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Discussion Starter #1
















Cheers,


John




.
 

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This is a good study but one thing is noteworthy. The front loaded horn's low knee is about a half octave below the other two designs. This is a bit unfair to the flh.

It's tricky to do a fair comparison with front loaded horns vs ported or tapped horns because a front loaded horn's low knee is below the frequency at which the tuning excursion minimum occurs while in the other two designs the low knee is above the tuning excursion minimum frequency. This also implies another problematic issue as well, namely that any high pass filters that are used will considerably lower the output of the front loaded horn down near the low knee but won't affect the other two alignments much. The extent of the effect of this hpf issue for all three alignments depends on the particular designs being studied but in general the preceding comment is a factor that definitely deserves attention.

Therefore it is my belief that the only fair way to compare these three different alignments is to use designs that have the same low knee (not the same tuning) and compare them at max spl with any applicable high pass filters in place. Overall these two considerations might not change things a lot (raising the low knee on the flh would give more output but adding a hpf would take some away), but I think that's a more fair way to compare and I think it would show the flh in a more flattering light.

Also, to keep things really fair all three designs should be simulated with the same program. Again, this might not make a whole lot of difference but there will be some difference.
 

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Great analysis. The horns still rule if power is limited, though, and space and bldg materials are easily obtained. If you have the space and the time, and not so much $$, horns are a pretty good deal for low cost, low distortion SPL if you don't tune too low. Once you tune below 20Hz, the excursion demands become quite real and can only be partially offset by using multiples to raise the low corner SPL.

JSS
 

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John,

Thanks so much for this informative simulation and comparison!

As you know, I've been wanting to build a low tuned horn for some time now, but I've never found a design that would go as low as I wanted. Now I know why! It would be monstrous, and the laws of diminishing returns certainly apply in this case! For the gain of just a few dB, you pay a huge space penalty. I guess I'll stick to my Marty sub (hopefully SUBS, by the end of summer).

Really nice comparison. Thanks again!

Mike
 

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Discussion Starter #6
"Therefore it is my belief that the only fair way to compare these three different alignments is to use designs that have the same low knee (not the same tuning) and compare them at max spl with any applicable high pass filters in place."

this is what I used to think as well and is what makes comparing these three systems so tricky. however, where the rubber hits the road -- max spl -- all three have the same 20hz point where excursion hits a minimum (in this comparison) and a steep rolloff under that, so the comparison is fair. it is true that under 20hz, the front loaded horn is more sensitive, so it will get to its max spl point with less power, but so what? under 20hz all three are excursion limited though, so sensitivity isn't terribly important.

the front loaded horn may have a bit of additional spl relative to the other two under 20hz, but since excursion is highly uncontrolled in all three cases under 20hz and as a result all three should have some sort of protective filter in place filtering out sub20hz content, I wouldn't want to gamble on trying to capture any of the slightly higher sub 20hz spl provided by the front loaded horn.

thank you for reading and commenting, dsg.
 

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"Also, to keep things really fair all three designs should be simulated with the same program. Again, this might not make a whole lot of difference but there will be some difference."

good point. in this particular analysis, it turns out that the areas of interest (the excursion limited zones immediately above and below 20hz for the ported enclosure) model similarly in winisd and hornresp. I just double-checked.
 

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Discussion Starter #8
"Great analysis."


thank you. that means a lot to me, coming from you.




"The horns still rule if power is limited, though..."


no doubt and there may actually be other benefits that aren't captured with these models, as good as they are.
 

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"As you know, I've been wanting to build a low tuned horn for some time now, but I've never found a design that would go as low as I wanted. Now I know why! It would be monstrous, and the laws of diminishing returns certainly apply in this case! For the gain of just a few dB, you pay a huge space penalty. I guess I'll stick to my Marty sub (hopefully SUBS, by the end of summer)."


i suspect that is the right call. if you have some idea/desire for a different form factor, I'd be happy to work with you on your next one--maybe some sort of push-pull, slot-loaded, mega-marty? ;-)
 

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People around here chase the last 3-6db with great fervor and in that view 4db is significant, the sensitivity advantage is also probably lost on many who simply look at max SPL charts and disregard sensitivity and its subjective impact. Also to really chase a low tuned FLH people would need larger enclosures and multiple high xmax drivers in each from my understanding, the LAB is probably not a good choice for this since excursion is the limiting factor in the lower range. In my view a FLH is the only no compromise solution at any part of the spectrum given enough size and that is precisely why it isn't popular because no one really has the space for an optimally sized horn. I am facing this problem, I want a low tuned FLH but I don't have space for it but I also don't want to compromise and go ported/sealed. This is also why the TH has grown popular as it provides more gain around tuning in the lower region for a given size.

Just my view, appreciate the comparison John!
 

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This argument is not unlike that comparing sealed to vented subs. Yes, sealed do have the advantage below the tuning frequency of vented, in a smaller package, but they don't have the advantage above the tuning frequency. By the same token, direct radiators can have an advantage below the knee frequency of a horn, but not above it. This chart shows the maximum SPL, displacement limited, of a pair of Lab 12 in a 300L 20Hz VB, and in a 600L 28Hz horn. The advantage goes to the VB below 24Hz, but above that it's not even close. Even a pair of the VBs driven with twice the power wouldn't match the output of the horn above 26Hz.


If one is going to make a simplistic assessment of the value of different alignments it would be that sealed/IB goes the lowest, at the highest cost per dB; horns have the lowest cost per dB at the expense of size, and vented box characteristics lie in between the other two. None is inherently superior across the board, neither is any inherently inferior across the board. The one to use is the one that fits your response and output needs, available space and bank account.
 
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 This subject has been if particular interest to me as of late. I've spent a lot of time reading some great material. So thanks for this LTD02.


QUOTE=LTD02;25998458] there may actually be other benefits that aren't captured with these models[/QUOTE]


^ This, ... the "je ne sais quoi" with regard to the flh' characteristics.
 

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This is a good study but one thing is noteworthy. The front loaded horn's low knee is about a half octave below the other two designs. This is a bit unfair to the flh.
I thing this is a very important point, since lowering the freq x amount costs x cubed in volume, so that half octave really skews the results.

I think it's also interesting that when it comes to speakers we (myself included) are a lot more tolerant of power differences than with amps.

4 dB for the former is not *that* big of a deal, but if it was an amp we say "that's 2.5X the power!"
 

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John you are still using winisd? It’s really only good for having a database of driver parameters saved. You know HR can easily do vented enclosures and directly compare them to the horn you are modeling with a quickness… You have to use the same program for all enclosures at least!:p

Ports compress at the highest output levels so you never really get quite as much out of vented enclosures near tuning as the simulations say. Even my 10” flared power ports compress some and those will shift a TON of air. Horns can compress some too once the flow and pressures get high enough but in general the cross section is almost always much larger than typical vents and is also expanding continuously so it is less of a problem usually. Sealed or IB has no vents, or horn throat or compression chamber at all so they are free from this type of compression. You can also get noises from all of the air flow at high output levels. Once again in this aspect it is sealed/IB>horn>vented generally.

Another thing to consider is with sealed/IB/vented and other direct radiator systems the sensitivity is lower as is the maximum output and it is often easy to hear suspension and mechanical noises start to creep in once the driver gets near xmax or a bit past. Especially at the lowest frequencies where the ear is less sensitive and excursion and distortions are higher. With FLH’s and some kinds of BP enclosures the driver is buried inside of the box and any suspension or mechanical noises from the driver are filtered quite effectively so that these sounds cannot reach the ear. (Note I’m not talking about harmonic distortions here but those can be reduced a bit as well.)Not to mention that these boxes often offer a solid gain in sensitivity and max output as well which also helps offset these driver noises. What I’m saying here is that while you may be able to produce roughly the same SPL with a double driver vented enclosure versus a single in a FLH, if the drivers are being driven near their limits the FLH may still sound cleaner with the mechanical distortions and noises from the drivers operation buried inside of its enclosure.Tapped horns I would put somewhere in between direct radiators and FLH’s (or bandpasses).

Also the reduced power demands of more sensitive and efficient systems can have impacts on long term heating and distortions of the drivers. Increased current through the voice coils can have all kinds of effects on the output of the system and most of them are negative.

When you add all of that up the: Sensitivity, efficiency, lack of vents compression or noises and reduced excursion demands from a FLH, combined with the natural filtering effect on some of the garbage noises from a driver under heavy operation produce a system that sounds quite a bit different than direct radiator based systems even if you double or triple up on the direct radiators to match the output capabilities.

I really like the way a good FLH sounds and I’ve heard more than a few…There is just something about them that is different and really worthwhile. But whenever I get to designing a new system I never seem to go with them. Ever. The size is always an issue. They are either too big or they won’t go low enough or they don’t have enough output in the amount of space I have available. I tried to force myself to design one for the PH and ended up getting frustrated and scrapping the design because I couldn’t at least match a TH or vented subs with the amount of cab I had available and extension needed. I still want to design one I feel good about sharing.

Something I would like to hear one day is an uber FLH bass system covering 30-120Hz paired up with a couple TRW-17’s for the 1-30Hz.
 

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Here's a couple of pictures with a bunch of screen caps that show a few interesting things. They also show how I prefer to compare different alignments. I'm not implying you did it wrong, simply that I do it differently. I prefer to compare max spl with the same low knee. Usually I do it with the same low knee with high pass filters in place but in the instance I did the same low knee without the hpf in place to make a point with row 3 and 5 in picture 1. There are a few points I want to get across and I wanted to do it without 200 screen caps. None of these designs are ideal but I didn't want to spend more than 15 minutes on this.

PICTURE 1
Row 1
- Hornresp inputs for a ported box and a front loaded horn, both with same driver
Row 2 - Schematic showing these designs are the same size (the ported box needed a massive vent to keep velocity down and it's still at 18 m/s at xmax which is a bit high)
Row 3 - Acoustical power of each design at xmax
Row 4 - Diaphragm excursion, just shown to show I am playing fair
Row 5 - Acoustical power of both designs overlaid to show that when the designs are the same size there isn't much difference in output at the low knee - this is true of most resonant vented designs including tapped horns
Row 6 - Acoustical power with hpf in place
Row 7 - Diaphragm excursion with hpf in place



This shows pretty clearly that there isn't much difference in output at the low knee when the ported box and front loaded horn are the same size and have the SAME low knee. Once the hpf is in place the ported box wins by a bit. This also shows that low tuned ported boxes often have problems with port size and resonances inside the passband due to velocity issues.

Horns need to get exponentially larger as tuning decreases if you want flat response and ideal loading. A 30 cubic foot box with a 16 hz low knee as shown in the first post is extremely undersized, but as shown, even with this extreme limit some amount of gain is possible. Approximately the same amount of gain as a tapped horn of the same size with the same low knee.

Now let's look at the other extreme, the same ported box compared to a much larger front loaded horn. The horn still isn't large enough to be ideal size for the tuning but Hornresp has a mouth size limit so I did what I could. At over 14000 liters this isn't a practical living room design but it does show that massive gain and flat response are possible with massive enclosure size. While this design isn't practical it does become more practical if something like this is broken down into multiple units with multiple drivers and used in a large space. Multiples do work and if enough are used they will add up to an ideal full size horn, assuming the original design was an ideal full size horn with multiple drivers.

 

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John you are still using winisd? It’s really only good for having a database of driver parameters saved. You know HR can easily do vented enclosures and directly compare them to the horn you are modeling with a quickness… You have to use the same program for all enclosures at least!:p

Ports compress at the highest output levels so you never really get quite as much out of vented enclosures near tuning as the simulations say. Even my 10” flared power ports compress some and those will shift a TON of air. Horns can compress some too once the flow and pressures get high enough but in general the cross section is almost always much larger than typical vents and is also expanding continuously so it is less of a problem usually. Sealed or IB has no vents, or horn throat or compression chamber at all so they are free from this type of compression. You can also get noises from all of the air flow at high output levels. Once again in this aspect it is sealed/IB>horn>vented generally.

Another thing to consider is with sealed/IB/vented and other direct radiator systems the sensitivity is lower as is the maximum output and it is often easy to hear suspension and mechanical noises start to creep in once the driver gets near xmax or a bit past. Especially at the lowest frequencies where the ear is less sensitive and excursion and distortions are higher. With FLH’s and some kinds of BP enclosures the driver is buried inside of the box and any suspension or mechanical noises from the driver are filtered quite effectively so that these sounds cannot reach the ear. (Note I’m not talking about harmonic distortions here but those can be reduced a bit as well.)Not to mention that these boxes often offer a solid gain in sensitivity and max output as well which also helps offset these driver noises. What I’m saying here is that while you may be able to produce roughly the same SPL with a double driver vented enclosure versus a single in a FLH, if the drivers are being driven near their limits the FLH may still sound cleaner with the mechanical distortions and noises from the drivers operation buried inside of its enclosure.Tapped horns I would put somewhere in between direct radiators and FLH’s (or bandpasses).

Also the reduced power demands of more sensitive and efficient systems can have impacts on long term heating and distortions of the drivers. Increased current through the voice coils can have all kinds of effects on the output of the system and most of them are negative.

When you add all of that up the: Sensitivity, efficiency, lack of vents compression or noises and reduced excursion demands from a FLH, combined with the natural filtering effect on some of the garbage noises from a driver under heavy operation produce a system that sounds quite a bit different than direct radiator based systems even if you double or triple up on the direct radiators to match the output capabilities.

I really like the way a good FLH sounds and I’ve heard more than a few…There is just something about them that is different and really worthwhile. But whenever I get to designing a new system I never seem to go with them. Ever. The size is always an issue. They are either too big or they won’t go low enough or they don’t have enough output in the amount of space I have available. I tried to force myself to design one for the PH and ended up getting frustrated and scrapping the design because I couldn’t at least match a TH or vented subs with the amount of cab I had available and extension needed. I still want to design one I feel good about sharing.

Something I would like to hear one day is an uber FLH bass system covering 30-120Hz paired up with a couple TRW-17’s for the 1-30Hz.
Exellent post Ricci, spot on comments that I can fully agree with. No matter how many stacked direct rads I hear, it just doesn't do what FLHs can do, its not just the sound, its also the raw force of impact. Size is the curse of the FLH...

I think something like you described in your last line would be superb and pretty much as close to perfect as one can get without an insanely sized FLH covering below 30Hz. Perhaps the Sonic Boom Generator... as I recall it was about 130db at 3Hz outdoors.

I am looking forward to your FLH design.
 

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...Now let's look at the other extreme, the same ported box compared to a much larger front loaded horn. The horn still isn't large enough to be ideal size for the tuning but Hornresp has a mouth size limit so I did what I could. At over 14000 liters this isn't a practical living room design but it does show that massive gain and flat response are possible with massive enclosure size...
Not *in* the living room, but if you just think of it as an 8' cube it doesn't seem so bad :)
 

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Ricci, have you seen this yet?
http://www.klipsch.com/kpt-1802-HLS/details

It's a FLH with a port into the throat (a Klipsch patent)

I think you need to measure one, or at least put a couple into your home...they're only 72" x 48" x 31". While you're at it, drop a massive xmax 18" driver into it too.

Btw, hornresp assumes that the speaker is firing into an anechoic space....how does horn loading change in a finite sized room where you have a lot more loading from nearfield boundaries? I think it's different than what happens for the direct radiator.
 
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Ricci, have you seen this yet?
http://www.klipsch.com/kpt-1802-HLS/details

It's a FLH with a port into the throat (a Klipsch patent)

I think you need to measure one, or at least put a couple into your home...they're only 72" x 48" x 31". While you're at it, drop a massive xmax 18" driver into it too.

Btw, hornresp assumes that the speaker is firing into an anechoic space....how does horn loading change in a finite sized room where you have a lot more loading from nearfield boundaries? I think it's different than what happens for the direct radiator.
That thing is just massive. Again, space vs power/displacement.
 
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