"Maybe once DJK posts we will learn how he is getting more out of the design. HR vs BB issue? "
There really is no such thing as a free lunch.
A few years ago the Journal of the Audio Engineering Society (JAES) did a music survey with a spectrum analyzer. 98% didn't go below 40hz, 99.99% didn't go below 28hz, and you could count on one hand ones that went below 28hz (and they were all synthesized). If you hold the box size constant, going from 40hz to 28hz costs you 4.65dB, and going from 28hz to 20hz another 4.35dB .
I used to build and sell what I thought was the optimum trade-off, a 40hz sized box with 28hz 'step-down-tuning'. On 98% of the music it had 9dB more output than the 20hz box. A modest amount of EQ was designed in to the amplifier to make it flat to 28hz. While there is no such thing as a free lunch, good engineering choices can seem almost 'free'.
There really is no such thing as a free lunch.
A few years ago the Journal of the Audio Engineering Society (JAES) did a music survey with a spectrum analyzer. 98% didn't go below 40hz, 99.99% didn't go below 28hz, and you could count on one hand ones that went below 28hz (and they were all synthesized). If you hold the box size constant, going from 40hz to 28hz costs you 4.65dB, and going from 28hz to 20hz another 4.35dB .
I used to build and sell what I thought was the optimum trade-off, a 40hz sized box with 28hz 'step-down-tuning'. On 98% of the music it had 9dB more output than the 20hz box. A modest amount of EQ was designed in to the amplifier to make it flat to 28hz. While there is no such thing as a free lunch, good engineering choices can seem almost 'free'.
Errata:
The 6th order 30hz PPSL has a reduction of about 2dB around 56hz compared to a 4th order design tuned to about 42hz. The 6th order 35hz PPSL has a reduction of about 3dB around 56hz compared to a 4th order design tuned to about 50hz. According the EAW, 56hz is the peak output frequency of dance music (the worst case for the PPSL excursion).
One PPSL with a pair of the Kappa Pro 15LF will need about 1.2KW on peaks (per driver) to hit 130dB around 50hz, this would be about what a Crest CA12 will do on program material (most of the older Crest amps have about 3dB of dynamic headroom at 4Ω).
http://i56.photobucket.com/albums/g196/dkleitsch/COE08-3.jpg
This system played 122dB (C scale) at 20 foot on dance music with all four PPSL on one channel of the Crest CA9 (1000W at 2Ω). Inverse square law would suggest this is about 138dB at 1M, everyone that spend the whole evening there was a bit ill near the end (from all the bass).
The 6th order 30hz PPSL has a reduction of about 2dB around 56hz compared to a 4th order design tuned to about 42hz. The 6th order 35hz PPSL has a reduction of about 3dB around 56hz compared to a 4th order design tuned to about 50hz. According the EAW, 56hz is the peak output frequency of dance music (the worst case for the PPSL excursion).
One PPSL with a pair of the Kappa Pro 15LF will need about 1.2KW on peaks (per driver) to hit 130dB around 50hz, this would be about what a Crest CA12 will do on program material (most of the older Crest amps have about 3dB of dynamic headroom at 4Ω).
http://i56.photobucket.com/albums/g196/dkleitsch/COE08-3.jpg
This system played 122dB (C scale) at 20 foot on dance music with all four PPSL on one channel of the Crest CA9 (1000W at 2Ω). Inverse square law would suggest this is about 138dB at 1M, everyone that spend the whole evening there was a bit ill near the end (from all the bass).
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RE: nope
Posted by djk (M) on December 14, 2010 at 06:53:43
In Reply to: RE: nope posted by Scholl on December 13, 2010 at 14:46:43:
You don't need any real math to understand what is going on here.
We have a fixed box size and cut-off frequency. Each box requires a different driver to be optimum for the box type (2nd, 4th, 6th). This can be seen as if you would convert a 2nd to a 4th the reference efficiency cannot change, but the 4th would go about 1/3 octave lower.
In theory we should be able to see about a 3dB difference in a 2nd vs a 4th if the box size and cut-off frequency are kept constant (which we do, 84.55dB vs 87.56dB).
What you need to ask is how the 6th can be 91.54dB, an increase of 3.98dB?
The answer lies in the optimum driver having a lower Qts which in turn raises the mid-band reference efficiency, but causes the deep bass to roll off. There is no such thing as a free lunch, and there isn't one here either. The deep bass roll-off is compensated for by the bass boost in a 6th order system, typically 6dB at the box tuning frequency.
That's cheating!
Well, sort of.
Comparing output at Fc (2nd order) vs Fb (4th and 6th order), the 6th order is only about 1dB more that the 2nd order, and is actually 2dB less than the 4th order (low Qts drivers have no low bass). But the mid-band reference efficiency really is 6.99dB more that the 2nd order, or 3.98dB more than the 4th order. The 6dB boost in the 6th order is mainly at Fb and drops off rapidly above there. An octave above Fb the boost has declined to only 1.5dB or so. Distorting is not excessive as the largest boost is at Fb and does not cause excessive cone motion. Levels of F1 in program material tend to be on the order of 6dB~10dB lower than F2 on most musical instruments, so the boost at Fb doesn't eat up all the power on real music.
The 6th order vented system looks to be a free lunch (violate the Iron Law), but as we see, doesn't. Keele's actual examples were for a 2nd order with a 15, 4th order with a 10, and 6th order with an 8!
See example 2 on page 29 of the pdf (which was pg.28 of the actual paper)
From examining various equations for efficiency and LF cut-off I have concluded the optimum driver for the highest efficiency and lowest cut-off would have a Qts=0.312 and be a 6th order system with an Fb=F3=Fs=Faux with the filter (Faux) having a Q=2.
I can address alignment jamming (using non-optimum drivers) if desired.
• DIRECT LOW-FREQUENCY DRIVER SYNTHESIS (Open in New Window)
Posted by djk (M) on December 14, 2010 at 06:53:43
In Reply to: RE: nope posted by Scholl on December 13, 2010 at 14:46:43:
You don't need any real math to understand what is going on here.
We have a fixed box size and cut-off frequency. Each box requires a different driver to be optimum for the box type (2nd, 4th, 6th). This can be seen as if you would convert a 2nd to a 4th the reference efficiency cannot change, but the 4th would go about 1/3 octave lower.
In theory we should be able to see about a 3dB difference in a 2nd vs a 4th if the box size and cut-off frequency are kept constant (which we do, 84.55dB vs 87.56dB).
What you need to ask is how the 6th can be 91.54dB, an increase of 3.98dB?
The answer lies in the optimum driver having a lower Qts which in turn raises the mid-band reference efficiency, but causes the deep bass to roll off. There is no such thing as a free lunch, and there isn't one here either. The deep bass roll-off is compensated for by the bass boost in a 6th order system, typically 6dB at the box tuning frequency.
That's cheating!
Well, sort of.
Comparing output at Fc (2nd order) vs Fb (4th and 6th order), the 6th order is only about 1dB more that the 2nd order, and is actually 2dB less than the 4th order (low Qts drivers have no low bass). But the mid-band reference efficiency really is 6.99dB more that the 2nd order, or 3.98dB more than the 4th order. The 6dB boost in the 6th order is mainly at Fb and drops off rapidly above there. An octave above Fb the boost has declined to only 1.5dB or so. Distorting is not excessive as the largest boost is at Fb and does not cause excessive cone motion. Levels of F1 in program material tend to be on the order of 6dB~10dB lower than F2 on most musical instruments, so the boost at Fb doesn't eat up all the power on real music.
The 6th order vented system looks to be a free lunch (violate the Iron Law), but as we see, doesn't. Keele's actual examples were for a 2nd order with a 15, 4th order with a 10, and 6th order with an 8!
See example 2 on page 29 of the pdf (which was pg.28 of the actual paper)
From examining various equations for efficiency and LF cut-off I have concluded the optimum driver for the highest efficiency and lowest cut-off would have a Qts=0.312 and be a 6th order system with an Fb=F3=Fs=Faux with the filter (Faux) having a Q=2.
I can address alignment jamming (using non-optimum drivers) if desired.
• DIRECT LOW-FREQUENCY DRIVER SYNTHESIS (Open in New Window)
35hz high pass per DJK's post #34.
DJK, thank you for the write ups. IF my interpretation is right (might be affected by a head cold
) then all things being equal/no free lunch the PPSL should be have more output than TH. And it does if it is the same tuning. I think I made the mistake of modeling the PPSL as a 30Hz box when it really is 40hz. Pretty big difference. When I then compare a 40hz PPSL to a 40Hz TH, the PPSL wins. I easily get 130db+ and at least 3-5dbs, maybe six if I really get accurate with HR.
DJK, thank you for the write ups. IF my interpretation is right (might be affected by a head cold
) then all things being equal/no free lunch the PPSL should be have more output than TH. And it does if it is the same tuning. I think I made the mistake of modeling the PPSL as a 30Hz box when it really is 40hz. Pretty big difference. When I then compare a 40hz PPSL to a 40Hz TH, the PPSL wins. I easily get 130db+ and at least 3-5dbs, maybe six if I really get accurate with HR.
Yeah, but you need another driver, which doubles the cost, and more power to drive them.
There is no such thing as a free lunch...
35hz high pass per DJK's post #34.
DJK, thank you for the write ups. IF my interpretation is right (might be affected by a head cold
How steep a slope on the hp? 48db? Linkwitz riley?
Thanks, this will help me fhoose a processor.
The bill for lunch would also includes amplifier power too BUT these cost are only paid once and the benefits of higher SPL per pack space continue to repay themselves. As it has been said already, it's all tradeoffs.
Honestly, I am still in shock how easy it was to get 30hz with PPSL, even if it was 3-6db less max than the 40hz design. Then, the corner gets lower as you add more. Actually now that I think about it I bet a 4 pack of 40Hz PPSL will make it down to 30hz... Something DJK probably already knew
Honestly, I am still in shock how easy it was to get 30hz with PPSL, even if it was 3-6db less max than the 40hz design. Then, the corner gets lower as you add more. Actually now that I think about it I bet a 4 pack of 40Hz PPSL will make it down to 30hz... Something DJK probably already knew
I defer to DJK for a professional recommendation but IMO 48db LR is the best but typical HPF built in to an amp should suffice. Last time I asked around there weren't strong opinions about it.
I use a Q=2 HPF at Fb (35hz for this design), this is the traditional filter to convert the SBB4 into a B6 alignment.
Another filter could be added at a lower frequency.
I change the filter in either an EQ, electronic crossover, or an amplifier. It's generally only two resistors in whatever the existing filter is in the piece you choose.
Someone at Speakerplans figured out how to do it with a PEQ in a DSP management device, I'll see if I can find that thread. IIFRC they set a Butterworth HPF at Fb and a PEQ for +9dB at the same frequency (the Butterworth filter being 3dB down, so you have to add 3dB to the PEQ to bring it back up, and then the EQ needed at Fb (6dB with a Q=2)).
Another filter could be added at a lower frequency.
I change the filter in either an EQ, electronic crossover, or an amplifier. It's generally only two resistors in whatever the existing filter is in the piece you choose.
Someone at Speakerplans figured out how to do it with a PEQ in a DSP management device, I'll see if I can find that thread. IIFRC they set a Butterworth HPF at Fb and a PEQ for +9dB at the same frequency (the Butterworth filter being 3dB down, so you have to add 3dB to the PEQ to bring it back up, and then the EQ needed at Fb (6dB with a Q=2)).
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" So I am getting getting schooled in Hoffman's Law AND Bass Horn History "
In theory a full-sized horn can be about 50% efficient, and the best you can do with (multiple ) reflex is about 25%. The drivers I had custom made are about 3.5% efficient, so one box is about 7%, two boxes about 14%, three boxes about 21%, four boxes about 28% (theoretical maximum). I have only done a couple of shows with four boxes a side, it's overkill. One job was a LFE in a 2,000 seat theater to accompany an orchestra performing Jurassic Park. Four PPSL with only 650W was causing structural damage, chunks were falling out of the ceiling!
If you only do big shows, and have a big truck, go with the horns. I used to carry 12 single 15 folded horns, it was a bit of a PITA, and had no real bass unless you took in at least 4 per side.
If you need flexibility, go with multiple PPSL. You can haul in one, two, four, or six as needed; and one will still go down deep in a small space (try that with one small horn).
I still run horns above 150hz, PPSL below there.
In theory a full-sized horn can be about 50% efficient, and the best you can do with (multiple ) reflex is about 25%. The drivers I had custom made are about 3.5% efficient, so one box is about 7%, two boxes about 14%, three boxes about 21%, four boxes about 28% (theoretical maximum). I have only done a couple of shows with four boxes a side, it's overkill. One job was a LFE in a 2,000 seat theater to accompany an orchestra performing Jurassic Park. Four PPSL with only 650W was causing structural damage, chunks were falling out of the ceiling!
If you only do big shows, and have a big truck, go with the horns. I used to carry 12 single 15 folded horns, it was a bit of a PITA, and had no real bass unless you took in at least 4 per side.
If you need flexibility, go with multiple PPSL. You can haul in one, two, four, or six as needed; and one will still go down deep in a small space (try that with one small horn).
I still run horns above 150hz, PPSL below there.
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Suggestion for a small sound company just starting out.
Dual 12 reflex with a large format compression driver. May be used in small venues by itself (biamped).
Add a pair of PPSL for bigger jobs, take in one or two as needed (now you are triamping).
Add another pair of PPSL if doing dance music, or if you plan on expanding bigger.
Build dual 12 straight horns for mids, and another set of large format compression drivers.
Build another set of PPSL and you're done.
For the largest jobs you will have three PPSL per side, dual 12 horns and a large format compression driver driver for FOH, and the dual 12 reflex and a large format compression driver for side fills.
If you need two stages at once you run two PPSL per side and the dual 12 horns + HF on the main stage, and the dual 12 reflex + HF with one set of PPSL for the secondary stage (or at another show across town).
Dual 12 reflex with a large format compression driver. May be used in small venues by itself (biamped).
Add a pair of PPSL for bigger jobs, take in one or two as needed (now you are triamping).
Add another pair of PPSL if doing dance music, or if you plan on expanding bigger.
Build dual 12 straight horns for mids, and another set of large format compression drivers.
Build another set of PPSL and you're done.
For the largest jobs you will have three PPSL per side, dual 12 horns and a large format compression driver driver for FOH, and the dual 12 reflex and a large format compression driver for side fills.
If you need two stages at once you run two PPSL per side and the dual 12 horns + HF on the main stage, and the dual 12 reflex + HF with one set of PPSL for the secondary stage (or at another show across town).
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*Some* of it is mutual coupling, and some is just due to the increase in directivity (radiating into effectively less pies). You seem to get the full 6dB for the first doubling, most of 6dB with the 2nd, but after that you might only get a dB or two - or close to the full 6. That *really* depends on how well the sources couple and correlate, given the spacing which gets larger and larger as the stack grows.
I bought an Ashly Protea NE24.24M, I think it will grow with my system Nicely
I worked With a 24.24M in a large installed system at my previous church. The NE is basically thew same but has a network port so I don't have to mess with serial to usb adapters for my laptop, which have been crashing it lately (I still deal with a lot of legacy serial stuff at work) 15 bands of PEQ on each input and HPF/LPF and another 15 Bands of PEQ on each output, plus delay on inputs and outputs and a limiter on outputs.Did you ever find the thread referenced above? Ill see if I can find it too.
Thanks again.
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