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Multi-Way Conventional loudspeakers with crossovers

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Old 23rd August 2010, 08:51 PM   #1
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Default newb general questions

Hello everyone. I sometimes think or dream about building a DIY speaker. The speaker that I have in mind is a 3way system with a high/mid cabinet and a separate bass cabinet. So I want to try to build the bass cabinet first as a practice object. Just to see and feel how it is to build something. The cabinet is a straight forward box. But there is always a "but". But before I start building there are some thing I would like to know. First the design I have in mind uses a 60liter bass cabinet of 70cm high. So I calculated a cabinet with a 65liter content. The 5liter extra is for the volume of the 10" driver bracing and the port. Now the question is that 5liter extra enough or to much? The vent has a volume of about 1.1liter. Second the design uses a vent of 7cm diameter and 30cm length. The internal depth of the speaker is 36cm. So the distance of the vent beginning of the vent to to front of the speaker word be: (36-30)+thickness of the MDF used. so in total that would be about 8cm. Would this cause any problems? Third does it matter where the vent is placed relative to the driver? Also does it effect the sound if the vent fired to the top or bottom, front or rear? Forth, the first time I will test build something I will use 22mm MDF since that is cheap. If that works out ok. I might use thicker say 30mm MDF for some parts of the cabinet. But I also heard that Birch multi plywood (if that is the correct term) will yield better results. Or I even thought about solid maple although that might prove to expensive. But how much does the building material effect the sound. Fifth I have seen people using very expensive and very cheap caps. Does this really effect the sound so much? The system I am thinking about uses a 120uF cap and those can get pretty expensive. Sixth and last. From what I have seen Scan Speak and Seas are the most popular brands of drivers. I there a big difference in sound between Scan Speak Revelator and Seas Excel Nextel drivers? Or does the cabinet and filter have the bigger influence on the sound. To bad that Audio Technology drivers are to expensive. That is it for now. Thank you for reading and some answers would be great.
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Old 24th August 2010, 03:44 AM   #2
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Hi- questions beget questions . Have you chosen your woofer driver yet? If not, I'd suggest choosing it first, and then designing the cabinet around it. If you have chosen the driver, what is it?

I prefer MDF, as it is self damping. Depending on the power and range of the woofer, you may want to make the front panel a bit thicker than the rest of the cabinet.

Do you have a technical background or a friend who does? Access or own measuring equipment? Have design aid programs for XO and box calculations? Have you read any design guides, like the Loudspeaker Design Cookbook? If no to the above, perhaps a kit or pretested design would be a good starting place.

I have had the best luck with the Extended Bass Shelf alignment. Sloping the back panel, perhaps 10-15% (the bottom of the cabinet is deeper front to back than the top by 10-15% or so) helps reduce standing waves, as does stuffing. I use Acousti-Stuf. Many use an irrational ration for the inside dimensions. I use the square root of 3, 1.732; others like the Golden Ratio, 1.618. So for example, the internal front panel dimensions might be 1 foot by 1.618 feet. This also applies to bracing placement; don't put the brace exactly half way up the cabinet.

I've used the Scan-Speak "Classic" 25W/8565-01 with what I considered great success. (In a 6 cubic foot cabinet tuned to 17Hz.) Very neutral, no overhang. (Unless you quit in the middle of a tuning session, forget, and leave the port mistuned... ) The 21W/8555-00 might be worth investigating...

I feel strongly that good drivers require good crossover components. It's been a while since I've evaluated capacitors and such, and tastes do vary. I like Mills resistors; dubya3 humblehomemadehifi dawt kom (corrected of course) might be helpful on capacitor selection.
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Old 24th August 2010, 06:28 AM   #3
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The driver in question is a ScanSpeak 26W/8861T00. The desgin I might try reproduce is the Jensen-1071 by troelsgravesen. According to his information you can either use a 60 or 80liter cabinet. Due to various reasons among which is WAF I think I will chose the 60 ported version. The rest of the drivers are Scan Speak 18W/8531G00 + D2905/9900. For more info on the system look here. I don't intend to make a DIY a full blown hobby but I do think with a pair of DIY speakers I can get better results then the commercial speakers I currently own. But I'm not 100% sure yet what I will do, so for now I will just try to gather some info.
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Old 24th August 2010, 07:01 AM   #5
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Thank you for the links I did know some of them. The Soup Sandwich is also a speaker I have had in mind. But it's cabinet construction seems a bit complex compared to the Jensen-1071. Also I haven't seen any detailed cabinet drawings of the Soup Sandwich. According to the site the bass enclosure is about 50liter and the mid has about 4liters but I don't know the port dimensions. Another thing I am nor 100% sure of if a down firing port is a good idea. The Soup Sandwich has a down firing port and if the port is only a few mm from the floor wouldn't that have an impact on the sound? But otherwise the Soup Sandwich is a very nice design it seems and I like the fact that is has a serial filter.
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Old 24th August 2010, 08:46 AM   #6
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[QUOTE=mordante;2281253]

1. First the design I have in mind uses a 60liter bass cabinet of 70cm high. So I calculated a cabinet with a 65liter content. The 5liter extra is for the volume of the 10" driver bracing and the port.

4. Forth, the first time I will test build something I will use 22mm MDF since that is cheap. If that works out ok. I might use thicker say 30mm MDF for some parts of the cabinet. But I also heard that Birch multi plywood (if that is the correct term) will yield better results. Or I even thought about solid maple although that might prove to expensive. But how much does the building material effect the sound.QUOTE]

I see that you are in the same position as I am, that is, I'm still gathering both info and the drivers. So far I only have the tweeters. So you will have to take my info for what it is, but it is what I am planning to do myself do to the info I've collected so far.

1. You can get much more exact with your volume deduction. You can put the driver in a plastic bag which you then put in a bucket filled with water up to the rim. Put the driver in the bucket (magnet first of course) until the rim reach the surface. Take out the driver, fill up the bucket again and take notice of how much water you put back, becouse that's the volume of your driver in the box. The volume of the port and braces is straightforward.

4. For the bass box I would chose Baltic Birch plywood and brace it quite extensively. I might consider MDF for the mid/tweet box only due to its greater weight, that I've been told is better for the mid/tweet box. Bass box = stiff, mid/tweet box = heavy. Don't forget that MDF dust is toxic. (Short version).

There are several threads on this forum discussing the merits of various materials if you want to get started on forming your own freference.
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Old 25th August 2010, 12:04 AM   #7
sreten is online now sreten  United Kingdom
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Quote:
Originally Posted by mordante View Post
Thank you for the links I did know some of them. The Soup Sandwich is also a speaker I have had in mind. But it's cabinet construction seems a bit complex compared to the Jensen-1071. Also I haven't seen any detailed cabinet drawings of the Soup Sandwich. According to the site the bass enclosure is about 50liter and the mid has about 4liters but I don't know the port dimensions. Another thing I am nor 100% sure of if a down firing port is a good idea. The Soup Sandwich has a down firing port and if the port is only a few mm from the floor wouldn't that have an impact on the sound? But otherwise the Soup Sandwich is a very nice design it seems and I like the fact that is has a serial filter.
Hi,

i'd guess most details are in the "soup ceramique" and rather than
repeating infrormation some details are described in the other designs.

rgds, sreten.
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Old 25th August 2010, 01:56 AM   #8
tinitus is offline tinitus  Europe
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It seems there have been a change on his site, regarding cabinet drawings

my guess is you may have to contact Tony Gee
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Old 25th August 2010, 06:40 AM   #9
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I already contacted Tony for the drawings of the Soup, I now have the drawings of the soup ceramic. The cabinet as I feared is rather complicated but according to Tony if I keep the baffle with more or less the same I can change the cabinet. Also I prefer not to have the port at the bottom, if If I move it to the side I need to add about 10% of the length. The Soup Sandwich port is 140mm so that will be 154mm. So if I make a ported cabinet with aprox 50liter internal volume and a 75*154mm port I should be ok. The mid and tweeter are in a 4 liter closed cabinet. That still leaves the question. How would a Tony Gee Soup Sandwich compare to a Troelsgravesen Jensen 1071. As far as I could determine the total costs for the units is about the same.
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Old 26th August 2010, 08:50 PM   #10
sreten is online now sreten  United Kingdom
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I doubt anyone has built both and compared them, Soup appeals to me. rgds, sreten.
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