Bill Fitzmaurice

[quote name='RJB280' timestamp='1420362623' post='2648332'] Thanks Bill, I understand where you are coming from ref drivers but surely the design of the enclosure would have a large part to play ? Ported versus sealed etc ? [/quote]Yes, but that has nothing to do with transient response, which is primarily seen above 500Hz, whereas the effects of the cabinet are primarily seen below 200Hz. [quote]making the cab a bit too small gives a bump in the low mids, which may or may not be a good thing depending on your preference[/quote] The effect of a too small cab is usually seen between 80-160Hz, which is technically midbass. A hump there is usually heard as 'boom'. It's pretty much the typical sound of inexpensive combos.

[quote name='Dan Dare' timestamp='1420322324' post='2648147'] Looking at the original question, I wonder if amp clipping may be to blame. Most combos will struggle once the master volume goes over the half way mark. [/quote]Perhaps, but it's a crapshoot with combos which will run out first, the amp headroom or the driver xmax. It's not unusual for combo drivers to run out of excursion capability with even 40 watts input.

There's precious little difference in the transient response of most electric bass drivers, even irrespective of size. Transient response is mainly limited by the driver voice coil inductance, T/S spec Le, which tends to be very low with most drivers. Those which do have high Le tend to be subwoofer drivers, where transient response is a non-issue anyway.

[quote name='Dan Dare' timestamp='1420317810' post='2648083'] A flat sheet of solid foam (especially hard foam) will, at least in part, reflect sound waves back at the cone [/quote]True, hard foam will do so. Acoustical foam isn't hard. Acoustical foam does have reflective properties where the wavelengths are short compared to the solid bits of the material that make up the foam matrix, but those wavelengths are far shorter than those produced by woofers. Even at 4kHz a wavelength is better than 3 inches/85mm.

[quote name='taunton-hobbit' timestamp='1420294424' post='2647651'] That'll be back to carpet felt underlay then............. [/quote]Felt underlay works well. On this side of the pond you can't find all you want for free if you're not adverse to dumpster diving for scraps at a carpet store.

[quote name='Dan Dare' timestamp='1420291390' post='2647566'] It ain't cheap, but proper contoured acoustic foam is best. [/quote]Actually, it isn't. The main benefit of the contouring of acoustic foam is visual. It looks like it should work better than plain foam, but it doesn't. Compared to an equal thickness of plain foam acoustical foam is a lot less foam, a lot more air, and air has no damping properties. The reason acoustical foam is made that way is to make it resemble diffraction grids, which serve a totally different purpose than damping foam. It's often called 'eggcrate foam', and in fact decades ago recording studios really were lined with pulp eggcrates. It's often assumed their purpose was damping or soundproofing, but their actual function was to scatter reflected waves. That's not what one wants to do inside a speaker enclosure. When the change was made in studios from low tech egg crates to high tech foam the shape of the crates was retained, but not the function, as foam doesn't scatter reflected waves the way that solid pulp does.

[quote name='Mr.T' timestamp='1420193488' post='2646462'] We are happy with the sound of our singer's Mackie SRM650's [/quote]Obviously, as you would have ditched them already were that not the case. That's where getting user recommendations is dodgy, because most people will recommend what they have, and who is going to keep something that they don't like?

[quote name='Lord Sausage' timestamp='1420037998' post='2645065'] Who is right? [/quote]Both and neither. Hi and low may refer to the output level of the instrument, usually active versus passive, but it also may refer to the gain applied to that input by the amp, hi gain for passives, low gain for actives. As a method of last resort, and at the risk of having your Man Card revoked, you might consider looking at your amp manual to find out which applies to your amp. Nah...

[quote name='DiMarco' timestamp='1419923660' post='2643931'] Bill, with the larger xmax but smaller surface area, isn't the 12" pushing less air harder and because of that having a radically different dispersion? Just wondering in which aspects (if any) this makes the smaller speaker behave in relation to room acoustics. [/quote]Twelves do have different dispersion than fifteens, it's wider, and that's better.

[quote name='DiMarco' timestamp='1419885381' post='2643659'] But the fact is the speaker surface is only about two thirds of that of a 4x10 and even less then that of a 2x15 [/quote]Moot. Speaker surface is only two dimensions. The third dimension is excursion, xmax, and that, combined with the surface area, Sd, gives you the all important spec: Displacement, Vd. The bad news is that most commercial cabs don't reveal the Vd of the drivers used, so you have no basis for comparison between them. If you can find out what drivers are used you can look up the Vd on the driver manufacturer spec sheets, but speaker manufacturers aren't forthcoming about the drivers that they employ either. For the most part that means having to try before you buy, to be sure that what you're considering meets your needs.

[quote name='Mr.T' timestamp='1419880594' post='2643580'] Am I missing the point of active speaker cabs? [/quote]They appeal to newbies, as they appear to be easier to set up and work with than separates. They're not. If anything they make setup more of a chore, requiring both a signal cable and a mains cable to each cab, as opposed to a speaker cable from an amp. A few years ago I went from a separate mixer/power amp rack to a powered mixer, as it has built in effects and EQ and four 400w amps in a 40kg package.

Ditch the fifteens. If you're only running vocals there's no need for them, and for that matter if running a full mix there's still no need for them, as you'd need subs for the lows anyway. I don't have any experience myself with self powered plastic PAs but from what I hear Mackie are among the worst of the lot, while RCF and QSC are among the best.

An undamped cab is a defective cab. There's no justification for any manufacturer saving two or three quid by not using damping, other than that they just don't give a flying f..k how it sounds, and telling the consumer "if you want a better amp, spend more money". But as for damping taming midbass boom, it won't. Midbass boom is caused by inexpensive drivers and/or a cab that's too small for them.

[quote name='Jus Lukin' timestamp='1419337086' post='2638840'] does the simultaneous cone movement equate to a 4mm Xmax in relation to the same signal? [/quote]It does.What you're really comparing is displacement, T/S spec Vd. If you use a single driver with 4mm xmax or four drivers with 1mm xmax the resulting system Vd, and therefore system displacement limited output, is the same.

[quote name='SingleMalt' timestamp='1419190353' post='2637444'] Pretty cool buying valves made in the 70s for the Russian Military.... [/quote]They probably were the best ever made, having to stand up to battle conditions. They kept valves long after everyone else, not only because they lacked the SS technology, but also because valves are immune to EMP.

The only way to be sure is to compare the SPL charts for what you have against those of what you're considering. Catch 22: No one publishes charts for their cabs.

[quote name='dumelow' timestamp='1418646485' post='2631925'] i was recommended a 2x10 cab to add definition, rather than change the sound. [/quote]Said recommendation did not come from an informed source. There is no difference in 'definition' based on driver size. The only dfference attributable to driver size alone is the dispersion angle of the mids and highs. Those telling you that tens have better 'definition' than fifteens probably don't know even what dispersion is, let alone how it is defined by driver size. That doesn't mean that you might not find a different cab that does have better definition than your current cab, just that definition and driver size are not related. One of the worst drivers made as far as definition is concerned is the Eminence BP102 ten, one of the best ever made was the Electro-Voice EVM 15B fifteen.

Mixing drivers is like a box of chocolates: you never know what you're going to get. If you don't like the sound of your current cab get out shopping, try as many as you can, buy the one you like the best. If one doesn't go loud enough buy two.

[quote name='VTypeV4' timestamp='1418466211' post='2630384'] Did anyone else clock the 'Turbosound' badge on the cab..? I would like to think it's of some significance...Or maybe Turbo simply desiigned the cab. [/quote]If the engineers at Turbosound had any input into the design the badging would be rotated 90 degrees, and the result would look like this:

[quote name='spacey' timestamp='1417513832' post='2621062'] his voice well lets put it kindly, its gone. [/quote]It wasn't when I saw him last February, for the first hour anyway. He can't maintain full tilt for a two hour concert, so he does have to back off after a bit. But he still managed to hit it all at the end of the night with [i]Won't Get Fooled Again, [/i]scream and all. I've seen every major act over the last 50 years, and no doubt [i]The Who [/i]is the best band ever. No offense to Mick and Keith.

[quote name='Beer of the Bass' timestamp='1416998988' post='2615829'] I have an EA Wizzy 10 which uses one and it does seem to make the orientation of the cab a little less critical, rather than only sounding right when it's pointed straight at you. [/quote]That's because the whizzer acts as a 4 inch midrange driver. Beaming occurs when the driver cone is larger than one wavelength. With the 13 inch cone of a 15 inch driver that's above roughly 1.2kHz, with a 4 inch whizzer that's above roughly 3.5kHz.

[quote name='JohnOH' timestamp='1416963345' post='2615641'] I seem to recall reading something to the effect that smaller speakers physically close together can beam like one larger speaker, is that correct? Is that why you recommend vertical stacking? [/quote]Two speakers side by side will have half the horizontal dispersion angle as one, up to the point where they're one wavelength apart center to center. Above that frequency, roughly 1250 Hz with tens, the situation worsens, as they no longer act as one larger driver but rather as individual sources, and the result is comb filtering. Response literally changes as you go across the soundfield, with no two listening positions being the same. Placing the drivers vertically remedies both of those issues, as they're shifted to the vertical plane, where the audience doesn't reside. [quote]my preference for sealed speakers extends to listening to recorded music too. It's hard to quantify but to me, sealed sounds more coherent.[/quote]If sealed sounds better it's because the ported cabs you listened to were poorly done, or improperly EQ'd, or both. In blind testing of well designed speakers EQ'd to identical response and level matched even the most golden eared audiophiles can't tell one from the other, to their extreme chagrin.

First off, no fifteen will give useful response to 4kHz. On-axis you'll hear something, but off-axis the highest a fifteen will go is perhaps 1.5kHz. Even twelves aren't much good past 2kHz or so. If you want to run without a midrange driver you need to go with tens. Second, your preference for sealed versus ported has nothing to do with the cabs, everything to do with the instrument. Double bass just doesn't go low enough to require the lows that a ported cab produces. For the same reason you don't need huge xmax, nor do you need to be concerned about the sensitivity below 80Hz. Frankly I can't imagine a worse cab for double bass then an Acme, unless you don't want your double bass to sound like a double bass. You do need to be concerned about the mids. For these reasons I'd use the Eminence B102 in a 30 liter (net) box. It's whizzer cone gives it useable off-axis response to 4kHz. I'd do them as 1x10s, stacking vertically as many as you need. You could do a vertical 2x10 in 60L net, but IMO it's easier to carry two small cabs than one large one. If you want flat response to 50Hz you could put a B102 into a 60L ported box tuned at 45Hz, but IME double bass doesn't need to go that low.

[quote name='lowendgalore' timestamp='1416785681' post='2613642'] Tonally identical though yeah? [/quote]Yes, if the specs are otherwise the same. Sometimes they are, sometimes they aren't.

[quote name='Dad3353' timestamp='1416756383' post='2613200'] All things being equal elsewhere, the 4 Ohm cab will sound slightly louder. [/quote]Only at small signal levels. Maximum output is determined by the driver xmax. That's usually the same for 4 or 8 ohms, so maximum output is also the same.