Throat Size of a speaker....does it matter?

[rschultz]

I've noticed in looking at the different speakers how they have the same driver mid (k-55v) but different Lens sizes....does that change the sound of the driver or just disperses the sound differently?

Thanks

[Malcolm]

The bigger the mouth, assuming everything else is correct, the lower the cutoff frequency. In other words, you can generate lower frequenices at usable volumes with a big horn than you can with a little horn. That is why the Heresy crosses over to the woofer at 700 Hz and the Klipschorn crosses over at 400 Hz or so. Assuming similar horn design, dispersion will be similar. However, a change in horn design can affect dispersion.

[D-MAN]

Malcolm is right. The size of the horn mouth and the length of the horn determine the Fc (without a discussion of expansion rates, etc). Also, I would imagine that the crossover frequency points would also be different, bearing in mind that the respective horns in question have various Fc's. Typically the crossover low freq cutoff point is above (or at least AT) the respective horns Fc.

The particular dispersion pattern of a given horn is also determined by the expansion rate and horn mouth employed.

Never the less, the same driver can be used on many horns of various dimensions in combination with the crossover points employed.

DM

[rschultz]

Let me see if I get this...let's say I use a "k-55-v" driver with a horn lens 24x9" would result in a sound with more bass with more dispersion than a lens with a size 5x12" and the same "k-55-v"?

[D-MAN]

If I understand the question, I think that the answer is yes.

For clarity, I'll rephrase. In this example, we are assuming a midrange compression driver and that the crossover point is "adjusted" to match the lc of the horn and driver combination...

If a horn is selected with an appropriate cutoff (that is the fc of the horn is equal or higher than the driver's lower range rolloff)within the "safe" operating range of the driver, the answer is yes a larger horn mouth can be employed and you will have a lower midrange response from the same driver (in as much as it is rated). Again, the driver in question must be capable of safely reproducing the respective frequency. I am also assuming that the horn throat is also the appropriate size for the driver.

One should not exceed the driver's recommended low freq cutoff as the lower one goes in freq, the more wattage (and excursion) is required by the driver. This will blow the diaphram in most cases.

DM

[JohnA]

Based on my understanding you are all in the black, but out in the 10 ring. With a horn, the mouth area is intimately tied to the length, but it is the length, more than the mouth that lowers the cut-off frequency. Neither has a direct effect on dispersion. However, the shape of the walls caused by the expansion rate of the crossectional area dictate the dispersion angles of the horn. That ends up controlling mouth area. So, the mouth area is also tied to the dispersion angles. I'd imagine the engineer selects an expansion rate and length that gives the desired cut-off and dispersion angles and lives with the mouth area.

[WMcD]

There is a lot going on.

First, the driver has output only with a certain range. The low limit is about the diaphragm resonance frequency. The high end is usually limited by the mass of the diaphragm. Therefore tweeters have small, light diaphragms.

The expansion rate of the horn, usually expressed as a function called Fc (cutoff frequency). The function of the horn as a transmission line becomes very poor at Fc and that is roughly the lower limit. Klipsch describes there horns as K400, K500, etc. That is not Fc but is about 1.4 of Fc. It describes a bit of a safety margin. E.g. the K400 presents a good load down to 400 Hz.

The Fc really also describes how fast the cross section grows. If you want a lower Fc, the horn grows in area slowly. This means it must be physically big.

The next issue is mouth size. Classic design theory says if you take Fc you can get an eqivalent wavelength. A round mouth (big end) should have a circumfrence of that wavelenght. You have to do the math to find the area of that circle. It assumes the mouth is in free air, no baffle or cabinet surface.

You can use a smaller mouth if it is mounted in a plane. Klipsch does that and assumes a mouth area of about half the classic, because they are mounted in flat surfaces.

Also, you can shift from round mouths to square or retangular mouths.

There is a lot more to the geometry of the horn and mouth. But the above are the basics.

Gil

[D-MAN]

Unless you are building your own horn, it is typical to buy a horn and/or horn driver based on:

1) the overall size of the mouth

2) the size or diameter of the horn throat

3) the overall depth of the horn and mounted driver

4) the horn lower frequency cutoff (fc)

5) the lower frequency rolloff of the driver in question

6) the desired dispersion pattern of the horn

All of the above are required to make an informed decision...

For example, several different horns can be found that have virtually the same overall parameters, but different dispersion patterns. The horn expansion rates of course are different, but this doesn't always change the mouth size, throat size, or even the respective horns fc, etc.

Without overcomplicating the subject, the answer is that if you select a horn and driver combination based on the above, it is conceivable to have a larger horn mouth with a lower fc than a smaller and/or shorter horn and, using the same driver, reproduce a lower frequency with the large horn than before with a "smaller" horn. The "size" of the horn may or may not have alot to do with it, although, typically, the larger-the-mouth-the-lower the fc (with the above mentioned reservations).

If all of these fit the application, then one can reasonably mix-and-match the horns and driver combination to meet the desired goals of size and frequency response.