Vikash said:
Don't take it personally😉 FWIW, I know it feels: http://www.diyaudio.com/forums/showthread.php?s=&postid=397001#post397001 😉
Still looking for tweeter recommendations after Gaz's comment
This should be fine in this application. Be aware that the tweeter will need less power than the woofer, so you might want to consider some sort of limiting system - the easiest way to achieve this is to use a smaller (lower voltage) transformer for the treble amp, but I'm not completely sure if that's necessary in this instance...
Some examples: The BBC-modified Quad 405 that is used to drive the LS5/8 provides nominally 100W for the bass amp (more in practice) and around 12W for the treble. This is achieved by fitting a resistor in the position Quad provides for limiting the output to make the 405 compatible with ESL's. The value Quad recommends reduces the output to around 20V RMS (50W), but a different value is chosen to give an even lower output voltage for the LS5/8, corresponding to around 12W. The amp might get driven into clipping, but as the Audax TWO34 is rated at much more, it is virtually indestructible in practice.
In the ATC SCM20A, the bass section is 250W, and the tweeter has a 50W amp. Additionally, there is a JFET limiter in each amp, plus a lamp and LDR limiter in the treble section. There are separate secondary windings for each amp on the mains transformer, but even ignoring the different power requirements, these are necessary because of the "grounded source" scheme that ATC use for their power amps.
As I say, these measures probably aren't necessary for controlled domestic use, but they save a lot of "down-time", which is important in the professional sector when studio time equals $$$
A possible trick might be to choose a transformer that gives relatively "safe" output levels for the tweeter (say, 25-30W), and then use something like a parallel configuration LM4780 that will drive 3 ohm loads happily. This will drive a pair of the AP100Z0's in parallel to their power limits quite comfortably. This is possibly easier than driving them in series with higher voltage rails. Additionally, simple resistive potential dividers between the treble amp and tweeter will offer protection easily - when matching the level between the drivers, if you need to reduce the tweeter by, say 3dB, then doing that after the power amp will help to protect the tweeter from the amp clipping. Obviously, you'd make sure that normal use doesn't cause the power amp to clip…
If you wanted, you could buy BrianGT's PCB's for this - an LM3875 for the tweeter, and one or more parallel LM4780 PCB's for the bass drivers...
Sorry for the long post - hope it makes sense 😉
Mark 😉
Thanks for the replies regarding the amp...at least I know it's a possibility now. I've got a lot more questions and will probably be best to start a 'Maplins close-out on AP100Z0' thread in the chip amps section...
sreten said:
Well...I wanted to keep the design small enough to sit on my computer desk table....but screw it...gonna move around the furniture and make some room to fit in some floorstanders next to the desk. 🙂
Gonna go with what sreten suggested with the 2 rear bass drivers mounted magnet out in a push-pull config.
Just clarification. The rear driver is wired out of phase to the front driver....I would wire a front/rear pair in series and then the two pairs of drivers in parallel? (or would I wire the rear pair in series, the front pair in series and then both sets in parallel?)
I've opted to go for a slightly wider baffle now at a whopping 200mm with a depth of 180mm (not including pertrusion of rear driver magnets).
This leads to 4184cm³ (4.20 litre) internal spacing for the midrange drivers, and 23844cm³ (23.80 litre) for the bass drivers using the same internal bracing split as in previous pictures. (I could close off the top section and increase the mid internal volume to 7439cm³ (7.40 litre, consequently reducing bass internal volume to 21608cm³ (21.60 litre))
I have sketched up a design where the center of the top midrange driver is exactly in line with 'ear level' with 10mm spacing between the top 3 drivers. The sketch also has a mock-up of where the bass speakers 'could' be situated....
...looks wise I don't care how the speakers end up looking but where do you guys/gals reccommend placement of the 4 bass drivers with regards to best accoustic performance and near-field soundstaging?
An externally hosted image should be here but it was not working when we last tested it.
With limited searching results I've messed around with the concept of vent port dimensions and placement. According to loudspeakers101.com their vent types page mentions that the end of the "port is at least the equivalent of one vent diameter away from the back of the box or any bracing materials". Unless the required port is very small I doubt I can fit a port in the rear space behind the midrange driver caged area...or could I get away with a 'slot' type vent venting out the top of the speaker enclosure? What do you recommend in terms of port placement/dimensions?
And onto the ever present question...how do I go about desinging a crossover network? Everything I've seen about designing a crossover is in relation to real world measurements with the speakers already in an enclosure of some sorts. How do I go about simulating a speakers response in a hypothetical enclosure and subsequently design a basic crossover ideology?
I've also been thinking along the lines of speaker sensitivity. With a set of 4 AP100Z0's in series/parallel config for the bass I have a 6ohm rating and 96db sensitivity. With a pair of AP100Z0's in series configuration for the midrange I have 12ohms and only 87db sensitivity...and then the tweeter, Audax TM025F1 with a rated 8ohm's and 92db sensitvity.
Surely this mismatch of sensitivities will cause problems or is that something that can easily be taken care of by careful selection of crossover frequencies?
On that note...couldn't I just go a lil crazy and double up the midrange drivers (such as with the bass situation) to even out the sensitivies?
Sorry it's turned into a long post but it's hard to find and string together the information I need (either that or it's just not presented in a useful and understandable manner).
Thanks for all the help.
A hopeful nub. 😀
Why increase the baffle width ? why not the depth ?
Your driver arrangement as it stands will give baffle step
correction with the right 1st order bass mid c/o frequency.
The tweeter will need padding back to the midrange.
I'd wire each push pull pair in series, and the two pairs in parallel.
I'm not going to go into c/o design, hopefully someone else will help you.
with ~ 6L per bass driver around 55Hz is good for port tuning.
Also note as a nearfield monitor the design is total overkill.
A simple TMM or MTM 2 way with no BSC is all you need for a
desk monitor, 12L tuned to 55Hz or 14L tuned to 50Hz.
🙂 sreten.
Your driver arrangement as it stands will give baffle step
correction with the right 1st order bass mid c/o frequency.
The tweeter will need padding back to the midrange.
I'd wire each push pull pair in series, and the two pairs in parallel.
I'm not going to go into c/o design, hopefully someone else will help you.
with ~ 6L per bass driver around 55Hz is good for port tuning.
Also note as a nearfield monitor the design is total overkill.
A simple TMM or MTM 2 way with no BSC is all you need for a
desk monitor, 12L tuned to 55Hz or 14L tuned to 50Hz.
🙂 sreten.
I'm still trying to maintain a smallish footprint...the width is something that I can increase easily to accomadate the room and furniture where as increasing the depth means that the speakers will stick out too far in accordance with the rest of the room.
When you say the tweeter needs padding you mean physically right?
I was thinking of putting the tweeter in it's own cylindrical enclosure and padded with foam or some sort to reduce vibrations.
Total overkill? Is that good/bad/indifferent?
The speakers will beused primarily in a monitoring situation for general PC gaming/CD audio but they'll come to life at parties and when I want to turn on the turntables and have some phun...loud phun.
With 23.8 litre's for the bass enclosure I figured a tuning down to 53Hz will give a -3db reading of 50Hz (according to WinISD and if I've done things right 🙄 )
As far as crossover design....any idea's on where to start?
Thanks for your input.
When you say the tweeter needs padding you mean physically right?
I was thinking of putting the tweeter in it's own cylindrical enclosure and padded with foam or some sort to reduce vibrations.
Total overkill? Is that good/bad/indifferent?
The speakers will beused primarily in a monitoring situation for general PC gaming/CD audio but they'll come to life at parties and when I want to turn on the turntables and have some phun...loud phun.
With 23.8 litre's for the bass enclosure I figured a tuning down to 53Hz will give a -3db reading of 50Hz (according to WinISD and if I've done things right 🙄 )
As far as crossover design....any idea's on where to start?
Thanks for your input.
If I pad the tweeter back to the midrange, I'll have effectively an 87db tweet/mid setup with 96db in the bass department....is this of no concern due to the nature of frequencies being played?
Use an adjustable pad to tweek the levels once the box is complete, a computer FFT and measurement mic is useful for this, and doesn't even need to be mega quality, a cheap headset mic is good enough.
Another thread I have been watching this for a while. I have 12 of these and I am looking for a nice design that I can use. Something that uses 6 drive per enclosure and produces great quality would be nice 🙂 , then I can use them for as either rears or backs with my Ruarks.
However being a complete dunce and a lazy dunce at that, Its completely beyond me to design anything. So please post your complete designs here along with build instructions...
Thats not too much to ask is it ??? ;-) 🙂
However being a complete dunce and a lazy dunce at that, Its completely beyond me to design anything. So please post your complete designs here along with build instructions...
Thats not too much to ask is it ??? ;-) 🙂
Well, seen as I just got reminded about this, I just though I'd let you know I ahven't forgoten to keep tweeking and listening, but I cam back from work today with a distinct lack of new crossover componets in my bag (you would think that if you placed a special order for delivery to the store it might actualy come in with the delivery right?).
Anyway, I have been listening to the slightly dodgey setup I have, and I found that with a littel tweeking with winamps equaliser, it was possible to almost make the speaker sound decent (give it a bit of a suck out at the higer frequencies, as I think the tweeter needs to come down a bit more, and a bit more again around 3000hz where I messed up the original crossover). However, I am still experiencing a severe lack of bass from these litte drivers.
I'm not sure so far if this lack of bass is simply to do with my rather leaky/selaed cardboard box design, or if it is in fact the speakers themselves not being up to the task. Either way, I'm thinking about redesiging my proper wooden cabinet before I build it to add a lot more volume, and enough space on the side to mount an 8 inch AP2100Z0 if the bass still isn't up to much when the drivers move homes.
Anyway, I have been listening to the slightly dodgey setup I have, and I found that with a littel tweeking with winamps equaliser, it was possible to almost make the speaker sound decent (give it a bit of a suck out at the higer frequencies, as I think the tweeter needs to come down a bit more, and a bit more again around 3000hz where I messed up the original crossover). However, I am still experiencing a severe lack of bass from these litte drivers.
I'm not sure so far if this lack of bass is simply to do with my rather leaky/selaed cardboard box design, or if it is in fact the speakers themselves not being up to the task. Either way, I'm thinking about redesiging my proper wooden cabinet before I build it to add a lot more volume, and enough space on the side to mount an 8 inch AP2100Z0 if the bass still isn't up to much when the drivers move homes.
Well that would depend on whether the Royal Mail were involved...bigparsnip said:
I would assume that you need to encapsulate the back wave in a much sturdier fashion than with merely cardboard to get any appreciable bass. If you have some wood lying around, then why not knock up a quick cabinet to replace your cardboard one.bigparsnip said:
Yeh, the bass won't be held in by cardboard I don't think. Certainly be losing lots, especially with leaks.Vikash said:
Also, the AP2100Z0 isn't exactly a legend at making stonking bass. But there is another 8", for just £15 which looks good, can't remember the model. Richie00boy, iirc, is contemplating using it.
bigparsnip said:
Your crossover description implies you are not compensating for
baffle step, which will give weak bass by (my) definition. Sealed
bass should be decent to around 80Hz, to go lower you need to
reflex to get down to ~ 50Hz (in a bigger box).
2.5 ways are easier tham MTM's to play around with baffle step
compensation, but 2.5 way gives you full 6dB BSC, in a 2 way
you can choose the amount of BSC, I recommend at least 3dB.
Painting your test enclosures inside and out with polyeurathane
floor varnish will have a dramatic effect on stiffness, adding a
layer or two of very cheap vinyl floor tiles for damping is a
excellent way of prototyping enclosures or open baffles.
🙂 sreten.
How do you choose it? (Other than actively, between pre and power amp)sreten said:
edit: are you suggesting a circuit that will attenuate the higher range, losing sensitivity?
SimontY said:
Well that how its done in (good) commercial speakers,
you lose midrange and treble sensitivity, but they are
easy to drive in the midrange and treble.
(Also the same for good amateur designs)
Generally the first inductor of the bass/mid c/o is a lot larger
than you would expect, it may also have a resistor in parallel.
Exact details are impossible to give as the inductor is adjusted
for baffle step, driver EQ and any diffraction irregularities of the
driver mounting on the baffle, along with the other c/o components.
Midrange / treble sensitivity of an MTM should pan out to be
~ equal to that of a single nominal driver, ~ 85dB/2.83V here.
With less BSC it can be up to 88dB/2.83V, but weaker bass.
🙂 sreten.
6db BSC wired in parallel, or 3db wired in series right? If I wire in series to give the opamp an easier load, then is 3db BSC enough?sreten said:
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