New Project, Peerless HDS/Vifa

[gmed]

Few years ago I made a HT system using Peerless HDS PPB 6.5" Midwoofer and Vifa Tweeters and PE 0.75 cf MTM enclosure. I really wasn't happy with the sound, since I chose an enclosure that was too large for one HDS woofer, and I always wanted and MTM for HT.

So I finally started my modification of the speakers.
In this new system, Im using the same enclosures, sealed, 2 HDS woofers and I am using the Vifa BC25SC55-04 tweeter in a time alignment manner. I have not gotten to the XO yet. That is my last step.

I have built new baffles using baltic birch plywood, that I had my shop in WI CNC them. Didn't cost a lot.


old version


New version. In the picture, I used the SLS 6.5" just for visual. That is going to be used in a 1.0 cf PE enclosure , WW, and is going to be going under the MTM as a stand.

The process of making the Time alignment flares. Two baffles, one scrap, sandwiched together using nails and 1" round over bit.


The baffle is made of 0.75" and 0.5" BB plies, sandwiched together.
The hole on the 0.5" ply is made using a flush bit, cloning the hole on the 0.75" ply done with CNC router.


The baffle is still not finished. Im going to chamfer the back of the holes and do a 3/8" round over of the corners.

More to come soon.

[Johnloudb]

Really nice work!!

Would you recommend Baltic Birch over say MDF.
I'm now starting to design baffles for my OB dipole speaker that I've been contemplating for some time. I'm not sure what wood to use. But, that wood you're using would be strong, and looks nice and easy to finish?

[gmed]

I think MDF would be a better material, but since Im using a sandwich of 2 layers, I believe it should be enough. The other reason is the finish. I love the look of BB plywood. sand, seal and poly.

[gmed]

Almost finished with the baffles.

[HareBrained]

Looks like a good start for the upgrade. Just a quick hi-jack, what's your opinion of the SLS 6.5 (830946)? They're one of the opinions I'm considering for 350Hz and down.

[gmed]

I still haven't used them. Very affordable though! I cant wait till I try them.
This isnt what Im using for this speaker system. Im using the HDS. The SLS is making up the sub, which is going under the MTM.

[HareBrained]

I still haven't used them. Very affordable though! I cant wait till I try them.
This isnt what Im using for this speaker system. Im using the HDS. The SLS is making up the sub, which is going under the MTM.

I knew you were using the HDS, I was just hoping to gain a little insight. Thanks for the reply.

[gmed]

speakers almost finished.

[juliovideo]

Excellent !! :T ................. congratulation






''''''''''''''''''''''''''''''''''''''''''

[Smokinghot]

2 HDS woofers and I am using the Vifa BC25SC55-04 tweeter in a time alignment manner. I have not gotten to the XO yet. That is my last step.


The process of making the Time alignment flares. Two baffles, one scrap, sandwiched together using nails and 1" round over bit.

Curious if you have, or are going to have an A/B comparison of the Vifa response before and after the use of the flare...?

I'm considering something similar in an upcoming project for sake of time alignment, but have concerns in regards to internal reflections within the flare hurting the response.

[johngalt47]

Finish?

What did you use to put a finish on the plywood?

[gmed]

no comparison. Being a scientific guy, I realize there are things that are theoretical and there are things that are noticeable to you. I just do not think the human ear is capable of making out these differences. I mean if I do a double blinded test, i dont think anyone will be able to tell the difference! I may be wrong. I mainly did it for the cosmetics, and maybe a little because of the theoretical reason. I was looking for the challenge of building it this way.

to answer your question about the polyurethane, I used the hand rub on poly. All you need is a clean rag. I cut them up in 1"x2" pieces, once I used them for each layer, i throw them away. I wait 24 hours, lightly sand using a 1000 grid sandpaper, then put the subsequent layer.

for the final layer, I used 2000 grid, but i think 1000 works just as well

[jwr]

Hi gmed, I am not sure if you realise it, but you have created a horn loading. I am pretty sure that is going to have a big effect frequency response and give the tweeter a big boost in output. Normally the difference between a flush mounted tweeter and non-countersink is something that is very obvious when measurement system is used. But that is something that might not be audible in many designs. In your case I have no doubt that it will be audible.

The tweeter response is likely to have a peak in it. I have seen a design where this type of horn loading was used to work as part of the crossover. I think the design I saw only used a first order network to act as filter and equalisation. I think you will need some type of basic measurment system to get this one sorted out.

John.

[jwr]

I found an example of horn loading here:

http://www.zaphaudio.com/hornconversion.html

[minkuni]

Most likely this "horn loading" will not have a response quite as nice as Zaph's waveguided tweeter. I did a similar thing on some compact speakers I built for a friend. The hornloading I did consisted of routing a hole big enough for the dome through the 19mm MDF baffle and then adding a 19mm radius/flare. The effect was a relatively sharp peak (Q around 2) of 5~6dB around 2500Hz if my memory serves me right. A notch (bandstop) filter would be necessary to make it nice and smooth, a simple first order filter would not have been enough.

Since the shape of the horn loading is slightly more irregular in this case it is a little harder to predict the effect on the response. Looking forward to seeing the measurements! :T

[---k---]

Dan took a lot of measurements of different "flares" on the tweeter for his latest project. His measurements showed significant differences between a flush tweeter and a 3/4" roundover, and even 1/2" roundover in his Bassline design.

See starting here: http://www.htguide.com/forum/showpos...&postcount=308

[Smokinghot]

The real screwy part will be the response on the CC. Gmed did say that this for his HT. So unless he's one of the few that actually can have his CC placed vertically, his CC's tweeter will sound different than both the L/R.

His off axis tweet response will be quite different.

It's unfortunate he doesn't plan on doing any testing. I'd be very curious to see an A/B of the speaker vertically vs horizontally.

[jwr]

I agree the results aren't going to be as nice as the one on Zahp's site or those posted here:

http://www.htguide.com/forum/showpost.php4?p=421279&postcount=308

The results with the 3/4" recess on the link above, look promising for a 2kHz xo point with a very low-Q second order network. In the Gmed's case, the horn cut off is probably going to be much lower due to the larger size of the horn and it may not work in his favour.

[gmed]

actually Im planning on using the CC vertical just like the LR. I wish I had the means of measuring them. If anyone in San Diego area has the means, let me know.

as far as the sound, they are amazing, at least to my ears. I went with sealed simply because I was trying to work with what was available, and for using the Dayton enclosures, based on the calculations, pretty much my only option was to go sealed with two woofers. Besides, Im going to be using a sub so low frequency output isn't that important, but considering it is sealed, I still get good bass response.

[gmed]

Does anyone think there will be noticeable difference if I place the CC horizontal? Since I had them cut with CNC, I just made one plan and didn't think about this. I actually realized today as you guys brought it up. If I can place it vertically, Ill be OK, but if my theater doesn't allow me, then oh well.

btw, my recess is slightly less than 3/4".

[Dave Bullet]

I'd be worried about the diffraction ripple of the surface mounted woofers on the response. You'll probably get worse power response (= drooping off-axis) with the countersink like that.

I would personally build a hack baffle out of MDF and take some measurements to see the effect of the mounting on the diffraction ripple. Flat measurement isn't a pre-requisite to a nice sounding speaker, but you are severly limited in dealing with diffraction ripple with a passive crossover. Felt treatment and roundovers are about all you have in your arsenal.

Personally - the baffle design and crossover go hand in hand. I would never design a speaker without considering both at the same time.

I presume you will be taking actual measurements?

Sorry if I sound negative... just trying to forewarn you of any problems you might have and the options you might be left with for dealing with them.

[Smokinghot]

I presume you will be taking actual measurements?

actually Im planning on using the CC vertical just like the LR. I wish I had the means of measuring them. If anyone in San Diego area has the means, let me know.

... :W

[gmed]

As I mentioned before, true test is always the human ear, not a measurement, and Im pretty darn happy with the sound. For me performance is not measured by what the graph shows me, but whether I like the sound or not. I know a lot of people here get into measurements, simulations, etc., but in actuality, How many people will be able to tell between two designs in a double blinded test? I dont think many of us.

I know its not the same thing but In medicine, a lot of things were done based on theory, and every day things are changing since we simply can not find a lot of difference based on evidence.

[Smokinghot]

I know its not the same thing but In medicine, a lot of things were done based on theory, and every day things are changing since we simply can not find a lot of difference based on evidence.

ah... not that I want to be arguementative but... isn't lab testing done to a great extent before submitting new procedures/drugs to human exposure...?

:W

You're right of course...if it sounds good to you, then why bother. To ease you're own curiousity though (and mine ). Why not just play around with one of your enclosures. First vertically, and then horizontally... post back your impressions.

I for one am interested if it's audible.

[gmed]

I sure will.

I wasn't referring to drugs but more medical practices.

[JonMarsh]

As I mentioned before, true test is always the human ear, not a measurement, and Im pretty darn happy with the sound. For me performance is not measured by what the graph shows me, but whether I like the sound or not. I know a lot of people here get into measurements, simulations, etc., but in actuality, How many people will be able to tell between two designs in a double blinded test? I dont think many of us.

I know its not the same thing but In medicine, a lot of things were done based on theory, and every day things are changing since we simply can not find a lot of difference based on evidence.

There's things like this in audio, too, but it's generally because people are changing things that don't have much bearing on matters, just moving laterally, not up or down in performance, AND, there may be other factors in the system limiting performance.

Something to think about...