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Old 13th August 2004, 11:57 AM   #1
Jennice is offline Jennice  Denmark
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Default Would I be able to DIY decently?

Hi folks,

As some of you may heve noticed, I have posted replies and had threads, where I asked about duggestions for making DIY speakers.

Everybody suggests me to make my first project from a well tried kit. However, I can't seem to find a suitable kit, using drivers that I have access to.

Thus, I would like to know what kind of measuring tools it takes to make it right.

Driver info's are available from the manufacturers (data sheets),
filter calculation programs are available on-line, and I am aware of problems such as baffle step and port calculations.

Furthermore, I have access to audio-band analysis hardware and measuring mic's from Brüel & Kjær. If needs be, I can also get access to ons of those rooms with no reflections (accoustic damping on all surfaces). (BTW: Is that what is called an anechoic chamber?)

My thought was to build a 2-way, ported, TMM configuration, crossing at about 2kHz. Maybe a 2.5 way?
I'd like to use the Peerless HDS164 mid-bass, and probably VIFA DX25 or XT25.

Have I missed any development tools, or other pitfalls?

Hoping for feed-back

Jennice
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Old 13th August 2004, 12:21 PM   #2
SY is offline SY  United States
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Pitfall one- don't trust anything from manufacturers' data sheets for design purposes. You need to measure yourself with your particular drivers.

Pitfall two- you need to measure in your boxes.

Pitfall three- you need to look at on-axis AND off-axis. And you need to know relative driver acoustic center offsets.

Pitfall four- you need to measure impedances.

Pitfall five- you can't use simple crossover calculators unless your drivers are perfect resistor loads. They aren't.

Pitfall six- you have to take into account power handling and distortion, especially for the sort of low crossover frequency you're proposing.
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Old 13th August 2004, 12:57 PM   #3
Jennice is offline Jennice  Denmark
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Thanks for your feedback

Quote:
Originally posted by SY
Pitfall one- don't trust anything from manufacturers' data sheets for design purposes. You need to measure yourself with your particular drivers.


You refer to T/S paramaters, right?

Quote:
Pitfall two- you need to measure in your boxes.
Repeating those measurements, or are you referring to something else? Overall frequency response of the system, using the first X-over attempt, is one of my plans.

Quote:
Pitfall three- you need to look at on-axis AND off-axis. And you need to know relative driver acoustic center offsets.
I can try to cross over before the woofer begins to show too much on/off axis difference, but other than that???
By accoustic centre offsets, I suppose you mean an angled baffle so the voice coils are aligned? (the closest thing to the real centre without getting really advanced?)


Quote:
Pitfall four- you need to measure impedances.
They're part of the manual driver measurements, suppose. I "read" you as saying that I cannot rely on the data sheet impedance of the unit, especially at x-over frequency?


Quote:
Pitfall five- you can't use simple crossover calculators unless your drivers are perfect resistor loads. They aren't.
Are you suggesting some other tool, or the need for plain trial-and-error in the X-over? I know that an active X-over would make things easier and simpler to try/modify as components are cheaper.
I do have access to a 4 channel amp. Would an active x-over be a benefit regardless of design?


Quote:
Pitfall six- you have to take into account power handling and distortion, especially for the sort of low crossover frequency you're proposing.
I suppose that you refer to the power handling of the tweeter (?). This is why I am thinking 2nd order or higher for filter, and a tweeter with fairly large cone area. Am I having the correct considerations, or is it something else?


Thanks-
Jennice
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Old 13th August 2004, 01:14 PM   #4
SY is offline SY  United States
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Quote:

You refer to T/S paramaters, right?
And impedance. And frequency response.


Quote:
Repeating those measurements, or are you referring to something else? Overall frequency response of the system, using the first X-over attempt, is one of my plans.
It's useful to know the frequency response of the raw driver in the proposed box before designing the crossover.


Quote:
I can try to cross over before the woofer begins to show too much on/off axis difference, but other than that???
This is a matter of deciding ahead of time what you want the dispersion to look like (there are several schools of thought here), then seeing if your design meets your goals.

Quote:
By accoustic centre offsets, I suppose you mean an angled baffle so the voice coils are aligned? (the closest thing to the real centre without getting really advanced?)
Angled baffles are one way of compensating for acoustic center offsets. There are other ways, too, but if you don't know what that offest is, you can't design the crossover properly. If you calculate the crossover assuming zero offset, you'll have some nasty surprises in the final frequency response. But if you include the offset in the crossover design, you may find that you don't need to do anything like baffle angling. This is yet another reason why simple crossover calculators are inadequate- you need some actual speaker CAD software (I use an ancient, creaky DOS-based program, CALSOD).



Quote:
They're part of the manual driver measurements, suppose. I "read" you as saying that I cannot rely on the data sheet impedance of the unit, especially at x-over frequency?
You may as well trust a politician as trust a data sheet impedance curve. Every once in a while, they tell the truth, but it's so rare that it's remarkable when it happens.



Quote:
Are you suggesting some other tool, or the need for plain trial-and-error in the X-over? I know that an active X-over would make things easier and simpler to try/modify as components are cheaper.
I do have access to a 4 channel amp. Would an active x-over be a benefit regardless of design?
Active crossovers and multiamping are a matter of debate. I come down firmly on the "yes" side. Watts are cheap and easy these days. I haven't had the opportunity to use the new digital crossover systems, but I would absolutely do that if I were crazy enough to do another multi-way speaker design.


Quote:
I suppose that you refer to the power handling of the tweeter (?). This is why I am thinking 2nd order or higher for filter, and a tweeter with fairly large cone area. Am I having the correct considerations, or is it something else?
That's part of it. So's the tweeter resonance frequency. And the motor design.
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Old 13th August 2004, 07:41 PM   #5
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Hey Jens,

SY is right, and especially with the Peerless woofers, you might as well measure them yourself than believe the datasheet specs. They're good drivers, but the specs are probaly considerably off. This would go for any driver out there. I just had a look at several FR plots of the DX tweeter from different sources, and both show a more severe HF rolloff than the datasheet would lead you to believe. That's why I just changed my mind to use MG tweeters instead (the ones with the 630Hz Fs).

To be more on topic, I have to say that to obtain proper driver measurements, you would need an anechoic chamber. While it is true that driver impedance does give sime indication of peaks and dips of FR, the less severe ones don't seem to show up.

Dmitriy
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Old 13th August 2004, 09:21 PM   #6
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Jennice,

There's enough online resouces to copy someone else's proven project without buying a kit. If you want to start from scratch and are willing to do the extra measurement work, it is possible and you don't need a special chamber to do it. To me in room measurements are much better than what they sound like in a chamber anyway, since that's where you are going to listen to them.

Keep in mind that your ears are the most sensitive instruments available. Once you get your drivers, break them in first. Then give them a listen using test tones and music using an EQ to hear what they do at different frequencies on and off axis. Measure them as well, to graphically see what you heard. Then determine your crossover.

Building speakers is a special blend of art and science, and if you apply only the science you may end up with speakers that don't sound good to you even though they may be perfect graphically.
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Old 14th August 2004, 12:50 AM   #7
extremy is offline extremy  United States
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Exclamation reply for testing items,

I just read about the "jig" for testing. It looks simple, and probably reliable.
This link, Speaker Workshop: the best and how to use it?
Look through the posts, and follow the ones about the "jig", and the ones about the freeware software.

You asked for testing needs. Looks like here's a step above!

I'm glad to see so much high grade interest in this forum.

Thanks again all,
Greg

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Old 16th August 2004, 08:20 AM   #8
Mark25 is offline Mark25  United Kingdom
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Default Would I be able to DIY decently?

Hi Jennice,

Less technical - more philosophical.

Would I be able to DIY decently? YES, in my experience the most important and most forgotten part of DIY is the D, for Do it!

Doing it adds a whole new dimension to the hobby, you could spend a lifetime on here formulating the best DIY, but your priorities and expectations would then quickly be re-arranged by actually doing it.

IMO a more pertinent question is WHY DIY? Challenge, sound quality, individual looking boxes, higher SQ than you can afford commercially, speakers tailored to your music/room, etc, etc. These are all good reasons for DIY. I think it would be helpful to decide what your priorities are for your DIY, and what you want to get from it, before starting.


You could build a technically very good pair of speakers, following all the very good advice offered thus far. Only to find you don't like how they sound because they are voiced wrongly for you/your type of music. This is where kit manufacturers with listening rooms come into their own. You can determine very quickly if the type of voicing chosen by the designer and certain drive unit manufacturers, suits your personal taste or not. This in essence, is the crux of speaker design, there's no right or wrong, just differences according to taste, at any given price/quality point.

Some personal observations about speaker design which may/may not, be interesting to you:

It's almost impossible to have one pair of speakers to suit a wide range of musical tastes. It's far easier and cheaper to have one target musical style for your design.

All the commercial speakers that stick in the memory for one reason or other tend to have been years in the development process.

Actively driven, high SPL, wide bandwidth monsters tend to get a lot more "wow" factor from the non-hi-fi types.

Drivers with a nice gentle roll-off (usually expensive) are easier to integrate into your design. Sometimes it's worth offseting the cost of the extra X-over components and time, against more expensive drivers to start with.

Above all - Have fun.
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Old 16th August 2004, 09:14 AM   #9
Jennice is offline Jennice  Denmark
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Mark,

Thank you for your "alternative", yet interesting post.

In terms of sound quality, do you think I could get better sound for the money by investing my own labour time, rather than buying some complete speaker? The shops have to earn a living, but so do the shops that sell DIY parts. This makes me wonder, if I'm just giving the money to someone else, in stead of saving the money. after all, manufacturers have the financial advantage of quantity.


On another note... What do you think of the drivers I suggested in my original post?

Thanks for the input
Jennice
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Old 16th August 2004, 11:04 AM   #10
Mark25 is offline Mark25  United Kingdom
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Quote:
Originally posted by Jennice
.................
In terms of sound quality, do you think I could get better sound for the money by investing my own labour time, rather than buying some complete speaker? ..........
For ME, Yes. I looked at speakers in Hi-fi shops upto 2000 UKP to find the sound i was after. At this point i decided things were getting silly, so turned to kit manufacturers. I got MOST of the attributes i was looking for in a speaker kit for 550 UKP, (not all, that's why I mention having a target musical style). There is an approach to speaker kits which consists of putting very expensive drivers in simple cabinets. This works for ME, certainly the weakness’ of this approach are benign to MY ears and the benefits enormous. The neutral balance adopted by most kit manufacurers is another advantage for me, over the "boom 'n' tiss" offered by many commercial offreings.

OTOH, there is a school of thought that suggests musical magic is made by the perfect integration between two drivers, *almost* regardless of the driver's inherent quality. Small speakers that are in production for many years, tend to get this aspect of musical reproduction more right than most. Probably those same speakers that took years to develop in the first place!

EDIT: I was going to suggest a couple of great little 2-ways that are great at this IMO (at the risk of getting flamed). However, single driver speakers really lead the way in this respect, so are a good reference, although generally flawed in other ways. I'm even thinking of getting a single driver speaker as an integration reference for my 2/3-way designs.
/EDIT

Sorry i can't be more forthcoming, maybe it would be useful if you suggested a few commercial speakers that "float your boat", or not, as the case may be. Or, start with bargain basement drivers, in a common design on DIYAudio, and tell us what extra attributes you are looking for.



Quote:
Originally posted by Jennice

On another note... What do you think of the drivers I suggested in my original post?
I will leave it to other, MUCH more experienced members to comment on the relative quality of the drivers you have mentioned. There's nothing inherently wrong with either unit though. This guy, Benny Glass , in Antwerp is happy to share his opinion about different DIY drivers though, he's quite positive about the new Peerless range. There are more tips in the actual pricelist.

Good luck.
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