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Old 4th March 2008, 10:22 PM   #131
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Default To American Elsinores

Could someone tell me where you bought your felt? Also what type of felt it was.

I googled a few potential sources, some with lots of different types of felt. I found it difficult to determine what kind of felt is the correct type to use for the Elsinore.

Thanks in advance.
Francois
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Old 5th March 2008, 01:34 AM   #132
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Default Re: To American Elsinores

Quote:
Originally posted by Francois G
Could someone tell me where you bought your felt? Also what type of felt it was.
Your good for felt in the US. Try the SAE F 13 type from:

http://www.mcmaster.com/

(Type in felt in the search bar and you'll get a wide range of choices).


Now my question is where in the heck do you find quality natural wool felt in Europe?
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Old 5th March 2008, 07:36 AM   #133
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Default design point

I have read the design pages thru several times and I dont think I have seen mention of why the drivers are vertically spaced as they are.

I'm just trying to understand principles here, not argue how a speaker should be designed, but given the attention paid to the timing from the mtm center to ear vs the lower woofer, why might one not mount the drivers vertically closer to one another to reduce the phase variance between the bass and the midranges?

Is this part of diffraction control?
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Old 5th March 2008, 01:05 PM   #134
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Default Re: design point

Quote:
Originally posted by mantraxl
I have read the design pages thru several times and I dont think I have seen mention of why the drivers are vertically spaced as they are.

I'm just trying to understand principles here, not argue how a speaker should be designed, but given the attention paid to the timing from the mtm center to ear vs the lower woofer, why might one not mount the drivers vertically closer to one another to reduce the phase variance between the bass and the midranges?

Is this part of diffraction control?
It is such an open-ended question, in fact several of them.

Why did they, when they designed the DC10, put the third engine in the tail, why do some planes use two and others four engines. To quote the best book ever written: "Does not the potter not have authority over the clay?"

You have to find a way to make the many parts act as a whole, that is the measure of success.

Diffraction? Yes, that is part of it for sure. I have been asked why I haven't made the box narrower and I generally answer that it is a compromise - one that involves other not so obvious issues. I appreciate you saying that you have read the pages several times, but not everything gets translated into those pages. A dialogue face to face can only overcome those shortcomings.

But I will try: I wanted to make a design where the box was as simple to make as possible, and that is a complex problem in itself. A kind of paradox. Arguably the bottom part of the front panel should ideally be curved or angled towards the listener. That would fix up some timing issues - not walking away from that. But the top three drivers forming the MTM needs to be vertically aligned and near equidistant relative to the listener. Such a box would be doable for a manufacturer. But DIY?

But what would be gained? Would it be commensurate with the added complexity? I don't think so. How do I put it? This is a 2 1/2 Way system. The bottom two drivers are rolled off starting very slowly from about 200Hz and the effective centre where the acoustic output becomes the same as the M(notT)M array is near 400 Hz. The timing issues are minimal due to the long wavelength and also the four drivers are acting within their piston range. So where does the timing issue become serious? Here is the curious thing, it is not the bottom drivers as a block that is the issue but the difference between them within the block. There is very little time difference from the bottom of the MTM and the third 6.5" driver from the top. It is between the third and fourth. Do you follow what I am saying. If you look at the pages you will see that at 2 Metre acoustic measurements this shows us as a major dip at 4KHz. As I listen to speakers near 3 Metres, the dip then becomes 6KHz.

See graph where BLUE is the combined response of the M's in the MTM array, and RED is the combined response of the bottom two drivers. GREEN is the port. These are RAW measurements in the box, no crossovers.

Click the image to open in full size.

But the dip is negative and is then way down by the time we get near the point/the frequency where the timing issue becomes significant.

www.customanalogue.com/elsinore/elsinore_7.htm shows the actual physical differences - see where it says "Maintaining Phase Info During Measurements."

When we look at the two bottom drivers, their purpose is to fill in the Diffraction Loss and the main 9mH inductor controls that. By the time we get high enough in frequency, they have done their job and the timing issue has subsided.

Click the image to open in full size.

5dB/division. At nearer to 3 Metre listening, it is improved even further. The dip will be near 6KHz and even further down in the mix and the 5.5KHz peak shown virtually disappears. The timing error is now inconsequential.

The layout of the drivers also has to take into account my preference for a vertically aligned array that has lateral symmetry. Then there is the problem of physical rigidity and strength of the front panel. Make no mistake, the front panel needs to be the strongest part of the box. Easy, right? Wrong! Those damned drivers, why do we need to cut holes in a lovely strong front panel? Wouldn't be nice if we didn't have to cut those damned holes. But we must. I know this is the bleeding obvious, but how do you deal with it? The best you can and the best methods you can think off. I claim no more.

Then there is the desirable need to drive the column within the box without causing a vertical 'pipe' resonance. The internal height versus the second largest dimension (depth) is about 3:1 - hardly near the Golden Ratio. But driving the line from several points (4) along it length (in this case the height) is very effective. Actually lumping the drivers close together and you loose the effect. And how does it affect the rigidity of said panel. What changes to your technique is now required. A change of material? Carbon Fibre? Or High Density Fibreboard - HDF. Simple DIY? See what I mean?

Then there is something else in the box that is difficult to define scientifically. Most so-called reflex/ported boxes are lined and not filled with absorbent material. You will note the Elsinore does not line the box in an conventional way. The volume in front of the internal brace is lined on its sides and inside the top, but not the bottom. The volume behind the brace is filled, not lined.

This is, over a period of time, achieved experimentally rather than any scientific formula. It introduces a certain 'resistive' element into the alignment, similarly to TL (which this isn't). Note too that the vertical air velocity is different at the back of the box (slower) than the front of the box (faster). Combined this with the distribution of the drivers and certain desirable characteristics are achieved audibly.

Now even the port location becomes important as well. Note again that it pokes into free air of the front of the box, even if mounted from the rear. The approx 90mm diameter just happens to contribute to the correct length and the correct tuning frequency. So you can see that internal air flow has had a lot of attention made to it.

Many have commented on the sheer quality of the bass emanating from the Elsinore boxes. It has depth and power and the ability to get that bass out of the box. I am very proud of that and I think justifiably so. It is the way the box is put together and much experimentation over many years. Indeed the split acoustic character of the box was invented by a renowned acoustic engineer, my late father.

I am not sure if the above has answered your question, but hopefully illuminated it. Clear as mud?

Joe R.
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Old 5th March 2008, 01:36 PM   #135
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Default Thanks Re: Felt for American Elsinores

Quote:
Originally posted by ShinOBIWAN

Your good for felt in the US. Try the SAE F 13 type from:
Thanks ShinOBIWAN -- just what I needed as beginner Elsinorian. I assume you chose the adhesive backed felt, or does that interfere with the acoustical purpose.

Thanks,
Francois
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Old 5th March 2008, 02:24 PM   #136
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I guess you could argue that the adhesive backed version might alter the effect of the felt but I'd imagine it to be negligible at best.

BTW I'm looking at felt for another project rather than the Elsinore.
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Old 6th March 2008, 02:31 AM   #137
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Quote:
Originally posted by ShinOBIWAN
I guess you could argue that the adhesive backed version might alter the effect of the felt but I'd imagine it to be negligible at best.

BTW I'm looking at felt for another project rather than the Elsinore.
Being adhesive should not be a big problem - the adhesive side makes contact with a part of the other felt which is not exposed. It is really the shape that is more important than anything else and it helps the the exposed surface part is nice decent felt. So if that is what you can get, so be it.

Joe R.
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Old 6th March 2008, 05:07 AM   #138
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Very helpful information, thank you. The latter half of your post, re: baffle strength and pipe resonance were exactly the information I was looking for.
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Old 17th March 2008, 09:29 PM   #139
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I must say that I find the design of this speaker, and the narrative of the thought process behind it invaluable in learning the considerations to be made in loudspeaker design. I can honestly say that the reading and rereading of it, and the tangents it has sent me on has given my largest single educational benefit in this hobby.

My hat is off, Mr. Rasmussen!

I have one question to ask in the interests of picking your brain further:

You have said that there were a number of simplifications or mild compromises in the design in order to control cost and simplify construction for the DIY community. IF you were designing wiithout the consideration of ease-of-construction, what are some areas of the design in which you might be tempted to get more adventurous?

Thanks again.
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Old 17th March 2008, 10:25 PM   #140
Peter N is offline Peter N  Italy
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I was thinking to put screws for the front baffle from the inside of the box cause it's better looking, is it a good idea?
I would do it because I don't have the countersunk tool and so if I tried to screw them too deep I risk to split the wood... or there is always the hammer to push down the screws...
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