how low can go with beyma 15K200?please help - Page 2 - diyAudio
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Old 17th December 2006, 02:39 PM   #11
kyselym is offline kyselym  Czech Republic
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hi bjorno

thank you again will go through as soon as possible

my L26 are closed box around 85L 60% fill. it is made as 2.5way for DD8. Also have two L21 as subs for dd8 and have strong feeling that those L21 are "faster". but I decided to do it the same like tony (br 12l for DD8) and have separate amp and filters for subs. Im not sure if 2x L26 will be enough, because now if I go loud they go out of xmax (if there is a lot of "sub" in program)

how big are the enclosures for your box? 1.22m x 0.42m x 0.35m ?
not sure if I have so much room for 2 or 4 of these
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Old 22nd December 2006, 06:55 AM   #12
kyselym is offline kyselym  Czech Republic
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hi

I decided to give L26 a try again I have gone through all the images. But don't know how to conctruct it. Firstly I miss some deatiled cabinet drawing to be able to copy and secondly I'm not sure how scheme of baffle step circuit will look. Also don't understand those circles with a,b, h in picture seasl26mltqwt-5.gif.

and one more questin on baffle step correction: why it is needed for sub? I thought that it is need 2,3ways to join midrange or tweeter. will be active baffle step correction possible? if so isn't it better?

ps. still can't believe that it goes down to 20's and doesn't overcome xmax.

any help will be greatly appreciated
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Old 26th December 2006, 11:12 PM   #13
bjorno is offline bjorno  Sweden
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Hi kyselym,

From post #11:

Quote:
Also have two L21 as subs for dd8 and have strong feeling that those L21 are "faster
Is it your opinion you have also 2 L21 subs that are more ‘blameless’ than your L26’s closed subs?

Do you blame the speaker box or the drivers?

From what I know the adjective ‘Fast’, speaker or driver is not used at all when considering the art of building speakers and conceptually, “fast (er)” has no meaning at all considering driver qualities or characteristics.

Nobody but you knows what you really mean when stating the word “faster”.

Quote:
br 12l for DD8
I recommend don’t convert your closed boxes to 12 L BR because this may destroy all possible fidelity when passing over to the L26 subs with a huge ‘footprint’ at and around the crossover frequency.

Quote:
how big are the enclosures for your box? 1.22m x 0.42m x 0.35m
The sub enclosure have a net volume of 132.5 Litres and is of less volume than you suggested in your post #1:

Quote:
My limits: max 160Liter volume’ for the Beyma driver.
I calculated with 21 mm MDF 1.242 x 0.342 x 0.438 H x W x D (m).

A box variant with a height of 0.942 x 0.442 x 0.438 with almost the same performance and more suitable for use as a ‘stand’ can be found in submitted pictures: 1standL26.gif.and 2standL26.gif.

Observe in this case and as before posted plots, the speaker is placed stand alone close to the rear wall.

If you want to place this sub as a stand for the DD8 and away from the rear wall, look further down for the pictures labelled; standL26_1 to _3.

Quote:
Im not sure if 2x L26 will be enough, because now if I go loud they go out of xmax
My first reaction is that you randomly misused the sub amplifier level control; forcing some of the drivers to levels they are not designed for or secondly simply failed when balancing the different speaker drivers characteristics.

Are you using measurement equipment for this purpose?

I don’t know what the reason is, any driver can reach mechanical x-max but in my opinion the L26 is a very good sub driver/match for L18RNX/P and can be used down and even safely below 20 Hz if necessary.

Look at the first submitted pictures; 1a and 1b, they are simulations for your 12L DD8 measured 1m on-axes at 1m from rear wall where the speaker is at ear-height (stand=28 in or 71 cm) and the reflexes from the floor and rear wall is taken into consideration.

You can then turn your amplifier volume-knob up to about 18W before exceeding linear x-max at 70 Hz (about 5 mm peak cone displacement).

This input power level and a high pass with near 2:nd order BW slope (Qtc= 0.68) will return 90 dB SPL at 1m distance at the pass band.

Your 85 L L26 sub bass speaker/amplifier is then supposed or should take over with a BW low pass filter somewhere close to 70 Hz or at what frequency?

The far field closed box system and infinite baffle SPL (pass band at 102 dB SPL) plot may suggest this is a good choice, but the ‘plotted SPL response for the system’ indicates a lower – 3 dB point = 30 Hz as optimal when the DD8: s are driven stand alone.

Thus if you don’t turn your main amplifiers bass tone control down (if you have one) you will have a huge spectral overlap.

Passive filtering is of course out of question for quality reasons.

How can you be sure your 85 L subs and DD8 not should integrate smoothly?

I assume you are using the closed L26 subs as stands for the DD8 and away from the rear wall?

Referring to picture 2a and 2b where the L26’s are modelled as stands for the DD8’s:
The L26 sub will match the DD8 with ease, 4 W input from the sub bass amplifier causes a peak (RMS*1.414) displacement of less than 6 mm and is very safe from hitting x-mech.

Post # 12

Quote:
I decided to give L26 a try again I have gone through all the images. But don't know how to conctruct it. Firstly I miss some deatiled cabinet drawing to be able to copy and secondly I'm not sure how scheme of baffle step circuit will look.
I think you should spend some time visiting MJK: s site reading the definitions of the ML-TQWT .

Quote:
Also don't understand those circles with a,b, h in picture seasl26mltqwt-5.gif. and one more questin on baffle step correction: why it is needed for sub?
A, b and h is only an approximation of a straight conical layout using the same CSA’s as in the simulation and here used for checking purposes only.
You don’t need baffle step correction for a sub, but is provided with MJK: s simulation programs.

Quote:
I thought that it is need 2,3ways to join midrange or tweeter. will be active baffle step correction possible? if so isn't it better?
Agree.

Quote:
ps. still can't believe that it goes down to 20's and doesn't overcome xmax.
Why? Can you show measured evidences proofing your assertions?
Look at the following plots of a L26 ML-TQWT with an internal length of 1.8 m placed at 1 m from the rear wall also is within its x-max limit, see pictures standL26_1 to _3.

B
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File Type: gif 1standl26.gif (92.8 KB, 155 views)
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Old 26th December 2006, 11:15 PM   #14
bjorno is offline bjorno  Sweden
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Old 26th December 2006, 11:16 PM   #15
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Old 26th December 2006, 11:18 PM   #16
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Old 26th December 2006, 11:20 PM   #17
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Old 26th December 2006, 11:21 PM   #18
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Old 26th December 2006, 11:23 PM   #19
bjorno is offline bjorno  Sweden
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Old 26th December 2006, 11:24 PM   #20
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