Horn design parameter question

[heijnsva]

Hi there,

I'm designing a backloaded bass horn for a 15" Tannoy Dual Concentric unit. My goal is to extend the bass respons, because in the closed box that i now have it falls off at about 100Hz.

I tried various designs and simulations but i keep getting quite silly results, such as mouth openings of a couple sqm, or compression chambers with a negative volume....:-(

So i'm beginning to suspect that there's something fundamentally wrong in my approach. The big question is this:

Can you just pick a cutoff frequency ( f0) for the horn depending on how big you want to make it, or is this bound to the free air resonance of the speaker you want to use?

The unit that i've got has a Fs of 70.5 Hz which is clearly quite high,
and a Qms of 2.83, Qes of 0.81, Qts of 0.63 and Vas of 75.60L.

Is there an experienced horn designer that wants to comment on this?

Thanks in advance!

Kind Regards,

Vincent van Heijnsbergen
The Netherlands

[AndrewT]

Hi,
a Tannoy dual con with a Qts of 0.63?

That sounds almost impossible.

Most of the 15 inch dual con had an Fs between 20Hz and 35Hz.

Are you sure you have the correct T/S parameters?

[AndrewT]

Hi,
for a bass horn the area is [340/Fr]^2 / 4 /Pi.

for 20Hz A=22sqm,
for 30Hz A=10sqm.
For floor and wall reinforcement divide those areas by 4 and for corner loading divide by 8.

The length should be between 340 / 2 / Fr and 340 / 4 / Fr.

You can truncate these sizes at the expense of introducing severe ripples in the passband response and unloading the diaphram at low frequency.

Compare your numbers to the Westminster Royale. The mouth is about 2 times 1.5 by about 0.25m = 0.7sqm.
Tannoy claim response down to 18Hz (I don't believe that it is smooth all the way down to 18Hz because the Westminster is seriously truncated to about 3m long. But they have specially developed the driver specifically for this model even to the extent of re-introducing an Alnico magnet for the Westminster range.

[heijnsva]

Originally posted by AndrewT
Hi,
a Tannoy dual con with a Qts of 0.63?

That sounds almost impossible.

Most of the 15 inch dual con had an Fs between 20Hz and 35Hz.

Are you sure you have the correct T/S parameters?

I'm afraid they are correct. They come from the Cougar stage monitor.
I got the info directly from Tannoy this week.

Would you say this speakers would benefit from a horn cabinet instead of a huge BR cabinet of 350L. with enormous ports? I'd be happy with a response of let's say 40 Hz but i'm mostly concerned about the high Fs.

Kind regards,

Vincent

[AndrewT]

Hi,
I am no speaker expert.

Sounds like the Cougar has a driver that Tannoy have optimised for highest efficiency and moved away from their domestic style. All to get max SPL in PA applications.

If you start from Fs=70Hz then all box configurations will have a roll off starting above Fs.

I only know of two non box configurations that may allow unequalised performance below Fs, namely, open baffle and bass horn.

I suspect closed box, open baffle and bass horn will all benefit from equalisation to extend bass response. But at the expense of using up Xmax and needing prodigious power.

If you go to horn I think any rear box will strangle the bass response, so it may be that you should try a sym without a rear box to let the full length horn resistively load the driver and high pass half to one octave above the horn lower limit. This was a suggestion by DK Speakers some years ago when talking about a loft mounted horn loaded driver.

[heijnsva]

Hi Andrew,

Thanks for your opinion, i'll go futher with the horn design. I just discovered that there a beautiful wiki on the subject on this site that i had'n seen before. ( I never got out of the forum pages)

Especially the explanation of the hornresp software seems very helpfull , as well as the guidelines for a proper design.

Goodbye for now.

Vincent

[Rademakers]

If you want, it's also available in Dutch, tho the diy wiki version is more extended at the moment.

klik/click en/and click/klik

Wkr Johan

[GM]

Greets!

According to Leach's math, it theoretically wants a ~28.35 Hz Fc, M = 0.624, 357.607"^3 filter chamber, and 97.883"^2 throat. It's probably not the best response for your app, but it will at least give you a starting point........

GM

[Rademakers]

What's M ?

Wkr Johan

[GM]

Greets!

Flare factor, aka 'T'. 'M' = 0.5 = hyperbolic, 'M' = 1.0 = exponential, ergo an 'M' factor in-between is typically called a hypex flare.

GM