3-way Crossover (Beyama 8BR40, Seas MCA15RCY, Seas 27TFFC)

[jojino]

Hi All,
I am not very familiar with LspCAD. Is there anybody out there who can hepl me with simulation of crossover for Beyma 8BR40, Seas MCA15RCY and Seas 27TFFC? Links bellow with characteristics:
http://profesional.beyma.com/pdf/8BR40NE.pdf, H1262-08 MCA15RCY,
H0881-06 27TFFC. Here is the project from Troels, but there is different woofer Poor Man'
My vented cabinet has 28 litres (l, w, d -620 mm, 200 mm, 230 mm). Thank you in advance.
Jojo

[mdocod]

I could model up something that might be acceptable as a starting point for experimentation, however, I don't think the driver selection is very good for the box size you have there. That woofer really would be a better choice for a much larger floor standing box if you want to go vented. You *might* be able to use that woofer in the 1ft^3 box you have, but I'd suggest sealing up the box. Vented isn't going to have desirable results unless the box is at minimum 2-3X that size IMO.

Also.... The woofer selected is 211.5mm wide... I hope the 200mm width listed is the inside dimension, otherwise that woofer won't even fit on the front of that box. Even still it would be a pretty tight fit.

[EngelholmAudio]

A Qts of 0.57 isn't what normally is used in ported enclusures.

[jojino]

Originally Posted by EngelholmAudio

A Qts of 0.57 isn't what normally is used in ported enclusures.

Thank you for your answer. Yes I know that my cabinet is really small, but I have it and I would like to use it. My question is, if the smaller volume of cabinet will make influence on the crossover in the part of middlerange and tweeter. I would like to use same scheme as here (crossover version 5) Poor Man'
thank you
Jozef

[giralfino]

Maybe some basics about box design would help.
1) Box volume and/or tuning affect only the bass
2) Baffle width and type of borders influence the baffle step effect
3) baffle dimension and driver position influence diffraction
Just for giving some round numbers, 1) is sub 100 Hz, 2) is 100-1000 Hz, 3) is over 1000 Hz.

How all this relate to your question? If you only change the internal volume but keep the baffle unchanged, then there are chances that you can retain the mid-tweeter c/o part of the Poor Man design. However since you want to change also the bass driver, you have to design from scrap the bass-mid c/o part (bass low-pass and mid high-pass) and this can require also a mod on the mid part of the filter (mid low-pass).
That sounds a lot of work. I would build the Poor Man as-is, or learn how to use speaker design SW. Check the sticky post section in this forum.

Ralf

P.S. I concur with mdocod, the Beyma driver won't fit in your box

[jojino]

Originally Posted by giralfino

Maybe some basics about box design would help.
1) Box volume and/or tuning affect only the bass
2) Baffle width and type of borders influence the baffle step effect
3) baffle dimension and driver position influence diffraction
Just for giving some round numbers, 1) is sub 100 Hz, 2) is 100-1000 Hz, 3) is over 1000 Hz.

How all this relate to your question? If you only change the internal volume but keep the baffle unchanged, then there are chances that you can retain the mid-tweeter c/o part of the Poor Man design. However since you want to change also the bass driver, you have to design from scrap the bass-mid c/o part (bass low-pass and mid high-pass) and this can require also a mod on the mid part of the filter (mid low-pass).
That sounds a lot of work. I would build the Poor Man as-is, or learn how to use speaker design SW. Check the sticky post section in this forum.

Ralf

P.S. I concur with mdocod, the Beyma driver won't fit in your box

Thank you Ralf,
Beyma driver will fit (20 cm is internal dimmension, 23,5 is external). Yes, you are right, I know, that if I will change bass section, I have to modify everything. But I hope, that characterisitcs at cutoff (about 350 Hz) of Beyma 8BR40 and Seas CA22RNX are quite similar, so I will not make correction at all.
Many thanks,
Jozef

[sreten]

Originally Posted by jojino

Thank you for your answer. Yes I know that my cabinet is really small, but I have it and I would like to use it. My question is, if the smaller volume of cabinet will make influence on the crossover in the part of middlerange and tweeter. I would like to use same scheme as here (crossover version 5) Poor Man'
thank you
Jozef

Hi,

A x/o designed specifically for a very wide baffle won't work well with a normal box.

rgds, sreten.

[system7]

jojino, I think everyone is telling you that Beyma driver is unsuited for bass reflex. Qts 0.48, Vas 82L. Fs 31Hz for the 8BR40, as opposed to the linked 8BR40NE which is a different animal.

Qts of 0.28-0.45 is where you want to be for reflex. That Beyma bass doesn't get enough electrical damping and is too big to behave well in a small box. Troels had a headscratcher with the Qts=0.41 Vas 97L Fs 29Hz SEAS CA22RNX as it goes. The suspension was a lot stiffer than specified giving Vas 46L. That helped him with a smaller 38L bass reflex box.

I just did some sums for a changed "Poor Man" Closed Box with the SEAS measurements and got 50L and F3 50Hz for flat (Qc 0.71) response. 23L and F3 70Hz with Troels' measurements.

The Beyma 8BR40 gives 70L and F3 46Hz. OK, that's IB not reflex, but a huge difference, no? You will end up with a speaker that is peaky in the bass and doesn't have much low extension in a small 28L cabinet.

(FWIW, Morgan Jones explains closed box calculations rather well here:
Arpeggio Loudspeaker
I haven't tried my hand at reflex, as it goes, but it's a start. )

I see no reason why you can't use the nice SEAS 27TFFC tweeter in some way though. Easy enough to attenuate them!

[jojino]

Originally Posted by system7

jojino, I think everyone is telling you that Beyma driver is unsuited for bass reflex. Qts 0.48, Vas 82L. Fs 31Hz for the 8BR40, as opposed to the linked 8BR40NE which is a different animal.

Qts of 0.28-0.45 is where you want to be for reflex. That Beyma bass doesn't get enough electrical damping and is too big to behave well in a small box. Troels had a headscratcher with the Qts=0.41 Vas 97L Fs 29Hz SEAS CA22RNX as it goes. The suspension was a lot stiffer than specified giving Vas 46L. That helped him with a smaller 38L bass reflex box.

I just did some sums for a changed "Poor Man" Closed Box with the SEAS measurements and got 50L and F3 50Hz for flat (Qc 0.71) response. 23L and F3 70Hz with Troels' measurements.

The Beyma 8BR40 gives 70L and F3 46Hz. OK, that's IB not reflex, but a huge difference, no? You will end up with a speaker that is peaky in the bass and doesn't have much low extension in a small 28L cabinet.

(FWIW, Morgan Jones explains closed box calculations rather well here:
Arpeggio Loudspeaker
I haven't tried my hand at reflex, as it goes, but it's a start. )

I see no reason why you can't use the nice SEAS 27TFFC tweeter in some way though. Easy enough to attenuate them!

link on Beyma 8BR40N is correct, unfortunately in title is 8BR40 because I didn´t suppose that there is difference in data. There is recommendation of enclosure volume 20/60L. If you already make some Troel´s measurements, can you please predict f3 of beyma 8BR40/N in 28L cabinet with bass reflex?
I know that create Troel´s project as it is is much better, but I have nice cabinet from old speakers and beyma 8BR40/N.
Thank you.
Jozef

[system7]

I'm no expert on bass reflex calculations, but here goes:

Beyma 8BR40/N has Vas 61L, Qts 0.57, Fs 33Hz.

The SEAS has Vas 51L, Qts 0.42, Fs 38Hz.

A flat Butterworth 4th order reflex response needs 182L on the Beyma I reckon. F3 18Hz.
Troels' SEAS unit needs 63L as HE measured it for F3 34 Hz. I reckon he's not aimed quite at that response with his 38L box.

I'm using reflex equations Vb=(15 X Vas)X(Qts^2.87), F3= (0.26X Fs)/(Qts^1.4).

What I can tell you is the Beyma in a 28L CLOSED box will have a Q around 1, and a F3 of 60Hz. That Q of 1 will lift lowest bass by 3dB from maximally flat. You will approach a cabinet Q of 0.8 on a 60L CLOSED box, which is a lot better.

I really don't think you will get any sensible results by adding a reflex here, it will get worse. At bottom the driver has too high a Qts @ 0.57 and a 28L cabinet is too small for reflex which needs bigger enclosure than closed box, and is barely appropriate for 28L closed box. It will sound boomy in IB, and just be horrible in reflex because everything you do with ports will make it worse.

Phew, things I do for people!