Bass Bandwith for PA Sub?

[Xoc1]

I am playing around with tapped horn designs in hornresp and am wondering what would be the highest roll off (-3db point) frequency that would be concidered usable for a PA sub.
Usage is for a guitar rock music band PA system, for local small clubs and pubs.
The obvious trade off is size versus bandwidth. Less obvious but also tempting is the increase in efficiency when the bass roll off frequency is increased.
I am familiar with J Bells and screamersUSA,s tapped horn cabinets. I am trying to make something that would be hopefully
smaller. ScreamersUSA,s Furyboxes seem to have a -3db Roll off about 42 Hz.
I can respect that as it is about the lowest frequency on a bass guitar.
Pushing that frequency up to 60hz would loose half an octave of notes. Question is would this sound terrible or not?
Maybe I should try setting up my DCX246 crossover for the higher roll off and try it at a gig!
I am in the UK and have been simming up designs using Precision Devices and Royal Loudspeakers drivers.

[cowanaudio]

G'day

You could do much worse than having a look at the Andershorn.

15" tapped horn plans - Speakerplans.com Forums - Page 13

100dB/W/M, 42-150Hz, small enough to be a one man lift.

Cheers

William Cowan

[Xoc1]

Thanks William for the Link I will spend some time studying that design.
More compete details here:
Martinsson`s Blog - high end mid/high end
I was hoping to extend the response to 180 hz to meet my compact 10"/1" horn mid top cabinets. I have four of these with Fane 10M & MD2050 compression drivers. The 10M,s are dedicated midrange drivers and quickly run out of steam below this frequency.
My current bass bins are Fane XB 15" in a 125 litre reflex cabinet tuned to approx 50hz
I note that when I sim the reflex cabinets in Hornresp with similar settings (2pi & 2.82V) I get an efficiency rating of about 95db/W so I suppose an actual rating of 100db/W is not so bad.
My brother uses a set of bandpass horns that are 105dbw, but you need a truck to carry them around in!

[Xoc1]

OK
I have looked at the various drivers I have played around with in Hornresp and the best result I have so far is with the 18" Royal 1500i M2

Technical Specifications:
Nominal Impedance: 8 Ohms
Power 1500 Watts AES
Short Peak 6000 Watts
Usable Frequency range 25 – 450 Hz
Maximum cone displacement: 50mm
Cone material: Fibrulated Nylon reinforced pulp
Cone design: Curved
Cone surround: Permaflex
Mounting Information
Outside diameter: 475mm
Flange diameter: 423mm
Cut out diameter: 425/8mm
Mounting holes: 8x 6mm on 448mm P.C.D.
MANUFACTURER Royal
MODEL 1500
Fs 28.5864
Rms 12.9121
Qms 4.4120
Qes 0.2183
Qts 0.2080
Cms 0.0977
BL 35.3893
VAS 184.9484
L 1kHz 5.7350
L 10kHz 2.0535
CAS 1.324499E-0006
RAS 952.7413
MAS 23.4028
RAT 20204.9000
SD 0.1164
xmax 12.75

Not cheap though £646 for a pair inc delivery in the UK!

Hornresp results attached. I tried to get as linear a response as I could without dropping below 100db/W Sizes tweeked for an 18" Driver,and a bit of taper added to the start of the horn chamber.
Martinsons Tapped horn design shown superimposed grey line.
Bonus is that Xmax is reached at over 250w
instead of approx 100w for the B&C 15tbx100 design

[Xoc1]

OK I am still playing around with the parameters and I think that my most fundamental error is with the compression ratio that I used in the sim above.
3.65:1
Could anyone give me some pointers to what is an acceptable compression ratio for a robust 18" driver?
I still seem to get the best results with the Royal 1500 18" driver 12.75 Xmax
I also have been concidering the Void Accoustics V18 1000 which is available in the UK for about £210 each.
Pro Audio Parts - Void Acoustic Products - V18 - 1000
This is a 1000W aes speaker with a 5" voice coil and 35.88 BL 10.5 Xmax
I am currently finding that most 15" drivers seem to run out of Xmax at 50v
(300W @ 8 ohm ). The 18" drivers are OK at 90v (1000w @ 8 ohm).
Given that the Void spec for SD is 1230 sq cm would anyone give me an acceptable minimum size for S2 in horn resp

[cowanaudio]

G'day again

3.65:1 is just asking for trouble. I wouldn't push a robust 12" that hard. Try to stay below 2.5:1. That will give you a greater chance of your drivers surviving.

Cheers

William Cowan

[Xoc1]

Thanks for the reply William.
2.5 : 1 was a ratio that I had concidered.
this gives an s2 of approx 500 sq cm.
Ideally I would like the tapped horn to be smaller in size than the eqivalent reflex box. For an 18" PA that is about 200 litres.
The sim below is at least 99db from 45 to over 180 hz.
I found that reducing the throat side of the horn helped to extend the high frequency response.
This outperforms a reflex cabinet at these frequencies by a large margin.
At 1000w /8ohm (89V) xmax is reached at 40hz and is within limits in the passband.
My DCX 2496 will be essential!

[FlipC]

Have you looked at the TH Mini clones?
There are several and you can get drivers easily (B&C, PD, Beyma, Ciare, Faital Pro)
24"x22.5"x15" = 50-200 Hz I have 24DB slope set at 42 Hz.

[Xoc1]

Hi Flip
Thanks for the input (Been occupied with gigs over the weekend)
I had a good look at the TH-Mini as you suggested.
I see this has a higher frequency roll off - Are you happy with the perfomance that you get from your TH-Mini Clone?
The best result I managed with a 12" driver was with a B&C 12ps100
This was 99db / 105 litres /Xmax reached about 400W
With the Void V18-1000 rolled off to approximate the low end performance of the TH-Mini I Ended up with 100db / 150Litres / Xmax reached at 40Hz with 1100W (93V) -
This is probably closer to the wattage that I would be likely to use!
It is very tempting to loose a few Hz on the bass response -as this makes a big difference to the size & efficiency of the speaker-
(And of course that was my original question )

[Xoc1]

OK This is where it gets complicated!
This is my first attempt at folding a horn and taking account of all the real physical restraints that exist.
Hopefully I have met all my objectives within reason. Major doubt in my mind is if I have allowed enough freespace around the actual speaker driver, in the throat of the horn.
Any constructive comments are most welcome!