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21" reflext enclosure needed
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smitske96 View Drop Down
Young Croc
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Points: 1092 		Post Options Post Options   Thanks (0) Thanks(0)   Quote smitske96 Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2020 at 1:37pm
Originally posted by knet94 knet94 wrote:

Originally posted by Mel_Gibson Mel_Gibson wrote:

Because I can't afford subs that would give me the same performance as the custom subs i'm thinking of building or having built. I'd say to buy a pair of subs 21" that would be as good as ones I can custom make would probably cost about £1,500 each.

I can't see the design that you have posted up costing anywhere near £1,500 each to build. 

He meant a factory cab with that 1500 each.
Secondhand would also be a good one. You can get some hefty subs for that kind of money (or even less).
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knet94 View Drop Down
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Points: 1510 		Post Options Post Options   Thanks (0) Thanks(0)   Quote knet94 Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2020 at 12:18pm
Have you considered going the 2nd hand route. Seen some really good cabs going for small money recently. Tho tbh far bigger than the Beyma ones.
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knet94 View Drop Down
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Points: 1510 		Post Options Post Options   Thanks (0) Thanks(0)   Quote knet94 Quote  Post ReplyReply Direct Link To This Post Posted: 07 December 2020 at 12:15pm
Originally posted by Mel_Gibson Mel_Gibson wrote:

Because I can't afford subs that would give me the same performance as the custom subs i'm thinking of building or having built. I'd say to buy a pair of subs 21" that would be as good as ones I can custom make would probably cost about £1,500 each.

I can't see the design that you have posted up costing anywhere near £1,500 each to build. 
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MarjanM View Drop Down
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And what is your actual budget? 
BTW that Beyma 21 inch is not in the highest ranks of 21 inch drivers.
Marjan Milosevic
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Mel_Gibson View Drop Down
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Points: 36 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2020 at 5:09pm
Because I can't afford subs that would give me the same performance as the custom subs i'm thinking of building or having built. I'd say to buy a pair of subs 21" that would be as good as ones I can custom make would probably cost about £1,500 each.
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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: 05 December 2020 at 4:49pm
Why dont you just buy some subs? DIY is not always the answer.
Marjan Milosevic
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smitske96 View Drop Down
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Points: 1092 		Post Options Post Options   Thanks (0) Thanks(0)   Quote smitske96 Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2020 at 4:36pm
Round ports would be the best, but can be difficult to omplement if they need to be long (and enough cm2). Slot ports can make inplementing much easier. The point in the end is that triangle shaped ports need to be bigger to be equal in terms of compression and the resulting distortion.
If you use said port area, you would get velocity of around 26m/s (with 1600 Watt AES input). If you go with something like 800cm2 you'll around 18m/s. I have write up somewhere from a fb forum were the 3 ports are compared. 

Personally i don't dig the 6dB crest factor measurements a lot (for any manufacturer). It only tells you one part of the story. Therefore I think CEA2010 would be more suitable.
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jammin75 View Drop Down
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Points: 2375 		Post Options Post Options   Thanks (0) Thanks(0)   Quote jammin75 Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2020 at 3:04pm
Originally posted by cravings cravings wrote:

it's yet another account for djteknovibe / Jack_The_Ripper / richard stringer / Fred_Dibnah / richardstringer1993... so he's in Boston in Lincolnshire.


Originally posted by Fred_dibna Fred_dibna wrote:

I have a quick port question, are circular, triangular or under driver slot ports best? The driver will be the RCF LF18X401, cabinet tuned to 36hz and i'll be powering a pair with a bridged QSC RMX4050HD giving the subs a combined 4k.

I was just curious, thanks.




LOL
feel the vibes !!!   "Who Feels it Knows it"            Strong like Lion              
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Mel_Gibson View Drop Down
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Points: 36 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2020 at 2:46pm
Don't round ports suffer more from the chuffing sound? I heard the chuffing sound on some old hi-fi speakers years ago and it sounded unpleasant. 
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Contour View Drop Down
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Round, has the best ratio port area versus port wall surface. Use a very big radius at start and end of the port, google intertechnik jetset for an example. 
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Mel_Gibson View Drop Down
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Originally posted by Chris Grimshaw Chris Grimshaw wrote:

Originally posted by Contour Contour wrote:

The ports indeed may be perfectly sized for the required optimal reflex tuning, but same tuning can be achieved using larger area, but longer port. The larger port area results in less port losses and higher output.


... With the compromise that the larger ports directly mean a larger cabinet.

There's also the potential for 1/4-wave resonances to mess up the top of the bandwidth.


The time when under-sized ports become obvious is when you're demanding full output at/near the port tuning frequency. Whether that's likely to happen will depend entirely on the program material.

Example: https://www.youtube.com/watch?v=UnQY3swM4tA (caution - lyrics are nsfw)
Has a very compressed bass line which gives subs a hard time. If your port is tuned to 36Hz, you better make sure it has lots of area. You'll also need to make sure the magnets on the drivers are adequately ventilated.

Most program material isn't so demanding, and you can "get away with" smaller port areas without suffering much/any compression.

Chris

In your opinion Chris which ports are the best overall shape? 
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Chris Grimshaw View Drop Down
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Points: 281 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Chris Grimshaw Quote  Post ReplyReply Direct Link To This Post Posted: 05 December 2020 at 12:49pm
Originally posted by Contour Contour wrote:

The ports indeed may be perfectly sized for the required optimal reflex tuning, but same tuning can be achieved using larger area, but longer port. The larger port area results in less port losses and higher output.


... With the compromise that the larger ports directly mean a larger cabinet.

There's also the potential for 1/4-wave resonances to mess up the top of the bandwidth.


The time when under-sized ports become obvious is when you're demanding full output at/near the port tuning frequency. Whether that's likely to happen will depend entirely on the program material.

Example: https://www.youtube.com/watch?v=UnQY3swM4tA (caution - lyrics are nsfw)
Has a very compressed bass line which gives subs a hard time. If your port is tuned to 36Hz, you better make sure it has lots of area. You'll also need to make sure the magnets on the drivers are adequately ventilated.

Most program material isn't so demanding, and you can "get away with" smaller port areas without suffering much/any compression.

Chris
Quality sound from Sheffield
www.grimshawaudio.com
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