paulspencer said:
Greets!
I enjoy 'bench racing' audio too or I wouldn't be here, but you've made it plain that you have no real interest in learning from history, which is fine, but I prefer to spend my time with folks who do.
FWIW, most folks who engineer big projects build scaled down models to answer such Qs, it's what I did to learn about what to expect with big cabs, horns and learned things I never would have working full scale for the simple reason I wouldn't have gambled the time/$$/effort to build an optimum sized behemoth that would have taken up most of my backyard and required a 256 ft^2 hole in one of my exterior walls.
Anyway, good luck with it, hope you don't wind up with BD's remorse.
GM
For the cause of audiophile research I will go one better! 5 cents! (smaller again).
Gentlemen of the jury, I present exhibit A:
Shown is a 5c coin on top of a curved top MDF box with a thickness of somewhere between 18 and 30mm, while playing Jenny Morris "A break in the weather" (plenty of bass), turned up fairly loud.
Gentlemen of the jury, I present exhibit B:
What you see, gentlemen, is a fine example of speaker building technology, a new benchmark - 15mm particleboard! Without bracing this enclosure is able to withstand the assault of any bass with finesse and unflappable ease.
The plaintiff would have this evidence removed, but the jury should note: music was playing while these shots were taken. When the coin was being placed, it fell over many times (without music) due to the slightest amount of wind while the photographer moved about.
Gentlemen of the jury, what say you?!
Jury:
On the charge of being unable to sustain a 5 cent coin, we find the accused MDF not guilty!
Judge:
Case dismissed.
On a more serious note:
How did I manage that? As far as I'm aware, I'm trying to also learn from others mistakes, other people's history.
Gentlemen of the jury, I present exhibit A:
An externally hosted image should be here but it was not working when we last tested it.
Shown is a 5c coin on top of a curved top MDF box with a thickness of somewhere between 18 and 30mm, while playing Jenny Morris "A break in the weather" (plenty of bass), turned up fairly loud.
Gentlemen of the jury, I present exhibit B:
An externally hosted image should be here but it was not working when we last tested it.
What you see, gentlemen, is a fine example of speaker building technology, a new benchmark - 15mm particleboard! Without bracing this enclosure is able to withstand the assault of any bass with finesse and unflappable ease.
The plaintiff would have this evidence removed, but the jury should note: music was playing while these shots were taken. When the coin was being placed, it fell over many times (without music) due to the slightest amount of wind while the photographer moved about.
Gentlemen of the jury, what say you?!
Jury:
On the charge of being unable to sustain a 5 cent coin, we find the accused MDF not guilty!
Judge:
Case dismissed.
On a more serious note:
How did I manage that? As far as I'm aware, I'm trying to also learn from others mistakes, other people's history.
Gimme a jingle when you're ready to burn wood.
GM, are you suggesting a scale model here? How do you scale such a horn when tuning is based on size? A 40 Hz horn where it is scaled down based on tuning and using the same geometry?
Regarding delay, I have the facility to delay the mains so it will be time aligned. I have played around with delay and so far I've found quite a big delay is required before you really notice the difference. There is a big grey area in the middle.
I looked into what has been said about Bert's horn. Thanks for mentioning it - interesting read. The only negative thing I heard about it was that it required delayed mains, which he prefers not to do, but it doesn't bother me.
Regarding delay, I have the facility to delay the mains so it will be time aligned. I have played around with delay and so far I've found quite a big delay is required before you really notice the difference. There is a big grey area in the middle.
I looked into what has been said about Bert's horn. Thanks for mentioning it - interesting read. The only negative thing I heard about it was that it required delayed mains, which he prefers not to do, but it doesn't bother me.
Good point. Thanks for bringing it up.
I don't plan to delay the video. Do you think it's really necessary?
6m delay >>> 57ms
At 30 fps, that's 33ms per frame. So in effect the mains would be delayed less than 2 frames. It doesn't sound like a problem to me. Ok, but numbers are one thing ... I just did a quick test. An 8m delay seems to be ok. Lip sync seems ok. At 50m the problem is obvious. I tried some in between delays and I can't really say I have come up with a point where it becomes a problem, but with my quick test, I tend to think somewhere between 6 and 12m it becomes a problem.
I understand that HTPC can easily delay the video, and may look into this in the future.
Thinking about it further - what happens at the cinema? Lets say you sit at the back, so the audio will be delayed since sound travels slower. You could be sitting 30m back or more.
I don't plan to delay the video. Do you think it's really necessary?
6m delay >>> 57ms
At 30 fps, that's 33ms per frame. So in effect the mains would be delayed less than 2 frames. It doesn't sound like a problem to me. Ok, but numbers are one thing ... I just did a quick test. An 8m delay seems to be ok. Lip sync seems ok. At 50m the problem is obvious. I tried some in between delays and I can't really say I have come up with a point where it becomes a problem, but with my quick test, I tend to think somewhere between 6 and 12m it becomes a problem.
I understand that HTPC can easily delay the video, and may look into this in the future.
Thinking about it further - what happens at the cinema? Lets say you sit at the back, so the audio will be delayed since sound travels slower. You could be sitting 30m back or more.
Retsel, potentially yes, however this does not overcome the problem that has lead to the bass horn idea - not happy with the sound of my sub drivers. I have tried my existing drivers sealed, vented and dipole, push pull for all except vented. Dipole seems to extract the best performance so far, but even there I can tell that it's a sub driver working. They just don't have the definition to resolve mid and upper bass detail. If I eq everything flat to compare mains alone and mains with subs, you can tell when the subs are in use even with the same response - bass sounds blurred, more powerful and exciting for home theatre but less articulate. I'm convinced this is a limitation of my drivers. Rob Wells seems to have the same experience with his scan speak/tempest/lab horn comparison.
My Rythmik kits are on the way, I'm pretty sure they would do just fine in IB and wouldn't have the same problem, but then I have only 2 x 12" drivers. There is a fireplace which previously had an oil burner which is now out of use. I could potentially use it and seal it up. I may in fact give it a go just to see how it goes.
I have one issue with IB - it relies much more on the linearity of the driver suspension system. In most subwoofers, forces are applied to the cone which are more linear than the suspension of a driver. This is one of the advantages of a horn, which when designed correctly loads both the side of the cone with equal pressure, thus forcing lower distortion and greater linearity than the driver would otherwise have.
OTOH, my dipole setup does sound subjectively better than box sub versions. How much of that is due to room interaction, and how much due to removing the box is hard to say.
I suppose an alternative is to put the Rythmiks in IB and AV12s in a pair of tapped horns crossed low.
I do think the bass horn has no peers for a given price point. If cost was no object, one could make an IB with a lot of displacement and power, using the best drivers available, and probably match the bass horn in terms of distortion and output, but last time I checked it cost about 50x as much.
My Rythmik kits are on the way, I'm pretty sure they would do just fine in IB and wouldn't have the same problem, but then I have only 2 x 12" drivers. There is a fireplace which previously had an oil burner which is now out of use. I could potentially use it and seal it up. I may in fact give it a go just to see how it goes.
I have one issue with IB - it relies much more on the linearity of the driver suspension system. In most subwoofers, forces are applied to the cone which are more linear than the suspension of a driver. This is one of the advantages of a horn, which when designed correctly loads both the side of the cone with equal pressure, thus forcing lower distortion and greater linearity than the driver would otherwise have.
OTOH, my dipole setup does sound subjectively better than box sub versions. How much of that is due to room interaction, and how much due to removing the box is hard to say.
I suppose an alternative is to put the Rythmiks in IB and AV12s in a pair of tapped horns crossed low.
I do think the bass horn has no peers for a given price point. If cost was no object, one could make an IB with a lot of displacement and power, using the best drivers available, and probably match the bass horn in terms of distortion and output, but last time I checked it cost about 50x as much.
Paul, I can appreciate your thinking as much of it makes sense except I take issue with two points that you made. A horn is a sealed box with an expansion at the end of it. Sure it has lower distortion than sealed box drivers because it moves a lot less to create the same output above the horn cutoff and it loads the driver on the front side of the driver which helps to reduce the nonlinearities of the driver.
However, the driver still has a variable load against the fixed air mass in the compression chamber (as the driver moves against the air mass, the resistance increases) which still leads to distortion. Also, the horn is similar to a sealed box in that the sound wave which bounces around in the compression chamber returns back through the cone creating distortion.
An infinite baffle system (like a dipole) has essentially no variable load in either direction because the air mass is so large in both cases the driver sees a constant load (you cannot compare that sound of sealed boxes, even those mounted in relatively large boxes, with that of infinite baffle systems because of the very large difference in the size of the "box"). This leads to low distortion. Also, the rear wave of the driver can dissipate in the large area behind the driver resulting in lower distortion from the return of that energy back through the driver. The sound quality of an infinite baffle is similar to that of a dipole, except that infinite baffle systems can go very low to reproduce the lowest frequencies.
If you find drivers that have a high x-max, particularly those which use xbl technology or shorting rings, they are designed to be very linear even at higher x-max and their surrounds add very little in the way of distortion. If you have a bias towards lower mass cones, then pick up a bunch of those, but you would need more of them because they typically have low x-max.
As far as the amount of output and drivers that you need. Your calculation about the number of drivers that you need is silly. First, you don't need 140 db. Have you EVER listened to 140 db in your room???? Even for a very large room, four 18 inch drivers with decent x-max would be enough and at the levels that you will be listening at, they will hardly move in an infinite baffle set-up. You will also be able to reproduce bass down under 10 hz. If you don't think that bass under 20 hz makes any difference, read reviews about the impact that the fan subwoofer makes.
I think that horns are cool to engineer and are great for very large venues. I purchased the plans for one, but after further research, I did not feel that they are the best for subwoofers because they cannot reproduce the lowest frequencies and they have disadvantages compared to dipoles and infinite baffle systems.
I also love subwoofers with servos. I had a Genesis 900 which was just OK until I sent the driver back to Genesis and they used an improved system to attach the accelerometer. WOW was that great bass. It was much better than the Edgar's horn sub, both because the bass was phase-alligned, and because the sound quality was better. I think, though, that the increased demand on the amp was too much for it and it died. But Genesis sure knows how to make great bass. I suspect that the Rythmik has similar quality bass, although it may not equal the improved Genesis system.
Retsel
However, the driver still has a variable load against the fixed air mass in the compression chamber (as the driver moves against the air mass, the resistance increases) which still leads to distortion. Also, the horn is similar to a sealed box in that the sound wave which bounces around in the compression chamber returns back through the cone creating distortion.
An infinite baffle system (like a dipole) has essentially no variable load in either direction because the air mass is so large in both cases the driver sees a constant load (you cannot compare that sound of sealed boxes, even those mounted in relatively large boxes, with that of infinite baffle systems because of the very large difference in the size of the "box"). This leads to low distortion. Also, the rear wave of the driver can dissipate in the large area behind the driver resulting in lower distortion from the return of that energy back through the driver. The sound quality of an infinite baffle is similar to that of a dipole, except that infinite baffle systems can go very low to reproduce the lowest frequencies.
If you find drivers that have a high x-max, particularly those which use xbl technology or shorting rings, they are designed to be very linear even at higher x-max and their surrounds add very little in the way of distortion. If you have a bias towards lower mass cones, then pick up a bunch of those, but you would need more of them because they typically have low x-max.
As far as the amount of output and drivers that you need. Your calculation about the number of drivers that you need is silly. First, you don't need 140 db. Have you EVER listened to 140 db in your room???? Even for a very large room, four 18 inch drivers with decent x-max would be enough and at the levels that you will be listening at, they will hardly move in an infinite baffle set-up. You will also be able to reproduce bass down under 10 hz. If you don't think that bass under 20 hz makes any difference, read reviews about the impact that the fan subwoofer makes.
I think that horns are cool to engineer and are great for very large venues. I purchased the plans for one, but after further research, I did not feel that they are the best for subwoofers because they cannot reproduce the lowest frequencies and they have disadvantages compared to dipoles and infinite baffle systems.
I also love subwoofers with servos. I had a Genesis 900 which was just OK until I sent the driver back to Genesis and they used an improved system to attach the accelerometer. WOW was that great bass. It was much better than the Edgar's horn sub, both because the bass was phase-alligned, and because the sound quality was better. I think, though, that the increased demand on the amp was too much for it and it died. But Genesis sure knows how to make great bass. I suspect that the Rythmik has similar quality bass, although it may not equal the improved Genesis system.
Retsel
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