Tops / Bass x-over settings for night club PA...

[billfitzmaurice]

Re: Tops / Bass x-over settings for night club PA...

As for those 18" drivers some Cubo subs may be just the ticket, this design produces the output of a double 18 reflex in a box a little more than half the size without giving up lowend extension into the 35hz territory.

I've modeled them and they're not all that special. Sensitivity is high, but they don't go very low. Hoffman's Iron Law remains unbroken.

[Brian Steele]

Re: Tops / Bass x-over settings for night club PA...

WOW... what a mess. This is likely a good example of where less is more. Do they really need 6 tops on the dance floor? Mixing 2 different brands here is likely making things harder than they need to be and possibly causing overlaps in coverage with further messes things up, much depends upon the layout of course.

LOL, interestingly enough it seems to work out well in the night-club (except for the wonkiness at the top end, the reason for which I previously referred to). I RTA'd a few locations on the dance floor and I was very surprised that the response was as smooth as it was. It does need a bit more work however. I've suggested that they relocate two of the tops to make the coverage a bit more even. Less monitors would have resulted in more "hotspots".

And same goes for the electronics, there's really no need for the sonic crapitizer or compressor with the DRPA in the loop and the DJ's should have ZERO access to everything but the DJ mixer so I'd suggest you put a locking cover on the rack if the gear is located near the DJ booth.

I can understand the thinking behind the compressor and the AAE added to the loop. The compressor is basically to ensure that nothing gets by that can result in clipping BEFORE it hits the DRPA, and the AAE is basically to make older tracks sound a bit better. I will experiment with taking the AAE out of the loop. However I'm going to leave the compressor in, and leave it as basically a "master volume control" for the entire system. The gear is now located well away from the DJ, but it's still more accessible than I'd like.

As for those 18" drivers some Cubo subs may be just the ticket, this design produces the output of a double 18 reflex in a box a little more than half the size without giving up lowend extension into the 35hz territory.

The Cubos look interesting. I'm exploring a couple of options now, including THs, but so far the most practical solutions (size and output) seem to be EBS vented alignments. One of the THs I came up with required 22.cu.ft. of space total, which sounds a bit big. The existing D.B.Keele style W-bin boxes featured a response that dropped significantly below 60 Hz with the original drivers it was designed for. Maybe it goes a bit lower with the B&C 18TBX100s. I'm trying to find a HornResp model of the bins to see what the sim looks like.

Having seen a cutout diagram of the W-bin build, I'm also a bit concerned that it may be possible for the cones of the drivers to hit the mounting plate at higher volume levels.

[Paul O]

Re: Tops / Bass x-over settings for night club PA...

The Cubos look interesting. I'm exploring a couple of options now, including THs, but so far the most practical solutions (size and output) seem to be EBS vented alignments. One of the THs I came up with required 22.cu.ft. of space total, which sounds a bit big. The existing D.B.Keele style W-bin boxes featured a response that dropped significantly below 60 Hz with the original drivers it was designed for. Maybe it goes a bit lower with the B&C 18TBX100s.

A Cubo will produce the output of a double 18 reflex with a single driver, I have built and measured them and they deliver the exact response the designer suggest which means they benefit from some EQ but that isn't unusual. I didn't have time to do any measurement before winter but this design also benefits quite a bit from barn doors or horn extensions too, enough to make a single cabinet something that can produce pants flapping lowend.:D
You have some very good drivers there so I don't think you will have much problem getting better results from them with one of the designs discussed here.

[wg_ski]

Re: Tops / Bass x-over settings for night club PA...

The existing D.B.Keele style W-bin boxes featured a response that dropped significantly below 60 Hz with the original drivers it was designed for. Maybe it goes a bit lower with the B&C 18TBX100s. I'm trying to find a HornResp model of the bins to see what the sim looks like.

there is enough information in the drawings posted in the diyaudio thread to generate a hornresp sim. It doesn't have to be super accurate to see where the cutoff is. The paper claims "full horn loading to 40 Hz" in a 4-pack, but I sure don't see enough path length to make that happen. I have some 40 Hz horns that are "almost" full loaded to 40 Hz in a 4-pack - that have about the same overall volume and a 103 inch air column. Changing the driver may increase output, but it usualy won't do much for the frequency response - the low end is dictated by the box. The path length determines the knee, and the volume determines sensitivity. How well the driver is matched to the horn determines how "wonky" the response is. You need some sort of a new design. The 18" B&C's model quite well in horns with a true 40 Hz cutoff or a little below.

The "1540" horns required a 1/2" plywood gasket at the mounting plate - and that's with a cheap Eminence driver. With the TBX's in the W-bins, I'm surprised they're not already creased at the surround/cone junction. Especially with the low bass boost they must have been using to get any 40 Hz out of them.

[Brian Steele]

Re: Tops / Bass x-over settings for night club PA...

there is enough information in the drawings posted in the diyaudio thread to generate a hornresp sim. It doesn't have to be super accurate to see where the cutoff is.

I could do it. I've already done it for the EL36. I was hoping not to have to "reinvent the wheel" in this case.

The 18" B&C's model quite well in horns with a true 40 Hz cutoff or a little below.

See attached - one of the ideas I'm considering at the moment .

The "1540" horns required a 1/2" plywood gasket at the mounting plate - and that's with a cheap Eminence driver. With the TBX's in the W-bins, I'm surprised they're not already creased at the surround/cone junction. Especially with the low bass boost they must have been using to get any 40 Hz out of them.

Well, that's worrying. I've forwarded your note to my brother, who manages the night club. Maybe it's best they load them into the EL36 cabs they have instead, while we try to decide what to build for them.

[Brian Steele]

Re: Tops / Bass x-over settings for night club PA...

The "1540" horns required a 1/2" plywood gasket at the mounting plate - and that's with a cheap Eminence driver. With the TBX's in the W-bins, I'm surprised they're not already creased at the surround/cone junction. Especially with the low bass boost they must have been using to get any 40 Hz out of them.

I had a chance to get a closer look at what those W-bins looked like inside. They used 18mm ply to build the entire box, so maybe that would be enough to provide the needed clearance. The driver's cone would need to travel almost 25mm forward before it hits the box. to I will suggest to him though that we consider adding a 3/4" spacer to each box just to be on the safe side.

As for the boxes themselves, they were in a bit of a state - evidently the carpet covering them was hiding quite a bit of rot caused by damp. Luckily my cousin builds and repairs boats for recreation and business purposes, so he was able to cut out and replaced the damaged sections. While his helpers were completing the repair work on the boxes, I noticed that something was missing - the bracing between the central cabinet and the sides! The panels rang like bells when knocked, LOL. Luckily it was an easy fix, with four new braces cut, screwed and glued into place.

Unfortunately, even though I had all the measuring equipment ready and waiting to measure them, there was no time to do so - there were needed for use in the club that night. We actually wheeled them into place and plugged them in around 10PM.

So, all I have to go by at the moment is my subjective opinion of their sound, which matches the "mid-bassy" characteristic that I was expecting. And it was clear from the violent pants-flapping gusts of wind coming out of the vents at low frequencies that it's likely some sort of port compression was going on. But they were LOUD. So loud in fact that the DJ had to turn DOWN the bass, LOL.

As for the TH, construction is still ongoing. Basically the bracing has to be completed, then the rest of the external panels can be attached. And once that's done, there's the very good possibility that in the future I will be able to measure their performance compared to an EL36 cab (loaded with the same driver) and one of those DIY W-bins (ditto). I think it will be quite an interesting comparison.

[Brian Steele]

Re: Tops / Bass x-over settings for night club PA...

So, all I have to go by at the moment is my subjective opinion of their sound, which matches the "mid-bassy" characteristic that I was expecting. And it was clear from the violent pants-flapping gusts of wind coming out of the vents at low frequencies that it's likely some sort of port compression was going on. But they were LOUD.

....and here's the impedance curves for the two rebuilt W-bins.

The lower minimum point suggests a tuning of 34 Hz for each, which is lower than expected. These may "look" like the D.B.Keele design, but that calls for a 40 Hz tuning, if I remember correctly. That the minimum is so close to Re at this point suggests that the cabinet is properly sealed - no leaks to worry about.

I'm not sure what's happening between 60 Hz and 100 Hz though. One W-Bin is mounted on top of the other, which may account for the differences in measurements in this section. Or it could be that the panels are better braced in one box compared to the other. That the upper minimum and peak are not "well-developed" suggest that even with the new bracing, the boxes could be better braced.

In other news, the TH should be hopefully finished this weekend. And my brother has bought another iNuke 6000D DSP for the club.

[GordonW]

Re: Tops / Bass x-over settings for night club PA...

Some do, but the original 18" W horn designed by Don Keele for JBL, upon which most of these are based, only had a 60Hz f3. That was fine in 1977 when he designed it, but not today. The advantage to a W horn is large mouth area, which gives high sensitivity, but it comes at the cost of the path length necessary to go low.

Yep. And, I bet, the low frequency low pass (50-60 Hz) is an attempt to "shelf filter" the subs, to bring down the higher frequency range to closer match their output below 50 Hz, to make those W-bins "seem" like they have some low bass.

Raising the crossover may just make a lot of "boom" at 80 Hz or so...

I think that you're going to have to minimally raise the lowpass on the W-bins, but bring down the highpass frequency on the mid-high cabinets down significantly, to get anything resembling flat response...

BTW: One thing that can help, marginally, with W-bins- if there's any way to turn the W-horn around backwards, where it can fire off of a rear wall- you can make the rear wall act as a sort of makeshift horn mouth extension. This can lower the rolloff point, and give more low bass output. Even better if you can get the W-bins into a corner, and do the same thing (fire the mouth into the corner)...

Regards,
Gordon.