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Old 20th July 2006, 03:54 PM   #21
sreten is offline sreten  United Kingdom
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Hi,

Just finished reading the old stereophile review of the speakers.

http://stereophile.com/floorloudspeakers/385ml/

Hmmm.... a lot of the comments are due to crossing over an
omni to a line source dipole and the way said things interact
with a room and the users listening distance.

2.5 ohm Re bass driver is very low for an 8 ohm nominal speaker.

Also lots and lots of waffle in the above review too,
woulf have preferred less waffle with measurements.

It is true a high mmd speaker is never go to make a bass/mid driver.

But your never going to find a 4 ohm 92dB driver that
works well in your box that has particularly high mmd.

The general problem with any driver is the higher the frequency
is remains clean and piston, the more severe the breakup modes
thereafter, for metal drivers you can notch filter the break up.

Stiffness and including damping is the holy grail, but the real
parameter is youngs modulus, stiffness for a given weight
i.e. the lower the density the better, but damping adds weight.

A tip - ripples on the impedance curve indicate cone effects.

Your main problem is 4 ohm drivers have been taken over
by car audio nuts, hi-fi for 4ohm generally uses two drivers
in parallel because of the more acceptable form factor.

12" car drivers are designed for ~ 1cuft sealed not 3 cuft.

And 4 ohm subwoofers (or 8+8 dual coil) are not generally
designed to be used with 1st order crossovers, midrange
quality is not considered an issue.

Like I've said already, you are going to have a hard
time finding a driver that is a suitable replacement.

/sreten.
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Old 20th July 2006, 05:56 PM   #22
ScottG is offline ScottG  United States
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Quote:
Originally posted by sreten


Hi, no, but I assume it doesn't matter, /sreten.

Tsk, Tsk..

Consider of few things:

1. Martin Logan doesn't make very efficent panels.

2. Their 90 db spec. is sensetivity - NOT eff.. (and its likely even this is a lie - probably 88 db sensetivity)

3. The nominal impeadance is 8 ohms.

4. This is a sealed design.

5. The spec'ed freq. range is an extraodinary (if optimistic) 28Hz–22kHz.

Now think a little harder about how the driver coils are being used.
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Old 20th July 2006, 08:51 PM   #23
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Maybe you should be looking at the frequency response instead of the Mms.
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Old 20th July 2006, 10:36 PM   #24
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Here is the crossover of the Martin Logans, I doubt the ELS pannels are 92db efficeint so they would have cut back the efficeintcy of the Eminence to suit wouldn't they? So maybe I can use a lower effciency bass driver?

Cheers George
Attached Files
File Type: pdf monolith 3 passive crossover schematic.pdf (9.4 KB, 33 views)
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Old 20th July 2006, 11:35 PM   #25
ScottG is offline ScottG  United States
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ick..

It looks like its probably connected in parallel and the nominal 8 ohms is due to the added resistance. My opinion of Gale Sanders just dropped several notches (..even though this design is very old).

This is NOT how you want to design *any* standard moving coil based loudspeaker.
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Old 20th July 2006, 11:36 PM   #26
ScottG is offline ScottG  United States
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Quote:
Originally posted by ScottG



Tsk, Tsk..

Consider of few things:

1. Martin Logan doesn't make very efficent panels.

2. Their 90 db spec. is sensetivity - NOT eff.. (and its likely even this is a lie - probably 88 db sensetivity)

3. The nominal impeadance is 8 ohms.

4. This is a sealed design.

5. The spec'ed freq. range is an extraodinary (if optimistic) 28Hz–22kHz.

Now think a little harder about how the driver coils are being used.

My bad.
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Old 20th July 2006, 11:52 PM   #27
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The switch that brings in the resistor is only a 3db bass cut if your in a small room were the bass can be too much. the inductors are large air core very thick wire and look to be of low resistance, so i cannot see how the ELS can mate with a 92db efficent bass driver, unless the Eminence specs are way off, or somehow Gale Sanders has managed to do the impossible and produced a ELS pannel that has 92db efficency?

Cheers George
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Old 21st July 2006, 12:17 AM   #28
ScottG is offline ScottG  United States
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large air core inductors have a fair amount of resistance - it is (all else equal) a good way to "pad" down a speaker.

the -3db switch however is bad.

..who knows though, the overall design could be so bad that you wouldn't hear the negative effects of its insertion with a good amplifier.

Have someone model the crossover to "see" *exactly* what its doing - only then will you be able to really "hunt" for new driver.
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Old 21st July 2006, 04:52 AM   #29
zlast is offline zlast  United States
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Default NHT 1259

THe NHT 1259 4 ohm would be really close - 3.5 ohm and recommended enclosure is 3.5 ft3. Sensitivity is 89db.
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Old 21st July 2006, 12:01 PM   #30
sreten is offline sreten  United Kingdom
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Default Re: NHT 1259

Quote:
Originally posted by georgehifi
The switch that brings in the resistor is only a 3db bass cut if
your in a small room were the bass can be too much. the inductors
are large air core very thick wire and look to be of low resistance,
so i cannot see how the ELS can mate with a 92db efficent bass
driver, unless the Eminence specs are way off, or somehow Gale
Sanders has managed to do the impossible and produced a ELS
pannel that has 92db efficency?

Cheers George
Please get out you multimeter and measure the DC resistance of :
a) The woofer
b) input switch on
c) input switch off

If the woofer is 2.5 Re and the inductors are very low DCR then
2R will cut levels more than 3dB, but the bass will come back up
again as the Qts of the driver will be changed drastically.

From ~ 0.4 to ~ 0.7 , inbox Q will change from ~ 0.65 to ~ 1.1.

A very good question is do you use this switch ?
I understand it gives an "alternative" bass response that
may or may not work better in difficult positions in rooms.

The crossover diagram is very helpful.
The bass unit c/o is 2nd order, give me the values above and I'll sim it.
your concerns about cone breakup should be much less with

To clarify one point : the specs given are for an Eminence driver
to match a driver provided by ML, presumably ML sourcing spares.
The driver provided by ML ? was this also an Eminence ?
Are you sure that it is the driver fitted to your speakers ?
You can check whether it has double voice coil connections.
If it hasn't its likely "the driver provided by ML".


Quote:
Originally posted by zlast
THe NHT 1259 4 ohm would be really close -
3.5 ohm and recommended enclosure is 3.5 ft3.
Sensitivity is 89db.
Unfortunately currently unavailable as it is being redesigned.

Due to the fact that bass loudness curves are closely spaced,
(you ~ get an apparent 100dB range in an actual 50dB range)
the exact level of bass is more critical than most assume.

A 3dB reduction (92 to 89) will have a major effect. The 3dB
switch does not simulate this as it effects Q far too much.

You need to be very clear about whether it is acceptable to
reduce the voltage sensitivity of the bass unit. I can simulate
other effects e.g. diffrent Re and Le (assuming that the specs
in the original post are the specs of the driver currently fitted).

You could temporarily bi-amp one speaker (need a monoing lead)
and simulate this with your balance control to see if reduced
output level is acceptable.

Personally I'd be heading in the direction of replacing the 12"
with two 10" vertically aligned very low distortion units, I'd
probably go metal coned and add as trap circuit for break-up.

/sreten.
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