K-77 Rating?

[jorjen]

Cannot remember what the efficiency rating is and could not find it in a search. Could use some help. Thanks.

[WMcD]

It is 104 dB at 1 watt, 1 meter.

In the K-Horn, LS, and Belle, it is running wide open without attenuation. The bass horns are the same. Only the midrange has to be reduced from 107 to 104 dB with the autotransformer.

The overall system in those is rated at 104 dB, of course.

Gil

[Rdmarsiii]

So is the reason why the Heresy's are only 96 db sensitive because of the woofer? So the Mid and K77 have to be stepped down about 8 db?

[jorjen]

Thanks Gil. I don't know what I was thinking, but I thought I remembered it being somewhere in the neighborhood of 101-103. OK, now I at least have a starting point for my L-Pad. The JBL 2404H is 105db and I have gone from 5-2 on the autoformer on the ALK's to 4-X. So, I am going to try 2.5db attenuation on the JBL's to start the dance and go from there.

[crazytubepower]

Im fairly sure thats how it works dave

[BEC]

Gil,

The K-55V is actually about 110db. Being a 16 ohm driver, it is down another 3 db from the 8 ohm tweeter at the same voltage. So that is a total of 6 db attenuation compared to the tweeter making them both about 104 db.

Bob

[WMcD]

To answer Rd's question.

Yes.

It is not uncommon even in pure direct radiator systems that the midrange and the tweeter are more efficient or sensitive than the woofer. Therefore the mid and HF are knocked down with an L-pad.

In the CW or the H, the bass box is the limiting factor. You can look at the crossover schematics and see that the auto transformer taps are used to reduce the drive to the mid and tweeter.

- - - -

There is a basic issue with direct bass drivers. They are relatively small transmitting antennae in view of the wavelenghts involved. I.e. small radiation resistance.

Much of the design of bass systems stems from that basic fact. Even a 6 inch driver has some baseline output at, say 50 Hz. It might be 84 dB. Then it could get better as frequency goes up and the diaphragm becomes relatively larger in terms of wavelenght.

The rest of the issue is making the mass of the diaphragm so big, and the motor so weak, that there is a form of equalization to knock down the potential rising output.

Gil

[Rdmarsiii]

Thanks! So technically its the woofer that is 96 db sensitive and the k-55/53 and k-77 is knocked down to match it?

[Deang]

Yep, that's the way it works.

The spec sheet I have on the T-35 shows it as a 105db driver, and in the range we use it -- it runs at 7 ohms. The bass bin: with the single 2.5mH inductor, it's actually 108db -- unless you play music that never has a B note.

[djk]

The T/S parameters on the K22E work out to 95dB/2.83V/1M in 2Pi (half space).

As Bob pointed out the K55V is 110dB/W/1M, but because it is 16 ohms it is about 107dB/2.83V/1M, and the 8 ohm K77 is about 104dB/2.83V/1M.

The T2A provides 9dB attenuation on the K55V, and 6dB on the K77, for about 98dB overall.

Many like the Heresy with the T2A set to 12dB attenuation on the K55V and 9dB on the K77, to match the 95dB on the K22E.

If using your Heresy in 1Pi (quarter space) you may prefer in with the stock taps.

[Rdmarsiii]

So since I have my heresys set as small, how do I make it to where its the 9 db for the K55 and 6 on the K77? Or is that possible?

[Malcolm]

You got it, the k-55/53 and k-77 are knocked down to match the woofer.

But the woofer isn't even 96 dB. The 96 dB rating of the Heresy is the manufacturer's average rating for the entire system, not the woofer. The manufacturer is free to arrive at this figure by whatever means they like. If you plug the T/S parameters for the various woofers used in the Heresy over the years into a spreadsheet or program for a sealed box, you will typically get figures for the woofer a little below this. Similar woofers with published specs are typically in the 92 to 95 dB range.

[Deang]

So since I have my heresys set as small, how do I make it to where its the 9 db for the K55 and 6 on the K77? Or is that possible?

That's the way it's set now.

[Rdmarsiii]

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On 6/28/2005 10:22:05 PM DeanG wrote:

So since I have my heresys set as small, how do I make it to where its the 9 db for the K55 and 6 on the K77? Or is that possible?

That's the way it's set now.

----------------

So It's not the 12 and 9?

[Deang]

No, you would have to drop to taps 1 and 2. You have to add resistors to the tweeter and squawker to keep impedance at a workable level, and to keep the crossover points the same. I actually prefer just to use a different network all-together.

The T-35 had a RETMA (EIA) sensitivity rating of 57db. Dennis, you once said, "EIA is 1mW at 30ft, add 30dB for 1W, add 19.216dB for 1M." This is 106db. Does it drop back because the original spec was on the 16 ohm version of the driver?

[Rdmarsiii]

Dean, You have a PM

[Deang]

I decided to look up that spec sheet I was thinking about in the other post. I guess it would've helped if I'd remembered the right sheet. So, what in the heck is this thing?

[djk]

"This is 106db. Does it drop back because the original spec was on the 16 ohm version of the driver?"

"The spec sheet I have on the T-35 shows it as a 105db driver, and in the range we use it -- it runs at 7 ohms"

Hard to say what is going on here. I have seen so many specs on that tweeter. The last catalog from MCM that had the OEM version of the K77M/T35A in it only claimed 101dB.

Could be handwaving. Could be just how they were measuring it. The frequency and distance (distance more so on mid horns rather than tweeters) can make a big difference, as will baffle mounted vs freestanding.

"You have to add resistors to the tweeter and squawker to keep impedance at a workable level, and to keep the crossover points the same."

You only need add a 15 ohm 10W resistor to the K55V when moving the taps down one to keep the frequency the same. The tweeter is fed from its own cap after the tap so it crosses at the same frequency no matter what tap it is fed from. I agree with your comment about a new network being better, but there are so many diferent parts groups that constitute a 'Heresy' that they really would need a different network for each group.

[Deang]

Yes, all true. With the tweeter, I was thinking of the impedance. On tap 2, the tweeter climbs to 64 ohms. I typically have tube amps on the brain when I think about this stuff. I honestly don't know if it matters or not. Warren taught me that current to the coil goes down as impedance climbs, and as the driver approaches resonance. The idea being that since current is decreasing, elevated acoustic output at high impedance shouldn't be assumed.

You have a PM.