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Multi-Way Conventional loudspeakers with crossovers

Compression driver attenuation help..
Compression driver attenuation help..
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Old 12th September 2017, 11:57 AM   #1
Rehdekolover is offline Rehdekolover
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Default Compression driver attenuation help..

Hi guys,
This is my first post so please be gentle.

I have enjoyed my Rehdeko RK115 speakers for many years and have recently added B&C 250 ( 16 ohms ) compression driver with a Stereo-lab 800hz horn.

I wanted to use a simple cross over as possible. I've tried many cap values crossing over from 5kz up to 14khz. All was great and I could clearly hear the crossover frequencies but the volume / level was too high. Instead of using resistors I used a 0.22uf cap crossing over at 46 khz. This cap sounds great as it attenuates the audio band enough to match the Rehdeko output.

Is this a good method ?
I can't find any reference to people using this method to crossover and attenuate the tweeter level.

Any help or reassurance would be great.

Last edited by Rehdekolover; 12th September 2017 at 01:07 PM.
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Old 12th September 2017, 04:21 PM   #2
GM is offline GM  United States
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Sure! Worked for the pioneers until it became necessary to use higher orders to get more power protection, so as long as there's no problems with over powering them......... FWIW, I used only a cap for a nominal 500 Hz XO back when I had a ~112 dB/m eff. system [in room].

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Old 12th September 2017, 04:32 PM   #3
Rehdekolover is offline Rehdekolover
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Many thanks for the reply. I'm using a custom built 2a3 SET. 3 glorious watts.
Crossing over at over 40k and letting the 6db per octave do the attenuation really is a good sounding simple crossover.
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Old 13th September 2017, 10:31 AM   #4
AllenB is offline AllenB  Australia
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Maybe by using tractrix horns you can accept a rising response. All I can say is sometimes using a capacitor this way works, but I wouldn't set out to do it this way. Also it may be preferable to get to 1600Hz but cut 800Hz due to the tractrix group delay, calling for a more clear demarcation?
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Old 13th September 2017, 03:22 PM   #5
Jack Arnott is offline Jack Arnott  United States
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I have done something similar with good results. I ran a single capacitor at a high frequency, to knock out the sensitivity hump from the compression driver at 5K. I put my crossover point at about 16K. I have read somewhere that using a single order crossover is not great, but didn't understand the context, and why not. In my case the signal is down over 24 db by the time it gets to the crossover point, and my driver has a high mechanical power handling, so I don't see the down side.
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Old 13th September 2017, 04:07 PM   #6
kevinkr is offline kevinkr  United States
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Compression driver attenuation help..
The problem with this approach is that the output is falling at 6dB/octave across the desired passband of the driver.

For low powers a cap and simple two resistor attenuator is sufficient. To get things right use an L-pad to figure out the attenuation you need, remove it and measure the resistances from wiper to each of the other tags and purchase the closest values you can find. (or use combinations of values to get closer) Somewhat more complex solutions may be desirable if you have a shelf, dip or peak in the driver response that you need to correct.
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Old 13th September 2017, 05:15 PM   #7
Jack Arnott is offline Jack Arnott  United States
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Quote:
Originally Posted by kevinkr View Post
The problem with this approach is that the output is falling at 6dB/octave across the desired passband of the driver.
This is a compression driver, not a dome tweeter. (Read, constantly dropping HF, not a flat response.) If the resulting frequency response is flat, why is this a problem?
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Old 13th September 2017, 06:01 PM   #8
Rehdekolover is offline Rehdekolover
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The Rehdeko speakers are a very lumpy full-range drive unit with peaks and troughs up to about 10khz and about 97db sensitivitie.
My thoughts were to add a compression driver at 106db crossed over really high ( 30 to 40khz) and let the 6db slope take care of the attenuation.
Playing around today I found 0.33uf ( 30khz cross over) to give the best balance of sound to match the Rehdeko unit.
Because the Rehdeko is far from a flat response I just need a good balance between the two drive units.

Last edited by Rehdekolover; 13th September 2017 at 06:24 PM.
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Old 13th September 2017, 08:55 PM   #9
kevinkr is offline kevinkr  United States
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Compression driver attenuation help..
Quote:
Originally Posted by Jack Arnott View Post
This is a compression driver, not a dome tweeter. (Read, constantly dropping HF, not a flat response.) If the resulting frequency response is flat, why is this a problem?
My system is based on horn loaded compression drivers that exhibit a pretty flat on axis response over most of their operating bandwidth. Mine do roll off, but I don't operate them in that region, I cross over to another one with the required bandwidth.

If you have you actually measured the acoustic response in the room, and as you state it's flat then you apparently don't have an issue. That would be a first in my admittedly limited experience.

I have measured in room response at various points as the system evolved, and use a very modest amount of EQ to correct deviations at the listening position..
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Old 14th September 2017, 09:36 AM   #10
AllenB is offline AllenB  Australia
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The response of a compression driver may be flat on axis with a tractrix horn. It will be falling toward higher frequencies with a more constant directivity device. However I find tractrix better when it is closer to flat, and a wider horn better when it is falling with frequency, so I can't find sense within that argument..

Where the capacitor type crossover you suggest has worked for me seemed to be with higher crossover frequencies, say 5k, where the knee of the rolloff is already extending into the top octave. Crossing below 1k as I do, it is less appropriate to let these cards 'fall where they may'.

Importantly you will have a problem with the impedance of a compression driver. In the case of a tractrix horn you will want to cut the response above the horn cutoff, and if you do that slowly, the impedance hump can hinder the attempt. In the case of a wider horn, the compression driver impedance peak can be sharp and complicated.
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