choosing tops to match a sub

[DJ Matt]

im like that child who keeps asking "why" on this forum lately, but it people on here have been very helpful, and I always learn something new when i come here.


so my current situation is i have a 18" powered sub
and im in the market for a set of tops to go with it.

i quite like the yamaha dbr12s, but im tempted to go with the 15s, because i find that i may be making the sub work a little hard. i find the crowd tends to sort of gather around the sub while the tops themselves dont get that kind of attention, in fact people tend to distance themselves from them when they are loud which is why im wondering if i should just go with bigger bassier tops

• what would be the benefits, if any, in using 15s with a 18 sub? is it just that they go lower or are 15s likely to throw further also? meaning less drop off in volume as you go away from the speaker?
• and should i really be using a hi pass filter at 100hz on my tops when using them with a sub even if they are large 15" ? in what kind of scenario would you leave them at full range vs using a crossover ?

im a bit of a bass junky, so my gut says just leave everything at full range, it feels like a waste of bass otherwise lol but am i concerned that i may be being irresponsible/ amateurish and unintentionally causing a negative effect on the sound by doing this

• and if i do x over should i be matching perfectly the cross over point i have on the sub with that of the tops or is it ok to allow an overlap? lets say ,set the tops to 100 and the woofer to 120?
• or does this all just depend on the room im working with on the night?

• and if im crossing over at 100hz, is there really any point in having 15" tops at all? or even anything other than 10"? would 2 subs and 2 or even 4 10" tops be absolute the best scenario?

[Bill Fitzmaurice]

what would be the benefits, if any, in using 15s with a 18 sub?

None. If you don't have enough low end with one sub get a second sub, not larger tops.

if they are large 15" ? in what kind of scenario would you leave them at full range vs using a crossover ?

Never.

im a bit of a bass junky, so my gut says just leave everything at full range,

Ignore your gut, it's wrong. Fifteen loaded tops exist to satisfy the wants of those who don't know how gear works and assume that bigger means better. If anything fifteen loaded mains don't work as well as tens or twelves, as their midrange is weak. A well thought out system will consist of a pair of ten or twelve loaded tops and a pair of eighteen loaded subs.

[Daniel S]

There's no reason at all to go with 15" tops together with 18" subs. You should be crossing them over at around 80-100 Hz anyway and 10-12" work very well down to those frequencies, so you would only be carrying bigger speakers for no reason with 15" tops.

Also, 15" drivers don't have as good midrange as 12", since they tend to have a narrower dispersion the higher up they go. This means there are more compromises on a 15" top, depending on the quality of the speaker in question. To meet a 15" driver usually a 2" compression driver is needed, in order to have a low enough crossover frequency between the two. Cheaper cabs usually use a 1" or 1.4" compression driver, which usually results in muddier mids if the crossover frequency is chosen to match the compression driver's specs, or harsher highs if the crossover frequency is chosen to match the woofer's specs.

If you run the tops full range together with subs you might end up with cancellations and get less bass than if crossing them over properly. If you want more bass, get more subs.

[DJ Matt]

If you want more bass, get more subs.

ok thanks guys, very informative

would I be ill advised to mismatch the size of the subs? (aside from the obvious visual assymetry)
reason i ask is because ,i may grab a 15" or even a 12" sub, for smaller events, and then use both the 15" and the 18" together for large events.

and in this case, would i be sonically better off stacking the subs on top of eachother? or placing side by side, or placing them far left and right underneith the tops?
i believe keeping them side by side should be the better option there, but im really not sure which of these options is worse for cancellation.
i guess it does depend on the venue shape also...

[conanski]

im like that child who keeps asking "why" on this forum lately, but it people on here have been very helpful, and I always learn something new when i come here.

The best forums have members who are willing to help. Asking questions about gear before a potential purchase is always the best way to spend your money.

so my current situation is i have a 18" powered sub
and im in the market for a set of tops to go with it.

i quite like the yamaha dbr12s, but im tempted to go with the 15s, because i find that i may be making the sub work a little hard.

Sub are always going to work hardest.. particularly with modern music genres where it's all about da bass. From the '80s to present day the lowend boost that is built into recordings has increased dramatically and this has turned people into real bass junkies. So what you observe with guests at an event is natural and common, I don't understand how a DJ can operate these days without subs in the audio system but some do and say there is no problem, but I don't buy it.

what would be the benefits, if any, in using 15s with a 18 sub? is it just that they go lower or are 15s likely to throw further also? meaning less drop off in volume as you go away from the speaker?

Nope, the low driver in a 2-way "fullrange" PA speaker really doesn't go that low.. not compared to a dedicated sub, and part of what makes a sub so impressive is that it gets a boost from boundary loading with the floor. But a driver that is elevated 5-7ft above the floor will actually result in cancellation of low frequencies that have wavelengths that are multiples of that distance, so actually the worst thing you can do is allow a top to play sub frequencies.

should i really be using a hi pass filter at 100hz on my tops when using them with a sub even if they are large 15" ?

Yes, you have to think of the system as a 3-way and let each section do it's job, the woofer in a top becomes the midrange and for that purpose a 15" is a terrible choice.

in what kind of scenario would you leave them at full range vs using a crossover ?

Only when they are standing alone without a sub, but even then it has been my experience that a 12" box sounds just as good as a 15".

and if i do x over should i be matching perfectly the cross over point i have on the sub with that of the tops or is it ok to allow an overlap? lets say ,set the tops to 100 and the woofer to 120?

This is where brand matching the whole speaker system pays dividends with powered speakers.. they will be designed for the best possible performance through the crossover region.

and if im crossing over at 100hz, is there really any point in having 15" tops at all? or even anything other than 10"? would 2 subs and 2 or even 4 10" tops be absolute the best scenario?

If you want/need more bass add more subs, but only add more tops if you want to cover a larger area. If you need more mid-hi output substitute more powerful speakers.

[Bill Fitzmaurice]

ok thanks guys, very informative

would I be ill advised to mismatch the size of the subs? (aside from the obvious visual assymetry)
reason i ask is because ,i may grab a 15" or even a 12" sub, for smaller events, and then use both the 15" and the 18" together for large events.

That's creating a chain with weak links. Keep them not just the same size but identical.

and in this case, would i be sonically better off stacking the subs on top of eachother? or placing side by side, or placing them far left and right underneith the tops?
i believe keeping them side by side should be the better option there, but im really not sure which of these options is worse for cancellation.
i guess it does depend on the venue shape also...

While it’s customary with PA to have speakers to either side of the stage, that’s usually not the best way to place subs. Subs work best when they’re placed either close together for mutual coupling, or spread very wide to cover large areas. The basic rule is to have them either less than a quarter-wavelength apart or more than two wavelengths apart for their pass band, which for 40 to 100 Hz means less than 2.8 feet or more than 56 feet.

Boundary loading should be used whenever it’s practical to do so. Having subs next to a wall gets you 6dB of additional sensitivity, and putting them in a corner an extra 12dB. In most cases you’ll have best results aiming the subs towards the wall or corner with the cone about a foot away from the boundary.

[DJ Matt]

Boundary loading should be used whenever it’s practical to do so. Having subs next to a wall gets you 6dB of additional sensitivity, and putting them in a corner an extra 12dB. In most cases you’ll have best results aiming the subs towards the wall or corner with the cone about a foot away from the boundary.

is boundry loading what we call it when its near a wall?

im curious to know why facing the sub backwards at the wall wouldnt sacrifice clarity. my gut (which is often wrong ill admit) tells me the clearest crispest sound would be to have cone facing forward and un inhibited by any obstacles. Im assuming that this was the primary configuration that was considered when it was manufactured, tested and so on.

would facing it into a wall boost some lower frequencies that it might not otherwise be able to perform well on? and/or is the frequency range of a sub, such that it doesnt sacrifice clarity to do this

[Bill Fitzmaurice]

im curious to know why facing the sub backwards at the wall wouldnt sacrifice clarity?

Because clarity is contained in the midrange. Subs don't work in the midrange. Aiming at the wall prevents boundary reflection sourced cancellations and reduces THD. You need to approach acoustics with an open mind and a blank sheet of paper, because at least 80% of what seems logical is incorrect. Being visually oriented we naturally assume that sound waves and the devices that produce them operate in the same fashion as light waves and the devices that produce them. They don't.

[conanski]

is boundry loading what we call it when its near a wall?

Yes but so is the floor. Bass reflex subwoofers produce equal output in 3 dimensions(omidirectional) so when a sub is placed next to a boundary that portion of the output is reflected back towards the listener creating a free boost in output. 2 boundaries(floor/wall or ceiling/wall) reflects more energy than 1, 3 boundaries(corner) reflects more energy than 2.

im curious to know why facing the sub backwards at the wall wouldnt sacrifice clarity. my gut (which is often wrong ill admit) tells me the clearest crispest sound would be to have cone facing forward and un inhibited by any obstacles. Im assuming that this was the primary configuration that was considered when it was manufactured, tested and so on.

would facing it into a wall boost some lower frequencies that it might not otherwise be able to perform well on? and/or is the frequency range of a sub, such that it doesnt sacrifice clarity to do this

Bass reflex subs produce a relatively high level of distortion, and as mentioned above they are omnidirectional so technically it should not matter which way the cab is facing when placing it in a corner. But if you do an experiment with the driver facing out and then facing the corner you will hear a difference in the sound produced. Why? it's because with the driver facing the corner the extra higher frequency output that shouldn't be there(distortion) is dampened or filtered out and you are left with just the pure subbass output. The same phenomena gives horn loaded subs thier characteristic clean output, those bends in the cabinet naturally filter out the distortion the driver produces.

[light-o-matic]

Matt.. most of your questions have been well answered but for a few small points...

1. No, don't mix different sized subs, because they will have different frequency responses and different phase responses.. the sum of them together may be quite odd compared to either one by itself. It may not sound terrible but it really depends, and you're always better off with matched subs.

2. Re 15 inch tops and bass.. the amount of bass you will get out of them is nothing compared to what you will get from a proper sub on the floor.. so it's just not worth compromising your sound to milk that. If you for example use different crossover points on the top vs the sub to cause them to overlap more.. you THINK that you will get more output but in truth you could end up with less depending on how things are positioned etc. And if you do get more output, why exactly do you want a peak in output at just that one little slice of your bass where they overlap? The goal is to get a smooth transition from the sub to the top so that they sound like one speaker and so that it sounds good throughout your dancefloor. By increasing the amount of overlap between the top and sub you are creating phase problems that will hurt your sound more than help it.

3. Re, why 15 inch tops are so bad: It's not so much about the fact that when you are using subs, the capability that 15's have to produce deeper bass (vs a 12 or 10) is wasted because you are sending that signal to the subs anyway. What it's really about is that in a typical DJ speaker, you'll get a much better sounding midrange in a smaller top than you will in a larger top. That 15 is better for bass but worse for midrange. Since you aren't sending any low bass to the top anyway, the bass will sound the same regardless of whether you use a 15 or a 12. But the midrange will sound better with the 12. And it'll usually sound even better with the 10...

I will note tho.. that when I say "typical DJ speaker", I mean a 2 way speaker with a 1 inch throat horn. That's what most of them have. When you see more pro level boxes that are using a single or dual 15, they will either use a 3 way design (separate driver for midrange), or they will use a larger horn, eg. a 1.4 inch or 2 inch throat horn, which can play at lower frequencies so it can transition to those 15's smoothly. But those are much more expensive speakers than what you are looking at.