Port tuning question...

[Sundogue]

I'm making a couple of 115 cabs using Eminence C2515 speakers.

The usable frequency range of these speakers is 52Hz - 2.5KHz (according to listed specs). Now I never play anything but a 4 string (standard tuning). The low E is 41Hz.

Usually I tune my cabs to 40Hz, but I was wondering what I could expect if I were to tune these cabs to some other frequency. If I tune them to 52Hz (lowest usable frequency of speaker?), I would get a 3.2 dB gain at around 100Hz, but I wonder about overexcursion below that. If I tune them to 40Hz, I still get about a 2 dB gain at the same 100Hz.

I could get crazy and tune it to 80Hz and get a huge 7dB gain at 100Hz (but of course a faster dropoff below that).

I always have PA support and the subs of the PA provide me with more volume and feel below 100Hz than my stage rig ever does (and I often EQ much of those frequencies below 100Hz out of my stage rig).

So...anyone have any opinions on what they'd tune the cabs to, and why? I've always been under the impression that one should tune their cabs to the lowest note they play (in my case 41Hz), but I also know that most manufacturers tune their cabs to get a big bump higher up to give them more perceived volume.

Any thoughts on what effect tuning has on possible overexcursion, usable tones at frequency, volume, etc.? I realize no matter what I do, it's a trade-off. Just interested in some ideas, opinions, etc. Thanks.

 

[ehque]

if you want pure power, the fundamental (low E, 41 hertz) is a sure way to waste it. much of the information of a vibrating string is carried by much higher harmonics. the first harmonic of a low E is already 82 hertz.

do you want it loud, or "accurate"?

 

[alexclaber]

Have you tried modelling the different tunings in WinISD Pro? That lets you really understand what's going on with cone excursion under power.

For low B power handling, I've found the best compromise is to tune to about 37Hz (assuming a typical slightly undersized cab). For low E I'd be looking to tune somewhere in the high 40s.

How big are you looking to make the cabs?

Remember, the lower you tune, the more space the port takes up.

Alex

 

[Sundogue]

Have you tried modelling the different tunings in WinISD Pro? That lets you really understand what's going on with cone excursion under power.

For low B power handling, I've found the best compromise is to tune to about 37Hz (assuming a typical slightly undersized cab). For low E I'd be looking to tune somewhere in the high 40s.

How big are you looking to make the cabs?

Remember, the lower you tune, the more space the port takes up.

Alex

Yes, I've modeled it in WinISD (not Pro). Not using Pro, I'm not sure what the cone excursion is, but I'm assuming it will probably be significant at lower frequencies. But I don't plan on pushing it very hard anyway, and I certainly don't need the power at low frequencies (below 90-100Hz) as I am always right next to/behind the left sub of our PA and I hear and feel more coming from that than my stage rig, and thus EQ those lower frequencies out of my stage rig anyway.

The cabs are small (think Bag End S15) at 20X20X16. If I tune it to 40Hz, I need two 3" ports at 5.5" long (each cab). The higher I tune it, the shorter those two 3" ports will be.

I won't need to tune it any lower than 40 Hz. I never play a five string (and never will, though I have in the past).

Tuned to 40Hz, the group delay is really flat down to 40Hz and doesn't go higher until at much lower Hz than I'll ever play. Tuned to 52Hz, the group delay is slightly higher at 80 Hz, but not much. Tuned to 40Hz, the SPL (1 watt at 1 meter) is over 100dB from 80Hz to 147Hz, leveling out at 99dB from there on up. Tuned to 48 Hz, dB's are above 100dB from 80Hz to 135Hz.

So, no I really don't need to accurately reproduce the fundamental of the low E. I'm more interested in a fairly loud (above 90Hz), but very light 115 cab (that should come in around 25 lbs. total, with neo speaker).

 

[alexclaber]

It really is worth getting to grips with WinISD Pro - it does SO much more than the basic version, letting you understand cone excursion, power handling, port gain, port air speed etc.

Alex

 

[alexclaber]

Just been messing around with it in WinISD pro. I'd be inclined to tune it to 50Hz as that minimises excursion above 40Hz and the hump it causes at 100Hz is only a couple of dB. If I were you I'd make sure the ports are accessible so you can plug them to get sealed cab response when you're in boomier rooms - though obviously when the ports are plugged don't try and push a lot of bass through the cab.

Interesting to note how much easier it is to get good performance from a compact ported design with a lower power and Xmax driver like this - my recent forays have been with a mean 600W 12" with 9mm Xmax, which likes to be in a very small cab volume, which thus causes real problems containing a large enough port to tune low enough and have enough csa not to chuff...

If you're willing to gain a few inches of size and a few lbs of weight, check out the Bill Fitzmaurice OmniTop15. It's tuned similarly but is also horn loaded and the horn gain takes over just as the midbass small cab / port tuning hump rolls off, which equals flatter response and greater sensitivity above 100Hz, and the horn loading also gives better off-axis response. This is a plot with the Deltalite II 2515 which sounds very similar to the Basslite, just handles a bit more power:

Why not build one OmniTop15 and one direct radiator of your design and see how they compare?

Alex

 

[Sundogue]

It really is worth getting to grips with WinISD Pro - it does SO much more than the basic version, letting you understand cone excursion, power handling, port gain, port air speed etc.

Alex

OK, I ran it in WinISD Pro, and from the looks of it the cone excursion is far below the red line (which I'm assuming is the safe limit line based on the speaker parameters?) all the way across the range.

Everything else looks to be about the same as in WinISD. I'm not real familiar with the Pro version, but it looks good.

Any other thoughts, suggestions, etc.?

 

[Sundogue]

Just been messing around with it in WinISD pro. I'd be inclined to tune it to 50Hz as that minimises excursion above 40Hz and the hump it causes at 100Hz is only a couple of dB. If I were you I'd make sure the ports are accessible so you can plug them to get sealed cab response when you're in boomier rooms - though obviously when the ports are plugged don't try and push a lot of bass through the cab.

Interesting to note how much easier it is to get good performance from a compact ported design with a lower power and Xmax driver like this - my recent forays have been with a mean 600W 12" with 9mm Xmax, which likes to be in a very small cab volume, which thus causes real problems containing a large enough port to tune low enough and have enough csa not to chuff...

If you're willing to gain a few inches of size and a few lbs of weight, check out the Bill Fitzmaurice OmniTop15. It's tuned similarly but is also horn loaded and the horn gain takes over just as the midbass small cab / port tuning hump rolls off, which equals flatter response and greater sensitivity above 100Hz, and the horn loading also gives better off-axis response. This is a plot with the Deltalite II 2515 which sounds very similar to the Basslite, just handles a bit more power:

Why not build one OmniTop15 and one direct radiator of your design and see how they compare?

Alex

Well, these cabs are small and light. I already have the plywood cut and are ready to put together. The only thing I'm thinking about is the tuning. Yes, I messed around with some different figures in WinISD Pro and am coming to pretty much the same conclusion. 48-50Hz seems to be a good frequency to tune it at.

Quick question...what does the end correction mean in the port section of Pro? I usually have straight port tubes (either purchased or made of PVC). Edit: After looking at the Help files it doesn't appear to mean anything regarding something I need to do with them.

 

[alexclaber]

OK, I ran it in WinISD Pro, and from the looks of it the cone excursion is far below the red line (which I'm assuming is the safe limit line based on the speaker parameters?) all the way across the range.

You need to change the input power to see what's going on with the excursion - I presume you're looking at it at 1W which won't cause much movement! Have a look at the maximum power plot as well - you want to minimise those dips in power handling where it becomes excursion rather than thermally limited.

The end correction compensates for the fact that how the port is mounted affects how the air responds. If you're mounting the tubes in the baffle but away from the side wall use one flanged end. In reality the port length will need to be adjusted in situ - start with them longer and trim them back until it's how you want.

You can't really go wrong because you're not looking for deep bottom or really high SPL and they're the two issues that cause the most problems in bass cab design.

Alex

 

[Sundogue]

You need to change the input power to see what's going on with the excursion - I presume you're looking at it at 1W which won't cause much movement! Have a look at the maximum power plot as well - you want to minimise those dips in power handling where it becomes excursion rather than thermally limited.

The end correction compensates for the fact that how the port is mounted affects how the air responds. If you're mounting the tubes in the baffle but away from the side wall use one flanged end. In reality the port length will need to be adjusted in situ - start with them longer and trim them back until it's how you want.

You can't really go wrong because you're not looking for deep bottom or really high SPL and they're the two issues that cause the most problems in bass cab design.

Alex

Thank you much for that info. I did change the input power and now see that there will be some excess excursion going on about +/- 80Hz, so I need to be aware of that at higher power. I'll have to play around with it a bit and perhaps keep that in mind when I EQ. Everything else falls under the red line though and I don't play terribly loud, but it does help me understand it more.

Thanks so much for your 'input' on this. I appreciate it.

 

[Beej]

I agree with alexclaber in that I'd start with a longer port tuned to a lower frequency and see how you like it. You can always cut the ports back to retune it if necessary...

 

[Sundogue]

I agree with alexclaber in that I'd start with a longer port tuned to a lower frequency and see how you like it. You can always cut the ports back to retune it if necessary...

Yeah I agree, I'm using PVC so I'll have plenty to experiment with.

 

[Matthijs]

I ran your speaker through the eminence design program. I generally came up with the best results in cone excursion with the cab tuned at about 60 hz. How big are those cabs?

 

[Sundogue]

I ran your speaker through the eminence design program. I generally came up with the best results in cone excursion with the cab tuned at about 60 hz. How big are those cabs?

As posted earlier...they are 20X20X16. I'm leaning more towards 50Hz, but my options are open. I can easily port it with two 3" ports and get down to 40Hz with ports longer than 5.5". The higher I go, the shorter the tube.

 

[Geoff St. Germaine]

I'd tune the cab to get the flattest response possible. I'm not going to model it, but if the cone excursion goes beyond xmax below the tuning frequency, then you can use a high pass.

When you're modeling it in WinISD Pro there is a tab for signal. Whatever you have that set to is what it is going to show you the cone excursion for. The red line represents Xmax. Exceeding Xmax may not be a big problem if the Xmech is larger.