Which replacement drivers to choose?

[parisonj]

Hi all,

 

This weekend my pv hisys 18" subs developed a fault. i.e. one stopped working.

 

In opening up the boxes, I noticed that the original OEM parts had been replaced with beyma sm118's, rated at 8ohm each. I had always thought the cab was rated 4ohms (the back plate said so) - so I decided I may as well replace both with some new 4 ohm drivers to get the output power back up.

 

I am also told that the sm models should never really have been in a sound reinforcement cab, they're designed more for studio monitor work.

 

So my question is, which models should I be looking at? And have people done a/b comparisons, etc.

The basic parameters are:

18", 4 ohm, 700W rms, 1400W music power output.

 

I have been recommended B&C PZB100s. Are there any others (Precision Devices, JBL, Eminence, etc).

 

Thanks

[MarkPAman]

Why not put some Black Widows in? Will almost certainly give the best result for those cabs. Peavey will be able to tell you which ones to use & where to get them.

[parisonj]

It's certainly an option. I just wondered whether there were any better drivers out there?

 

I assume I'm right in thinking that if the t-s parameters are generally similar, I won't be adversely affecting the response and quality?

[Jivemaster]

Bass cabs are very sensitive to driver changes, Phone Peavey in Corby and get the proper drivers. All the ones I have wanted were supplied by courier and arrived next day.

[Simon Lewis]

I assume I'm right in thinking that if the t-s parameters are generally similar, I won't be adversely affecting the response and quality?

 

As mentioned above, small changes in tuningcan have quite an effect - maybe not to the extent that it would damage the drive unit or sound terrible, but certainly not delivering the best from your new speaker. To be honest, if I was spending that kind of money on drivers, I would want a solid, well designed box to compliment it...

[Rich]

Download a copy of WinISD and simulate your cab with different drivers. You'll need to measure your cabs to work out the volume, and measure your port area, and port length. WinISD will give you a graph to indicate the response of the cab which will let you know if the drivers are suitable. They probably will be.

 

B&C produce good drivers. Other good ones to try are the PD 186 (if you can get hold of one), Fane Colossus 18XB, P Audio C18-650EL, and the Void Acoustics V1200. All of these drivers (if they suit your cabs) will make a vast improvement to your bass.

 

EDIT: Links

[parisonj]

I've tried WinISD, with 3 drivers (PV BW, the current Beyma, and the B&C PZB100). With the dimensions of the cab as it stands, I get a significant peak with the B&C.

I'm not quite sure how to use the tool with respect to the tuning frequency. Without me typing anything, it's generated a high figure for this driver, compared to the others. How can I change this tuning - presumably its related to the vents on the box - speaking of which, there is no tube, just a pair of rectangular openings.

Is the idea to get no dip, and the lowest frequency when the plot cross the purple (-3dB) line on the graph?

 

I knew there was a reason I never got into this part of sound...

 

Thanks

[Rich]

The box's tuning is dependent on the volume of the cab (which you've entered), and the area and length of the port(s), so in your case you need to measure the area of the rectangles, and the depth (presumebly 18m - baffle depth?)

 

Once you've collected this data you can input it into WinISD using the vents page. Click on the shape to turn it into a rectangle, and then put the length and width, select 18mm as the depth and check tht you've selected two vents. This should now be your cab.

 

Does this make sense? It's late.

 

Have a go with that, feel free to PM me you cabinet specs, I'll happily have a go too.

[parisonj]

The cab has the following dimensions:

 

W: 0.52m

H: 0.67m

D: 0.55m

 

thickness: 0.025m

 

this gives a volume of around 193litres, which I entered on the main 'box' tab (front chamber volume)

 

There are 2 rectangular openings, actually about 0.2 x 0.1m, but I could only enter 0.14 x 0.102. It won't let me enter a vent length that is just the thickness of the baffle (0.025m). It defaults to 0.242m.

[Rich]

http://img341.imageshack.us/img341/9025/50289698ew9.jpg

 

Just had a go myself and didn't have any problems.

 

This is your box with a 186 in it. It's either a bad match or WinISD is telling porkies. Try using the same box data with your Peavey TS parameters and see what curve it gives you.