Frugal-Horns Sachiko 8" horn speaker - Nasty dips in frequency response

[jmillerdoc]

Hello,
I am fairly new to high sensitivity horn style speakers, esp these rear loaded horn types. I have been building tube gear for some time now but generally the higher powered PP types of amps. I have recently taken an interest in the DHT / SET low powered designs and am in the process of sourcing parts for a build of the Wilson MK1 300B. I know that this new direction is going to require some different speakers with higher sens. than my current Proac 2.5s and Polk M10 speakers. Because of this I am also planning on building a speaker based on the Fostex 206 series driver. I have been hunting for the "perfect" DIY enclosure but have some serious concerns about the frequency response dips I see inherent in the rear loaded horn designs. The Frugal-Horn website has a perfect case in point. The Sachico has wonderful reviews but I can honestly say that I am skeptical given the response graphs that are shown (Here: http://homepage.mac.com/tlinespeaker...modeled-FR.gif ).

These are some pretty nasty dips that I would find totally unacceptable in the modeling of any 2 or 3 way design I have built or would build. But the reviews.....what about the reviews? They all claim the wondrous sound of these designs.

Well, based on my concerns I am here for some more subjective (and possibly objective) reviews of these speakers....particularly these Sachico horns.

I am also here to ask if anybody has considered or designed an asymmetrical twin path horn like these to where the dips and valleys of one path offset that of the other. It seems to me these dips occur probably near the transition of one cross section/length to the next as the horn unfolds. I am not sure exactly why the dips occur but it would seem to me that if one could design a horn with dips and peaks in a specific place on the freq response curve then another could be designed with the dips and peaks in other places on the curve.

My ultimate question is how would one model it to overlap 2 horns where there is cancellation of these effects. What I would love to do is get some pointers from a knowledgeable person here who could help me design something like this. Specifically, I want to build the Sachicko, at least 1/2 of it, and have somebody give me some estimates of what the other 1/2 might look like. I was thinking of just a trial by error shot at this by building it with one 1/2 exactly as in the plans and then build the other 1/2 scaled a little bit up or down, maybe 15-20%. What I am afraid of though is if I get the scale off too much where I actually place the dips and peaks of one 1/2 right on top of the other 1/2.

Is there a rule of thumb on figuring out what aspects of the horn cause the specific dip? If somebody here where to do what I am contemplating (scaling 1/2 different) what % would you try?

Am I making any sense?

Thanks guys (and possibly gals),
Jeff Miller
Lawton, USA

[planet10]

Jeff,

One of the reasons we are slowly pulling the sims out of the frugal-horn docs is that they are often misunderstood.

In practise those dips are not there. there might be a hint of the 1st big one, but the others dissappear in reality.

There are a couple reasons for this.

1/ the simulation software gets less accurate as the frequencies go up.
2/ when these models were made the sim sw did not take into account the room boundaries (Have a look at any of the BIB sims to see how bad things can sim as far as ripple goes)
3/ this sim was done based on a continually expanding line and does not take into account all of the 'bumps" in the expansion that takes place at every fold. Each one of these acts as a low pass filter (8 of them) which stack together to dramatically curtail HF coming out of the horn mouths. It is the HF combing with the front driver in the sim that causes the ripple.

dave

[jmillerdoc]

So, are there any real time measurements from a mic showing the actual curve anywhere. I did not realize this was a simulation generated curve, I thought it was measured. Where might I see some measurements taken from a similar design.

So, what exactly is the sim simulating, the response at the mouth of the horn or the wave at the front of the driver? Or does the sim somehow combine the 2 wavefronts together to create this curve?

The big dip that occurs at about 250Hz, is this the one you are speaking of that is audible? How many dB down is the real life response at 250Hz?

So, what do you think of the Sachico Dave? Have you had the chance to hear it? Is it really as fantastic as everyone claims it is?

I have access to a CNC in my town of Lawton and was thinking of actually making several sets of these for myself, friends, and family. My cost for set up is $225 then $15 a board, not including material.

I am planning to spend the $125 anyway so, if there is any interest in having some flat packs of the parts for these speakers, I have already spoken with the owner of the CNC and he will be willing to cut and ship some of these around the USA. I imagine the cost for a pair of these would run around $200 to $225 plus shipping for 3/4" MDF (estimate$35 a sheet x3 + $15 a sheet to cut x3, + Bit replacement fee rounds out to be about $15 a set = $165, add a little extra for sourcing the materials and packaging it up $???).

If anybody reads this and is interested in the above, drop me a message. I am not %100 certain this is the design I will end up doing but I feel pretty good about it. Understand, this is not for any sort of profiteering, just letting people in on some fixed startup costs if they think it is worth it or don't have access to a CNC.

Thanks again for the input, now that I know that was a sim I feel much better about it and don't have such a hard time believing the reviews while looking at those tracings.

[jmillerdoc]

I just looked at the Planet HiFI website and had no idea that you guys have already got a flat-pack product for these horns. Please disregard everything I said above, If I go with this design, I will just buy it manufactured. Looking at the prices there it seems it will be more affordable for me to do it that route. I didn't see specifically that the Sachico was offered there but I thought I saw something referencing CAD design so I am sure they could do it. I will investigate further. Thanks again.
Jeff

[jmillerdoc]

Dave, I am reviewing the Planet HiFi website again and it appears you do offer some custom design work. Can these be done by your facility? If so, please PM me, I would like to discuss this further with somebody.
Thanks alot.
Jeff

[planet10]

for 3/4" MDF

Again, making these out of MDF is a waste of time, money, and results. The cabinets were designed expressly for plywood, and you will not achieve what they are capable of using MDF.

If this gets beyond a few pairs you will need to factor in the cost of a commercial licence to the MJK software.

I would encourage you to proceed, but do it right, and don't undercharge. There are lots of gotchas, and don't underestimate the cost & time involved of packaging a flat pack that will be in excess of 6' long.

dave

[planet10]

Somehow i lost the 1st half of my reply... let's try again.

Originally Posted by jmillerdoc

...Where might I see some measurements taken from a similar design....what exactly is the sim simulating

I have not seen any valid measurements for these... to do so, one needs to have the measure mic in the farfield (3 or 4m) and to have any chance of not measuring the room instead of the speaker, that means humping one of these to a big, quiet, flat parking lot with no obstructions.

The sim is of the system. The sims do also give driver alone and mouths alone. The software, at the time, did not account for many details, and did not consider that the horn is bifricated. The designer (Scott in this case) to interpret what is real & what is not, and use feedback from previous efforts to craft a final design.

Scott has simmed literally thosands of configurations and has feeback from at least dozens of real world builds to guide him.

The big dip that occurs at about 250Hz, is this the one you are speaking of that is audible? How many dB down is the real life response at 250Hz?

So, what do you think of the Sachiko Dave? Have you had the chance to hear it? Is it really as fantastic as everyone claims it is?

I have yet to hear a pair so can't speak from personal experience. I do have a set of personal FE206eN set aside for some.

Reports from the field have been almost universally positive. People are sure enjoying them. This is one thread, a search here will find many more.

Further, the response of a speaker in the range of that 1st dip is dominated by floor bounce, so things are much complicated.

I have access to a CNC in my town of Lawton and was thinking of actually making several sets of these for myself, friends, and family. My cost for set up is $225 then $15 a board

I would encourage this, but do be aware that more than a couple sets for friends and family take you to a point where it would be considered commercial and you would need to comply with the use of design terms.

From inquires i know there is demand for a US source of flat-paks. The size of these makes shipping & packaging concerns significant and not having to cross borders greatly simplifies things.

I question $15/board. That implies MDF (which from 20/20 hindsight was your intent). Using MDF for these is a waste. IMO you'd save a lot of money just burning the sheets of MDF before spending the effort to machine & assemble them. You will not get a Sachiko if made with MDF (just something that looks like one)

You want to use a good multiply (the more plys the better). I would expect sheets of Applyply or similar to cost >$100/sheet. It could be made from BB, but that would need some effort to deal with the 60"x60" sheets, likely best to laminate the sides up out of 5 pieces of 12 or 15mm.

dave

[planet10]

Originally Posted by jmillerdoc

I just looked at the Planet HiFI website and had no idea that you guys have already got a flat-pack product for these horns.

Sachiko is not on the list of flat-pak products we do. If asked we would do one for local pickup, but my experience tells me that prep for shipment alone would add something like $200 to the cost. Packing & shipping 15 pair of Frugel-Horn flat-paks was a real eye opener.

We try really hard to keep anything we ship, below 30 kg and under 1m in length.

dave

[jmillerdoc]

I like Baltic Birch. The designs at Fugal Horn actually recommend MDF?!?! This is why I was going to go with MDF, to stay true to the original. If you say otherwise and think ply is better then by all means I will use ply. I had actually given alot of considerateion on how to get a 6ft speaker enclosure out of 5ft square pieces of BB ply...I was going to do this until I read the build sheets a little closer and saw the MDF rec.
With BB I was essetially going to make x2 3ft sections (top and bottom) and splice them together with an external 2ft splicing sheet overlapping 1ft on the top and bottom. I think there is enough square footage to build a pair with 3 sheets if cut properly. I can get BB ply here for about $55 a sheet. I was also thinking of making the internal pieces out of a lower grade ply where they are very short squatty pieces. I wasnt going to buid the stepped taper at the mouth either, just an angled piece. What about using MDF for the first 2-3 turns inside the horn right behind the driver. I would think here the good sonic qualities of MDF might come in handy (ie low resonance).

Well I appreciate the advice about the marketing of these flat packs but I really don't have the desire or time to do this for profit. I was originally just offering cause I figured only the hardcore would find this thread and few people would take me up on the offer....maybe I am wrong.

I am glad to hear that there is no real issue with those graphs in terms of the final sound quality. It makes me want to build them all the more. I am going to plan on building a pair as a prototype using the split design I mentioned spliced in the middle with x2 3ft sections "stacked" together. You aren't joking about the price of high grade ply at 3/4" 8x4 sheets, I recently priced them....from $85 for a decent grade to $130 for a single faced finish grade.

If a person wanted to add a super tweeter to one of these, where exactly would you suggest putting it? Clearly not up on top!

I have to admit that I was kind of excited to try doing what I originally intended by changing the top horns "wave guide" dimensions a little from the bottom to try and offset those peaks and dips. I wonder if there would be any benefit at all from trying to design something like this? Just curious still.

Thanks for the time you spent on your reply, it was well received.
Sincerely,
Jeff

[planet10]

Originally Posted by jmillerdoc

The designs at Fugal Horn actually recommend MDF?!?!

Definitly not.

If there is any hint of that anywhere it needs to be expiunged.

dave