Dual XLS10... to port or not to port...

[sploo]

...and other questions...

I have a set of four Peerless XLS10 4 Ohm (830452) drivers. I've been running a pair in a 40 litre (1.4 cu ft) sealed enclosure. The drivers are mounted on opposing faces of the box, wired in series to create an 8 Ohm load, and have been run off an Alesis RA500 amp (in bridged mode - claimed to deliver 500w into 8 Ohm). I'm quite happy with the amp dialled to around 50% volume (it measures level with an SPL meter with respect to my other speakers).

I'd like to make use of the other two drivers, and create a pair of subs for better room response.

I'm very tempted to look into ported enclosures, accepting that the XLS10 does appear to need large ports.

A quick design in BassBox Pro indicates 40 litres sealed, or 52 litres (1.8 cu ft) ported. Reducing the ported design to 45 litres (1.6 cu ft) doesn't appear to make a huge difference to the response, but still gives a reasonable SPL boost over the sealed enclosure (see attached image).

My initial plan was to run the RA500 amp in stereo mode (claimed 150w per channel into 8 Ohm in this configuration). I know this is less power than desirable, but as I run the amp pretty low now I'm hoping this will be sufficient.

Working on the assumption of 150w, the 45l ported enclosure hits the drivers' excursion limit at 14.8Hz. A sealed 45l enclosure looks safe (excursion limit hit at 7Hz, but only runs 0.5mm over at 5Hz).

Vent air velocity looks acceptable, at a max of 17.4m/s at 22Hz.

With this design, it looks like room constraints are going to force me into having both drivers on one face of a 50x50x35cm enclosure (20x20x14").

So, the questions...

• Am I completely kidding myself that the one amp will suffice (150w to each pair of drivers)?
• Should I worry about having both drivers on one face (opposing faces seems to cancel out the vibrations quite well)? I guess the enclosures will be pretty heavy, so shouldn't move much.
• I'm thinking that I could initially stuff the ports to make the boxes sealed, until I get a high pass filter to prevent driver damage. Sensible idea? Pointless to try to make one box to do both? Give up on the ported altogether and go for sealed?
• Any point in stuffing/damping the internals of a sub, given it's strictly for <100Hz?
• I have two floorstanding main speakers. For movies it's obviously the subs doing the LFE work, for music I don't tend to use the subs that often, but sometimes send bass to the speakers and subs for a bit of extra depth. Should I care about phase, given the RA500 doesn't have any phase setting?

Any thoughts/advice greatly appreciated!

PS I know the correct answer is either "use an XYZ brand/model driver instead" or "make 4 small subs, each with one XLS10 and a passive radiator". I've got 4 XLS10s, and an awkward room, so I'd like to try to get a reasonable solution with what I have!

[richie00boy]

Hi Gordon, good to see you again.

What port frequency are you using? Those drivers need porting really to get the most from them (they were designed to be used with the passive radiator).

Mounting the drivers like you had is great, but you should be fine with them both on the same face.

I think you will be OK for amp power. If it turns out not then just get another RA500 and run one per side. (Don't think that amp is rated for 4 ohm in bridge?)

[18Hurts]

Let me check the math

500 watts is +27 dB
150 watts is +22 dB (close enough)

If you have two subs that are sealed and drive them at 150 watts each, it will give you 1dB more output than one sub at 500 watts. Just for entertainment, say your one sub at 500 watts produces 110dB. Two subs at 150 watts is 105dB but you gain +6dB by having two of them for 111 dB.

Is it worth it? Sure! You already have them and with four drivers instead of two, throw in power reduction to produce the same SPL, you'll have a cleaner sound with less distortion. That massive 1dB jump in output won't matter to your ears much but the amp will generate less heat for the same power output with the pair of subs.

In reality, your gain will be higher than 1dB, subs when driven to their limits have power compression so assume at least another dB there. Basically, you are up 2dB with two boxes running at 300 watts.

If it is maximum output you want, ported would work for another boost and since Xmax won't be exceeded down to sonic boom levels--it should give you around a +5dB boost in total output. Other factors such as how the room works with 2 subs VS 1 sub, how far you sit from the sub etc also can see a perceived increase in output.

You can build one with the ported dimensions and listen to it to hear if you like the results. If not, seal it up and add material to get it to match the interior volume of your other sub. Can't have too many cross braces, right?

I built my sub to be ported and tried sealed first--it rolled off too high so I threw a passive radiator on it, tuned in place to be smooth and pressed on. If you have the space, I would build it as a ported box since it is easy to put things inside to make the box air space smaller for sealed use. You can "tune" the sealed box with extra braces to take up space that way. It allows the option to switch to ported easily so go for it. Always nice to have an option.

Try the amp in phase and out of phase by reversing the leads--go with the configuration that offers the most output. Since I have a habit of stuffing my boxes, my sub has a layer of material on the side walls--does it matter? I had it laying around and it can't hurt. If you really stuff a box, it will change the tuning which can be done to taste.

Having more output, less distortion while using less power is always a good thing in my book.

[sploo]

Originally Posted by richie00boy

Hi Gordon, good to see you again.

Hi Rich! Good to be back. I've been a bit busy over the last couple of years - a simple tale of boy loses job, boy meets girl, boy loses job, boy gets great job, girl moves in, boy gets fitted for ball and chain etc. etc.

I was planning on having a chat with you regarding the high pass filter, should I go for the ported approach.

Originally Posted by richie00boy

What port frequency are you using? Those drivers need porting really to get the most from them (they were designed to be used with the passive radiator).

I had a 100mm diameter port... just changed to 102mm (measured some pipe in Wickes today). OK. That gives me a 791mm length port, drops the VV to 16.7m/s at 20.5Hz, with an Fb of 25Hz.

I bought the drivers years ago for another project (which never got built). With hindsight, I probably would have been better with two drivers and two radiators, rather than four drivers.

Originally Posted by richie00boy

Mounting the drivers like you had is great, but you should be fine with them both on the same face.

I think you will be OK for amp power. If it turns out not then just get another RA500 and run one per side. (Don't think that amp is rated for 4 ohm in bridge?)

Thanks. Yes, the amp won't do 4 Ohms bridged. Just taken a look for pricing, and it appears to be discontinued, which is a shame.

Originally Posted by 18Hurts

...Is it worth it? Sure! You already have them and with four drivers instead of two, throw in power reduction to produce the same SPL, you'll have a cleaner sound with less distortion.

18Hurts - thanks. Yes, that's exactly my thinking. The bass output from the single dual sealed enclosure is OK at the moment, so I'm not trying to achieve massive SPL. My thinking is more in the terms of reducing driver excursion in order to improve quality, and to have multiple subs to even out room response.

Originally Posted by 18Hurts

You can build one with the ported dimensions and listen to it to hear if you like the results. If not, seal it up and add material to get it to match the interior volume of your other sub. Can't have too many cross braces, right?

Good point. I guess I could add the ports, then make it possible to seal them at the interior end - thus getting 45 litres internal, with no port.

As the enclosure face needs to be around 50cm square in order to fit both drivers (I can't make it tall enough to have the drivers inline vertically), going for the extra volume to add the port just increases the enclosure depth a little - it' something like 33cm vs 27cm, so it's no problem to make them big enough for the ports in the first place.

[revboden]

Originally Posted by sploo

...and other questions...

Vent air velocity looks acceptable, at a max of 17.4m/s at 22Hz.

What size port are you looking to get 17.4m/s through? 6" (15.23cm) i hope, 4" (10.16cm) has a 13m/s chuff limit.

Originally Posted by sploo

With this design, it looks like room constraints are going to force me into having both drivers on one face of a 50x50x35cm enclosure (20x20x14").

So, the questions...

• Any point in stuffing/damping the internals of a sub, given it's strictly for <100Hz?

sealed yes, stuff away. ported no.

Originally Posted by sploo

Any thoughts/advice greatly appreciated!

PS I know the correct answer is either "use an XYZ brand/model driver instead" or "make 4 small subs, each with one XLS10 and a passive radiator". I've got 4 XLS10s, and an awkward room, so I'd like to try to get a reasonable solution with what I have!

You do know the answer, get some 12" passive radiators. They will work better than ports in boxes that size.

if it was me, I'd go sealed if you dont want to get the passives

cheers,
rev.

[sploo]

Originally Posted by revboden

What size port are you looking to get 17.4m/s through? 6" (15.23cm) i hope, 4" (10.16cm) has a 13m/s chuff limit.

...

You do know the answer, get some 12" passive radiators. They will work better than ports in boxes that size.

Hi Rev - interesting that you note the chuff limit. I'd always understood 1/10th or 1/20th of the speed of sound (~34m/s or 17m/s) was ok, but in searching a couple of days ago I found: Flare Testing Raw Data

On the table "Rounds one and two data re-arranged and grouped by frequency", it indicates that with a 52mm flare, you can get away with 18m/s at 20Hz. That's quite a large round over, but I should be able to create that on both ends of the port.

As for the (10") passives; I took a quick look to see what the pricing was now... and they're discontinued! All the retailers I could find list them as being unavailable, and the Tymphany website doesn't show them anymore. Odd that they'd ship the XLS10 driver but not the passive, considering that the passive solution did seem to be very popular with that driver

You mention a 12". Which model are you thinking of? If it would be feasible to use a single 12" passive with each pair of XLS10 drivers, that might just work with my enclosures.

[revboden]

well... I was thinking of something like ScanSpeak Discovery 30W/0-00 but are they making these things out of unobtainium or seal pups what the $*&%*.

[sploo]

Originally Posted by revboden

well... I was thinking of something like ScanSpeak Discovery 30W/0-00 but are they making these things out of unobtainium or seal pups what the $*&%*.

Hmmm... Tymphany: "Manufacturer of Vifa, Peerless, Logic and Scan-speak speaker components and sound panels"

That 30W looks awfully like a Peerless XLS... but at about 3 times the price!

Looking at the specs of the 10" 26W/0-00-00 they are different to the XLS10 passive, but not massively so. Much more expensive though.

Looks like I might be sticking with the plan for plumbing!

[richie00boy]

I think a 100mm round port is too small, especially if quality is your goal. Rather than soil pipe which you might find difficult to accomodate that length in your cabinet, have a look at slot port. I'm sure with your setup this would not be a problem to make. The port can wind round a bit like a kind of mini transmission line.

If you have access to OpenOffice look on my website on the utilities page as I have a port calculation spreadsheet which will do slot ports. It would be up to you to work out the bends though. Try starting with a 30mm slot height.

[katarakt]

I've a little project in the pipeline with 4x XLS10 + 4x scanspeak 26W/0-00-00 passive radiator.

As these XLS10 passives are discontinued i've done some research on the internet and the scanspeak 26W/0-00-00 is a perfect replacement for the xls passives! I'm sure the scans are "updated" xls passives and are the better pr if compared! Why? scan xmax = 28mm / xls xmax = 22mm !! ....and i've done the simulation with both pr's, you can see there's no significant difference:

XLS10 + XLS10 400g SPL


XLS10 + Scan-Speak 400g SPL


XLS10 + XLS10 400g EXCURSION


XLS10 + Scan-Speak 400g EXCURSION



Volume netto 31,5 litres. Rember i've done the simulation with 250w input power! In theory the scan pr should work better with it's 28mm xmax than the xls pr.

I think there's no need for the 12" pr in this case because they have the same xmax. Xmax is the limiting factor. In other cases i think 10" active with 12" passive is the way to go.