Newbie - Designed crossover - Pls let me know if its okay

[Ronnie22]

Hi All,

I am new to this forum but have been going through a lot ot the previous posts over the last couple of months. I have been facinated with the word of audio. However after coming acros this site i realised it would be so much better to design speakers oneself and experiment to getthe music that one likes ratherthan shop for the closest to one's taste.

This becomes all the more imperative since I am based out of India where their is very few choices in terms of speakers and amplifiers. Hence this is my first foray into building a speaker.

I have taken a simple 2-way book shelf speaker and tried out some Vifa drivers (Again since I don't have too much of a choice in terms of driver availability)

The drivers that I am using are

VIFA TC18WG49-08 - Woofer
Specs are

Qts 0.47
Vas l 44
Fs Hz 37
Re Ohm 5.5
Le mH 0.75
Xmax mm 4
Z Ohm 8
Qms 2.62
Qes 0.58
SPL dB 86
Pe W 35
BL 5
Dia mm 25
Sd cm^2 138

AND

VIFA D27TG05-06
Tweeter

Specs are

Qts 0.77
Vas l 0.006
Fs Hz 1000
Re Ohm 4.6
Le mH
Xmax mm 0.2
Z Ohm 6
Qms 2.15
Qes 0.19
SPL dB 92
Pe W 100
BL 2.7
Dia mm 26
Sd cm^2 7.1

I have adopted a simple 2-way 2nd order passive filter
with the crossovers set at 2800

I have also used a Zobel network and an L-pad attenuator.

I have attached an xcel sheet that shows the values of the crossover network used.

I am trying to keep this as simple as possible since this is the first speaker set that I am attempting and would like to learn from here on.

Also pls keep in mind that I have access to absolutely no measuring instruments, etc which will help me to figureout the behaviour of my drivers.

Hopefully once I am done with the crossover, I can moveon to the actual buidingof the cabinet.

Pls letme know if there are any problems withthe crossover network.

I am using WinISD and Speaker workshop. I have also downloaded some more sheets from various DIY enthusiasts across the net for designing the cabinet and also for various filters.

PLS HELP............................

 

[Ronnie22]

Sorry about that.............failed to upload the attachment earlier.

Have now uploaded the attachment containing pics ofthe crossover network

 

[tcpip]

How did you get to the xo design?

I'm a little confused with your post. How did you arrive at your xo design?

From what I've understood of speaker design, it's impossible to design a passive speaker-level xo (PSLXO) unless you use some speaker design and measurement software (Speaker Workshop would do) and actually take measurements of SPL and impedance, and then optimise the xo. (I've never designed a speaker myself, so my understanding may be shaky.)

Also, from what I understand, you have to follow the following sequence for speaker design:

1. first, get the T/S parameters of woofers. Measure them if needed
2. then design a suitable box using those T/S parameters
3. then build the full box, and actually mount the drivers on them. This includes all drivers, tweeters, midrange, woofers, etc.
4. then take SPL, phase and impedance measurements of the relevant drivers for which you need to build the xo. These measurements can't be taken accurately till you actually build the final box and mount the drivers on them. Therefore, the xo can't be designed "in the air".
5. then design the xo and computer-optimise it using software. It's practically impossible to design a PSLXO without computer optimisation these days. I tried for more than a year to find a short-cut to avoid this, and I've finally given up. You can't do it.

Therefore I can't figure out how you've arrived at xo design before doing the earlier steps.

Other than the Panasonic electret mics used by many builders for SPL measurements, everything else is available in India. So being in India is really no disadvantage for this activity, thanks to forums like diyaudio. And Peerless India drivers are available at pretty affordable prices too... you don't have to go for Vifa drivers for your first project.

 

[Ronnie22]

Nobody!!
Any ideas/suggestions is welcome.....i'm obviously not looking for somebody to fig out exact values in the network but some of the experience ppl would have some idea about things like

1. Whether the crossover is correct for the drivers mentioned

2. What would be the correct cabinet size

3. Whether the tweeter connected in reverse polarity is okay?

4. If the values are okay on first impressions. Obviously ppl with experience in tweaking crossovers can make out atleast any anomalies (Maybe some are too glaring for me to pinpoint)?

5. Are the drivers matched properly or should i go in for MTM?

6. Bookshelf or Floorstanding?

7. VEnted or ported........

This is the first speaker that I am building so any other mistakes that I may avoid can be pointed out.

Thanks and hoping for some one to take the plunge........

 

[Ronnie22]

Highly unstructured so pls bear

Thanks for that post, tcpip. I was beginning to wonder if anybody was going to reply.

Frankly, this DIY business is very new to me. Not more than 6-7 months at the most. Being in a bank, free time is a premium for me, however I love music and its only now that I am able to indulge myself in some luxuries that in my college days were confined to a sony deck. However after coming across this and some more sites, I was fascinated with the world of building speakers, amplifiers, etc.

Apart from my electrical and electronic papers in Engineering that incidentally has been around 5 years back, I have done no formal reading on this subject. I have mostly read up on other ppl’s posts, white papers by some audio manufacturers, help manuals by softwares like Winisd, speaker workshop, etc. I usually don’t follow the route of picking up a textbook and going through the stuff. Also been very impatient, I wanted to get something off the ground. Hence you may have noticed that the “process” adopted by me for building a speaker may have seemed highly unstructured.

I tired getting peerless drivers in Chennai but with little success. Went to a lot of local manufacturers including Torvin but nobody seemed to have any to spare. Finally hit upon a site (Corrson) where some Vifa drivers were advertised. If I can get my hands on cheaper drivers to work with, I would do so most gladly. However money is secondary here for me(I’m very middle class by the way) if I can get this project rolling so that I can experiment, make mistakes and learn. I don’t like to do too much reading so maybe that could be a mistake here.

I got the cross-over measurements from the T/S and other parameters mentioned for the TC18WG49 driver on the DST website. Simulated that in Winisd. Also got the calculations for the Zobel filter and L-pad using basic formulae from various papers and using the specifications provided for the drivers. Let me know how to setup a kit to measure speaker drivers. I have a fast computer with a pretty good soundcard to begin with. However if the measurement thing is tough or needs stuff that is expensive to procure, I might as well build the thing and then see how to take it forward. If I keep it lying for too long, I’m scared that things may never happen if other considerations take priority tomorrow.

Lots of questions above so don’t mind. However pls let me know how to take it forward keeping in mind my long post. Thanks and keep it coming.

 

[tcpip]

I know where you are coming from, because I too got into audio because I had more brains than money (now you know how incredibly poor I am!)

However, if this is your starting point, you should not get into speaker design now. You should first build something which is very feasible using parts from India. And I have a suggestion for an excellent pair of standmount speakers which, if built well, will beat any commercial speakers costing upto Rs.50,000 a pair, maybe even higher. Check out

http://users.ece.gatech.edu/~mleach/labsp2/

A friend has made this pair, and they sound excellent. I have a pair of Wharfedale's supposedly premium Pacific Pi-40 floorstanders, and these bookshelfs sound better than my Wharfedales. The Wharfedales had cost me Rs.45,000/pair four years ago. It's quite amazing how a stand-mount 2-way can beat a so-called premium quality floorstander even in the bass quality, let alone the rest.

I suggest that if you build these speakers, you should use 1" thick MDF, not 18mm as specified. Also, use double-thickness for the front and back of the box, i.e. 2 layers of 1" thick MDF. All these modifications are safe provided you keep the internal box dimensions unchanged.

The drivers (and all other parts) for this stand-mount model are available from Corrson.

A word of warning about the "TC" series of Vifa. They are not sufficiently well-made to be good midbass drivers for two-way designs. Their frames are made of polycarbonate material, which is not strong enough to give you strong low-distortion bass. The magnets too are not large enough for good control. The "P" series is more expensive but is excellent value-for-money, i.e. the extra money is more than justified in much better sound quality. I suggest that you forget "TC" for two-ways, and use them only as mids for 3-ways, or some other lower-power application (e.g. surround speakers in a multi-channel setup, etc.)

 

[Ronnie22]

Taking your advice, tcpip

Hi tcpip,

Thanks for that design.Looked over the design. Don't get me wrong but I don't want a great sounding Speaker. What i want is to experiment since the subject is so damn interesting. If in that process I happen to hit upon something i like then all the better. But by experimenting I would like to attain some level of proficiency to design something I want. In the end the objective is obviously to get myself a good pair of speakers but if I don't have an idea about what to tweak to get the desired outcome, the whole exercise will be futile.

To start off, I am going to work on the design that you suggested but will be running the pair ragged by working out all possible combinations on the crossover. I guess that will help me understanda bit. Will also use this project to setup a rig to start measuring drivers. And then hopefully go on to different kinds of speakers.

Will be needing your help as I go along with this project so would appreciate if you could keep in touch. Will be ordering the drivers (P17WJ and D25AG) from Corrson soon. BTW I am not able to get across to them either by the email id or contact nos that they have provided on their site. Would you have an idea about a better way to contact them rather than landing up at their doorstep??

 

[tcpip]

I don't have any other access information for Corrson, but email worked fine for my colleague and me (we're in Bombay, so it's all long-distance commerce). And regarding the ordering of drivers, why don't you order the xo components too at the same time? Their caps are pretty good... it's hard to find MKP/MKT caps of that rating and value in India over the counter.

The original construction article says something about alternate values for the L-pad of the tweeter in order to make the speaker less "bright" sounding. It may be a good idea for you to get those alternate resistor values for some alternate L-pads right away, to be able to play with the tweeter's level.

And yes, this design will act as a good platform for experimentation. You can make the design as-is as a first approximation, and then learn about measurements and optimisations so that you can (i) fine-tune the bass-reflex behaviour, and (ii) experiment with alternate xo. Starting with a fundamentally functioning design on Day 1 helps with the subsequent experimentation... at least you know you have a basically sound design.

Based on my colleague's experiences, I feel there is a lot of scope for experimenting

• re-design the enclosure+port to fine-tune the low end, maybe re-build the box entirely, keeping the drivers and xo the same
• measure the midbass driver and port response to see whether the overall box has been built "to spec", i.e. whether there's boominess or peaks in the response, and if there is, then correct by fine-tuning the volume and port dimensions
• try to create a new xo from scratch using measurements and optimisations of Speaker Workshop
• spend a few months in hand-tweaking the xo values accompanied by extensive listening, to "voice" the system as per your judgement and taste.

All in all, an excellent platform for experimentation. I feel that anyone working on this design for six months this way will be able to get a much better speaker than what a novice like me can make out-of-the-box from the design article. There's lots of scope for improvement and learning, at little incremental cost once you have the drivers.

Best of luck.

 

[Ronnie22]

Indusctor in series with woofer not working...help

Hi all,

I am using the crossover as given in the link below as was advised by a fellow DIY in this forum. I got the components today and tried out the schematic to see if everything is working.

http://users.ece.gatech.edu/~mleach/labsp2/crsnet.gif

However when the woofer is connected in series with an inductor(0.42 mH) as given in the crossover network............nothing seems to work. The tweeter is working fine but no sound from the woofer

If i remove the inductor and keep the woofer connected directly to the terminals without any other components, then it works fine.

The inductor is an air-core, 18awg.

Can anybody tell me why this is not workingout?? I have connected the entire crossover using slim silver wires just to check if they are working.

BTW the Wooferis Vifa P17WJ and tweeter is Vifa D25AG

 

[Cal Weldon]

Try a continuity test on the coil. There may be a problem with it. Although problems with coils are rare.

This may be too simple but did you remove the magnet coating from the wire?

 

[Ronnie22]

Will try the continuity test tomorrow morning (Late night back here in India) but have got the coils made to order from an audio dealer....so i don't think that he would have made the mistake of leaving the magnet coating on the wire (BTW I don't know what that is ?? )

I have also tried either of the two 0.42 inductors with the same woofer and neither seems to make it work

 

[Ronnie22]

Thanks Cal...u made it work

Hey Cal, thanks man!! After that post i noticed a dark colouring on the wire and stripped that off with a knife till i got a golden colour inside, then i reconnected and voila....it works

 

[Cal Weldon]

Not to worry, you're not the first to overlook that little detail

Cal