Hestia OB, an ambitious low cost, 3-way OB design

fdandrews · « **Reply #20 on:** 12 Jul 2012, 04:17 pm »

It is interesting that you don't have a second tweeter facing backwards to get dipole high frequencies. What are the tradeoffs involved in using dipole bass and mids but "monopole" highs?

matevana · « **Reply #21 on:** 12 Jul 2012, 05:08 pm »

Quote from: fdandrews on 12 Jul 2012, 04:17 pm

It is interesting that you don't have a second tweeter facing backwards to get dipole high frequencies. What are the tradeoffs involved in using dipole bass and mids but "monopole" highs?

A "true" dipole flat panel may either use a cone type high frequency driver, or a planar driver with it's back exposed, or a 2nd dome facing rearward with it's polarity reversed as you mention. IMO this really comes down to a preference. A true dipole may sound slightly more diffuse with an emphasis on creating natural reverberations. This can offer a pleasing effect, but may also detract from the sound stage due to high frequency directionality. In more extreme cases it is possible to smear the stereo image, but this may be more a factor of the room. I have found that I really love dipole bass and mids, but am less decisive when it comes to high frequencies. I prefer a more intact stereo image that can otherwise be softened by the presence of additional rear wall reflections, etc... but still, many prefer the opposite.

Tyson · « **Reply #22 on:** 12 Jul 2012, 05:19 pm »

Ideally you'd want both a waveguide and an open back on the tweeter, to match the dispersion characteristics of the mids and bass. But highs seem to be less critical to do full OB, especially above 3k or so.

SteveRB · « **Reply #23 on:** 13 Jul 2012, 03:45 am »

How do they sound...?

matevana · « **Reply #24 on:** 13 Jul 2012, 11:48 am »

Quote from: astronaut_glen on 13 Jul 2012, 03:45 am

How do they sound...?

They sound great... better than a pair of OB's I own at 3 times the cost. At $85 per side (all 3 drivers) they are also an amazing value. Their strength lies in the fact that all 3 drivers integrate well, and are well suited for OB. The crossover targets a roll back in an area where the mid and tweeter intersect, and greatly reduces "shout" associated with many systems. This slight dip in the response makes the Hestia sound refined, but not weak in the critical mid range area. The 10" mid has a great power curve and is surprisingly fast and articulate despite it's size. Acoustic instruments in particular are reproduced with proper weight and proportion. They image better than my other OB pair, which are dipole throughout their range.

I am especially pleased with the $16 Vifa D19's, which have been tasked to play below their comfort zone. At moderate levels, I can detect no audible strain in their sound. Oddly enough, this was not the case with other HF drivers I tested, many with a lower Fs. All of the drivers have a fairly polite roll off, so the x/o component count can be kept low. I can also detect no obvious phase issues with the x/o; the polarity of all 3 drivers should be maintained (not inverted) despite the existence of two Linkwitz Riley pairs.

While they excel in reproducing quality recordings, they are also comfortable with more modern music, which are typically recorded with a lot of compression. This is not the case with my former dipole pair, which were almost unbearable with certain types of recordings.

Lastly, I also happen to think they are pretty handsome.

Their sleek footprint is minimalist and they they are unassuming in a living room environment. When you compare them to an H or U Frame, they have a more modern and clean look. For my prototype I built one side in a beech finish and the other in ebony... not sure which I prefer but both look nice.

I am really hoping someone chooses to build them, as I would certainly appreciate the additional feedback! I would be glad to assist where possible.

Plund · « **Reply #25 on:** 13 Jul 2012, 01:42 pm »

Quote from: matevana on 13 Jul 2012, 11:48 am

Lastly, I also happen to think they are pretty handsome. Their sleek footprint is minimal and they they are very unassuming in a living room environment. When you compare them to an H or U Frame, they have a more modern and uncluttered look. For my prototype I built one side in a beech finish and the other in ebony... not sure which I prefer but both look nice.

Matevana,
Great job on your design...I do think in their simpleness, they are sleek/handsome! I am yet to own, or even heard an OB speaker, but am interested. How do you suppose the sound would be affected if the flat/square top of the baffle was modified to instead be somewhat rounded/arched, raising the overall height by an inch or two?

Pete

matevana · « **Reply #26 on:** 13 Jul 2012, 02:39 pm »

Quote from: Plund on 13 Jul 2012, 01:42 pm

How do you suppose the sound would be affected if the flat/square top of the baffle was modified to instead be somewhat rounded/arched, raising the overall height by an inch or two?

Pete

Hi Pete,

You should be fine. Try to keep the baffle width as close to 15" as possible. An increase in baffle height of a few inches should have little or no effect... I would keep the drivers in the same position as measured from the base. A rounded "tombstone" style baffle should look nice! Good idea.

SteveRB · « **Reply #27 on:** 13 Jul 2012, 05:28 pm »

Quote from: matevana on 13 Jul 2012, 11:48 am

While they excel in reproducing quality recordings, they are also comfortable with more modern music, typically recorded with a lot of compression. This is not the case with my former dipole pair, which was almost unbearable with certain types of recordings.

That is so important. When music tastes range from 60's folk and world, garage rock, 70's folk, 90's hip hop, modern rock and remasters.

I'd be interested in building a pair this fall. My summer is a little too busy.

matevana · « **Reply #28 on:** 13 Jul 2012, 06:11 pm »

Quote from: astronaut_glen on 13 Jul 2012, 05:28 pm

I'd be interested in building a pair this fall. My summer is a little too busy.

Sounds good! Keep an eye out for coupon codes from MCM. On occasion they offer 10% or 15% off, and sometimes free shipping. I've seen the 10" mids as low as $23, which is truly amazing, considering they are very well made, with nice cast frame baskets, spring loaded gold terminals, and are very efficient.

Plund · « **Reply #29 on:** 13 Jul 2012, 07:43 pm »

Quote from: matevana on 13 Jul 2012, 02:39 pm

Hi Pete,

Try to keep the baffle width as close to 15" as possible. An increase in baffle height of a few inches should have little or no effect... I would keep the drivers in the same position as measured from the base. A rounded "tombstone" style baffle should look nice! Good idea.

I think the "tombstone" style baffle would be "killer", and wouldn't deviate from the nice, simple design.

Your design goal of keeping the drivers <$50 each (WELL below <$50 each) certainly appeals to the "thrifty" side of me. I'm with the astronaut...need to finish some things up before I can take on another project.

Poultrygeist · « **Reply #30 on:** 13 Jul 2012, 08:34 pm »

Neat project. How bout some rear views?

matevana · « **Reply #31 on:** 15 Jul 2012, 08:22 pm »

Quote from: Poultrygeist on 13 Jul 2012, 08:34 pm

Neat project. How bout some rear views?

Hey Poultry,

Here's the butt shot you requested

Poultrygeist · « **Reply #32 on:** 15 Jul 2012, 09:16 pm »

nice butt

matevana · « **Reply #33 on:** 18 Jul 2012, 05:54 pm »

Here's a few pics of the finished pair w/matching Audio Cabinet.

Poultrygeist · « **Reply #34 on:** 18 Jul 2012, 09:11 pm »

Great effort and no doubt great results. You should be proud.

zipidachimp · « **Reply #35 on:** 19 Jul 2012, 08:52 pm »

any thought about a passive version of this? I have a pair of alpha 10's gathering dust. would need new crossover pair. just finished a new 3-way, OK but no bass, as expected. there's room for me to cut in a 10" in place of my current mid. would look way cool!

matevana · « **Reply #36 on:** 20 Jul 2012, 02:25 pm »

Quote from: zipidachimp on 19 Jul 2012, 08:52 pm

any thought about a passive version of this? I have a pair of alpha 10's gathering dust. would need new crossover pair. just finished a new 3-way, OK but no bass, as expected. there's room for me to cut in a 10" in place of my current mid. would look way cool!

An all passive version using the current drivers would be difficult since the MCM mid woofer is so efficient, at around 94dB @ 1w/1m. As Martin King illustrates on his website, you ideally want your bass driver to start out around 10dB more efficient than other drivers in an all passive design. This would ensure an adequate level match once the crossover is applied. You will not likely find a bass driver that exhibits 104dB efficiency @ 1w/1m in it's requested range of < 90Hz, including your Alphas. This is why I use a separate plate amp; where a proper level match can be achieved w/o taxing your main amplifier.

A decent quality plate amp for this project would be something like a Bash 300, or a Yung 300. Both are cool running class D amplifiers, and periodically go on sale around $100. You basically set them up once and you're done.

zipidachimp · « **Reply #37 on:** 20 Jul 2012, 09:29 pm »

my knowledge of plate amps is nil. more research required. thanks.
can you supply a finished wiring diagram, including the receiver, or point me in that direction? thanks again.

Poultrygeist · « **Reply #38 on:** 20 Jul 2012, 11:36 pm »

Since you're already b-amping, have you considered tri-amping with a separate amp and a simple cap filter for the tweeters and allowing the MCMs to run full range?

matevana · « **Reply #39 on:** 21 Jul 2012, 12:35 am »

Quote from: Poultrygeist on 20 Jul 2012, 11:36 pm

Since you're already b-amping, have you considered tri-amping with a separate amp and a simple cap filter for the tweeters and allowing the MCMs to run full range?

I have not considered tri-amping, only because I feel the cost/benefit isn't quite there with this design. I honestly could not be happier with the mid/high SQ, considering the nominal cost of the drivers.

For the money, I would rather invest in a 2nd plate amplifier and run stereo from 90Hz down. For me that would be the next logical upgrade. In doing so I might raise the lowpass to around 120 Hz depending on the result.