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Old 14th March 2013, 05:20 PM   #21
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Quote:
Originally Posted by ClackS02 View Post
HA! Thats not me! i want something with headroom! Id rather have a set of subs at half volume than at full with the same SPL !

This is it! I need to speak to someone that has first hand knowledge ! Its all well looking at graphs, but id like to know that what im building is going to impress!
Simple.
Build these.

Keystone Sub Using 18,15,&12 Inch Speakers

"Half volume" is about a 10 dB difference in level. The Keystone is about 6 dB more efficient than a bass reflex nearly the same size.
It is an easy to build cabinet, and works well with a variety of speakers, though best with the B&C 18SW115-4 or B&C 18TBW100-4.

Having designed subs to beat any other designs I have heard for over 30 years, the Keystone, for it's size, does that.

Art
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Old 14th March 2013, 05:37 PM   #22
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Based on the type of music he's interested in I think the Keystone is tuned at least 1/2 octave too high for his needs.
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Old 14th March 2013, 06:09 PM   #23
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Originally Posted by weltersys View Post
The Keystone is about 6 dB more efficient than a bass reflex nearly the same size.
I found this statement to be extremely compelling so I did a quick sim using tb46's Hornresp inputs for the Keystone in post 96 of the Keystone thread compared to a ported box. Both sims use the B&C 18tbw100, both shown at xmax. The ported box is half the size of the Keystone. The ported box is obviously the light grey line.

Click the image to open in full size.

Clearly the graphs don't tell the whole story, the ported box will suffer more from both power and port compression than the tapped horn but the answer doesn't look quite so simple to me. I know you've mentioned that you get different measured results than simulations predict but this simulation shows that either you are exaggerating a bit or Hornresp has no correlation to reality at all.

Last edited by just a guy; 14th March 2013 at 06:17 PM.
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Old 14th March 2013, 06:51 PM   #24
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Originally Posted by just a guy View Post
Both sims use the B&C 18tbw100, both shown at xmax. The ported box is half the size of the Keystone. The ported box is obviously the light grey line.

I know you've mentioned that you get different measured results than simulations predict but this simulation shows that either you are exaggerating a bit or Hornresp has no correlation to reality at all.
As David McBean has mentioned, he is a programmer, not a cabinet builder.
He relies on builders to convey differences in the actual results to predicted.
Many builders have noted that Hornresp often exaggerates peaks and dips.
There is also the basic problem of Hornresp using a circular expansion, while very few bass horns are ever built in that fashion.

I find his program quite useful, though seldom find exact correlation to the actual builds.
The actual measurements and performance of a cabinet are more useful to me.

Of interest, the ported cabinet does suffer from "port compression" at high power levels, having less LF compared to upper output, while the tapped horn is the inverse, LF gains linearly, while upper output reduces.

The results below are the ported cabinet and the Keystone, both loaded with the BC18SW115-4, and a pair of Lab 12s, each measured in the same place outdoors, same amp, filters (25 &125Hz BW) same pink noise output.

I have no reason to lie about any test results, the only way to learn how (and how well) a design works is to measure, listen and compare. If the results are not good, change the box (or driver) until they are.
The Keystone design encompassed more than 100 separate cabinet changes and tests to determine the results of those changes.

Art
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Old 14th March 2013, 07:50 PM   #25
tb46 is offline tb46  United States
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Hi just a guy,

I should not have posted any Hornresp simulations for the Keystone sub (even though I noted that they do not take the Keystone mouth into consideration) as these simulations only lead to confusion. Because of the Keystone exit (mouth) Hornresp will not arrive at a correct simulation. It really does take AkAbak to get close on this one. Djim tried different methods, e.g.: see Page 13: Keystone Sub Using 18,15,&12 Inch Speakers . Even Tom Danley states that measurements beat simulations.

PASC build a Keystone sub and posted pictures and measurements in the Keystone thread. He seems to be very impressed with the results.

Regards,
__________________
Oliver
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Old 14th March 2013, 09:42 PM   #26
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Quote:
I have no reason to lie about any test results...
I understand, and please don't think I'm claiming you are doing so.

Quote:
As David McBean has mentioned, he is a programmer, not a cabinet builder.
He relies on builders to convey differences in the actual results to predicted.
Many builders have noted that Hornresp often exaggerates peaks and dips.
There are a couple of good reasons why peaks and dips (especially very narrow band, high amplitude peaks and dips) might not agree completely with the simulation. First, the physical wooden cab walls are not infinitely rigid so there are some internal losses that the simulation cannot accurately account for. This is mainly going to affect the really narrow peaks you often see in Hornresp tapped horn sims, if the peak is narrow enough it might not show up in the measurement at all. Second, when there are solid boundaries in the physical build you can create nulls, just like the nulls that are created by the solid walls reflections in a room. There is no way for Hornresp to account for this because Hornresp does not concern itself with the physical boundaries inside an enclosure, especially a folded horn.

Quote:
There is also the basic problem of Hornresp using a circular expansion, while very few bass horns are ever built in that fashion.
From my own experience and what I've read this isn't really a concern unless your horn mouth gets big enough to cause problems with dispersion - and it needs to be pretty big to affect the frequencies a sub is playing.

Quote:
I find his program quite useful, though seldom find exact correlation to the actual builds.
The actual measurements and performance of a cabinet are more useful to me.
You might (or might not) remember a member here named soho54. (He posted here a bit but was much more active at avsforum and hometheatreshack.) He did dozens of accurate simulations and over and over again, he showed that measurements actually do match simulations very very well. He used Akabak and broke the horn into 50+ sections and his simulations regularly matched measured results. Several times people complained that Hornresp was not accurate and he simulated their physical build and showed that they in fact did not build what they simulated and that's why the sims and measurements did not match. He showed that if they simulated what they built accurately the sims match the measurements very well.

This matches my experience, my sims overlay my measurements almost exactly. I've had problems a couple of times with nulls in the 80 - 90 hz region which is most likely due to having multiple segments of the physical build having the same length and being long enough to cause nulls based on their physical dimensions.

I agree with your assessment that response can change with extremely high power level but I'm not seeing the large discrepancies that you are talking about.

Quote:
The results below are the ported cabinet and the Keystone, both loaded with the BC18SW115-4, and a pair of Lab 12s, each measured in the same place outdoors, same amp, filters (25 &125Hz BW) same pink noise output.
In the simulation I provided the ported box needs quite a bit more power to hit xmax than the tapped horn, so I'm not sure this is a fair comparison. A more fair comparison would be to apply enough voltage to each box to get it to the point of onset of clearly audible distortion. And to be fair, to accurately compare there should be more details about the ported box. All I know about it is the driver used. No info about tuning frequency, volume, port size, etc etc etc.

Please understand that I'm not trying to give you a hard time but I'm not seeing the gross discrepancies that you are describing. I can see power and port compression accounting for maybe 3 db difference but not 6. And to be honest, I'm much more interested in the flh vs tapped horn discrepancies you mentioned earlier but that discussion didn't go anywhere. You didn't provide a simulation for the front loaded design.

Last edited by just a guy; 14th March 2013 at 10:03 PM.
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Old 14th March 2013, 09:45 PM   #27
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Originally Posted by tb46 View Post
Hi just a guy,

I should not have posted any Hornresp simulations for the Keystone sub (even though I noted that they do not take the Keystone mouth into consideration) as these simulations only lead to confusion. Because of the Keystone exit (mouth) Hornresp will not arrive at a correct simulation. It really does take AkAbak to get close on this one. Djim tried different methods, e.g.: see Page 13: Keystone Sub Using 18,15,&12 Inch Speakers . Even Tom Danley states that measurements beat simulations.

PASC build a Keystone sub and posted pictures and measurements in the Keystone thread. He seems to be very impressed with the results.

Regards,
Understood, but soho54 has shown over and over that accurate simulations match measurements very well, at least at small signal levels. Weltersys has claimed over and over that accurate simulations don't match measurements very well at all. I'm just trying to get to the bottom of this, I think it's in everyone's best interests to determine how much trust to place in our simulations.

I'm not trying to say the Keystone is a bad design, I just don't see it being 6db ahead of a similarly sized and tuned well designed ported box with the same driver when both are provided enough power to get them to the onset of audible distortion (not the same power applied to each).

Last edited by just a guy; 14th March 2013 at 10:04 PM.
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Old 14th March 2013, 10:42 PM   #28
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Originally Posted by just a guy View Post
And to be honest, I'm much more interested in the flh vs tapped horn discrepancies you mentioned earlier but that discussion didn't go anywhere. You didn't provide a simulation for the front loaded design.
You provided none of your simulations or measurements...

I used a Hornresp FLH simulation that did not represent the actual results.
It would be of no use to post up a simulation that bears so little resemblance to the finished cabinet.
It is not possible to model a DFLH in Hornresp, the ducts did bring it closer to the original FLH Hornresp model.
I was not greatly pleased by the design, other than it is adequate for providing bass for a small system that can be towed behind my Mustang.
As it sits, I spent far more time designing, building and trying to get the DFLH to work decently than I have using them. I posted them more as a curiosity, as the design is quite unusual.

If you want to take the time to simulate the DFLH design in Akaback and find you get the same results as the cabinet as built, good on you.
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Old 14th March 2013, 10:51 PM   #29
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Originally Posted by just a guy View Post
Weltersys has claimed over and over that accurate simulations don't match measurements very well at all.
I never claimed my simulations were accurate.
An accurate simulation by definition would match measurements .

Art
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Old 14th March 2013, 10:59 PM   #30
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Originally Posted by weltersys View Post
You provided none of your simulations or measurements...

I used a Hornresp FLH simulation that did not represent the actual results.
It would be of no use to post up a simulation that bears so little resemblance to the finished cabinet.
It is not possible to model a DFLH in Hornresp, the ducts did bring it closer to the original FLH Hornresp model.
I was not greatly pleased by the design, other than it is adequate for providing bass for a small system that can be towed behind my Mustang.
As it sits, I spent far more time designing, building and trying to get the DFLH to work decently than I have using them. I posted them more as a curiosity, as the design is quite unusual.

If you want to take the time to simulate the DFLH design in Akaback and find you get the same results as the cabinet as built, good on you.
So to be clear, you didn't even try to make an accurate simulation of the front loaded horn at all but still claim that the simulation doesn't match the measurement? I think that's all I need to know.

I did show you the sims and measurements I could find online from several years ago, which were first run measurements with no care taken to get an accurate result, only to make sure there were no major problems like air leaks. Even after changing the design in Akabak, raising the tuning, the sim still almost exactly overlays the measurement except for an unexpected null at 90 hz which I've already explained twice. I already explained that my old computer died and I lost my more accurate measurements hat I never posted online (taken outside at 10m) which look just like the measurements I did show. I went out of my way to show you what I have. I haven't built or simmed anything new in the last 2 or 3 years so I don't have anything new to show you.

As far as I can tell you are the only one claiming Hornresp is not accurate at small signal levels. Clearly there are differences at high power levels but if you can't get your response curve shape to match your sims at 1 watt you are doing something wrong. Lilmike is a member here (but more active at avsforum) and he's posted sims and measurements of ALL of his SEVERAL designs and they ALL overlay within about 1 db across their entire bandwidth. He's posted both front loaded and tapped horn sims and measurements overlaid on the same graph of each design. His experiences mirror mine and dozens of others.

I understand that you are a trial and error kind of guy and there's nothing wrong with that, but from what I can tell you never bothered to try to get an accurate simulation on either of your designs.

Quote:
If you want to take the time to simulate the DFLH design in Akaback and find you get the same results as the cabinet as built, good on you.
I have no desire to take the time to simulate your design just to prove that it can be simulated accurately and that you could have done so yourself if you had taken the time.

Last edited by just a guy; 14th March 2013 at 11:16 PM.
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