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Multi-Way Conventional loudspeakers with crossovers

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Old 10th September 2012, 08:41 AM   #1
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Default loudspeaker enclosure design

hi I want to put these two loudspeaker into one box
the tweeter HT-22/8
and the woofer http://coralelectronic.com/pdf_retur...df=1&prod=1791
In my design every loudspeaker has its own amplifier which means that the music signal goes through an electronic active crossover of the 2nd order, where the frequency band is splitted in two bands one from 20 hz to 2.5 khz for the woofer, the other from 2.5 khz to 20 khz for the tweeter. now i've asked the two companies for the thiele parameters but they don't have them so i've noted that the tweeter has a chamber behind the membrane, does it mean that the tweeter doesn't have back emission? if so can i consider the enclosure as if there is only the woofer inside it? the woofer doesn't have a chamber behind the membrane so it has a back emission right?
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Old 10th September 2012, 08:50 AM   #2
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If the tweeter is completely sealed from the rear you should be fine.
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Old 10th September 2012, 09:19 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

In this case active bi-amping is a waste of time and money.

The passive filter functions you need are nothing like the
active filter functions provided by "off the shelf" x/o's.

The tweeter is most probably designed to have a single
series capacitor giving you a 3rd order acoustic roll-off.
(True for nearly all cheap (high Fs) tweeters.)

You just put this in parallel with the bass/ mid. The simple
treble x/o usually means the skill is getting the bass/mid
to match with proper BSC and complementary x/o point.

rgds, sreten.

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Last edited by sreten; 10th September 2012 at 09:30 PM.
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Old 10th September 2012, 10:17 PM   #4
tvrgeek is offline tvrgeek  United States
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You use tweeters at least an octave above their resonance frequency, so T/S parameters are not relevant. Good info above.
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Old 11th September 2012, 12:03 AM   #5
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by tvrgeek View Post
You use tweeters at least an octave above their resonance
frequency, so T/S parameters are not relevant.
Good info above.
Hi,

You are so wrong regarding cheap tweeter design it is untrue.
Cheap tweeters have high Fs and moderate high Q such that
a single series capacitor yields a usable 3rd order roll off.

I'm peed off that i even have to explain this :

e.g. a cheap tweeter around 4KHz Fs ferrofuild damped :

Click the image to open in full size.

The same with a series capacitor :

Click the image to open in full size.

a flat 3rd order roll off you can work with.

rgds, sreten.
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Old 11th September 2012, 08:08 AM   #6
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I have been very pleased with my use of the HT 22/8 (which I use with a 3.3uF capacitor). One tweek that I use is to damp the rear of the tweeter with blutak. It is made of thin pressed metal and I feel that the rear radiation of the main driver could vibrate it. I think it improves things (but it could just be my imagination).
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Old 11th September 2012, 09:41 AM   #7
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ok but what about the power? how can i limit the power to the tweeter using only one amp and connecting the woofer in parallel with the tweeter considering that the tweeter can have max 10Wrms while the woofer in my design gets 60 Wrms ?
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Old 11th September 2012, 10:27 AM   #8
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The capacitor before the tweeter decouples it from the amplifier , letting only the high frequencies pass . Only after having mounted the tw & wf in place
( I suggest to leave the tw outside the box , but ...) you'll hear and decide
if the tw needs to be attenuated .
As Sreten said , also the wf needs a minimum filtering , to limit noisy break ups
of the cone ( in the mid-treble ) and for correct baffle step .
As Sreten said, passive filtering provides also the equalization needed to correctly assemble a 2 way .
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Old 11th September 2012, 10:53 AM   #9
tvrgeek is offline tvrgeek  United States
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Well Sreten, we will just have to disagree with the description on this one.

You are only showing the frequency responce, not the impedance, so you do not show the free air resonance for this tweeter. I bet it is about 1200. ( yes, pretty high)

If it's free air resonance is 1200, you should use it above 2400 or so. I am not talking about it's low frequency rolloff, I am talking about it's resonance. The question was about T/S parameters. If you are going to push a tweeter anywhere near the resonance, you will need to put in a notch to deal with the impedance peak and you are going to find the distortion is terrible anyway. Just plain bad design no matter how pretty the SoundEasy pictures look.

I am not saying a first order electric crossover, if selected a couple octaves above the resonance is not a good design. Actually, first order at 5K may be a very good design if you can find a midrange that can get that high. ( Mark Audio maybe) A first order that overlaps the low frequency roll-off resulting in a third order acoustic is often tried. I learned it is usually too close to the free air resonance and not steep enough to keep the distortion down. My last two builds were second order electric, overlapping the roll-off for a forth order acoustic. My rule of thumb is now, two octaves for first order, but you can get away with one octave if second or higher. In your above example, you have achieved about a 3500 crossover, so all is well.

PS, don't know which cheap tweeter you were measuring, but to have breakup below 20K is not good. Not good at all.
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Old 2nd October 2012, 10:42 PM   #10
Dissi is offline Dissi  Switzerland
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The Monacor tweeter HT-22 has been tested in the german loudspeaker magazin Klang+Ton 2-2012. And surprise, it is a really well performing closed cone tweeter! The spl is 91 dB and flat from 1.3 to 16 kHz (+/-2dB). The distortions are below 0.5% above 2.5 kHz, only a single peak at 6.8 kHz disturbs at high levels (3 % at 105 dB). This is an excellent result for a 8 Euro driver. Combined with your active crossover, it will make no troubles at 2.5 kHz. The spl at 30 rolls of early because of the large radiating surface. Maybe you want to equalize that with a first order boost of 5 dB at 15 kHz.

The woofer is unknown to me. It seems to have the same basket as the Ciare CM 200, but with a different dust cap and magnet. I suppose it will also have a spl of 90 db, but a Qts above 1 and a Fs of 80 Hz. Maybe you should try to measure the impedance and find out the TS-parameters yourself. The driver will probably not work in bass reflex. But you can use a closed box and maybe also equalize the range below 100 Hz in your active crossover.
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