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Double 15 WinISD help please
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odc04r View Drop Down
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Points: 5482 		Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 20 December 2018 at 11:23am
Originally posted by MarjanM MarjanM wrote:

Am i the only one here that have problem with this sort of cabinets that needs +9db of eq at the tuning frequency?


I don't see the issue, it just means you need to design and build correctly to match the EQ. If you know what you are doing with regard to testing the final design properly it'd likely be fine, but I wouldn't suggest it to a novice. The port is doing all the work at system resonance anyway, with an appropriately Q'd boost EQ and HPF set it could be fine.Iwouldn't necessarily integrate another cab under it but then the average user of such a box typically wouldn't either.
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Originally posted by MarjanM MarjanM wrote:

Am i the only one here that have problem with this sort of cabinets that needs +9db of eq at the tuning frequency?


But the box is very efficient at that point so the boost often doesn’t have as much effect in output, but can help massively on cooling or similar.

Hell, go measure the settings for an SB28 / KS28 / JSub or Jinfra...
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MarjanM View Drop Down
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Originally posted by toastyghost toastyghost wrote:

Originally posted by MarjanM MarjanM wrote:

Am i the only one here that have problem with this sort of cabinets that needs +9db of eq at the tuning frequency?


But the box is very efficient at that point so the boost often doesn’t have as much effect in output, but can help massively on cooling or similar.

Hell, go measure the settings for an SB28 / KS28 / JSub or Jinfra...

The box also have a minimum impedance on tuning point, add 400% more power that you are applying at tuning frequency then on the rest of the spectrum, nad that to me is not a good way to achieve low end extension.
If you take a look at SB28, it is only rated at 1225W per box. Beside the fact it has two very powerfull 1200W AES BMS 18s inside.
The companion amplifier for that box is only 1800W at 4 ohm. So the box is pretty much underpowered because it can not take more.
Marjan Milosevic
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Elliot Thompson View Drop Down
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Originally posted by MarjanM MarjanM wrote:

Originally posted by toastyghost toastyghost wrote:

Originally posted by MarjanM MarjanM wrote:

Am i the only one here that have problem with this sort of cabinets that needs +9db of eq at the tuning frequency?


But the box is very efficient at that point so the boost often doesn’t have as much effect in output, but can help massively on cooling or similar.

Hell, go measure the settings for an SB28 / KS28 / JSub or Jinfra...

The box also have a minimum impedance on tuning point, add 400% more power that you are applying at tuning frequency then on the rest of the spectrum, nad that to me is not a good way to achieve low end extension.
If you take a look at SB28, it is only rated at 1225W per box. Beside the fact it has two very powerfull 1200W AES BMS 18s inside.
The companion amplifier for that box is only 1800W at 4 ohm. So the box is pretty much underpowered because it can not take more.


The majority of Impedance vs Frequency plots on simulators are not accurate. In order for accurate results, you must measure the impedance curve of the loudspeaker(s) in the actual box. I tend to use LIMP which is a product of ARTA.

Bear in mind just touching the cone with the driver in motion will alter the impedance curve. So there is no way a simulator can give accurate results from an impedance curve perspective.   

 

If you want low end extension, the cabinet needs to be large enough to generate a substantial amount of low end extension… hence the importance of VAS. When the cabinet is very small, the trade off is less extension. The majority are content to reach to 50 Hertz as it can give one the impression of low end extension. 

 

Although you may not find such a design to your liking, I can assure you the majority of users are willing to sacrifice extension for a compact enclosure. Excluding I and, 2 to 3 others I have interacted online, the majority wants a large speaker in the smallest cabinet possible. Although I only tote large drivers in large cabinets, I can understand the majority do not care to move around large loudspeaker cabinets.   

 

Best Regards,

Elliot Thompson
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Originally posted by MarjanM MarjanM wrote:

Originally posted by toastyghost toastyghost wrote:

Originally posted by MarjanM MarjanM wrote:

Am i the only one here that have problem with this sort of cabinets that needs +9db of eq at the tuning frequency?


But the box is very efficient at that point so the boost often doesn’t have as much effect in output, but can help massively on cooling or similar.

Hell, go measure the settings for an SB28 / KS28 / JSub or Jinfra...

The box also have a minimum impedance on tuning point, add 400% more power that you are applying at tuning frequency then on the rest of the spectrum, nad that to me is not a good way to achieve low end extension.
If you take a look at SB28, it is only rated at 1225W per box. Beside the fact it has two very powerfull 1200W AES BMS 18s inside.
The companion amplifier for that box is only 1800W at 4 ohm. So the box is pretty much underpowered because it can not take more.


The only real risk with EQ'ing heavily at system resonance is that the voice coil cooling is significantly reduced due to reduced excursion, and your port should be high enough in area to deliver the increased volume of air without chuffing. I can't see much more of a problem as long as you have an appropriate HPF set.

You make the box too small such that the alignment is over damped, then you get some of the output at resonance back by EQing. Providing the cooling is sufficient, and your amplifier has sufficient head room to deliver the signal, and your box design works as intended from small to large signal, it is a valid design choice given the infinite number of alignments available.

Hoffman's law holds. Smaller box, same-ish extension, but you need more power.

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MarjanM View Drop Down
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So we agree that you are pushing the driver 4 times harder to achieve the same results as you would have with a optimum box volume.
Now, do you think the life span of the drivers in those two boxes will be same? having the fact that the one in the small box is working 4 times harder.
Marjan Milosevic
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Given your knowledge of the bms drivers marjan, what volume would you advise me to use?

I've decided not to do the eq'd box.  I need them for new years eve party so don't have the time to sort a more complicated design. All your input was helpful in making this decision.
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Elliot Thompson View Drop Down
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Just make the 180 litre box as planned. The limitation is the BMS 15 N630 not enclosure size....

Originally posted by Elliot Thompson Elliot Thompson wrote:



This speaker is limited to 40 Hz (-3dB) not only by the QL 6 alignment, but by the loudspeaker’s TS Parameters as well. Even if you decide to design a 300 litre box, you would still be -3 dB @ 40 Hz despite using a lower tuning scheme regardless of the alignment.

 

Such characteristics are the nature of the driver as it cannot take advantage of a larger enclosure. Bear in mind the fs, VAS in addition to the qts dictates the overall performance.The driver offers a high fs and a low denominator in terms qts so, you are pretty much at optimum performance using two fifteens in a 180 litre box.


Whether you choose a 120 litre or 180 litre box, the cone excursion differential amongst the two drivers in each box (120 litre vs 180 litre) is so minuscule @ 1200 watts you will not lose the drivers faster in the 120 litre box vs the 180 litre box. What you will attain is a -3 dB around 62 Hertz in a 120 litre box as oppose - 3 dB around 50 Hz in the 180 litre box. At -10 dB, the 180 litre box is 34.8 Hz whereas, the 120 litre box is 37.9 Hz @ - 10 dB.

So the 180 litre box will sound a little heavier than 120 litre box.

Best Regards, 
Elliot Thompson
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Originally posted by MarjanM MarjanM wrote:

Originally posted by toastyghost toastyghost wrote:

Originally posted by MarjanM MarjanM wrote:

Am i the only one here that have problem with this sort of cabinets that needs +9db of eq at the tuning frequency?


But the box is very efficient at that point so the boost often doesn’t have as much effect in output, but can help massively on cooling or similar.

Hell, go measure the settings for an SB28 / KS28 / JSub or Jinfra...

The box also have a minimum impedance on tuning point, add 400% more power that you are applying at tuning frequency then on the rest of the spectrum, nad that to me is not a good way to achieve low end extension.
If you take a look at SB28, it is only rated at 1225W per box. Beside the fact it has two very powerfull 1200W AES BMS 18s inside.
The companion amplifier for that box is only 1800W at 4 ohm. So the box is pretty much underpowered because it can not take more.

I always thought the 1225W rating for the SB28 was for the opposite reason. A large cab tuned low would mean pushing the full rated power into the drivers would result in over-excursion so the power rating would be the mechanical limit of the drivers, not the thermal limit. Should be great for keeping power compression down though.

For the BMS 15S330/630 the balance between excursion and power seems to be around 80 litres per driver, tuned around 40-45Hz, basically the manufacturer’s recommendation. I’ve tried these drivers in a number of different configurations and that’s personally my preference. The excursion for the same SPL output is more or less the same (for the same tuning), the difference is how much power it takes to move the cone by that amount; in a smaller enclosure it takes more power.

Incidentally, I also have a pair of Tony’s Q15s which must be around 6 years old now and still going strong. For general use the B6 alignment has no issues at all, only in some extreme cases with very compressed bass-heavy music playing over a long time has there been any noticeable heat build up. For me, the ability to be able to carry one in each hand into a gig and out-play many cabs twice their size means the loss of a little bit of efficiency down low isn’t much of a trade-off.
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MarjanM View Drop Down
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Points: 7816 		Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 21 December 2018 at 9:15am
Originally posted by JonB67 JonB67 wrote:

Given your knowledge of the bms drivers marjan, what volume would you advise me to use?

I've decided not to do the eq'd box.  I need them for new years eve party so don't have the time to sort a more complicated design. All your input was helpful in making this decision.

Here is what i did.
Marjan Milosevic
MM-Acoustics
www.mm-acoustics.com
https://www.facebook.com/pages/MM-Acoustics/608901282527713
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odc04r View Drop Down
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Originally posted by MarjanM MarjanM wrote:

So we agree that you are pushing the driver 4 times harder to achieve the same results as you would have with a optimum box volume.
Now, do you think the life span of the drivers in those two boxes will be same? having the fact that the one in the small box is working 4 times harder.


As is all these things, it depends. Primarily on the frequency content of the signals the box gets on average. I don't think I would expect a significant reduction in mean failure time if you were sensible
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The link was useful marjan. Dimensions and some guesswork gave me clues. 

I've gone for 180litres, which is approx 200 once you add in all the handles and drivers and bracing.

The ply is now cut! Thanks all for your input and discussion.  I'll post pics once they're operational.  They've got to be used on new years eve so it won't be long.  
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