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Old 6th January 2006, 11:51 PM   #1
SCD is offline SCD  Canada
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Default Extremis 6.8 as a dedicated bass driver

Rather than hijacking an existing thread I figured I better start one of my own. I am seeking some help in designing a pair of bass drivers to mate with a set fe127 bipoles I built last year. I have had some reasonable success in the making of cabinets. I am a little weak in the modeling aspects of speaker design.

I picked up a pair of extremis 6.8 drivers with the plan of using them to augment the lower octaves of my audio system. I am targeting primarily 2 channel audio with the bass boxes covering only the lower octaves. I was thinking about 100htz or lower. I would like to keep the cabinet small if possible. I have been advised that I might get good performance by putting them in 9 litre sealed boxes. Thoughts comments or input is greatly appreciated. I have heard this driver and realize it is a good performer.
The next question is the x over design and location. I am thinking about line level as I made a set of LM4780 mono blocks with room in the chassis to include a bit more circuitry.

So the help I am seeking is the design of the cross over and sizing of the cabinet, thoughts and comments on my intended use of the drivers i also appreciated.

The tools of my trade are bulldozers and chainsaws. I am getting better at using a table saw and a router but it takes time.
Thanks in advance
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Old 7th January 2006, 01:14 AM   #2
TerryO is offline TerryO  United States
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Default Re: Extremis 6.8 as a dedicated bass driver

Quote:
Originally posted by SCD
I am seeking some help in designing a pair of bass drivers to mate with a set fe127 bipoles I built last year. I have had some reasonable success in the making of cabinets.
Dear Mr. SCD,
Having seen your "reasonable successes", I really can't imagine how beautiful your speakers will be when you start putting your mind to it!

Quote:
[i]I picked up a pair of extremis 6.8 drivers with the plan of using them to augment the lower octaves of my audio system. I am targeting primarily 2 channel audio with the bass boxes covering only the lower octaves. I was thinking about 100htz or lower. I would like to keep the cabinet small if possible. I have been advised that I might get good performance by putting them in 9 litre sealed boxes. Thoughts comments or input is greatly appreciated. I have heard this driver and realize it is a good performer.[/B]
I think that any of the better freeware box design programs will work if you have the TS data. One problem you will run into is the relative differences in efficiency between the Bipoles and the Extreamis. The next problem is the old triad: Loud, Deep and Small. You only get to pick two, there are ways to fudge on this, but realistically you're pretty much locked into these choices.

Quote:
[i]The next question is the x over design and location. I am thinking about line level as I made a set of LM4780 mono blocks with room in the chassis to include a bit more circuitry.[/B]
I'm not one to give much advice on crossover design as I don't feel I'm good enough, but I'd start with a 2nd order LP on the woofer and see if the Bipoles will roll off and blend without any problems (or a crossover). The extremis are not very efficient, so if you use EQ with a small box, the 4780's may run out of juice before the speakers reach the SPL levels you're looking for. I'm assuming that the 4780's are good for around 70 watts or so.

Quote:
[i]

The tools of my trade are bulldozers and chainsaws. I am getting better at using a table saw and a router but it takes time.
Thanks in advance [/B]
Hey, I used to have a pair of corks, stags and suspenders myself, you do high lead or skid? Next time we meet, we'll have to swap true stories :^) ..........RIGHT!
Best Regards,
TerryO
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Old 7th January 2006, 05:36 AM   #3
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Default Re: Re: Extremis 6.8 as a dedicated bass driver

Quote:
Originally posted by TerryO

The next problem is the old triad: Loud, Deep and Small. You only get to pick two, there are ways to fudge on this, but realistically you're pretty much locked into these choices.

I think it's Deep, Small, and Effecient, pick two. With enough power I would think you could push them fairly loud. Of course I don't really know anything about the Extremis driver, depends on x-max and power handling.
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Old 8th January 2006, 07:40 PM   #4
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Default Re: Re: Re: Extremis 6.8 as a dedicated bass driver

Quote:
Originally posted by TerryO
Loud, Deep and Small. You only get to pick two
Quote:
Originally posted by Josephjcole
I think it's Deep, Small, and Effecient, pick two.
What's the difference?
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Old 8th January 2006, 08:03 PM   #5
BWRX is offline BWRX  United States
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Default Re: Re: Re: Re: Extremis 6.8 as a dedicated bass driver

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Originally posted by Cal Weldon
What's the difference?
Loudness is measured in phon and efficiency is measured as a percentage?
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Old 8th January 2006, 08:43 PM   #6
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Well since every high efficiency speaker I know is made to go loud, I didn't see the point in the correction.
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Old 9th January 2006, 12:04 AM   #7
BWRX is offline BWRX  United States
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If you get technical you could say that an inefficient speaker could play loud IF capable of handling the power needed to reach those levels. They can certainly get loud but not because they're efficient. Thus, efficient may the more appropriate term.
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Old 9th January 2006, 12:53 AM   #8
GM is offline GM  United States
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Greets!

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Old 9th January 2006, 04:45 AM   #9
TerryO is offline TerryO  United States
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Default Re: Re: Re: Extremis 6.8 as a dedicated bass driver

Quote:
Originally posted by Josephjcole



I think it's Deep, Small, and Effecient, pick two. With enough power I would think you could push them fairly loud. Of course I don't really know anything about the Extremis driver, depends on x-max and power handling.
Joe
I'm afraid that I've commited a "fox paws" in using the technically incorrect term and I apologize to Joe and the members of this forum. The problem began when I made a couple of assumptions. (I know, that always means trouble:^)

Given that the Extremis is not what anyone would refer to as efficient, at least as is generally understood on this forum, and as Scott indicated that he would be using an LM 4780 chip amp, which in the basic configuration outputs about 70 watts, then the only missing factor is loudness. Any EQ that I'm aware of requires additional power and my concern was that there might not be enough wattage available to match the SPL levels of his bipoles. I "do" have a tendency to try to simplify these things as it eases the "brain pain" that my rather limited intellect seems to accumulate when confronted with anything more complex than a popsicle stick.

The Extremis certainly has abundant x-max and more than adequate power handling for this application, AFAIK.

Best Regards,
TerryO
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Old 9th January 2006, 07:07 PM   #10
SCD is offline SCD  Canada
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Thanks for the input guys:
I should know better than starting a thread just before going away for the weekend.
I do not have a computer at home so I need to rely on the helpful folks on the forum to help me in my designs.

Here is the concept I am trying to make come to life:
Try and augment a very good sounding bipole. The bipoles are efficient to somewhere around 93db and tuned to somewhere around 50htz. In a TL with a smooth role off. I do not intend to use it in home theatre. I am targeting +-30 htz to <100htz for the woofers. I was hoping that the LM4780 would be enough for "normal" listening levels in my living room. I was hoping that a line level filter (after the pre amplifier) of some sort would work to only feed the woofers the lower frequencies. I was also planning on placing the lm4780 amps right beside the woofer cabinets. A stereo pair should provide a reasonable amount of woofing I hope.

If I am way off track, please let me know. I can always use this driver for a nice set of regular speakers if this concept does not work out.

This is the link Planet10 has for the driver data

http://homepage.mac.com/tlinespeaker...is-6.8Data.pdf

I understand the discussion on the trade offs thanks GM. Next is to come to balance on the real possibilities with this pair of drivers. I am open to suggestions.

I will also need help in designing a line level control filter to feed the woofers just woofing type sounds.
If someone could help I would be most appreciative.

I hope that clarifies things a bit
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