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21" reflext enclosure needed

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bob4 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Topic: 21" reflext enclosure needed
    Posted: 20 March 2021 at 9:41am


Bit late to the party........

This is a Josh Ricci Ckram (without front chamber attachment)

Loaded with B&C 21DS115, built by a friend of mine upon my suggestion.

Roughly about the same size as the beyma plan, but with a slot port with roughly twice the surface area, and nearly 1m port lenght in L shape. The tuning is exactly 30 Hz. 

It goes flat to 30 Hz, according to Joshs akabak simulation about 92 -93 dB sensitivity at 30 Hz! Averages about 95-96 dB in the upper band. Without processing. 

Box is mostly rebated, hasnt been glued up yet, currently assembled for testing with screws only. With most of the bracing in place, it is already quite impressive. We run it on a bridged yamaha h7000, and have not managed to get the amp to clip in the small workshop we are currently confined to by the weather. We have also not been able to get the ports to chuff yet. It sounds balanced,  very round and punchy, and plays all the sub 40 Hz stuff with authority. 

I assume the Beyma design you were talking about is this:

If you check the Beyma pdf, except for the unrealistic peak spl figure (without frequency reference!!!), the response of the box is 6-7 dB down at 30 Hz.
 This means  that  
1) the actual sensitivity of the beyma design at 30 Hz is 99 -6 = 93 dB AT BEST , but probably lower, plus the likelyhood of strong port compression and  chuffing
2) you will have to apply serious eq to get a flat response down to 30 Hz.


 To add further smoke and mirrors, their response graph is normalized, not telling you the true sensitivity of the design.

There is also a chart of eq settings, with a 2,5 dB boost at 45 Hz. 
If you look at the lenght of the triangle ports it is very obvious that the box is tuned very high, not lower than 45-50 Hz. 

Based on my experience i would strongly recommend the ckram in standard reflex configuration over this beyma design. I don't think the beyma design is any good if you need flat response down to 30 Hz.





Edited by bob4 - 20 March 2021 at 9:44am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 13 December 2020 at 9:52am
Thanks Marjan.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 13 December 2020 at 12:49am
My advice to you is to be patient and wait for a bargain on the used market. 
At this time many rental companies are trying to off load some of their gear in order to survive the crisis.
Here is one example of a pair of very solid double 18 inch box that goes for very little money.

Marjan Milosevic
MM-Acoustics
www.mm-acoustics.com
https://www.facebook.com/pages/MM-Acoustics/608901282527713
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 12 December 2020 at 10:43pm
Thank you Marjan for your advice, your subs are beautiful but way out of my price range I live on a council estate and am poor, i'm a poor guy with a passion buring inside me for dj'ing and doing dance music parties but my lack of money is such an obstacle it's hard to decide what the best route for me is. 

Anyway thanks again mate.
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MarjanM View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 11 December 2020 at 11:28pm
Or like this. 
Marjan Milosevic
MM-Acoustics
www.mm-acoustics.com
https://www.facebook.com/pages/MM-Acoustics/608901282527713
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 11 December 2020 at 11:27pm
I am saying that for 1000 pounds you can not make them looking like this. 




Marjan Milosevic
MM-Acoustics
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 11 December 2020 at 8:46pm
Are you saying a properly designed and built sub for example using the RCF LF21X451 won't be as good as a big name manufacturer sub that costs £1,000 new?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 11 December 2020 at 1:46pm
I dont really have much time for internet these days, but you should know few things.
That Beyma 21 inch driver is not that good as you think it is. 
One good reflex 21inch sub will never be louder then two good 18 inch subs. 
It might go lower, but not in a "compact" box.

If you buy any driver for like 450, and you pay 350-400 or so for the box, (which i purely speculate the cost) , how will that box look at the end?
Will it have professional box fit and finish?
What will be its resale value?

I am all for a DIY, but not when you can not actually do it your own but you have to pay someone to make it for you. That does not make any economical logic. At the end you will spend 1000 for a box that will kind of look well done, but not as good as a professionally made one.
Marjan Milosevic
MM-Acoustics
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https://www.facebook.com/pages/MM-Acoustics/608901282527713
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 10 December 2020 at 8:49pm
If I was to buy an RCF LF21X451 driver who could design and build me an enclosure for it and how much would it cost? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2020 at 9:06pm
Originally posted by MarjanM MarjanM wrote:

And what is your actual budget? 
BTW that Beyma 21 inch is not in the highest ranks of 21 inch drivers.

Maybe not their 21" but their 18LEX1600Nd I read somewhere was voted by Pro Sound Web as the best subwoofer driver in 2014. I don't mind going for the RCF LF21X451 driver it's cheaper, has an xmax of 14mm, it's rated at being able to handle 2,000 watts continuous average power and according to the frequency response chart is -3db at 45hz which I believe is free air and has a sensitivity of 98db at 55hz with a pretty flat'ish curve. It states it's good for reflex as well as horn loading. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2020 at 8:58pm
Originally posted by knet94 knet94 wrote:

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.

Yeah I have but one problem is finding the right pair of subs that are as compact as the Beyma 21LEX1600Nd Beyma enclosure plan which could give me the same kind of spl output and depth of bass is i've found near impossible. Even a pair of Martin Audio WS18x are smaller, tuned higher and wouldn't be as loud spl wise. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mel_Gibson Quote  Post ReplyReply Direct Link To This Post Posted: 08 December 2020 at 8:55pm
Yeah I meant to buy a brand new subwoofer which would or could be as good as a custom made one using the Beyma 21LEX1600Nd I believe would cost around £1,500 brand new. Obviously it wouldn't cost £1,500 to custom make the subwoofer. The driver is around £450 but I have no idea how much someone would charge me to build me an enclosure for the driver. 
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