RLA style JBL/VOTT Club System, advice needed

[Horn Fanatic]

took me a few days to process all that info



does that mean that any frequencies below the 'cut of' frequency emanating from the horn are not in phase with the cone? only at the cut off are they in phase?




what do you mean by a discontinuity?

Hi budney -

I think you may be confusing the roll-off frequency of the acoustic low-pass filter, with the cut-off frequency of the horn. They are not one in the same. A typical roll-off frequency would be approximately 3 to 3 1/2 octaves above the horn cut-off frequency.


A low-pass filter is just that. The driver, chamber, and throat parameters dictate at which frequency where no higher frequencies will pass through the horn. Essentially, an acoustic 1st order cross over. It is at the roll-off frequency when the cone front will be acoustically in phase with the bass horn as long as the total length of the horn, not including the chamber, is multiples of half wavelengths of the roll-off frequency. Instead of the typical -3dB drop in amplitude that is found with a passive crossover network, think of the cone and horn acting in tandem, behaving as a single diaphragm. Otherwise called mutual coupling.


As for the discontinuity, allow me to quote Leo Beranek from his book, 'Acoustics' page 141 Part XIII under Acoustic Elements;


"An exponential connector....acts as a simple discontinuity when its length is short compared to a wavelength, and as a transformer for acoustic impedances when its length is greater than half a wavelength". In this section he describes an exponential connector as a transition between two pipes of different areas. A horn is in fact, an acoustical transformer. A transformer that serves to transition the very high impedance at the horn throat, to a lower impedance at the horn mouth. The ideal condition being a transition to the impedance of air which is 407 Acoustic ohms. Easy enough to accomplish for high frequency horns, but not so for low frequency horns. In order for a 30 cycle horn in free air, or 4 x Pi for example, to achieve an acoustic impedance of 407 ohms at the mouth, would be so immense it would be cost prohibitive to build it. All commercial bass horns are a compromise. Mutually coupling an array of small bass horns is a more practical approach to reach and impedance of 407 ohms.

This is why horn loaded speakers are more efficient than direct radiator speakers. The acoustic impedance of a cone is considerably greater than the acoustic impedance of air.

As per my previous example, a 22.5" long bass horn lacks the length and mouth area to allow support of very low frequencies. Ergo, a short horn would behave more like a horn loaded port, than a horn.

Regards,

H.F.

[budney]

Hi HF,

So if I'm understanding this correctly, a horn, comprising of driver, chamber, and throat, acts as an acoustic low pass filter. And the frequency that it begins to roll off is determined by their component values/measurements, like an electronic filter does with resistors, inductors and capacitors. Makes sense so far. What I'm having trouble with is understanding how the roll off frequency, which is determined by the physical components, differs from the cut off frequency. Is the cut off frequency the lowest frequency the horn can produce, and the roll off the highest due to the acoustic filter?

If you build a horn correctly, so that the length is multiples of half wavelengths of the roll off, then only the frequencies above the roll off will be out of phase with the cone?

When I was initially told about the 4520 by RMC I assumed it to be used as a midrange speaker up to 1khz. But if above the roll off its out of phase, would it not make more sense to have the 4520 electronically crossed over at the roll off frequency, and use a separate box for the midrange, roughly 100hz to 1khz? If this was to be done then would the 4520 only be used in its rear loaded horn capacity and not be used as a direct radiator?

I was also confused by the suggestion of the 4520 as I assumed that it would be a midrange box, and then a separate sub would be required. However if using a separate speaker for the midrange, I now see that what I thought would be a sub, anything below 100hz, would infact be the 4520!

Thanks for taking the time to explain this, I really appreciate it!
budney

[RMC]

Hi Justin,

RE your Post # 11, Sorry for my late reply as I was out of the country for vacation.

"All these stats and numbers don't mean much to me..." If you don't understand what they mean and their importance in designing any enclosure the risk of project failure or poor cabinet performance increases rapidly... In General Audio Discussion Forum here there is a sticky Thread with Thiele/Small parameters definitions. You should have a look at that to at least understand the basics.

"I think I'll end up with what drivers I can find the cheapest/closest" To go with the cheapest isn't a good idea in a Sound Reinforcement system for Public Address, specially considering you seem to want very high SPL. Purchasing the closest T/S ( with more Pe/Xmax) is a must if you want to achieve expected LF performance.

"Shipping and customs for 8 drivers from the USA will surely add up quickly" In a previous post, didn't I give you a worthwhile suggestion of looking at Fane drivers from the UK ? This avoids costly shipping and customs for stuff imported from the USA...

"This is what I'm finding most difficult to understand...from the info I've found online about the Stanley Screamer subwoofers, they are a ported reflex box? Is that right HF? From what I've read online, again this might be completely wrong, is that you don't really want to use direct radiating boxes for dance floor subs. But again all I have experience of when working in clubs is folded horn double 18 subs, never of direct radiators. I feel like the full range system I want to build should be quite 'high fidelity', perhaps the subs don't need to be? Again I'm not experienced with different types of subwoofers so I'm not too sure what to go for. I gather from what you guys have told me that a folded horn/front loaded sub would not be right for me because of the throw/dispersion that cab produces? From what I've read, quite a few clubs in New York used Altec gear, is there someone out there who knows more?? I can only learn so much from reading online"

It is curious that on one hand you are so concerned about vented-box subs, while on the other hand you are so focused on Altec's 816A/828 cabinets which both use the bass-reflex principle for the low-end (down to 50 hz or so), while its front-loaded horn loads the bass driver down to 200 hz according to Altec's spec sheet!

The Stanley Screamer (2X15") type of box given to you is an intelligent alternative/option offered by HF for its cost effectiveness, performance and parts availability (in the USA), not necessarily to be the loudest guy in town. Personally, I would rather use the 421-8 LF driver instead of the 421-8 H driver mentioned. The former is a low-frequency loudspeaker (similar to JBL 2205/2225), has flatter response and lower Fs, higher fidelity, compared to the latter being a Musical Instrument loudspeaker (similar to JBL K-140) with rising response, little higher sensitivity and Fs, higher output. HF's suggestion to satisfy your appetite for SPL ?

There is nothing wrong with a ported reflex box used as a sub in a Club. I've seen that in the past with JBL's 2245H 18" driver for example. "...you don't really want to use direct radiating boxes for dance floor subs" is beyond logic and probably science too. They do have lower efficiency/sensitivity (though not lower than 816A at the low-end where bass-reflex applies)(*see below) but higher fidelity and deeper bass than a reasonable same size horn-loaded cabinet. I'm skeptical that Club "subs", made of folded-horn with double 18" as you say, are REAL subwoofers with high fidelity, unless they are pretty large in size... To get real deep bass from a horn enclosure you need a really large box (Klipschorn is a special case), this is why they fold the horn to reduce size or use bass-reflex on the rear wave to improve lacking LF performance. Therefore, a vented-box does make sense in most cases, plus Horn Fanatic rightly suggested a bass-reflex design even though he's a horn guy! Clever fellow, contrary to some others, at least HE knows when to or not to specify a bass horn in a situation, instead of being a one-track mind. Moreover, look at JBL's recent Cinema sound subwoofers for example, no horns there just vented boxes... Good reasons are involved. The low-cost of the Watt today is one of those, along with space, portability, cost/performance ratio, etc.

(*) RE Ported horn systems like Altec 816A and JBL 4560A: " The sensitivity of the ported portion of the system is no greater than a simple ported system using the same transducers in the same volume, and unless there is a specific need for the added sensitivity in the mid-bass region, it is best to use a simple ported system." John Eargle (JBL), Handbook of Sound System Design, ELAR Publishing, 1989, P. 112

Again, the distinction between amplitude (bump) and bandwidth (deeper reach in the lows) in response is of importance about what you hear or heard or think you did (on a graph, the first is vertical and the second is horizontal). Altec says "useful response to 50 hz" for the 816A, still far from subwoofer class... Did you hear amplitude or bandwidth ? Why would the subs need not be "quite high fidelity" like the rest ? If you insist on having real subs then they have to be appropriate and blend correctly with the main 4520 boxes (this does not imply nor mean the subs have to be horn-loaded).

"...you guys have told me that a folded horn/front loaded sub would not be right..." I never said that a folded horn would not be right, instead I suggested one to you (its NOT a sub): the rear-loaded JBL 4520 ! As for the front-loaded horn, I discussed the errors of mixing in same stacks for example long-throw with short-throw equipment often in random ways with no consideration for acoustical issues involved...

RE Final choice: 4520 or 4530? I'd go for 4520 since it's basically the same work involved in building the two models, but on larger panels with 4520 plus an extra hole for the second driver. However, the 4520 has deeper bass (-5db @ 42hz, VS -5db@50hz for 4530, both with 2205 driver), higher sensitivity and more SPL because of the two drivers.

RE Why two woofers in a box instead of one? Because it's a relatively easy way to increase sensitivity and maximum output in sound reinforcement. Two identical LF drivers close to each other on the same baffle and driven electrically in parallel will give you 3 db more output when both driven by the same power input, compared to a single driver. This is because two drivers close behave essentially as a single one with twice the cone area (2 x cone area = 2 x efficiency), but the overall LF alignment stays essentially the same. Naturally, such a double driver box can also take double the input power vs a one-driver box, so another 3 db of output is now possible, for a total of 6 db greater output capability. Not bad. { John Eargle (JBL), Loudspeaker Handbook, Chapman & Hall, 1997, P. 79-80}

You mentioned being used to see 18" drivers, not 15" ones. The 2x15" mentioned by HF didn't seem to be good enough. However, you should know that when two 15" drivers are used as mentioned above, their radiating surface becomes equivalent to about 1.4 times that of a single driver: 15 x 1.4 = 21. So the combined radiating surface of these two is now about equivalent to that of a single 21" driver. (Both John Eargle manuals, pages 80 and 113 respectively) Good enough air moving for you now ? Naturally, other driver specs/parameters also matter.

RE rear-loaded horn phase issue: "Phase inversion of the rear waves, due to the propagation time through the horn length, further augments response in the lowest operating range." JBL, Professional Series, Low Frequency Enclosures, May 1980, P.2 That phase inversion of rear wave is such that it works in conjunction with the front wave, not in opposition to it, since if they were out-of-phase they would tend to cancel each other, decreasing bass output.

By analogy, in a vented box the port also emits sound. A phase inversion of the rear wave inside the box occurs when going in the port and that wave comes out of the port in phase with the direct-radiating one. Low frequency output is therefore increased with port contribution.

RE Amps driving the boxes: providing the amps have enough juice per channel and capability to work at 2-4 ohms (8 ohm drivers in parallel) then I would prefer to use one amp channel per box for simpler control from Electronic X-overs for example. Would do the same for subs (2x 8 ohm drivers in parallel per cab).

Richard

[budney]

Hi Richard,

Sorry for all the stupid questions...thanks for taking the time to explain them. I have ordered the books you recommended so I will study before trying to build anything. I'm eager to learn the actual science behind sound system design, not just throw some boxes together without any thought for why.

Re to being concerned about spl, or whether the boxes are reflex or horn loaded, or have 15 or 18 inch drivers etc. I'm sure they definitely do the job, I was just curious as to why you recommended them, when all club systems that I'm familiar with are different to your suggestions. The systems I am familiar with are moderns ones for modern dance music, and I'm just interested in why they would different from the old designs.

I have to apologise for confusing your initial recommendation. When you first mentioned the 4520 I wrongly assumed that another speaker would be required, hence my need to find another 'sub'. I see now that the 4520 would in fact be doing the job of what I wanted in a sub, without actually being a dedicated speaker for the low frequencies. When initially asking for advice in my mind I needed a speaker to cover about 800hz where the 2395 kicks in, to about 100hz where I thought a sub would take over. I thought you were recommending the 4520 as a midrange speaker only, even though you said a sub was not required...I see that I was wrong in that respect, a bad habit taken from the systems I'm used to.

An example of the club 'subs' I am familiar with are the Funktion 1 f218, folded double 18s normally running from 114hz, which is all you really see in England for dance music systems. Far from high fidelity, speakers that just sound okay 'off the shelf'. Funktion 1 also do a 21 inch sub range, quite a lot bigger than 15s! With the current dance music of today they sound fine when heavily processed, but play some old disco through them and they just don't cut it.

I would have heard amplitude, the system I heard with the altecs had lab subs for the low frequencies, so I was only thinking about the midrange when considering the altecs. I'm only still thinking about the Altec range because thats they're the only ones I've actually heard. I'm just going to start with the 4520 and the JBL 2395/2405, and take it from there. I like the idea of the stanley screamer subwoofers, if I'm still chasing those really low frequencies once I've built the 4520 then I will consider building some.

Also when I said the cheapest, I meant cheapest from the ones you recommended that have the required specs, not just any dirt cheap driver that fits the hole. I would test out the drivers first to make sure I liked them, before buying 8 of them!

Thanks
Budney

[cooky1257]

Hi Richard,





An example of the club 'subs' I am familiar with are the Funktion 1 f218, folded double 18s normally running from 114hz, which is all you really see in England for dance music systems. Far from high fidelity, speakers that just sound okay 'off the shelf'. Funktion 1 also do a 21 inch sub range, quite a lot bigger than 15s! With the current dance music of today they sound fine when heavily processed, but play some old disco through them and they just don't cut it.


Thanks
Budney

I think you need to get out more, listen more and get in the club before the dj red lines the mixer, other excellent uk club systems come via Voyd Acoustics, TurboSound, Martin Audio and Opus. Describing Funktion1 as 'sound ok off the shelf' and 'far from hifi' is just plain wrong-I can only assume the usual idiot dj's messing with tone controls and levels as being responsible as properly installed and set up the F1 dance stack is the closest thing to huge scale hifi I have ever heard, though the latest Voyd Air Motion system (voidacoustics.com/docs/range_intros/Air.shtml)ran it very close.

[budney]

I think you need to get out more, listen more and get in the club before the dj red lines the mixer, other excellent uk club systems come via Voyd Acoustics, TurboSound, Martin Audio and Opus. Describing Funktion1 as 'sound ok off the shelf' and 'far from hifi' is just plain wrong-I can only assume the usual idiot dj's messing with tone controls and levels as being responsible as properly installed and set up the F1 dance stack is the closest thing to huge scale hifi I have ever heard, though the latest Voyd Air Motion system (voidacoustics.com/docs/range_intros/Air.shtml)ran it very close.

I feel like I need to get out less! I work in clubs most weekends as an engineer, mainly using Funktion 1 soundsystems, and when I'm not working I'm out dancing! I've lost count of the amount of installs I've done with the resolution ranges of their speakers and blown drivers I've replaced. Also I've lost count of the amount of times I've told idiot dj's to stop redlining that being said we never had the dance stack range where I've worked. I've only heard a Funktion 1 dance stack once, that was in the club Berghain in Berlin. That was a meaty system, and worked well for the heavy techno they were playing, but still I was never blown away and overwhelmed by the quality of the sound. Where did you hear Funktion 1 dance stacks? Whenever I used to pull Funktion 1 speakers 'off the shelf'(or technically from under the shelves) and loaded the default settings into the processors, it was always just, meh. Once I had them in the room and could tweak throughout the night it got better, but I was still never wowed by them. Whereas when I heard the vintage jbl/altec system not too long ago, I could not believe the sonic quality of the music I was hearing. I could hear the compression of modern tracks when compared to old tracks. I could hear the vocalist take breaths before phrases, I could hear the stereo spread of all the instruments around the room. I've never gotten that from any Funktion 1 sound system no matter how much processing and tuning you do. But again I'm comparing them when playing old dance music, disco etc. For modern stuff, they are good, sometimes very good, when the dj knows how to use a mixer properly (and a good mixer, not this pioneer crap), when they have enough power to not clip the amps constantly, when the room they're in isn't an acoustic nightmare etc

We had a few old Turbosound boxes, not enough to make a good judgement on I feel. Although they are the precursor to Funktion 1, I'd imagine F1 had improved on the Turbosound range. I've heard Void a few times before, I'd say that they are better than Funktion 1, but I rarely see them to be honest, I don't know of any venues nearby that have them installed. The Martin Audio system in Fabric is the only experience I have of big Martin Audio dance systems, that was great for techno etc, but play any music with real instruments and it didn't give me what I wanted. They have the body sonic floor there, that was incredible! but I'm not in any hurry to get a load of transducers installed under a dance floor. Opus is one I've heard of, but unfortunately never heard myself, whats it like? I have heard good things about it.

One sound system that stands out to me was the RC1, from Bristol I think. They brought their speakers to a venue I was working in once, and I thought the building was going to fall down. Dust falling into peoples drinks, ruining the dj's records, that was a good system! But they ran it far too loud, they had a bucket of earplugs by the bar and they had ran out long before the night had finished. I've also heard a fair few reggae/dub systems. I find that the ones made by just a few guys, like the RC1, or the dub systems, well outperform the systems you can buy like Funktion 1, Void, Martin audio etc. But those systems are bespoke made for a specific genre, RC1 is mainly for bass heavy music, dubstep, dnb, bassline etc, and the dub ones are obvious. Thats why I want to build a system thats specific for disco and boogie! I think the bespoke systems work well in small spaces, in huge super clubs you do need the large format of the professional speaker manufacturers to have a consistant sound everywhere, as well as cater to wide ranges of genres. But in small spaces, which I think makes for a better more intimate party anyway, bespoke rule

[RMC]

Hi, RE YOUR POST # 19

Glad you're seeing things differently. This should not only benefit yourself, but also your future system. Starting with 4520/2441/2395/2405 makes lot of sense acoustically (its a well proven recipe around the Globe) and financially. Seeing later for possible additions is not really a problem if you keep that in mind while designing the system, because subs are relatively easy to add afterwards if need be. BTW with 4520 on the floor, a number of Clubs did have 2440/2395/2405 hanging from the ceiling and angled downwards, above the woofer boxes. This to keep some sight-lines, between low and mid/high devices, to the dance floor... Since you are now talking about a small dance floor with boxes around it or in the four corners of it, this may be an idea.

"Off the shelf" Sound Reinforcement (SR) bass cabinets or 2-3 way boxes, are frequently limited to about 50-60 hz in the lows for size, weight, portability, costs, space available, etc. Most people (like Club customers) don't really hear/know the difference between amplitude and bandwidth anyway.

Output below 40 hz is not often required in Sound Reinforcement: "In most music reinforcement systems, flat power response down to 40 hz is felt to be sufficient. However, certain special effects, both in music reinforcement and in the motion picture theater, require extension of the LF bandwidth down to 25 hz." John Eargle (JBL), Handbook of Sound System Design, ELAR Publishing, 1989, P. 112

If you were to put subwoofers for < 100 hz or so frequencies as in your example, this would defeat a good part of the purpose of having 4520 boxes, since their bass amplitude from rear horn-loading, giving "punch" to the bass notes, is mostly in the 60-125 hz range! Logically, proper subs should rather cover frequencies from about < 50-55 hz. As I said before, I don't see subs being required here IF: you choose a driver with correct T/S but with more Xmax AND/OR use a steep (18, better 24 db/oct) high-pass filter on the drivers signal in the 40-50 hz range (horn starts unloading at 42 hz according to JBL). Then, you can do some tests with volume control and EQ (amplitude/bump ) in the 50-60 hz or so range depending if you have a 1/3 or 2/3 oct. EQ .

Looking at large stacks of boxes doesn't mean much if you don't know anything about the Venue size, budget, challenges, acoustics, technical constraints, etc. (i.e. the context re how/why of box choices). Big stacks may look impressive for some, not really for me. I'm more impressed by quality, well balanced sound at a reasonably loud level, not by blasting the glasses off the table. Seen way too many of those. When you provide ear plugs to customers, your example, you have a BIG problem. Not only do you get too many people in the adjacent corridor (a red flag) since much too loud inside, but also making patrons deaf kills your own business slowly. Lot of SR guys and DJ's that don't seem to understand this elementary principle!

Why I suggested JBL 4520 bass cabinets ? Because of the intended application, also since high output SR front-loaded bass horns (e.g. Altec 816A or JBL 4560A) don't have "high fidelity" very high in their list of attributes, nor in their design goals. Higher efficiency/sensitivity is the name of that game. However, a rear-loaded horn and proper driver(s) with direct-radiating front waves is an interesting compromise. Not as "high fidelity" as a vented box, but much better for the application than a "gross" front-loaded horn. It's primarily a matter of better balanced sound output between the lows and mid-bass.

My Altec data sheet for 816A doesn't show a typical frequency response curve with one of the recommended drivers used, contrary to JBL. To get an idea of what a 816A response curve may look like, one can have a look at the curve published for JBL's 4560A (although with E-145), since both boxes use the same operating principles: front-loaded horn for the driver's front waves and bass-reflex for the driver's back waves. I'm NOT saying both curves are/should be identical, but they should show similar general shape. In their optimum operating range, front-loading horns add 6 db of on-axis sensitivity to the loudspeaker according to JBL. Looking at the curve one can in fact see quite a bump in response between the 100-800 hz or so range. The sad part is that below 100 hz or so the response does not benefit from that 6 db +, therefore it is at a much lower level than the other part, which means this box will sound much more mid-bassy, compared to a 4520. See JBL, Pro Series, Low Frequency Enclosures, May 1980, P. 2 & 4. That predominant mi-bass sensitivity/sound is what made John Eargle say (quoted in my previous Post) that if you don't have a specific need for that increased mid-bass sensitivity, then you're better off with a simple ported system.

Finally, In terms of technical books, you may want to start with Yamaha's SR handbook first as it is probably easier to understand (less math) than some others, but still good. Others mentioned can follow after, in addition to Don Davis, Sound System Engineering, 4th edition.

Richard

[budney]

Hi Richard,

Looking at large stacks of boxes doesn't mean much if you don't know anything about the Venue size, budget, challenges, acoustics, technical constraints, etc. (i.e. the context re how/why of box choices). Big stacks may look impressive for some, not really for me. I'm more impressed by quality, well balanced sound at a reasonably loud level, not by blasting the glasses off the table. Seen way too many of those. When you provide ear plugs to customers, your example, you have a BIG problem. Not only do you get too many people in the adjacent corridor (a red flag) since much too loud inside, but also making patrons deaf kills your own business slowly. Lot of SR guys and DJ's that don't seem to understand this elementary principle!

I couldn't agree more, every event that I've run I am constantly fighting the DJ to keep the SPL at safe levels. Whenever someone tells me that its not loud enough, I politely tell them to go stand in front of the stack if they want to hear it louder. If that doesn't work, then fiddling with some knobs that don't actually do anything and then asking them if thats any better normally results in a thumbs up!

My Altec data sheet for 816A doesn't show a typical frequency response curve with one of the recommended drivers used, contrary to JBL. To get an idea of what a 816A response curve may look like, one can have a look at the curve published for JBL's 4560A (although with E-145), since both boxes use the same operating principles: front-loaded horn for the driver's front waves and bass-reflex for the driver's back waves. I'm NOT saying both curves are/should be identical, but they should show similar general shape. In their optimum operating range, front-loading horns add 6 db of on-axis sensitivity to the loudspeaker according to JBL. Looking at the curve one can in fact see quite a bump in response between the 100-800 hz or so range. The sad part is that below 100 hz or so the response does not benefit from that 6 db +, therefore it is at a much lower level than the other part, which means this box will sound much more mid-bassy, compared to a 4520. See JBL, Pro Series, Low Frequency Enclosures, May 1980, P. 2 & 4. That predominant mi-bass sensitivity/sound is what made John Eargle say (quoted in my previous Post) that if you don't have a specific need for that increased mid-bass sensitivity, then you're better off with a simple ported system.

So if once I've built the 4520s, and I still find that I want a bit more in the midbass region 150hz up to 800hz, to forget the front loaded boxes and go for direct ported boxes? They would not be as efficient as a horn loaded speaker as HF explained earlier, but would be a better choice acoustically right? But then isn't that what the 4520s do above 150hz anyway, act as a direct radiator? However it's still a big IF, I'm going to see how I like the 4520s first, and it will take me quite a while to get to that point.

Thanks
Barney

[RMC]

Hi Barney,

"So if once I've built the 4520s, and I still find that I want a bit more in the midbass region 150hz up to 800hz, to forget the front loaded boxes and go for direct ported boxes? They would not be as efficient as a horn loaded speaker as HF explained earlier, but would be a better choice acoustically right? But then isn't that what the 4520s do above 150hz anyway, act as a direct radiator? However it's still a big IF, I'm going to see how I like the 4520s first, and it will take me quite a while to get to that point."

Why would someone want more mid-bass than normal is beyond me. Prominent mid-bass doesn't sound good in my book... Try it on any speaker with an EQ, boost that a few db and listen. I hate that sound.

I would not go with front-loaded boxes for added mid-bass. If need be, I'd be more tempted to go with a closed or vented-box with single 10" (e.g. JBL 2123H) or double 12" (e.g. JBL 2202), maybe higher sensitivity single 12" (e.g. JBL 2202H), for their smoother response, higher fidelity. The JBL 2020H 12" made for maximum output with even more sensitivity, has a less interesting too much rising response. These drivers (except 2020H) have, when used in quantity mentioned above, sensitivity about on par (± 1 db) with double 2205H in the 4520, and probably less directivity/throw issues than a front-loaded horn inside a normal room.

My preference is no mid-bass boxes, use your EQ for "a bit more in the mid-bass" as you say, if that is your wish, since yes the 4520 is direct-radiator above 150 hz. Why complicate things more than required by adding another box ? More x-overs, amps, boxes, money, work, level matching, and maybe directivity issues depending on box type chosen...

Looking at JBL's response curve for the 4520 (with 2205), there's a few db bump in the 60-125 hz range, then a dip of about 3 db in the 125-200 hz or so range, then the curve is reasonably smooth from about 200 to 700 hz. Difficult, in my view, to ask for better than that in Sound Reinforcement disco application. The reason being what you will be hearing with such a response. The dip in mid-bass has the advantage of giving more emphasis sonically to the bumped frequencies in the lows (i.e. the punch in discotheque music). JBL Engineers who designed the boxes weren't stupid, they listened to it extensively and tweaked things until they got it right for the application.

Try it with speakers and an EQ: duplicate somewhat the curve with more mid-bass than usual and listen, after duplicate somewhat the 4520 type of response curve and listen. I've done it for myself with my 2205H in vented boxes. No contest, it sounds much better to me the latter way. Sound with mid-bass emphasis to my ear is crap... Authoritative lows in the 50-60 hz range are much better sounding than the other in this application.

Richard

[budney]

Hi Richard,

Okay, gotcha, I understand. It was just purely another what if question I was curious about, as I'm used to 4 way systems. I won't bother with a mid bass speaker for now.

Thank you for all your help and advice, I really appreciate the time you took to explain this to me. I've still got a lot of reading up I want to do before beginning to build these speakers. I'm sure I'll have a few more 'what ifs' pop into my head at some point.

Best regards
Barney

[RMC]

Following my recent posts here, I had another look at the Dark Side, the other still in business major Sound Reinforcement (SR) Company (Electro-Voice) to see if things had changed on their side since the last time I checked and their approach in terms of 18" driver subwoofers.

They have 7 series of portable SR boxes, 5 of them with "subwoofers", each including models with 18" driver(s) mounted in vented-boxes (didn't see any horn-loaded ones in their current line-up). Though I looked quickly at all of them, to represent the group I took a few specs of the Tour X premium "subs", described as world-class, tour grade... These are loaded with E-V's EVS-18S 18" woofer(s).

Model TX 1181 (1 x 18") has a stated frequency response of 45-700 HZ (- 10 db) and 50-160 hz (- 3 db). The other, model TX 2181 (2 x 18") has response of 40-1500 hz (- 10 db) and 50-160 hz (- 3 db), still far from earthquake bass, though they do have pretty high output. The 3 db down point is much more meaningful in use than the - 10 db LF response in my opinion.

Some boxes in the 5 series line-up are recommended for use with a high-pass filter in the 30-36 hz range...

For a few among all the "subs", E-V did not mention the number of db down @ hz for LF response given, as other manufacturers also do, and this is sometimes a bad sign regarding real effective response...

The "subs" seen there seem mostly limited to 40-50 hz in the bass range (- 3 db), and the best ones to 30-35 hz (- 10 db). Remember, these are all single or double 18" driver(s) boxes! Deeper bass would probably require larger box volumes and that's too penalizing in terms of size, weight, portability... That's the way it is, also probably the way it should be in SR most of the time. In this type of application, an F3 at about 45 hz or so isn't that bad, it appears still quite acceptable for SR. Maybe, making cabs with 2 x 15" look better?

This short examination does show the use of large 18" driver(s) does not guarantee very low bass from a box. Remember in a previous post I said I was skeptical about "subwoofer" low-bass from a 2 x 18" folded-horn box Budney heard/ mentioned, unless it was really large. I even asked him if he heard amplitude or bandwidth, and he replied probably amplitude...

In my view, if the above 18" driver(s) vented-boxes from E-V don't achieve real subwoofer performance, then folded-horn boxes of comparable or reasonable size with 18" drivers, will achieve it even less...

This quick review also shows home Hi-Fi subs and Sound Reinforcement "subs" are two different things. To me, such low-frequency cutoffs (- 3 db) are more compatible with the "bass cabinets" name than real subs.

In the end, however, E-V remains constant/logical with its prior mention that "In general, subwoofers for dance environments and concert reinforcement are best limited to about 40 hz. Cinema sound and special effects applications require performance to 30 hz and below." Electro-Voice, Pro Sound Facts, No. 7, October 1984, page 2, Note # 2. This quote is quite similar to John Eargle's I made in a previous post here re 40 hz felt to be sufficient.

BTW E-V's previously known Cinema Sound LF loudspeakers were TL606M (2 x 15", - 3 db @ 45 hz), and two subwoofers: TL440M (1 x 18") plus TL880DM (2 x 18"), both with - 3 db @ 32 hz, also loaded with EVS-18S woofer(s)...

OTHER MEMBER'S COMMENTS WELCOME.

Richard

[1audiohack]

Since you are looking around, take a look at the Danley Sound Labs PGD series. This stuff will knock your socks off, it's made just for your application and it sounds great. The J94 is the best sounding large format fullrange speaker I have ever heard, ever. The fidelity is astounding and its impact is literally frightening.

These will kill anything else you have considered here with considerably smaller box count.

If by chance you think you need more sub than the PG218 look at the BC218.

Disclaimer: I have no business connection to Danley Sound Labs. I know some of the guys there and I have bought some of there products.

Barry.

[budney]

Hi Richard

I'd be interested in what you think about the flared levan horn extensions used on W subs for club sound systems, they are supposed to run all the way down to 30hz. These are what I was basing my initial ideas on, a few clubs in the 70s and 80s had these extensions and are still spoken about today as having the best sound around. These subs were used with special crossovers(the same kind that I wish to use) that allowed the dj to play with their gain throughout the night. Also I think they were used as well as already existing bass cabinets, so the levan horn would be running at 100hz and below, but the other bass cabinets would also output 100hz and below.

I know that technically this is a big no no because of all the time aligning and phase issues, but the clubs that had the system set up in this way still worked excellently and were known for their sound. I think that set up worked because the dj had control over them. Most of the time they weren't in use, and the dj could suddenly turn them on for added effect. Also they used a dbx boom box to increase the amount of low frequency content available.


I'm not saying that I wish to use these kinds of subs, I don't think its practical for a small room like I plan on having, they'd take up most of the floor space. That being said, I do like the idea of being able to control subs in that way by using that type of crossover and boombox. The system I plan on using does not have to take portability into consideration as once its there it won't be moving again.


Some more modern systems with the flare extension

[1audiohack]

This. This one goes to 11.

[budney]

This. This one goes to 11.

sure looks mean! That top box is bizarre, never seen anything like it. Would be keen to hear proper club kitted out with that system. It also looks expensive how are they any different from all the other 218 subs that all the big manufacturers make?