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Old 21st November 2006, 10:30 PM   #1
Paul W is offline Paul W  United States
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Default Large midrange for OB??? Scott G ?

Looking for a large, high output, low distortion midrange driver for OB use (which could evolve to cardioid radiation).

Will be used with a broad coverage waveguide HF driver so some directivity is desirable. Crossover will be at 200Hz and somewhere from 1k-2k, depending on how the drivers match up. Would like “good behavior” at least an octave on either side of xo. Budget around $200 each.

The Eighteensound 10M600 looks good, but I don’t know if it has shorting rings, cast basket, or other “good parts”…nor have I seen distortion measurements for it. Anyone have any 10M600 experience or distortion measurements?

What other drivers should I consider?
Thanks,
Paul
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Old 21st November 2006, 11:18 PM   #2
ScottG is offline ScottG  United States
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Ah.. A challenge!

How large? How eff.? What nominal impeadance?

What sort of off-axis performance for a given freq.? (i.e. do you want the off-axis performance to coincide with a dipole's radiation on a small baffle?) Whats the off-axis performance of the waveguide?

Do you want a response deviation and/or a high "q" driver to compensate for the loss in spl from the dipole? (or are you going to eq. it?)

(..also of course how "flexible" are you with the above?)
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Old 22nd November 2006, 12:28 AM   #3
ScottG is offline ScottG  United States
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Using the Edge.. we have a problem here with directivity and a free-air open baffle..

we are looking for a -3db point at 45 degrees off-axis (when the dipole is acting maximally as a dipole).

a 10" or even an 8" driver with as narrow a baffle as possible won't really display this behaviour until just below 300 Hz.

Now you *might* be able to achieve something more directive with a side aperiodic cardoid venting (..don't know, haven't tried this myself).

effectivly then what will likely have is a horizontal polar response that becomes less and less directive down, (i.e. wider dispersion), to about 450-500 Hz, and then the dipole will start "kicking-in" and dispersion will narrow and be constant somewhere below 300 Hz.

this may or may not be a concern to you.

by the way - the driver you mentioned looks very nice except for inductance (which increases IMD dramatically).. Their "Active Impeadance" series drivers (10 inch only) are conversly AWESOME (in this respect). Though less eff., perhaps the 10NDA520 would be a better solution (when considering inductance and dispersion).

Note:

I have know idea what the off-axis response of the driver is.. but, the Ciare OEM 12.75 NdMR looks pretty sweet in every category but excursion (but its SOOOO freakin eff.). (..and because its a 12" driver it should be more directive down to a lower freq.) However spl does drop quite a bit below 400 Hz..

http://www.ciare.com/oem/index.html

Price is not too bad either:

http://www.assistanceaudio.com/08_Ciare.html
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Old 22nd November 2006, 12:40 AM   #4
Paul W is offline Paul W  United States
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Good...I got the guy who knows every driver made by man!

Okay, here goes:

IHow large? How eff.? What nominal impeadance?

Size doesn't matter, except as it relates to off-axis response, fairly high output capability, and low distortion. I'm thinking around 10-12", so long as resolution is still razor sharp. Any efficiency above 85db. Any impedance 4 ohms or higher.

What sort of off-axis performance for a given freq.? (i.e. do you want the off-axis performance to coincide with a dipole's radiation on a small baffle?)

Higher priority in matching the waveguide at xo than in matching dipole. There is a strong chance this mid will end up with the HF end of the backwave absorbed in "just enough" wool felt damping well away from the driver...LF allowed to go free.

Whats the off-axis performance of the waveguide?

90 degree coverage OS.

Do you want a response deviation and/or a high "q" driver to compensate for the loss in spl from the dipole? (or are you going to eq. it?) EQ is no problem, so Q is very flexible.

(..also of course how "flexible" are you with the above?)

Smooth response (no high-Q spikes), low distortion, and high output are king and I'll sell the cat to get it...or maybe the neighbors cat
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Old 22nd November 2006, 12:48 AM   #5
Paul W is offline Paul W  United States
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You posted while I was typing...

Yes, I am thinking "sorta cardioid" for the midrange. Absorb the backwave up high to coincide with the monopole tweeter, move through cardioid in the "middle of the mid", ending up dipole at the bottom of the midrange...mating to a dipole woofer.

I'll take a look at the drivers you mentioned...keep 'em coming!
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Old 22nd November 2006, 06:30 AM   #6
ScottG is offline ScottG  United States
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Quote:
Originally posted by Paul W
Good...I got the guy who knows every driver made by man!

I'm not sure about that..

All else equal, the more eff. a driver the greater the resolution.. of course the same can be said for mms for a given sd.. the lower the mass the greater the resolution.

DDS Eng 1-90 Pro?

Hmmm, other drivers high resolution, high output, low distortion, low cost (relativly anyway). Tough one.

Well, there is the 18sound 8NMB420.. good excursion, LOW MASS for a pro driver (good resolution), decent inductance at 1 kHz for an 8 inch pro driver, and substantial excursion capability for an 8 inch pro driver. The only thing wrong with it (other than possible dispersion issues) is its lower fs. (..sounds odd huh?) In this case the lower fs means the driver will naturally want to extend its freq. response, thereby increasing excursion, thereby increasing distortion. Of course a good steep filter should fix that problem.

B&C PE21..frankly not as good as the 18sound 8 inch, but not bad (limited in output however because of x-max and particularly x-damage vs its sd). No off-axis data.

Then there is the new BMS Pro 8N215.. Mass is a little heavier than the above.. good excursion, good inductance - a nice driver.. No off-axis data though.

I've looked at a LOT of other Co.'s drivers.. all turned me "off" from one aspect or another.. Things like high inductance, poor excursion for a given sd and fs, high mass for a given sd, low eff for a given sd, poor high freq. extension, poor "break-up"/increased "ringing", availability, etc. ALL "played" a part in my driver sifting thought process. (..and of course cost was an over-riding factor.)

Of all the driver's I've mentioned.. I'd prob. go for the 12 inch ciare all things considered. It will likely be more detailed than the rest, while having the capability for greater spl's and a more directive freq. response.

IF I wanted a less directional driver I'd choose either the 8" 18sound or BMSPro.

From a purely "build-quality" perspective I'd almost certainly go with the BMSPro. ..Though I suspect all of the drivers listed are built VERY well.

So there you have it.. a very limited selection of drivers that *might* be well suited to your needs.
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Old 22nd November 2006, 06:48 AM   #7
MBK is offline MBK  Singapore
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Just because it seems to fit in here - dispersion pattern of my ca. 48H 24W 7.5D (inches) shallow U-frame. Driver is a SS8543 (6.5"); data are without filters, the rolloff is due to low Q plus dipole effect. With hindsight the active impedance 18Sound 10" would have fit in here nicely.

Purpose of my post though is just to show the off axis response of such a baffle, I expected more dipole like behavior until up high but it seems it went towards cardioid in the mids w/o even trying. Back of the baffle completely open, no stuffing.
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Old 22nd November 2006, 07:06 AM   #8
ScottG is offline ScottG  United States
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Quote:
Originally posted by MBK
Just because it seems to fit in here - dispersion pattern of my ca. 48H 24W 7.5D (inches) shallow U-frame. Driver is a SS8543 (6.5"); data are without filters, the rolloff is due to low Q plus dipole effect. With hindsight the active impedance 18Sound 10" would have fit in here nicely.

Purpose of my post though is just to show the off axis response of such a baffle, I expected more dipole like behavior until up high but it seems it went towards cardioid in the mids w/o even trying. Back of the baffle completely open, no stuffing.

Yours doesn't seem to hit actual dipole behaviour until about 230 Hz. The freq. response from 500 to 1 kHz is effectivly omni (in the forward plane) and only starts into a cardoid response above 1 kHz - strictly due to the dispersion character of the driver.

There is also the 12 inch active impeadance driver from 18sound that extends the limited dispersion down to lower freq.s.. unfortunetly the inductance of the driver (assuming it isn't a mis-print), is almost 20 times as much as the 10 inch driver.
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Old 22nd November 2006, 07:50 AM   #9
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I personally have the active impedance 10" driver although I havent got it playing yet in a finished speaker.
I regret buying it after reading about studies that conclude non linear distortion plays a small role in our perception of sound.

I spent a small fortune on it( relative to my pocket money) although it is a relative bargain compared to other offerings in the same class. In terms of non linear distortion it should be the best in its class, the active coil thingy I read is even better than faraday rings. There is literally nothing else out there with such low inductance and very high efficiency.
Although if I had to decide again i would simply buy the considerably cheaper 18sound mb600, eminence, or paudio 10"s without the bells and whistles.

To ultilize their potential(as well as the Ciare MR series mentioned) you want to hornload them because their frequency response drops considerably in the midbass.

For dipole use the Ciare midbass 12" 12.64NdW1 is more suitable than the 12.64NdMR. Still very efficient, much flatter response, and greater xmax.

The active impedance 12" is great too, not sure about the high inductance but im guessing it may not matter as its impedance is dead flat like its 10" relatives.
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Old 22nd November 2006, 08:03 AM   #10
MBK is offline MBK  Singapore
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I should add some caveats to my above data: in-room and closer to the baffle than I would like (80 cm or 32") for such a large baffle - the full baffle effects likely don't show up this close for the higher wavelengths since the rear-to mic distance is considerably longer than the front-to mic distance.

Quote:
The freq. response from 500 to 1 kHz is effectivly omni (in the forward plane) and only starts into a cardoid response above 1 kHz - strictly due to the dispersion character of the driver.
Agree on the dispersion above 1k. But even a cardioid would be failry omni in the +-60 degree range. I should complement this to a complete 180 degree polar view.
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