SB Acoustics SB34NRX75-6
MF - Scan-Speak 18M/4631T
HF - Wavecor TW030WA11
DSP and amplification will be courtesy of a Hypex FA-253.
Enclosure volumes TBD depending on site of installation, and crossover points/slopes TBD upon testing - only constant is that the focal point (between the midrange unit and tweeter) will be @ 4' from floor level - the studio standard.
Please take a look at the above idea, and help me understand what challenges I will be dealing with here.
I'm thinking edge diffraction/reflections. You should consider drivers off center/rounded edges/some kind of sculptured baffle to minimize this.
Baffle step should be easy to correct in DSP.
Maybe standing waves in the box, but it looks like you plan to put the woofer close to the center of the box, and that should minimize the problems. Asymmetric shape for the mid cabinet could be nice too.
Baffle step should be easy to correct in DSP.
Maybe standing waves in the box, but it looks like you plan to put the woofer close to the center of the box, and that should minimize the problems. Asymmetric shape for the mid cabinet could be nice too.
Are you actually going to use this in a studio as a monitor? If not, I seriously question the 48" height between tweeter and mid.
I don't have any experience with the wavecor tweeter, but it has a good reputation. The revolator Scan Speak is obviously a great driver. I use the 12 inch SB in a 3-way active system with Hypex FA-253 amps. Great woofer.
Your project has great potential. These drivers look well matched. Please note the point that Rallyfinnen is making: Even though your tweeter has a horn/waveguide, you will still get a performance benefit from carefully profiling the edges and flush mounting the drivers. Particularly the mid and tweeter, flush means flush.
Your project has great potential. These drivers look well matched. Please note the point that Rallyfinnen is making: Even though your tweeter has a horn/waveguide, you will still get a performance benefit from carefully profiling the edges and flush mounting the drivers. Particularly the mid and tweeter, flush means flush.
Exclusively in the studio as a monitor. A good portion of my income comes from building studios. For my current project, we are looking at the following two layouts:
Thank you for your kind suggestions. If I opt for a freestanding installation as opposed to an infinite baffle arrangement, I will definitely work on ameliorating edge diffraction problems.
My idea draws inspiration mainly from your build + the Apollo 7-MT from diysoundgroup. Great idea, putting the amps in the speaker stands... I might use it sometime and I hope you won't sue me! (Please note - I do not make money from building speakers.)
Very kind of you to say so, thank you. As I have mentioned in my other threads, I have a very superficial understanding of loudspeaker building, so your words are particularly encouraging and appreciated.
I would double up on the woofers if you are serious about 117 dB peak SPL.
When you push them hard with compressed material there will be a lot of
compression or ever burn out at high SPL. A pair goes a long way toward
reducing power and excursion. Or consider a pro audio woofer.
When you push them hard with compressed material there will be a lot of
compression or ever burn out at high SPL. A pair goes a long way toward
reducing power and excursion. Or consider a pro audio woofer.
If you go for the free standing version make them handed and off set tweeter and mid from the vertical centre line.
I missed the part about 117 dB. That is an impressive amount of energy.
My calculations for the SB34NRX75 in a sealed box shows that at 40 Hz it will hit Xmax at 111 dB (1 meter). Above 45 Hz, you will be limited by the 250 W capability of the Hypex, and for this driver that limit is about 112 dB. Even with 2 woofer per channel and used the 500 W FA503, I don't think you can get to 117 dB.
The same is true of the Scan Speak 18M Revelator. 250 W will drive it to about 113 dB, and 250 is its max power rating.
That is quite humorous... I doubt I am the first to think of it, and even if I am, so what. If anyone can copy an idea of mine and make a profit.... Go for it Dude ! I shamelessly copy both commercial and DIY ideas any chance I get.
Thanks again, a lot of valuable inputs here.
I think I will re-look at the SPL requirement I really need... I might have had unreasonable expectations, driven by greed.
The spec for a small format mix room like the ones I usually build, is an average SPL of 79 to 82 dB(C) @ the listening position (user preference, by trial and error), with a headroom of 20 dB... i.e. peaks of approximately 102 dB @ 3m, in my case...
The Scanspeak MF driver seems to be able to do it, with about 4 dB headroom, if the following calculation is correct. It's rated sensitivity is 92 dB (2.83V/1m), but being that it is a 4 ohm speaker, the sensitivity is taken to be 89 dB (1w/1m) for the purposes of this calculation. It's "long term max power" is 250w, which I will take to mean "peak power handling".
Using the above method of calculating sensitivity, the SB Acoustics woofer should be at about 88.5 dB (1w/1m), and it's "rated power handling" is 200w. This gives me an SPL of 104.8 dB @ 3m, which still meets my requirement, regardless of whether it is average or peak SPL.
@hifijim (or anyone else), how far away am I from meeting my new, more realistic/modest SPL requirements, considering the excursion potential of the SB Acoustics woofer? (I used to be able to do this using WinISD on my windows machine... don't know how to on this macbook...).
I think I will re-look at the SPL requirement I really need... I might have had unreasonable expectations, driven by greed.
The spec for a small format mix room like the ones I usually build, is an average SPL of 79 to 82 dB(C) @ the listening position (user preference, by trial and error), with a headroom of 20 dB... i.e. peaks of approximately 102 dB @ 3m, in my case...
The Scanspeak MF driver seems to be able to do it, with about 4 dB headroom, if the following calculation is correct. It's rated sensitivity is 92 dB (2.83V/1m), but being that it is a 4 ohm speaker, the sensitivity is taken to be 89 dB (1w/1m) for the purposes of this calculation. It's "long term max power" is 250w, which I will take to mean "peak power handling".
Using the above method of calculating sensitivity, the SB Acoustics woofer should be at about 88.5 dB (1w/1m), and it's "rated power handling" is 200w. This gives me an SPL of 104.8 dB @ 3m, which still meets my requirement, regardless of whether it is average or peak SPL.
@hifijim (or anyone else), how far away am I from meeting my new, more realistic/modest SPL requirements, considering the excursion potential of the SB Acoustics woofer? (I used to be able to do this using WinISD on my windows machine... don't know how to on this macbook...).
Based on the cone area and the Xmax displacement, we can calculate the maximum SPL this woofer can produce at a frequency.
I assumed an 85 liter sealed box, which results in a 12 dB/Octave roll off with an F3 of 34 Hz.
From Qes, Vas, and Fs, we can calculate the reference efficiency, and from that we can determine the required electrical power to achieve that max SPL.
Here are the results
20 Hz ..... 99.4 dB .... 244 W
24 Hz ..... 102.4 dB .... 239 W
28 Hz ..... 105.4 dB .... 240 W
34 Hz ..... 108.4 dB .... 258 W
Above 34 Hz, Xmax is no longer the limiting factor. Above this frequency the driver will be limited by the amplifiers 250 W maximum power rating, as well as the electrical power rating of the driver.
I attached an Excel spreadsheet with my calculations. This is based on the Vance Dickason "Loudspeaker Design Cookbook", 7th edition.
I assumed an 85 liter sealed box, which results in a 12 dB/Octave roll off with an F3 of 34 Hz.
From Qes, Vas, and Fs, we can calculate the reference efficiency, and from that we can determine the required electrical power to achieve that max SPL.
Here are the results
20 Hz ..... 99.4 dB .... 244 W
24 Hz ..... 102.4 dB .... 239 W
28 Hz ..... 105.4 dB .... 240 W
34 Hz ..... 108.4 dB .... 258 W
Above 34 Hz, Xmax is no longer the limiting factor. Above this frequency the driver will be limited by the amplifiers 250 W maximum power rating, as well as the electrical power rating of the driver.
I attached an Excel spreadsheet with my calculations. This is based on the Vance Dickason "Loudspeaker Design Cookbook", 7th edition.
Did you consider that a pair of woofers doubles the VD which provides 6 dB more output not just 3 dB? I didn't expect him to do 117 dB in the low bass even with a pair.
Well I thought it was just 3 dB, but I could be mistaken.
My thinking was based on the old rule about two drivers: 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). If two drivers are wired in series, there no change in voltage sensitivity: + 3 dB due to twice the radiating area, and - 3 dB due to doubling the impedance (halving the current).
So if he put two woofers in parallel and drive them with the 250 W hypex, he would get 6 dB more voltage sensitivity, but just 3 dB more output per Watt.
Does this make sense, or am I confused?
The other thing we are not considering is that there will be TWO speakers in that room, a relatively small room. That is an additional +3 dB. With both speakers running, he might just get 117 dB.
My thinking was based on the old rule about two drivers: 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). If two drivers are wired in series, there no change in voltage sensitivity: + 3 dB due to twice the radiating area, and - 3 dB due to doubling the impedance (halving the current).
So if he put two woofers in parallel and drive them with the 250 W hypex, he would get 6 dB more voltage sensitivity, but just 3 dB more output per Watt.
Does this make sense, or am I confused?
The other thing we are not considering is that there will be TWO speakers in that room, a relatively small room. That is an additional +3 dB. With both speakers running, he might just get 117 dB.
Last edited:
Using two woofers in an application like this is a good idea. For example, the Barefoot MiniMain12. It uses two 12 inch drivers in a sealed box that is about half the size it should be. I would expect the natural Qtc of those two woofers in that box to be something like Qtc=1. They use DSP EQ to transform the response into a lower Qtc with extended bass. In essence they use an excess of amplifier power to mimic the effect of a much larger box. However this approach gives them much greater headroom than a single 12 inch driver in an optimum box, except for the very low bass where the EQ cuts into the headroom.
I just dont know if Audiothings needs this kind of output. I can't see any valid reason for music to be louder than 110 dB peak... too much pain involved.
I just dont know if Audiothings needs this kind of output. I can't see any valid reason for music to be louder than 110 dB peak... too much pain involved.
I am not making this up... 🙂
The film mix standard (for larger rooms) is 85 dB(C) average + 20 dB headroom... i.e. peaks of 105 dB.
For small format mixing (stereo, TV, HT etc.) the standard is 79-82 dB(C) + 20 dB headroom... i.e. peaks of 102 dB at mix position. I know of great engineers who like to monitor as low as 75 dB - it works for them, but that is a matter of personal preference.
The reason for reference monitoring being so loud is perhaps because of the Fletcher-Munson (equal loudness) thingy... the ear is somewhat linear in it's sensitivity to frequencies when the SPL averages around 85 dB. No engineer is forced to monitor constantly at that level, but it is used for reference. Even a small format studio monitor like the JBL LSR308 Mkii claims to put out 112 dB peaks (wonder how they measured it, if their data is to be believed, they are putting out 102 dB @ 37 Hz @ 1m, out of a bookshelf!...).
If I may draw your attention back to the project at hand, it does seem that my choice of MF and HF drivers might still work... by my calculation, the Scanspeak MF driver should do ~106 dB @ 3m... The 91 dB sensitive Wavecor tweeter's power handling is 45 watts per IEC 268-5, so it should be capable of handling peaks of ~107 @ 3m. If this is true (and it would be great if somebody could confirm that my calculations are correct), then the limiting factor becomes the 20-150 Hz range... correct...?
If I am doing alright with the MF and HF driver combination, I'll focus the rest of my energy on trying to find a suitable LF unit/DSP/Amplification combo to go with it...
In other threads (and builds) I have explored CD + Waveguides, MMTs, MTMs etc... this is the closest I've gotten to something that feels right... hope you guys will hang in here with me and help me see this through...
Many thanks,
I had heard the reason for the headroom was that studios monitors have to handle the uncompressed RAW feed with no compression.
well, everytime I listen to a record, that time is a Studio Monitoring Session!
Or do you think that at home the result vary dramatically from the master recordings & auditions?
Or do you think that at home the result vary dramatically from the master recordings & auditions?
What you hear at home is considerably compressed (if only by gain riding) from the raw mic feed that started the process.
That is also absolutely true. Which is why i am greedy for as much headroom as i can get. That said, I'd probably be OK with a limiter kicking in to protect the drivers, as a practical compromise...
In most domestic listening environments, there will be a substantial amount of room gain... A 5" woofer can generate all the excitement i need in my bedroom. However, In a studio like mine which has absorptive treatments down to the very low frequencies, even high power three way monitors with dual opposing subs sound tiny, when compared to my main system. Hope I understood your question correctly...