The time is now, We should build A speaker FRD data Base

[wintermute]

Then the idea of using Holmimpulse for doing DIY is useless is what you are saying, yet many say it is great, but the information is of no value.

I don't think anyone is saying that at all. It is invaluable for doing measurements for your own circumstances once you get to the point where you can make reliable measurements.

What it won't do is give you a reference of how well any particular driver will perform in a specific design scenario, except the scenario under which it was tested. If that is generic (to aid in having "comparable") results, then some speakers might perform well in the generic config, but others may not, which may make some drivers seem to be unsuitable when in fact the opposite is true. This is no different to what manufacturers measurements often tell you. Provided that is understood, then I see no problem with the proposal to have a design database, but I don't believe it will tell you is that driver X will be better than driver Y for any particular purpose. It might tell you that driver X will be easier to use than driver Y or will be more suitable to pair with Driver Z however

In the end to design an optimal crossover, measurements in your own boxes will be necessary (this goes for impedance measurements of the woofers/midbass' as well).

Tony.

 

[gedlee]

There are ways that a generic setup could be used in a simulation package for an arbitrary configuration. That said, the techniques are beyond the scope of anything that a DIY could do. But it is possible. What you suggest above is far more practical. In fact thats the way that I do it.

 

[mcmahon48]

It would just make sense since

Everyone is looking for the behavior of many speakers that don't have a graph in print by the manufacturers. If we get an acceptable means of getting a data base going That has a good system for measuring developed by the DIY community, it would help others in making their decisions.
There are so many speakers available yet with no graph to help in deciding the feasibility of using that speaker For Example Same Speaker, but from 2 different well Known vendors.

From PE

Sealed back midrange eliminates need for separate enclosure. Features treated paper cone, paper surround, and steel mesh grill. *Power handling: 40 watts RMS/55 watts max *Voice coil diameter: 1" *Impedance: 8 ohm *Frequency response: 800-8,000 Hz *Fs: 470 Hz *SPL: 89 dB 1W/1m *Dimensions: Overall Diameter: 5-1/8", Cutout Diameter: 4-1/8", Mounting Depth: 2-1/2", Magnet Diameter: 3-1/8", Magnet Height: 3/4".

From Madisound

5.25” Midrange
Closed Back
10 oz. Magnet
Hi-Temp .75” Voice Coil
Rolled Foam Edge
Protection Screen
50W/RMS
92dB
550-15,000 Hz
8 Ohm
Outside diameter: 5-5/32" (131mm)
Minimum cut out hole diameter: 4" (103mm)
Depth: 2" (51mm)

now it be nice to see the graph, Yet the manufacturer does not have a graph

 

[mcmahon48]

which one would you be more like to choose based on the given information on each

Definitive Technology BP2000 6.5" WOOFER p/n W2A - eBay (item 180414513552 end time May-29-10 12:29:14 PDT) Well known Brand and Great reviews on almost all their speakers but not specs

6.5" Sub Woofer Poly Cone - SINGLE- NEW - eBay (item 310220549228 end time Jun-15-10 07:31:22 PDT) No name brand with T/S and no graph

Major Brand MW5530 Woofers 5 1/4" - 4 ohms New - Pair/ - eBay (item 250632987852 end time Jun-13-10 09:02:06 PDT) Well known Brand with T/S spec and Spl spec for 1w/1M

Parts-Express.comeerless 830657 6-1/2" Paper Cone SDS Woofer | Peerless SDS 830657 6-1/2" Woofer bass mid midbass mtm coated cone 2-way tymphany09
http://www.parts-express.com/pdf/264-1088s.pdf
Well known brand with T/S and graph of general behavior

 

[doug20]

1) a practical minimum is about 1 meter, but the optimal distance depends on the specifics of the room. The hardest to control is the floor - thats why you need a stand and if you are going to make a stand then why not let it rotate.


4) you simply cannot surpress reflections to the point where they are not a problem. You have to use gating so you need to have both the mic and the speaker as far away from anything reflective or diffractive as possible. But this isn't hard - just move the furniture out of the living room like I do.

Why not have free standing DIY sound absorbtion panels? 6" thick using OC703. That will tame any early reflection down to even 100Hz in rooms where there might be issues. The pannel can lay down in front of the speaker too and you just need to have the speaker up 3 feet or so.

I do have a question about mic placement. Generally they say it should be between the tweeter and the woofer but if we are design speakers for our own specific use then maybe the mic measurement height should be equal to what your listening height will be with respect ot the speaker? Its amazing how speakers sound different when you are 6' 3" vs someone who is 5' 7"....Responses change by moving the mic up only inches.

I design for the ear height while sitting in my HT room, I want the response to be perfect for that level (Especially if its my ribbons with their vertical issues).

 

[Loren42]

Just a reliable T/S database would be a big help and a lot easier to implement.

It would be an easy first step and can be expanded later to include frequency responses (on and off-axis), impedance, and anything else a contributor might want to include into the database.

Just a thought.

 

[Robh3606]

I do have a question about mic placement. Generally they say it should be between the tweeter and the woofer but if we are design speakers for our own specific use then maybe the mic measurement height should be equal to what your listening height will be with respect ot the speaker? Its amazing how speakers sound different when you are 6' 3" vs someone who is 5' 7"....Responses change by moving the mic up only inches.

That's a great question and I have wondered about that myself. FWIW I tend to stick with on the tweeters axis. Usually the tweeter is the closest to ear height depending on how large your speaker is. One thing for sure though is whatever reference point you decide on you should stick with it. When I am getting ready to run a measurement set for a crossover I do it all in one shot. I don't move the set-up at all until I am sure I have all the info I need. I will then document distance and height of the microphone and well as location of the speaker in the room. That way at least I can get a second set-up reasonably close to the original.

When it's all done I take measurements in a "listening window" to see how things look and then average them.

Rob

 

[gedlee]

Why not have free standing DIY sound absorbtion panels? 6" thick using OC703. That will tame any early reflection down to even 100Hz in rooms where there might be issues. The pannel can lay down in front of the speaker too and you just need to have the speaker up 3 feet or so.

Design height is a factor - you have to decide what it is, but it can be whatever you want as long as you are consistant.

I have done a lot of measurements in my day - contrary to what you might have thought, and lacking a "pit" for infinite baffle, which is not very practical at all, the next best is a nice sturdy well rounded closed box. Anything else is very hard to define the effect, A closed box with well rounded edges is very very nearly a sphere and the sphere is the only reasonable shape for which simple analytical solutions exist. Use the box and assume a sphere and you will be fairly accurate. Anything else and you are just guessing.

As far as measurements go there is no such thing as "absorption". I use foam and padding some two-three feet thick on the floor between the mic and the speaker and I can still see the reflection. 6" panels are basically nothing.

 

[doug20]

As far as measurements go there is no such thing as "absorption". I use foam and padding some two-three feet thick on the floor between the mic and the speaker and I can still see the reflection. 6" panels are basically nothing.

really? the data says that 6" of 0C703 gives 100% absorption of the soundwave down to 125Hz...that means no reflection. Foam isnt really useful for real absorption.

http://www.bobgolds.com/AbsorptionCoefficients.htm

its the biggest reason I love my custom room. the Reflections are almost completely controlled.

 

[doug20]

Thanks Dr. Geddes and Rob on the meaurement height opinion.

I just built some waveguides that I used the center axis as the design point but listening to them had me adjusting everything. I realized I should have just measured based on the speakers position relative to my listening position. They are just for me anyways.

 

[gedlee]

really? the data says that 6" of 0C703 gives 100% absorption of the soundwave down to 125Hz...that means no reflection. Foam isnt really useful for real absorption.

My comments are based on actual measurements of testing situations - not on some manufacturers data sheet. No absorption is 100% for all angle of incidence, except an open window, and even that is reflective if the wavelengths are the size of the window. NOTHING, I repeat NOTHING is 100% absorptive in all situations.


Unless you actually test the situation you don't know how its working.

 

[doug20]

My comments are based on actual measurements of testing situations - not on some manufacturers data sheet. No absorption is 100% for all angle of incidence, except an open window, and even that is reflective if the wavelengths are the size of the window. NOTHING, I repeat NOTHING is 100% absorptive in all situations.


Unless you actually test the situation you don't know how its working.

I agree but My measurements are improved when using the panels. Have you ever measured OC703 effectiveness?



btw, that link is well used and has been confirmed many times by 3rd party measurements. I didnt post as a manufacturer data sheet, I think someone like Bob Gold, didnt just summarize a bunch of manufacturer specs without some sort of confirmations.

 

[gedlee]

Some disparancy between the data shown on http://www.owenscorning.com/comminsul/documents/Fiberglas700Series.pdf
but at any rate HF absorption is unnecessary because gating works fine. Where absorption has some benefits is < 200-300 Hz and even the stuff at 6" is not good enough .9 is only 20 dB down - still an influence. But 6" on top of my 12" of foam might work well. The foam is much better at LF than the glass, which is better at HF. But, as I said HF is not the issue.

 

[doug20]

Thanks, I didnt know that foam is much better at LF.

 

[Loren42]

Some disparancy between the data shown on http://www.owenscorning.com/comminsul/documents/Fiberglas700Series.pdf
but at any rate HF absorption is unnecessary because gating works fine. Where absorption has some benefits is < 200-300 Hz and even the stuff at 6" is not good enough .9 is only 20 dB down - still an influence. But 6" on top of my 12" of foam might work well. The foam is much better at LF than the glass, which is better at HF. But, as I said HF is not the issue.

Where does the reflection occur? Does the LF wave travel through the foam obliquely and then reflect off the floor surface and return through the foam again?

If that is true, then the wave is actually traveling through much more than the thickness of the foam itself.

 

[gedlee]

By its nature, absorption material must be a different density than air. This yields a different impedance than air. Whenever sound impinges on an interface between two different impedances there will be a reflection. How much reflection depends on many factor and is identical to the prism problem in optics. There is a single angle at which there is total transmission. All other angles reflect.