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Re: Eminence LAB 12 drivers

Posted by tomservo (M) on February 28, 2003 at 19:43:38

In Reply to: Re: Eminence LAB 12 drivers posted by Wayne Parham on February 28, 2003 at 15:54:16:

Hi Tom!

You wrote:

>> Part of the reason for my designing the LAB horn and specifying
>> the driver parameters was to give the Pro-sound DIY'rs a modern
>> bass horn, so many people interested in horns still follow the
>> old " folk lore ", like for example that a bass horn driver
>> should have low mass and small excursion capacity.

In all fairness, the reason that low mass is chosen is to extend the range of the subsystem and it is not merely a "rule of thumb." If this isn't
important, then other design choices can be made.

Hi Wayne

Back when this project started the group determined that a 30 Hz low cut off and 150-200Hz HF cutoff was the target.
At the same time many were suggesting that a light cone driver was suitable for horn loading in that frequency range.
Give that another goal was to make a system which ran out of linear excursion in the same neighborhood as electrical power (and
making that point as high as possible), this need for high acoustic power and high efficiency eliminated the possibility of using a
more traditional "low mass" driver.

>> At some point, the folks who did a shoot out in Michigan will
>> have the measurements and listening results posted on the basslist
>> so more actual data will be available soon.

Here are the measurements from the "shootout."

All products that were represented performed well. The LAB Sub appears to be satisfactory, as were all the others. But all products were
also beginning to rolloff at 40Hz, with none of them better than 3dB down at this frequency. By 30Hz, all horns represented were at least
10dB down from their 80-100Hz midbass level. This is good response for a basshorn, but it is also important to point this out.

Wayne, you did not actually look at the numbers very carefully.
Compare the response curves, distortion, impulse responses.
The LAB out performs the rest or at least that's what most of the folks that were there thought.
It went lower, louder and with less distortion than anything else there.

All-in-all, the LAB bass horn looks pretty cool and I can see how some people have gotten excited about it. And the $100 Eminence
woofers are very reasonably priced, so cost of materials isn't high. But what about the cost of assembly and maintenance? How easy is it to
build and service in the field?

I would suggest to anyone considering the project that they not build them in the field, replacing the driver if ever needed (so far
no one has blown any but it has only been 6 months or so) would be easy however.
This is sort of the point, they work really well, they better everything people have put them up against and they are inexpensive.
Miles better than a W bin or Earthquake box like the group had been considering.

>> I had just designed a variation on the LAB sub horn and got it in my
>> living room last weekend, a little smaller, only 42 by 42 by 18 inches
>> which also uses a "trick" in its operation. In room, it is unusually
>> smooth for a small horn + - 3 dB from 30 to 225 Hz and with 10 dB of
>> eq (no problem because of high sensitivity ~ 106 db 1w) the measured
>> response is - 3 dB at 22 HZ.

I see.

In room it is +/-3dB from 20Hz to 225Hz as long as there is 10dB EQ.

>> Using the TEF machine to measure phase and the Omnidrive (BS366) to
>> mate them, I got it aligned with the Unity horn system on top.

The impedance chart of the LAB horn shows several resonant peaks, which indicates that the device is reactive and that therefore phase is
moving in these regions. This, combined with the long path length difference, makes alignment impossible without additional equipment. Even
with additional equipment, such alignment would be a non-trivial task and would only be possible at one target location. We've discussed
these issues many times before, but I felt compelled to respond to these comments here nonetheless.

The horn I am playing with now is only similar to the lab sub in that it has the same drivers and is a horn made of wood.
I do not care if such a task is non trivial and I do have the stuff to do it and measure it.
BTW, how much directionality results if one places two sources of any phase difference you choose, less than 1/4 WL apart?

This isn't terribly important to me, as you and I have discussed before. As long as the delay doesn't amount to a noticable echo and it doesn't
cause response anomalies from 180o interference, I'm not concerned.

Yes you have said that before.

So the fact that a horn's impedance has a reactive component at low
frequencies isn't unattractive to me; I see it as a fact of life, like gravity and friction. But I feel that it is important to point out the fact that the
Omnidrive product you've mentioned is a $3500.00 digital signal processor that you've undoubtedly setup to manipulate the signal quite a bit
in hopes of making the system time aligned in the regions where the speaker subsystems are moving phase around the most.

While I would prefer it to be zero every where, the acoustic phase is around zero starting at about 50 Hz upward to about 5
KHz.
The omnidrive is a powerful tool but I am not using it to correct anything with "time" except for the crossover delay.
The horn is quite smooth all by itself and I only EQ it to go down lower because there is sensitivity and excursion capacity to
spare in the home.

Cool stuff! A little bit expensive, but definitely cool. Will you be taking all that equipment to Lima? I look forward to seeing you there!

I am not sure what I will be bringing, I wanted to answer Kurt but I still don't know. We are getting ready for a trade show so
doing that "actual work" stuff takes up a lot of time, not enough time for home projects. This home type stuff is unfortunately
limited to my spare time.
If it is thought there is a patent able element in the horn, I will probably bring some servodrive something for very low frequencies instead and one form of Unity or another.
Cheers,

Tom

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