3 way, Visaton CBM130AW, Seas H1148 - some questions - diyAudio
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Old 27th August 2007, 12:31 PM   #1
PCM1702 is offline PCM1702  Poland
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Default 3 way, Visaton CBM130AW, Seas H1148 - some questions

Hello,

so, finally I got some time and a pair of Seas H1148 tweeters (http://seas.no/Prestige%20Diskanter%...TV1148ny06.pdf), a pair of Visaton CBM130AW midrange, so I decided to go DIY, buy woofers and make a pair of speakers

It's really hard to find data on Visaton drivers, so here's some data I got from an old Visaton catalogue:
Fs- 40Hz,
Qts- 0.18
Mmd- 5g
SPL@2.83V- 92dB@1KHz
As far as I know CBM will do down to approx. 150Hz (not considering baffle step loss) and it's usable frequency response goes up to 3550 Hz.

So I have some questions, here we go:

- is it worth going open baffle for midrange?
- how wide should the front baffle be so that baffle step loss would'd be a problem if I want to cross it with woofer at approx. 200 Hz? Would a 35 cm wide baffle be wide enough?
- Seas tweeters are a version w/o a ferrofluid in a magnet gap, so they exhibit a strong resonance peak at 900 Hz, should I consider this peak when calculating and xover for them? I planned to cross it with Visatons at around 3.5Khz, maybe lower would be better?
Does anyone have an Fs impedance compensating circuit for this driver? Any ideas on x/o schematics for this tweeter?

Another question - I planned 12dB lowpass for tweeter and 12 dB lo/hi-pass for midrange.. any ideas on this?

As for the woofer - not decided yet, which particular brand or model, anyway something cheap and playing in a sealed enclosure, close to the floor, so that I could gain some efficiency to match the rest (i really don't want to correct SPL for the drivers so resistors are not an option), correct me, if I'm wrong - because from what I remember if the woofer directly 'sees' the floor, it gains 3dB, does it?

Cheers
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Old 27th August 2007, 09:18 PM   #2
ente is offline ente  Germany
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Default Visaton

.. if you understand a just little german maybe this will help:

http://www.visaton.de/vb/showthread.php?threadid=13359

Regards
Heinrich
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Old 27th August 2007, 09:59 PM   #3
PCM1702 is offline PCM1702  Poland
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Yes, I understand a little bit

Looks like I will start from the x-over schematics provided there, but I am not going to use attenuation for CBM, because I want all of it efficiency.

Moreover, I thing that it's worth crossing it lower, maybe somewhere around 200 Hz.

From what I see (freq. response graph of CBM on that web page), this driver will rather need 18dB/oct lowpass), any suggestions on that?

Vielen Dank Heinrich
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Old 28th August 2007, 06:22 AM   #4
ente is offline ente  Germany
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Default BOXSIM & ARTA

Hi,

if you download BOXSIM (freeware) you can view the data of the CBM130AW (and an excellent simulation program).
But the best solution is to measure your driver itself

Here you will find all the necessary tools (and informations) :
http://www.fesb.hr/~mateljan/arta/download.htm

Regards
Heinrich
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Old 28th August 2007, 10:28 AM   #5
sreten is offline sreten  United Kingdom
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Location: Brighton UK
Quote:
Originally posted by PCM1702


but I am not going to use attenuation for CBM, because I want all of it efficiency.

Moreover, I thing that it's worth crossing it lower, maybe somewhere around 200 Hz.

Hmmm..........

Will need a seriously efficient bass unit to hit 92dB/2.83V midrange,
as usual it seems baffle step is being ignored. Crossing it low at
200Hz means all BS compensation must be built into the mid driver.
With 4dB of BS = ~ 88dB midrange, this will need 94dB/2.83V bass
units, best achieved with 2 ~ 88dB 8 ohm bass units wired in parallel.

Maximum efficiency comes with 2 ~ 92dB 8 ohm bass units, but these
would need to fill in the baffle step loss of the midrange driver, see :

http://www.deadwaxcafe.com/vzone/david/david.htm

/sreten.
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Old 28th August 2007, 02:29 PM   #6
PCM1702 is offline PCM1702  Poland
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Default Re: BOXSIM & ARTA

Quote:
Originally posted by ente
Hi,

if you download BOXSIM (freeware) you can view the data of the CBM130AW (and an excellent simulation program).
But the best solution is to measure your driver itself

Here you will find all the necessary tools (and informations) :
http://www.fesb.hr/~mateljan/arta/download.htm

Regards
Heinrich
Hello

I am going to make some measurements as fast as I get hold of some microphone that can be good for this specific task (i think I will need to buy for example a Panasonic capsule mic and moutn it on something ). Thanks for the link
The frequency plot of CBM looks quite nice, it also has a good waterfall, some very minor resonances, it'a actually a leftover from an old days (maybe rather: years), when I just started DIY.


Quote:
Originally posted by sreten


Hmmm..........

Will need a seriously efficient bass unit to hit 92dB/2.83V midrange,
as usual it seems baffle step is being ignored. Crossing it low at
200Hz means all BS compensation must be built into the mid driver.
With 4dB of BS = ~ 88dB midrange, this will need 94dB/2.83V bass
units, best achieved with 2 ~ 88dB 8 ohm bass units wired in parallel.

Maximum efficiency comes with 2 ~ 92dB 8 ohm bass units, but these
would need to fill in the baffle step loss of the midrange driver, see :

http://www.deadwaxcafe.com/vzone/david/david.htm

/sreten.
Beacause I haven't bought woofers yet, there's still much room for modifications.

Yes, I've been thinking about two woofers (8"), but mounted on sidewalls, opposite to each other, so I could minimize cabinet vibrations caused by the bass units. Would this be a good idea? I mean, two woofers mounted on side walls, approximately 20 cm above floor and 15 cm below midrange...

How about sidewalls mounted woofers compensating midrange baffle step loss?
As far as two 8" woofers are considered, and I am low on budget, I have to stick with some el-cheapo woofers available here in my country.

I was thinking about these: http://www.stx.pl/index.php?vMenu=2&...vItemDB=itemdb
(it's in Polish, but all the data provided and T/S parameters are in english, freq. resposnse is here: http://www.stx.pl/charakterystyki/GD...0-8-AW-ALL.jpg)
Correct me if I'm wrong - what would be actual efficiency at 2.83V of these two drivers in parallel?

If the efficiency in this configuration would be not high enough, would moving woofers closer to the floor be a good idea? (considering they would have to compensate for midrange BSL).

Or maybe leave the idea of two smaller woofers and use one bigger one, like this? : http://www.stx.pl/index.php?vMenu=2&...vItemDB=itemdb
(freq. response here: http://www.stx.pl/charakterystyki/GD...0-8-SC-ALL.jpg)
.. and simply cross it over, say 300 Hz? (well that driver has a huge VAS, though...)

*********************

Other questions - croosover for the Seas tweeter. I finally decided to go for an LCR impedance rise at Fs compensating circuit).
But, for calculating that I need a Qms and Qes for the driver, which Seas doesn't provide (at least in PDF). How about that?
(well, I made some basic calculations and it turned out that it should be an LCR filter with C=33uF, L=0.84mH and R=4.8 Ohms for Fs@900Hz, but I think I'm wrong here...)

Ok, that's all for now
Thanks and best regards,
Adam
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Old 28th August 2007, 03:42 PM   #7
sreten is offline sreten  United Kingdom
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Hi,

Two drivers in parallel gives +6dB.
Side wall mountings makes adding to the axial response difficult.
Generally for Audio-Physics-u-likes BSC is applied to the midrange.
I'm not sure compensating the tweeter is necessary.

/sreten.
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Old 28th August 2007, 04:09 PM   #8
PCM1702 is offline PCM1702  Poland
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So, if it's +6 dB, then looking at this graph: http://www.stx.pl/charakterystyki/GD...0-8-AW-ALL.jpg
... efficiency would be ok, to match this midrange?

I don't want to compensate in midrange, because I don't want to lose it's efficiency...

What about a bigger woofer?

Regards,
Adam
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Old 28th August 2007, 04:58 PM   #9
sreten is offline sreten  United Kingdom
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Hi,

Read that David article carefully. Because of the approach the bass
units also need good midrange performance as they overlap the mid.

The baffle step on the midrange depends on the cabinet size width :

Click the image to open in full size.

Its impossible in the above to use the mid drivers half space sensitivity.
The loudspeaker is ~ 85 dB/W whilst the mid driver is ~ 90 db/W.
(The above corrected for 4 ohm drivers).

/sreten.
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Old 28th August 2007, 05:54 PM   #10
PCM1702 is offline PCM1702  Poland
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Now I get it

What do you think about pairing these mids with some hi-efficiency 12" woofers (one for each speaker) in a wide front baffle? (sth. like a Naim SBL for example)

Best regards,
a.
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