# Tower of Power version 2



## mwmkravchenko (Jul 11, 2009)

Hello gents 

Fooling around with some drivers from Bob in simulations on another thread has gotten me a thinkin. I made a center channel that used 4 EL70's in a short line source. Great sound. I have been listening to two TRIO8's for almost 6 months and I never tire of their clear effortless bass. So to put this thread into perspective here is what I'm aiming to pull off.

A speaker that can go clear from the top end to the bottom end. We will define that as follows.

30hz to 24 khz.

It must be able to do this with at least 100db/watt efficiency. 

Why?

Well listen to a high efficiency system and tell me what you think. They are the most lifelike of all speakers I have listened to or built. I enjoy lifelike sound.

Must be able to reach 120db almost across the bandwidth stated.

The only problem with the top end on the EL70's at this level is that there will be some doppler distortion generated when you take musics spectral content into consideration. THey can and do go up this high. But I will be giving them a helping hand.

Driver complement:

8 pcs EL70
4 pcs Neo 3
2 pcs TRIO8

The mid and high frequency drivers will be set up as a large line source type MTM.
The TRIO8's will be in a front loaded horn.

Box size?

Big

But narrow and tall to accomodate all the drivers.

Preliminary design specs are 10" wide x 60" tall x 16" deep. I have to design the least compromised horn into this space. That's the fun part. And that's where I will start off. 

Mark


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## lsiberian (Mar 24, 2009)

mwmkravchenko said:


> Hello gents
> 
> Fooling around with some drivers from Bob in simulations on another thread has gotten me a thinkin. I made a center channel that used 4 EL70's in a short line source. Great sound. I have been listening to two TRIO8's for almost 6 months and I never tire of their clear effortless bass. So to put this thread into perspective here is what I'm aiming to pull off.
> 
> ...


100db/efficiency and 30hz don't really go hand in hand and efficiency has little to do with sound quality.


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## mwmkravchenko (Jul 11, 2009)

> 100db/efficiency and 30hz don't really go hand in hand and efficiency has little to do with sound quality.


Hi Isiberian

Your statement on face value is correct. High efficiency does not equal sound quality.

But I fail to understand how that statement applies for the driver complement quoted above. 

The EL70 is a wide band clear and clean driver. I have worked with them since they came out and have to say they are one of the few fullrange drivers that really lives up to the name fullrange. When used in a group they have a tight articulate low end a very clean midrange and a smooth pleasing top end. The tweeter is there to preserve all of that when they are called on to push a bit more air than usual. The Neo3 is acclaimed as a very good tweeter again I have used them in the past to great effect. They are clear and very crisp. Closest thing I have listened to at length that can hold a candle to an ESL. 

Using a very wide range mid woofers and tweeters allows the use of very gentle crossover slopes and therefore very little lobeing error vertically and horizontally. The cross overs have been simulated to create as little combing effect as is possible. I have endeavored to keep the tweeters response out of the area where the woofers are still non-directional and linear in their output. So this will be a very coherent system that will sound almost the same sitting or standing. Try that with most commercial speakers!

The use of multiple drivers allows a smoothing of the impedance peaks to the point that the speaker will be a nice light load for the amplifier. So you get a great deal of sound with as little stress on the amp as is possible.

The only higher order crossover will be on the Front Loaded Horn that the TRIO8's are loaded into. The rest as far as I have modeled are first order electrical that roll off to third order acoustical. Again keeping in mind the directivity characteristics of the piston size of the EL70 and the Neo3.

The tweeters chosen have a very tight vertical dispersion characteristic that can be a negative when used signally. It has been turned into a positive by setting them up as a four high column on the center of the baffle. This puts them at ear height when a person is seated and therefore creates a very controlled high frequency dispersion characteristic. The enclosure for the EL70 woofers has been tweeked to create it's own inherent baffle step compensation and the hornloaded woofers will easily keep up to the EL70's even if the cabinets are not close to a rear boundary as the horn exit is next to the floor. If the cabinet can be set close to a wall then there is the greater reinforcement of the bass that partial corner loading will accomplish. So yes 30 hz and 100db/watt can go hand in hand.

This is basically a larger version of Bill Fitzmaurice's David tower. I built one for a client back in 1997. He liked it and I listened to it at length before I delivered it. What I noted back then was that it sounded quite clean and dynamic. It could tempt one to turn up the volume quite a bit. I used a Motorola KSN1177 as a tweeter element back then. Basically I didn't know about the Neo 3. For the time it was pretty good. The short coming of the design was that there was not enough cone area in the midbass and midrange to keep up with the horn loaded bass section. As you played it louder close to concert level for classical or rack music it started to sound like a bose system. A bass hump and a large wide suckout in the upper bass and low midrange. Not my cup of tea. 

This new tower design I hope will do all that the simulations have promised. The software I have available today is light years ahead of what was available back then. Things we were using educated guesses on back then can be simulated with decent confidence. Time and experience is always a good teacher. And maybe this design will hit all the right buttons.

I attach the current simulation of the base section:


The simulation is in a 1 Pi acoustical environment. In practice there will be a 3 to 4 db drop on the higher end and bit of boost on the lower end when placed within a couple of feet from a wall boundary. If you are about 6 inches from a rear wall the low end will sound pretty flat down to 30 hz. This placement will make the most out of the room gain effect and the boundary loading effect.

Mark


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## mwmkravchenko (Jul 11, 2009)

A bit of a preview:

This is to scale. And the front should be tilted back about 5 degrees to help the vertical dispersion pattern.

The one on the left is the one I will probably go with. Both will have comb filtering errors. But the one on the left will sum to a more coherent response closer to the speaker baffle. It should sound a little more even. Probably have a more even sound stage.

Mark


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## mwmkravchenko (Jul 11, 2009)

So what can 8 El70's do when unburdened on the low end? Well the attachments speak for themselves. This is done in WinISD. It simulates in a 2 Pi acoustical environment. So it is safe to add another 6db to take into account ceiling and side wall reflections that are not factored in a 2 Pi calculation. The one watt efficiency is above the design goal as is the low end design. Now to reliably simulate the tweeters.

Mark


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## Mike P. (Apr 6, 2007)

What's the net volume for the 8 EL70's?


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## mwmkravchenko (Jul 11, 2009)

Hi Mike

The net volume is 18 litres. The enclosure is sealed.
This was chosen to give the broad shallow rise near cutoff that will somewhat compensate for the baffle being so narrow. You will get significant cancelation of the mid bass frequencies and the gentle rise will pretty much smooth out to flat once your a few feet from the baffle.

Mark


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## Mike P. (Apr 6, 2007)

18 liters for 8 EL70's?


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## mwmkravchenko (Jul 11, 2009)

Hi Mike

Yep. Think outside the box a bit. First the enclosure is sealed for good transient response. It is undersized providing both a bass bump that is usefull for baffles step diffraction losses. It also rolls off the low end by 12 db/octave below 100hz. Throw in the third order hipass network centered at 100hz and you have a bandwidth limited mid bass midrange array. Choose the crossover point to the tweeter so that there is minimal lobing error and you get nice smooth sound from sitting to standing. Gotta pull out all the dirty tricks sometimes. :R If all we ever do is read about the best where's the fun in that? We gotta try to make the best to!

Mark


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## Mike P. (Apr 6, 2007)

This is going to be an interesting project. Looking forward to the results!


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