Dennis Had Inspire Amps

[Musica Amantem]

Originally Posted by Analog Addict

Well, I don't purport myself to be a speaker expert, although I have a fair amount of hard won knowledge in the Altec realm. Anyways, to the best of my understanding, OB speakers have the advantage of the dipole effect, at least in any driver that's open to the rear as most woofers are. I have a set of Infinity RSIIb's that also ports some of the EMIT/EMIMs to the rear as well. They require placement away from walls to sound their best. Here's a nice summary from the Linkwitz Lab website

Open baffle speakers are inefficient in terms of the mechanical movement that is required to create a given level of sound. This not only applies to speaker cones but also to panel vibrations.


•Open baffle loudspeakers reproduce bass with less room interaction. It is more articulate than from box speakers.


•If dipole behavior covers the full frequency range, then the room response becomes perceptually masked by the direct sound.


•The radiation from the rear of the cone must not be absorbed, but the distance to the nearest reflecting/diffusing surface should be at least 3' (1 m).


•An open baffle circumvents the box problems of delayed radiation through cone and enclosure panels. They occur typically in the mid-frequency range and are difficult to suppress.


•Large panel radiators or long line radiators suffer from severe lobing at higher frequencies. It manifests in critical room and listener placement.


•Even though a dipole requires a 6 dB/oct boost towards low frequencies, it takes little power to drive it to maximum excursion at its lowest bass frequencies. Amplifier power could be an issue as frequency increases, where it requires higher cone acceleration to reach Xmax. Thus SPL is limited by driver volume displacement at the very lowest frequencies and becomes amplifier limited as frequency increases.


•Realistic bass levels can be obtained from dynamic drivers in open baffles, not from panels. For extreme SPL requirements the number of drivers could get very large and, therefore, below 50 Hz they are more economically replaced by sealed box subwoofers.


•At frequencies where a 8" driver would become directional it has wider frontal dispersion for an open baffle than if the baffle were closed in the back.


•Open baffle speakers reach deeper into the room and are less subject to the room response if their polar response is well behaved.


•ORION exemplifies open baffle loudspeaker design in terms of polar response control and dynamic range. It circumvents the limitations of large panel radiators and yields a small package.


•The low masses of the moving parts in an ESL, a planar magnetic, or a ribbon driver are necessary to generate useful sound pressure levels. The force generated by an electrostatic or planar magnetic motor is weak. Since SPL is proportional to air volume acceleration, and moving parts Acceleration is Force divided by Mass, the mass has to be lower if the force is too weak to generate sufficient acceleration. Furthermore, since excursion is limited with these drivers the radiating area has to be large to move a sufficient air volume.. These relationships seem to be difficult to grasp by audiophiles. Marketing departments and even some designers like to tout low mass as an inherent benefit giving greater "speed" or frequency response to their speaker, when it is only affecting sensitivity in SPL/W.


•It is difficult to screw up an open baffle speaker design to where it sounds worse than your typical box speaker.


The Inspire OB speakers sound wonderful in a relatively small space, perhaps 12' x 12' in my estimation. Of course this is a function of the room's acoustic properties, placement, source material, and of course, the upstream electronics.


I have no opinion, since I am unfamiliar with these speakers.

How do you define affordable?

I've been chasing good horn speakers for quite awhile, and as previously mentioned, am partial to Altec. However, if you can afford $250-$500 I would look for a set of Frazier Mark V's with the horn, not the bullet tweeter, a set of Klipsch Forte IIs, or possibly a cheap set of Cornwalls. Altec Boleros are also reputed to be very nice, but I have no personal experience with them. If you can swing up to $1000, I've bought Altec Model 19's and two pair of Altec 604-8Gs for this amount. Occasionally you can find Khorns for the same amount. My Khorns sound sublime on a SET 45 amp and Citation IV pre amp...

Thanks for the information!

All those horn-based alternatives are out of production (vintage). What about new ones like Klipsch Heressy III or even Cornwall III? The idea of having a competent 102+ dB sensitive pair of speakers is appealing if one is interested in exploring the realm of true DHT SET's. Zu Audio's Soul at 99 dB's looks interesting and affordable (somewhat) but what if at the end of the day these turn out not SET friendly either? I know Omegas are not SET friendly as these never go above 95 dB's (even if their crossovers are lenient).

The rest of the ones I've seen in the marketplace are really expensive. The Klipschhorns seem too massive and expensive for my intended application also (new ones are unaffordable whereas vintage require lots of ugrading investments which a neofyte like me would not even know where to start)

Yep, it seems this DHT SET business is taking me nowhere and I'm too old already to start learning a DIY trade. Maybe I should stick to the Beam-Tetrode strapped as a Triode and call it a day. Dennis's stuff sounds wonderful anyway, so I guess I'm just wasting my and your time with these crazy thoughts. Sorry!

BTW, I understand the physics involved in those OB concept statements, but that is not what I had in mind. I need testimonials from real-people having hands-on experience using OB's and recommending (if at all feasible for my application) a current market offer deemed suitable. My Tekton Lore 2.0, (not the other models) are particularly good in my setup, just not SET friendly as much as I thought and I was thinking maybe an OB would improve on these, but seeing their rated sensitivity (in general) there may not be many high sensitivity alternatives around either.

Finally, I may need to concentrate in a wonderful set of subwoofers to replace my aging single Velodyne to assist my gear in yielding better bass and dynamics. Of course, replacing speakers for me is very expensive given logistics costs (about a 50% mark-up over a nominal $1,000 set of speakers, more or less).

I apologize for my ramblings, you have been quite helpful and patient. Thanks!

[pstrisik]

Originally Posted by Musica Amantem

Thanks for the information!

All those horn-based alternatives are out of production (vintage). What about new ones like Klipsch Heressy III or even Cornwall III? The idea of having a competent 102+ dB sensitive pair of speakers is appealing if one is interested in exploring the realm of true DHT SET's. Zu Audio's Soul at 99 dB's looks interesting and affordable (somewhat) but what if at the end of the day is is not SET friendly either? I know Omegas are not SET friendly as these never go above 95 dB's (even if their crossovers are lenient).

Crossovers are not a factor. Most of his speakers are single driver. He has started with a 1.5 way with two drivers. One driver is full range and has no crossover. The other only has a 500hz low pass filter. His single driver Alnicos are 8 ohm 95db, but these 1.5 ways are 4 ohm 99db. I would be going this route if I didn't already have my active two way, two cabinet system from him (with Rythmik woofer and plate amp).

Trouble is, they are getting expensive.

The rest of the ones I've seen in the marketplace are really expensive. The Klipschhorns seem too massive and expensive for my intended application also (new ones are unaffordable whereas vintage require lots of ugrading investments which a neofyte like me would not even know where to start)

Yep, it seems this DHT SET business is taking me nowhere and I'm too old already to start learning a DIY trade. Maybe I should stick to the Beam-Tetrode strapped as a Triode and call it a day. Dennis's stuff sounds wonderful anyway, so I guess I'm just wasting my and your time with these crazy thoughts. Sorry!

BTW, I understand the physics involved in those OB concept statements, but that is not what I had in mind. I need testimonials from real-people having hands-on experience using OB's and recommending (if at all feasible for my application) a current market offer deemed suitable. My Tekton Lore 2.0, (not the other models) are particularly good in my setup, just not SET friendly as much as I thought and I was thinking maybe an OB would improve on these, but seeing their rated sensitivity (in general) not masny alternatives around either.

Replacing speakers for me is very expensive given logistics costs (about a 50% mark-up over a nominal $1,000 set of speakers, more or less).

I can relate living in Alaska! What makes your logistics expensive?

[o]

Originally Posted by pstrisik

His single driver Alnicos are 8 ohm 95db, but these 1.5 ways are 4 ohm 99db.

They add bass and midbass, but don't expect higher overall output with your tube amp.

The Super 3i's (93/94.5?) with 2 watts (EL84 set) was more than plenty for me.

[pstrisik]

Originally Posted by opnly bafld

They add bass and midbass, but don't expect higher overall output with your tube amp.

The Super 3i's (93/94.5?) with 2 watts (EL84 set) was more than plenty for me.

The design would at least help with added dynamics I would think. I can't recall, did you have 1.5's or have a chance to hear them?

I've got the KT-150 SEP but, even when running tubes that give five wpc, I never found it lacking with SAMs (similar sensitivity). The WolfEar Audio Kitoki SET with EL-84's was fine also at 1.5wpc.

[o]

Take a look at the First Watt products page amplifiers rated outputs into 8 ohms and 4 ohms.
Which ones do you think might benefit from a 4 ohm speaker load?
All of them or just some of them?

[pstrisik]

Originally Posted by opnly bafld

Take a look at the First Watt products page amplifiers rated outputs into 8 ohms and 4 ohms.
Which ones do you think might benefit from a 4 ohm speaker load?
All of them or just some of them?

As far as FW goes, and given the same speakers either way, the answer is some. The question though, is what happens with Inspires when given 8 vs. 4 ohm load?

Also, there is the increase in sensitivity along with the reduction in impedance when we change speakers, so it doesn't seem so simple.

[o]

The increase in sensitivity comes from an increase in current which now assumes 2 watts produced from the same voltage.
Efficiency has not increased. The 1w/1m number remains unchanged.

Tube amps that have more than one pair of output taps (2/4/8/16) are able to provide about the same power when matched to the speaker load.
Music Reference RM-200 test "the amplifier clips at its specified power of 100Wpc when the load impedance is equal to the nominal tap value; the lowest distortion, but also reduced maximum power, occur when the load impedance is much higher than the tap value,"
Distortion goes up and power goes down when the load impedance is lower than the tap value.
I believe damping factor also goes down, whereas light loading (like an 8 ohm speaker on a 4 ohm tap) increases it.

I believe the Inspire amps (like most tube amps with only one pair of outputs) will lose some power as you go above and below 8 ohms.

[Rosco65]

I can attest to two things: Omega speakers are very SET-friendly, and they sound wonderful with my 421a amp and both my Inspire amps. In contrast to most of the current Tekton speakers, Omega's use purpose-built drivers intended from the outset to be driven by low power amplifiers, most frequently paired with Decware Zen Triode amps (2 wpc) by dealers and long term owners. The current Tektons use prosound drivers that, while sensitive, seem to need a little more juice to get up and go. That is not uncommon: some JBL's and most Tannoy's share this characteristic as well.

If I were in Musica Amamtem's shoes, I would perhaps follow this approach:

1. Keep the triode-wired Inspire amp and Inspire preamp. It is easy to obsess over the SET 45 amp, but I don't think that is where most performance gains are to be had right now.

2. Pick up a pair of Omega Super 3i monitors. They really get you to about 85% of what Omega can get you. The Super Alnico's are nice (I own both) but the Super 3's are quicker and a bit better on the top end. They are also far less expensive and work very well in a small room, particularly in the near field. No one will ever believe that this medium sized bookshelf speaker with a single small driver is making all that sound.

3. Pick up one (or two) Rhythmik servo subwoofers. You could choose the dual 8" which are quicker and allow crossing over as high as 200hz, or the F12G (GR Research paper driver), which is still a lightweight cone. The latter has the advantage of being able to be connected at line level and speaker level. Some people feel that subwoofers integrate better when driven off the speaker output of the main amp, especially tube amps, as is takes on a bit of the character of the main amp.

The Rhythmik subs are also available without enclosures if shipping costs are a concern. The recommended designs are straightforward sealed enclosures that could be easily built locally.

A pair of Omega Super 3i's and a single Rhythmik subwoofer will cost less than the Inspire SET amp and will likely bring much more musical enjoyment. I have no doubt the 45 amp is a step up in the right circumstances, but my feeling is right now you would not receive benefit with your existing speakers.

[Rosco65]

Originally Posted by opnly bafld

The increase in sensitivity comes from an increase in current which now assumes 2 watts produced from the same voltage.
Efficiency has not increased. The 1w/1m number remains unchanged.

Tube amps that have more than one pair of output taps (2/4/8/16) are able to provide about the same power when matched to the speaker load.
Music Reference RM-200 test "the amplifier clips at its specified power of 100Wpc when the load impedance is equal to the nominal tap value; the lowest distortion, but also reduced maximum power, occur when the load impedance is much higher than the tap value,"
Distortion goes up and power goes down when the load impedance is lower than the tap value.
I believe damping factor also goes down, whereas light loading (like an 8 ohm speaker on a 4 ohm tap) increases it.

I believe the Inspire amps will act more like the SIT 1 and 2, J2, F3, F1, F1J, and the Aleph J.

This is true when speaker impedance is the only variable. In the case of the High Output Omega speakers, the number of speaker drivers in close proximity are doubled. The elec sensitivity of the speakers increases by 6dB with a 3dB in speaker efficiency. There may be question of the flatness of frequency response with two drivers, but that is another question.

[o]

Originally Posted by Rosco65

This is true when speaker impedance is the only variable. In the case of the High Output Omega speakers, the number of speaker drivers in close proximity are doubled. The elec sensitivity of the speakers increases by 6dB with a 3dB in speaker efficiency.

Correct, in theory; I forgot the 3 dBs in the passband of the second driver (thanks), but the other 3 dBs (from top to bottom) is actually somewhere between 1-3 dBs with most solid state amplifiers. IME with tube amps there is no difference in the overall output of the speaker system, not like say going from 90 dB 8 ohm speakers to 93 dB 8 ohm speakers.

Edited for clarification.