Horn or BVR design help for 3" TB or Peerless drivers - diyAudio
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Old 15th January 2008, 07:09 AM   #1
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Default Horn or BVR design help for 3" TB or Peerless drivers

I'm getting back into the diyAudio and speaker building after a gap of about 15 years or so. I've ordered a few books for my speaker and valve building library, but they haven't arrived yet...

I have an old Westinghouse turntable console that has seen better days and was rescued online from my local FreeCycle group, but I love the way it looks and I want to keep the style, but rework the cabinet to have FR horns or BVRs on the sides that can be enclosed behind the cabinet doors. The console itself will be repaired and refinished or re-veneered, but I do not want to change the dimensions or style of the console.

The interior dimensions of the two side cabinets limit the maximum exterior dimensions of my speaker to 135mm wide x 375mm deep x 680mm tall. If I use 19mm bamboo or birch plywood, I'm limited to a 3" FR driver. If I use thinner 12mm ply for the sides I can squeeze in a 4" driver.

My questions are:

Do I have enough room for a decent FR speaker? I'm willing to sacrifice the low end bass for better, flatter response in the mids and highs. I have room to put a 6-1/2" woofer in the center bottom, but then it's not really a true FR speaker is it? However, I also like the idea of having the low bass being on a separate woofer and amp so it can be turned off at night while the kids are asleep.

Would I be better off using thinner ply for the sides and using a 4" driver, or keeping the enclosure more rigid and sticking with a 3" driver?

My planned source will be a docked iPod running AAC Lossless or WAV files and a CD player. The amp will be a hybrid gainclone on the LM3875 fed by a AD797 based pre-amp design. External DAC may also be built in the future. I don't have plans to use vinyl as a source with this console since my a decent turntable won't fit inside the console. I don't want it sitting on top due to my 2 year old son and the possible outcomes which are for one or both of us!

I realize that I won't achieve the best possible sound out of the speakers due to their location and close proximity to each other and the floor, but I still think they would sound better than trying to build small MTM boxes and a subwoofer. Is this logic flawed? Would I be better off with 3" or 4" MTM speakers since I have room for a 6-1/2" woofer in the bottom of the console?


Thanks!


Here are pics of the console. The shelf in the middle of each side cabinet can be removed to achieve the full 680mm height.




Click the image to open in full size.



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- BMF
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Old 16th January 2008, 01:13 AM   #2
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Very cool freecycling there. It looks like you have room for a subwoofer underneath so I suspect that Planet10 will be able to come up with a WR driver that will work in that context.

I am sure that someone will chime in with a line array solution as the layout just looks right for it. You could probably build transmission lines in there too.

mike
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Old 16th January 2008, 06:46 AM   #3
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Quote:
Originally posted by mashaffer
It looks like you have room for a subwoofer underneath so I suspect that Planet10 will be able to come up with a WR driver that will work in that context.
135mm wide x 375mm deep x 680mm = about 34 liters .... lots of volume for an FE127

The point of a BVR or horn or TL is to get max bass out of the driver. If you incorporate a woofer you can concentrate on getting mod/top right.

12mm material is fine -- especially if use incorporate the existing plywood as reinforcement.

I could rejig a Fonken for that space with room to spare (it would probably only use half the space available)

Probably room at the bottom for at least 2 SDX7 -- you could easily get this thing to do 30-15k plus with midrange of exceptional quality.

I'm sure we could adapt the diyA FR Ref or do up a half-variation on Olivia that might fit if you insist.

dave
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Old 16th January 2008, 06:50 AM   #4
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Thanks. The turntable is actually behind the drawer in the center of the console. I was on Panel Express earlier and they have a bronze annodized finish so I know what color the replacement panel and knobs will be!

I also found an antique radio restoration supplier on line so I can buy replacement grill cloth that will be period correct if I can't get close enough.

You are correct, there is room for the TB 6-1/2" sub and I can probably fit a downward firing 8" or 10" passive radiator, so that was going to be my plan for the sub, at least initially.

I thought a line array of 3" drivers would look really sweet, but then the cost goes up significantly. I'd be willing to look at the design, but I definitely have room to fold a transmission line in that space too. Perhaps a WR foled horn or TL with a soft dome, horn loaded tweeter and slow 6dB slope XC? I'm definitely willing to listens to everyone's opinions and thoughts.

I also need to post pics of my Magnavox mono unit. It has (2) 12" FR woofers stacked on top of each other on the left side of the console. It's going to be converted to a 12" sub and 12" PR with two MTM separates. It will be going in my office since my wife informed me that this Westinghouse console will be going up in our bedroom. She has no idea it's going to have 57 or 68 watts of hybrid gainclone power going to the FR and another 75 to 100 watts going to a sub if it's installed. Heh heh heh.

- BMF
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Old 17th January 2008, 02:33 AM   #5
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Quote:
Originally posted by planet10


135mm wide x 375mm deep x 680mm = about 34 liters .... lots of volume for an FE127

The point of a BVR or horn or TL is to get max bass out of the driver. If you incorporate a woofer you can concentrate on getting mod/top right.

12mm material is fine -- especially if use incorporate the existing plywood as reinforcement.

I could rejig a Fonken for that space with room to spare (it would probably only use half the space available)

Probably room at the bottom for at least 2 SDX7 -- you could easily get this thing to do 30-15k plus with midrange of exceptional quality.

I'm sure we could adapt the diyA FR Ref or do up a half-variation on Olivia that might fit if you insist.

dave

Thanks Dave. I'd rather use the 12mm since I will not changing the width or height of the existing cabinet openings. I'm only willing to remove the center shelf since the speakers would reinforce the console and vise versa.

I definitely want to focus on maximizing the quality of the mids through the highs and use a separate sub. I know I can build a very tight, clean sub for the console in the space available, so let's take that load off the FR since their soundstage width is already challenged by their inherent close proximity to each other.

I only have room for one SDX7 to fire forward through the opening, or were you thinking of having both fire down or isobaric? I have the dimensions of the lower center sub woofer section at home, but I'm traveling this week so I can't post those until Saturday.

I'm still under moderation so I can't send you a PM with a couple of other questions that would sort of take this thread OT a bit.


Hey Mike, where are you located in Indiana?


- BMF
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Old 17th January 2008, 04:27 AM   #6
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1 SDX7 can generate a fair amount of volume, but there are ways to fit 2, I wouldn't want to downfire them.

Even an mFonken variant would get the bass you need out of the sats.

dave
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Old 17th January 2008, 08:43 PM   #7
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Quote:
Originally posted by planet10
1 SDX7 can generate a fair amount of volume, but there are ways to fit 2, I wouldn't want to downfire them.

Even an mFonken variant would get the bass you need out of the sats.

dave
Dave

I sent you an email with my other questions.

I will clean up the console this weekend so I can bring it in to the basement and I'll check to see how difficult it will be to remove the front panel with the single 6-3/4" opening in order to potentially replace it with a new panel cut out to allow (2) SDX7 drivers to fire through the front.

Do the SDX7 sound better in a sealed, PR, or bass reflex enclosure? The data sheets references an application sheet which I could not find on the website.

Would the Fonken design be modified to have two slot ports, one at the top and one at the bottom?

If I use 12mm sides, and run the face the full width of 135mm, then the FR125SR will fit, but it will be very close to the sides of the enclosures, with 8-10mm on each side.

- B
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Old 17th January 2008, 09:33 PM   #8
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Quote:
Originally posted by BoilermakerFan
I sent you an email with my other questions.
Got it, no time yet to give it a proper reply

Quote:
I will clean up the console this weekend so I can bring it in to the basement and I'll check to see how difficult it will be to remove the front panel with the single 6-3/4" opening in order to potentially replace it with a new panel cut out to allow (2) SDX7 drivers to fire through the front.
The ones i've seen, if it has a grill, it is usually a removable and replaceable panel (but even that is not totally necessary to use 2 SDX7)

Quote:
Do the SDX7 sound better in a sealed, PR, or bass reflex enclosure? The data sheets references an application sheet which I could not find on the website.
Sealed or aperiodic. The ap sheet for the SDX7 isn't up yet because i haven't had a chance to do it yet. It will also be a monstor as this is a hugely versatile driver.

Quote:
Would the Fonken design be modified to have two slot ports, one at the top and one at the bottom?
I have done a lot of variation. the theme can be transposed into all sorts of forms.

Quote:
If I use 12mm sides, and run the face the full width of 135mm, then the FR125SR will fit, but it will be very close to the sides of the enclosures, with 8-10mm on each side.
Choice of driver needs to be considered in light of the kind of amplification you plan.

When you are cleaning it up consider the possibility/feasibility of using the existing sides as primary structure. This might allow 3-9mm sides for the sole purpose of creating a sealed/controlled air space and the existing box as the mechanical structure.

With woofer support the size of the side panels can get pretty small. One could even consider ABX pipe.

dave
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Old 18th January 2008, 02:42 AM   #9
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Quote:
Originally posted by planet10


Sealed or aperiodic. The ap sheet for the SDX7 isn't up yet because i haven't had a chance to do it yet. It will also be a monstor as this is a hugely versatile driver.

I have done a lot of variation. the theme can be transposed into all sorts of forms.

Choice of driver needs to be considered in light of the kind of amplification you plan.

When you are cleaning it up consider the possibility/feasibility of using the existing sides as primary structure. This might allow 3-9mm sides for the sole purpose of creating a sealed/controlled air space and the existing box as the mechanical structure.

With woofer support the size of the side panels can get pretty small. One could even consider ABX pipe.

dave
I think 9mm would be the absolute thinnest material in order to ensure enough material for screws or biscuits. Unless I recessed the faces into the side and used a trim molding to finish off the exposed plywood edges, which actually might dress up the console even more. That would require a little deeper recess of the speaker to clear the face of the doors as well. My plan would be to also incorporate a removed grill cover that will be finished on retro cloth to tie it all together.

It will be an integrated unit, so I'm fine with using the sides as primary supporting structure, but I'm not sure how easy it will be to secure all together to avoid vibrations.

I really like the idea of the aperiodic enclosure to tighten up the bass in a smaller enclosure.

The amp for the FR speakers will be hybrid tube amp, either the hybrid design in the January 2008 issue of audioXPRESS or a hybrid tube gainclone built on the National LM3875 or an ST chipamp. The LM3875 is the probable candidate, but I'm researching the reviews of the ST chips. I think I'll buy one of the Parts Express 100W to 200W plate amps for the sub initially, but I might build a better sub amp in the future in the same wattage range. Preamp will be solid state to keep it's size small and allow it to fit in the allocated position where the knob holes are. I might even hardwire the preamp outputs into the amp since it's a dedicate, integrated console. No sense in spending money on interconnects that aren't really needed, I'll just allocate that money to better components elsewhere in the system.

- BMF
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Old 18th January 2008, 03:34 AM   #10
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Quote:
Originally posted by BoilermakerFan
I think 9mm would be the absolute thinnest material in order to ensure enough material for screws or biscuits. ... My plan would be to also incorporate a removed grill cover that will be finished on retro cloth to tie it all together.It will be an integrated unit, so I'm fine with using the sides as primary supporting structure, but I'm not sure how easy it will be to secure all together to avoid vibrations.
Biscuits actually make the boxes weaker, we just use glue to put them together. Ypi'd just want to have enuff material on the sides to hold the glue to attach it to the existing structure. If you go with one of the larger drivers -- FE127 or FR125, i'd be looking to get as much internal width as possible -- one thing we discovered developing the mFonken was that even 3/4 of an extra inch in width made a difference in openess (too narrow the reflections off the inside sides become significant). A smaller driver would give more latitude. (a standard µFonken could actually fi5 in the available space with 4.5mm each side to spare -- gives the possibility of pulling the grill off, pulling the speakers out and setting them a bit further apart for better imaging).

I expect ypu'll need to recess the inset cabs to accomodate a grill anyway (if you need any grill material i may be able to help -- i salvaged a lot and i'd rather give it away than see it trashed)

Quote:
I really like the idea of the aperiodic enclosure to tighten up the bass in a smaller enclosure.
I haven't finished surveying things yet, but a small enclosure for the SDX7 might not actually allow you to fit the driver. To minimize vibrations as push-push arrangement of 2 would be recommended.

Quote:
The amp for the FR speakers will be hybrid tube amp, either the hybrid design in the January 2008 issue of audioXPRESS or a hybrid tube gainclone built on the National LM3875 or an ST chipamp. The LM3875 is the probable candidate, but I'm researching the reviews of the ST chips
I can't get excited about the AXP hybrid, the tubes should be at the front. A Joe Rasmussen buffered 3875 is a really good amp.

Quote:
I think I'll buy one of the Parts Express 100W to 200W plate amps for the sub initially, but I might build a better sub amp in the future in the same wattage range.
One of the problems i've had with some of the plate amps is that the XOs aren't versatile enuff... this is only an issue with the smaller drivers. If you are already building a 3875 i'd just consider building an extra pair of (high voltage) channels for the woofers.

Quote:
Preamp will be solid state to keep it's size small and allow it to fit in the allocated position where the knob holes are.
If you build the buffered GC you really have no need for a preamp (line stage -- phono is another thing)

dave
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