Efficiency of RF-3 horn & drivers?

[Spider124]

Trey, Phil, Bob, anybody....

Can you tell me exactly what the efficiency and sensitivity of the K-105-K horn and the K-1038-S woofer are on the RF-3? (separately, as in what they are on thier own)

Are the woofers two 16 ohm in parallel, or two 4 ohm in series?

Thanks much

Charlie

[WMcD]

I can't give you specifics on this. However, generally, direct driver woofers have efficiencies of about 80 to 95 dB measured at one meter with 2.82 volts input. This is one watt into 8 ohms.

The really story is that direct drivers have poor bass because they are bad radiators, and so their motors are made to be weak, and thus are made to have poor, but equally bad, mid and upper bass. They are not powerful enough to move the mass of the diaphram at mid and upper bass frequencies. This is called "mass control."

You can't improve the deep bass, you equalize down the mid and upper bass. As you can see, smaller bass drivers do produce poor deep bass, and the upper bass must be equalized down, by mass control, even more.

Horn loaded drivers are typically about 103 dB in sensitivity. If there is a direct radiator bass unit, you have to used an electrical pad to cut down the output to be equal to the bass.

Gil

[Spider124]

Yes, I knew most of this.

But I need the exact sensitivities because I'm thinking about biamping. And it's hard (impossible?) to get the crossover point right unless you can get the levels matched precisely.

Charlie

[Spider124]

mdeenen,

Yeah, those are the sorts of numbers I've seen. At this point, I expect the woofer efficiency (individual) to be about 83, with 6db from having two, gives 89, and then add on 9db for shooting into 1/8th space as Klipsch measures it, gives 98db.

I will be doing an active phase-coherent Linkwitz Riley driving a 20 w Class A amp for the horn and a 120w AKSA PP Bipolar for the drivers. (At 2000hz, the power division is about 20/80 horn/drivers, so I shot for a LF amp of at least 4 times the HF, and some headroom) The crossover design already has level controls for both channels.

I suppose I can output a test tone at the crossover freq, and then run the amps one at a time, and use my trusty rat shack SPL meter, since 2000hz is above room gain, it should be close to within at least a db, hopefully. Without the efficiency ratings, though, it will be hard to come up with a decent starting point, though.

Charlie

[Spider124]

The Linkwitz-Riley is a 24db/octave phase-coherent crossover. The particular one I'm going to use is a implementation by Rod Elliot Project #9 . I plan to use surface mount AD825 op amps, all polystyrene caps, and Holco resistors.

Lower down the page he shows an output buffer that has attenuation. I'll probably rig them up as shown, then after I've dialed them in roughly, get a smaller (5Kohm) pot and put appropriate metal films above & below it, for super-fine adjustments.

Also, Rod designed the Class A amp I am planning to use called the Death of Zen . The LF amp I'm using is a kit from Printed Electronics called the AKSA . There is a four-output-device build out that gives the 8 ohm version an output power of 125w or so.

Anyway, I'm looking forward to doing this project this summer. We'll see how it turns out!

[Audio Flynn]

Dr. Gizmo from Listener Magazine had an interesting article in the last issue.

One of the key points is speaker manufacturers do not want to put the expense into 16 ohm drivers becuase the higher quality magnets drive the cost up too much.

He seemed to infer that alot of time and money is spent to keep distorion low in the signal path by the audiophile. When the music gets to the speaker we are subject to the greatest amount of distortion from low cost internal wiring, crossover components, drivers and lacsidasical cabinet construction.

He has a strange writing style, but he has some very direct opinions.

[Spider124]

I'm building this because I want to eliminate cheap internal wiring and eliminate the crossovers.

Also it gives a bit of a power advantage (total power is 145w) without buying some massive MOSFET thing. Also I want to hear how Class A amps will sound with these horns.

Most importantly, it gives me lots of fun things to build. However, at the cost it's going to be in the end, I'm probably in the territory of just buying a nice Outlaw 750 amp (which would be 5 channels, too) or something. :/

Charlie

[KGeist]

Spider124,

Off-hand, I don't know the sensitivities of the K-105 or K-1038, but I probably can add some clarity to this issue.

First, the way we measure loudspeaker sensitivity is not as you suggest. We measure the speaker at 3 meters, full space, in our anechoic chamber. We measure at 3 meter because this gets into the far field of the loudspeaker. Generally, we use bandlimited pink noise to make the measurement, but in our experience, this isn't always necessary to get an accurate result. The 3 meter measurement is converted to a 1 meter rating using the inverse square law (in other words, add about 9 db). From here we add a 4 dB for "room gain". This is a figure we add that represents the output gained from a typical listening environment. It is an approximation, but it does reflect a more accurate sensitivity measurement of the loudspeaker/room combination. Therefore, this measurement reflects a value that the average consumer "might" measure at one meter in their own listening room.

From this information, if the RF-3 is spec'd at 98 dB, then the spec without "room gain" would be 94. One woofer, as you suggest, would be 6 dB less, or 88 dB. However you must remember that this is with a passive network, and that the raw driver output may be 1 or 2 dB higher. In any case, 89 or 90 dB would be a good figure of merit to use.

The horn sensitivity is much harder to determine. This is because horn loaded tweeters do not have flat pass-band responses. They are resistance controlled devices, and do not play by the same rules as direct radiators. Typically they have a 6 dB/Oct roll-off above the mass break point of the diaphragm, and as a result, one sensitivity figure is hard to establish. This characteristic of horns is taken care of in the design of the passive crossover, but in order to design it properly you have to be able to measure it. This isn't going to be easy in your situation, so I don't know what to tell you.

Lastly, loudspeaker sensitivity and efficiency are only "loosely" associated with one another. They are NOT the same thing. I'm pointing this out because at some points in this thread the two were being clearly confused. For example, at low frequencies, adding a second woofer, in parallel, increases the sensitivity 6 dB, but the efficiency actually only increases by 3 dB. This is because when you place two woofer in parallel, you halve the impedance, and the amplifier delivers twice as much power, or 3 dB. So, the sensitivity at constant voltage would go up 6 dB (2 watts), but the sensitivity at "1 watt" would only increase by 3.

Hope this help.

Kerry

[Spider124]

Thanks for the clarification, Kerry.

Since nobody else has responded to this post, and since Trey hasn't responded to my email, I'm going to assume that I'm on my own for trying to figure out the exact numbers.

Also, are you saying the horn needs some kind of equalization? Or more like what you're saying is the horn has its own roll-off that is taken into consideration when designing the passive crossover. If this is the case, I don't know if a linkwitz-riley will work or not.

Charlie