2 x 15's or single 18 for bass bins ?

[SHADOW]

OK I haven't decided on the 15" driver thing for my bass bins but now been suggested that I look at a single 18 per side instead of two 15's so now looking for new advice as I've never used a single 18. Any I've heard for a live loud rock band sounded a bit wooly compared to what I'm used to but open to all suggestions. Basically I need something that will give good bass guitar reproduction and also give a real deep chest thumping bass drum but can also throw it in marquee situations etc. Will be used mostly for small - medium venues but also capable of dealing with 500 capacity halls and marquees. Any suggestions please ?

[JTH]

Well I have been through a similar thought process and have just made some changes to my system, which we use for indoor and outdoor gigs, mainly pop/rock etc. up to 500 - 1000 or so folk.

 

For the last 18 months, I have been using 8 Cabs in the following configuration:

 

2 x 18" Bass cabs per side, one used as a sub (around 40 to 80Hz) and another as a mid bass cab (80 to 200 Hz)

2 x 12" Mid/Top cabs per side (around 200Hz upward)

 

Sub cabs run in Mono, others as stereo although probably a waste as far as the bass cabs are concerned.

 

Whilst this does produce some quite impressive low bass, I have always felt it lacked a certain tightness in the kick drum and bass guitar departments and thought that maybe a nice improvement would be to add some 15 inchers.

 

I have just had built 4 x HD15 horn loaded cabs, fitted with Eminence Delta Pro drivers and have also bought an additional pair of HK mid/top cabs - the set up now looks like this:

 

14 Cabs in total

2 x 18" Sub Bass Cabs per side

2 x HD15 Mid Bass Cabs per side

2 x HK 12" Mid/Tops per side

1 x HK 15" Mid/Tops per side

 

All managed by a dbx Driverack PA+. Now I have only managed to use this at low level in the garden and it seems that the mixture of 18" and 15" cabs are a great improvement - but I will be stretching it fully on one of the smaller stages at a very well known tribute band festival this coming weekend and will let you know if I think the change has been worthwhile.

 

To get back to the original post, maybe you should consider mixing both 18" and 15" speakers types.

 

Tim

[azlan]

I would also go for a mixture of 15" and 18" speakers, though, if you can, it would be worth demoing the options in a store/hire them out first to see if you actually like the sound as its ultimately subjective

[Tony.a.s.s.]

I would use 2x15's. They could go as low as a single 18 and it would be tighter. Even consider Neo's, they seem even quicker.

[Simon Lewis]

The simple answer is "it depends".

 

We need to increase either the surface area or the displacement to get more bass.

- Increasing the surface area of a single driver may allow for more bass, but it also increases the mass, which means the high frequency response and transient response suffers due to the increased inertia.

- Increasng the surface area by using multiple drive units (especially smaller, lighter ones) may give us the increased cone area and maintain good transient response.

- Use of drive units with long displacement (termed Xmax) will help, but this has its own drawbacks (drive unit must have suitable suspension and magnet 'motor' system to provide suitable displacement without distortion.

 

The way we load the drive unit will have significant effect too. Your ported cabs are trying to use the rear radiated energy from the speaker cones, and by a process of acoustic phase inversion add the rear and front radiated sound to provide a constructive sound wave in front of the cabinet. This can provide extended low frequency response and power handling near the port tuning frequency at the expense of a sharper LF rolloff and lack of driver support below the resonant frequency.

 

Another approach is to provide better impedance matching between the cone and the surrounding air by use of a horn. Again, there are drawbacks to this approach (mouth area of horn determines horn cutoff frequency etc.).

 

You can make good bass bins from a number of different designs, but ultimately, it tends to be cone area, displacement and efficiency that are important. Look at a large PA system, and there will be multiple 21", 18" or 15" bins, often with ported or hornloaded enclosures.

 

In your case, I suspect that going to the speakerplans site, and getting someone to determine your existing box volume and port area, then modelling a few different drivers for suitability would be worth your while. Make sure you send a suitable payment in their direction! You could consider single or double 18" under your 2x15" to give extra thump, but it's not really possible to give a definitive answer as to which is best without knowing the drivers, enclosures and amps to be used...

 

Simon

[TimmyP1955]

Any box can give that irritating chest thumping bass. Belly shaking bass is another story. It all depends on the particular driver and box combination.

 

Do-it-yourself boxes typically save no money, don't perform well, or both. And when you want to upgrade, they are worth nothing. Find a box you like the sound of, and buy it used.

[Jivemaster]

A properly chosen bass driver will go lowest in frequency terms, an 18 will work best below 80 Hz so you need to suit the crossovers to that, bass 15s will work well from 60Hz to about 150, the response of a mid range 15 may fall off at higher frequencies. Two 15" bass drivers when close coupled, will go down to the same sort of frequency as a single 18

[Tony.a.s.s.]

I've read the above posts, and then I've read the original post. You are not talking about a large system and for bass you are talking about a narrow band. So, considering everything, I would still go for a 2x15 Reflex cab.

[K.W. Burnette]

Though you should always be careful when putting 2 sources of bass and sub-bass frequencies in the same room, as you can get some pretty odd frequency anomalies. I suggest reading through some of THESE, particularly the one labeled "Subwoofer Arrays: A Practical Guide". Best of luck, hope this can help.

[Tony.a.s.s.]

The crucial thing about the performance of bass and sub bass together is that that they are in time. Whether they are overlapped, as I would use them, or separated at the crossover point, anyone using them both together, should be using a delay unit in the system. Cabs can be lined up to achieve the same result, but you still have to know what you are doing.