Basic questions about a 2-way 12" & horn PA top

[chips and palsa]

Re: Basic questions about a 2-way 12" & horn PA top

What is the black dot on the top of the cab? Is that the handle? If so that won't help you place the cab up on a pole.. better to have 1 handle on each side. I like this style handle, you can buy these things in plastic but I have also carved something similar into the side of cabs too.
[ATTACH=CONFIG]52102[/ATTACH]

Those multi way handles are pretty neat looking

Here's the revised setup:


How would you guys recommend bracing this? I'm guessing it's not as heavily braced as a subwoofer gets. I will also be using mattress topper for damping/lining

[Brian Steele]

Re: Basic questions about a 2-way 12" & horn PA top

Those multi way handles are pretty neat looking

Here's the revised setup:
[ATTACH]52118[/ATTACH]

How would you guys recommend bracing this? I'm guessing it's not as heavily braced as a subwoofer gets. I will also be using mattress topper for damping/lining

To be honest, I don't like the profile of that design.

Here's a suggestion - replace the two round ports with triangular ones, located at each corner of the bottom of the front baffle. Then decrease the height and increase the depth of the box. This should also allow you to use longer and larger vents. Try to get the internal dimensions close to one of the golden ratios, e.g. 0.6:1:1.6 or 0.8:1:1.25. This should also provide enough space to insert a shelf brace for the back panel.

[chips and palsa]

Re: Basic questions about a 2-way 12" & horn PA top

To be honest, I don't like the profile of that design.

Here's a suggestion - replace the two round ports with triangular ones, located at each corner of the bottom of the front baffle. Then decrease the height and increase the depth of the box. This should also allow you to use longer and larger vents. Try to get the internal dimensions close to one of the golden ratios, e.g. 0.6:1:1.6 or 0.8:1:1.25. This should also provide enough space to insert a shelf brace for the back panel.

I was actually wondering about those ratios. I tried to make sure there was at least a port diameter's clearance to the back of the cab but what other benefit is there to following those ratios?

[Brian Steele]

Re: Basic questions about a 2-way 12" & horn PA top

I was actually wondering about those ratios. I tried to make sure there was at least a port diameter's clearance to the back of the cab but what other benefit is there to following those ratios?

It's supposed to spread any resonances caused by the cabinet dimensions. In this case the primary advantage is likely that with the increased depth of the cab you'll be able to have enough space to put shelf braces between the panels. The triangular corner ports will also act as braces.

[chips and palsa]

Re: Basic questions about a 2-way 12" & horn PA top

Okay understood. As far as calculating triangular port area/length, am I just simulating a square port in WinISD and using half of it for each port?

Also, if this cab sims as 96dB / watt and the OTop12 is around 102-103, does that really mean that it will take 2 of these to equal one OTop in output?

[billfitzmaurice]

Re: Basic questions about a 2-way 12" & horn PA top

Also, if this cab sims as 96dB / watt and the OTop12 is around 102-103, does that really mean that it will take 2 of these to equal one OTop in output?

It does. I wouldn't have made the OTop construction as complicated as I did if there wasn't a very good reason for doing so.

[Brian Steele]

Re: Basic questions about a 2-way 12" & horn PA top

Okay understood. As far as calculating triangular port area/length, am I just simulating a square port in WinISD and using half of it for each port?

Better if you sim it as two ports with equivalent cross-sectional area. Be prepared to adjust actual vent length when built however - these tools can sometimes over-estimate the vent length required to achieve a target Fb.

[chips and palsa]

Re: Basic questions about a 2-way 12" & horn PA top

It does. I wouldn't have made the OTop construction as complicated as I did if there wasn't a very good reason for doing so.

No free lunches I do suppose. As this builds #1 priority is economy and simplicity, I sure hope my friend can settle for ~125+dB @ 1m. (2 96dB cabs @300W) and if he needs the low 130's+ then maybe we can drop the drivers into a horn loaded mid like JBell's HS12. (Looking on Bill's forum the PA310 isn't recommended in the OTop)

Will start simming triangular equivalent ports in ISD and adjusting the box into more of an ideal ratio.

Pretty excited to hear these 18" subs =) was playing around with PEQ & HP filters on ISD today. Not sure if I will ever try it but it looks like I can get a good bit of extra extension by boosting EQ @Fb with a corresponding HP (B6 assisted alignment that no one seems to discuss much except Tony Wilkes of speakerplans)

[billfitzmaurice]

Re: Basic questions about a 2-way 12" & horn PA top

Looking on Bill's forum the PA310 isn't recommended in the OTop.

Since it does not have rising response into the midrange it's not going to work well in any horn above 1kHz or so.

[chips and palsa]

Basic questions about a 2-way 12" & horn PA top

Since it does not have rising response into the midrange it's not going to work well in any horn above 1kHz or so.

Wow a 5dB rise on my Deltalite indeed. I didn't know that's what dealt with the horn's filtering.

When it comes to crossing these boxes with the 18" BR's we're putting together, is a 100Hz LR on both boxes acceptable? Using both 4th order filters looks like a 4dB dip at the xover freq but 4th order BW filters looks like only a 1-2 dB dip. Is that the point of the LR filters to stop the responses from summing to a peak at 100Hz?

[chips and palsa]

Re: Basic questions about a 2-way 12" & horn PA top

Since it does not have rising response into the midrange it's not going to work well in any horn above 1kHz or so.

Wow a 5dB rise on my Deltalite indeed. I didn't know that's what dealt with the horn's filtering.

When it comes I crossing these boxes with the 18" BR's were putting together, is a 100Hz LR on both boxes acceptable? Using both 4th order filters looks like a 4dB dip at the xover freq but 4th order BW filters only look like only a 1-2 dB dip. Is that the point of the LR filters to stop the responses from summing to a peak at 100Hz?

[billfitzmaurice]

Re: Basic questions about a 2-way 12" & horn PA top

Is that the point of the LR filters to stop the responses from summing to a peak at 100Hz?

The point of LR filters is less bandwidth overlap, more protection for the high-passed cab, and no phase issues.

[ivandezande]

Re: Basic questions about a 2-way 12" & horn PA top

Had anyone suggested this instead?

http://www.diysoundgroup.com/waveguide-speaker-kits/fusion-12/fusion12-kit.html