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 Post subject: New Project
PostPosted: July 28th, 2020, 8:22 am 
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Joined: July 8th, 2016, 4:34 pm
Posts: 372
Just got some toys to play with (still waiting for second midrange horn from UPS) -

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Parts:
1 - Scanspeak M22WSR-46 8" Paper Cone Shielded Woofer 8 Ohm
2 - B&C ME75 2" Constant Directivity Horn 90 x 40 4-Bolt
3 - Radian 850PB-8 2" Aluminum Horn Driver 8 Ohm 4-Bolt
4 - Eminence APT 200 Super Tweeter with Bi-Radial Horn 90 x 90

The system will sit on top of an 18 inch subwoofer. Crossover points are:

1 - Subwoofer to midbass 80Hz or 100Hz (any suggestions?)
2 - Midbass to midrange horn 500 Hz
3 - Midrange to tweeter 3.5 kHz

Suggestions on enclosure for midbass are welcome. Should it be sealed box, ported box, transmission line, or horn loaded?


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 Post subject: Re: New Project
PostPosted: July 28th, 2020, 9:17 am 
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Joined: February 28th, 2013, 1:19 pm
Posts: 457
The midbass driver seems out of place in a horn system, does it have the efficiency (sensitivity) to keep up. Does it have the power handling and not suffer from thermal compression in comparison with the other drivers. Not looking at the parameters, but I would guess the Scanspeak 8" has a efficiency of around 88 dB, where as the other drivers installed in their horns would be on the order of 15 dB higher. The horn drivers would be coasting, whereas the Scanspeak would be working hard to keep up. I would look for a high efficiency pro-sound 8" or 10" driver to better match.

David


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 Post subject: Re: New Project
PostPosted: July 28th, 2020, 9:21 am 
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Posts: 372
What about horn loading the scan speak driver. I think about the old Altec Voice of the Theater configuration except that the driver would be in a sealed box and not ported since the subwoofer would supply the low bass.


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 Post subject: Re: New Project
PostPosted: July 28th, 2020, 9:46 am 
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brombo wrote:
1 - Scanspeak M22WSR-46 8" Paper Cone Shielded Woofer 8 Ohm

Why on earth are manufacturers still making shielded drivers? The CRT is dead....

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 Post subject: Re: New Project
PostPosted: July 28th, 2020, 9:55 am 
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Joined: February 28th, 2013, 1:19 pm
Posts: 457
Roscoe Primrose wrote:
brombo wrote:
1 - Scanspeak M22WSR-46 8" Paper Cone Shielded Woofer 8 Ohm

Why on earth are manufacturers still making shielded drivers? The CRT is dead....


Exactly my thoughts. It is a Buyout item on Parts Express, discontinued. JUst looked at the specs, it appears to be a decent 8" driver for a conventional vented or closed box in a 3 way system, using a nice 4" cone mid (or 2" dome) and tweeter of choice. Once you address the nasty peak at 3K, it looks like it has a smooth response, nice LF extension, so should pair well with a midrange driver. It is a nice looking driver, but not in a horn lineup.

David


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 Post subject: Re: New Project
PostPosted: July 28th, 2020, 10:13 am 
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Just a note on sensitivity and efficiency. They are often used interchangeably, but they are not always the same. Efficiency is how well the driver converts electrical energy to acoustic energy. I used to given from a practical standpoint when driving an 8 ohm speaker at 2.83 VRMS and measured at one meter. 2.83 V across an 8 ohm load is 1 W electrical.

Sensitivity is simply the acoustic output of a driver at one meter with 2.83 V regardless of the impedance. The popularity of that spec came about with the advent of low impedance solid state amps with stiff power supplies. It was the same as efficiency if the driver has an 8 ohm impedance, However, with a lot of drivers having a 4 ohm impedance, the 2.83 V represented 2 W. So with the "same" test the manufacturer could claim 3 dB more sensitivity than a driver with 8 ohms.

So remember when comparing drivers with different impedances if the sensitivity figure is used, for the same efficiency a 4 ohm driver will have to have 3 db higher sensitivity. If you are using a low impedance solid state amp that doubles its maximum power with each halving of impedance, the sensitivity figure will work OK. However, with a tube amp where you change taps, using the 4 ohm tap will result in a lower voltage for the same drive and the sensitivity measurement is going to result in 3 dB less output with a 4 ohm driver.


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 Post subject: Re: New Project
PostPosted: July 28th, 2020, 10:31 am 
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Location: Parkville, Maryland
Roscoe Primrose wrote:
brombo wrote:
1 - Scanspeak M22WSR-46 8" Paper Cone Shielded Woofer 8 Ohm

Why on earth are manufacturers still making shielded drivers? The CRT is dead....

Long live the LCD and OLEAD!!

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 Post subject: Re: New Project
PostPosted: July 28th, 2020, 10:31 am 
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Posts: 457
brombo wrote:
What about horn loading the scan speak driver. I think about the old Altec Voice of the Theater configuration except that the driver would be in a sealed box and not ported since the subwoofer would supply the low bass.


But that is an efficient 15" driver that is designed to work in horns. Usually Qt is around 0.2 or so. THis driver has a Qt of 0.38. There are other parameters of interest that determine the acceptability of horn loading, but need to model this in Horn Response to get an idea of performance. The front horn will not benefit all frequencies, my recollection is that it really helps in the midrange, but is too short for boosting bass response, which is dominated by the vented box loading at the back of the driver. The best you can really hope for is 10dB.

The driver is actually around 87 db 1W/1m. The Radian driver is 112 dB 1W/1m. Not sure if this included horn gain. This is a 25 db difference. The bass driver will need 316 times the power as the 2" Radian driver to deliver the same output power. This is not a good place to be. The RMS rating of the driver is 100W, peak at 200W. Not clear what the actual limit is thermally. The maximum this driver can deliver "theoretical" is +20dB over the rated sensitivity, not counting excursion or thermal limits. But you will be pushing alot of power through the driver, which will warm the voice coil and impact driver linearity, whereas the midrange will be running at fractions of a watt with little temperature rise and will have good linearity.

If you are talking a passive crossover, then you will be padding down the midrange and tweeter. Alot. This dissipates alot of power needlessly. You will need an active crossover and separate amplification.

This is not saying it cannot be made to work, it is just the 8" driver is constraining the potential of a nice horn system. You really need to look for a better suited driver rather than trying to make this one work.

David


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 Post subject: Re: New Project
PostPosted: July 28th, 2020, 10:43 am 
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Joined: July 8th, 2016, 4:34 pm
Posts: 372
DSP crossover and triamplification. Lower power amps on midrange and tweeter. The question is can the Scan Speak supply the spl I listen at in the room the system is in in the frequency band 100 Hz to 500 Hz?


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 Post subject: Re: New Project
PostPosted: July 28th, 2020, 11:25 pm 
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Joined: April 22nd, 2013, 12:58 pm
Posts: 199
Do a Mega-Textron...???
I agree with David, you want those mid-bass drivers loafing, otherwise they will never integrate nicely.

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