I'm going on holiday in January but in about Febuary or March i'm wanting two 21" reflex enclosures made, painted, handles, speakon sockets and grilles, painted black all the enclosure and grilles. Basically these plans are what i'd like built :

S-21LEX

http://www.beyma.com/en/enclosure-designs/ - http://www.beyma.com/en/enclosure-designs/

But i'd like handles on the side, castors aren't a big problem i'll be using a wheel board my mate made from plywood and attached castors to it. Is anyone able to do this professionally and give me a price for the two enclosures? I'll be buying the drivers when I get back from holiday.

Thanks.

Ports are kind of small (definitely for triangle shaped ones). For such drivers I would look for designs with ports >800 cm2 slot/round. 

Look at the current offerings of big pro manufacturers like LA,PK, Meyer, JBL etc. 

They use huge ports for a reason. That triangle ports have more problems regarding to port compression (which changes tuning and therefore large signal performance) is a fact.

Still every design is made out of making compromises. Beyma chose for a simpler and easier port layout.

What you do with this info is all up to you 

I've seen on Youtube people have used Beyma, RCF, B&C etc...drivers to build their own subs and as far as I could see most are bottom rectangular ports. 

9/10 times the youtube designs aren't particularly good. Most are really garbage.

A good design will cost time (and knowledge), after that you need to test and verifiy which again can take a lot of time. Maybe watch the enclosure design page of B&C for a while, they just put out some new designs and more are coming.

How would you say they're compromised?

When I said Youtube I didn't mean people who make designs and upload videos of the designs I mean videos of people who've made subs using designs from B&C, Beyma etc..and then uploaded videos of them testing their subs out. 

This.

Well they tested the enclosure and got peaks of 137db with pink noise with a 6db crest factor so all I can say to you is :

Best regards,

Walter

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" rel="nofollow - 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? 

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

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.

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. 

BTW that Beyma 21 inch is not in the highest ranks of 21 inch drivers.

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

https://www.beyma.com/wp-content/uploads/S-121LEX-SYSTEM-1.pdf" rel="nofollow - https://www.beyma.com/wp-content/uploads/S-121LEX-SYSTEM-1.pdf

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).

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. 

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. 

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.

Anyway thanks again mate.

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.

https://gebrauchte-veranstaltungstechnik.de/ad-549564-JBL+SRX+728s+" rel="nofollow - https://gebrauchte-veranstaltungstechnik.de/ad-549564-JBL+SRX+728s+

:)

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

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

https://data-bass.ipbhost.com/topic/868-riccis-ckram-subwoofer-and-files/" rel="nofollow - https://data-bass.ipbhost.com/topic/868-riccis-ckram-subwoofer-and-files/

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:

https://www.beyma.com/wp-content/uploads/S-21LEX1600-SYSTEM-2021-1.pdf" rel="nofollow - https://www.beyma.com/wp-content/uploads/S-21LEX1600-SYSTEM-2021-1.pdf

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.