Just for fun, I fired up Hornresp and did a quick model of an RCF MR8N301 driver on a 150Hz tractrix horn. I ran two calculations at about 110dB (very loud), changing only the compression ratio and taking a midband sample of both at 400Hz:
With an 8.4:1 compression ratio, the throat distortion 2nd harmonic content was 0.84% (inaudible).
With a 2:1 compression ratio, the 2nd harmonic was 0.32% (inaudible).
With an 8.4:1 compression ratio, the throat distortion 2nd harmonic content was 0.84% (inaudible).
With a 2:1 compression ratio, the 2nd harmonic was 0.32% (inaudible).
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In other words it will be used from 50 hz, but only horn loaded from 400-800 where it crosses over to the DE250.
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Thanks, thats why I wont go higher then a 2:1 CR due to phase plug design is to complex for me. Do you think 2:1 CR can do without it to reach 800 hz?
Do you have a source of data to support such a precise demarcation of audibility. Especially since this goes agianst everything that I have read or done.
15mi100 5:1 comp ratio
Hi i would like to put a 15" mid beyma 15mi100 in a ciare MT010 diy horn plan (intended for 12 inch driver) for the 200hz to 1300 hz (maybe 1000hz in fact).
that would give me a 4.5 air comp ratio.
http://www.ciare.com/pdf/Progetti/MyProfessionalSpeaker/mt010.pdf
Would it still be possible for my intended bandwidth, what would be the problems :
- phase issues in treble and limited treble bandwidth (at about which frequancies ?)
- risk for the speaker cone ?
if I added a phase plug the ratio would be even higher the plug blocking also the throat.
please help me.
Hi i would like to put a 15" mid beyma 15mi100 in a ciare MT010 diy horn plan (intended for 12 inch driver) for the 200hz to 1300 hz (maybe 1000hz in fact).
that would give me a 4.5 air comp ratio.
http://www.ciare.com/pdf/Progetti/MyProfessionalSpeaker/mt010.pdf
Would it still be possible for my intended bandwidth, what would be the problems :
- phase issues in treble and limited treble bandwidth (at about which frequancies ?)
- risk for the speaker cone ?
if I added a phase plug the ratio would be even higher the plug blocking also the throat.
please help me.
What many people do not understand about horns is that most of their efficiency gain comes from the compression ratio, the horn load itself is a relatively minor effect. So going to 1:1 would simply be throwing away most of the gain, making using a horn rather pointless since its size at LFs is just too big to be practical.
Going below 1:1 does little, but since 1:1 is already pointless why go even lower?
The higher the compression ratio, the harder it is to get good HF response from the device.
Going below 1:1 does little, but since 1:1 is already pointless why go even lower?
The higher the compression ratio, the harder it is to get good HF response from the device.
Does the lower efficiency gain from a lower compression ratio come with any positives? The horn loading should still present a resistive acoustic impedance to the driver, which should be a good thing over other types of enclosures.
Would a lower compression ratio and thus a lower volume velocity in the throat be advantageous to the system's impulse response?
The horn mouth size required for lower frequencies is typically too large to be practical in most living spaces, but increasing the horn's mouth area by using the room's walls could effectively bring an exponential horn's lower cutoff down around 100-120Hz while not requiring an insanely large enclosure. A sub could be used for below 100Hz.
Would a lower compression ratio and thus a lower volume velocity in the throat be advantageous to the system's impulse response?
The horn mouth size required for lower frequencies is typically too large to be practical in most living spaces, but increasing the horn's mouth area by using the room's walls could effectively bring an exponential horn's lower cutoff down around 100-120Hz while not requiring an insanely large enclosure. A sub could be used for below 100Hz.
A direct radiator also presents a resistive load to the driver, the only difference is the slope of this with frequency. They both start at zero and both are flat at HF at exactly the same level (assuming a 1:1 compression ratio), but the horn is steeper and gets to flat sooner, so over a small range there is some added gain of a dB or two.
The room "walls as a horn" is also a misnomer, because rooms ALL have six walls and when you take all of them into account (as you certainly have to at LFs) the "walls as horn" effect melts away into "modes". And the best way to handle modes is with multiple subs and DSP. A LF horn in a small room is a total waste of space.
Impulse response is frequency response and compression ratio doesn't change that very much.
PS: further to the above, the HF asymptote of the load resistance goes up precisely as the compression ratio and that is where virtually all of the gain of a horn system comes from.
The room "walls as a horn" is also a misnomer, because rooms ALL have six walls and when you take all of them into account (as you certainly have to at LFs) the "walls as horn" effect melts away into "modes". And the best way to handle modes is with multiple subs and DSP. A LF horn in a small room is a total waste of space.
Impulse response is frequency response and compression ratio doesn't change that very much.
PS: further to the above, the HF asymptote of the load resistance goes up precisely as the compression ratio and that is where virtually all of the gain of a horn system comes from.
Let's see your data. A one to one throat in a horn will deliver more than a db or two. Much more.
That's a nice way to visualize the loading differences. Thanks!
Many of the other compromised horn designs make good use of the floor boundary and/or corner loading. If it's a misnomer to say the mouth area is increased by the room's walls would it be more appropriate to say the acoustic impedance is altered by the boundary condition? My potential horn design would be wall mounted and have a cylindrical mouth area, so it makes good use of relatively wasted wall space.
Thanks for the information. It's much appreciated!
"More appropriate", not really. To me what you are saying is the same thing that I said, just a different way of saying it. The room boundary conditions will dominate the acoustic impedance in the modal region. What I was saying is that I think that it is faulty thinking to say that the room boundaries "extend" the horn into the room because this ignores the presence of the other walls. Take those into account and you get an acoustic impedance alteration that dominates this impedance, swamping out any "horn effect".
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Do you disagree that the load impedances both go to zero at Low ka?Let's see your data. A one to one throat in a horn will deliver more than a db or two. Much more.
Do you disagree that both load impedances go to the same specific acoustic impedance at high frequencies?
If you agree to both those (which are facts, of course) then you must agree that at these two extremes then there cannot be any efficiency differences.
Now in the region of ka = .7 the horn will have a greater load and hence a greater efficiency, but this will be highly dependent on the specifics of the device. It is conceivable that the efficiency gain could be greater than even 3 dB, but only over a fairly narrow bandwidth from say ka = .5 to ka = 1.2 or so, basically an octave.
If I get a chance I'll plot out the impedance on a piston with a and without a horn, but that does take some programming to do.
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I think that you are mixing up things, or I don't understand the question. Compression ratio is a ratio of areas, not excursions. The two things are quite different. Then you talk about a "chamber" which is a volume and again is unrelated to compression ratio.