Hope you can provide some insight.

I've been modeling a mid horn and got results that indicate very flat response from 150 Hz to 1000 Hz with a conical horn. That part seems great to me. The throat/Sd ratio is 0.5 which isn't out of line.

It's a 6" driver that seems to need a 3L back chamber - physically that's no problem given the driver dimensions.

What's bothering me is that the horn mouth has a radius of 10-1/8 (325 in^2) inches BUT a length of only 7 inches.

This seems incredibly short - why does the response plot look so good?

You set this value in the ANG field. If it is set for 0, you're modeling an infinite horn which always has a nice response curve. Generally, use in larger areas makes response more peaky. So worst-case is usually freespace response.

Is there any practical usage for the infinite horn setting?

I know that the early horns used the infinite models ,more simpler

basshorn transporter-
Cheers!

Nice backplate!

7" length is 1/4wl of 480Hz so this will be the lowest usable point. Depending on mouth dimensions, usable response may start at a higher frequency than this, but the right dimensions will let you use it to 480Hz.

I'm interested in what your doing - what driver are you using on this horn?

I've used Eminence Alpha 6" driver on tractrix and conical horns with success from 300Hz-2KHz.

Sd 141
CMS 7.87E-4
MMD 11
Re 6.16
Bl 6.5
Rms 1.91
Le 0.61

What's an "approximation" is MMD. The data sheet says MMS is 11.5 grams. If I let hornresp do its thing it want to come up with a 16 gram cone, which can't be right.

Sound plausible?

Once you look at finite horns, you start seeing its reactive nature much more, and the thing begins to show its response peaks. That lets you make some decisions about what to do to reduce those peaks, and where a particular horn is suitable and where it is not.

My conclusion was that it was just acting simply as a closed box down that low (which it would anyway). But the driver was more different as it's got an Fs of 91Hz and a very high Qts of 1.54, so I thought that could be the answer. The high Qts tells me that any rear box volume is going to peak quite a lot at the closed box resonance. Modelling the closed box response of the driver in a simple box modelling program (like Boxplot) showed a good +4.5db peak at ~90Hz when in an infinitly large box (like an IB or dipole). In a 17L box (volume size equal to Vas), it shifted to the 120-130Hz region and peaking at resonance became even more pronounced at almost +7db. This corresponds to what Hornresp showed me comparing the horn with no back chamber (like a dipole, with Qtc equalling Qts and the resonance equalling Fs) to the horn with a back chamber of 17L, the inclusion of back chamber shifting F3 from 80HZ to 100Hz in the horn (because the 17L rear volume raises its Qtc, so F3 rises too). The increase of peaking at resonance from 4.5db to 7db accounts for the increase in efficiency on the horn of ~2 to 2.5db between 100-150Hz. The peaking of the back chamber was boosting the low end response around 100Hz, and this major peaking of the closed box combined with the horn response was enough to make the F3 be at 100Hz. Response was within +/- 2.5db from 100Hz to 1KHz, so the high Qts made the output usable to 100Hz (although it required a lot more excursion at 100Hz than at 300Hz). If Qts was a lot lower, say 0.30, then I seriously doubt this would occur and low end cutoff would be 300Hz, as a horn length of 30cm supports, providing mouth is of adequate size.

However you have said your drivers got a Qts of 0.40, so something else must be going on. If Fs was around 30Hz then with the Vas of 30L and Qts of 0.40 you may see some more output down low, but its not peaking or anything so I wouldn't expect it to actually be flat down low, you could see a step from 480Hz (Fc of 7" long horn) and then the step giving more output down low but at an attenuated level (like an EBS ported box style response at the low end, 150Hz to 480Hz on your horn). Is this what it looked like?

Perhaps you've got some of the parameters wrong? Mmd can never be less than Mms seeing that Mms=Mmd+Mmr, so maybe theres an error in your inputs.

Mmr (air load) for a typical 6" driver with 125cm^2 Sd is only 0.8grams.

For referance, here are some Mmr approximations for different driver sizes:

Adrian